Trauma

The scaphoid is most frequently fractured carpal bone. Scaphoid fractures account for up to 15% of acute wrist injuries and 50% to 80% of carpal fractures. Scaphoid fractures have been reported in people aged 10-70 years but commonly occur in young, active individuals,  peak incidence being in the second and third decades of life.

Scaphoid fractures are most common following a fall, athletic injury, or motor vehicle accident.

They have a high incidence of nonunion, frequent malunion, wrist instability, and posttraumatic arthritis.

Scaphoid injuries are more common in men than in women.

Most of the scaphoid fractures occur at waist [see classification] – 65%, proximal third – 25% and distal third – 10%.

What Are Occult Scaphoid Fractures?

Occult fractures of the scaphoid are the fractures which are suspected clinically but do not show up in the x-rays. Up to 30% of all scaphoid fractures may not be detected on initial x-rays.

If an occult fracture of the scaphoid or severe concomitant wrist injury is suspected but not visible on initial x-rays, the wrist should be immobilized for 10 days in a forearm cast or splint, and the patient should be re-evaluated clinically as well radiologically.

MRI and radionuclide and MRI scans are reliable methods of diagnosing occult fractures of the scaphoid but are expensive investigations.

Anatomy of Scaphoid

The wrist contains eight small bones, which are arranged in two rows, proximal and distal.

The proximal bones, from the radial to the medial side, are the scaphoid, lunate, triquetrum, and pisiform.

The distal bones are, in similar fashion are the trapezium, trapezoid, capitate, and hamate.

Out of proximal four bones, only the scaphoid and lunate articulate with the radius and are responsible for transmission of the entire force of a fall on the hand to the forearm.

Anatomic snuffbox is often used to mark tenderness of the scaphoid injury. It is bordered by the extensor pollicis longus tendon medially, the extensor pollicis brevis and abductor pollicis longus tendons laterally, and the styloid process of the radius proximally.

The scaphoid is Greek for boat and the bone resembles a bent and twisted boat.

The plane of the scaphoid is 45⁰ of palmar tilt to the longitudinal axis of the forearm and 45⁰ radial angulation from the central axis of the forearm on the PA projection.

Major blood supply of scaphoid is a dorsal carpal branch, a branch of the radial artery which enters scaphoid in a nonarticular ridge on the dorsal surface. It supplies proximal 80% of scaphoid via retrograde blood flow.

Minor blood supply from the superficial palmar arch, a branch of the volar radial artery which enters the distal tubercle and supplies distal 20% of the scaphoid.

75% of scaphoid bone is covered by articular cartilage.

The entire proximal half of the scaphoid is an articular surface within the radiocarpal joint. Therefore, the blood supply can enter only on the distal palmar segment and dorsal ridge.

For this reason, proximal-pole fractures require the longest time to union and are associated with a high incidence of osteonecrosis. Approximately one-third of patients have no perforating vessels proximal to the scaphoid waist.

Intrinsic ligaments that attach scaphoid to lunate and distally to the trapezium and trapezoid stabilize the scaphoid.

These ligaments restrict the motion permitting a degree of rotation proximally and a degree of gliding distally.

The scaphoid acts as a link across the midcarpal joint, connecting the proximal and distal carpal rows.

The scaphoid is the key to the carpus because it allows both tremendous mobility of the wrist in flexion/extension and radial/ulnar deviation and provides stability as the intercalated segment linking the proximal and the distal carpal rows.

Both intrinsic and extrinsic ligaments attach and surround the scaphoid allowing the scaphoid to flex with wrist flexion and radial deviation and extend during wrist extension and ulnar deviation.

Much of the wrist motion is a result of the rotation of the scaphoid and the rest of the proximal row during radial and ulnar deviation. The scaphoid rotates to become more vertical, or collinear with the radius, with ulnar deviation bringing the lunate and triquetrum into the dorsal rotation (ie, the distal surface of the bone rotates dorsally).

With radial deviation, the scaphoid rotates to become more horizontal, or perpendicular to the long axis of the radius.

Mechanism of Injury

Read biomechanics of wrist

The scaphoid serves to coordinate and smooth the motions of the proximal and distal rows.

Any shear strain that occurs across the midcarpal joint is transferred through the scaphoid, and may cause fractures and dislocations.

The usual mechanism of injury is a fall onto the outstretched hand (FOOSH) that results in forceful hyperextension of the wrist and impaction of the scaphoid against the dorsal rim of the radius. On getting dorsiflexed >95 degrees, the proximal pole of the scaphoid is tightly held between the capitate, the dorsal lip of the radius, and the taut palmar capsule resulting in fracture of waist. Waist fractures are the type most commonly associated with transscaphoid perilunate fracture-dislocations

Another mechanism is compression injury caused by a longitudinal load or impaction of the wrist. It often leads to fracture of the scaphoid without displacement. When the hand is outstretched and the wrist is in ulnar deviation, the scaphoid is vertical aligned. The axial load combined with the normal palmar curvature of the scaphoid results in a bending moment that collapses the scaphoid. The fracture can involve the scaphoid waist, proximal pole, or the tubercle.

Fractures of the tubercle can be caused by either compression or avulsion.

Proximal pole fractures can be caused by an avulsion of the scapholunate ligament.

In many wrist sprain injuries, the dorsal rim of the radius and the waist of the scaphoid about, resulting in a contusion of the scaphoid and tenderness in the snuffbox.

Snuffbox tenderness is so common in scaphoid injury and considered to be clinical sign suggestive of scaphoid fracture even if the x-rays do not show fracture as the fracture line may be more visible after some resorption [another x-ray at 7-14 days]

Scaphoid fractures in children and the elderly are uncommon. In children, the force causes distal radial physis to fail first and in the elderly, the distal radial metaphysis usually fractures before the scaphoid.

Concomitant distal radius fracture also may occur, particularly radial styloid fractures and dorsal rim fractures, because the line of injury produces a shear fracture of the radius rather than a disruption of the radiocarpal ligaments..

An unstable scaphoid fracture results in a dissociation of the proximal and distal carpal rows and tendency to collapse.

In high energy injuries, other musculoskeletal system parts should be assessed.

Median nerve injuries can occur and can be addressed at the time of surgical treatment. If carpal tunnel develops late, it should be addressed urgently.

Classification of Scaphoid Fractures

Scaphoid fractures have been classified according to various criteria.

According to Anatomic Location

• Tubercle fractures
• Distal-pole fractures
• Waist Fractures
• Proximal-pole fractures

According to the plane of Fracture

• Horizontal oblique
• Transverse,
• Vertical oblique

According to Stability

Stable Fractures

Incomplete fractures or fractures with the incompletely disrupted articular surface (intact overlying cartilage). Neither displacement nor motion about the fracture occurs with wrist motion. Stable fractures are not associated with ligamentous injury. They are treated with immobilization alone.

Unstable fractures

These are complete fractures with motion about the fracture site.

Findings that indicate instability are

• Cortical offset greater than 1 mm
• Fracture angulation
• Associated ligamentous injury
• Motion with ulnar or radial deviation.

There could be associated ligamentous injury, most frequently involving the scapholunate ligament. It is indicated by widened  scapholunate interval may widen, or a DISI pattern

Unstable fractures require fixation.

Herbert and Fisher classification

It is a comprehensive classification and serves as a guide to the treatment of scaphoid fractures. It classifies fractures according to the time of injury and subsequent healing

Type A: Stable Acute Fractures

These are incomplete fractures which unite rapidly with minimal treatment

Type A1

Fracture of tuberosity

Type A2

Incomplete fracture through waist

Type B: Unstable Acute Fractures

These fractures are likely to displace in plaster. Delayed union is common and internal fixation is the treatment of choice

Type B1

Distal oblique fracture

Type B2

Complete fracture of waist

Type B3

Proximal pole fracture

Type B4

Transscaphoid-perilunate fracture dislocation of the carpus

Type B5

Comminuted fractures

Type C

Delayed union- There is a widening of the fracture line, the formation of cysts adjacent to the fracture and proximal fragment becomes relatively dense.

Type D

Established nonunion

The fibrous union can occur after conservative treatment. It is a stable non-union with minimal deformity and variable cystic change. It may progress to pseudarthrosis in time which is hallmarked by unstable progressive deformity and leads to the development of osteoarthritis.

 Type D1

Fibrous union

Type D2

Pseudarthrosis

Clinical Presentation

After an acute injury, the patient generally presents with pain and swelling in the wrist. Often there would be a history of falling on the outstretched hand

On examination, there would be tenderness in the snuffbox. For distal pole fractures, a reliable correlation exists with pain provoked by deep palpation at the volar tubercle of the scaphoid, which is the first bony prominence distal to the volar distal radius. For waist fractures, focal tenderness is most often found in the anatomic snuffbox.

For proximal pole fractures, tenderness is often found just distal to the Lister tubercle

An associated swelling may occasionally be noticed. There is a decrease in range of motion and extremes of motion may elicit pain.

It is not uncommon for a fractured scaphoid to go unnoticed. The range of motion may be decreased. Swelling around the radial and posterior aspects of the wrist is common. If

Differential Diagnoses

• Distal Radial Fracture
• De Quervain Tenosynovitis
• Wrist Dislocation
• Ligamentous injury

Imaging

The diagnosis of scaphoid fracture is usually made by x-ray. Following x-rays are done in case of suspected scaphoid fracture for radiological diagnosis.

• Posteroanterior view with the hand in a fist [This puts scaphoid in extension]
• Lateral view
• Radial oblique  view
• Ulnar oblique view

Scaphoid View

The patient with a scaphoid fracture often holds the wrist in radial deviation, thereby shortening the scaphoid and limiting its evaluation.

To elongate, the scaphoid view is often obtained by positioning the wrist in ulnar deviation and angling the tube cranially by 20-40.

If required comparative views of the opposite uninjured wrist can be done.

In spite of this, undisplaced scaphoid fractures may not be visible on the initial set of x-rays.

Sometimes the presentation is delayed and depending upon the period since the injury, late presentation of a fracture or an established nonunion may show resorption at the fracture site, subchondral sclerosis, and displacement may occur.

Fractures of the distal radius, perilunate dislocation may occur be associated.

There is almost always a ligament damage that accompanies this injury.

Scaphoid Series Xrays

Scaphoid series is a series of x-rays which can be filmed when there is a clinical evidence of scaphoid fracture but the lesion is not visible on routine projections.

Scaphoid series is helpful for better visualization of the scaphoid and other carpal and improves exposure of the intercarpal joint spaces.

Scaphoid series consists of a sequence of the following four radiographs-

• Wrist hyperextended and in ulnar deviation with the fist clenched and the thumb extended.
• 15° supination view.
• 15° pronation view.
• Lateral view in a neutral position

For negative x-rays in case of suspected scaphoid fracture.

A scaphoid cast is applied x-rays are repeated after 10-14 days. For earlier confirmation MRI, CT, or bone scan may be done.

In case of an athlete who wants to return to competition without waiting 7-14 days for repeated radiographs, a bone scan may be obtained after 72 hours. 

 Bone scanning – Sensitivity 99%, specificity of 86%

• MRI sensitivity 88% and a specificity of 100%,
• Bone scanning sensitivity 72% and a specificity of 99%

Fracture is typically visible as a lucent line with at least 1 disrupted cortex. In overriding fragments, a stress fracture, or fracture healing a radiopaque line may be seen.

Angulation of the scaphoid or separate fracture fragments may be observed

Small avulsions and incomplete horizontal-oblique or distal-pole fractures are more difficult to detect

Angulation of the scaphoid at the fracture is often called the humpback deformity and is associated with a greater likelihood of nonunion, worse clinical outcome, and arthritis.

Determination of the intrascaphoid angle on a tomographic image may reveal angulation.

A comparative view of the opposite wrist may aid in confirmation or rule out a finding.

Nuclear Imaging

Radionuclide bone scanning is typically performed 3-7 days after the initial injury if the radiographic findings are normal. Intense, focal tracer accumulation is considered a positive finding.

Bone contusions, degenerative disease, intraosseous ganglion, or active process cause increased activity within the scaphoid.

MRI

MRI is is noninvasive and readily available, and it can assess bone healing and evaluate bone contusions and ligamentous injuries. 

CT

Its sensitivity and specificity are estimated to be 100% when used 5-10 days postinjury. It is better in delineating the injury and identified small avulsions too. Intrascaphoid angle can be easily calculated.CT scan is helpful for evaluation of union

Treatment of Scaphoid Fractures

When displacement occurs about the scaphoid fracture, ligamentous injury and instability should be suspected.

The most common carpal instability pattern is scapholunate dissociation. It is frequently the first radiographic sign to suggest instability.

Recognition of carpal instability is important and helpful in treatment planning.

Nonoperative Treatment

Thumb spica cast immobilization

This is done in the stable nondisplaced fracture. This would constitute the majority of scaphoid fractures. if the patient has normal xrays but there is a high level of suspicion can immobilize in thumb spica and reevaluate in 12 to 14 days.

Beoth long arm spica and  short arm casting is advised by different authors and there is no consensus yet.

Duration of casting depends on the location of the fracture

• Distal-waist for 3 months
• Mid-waist for 4 months
• Proximal third for 5 months

Athletes should not return to play until imaging shows a healed fracture

Augmentation with the pulsed electromagnetic field has been found to be beneficial in a delayed union.

With conservative treatment, scaphoid fractures with <1mm displacement have a union rate of 90%.

Operative Treatment

This involves the reduction and fixation of the fracture. This could be an open reduction and internal fixation or closed reduction and percutaneous screw fixation.

This treatment is indicated in unstable fractures as seen by

• Proximal pole fractures
• Displacement > 1 mm
• 15° scaphoid humpback deformity/ intrascaphoid angle of > 35°
• Radiolunate angle > 15° (DISI)
• Associated with scapholunate ligament disruption/ carpal instability/perilunate dislocation
• Comminuted fractures
• Unstable vertical or oblique fractures

Other factors for consideration of surgical treatment are

• Early return is desired in cases of nondisplaced fracture
• Delayed presentation of acute fracture
• Carpal instability (lunate tilt on radiograph)
• Evidence of nonunion or osteonecrosis

The fractures are fixed by smooth Kirschner wires or a Herbert screw.  Dorsal approach is used in proximal pole fractures and volar approach is indicated in the waist and distal pole fractures and fractures with humpback flexion deformities. Arthroscopic assistance may be used in fixation.

Union rates of 90-95% have been reported with operative treatment of scaphoid fractures.

Complications of Scaphoid Fractures

Scaphoid Nonunion

Nonunion of scaphoid fracture occurs because of delayed diagnosis, gross displacement, associated injuries of the carpus, and impaired blood supply etc.

About 40% of non-unions are undiagnosed at the time of original injury.

Nonunion is 20% more common in smokers.

Timely recognized non-unions, without degenerative changes, can be treated by fixation and grafting.

Untreated scaphoid nonunion could lead to scaphoid nonunion advanced collapse of the wrist which, with time would lead to wrist arthritis.

In patients where the fracture has not shown any union even after 12 weeks of immobilization, the option of surgery should be discussed with the patient. If the patient wants a further trial of non-operative treatment, another cast can be applied for 4 weeks.

A fracture not uniting after 16 weeks should be considered for surgery.

The surgery consists of opening the fracture, removal of fibrous tissue, fixation with a compression screw and bone grafting.

Scaphoid nonunion can be of two types stable (Herbert Type D1) and unstable non union (Herbert Type D2) of scaphoid.

Stable nonunion of the scaphoid is characterized by a firm fibrous nonunion that prevents deformity from occurring

Xray of these cases would show a fracture line with variable cystic changes affecting the bone fragments. The patient in this kind of nonunion have minimal symptoms.

The patient with stable scaphoid nonunion should be encouraged to get treated in spite being symptom-free as fixation of stable nonunions give better results than unstable nonunions. [ And there is a risk of becoming a stable union an unstable union with additional trauma.]

An early treatment further reduces the incidence of secondary osteoarthritis. Percutaneous screw fixation provides good results.

Unstable Scaphoid Nonunion (Herbert Type D2) has sclerosis of bone surfaces, synovial erosion, fibrous cysts indicate an  unstable nonunion.

Unstable scaphoid nonunion leads to decrease in fragment size, collapse and deformity.

Time between the initial fracture and treatment of the nonunion and the presence of osteonecrosis are important determinants of prognosis.

MRI can be used preoperatively for assessing presence of osteonecrosis.

Treatment of Scaphoid nonunion

Inlay (Russe) bone graft

The procedure is done in the following cases-

• Minimal deformity – No humpback scaphoid
• No adjacent carpal collapse

Interposition (Fisk) bone graft

• An opening wedge graft that is designed to restore scaphoid length and angulation
• adjacent carpal collapse
• excessive flexion deformity (humpback scaphoid)

Vascular bone graft

• From radius or medial femoral condyle
• Good option for proximal pole fractures with confirmed osteonecrosis by MRI
• Absence of pancarpal arthritis and collapse

Scapholunate Dissociation and SNAC wrist (Scaphoid nonunion advanced collapse)

Scaphoid fracture non-union leads to wrist instability, collapse, and degenerative changes.

Nonunions of the scaphoid are treated in one of the following ways:

• Radial styloidectomy
• Excision of the proximal fragment
• Proximal row carpectomy
• Total or partial arthrodesis of the wrist

Osteonecrosis of the Scaphoid

• The incidence – 30-40%,
• Most frequently occurs in fractures of the proximal third.

• Poor reduction, delayed surgery, and inadequate fixation of the scaphoid can increase the incident of osteonecrosis.
• Revision surgery with vascularized bone grafts may be necessary..

Late VISI of Carpus

Read more on VISI deformity

the best way to prevent VISI deformity is to adequately repair the lunotriquetral interosseous ligament.

Late case of the VISI deformities can be treated with a dorsal capsulodesis involving the lunate and triquetrum or an ulnar four-bone arthrodesis.

Wrist Stiffness

Nearly all patients with transscaphoid perilunate fracture-dislocations will experience some decrease in wrist motion. Stable fixation in these injuries allows for early range-of-motion exercise, which may reduce the loss of motion. Static progressive splints can help certain patients regain motion postoperatively.

Wrist Arthrosis

In a number of cases, articular damage to the scaphoid or radius has been shown to be the inciting event for wrist degeneration. Osteonecrosis, poor reduction, and inadequate stabilization of the scaphoid can result in wrist arthrosis. In this cases, salvage procedures such as proximal row carpectomy or partial wrist arthrodesis can relieve pain and still allow some motion. In severe cases, a total wrist arthrodesis may be required.

Prognosis of Scaphoid Fractures

Proximal pole fractures have the poorest prognosis because the blood supply to the proximal pole is disrupted by the fracture.

Proximal 5th AVN rate of 100% and proximal 3rd AVN rate of 33%.

Transverse fracture patterns are considered more stable than vertical or oblique oriented fractures

The site of the fracture in scaphoid has been related to union rate. The reported rate of fractures in  scaphoid is

• Waist fractures –  80%
• Proximal pole     –  15%
• Tuberosity       –   4%
• Distal articular fractures – 1%

The scaphoid staple fixation is associated with the union in about 95% of patients.

Surgery is increasingly used for patients who will not tolerate prolonged casting.

References

• Carpenter CR, Pines JM, Schuur JD, Muir M, Calfee RP, Raja AS. Adult scaphoid fracture. Acad Emerg Med. 2014 Feb. 21 (2):101-21
• Karantanas A, Dailiana Z, Malizos K. The role of MR imaging in scaphoid disorders. Eur Radiol. 2007 Nov. 17(11):2860-71.
• Capo JT, Shamian B, Rizzo M. Percutaneous screw fixation without bone grafting of scaphoid non-union. Isr Med Assoc J. 2012 Dec. 14(12):729-32.
• Huckstadt T, Klitscher D, Weltzien A, et al. Pediatric fractures of the carpal scaphoid: a retrospective clinical and radiological study. J Pediatr Orthop. 2007 Jun. 27(4):447-50.
• Pao VS, Chang J. Scaphoid nonunion: diagnosis and treatment. Plast Reconstr Surg. 2003 Nov. 112(6):1666-76; quiz 1677; discussion 1678-9.

Scapholunate instability is a spectrum of wrist instabilities that have occult scapholunate interosseous ligaments sprains on one side and scapholunate advanced collapse on the other side.

Often the term is used interchangeably with scapholunate dissociation but in a strict sense, the scapholunate dissociation is one of the types of scapholunate instability.

To summarize, acute disruption of the SLIL can lead to painful instability, which can progress to chronic degenerative arthritis

Relevant Anatomy

The scapholunate interosseous ligament is a c-shaped structure connecting the dorsal, proximal and volar surfaces of the scaphoid and lunate bones. Its dorsal fibers are thicker than volar fibers and provide the greatest constraint to translation between the scaphoid and lunate.

The proximal portion of the ligament, being a thin fibrocartilaginous membrane,  does not contribute significantly to the stability.

The palmar and particularly the dorsal aspects of the SLIL are stronger.

The scaphoid, the lunate, and the triquetrum are joined by a strong interosseous ligament that causes these bones-the proximal row of the carpus-to move as a unit.

The scaphoid articulates with an irregular fossa at the end of the radius.

It flexes with radial deviation as it is compressed between the radius and the trapezium.  With interosseous ligaments of the proximal row intact, the entire proximal row follows the scaphoid into flexion.

Similarly, in ulnar deviation, the triquetrum is forced into extension, and the rest of the proximal row extends with it.

After the scapholunate ligament is injured, the bones do not move in one unit.

The scaphoid still flexes, with wrist flexion and radial deviation. But it flexes more than it normally does because of the tendency of the triquetrohamate joint to extend the proximal row is not transmitted.

Also, the scaphoid no longer extends with wrist extension or lunate deviation. The lunate follows the triquetrum into extension, no longer balanced with flexion forces through an attachment to the scaphoid.

This leads to relative malpositioning of the bones. When this occurs with motion or loading, the instability is dynamic. If the deformity is at rest too, it is called static.

In acute instability, the abnormally increased motion of the scaphoid can lead to painful clunk.

Over time, the scaphoid can develop a fixed flexion posture

• No longer seated in the radial fossa
• Radioscaphoid joint cartilage gets eroded with repetitive motion
• First at the radial styloid/scaphoid interface
  • then progresses to involve the entire radioscaphoid joint.

The lunate gets into a position of fixed extension but its rounded proximal surface will still articulate smoothly with the lunate fossa of the distal radius. Therefore, arthritic changes in the radiolunate joint as a result of scapholunate interosseous ligament injury are rare.

With further advancement, in the final stage of degeneration, the capitate migrates proximally into the gap between the fixed, rotated scaphoid and the lunate and erodes the cartilage of the capitolunate joint.

Mechanism of  Injury

Scapholunate ligament injury occurs because of fall over outstretched hand injury leading to wrist extension, ulnar deviation, and intercarpal supination, with structures beginning to on the radial side of the wrist.

The severity of the injury determines the extent of the disruption of wrist structures. This pattern of injury has been called progressive perilunate injury because the structures fail in a sequence progressing from radial to ulnar around the lunate which usually is

The injury may begin with a fracture of the radial styloid, fracture of the scaphoid, tearing of the SLIL, or some combination.

Greater energy can cause injury to the capitolunate joint, occasionally fracturing the capitate, and progress through the lunotriquetral interosseous ligament (LTIL) or the triquetrum.

If the injury crosses to ulnar side,  the ulnar styoid may be fractured, or the triangular fibrocartilage complex (TFCC) may be disrupted.

In its most severe form, the injury results in palmar dislocation of the lunate.

Scapholnate Instability can be considered a Mayfield stage I perilunate injury.

[Read more on perilunate injuries]

Acute injury occurs in approximately 10-30% of intra-articular distal radius fractures or carpal fractures.

Degenerative tears in >50% of people over the age of 80 years old.

Diastasis of the scapholunate complex occurs with complete SLIL tears and capsule disruption.

• Associated injuries are DISI (dorsal intercalated segmental instability)

Classification of Scapholunate Injury

The scapholunate instability can be stable or unstable and either acute or chronic.

Stable injuries may include partial tears of the SLIL with associated pain and swelling, occasionally with ganglion formation, but without findings of instability on radiographic or physical examination as described earlier.

Unstable injuries can be either static or dynamic.

An injury <12 weeks old is called acute and older are considered chronic. However, repair of the ligament hs been reported as late as years after an injury.

As we noted previously, scapholunate instability is type I of Mayfield Trumble’s subclassification of the Mayfield type I SLIL injuries separates the injuries into the following categories

• Ia: symptoms present, but radiographic studies negative
• Ib: arthrogram or arthroscopy positive, but no evidence of static or dynamic instability
• Ic: dynamic instability present;
• Id: static instability present.

Clinically these injuries can be classified as follows [Each type represents a higher stage of severity.

• Occult
• Dynamic
• Scapholunate Dissociation
• Scapholunate Advanced Collapse

Occult Scapholunate Instability

It is the mildest form of scapholunate instability.

It usually is initiated by a fall on the outstretched hand. The condition results from a tear or attenuation of a portion of the scapholunate interosseous ligament.

The x-rays are normal in these patients and most of them also have normal stress x-rays. The instability may be noted on fluoroscopy.

Occult scapholunate instability may benefit from conservative treatment such as casting, splinting and symptomatic medications.

In selected cases, arthroscopic debridement followed by pinning or capsule repair has been said to provide a satisfactory outcome.

Dynamic Scapholunate Instability

Patients with dynamic instability have a complete scapholunate ligament tear. The condition results from an injury of greater magnitude than that cause occult scapholunate instability. The x-rays might be absolutely normal like occult instability. But instability is noted in both the plains on stress x-rays.

Repair of the ligament and the capsule is necessary for the treatment of dynamic scapholunate instability.

Scapholunate Dissociation

Scapholunate dissociation or rotatory subluxation of the scaphoid may occur alone or in association with wrist fractures.

The injury  ranges from  grade I sprain of  scapholunate interosseous ligament to complete  scaphoid dislocation

Injuries to following ligaments may be associated with scapholunate dissociation

• Radioscapholunate ligament
• Radioscaphocapitate ligament
• Scaphotrapezial ligament complex
• Dorsal radiocarpal ligament
• Dorsal intercarpal ligament

Disruption of the scapholunate interosseous ligament results in separation of the motion between the scaphoid and lunate in the acute phase and the development of persisting widening of the scapholunate joint as a late clinical consequence.

Provocative stress test and Watson test may be positive. Watson test if present is highly suggestive of scapholunate instability.

Because scapholunate injuries may be associated with fractures of the radius [occurs in 10% of the cases], the x-rays of patients with fractures of the distal radius should be evaluated for ligamentous injury too.

A scapholunate gap >3 mm suggests scapholunate dissociation. If the gap is more than 5 mm it is considered a confirmatory sign. [Terry Thomas Sign]

If the scapholunate angle is more than 60 degrees or capitolunate angle is >15 degrees, it suggests scapholunate instability. If the scapholunate angle is  >80 degrees or capitolunate angle is greater than 20 degrees, it confirms scpholunate instability. [Dorsal intercalated segment instability]

If routine x-rays do not show any abnormality, clenched-fist views or radioulnar stress x-rays should be done.

MRI is helpful in discriminating the extent of ligament injury and should be performed in cases with normal x-rays and clinical suspicion.

Repair of the broken ligaments, internal fixation supplemented by a plaster cast.

Lunate extends when there is a loss of radial ligamentous stability.

Dorsal Intercalated Segment Instability

In scapholunate dissociation, scaphoid rotates into flexion with an increase in the scapholunate interval. The rotation of the lunate becomes independent of the scaphoid. With time, the lunate assumes an abnormally extended posture. This occurs due to forces exerted by intact triquetrolunate ligament [causes extension] and the capitate [causes dorsal translational].

This leads to static deformity which can be visualized on static x-rays.

With further passage of time, a dorsal intercalated segment deformity [DISI] develops  which is characterized by

• Flexion of the scaphoid
• Extension of the lunate and triquetrum
• Dorsal and proximal translation of the capitate and distal carpal row

Scapholunate Advanced Collapse

SLAC wrist or Scapholunate advanced collapsed wrist is the final stage of scapholunate instability spectrum, where there is a specific pattern of osteoarthritis and subluxation which results from untreated chronic scapholunate dissociation. The condition, however, can also occur in cases of chronic scaphoid non-union and degenerative changes abnormal loading.

The postural changes become irreversible with time and the changed kinematics [the way forces would be handled] lead to abnormal articular loading and progressive degenerative changes known as Scapholunate advanced collapse (SLAC).

Types of SLAC Wrist

Depending on the extent of arthritis,  the  SLAC wrist can be divided into

SLAC wrist  I – Arthritis along the scaphoid facet of the distal radius.

SLAC wrist  II – In addition to the above, arthritis  develops along the proximal radioscaphoid joint.

SLAC wrist III – Arthritis also develops in the radial midcarpal joint.

SLAC  wrist IV  – Arthritis involves radiolunate joint and entire carpus.

The x-rays would reveal the deformities and arthritis depending on the stage of SLAC.

Clinical Presentation of Wrist Instability

The injury could be traumatic [fall on outstretched hand] or a degenerative rupture.  Patient’s age, nature of the injury, duration since the injury, the degree of underlying arthritis, level of activity should be noted.

Chronic SLIL injuries sometimes present quite late, and often the patient will not recall a specific injury.

The patient usually presents with pain on the dorsal and radial side of the wrist which increases with the loading of the wrist.

Clicking or catching in the wrist may be felt. The patient may also complain of wrist weakness or instability.

On examination, there may be swelling over the dorsal and tenderness in the anatomical snuffbox or over the dorsal scapholunate interval which lies 1 cm distal to Lister’s tubercle.

Pain increases with extreme wrist extension and radial deviation.

Watson test

For this test, the examiner locates the palmar prominence of the distal pole of the scaphoid (most easily identified when the wrist is in radial deviation) and applies dorsally directed pressure to the distal pole while moving the wrist from ulnar to radial deviation and back.

When SLIL is intact, it keeps the scaphoid seated in the scaphoid fossa of the distal radius.

But if but an incompetent ligament will allow dorsal subluxation of the scaphoid proximal pole over the dorsal lip of the radius with progressive radial deviation. Returning the wrist to an ulnarly deviated position allows for reduction of the subluxation; the subluxation and reduction generally cause pain and a palpable clunk.

The test must be repeated on the uninjured side for comparison because ligamentous laxity can lead to a positive test without injury being present.

Imaging

X-rays

AP and lateral views of the wrist are the recommended views. Radial and ulnar deviation views, flexion and extension views and clenched fist views may be done as additional studies.

AP radiographs

• widening of the scapholunate gap  > 3mm with clenched fist view (Terry Thomas sign) (maximized in the grip and ulnar deviation PA views)
• Shortening of the flexed scaphoid, resulting in the cortical “ring sign” as the proximal and distal poles overlie one another
• Arthritic changes in late cases

Lateral radiographs

• Increased scapholunate angle
  • Angle formed by the longer axes of the scaphoid and the lunate.
  • Ranges from 30⁰ to 60⁰ [Average – 47⁰]
  • > 60⁰ after SLIL inury.
• capitolunate angle > 20°

Arthrography

Arthrography documents communicating defects, but these may not represent functionally significant tears. It may be used as a screening tool for arthroscopy. Always assess the contralateral wrist for comparison.

It cannot determine the size of the tear. A positive finding of a tear may indicate the need for wrist arthroscopy

MRI

MRI has been used successfully to evaluate TFCC injuries but has a reported sensitivity [37%]

Cineradiography

A diagnostic technique in which a camera is used to record images of internal body structures produced through radiography or fluoroscopy.

A simple alternative is to have the patient move the wrist through a range of motion under fluoroscopy device.

Arthroscopy

It is considered the gold standard for diagnosis but is the invasive technique.

Bone Scintigraphy

Bone scintigraphy has been reported as highly sensitive for complete tear but much less so for partial ligaments injuries.

Treatment of Scapholunate Instability

Nonoperative Treatment

This includes rest, pain medication and immobilization. It can be considered in acute, undisplaced scapholunate ligament injuries or chronic, asymptomatic tears

Operative Treatment

Scapholunate ligament repair

It is indicated in acute scapholunate ligament injury when there is ligament without carpal malalignment.

If the SLIL is repairable, the scaphoid reducible from its flexed posture, and there are no arthritic changes, most authors now recommend primary repair of the ligament using either drill holes or suture anchors, augmented with some type of dorsal capsulodesis. The procedure provides a checkrein that decreases palmar flexion of the scaphoid and prevents the scaphoid from shifting dorsally.

Repair of the ligament can be considered in chronic but reducible scapholunate ligament injuries. It has been done in cases as old as 18 months.

Scapholunate Reconstruction

Scapholunate reconstruction is indicated when there is acute scapholunate ligament injury without carpal malalignment but the pathoanatomy is not amenable to repair.

It is also done in reducible scapholunate ligament injuries > 18 months from the time of injury.

Scaphoid Reduction and Fixation

This could be either open reduction and fixation of the scaphoid or closed reduction and percutaneous fixation.

This is indicated in scaphoid fractures resulting in instability [trans-scaphoid scapholunate instability]

Stabilization with wrist fusion (STT or SLC)

This is indicated in rigid and irreducible DISI deformity with or without arthritic changes.

Fusions may be scaphotrapezialtrapezoidal (STT) fusion or scapholunocapitate (SLC) fusion.

Surgeries for SLAC Wrist

• Four corner Fusion
  • Excision of the scaphoid
  • Arthrodesis of the capitate, hamate, lunate, and
• proximal row carpectomy
• Wrist Arthroplasty
• Wrist Arthrodesis

Wrist Instability or carpal instability occurs when takes wrist is damaged by trauma, chronic inflammation or anatomical alterations like ulnar variance and neoplasms. Injuries to the ligaments of the wrist represent a broad spectrum of pathology.

There are a number of ligaments of the wrist maintaining a complex articulation of carpal bones. Ligament injuries are often implied by gross radiographic alterations but wrist instability patterns frequently present only after some time has elapsed.

Wrist instability or wrist ligament injuries are classified by radiographic pattern, behavior, and chronicity. The patterns of instability are changes produced within the carpus by ligamentous or bony disruptions.

A wrist is considered stable when the modifications brought about by the various forces acting on it are restored when the said forces stop to act.

In contrast, the alteration of one or more of the structures responsible for stability lead to preclusion of the restoration of the order and leads to misalignment and a decrease in performance of the organ.
This happens when takes wrist is damaged by trauma, chronic inflammation or anatomical alterations like ulnar variance and neoplasms.

Relevant Anatomy

Anatomy of Wrist

Types of Wrist Instability

Wrist instability can be due to various causes and depending upon its behavior. Wrist instability can be of many types.

Classification of Wrist Instability has been approached by various authors.

Dynamic and Static Instability

Taleisnik introduced the concept of static and dynamic instability.

Carpal instability often depends on capsular integrity and on the interosseous ligaments. It can be

• Dynamic instability – This occurs in incomplete injury. The wrist maintains normal alignment at rest but will collapse under applied load.
• Static Instability – This occurs in complete injury to the structure involved. This kind would show abnormal intercarpal alignment on static radiographs.

The static deformity is always present irrespective of whether the wrist is in the neutral position or under some stress.

With a dynamic instability, x-rays reveal abnormal carpal ligament only one stress is applied or when the wrist is in a non-standard position. Dynamic and static instability can be thought of as different stages in a clinical spectrum of partial or complete ligament injury.

Frequently, but, not exclusively, nondissociative instabilities are static. [see below]

Volar and Dorsal Intercalated Segment Instability or VISI

Volar and Dorsal Intercalated Segment Instability are instabilities of an intercalated segment of the wrist. The intercalated segment is the proximal carpal row.

As the name suggests, volar intercalated segment instability or VISI is opposite of dorsal intercalated segment instability or DISI.

Volar Intercalated Segment Instability

VISI is said to be present when there is volar flexion of the lunate>15 degrees [in relation to the longitudinal axis of the radius and capitate]  when the wrist is in a neutral position. This occurs because of loss of ulnar support from the triquetrum and the lunate has a tendency to flex.

VISI is found in

• Lunotriquetral dissociation
• Nondissociative carpal instability
• Carpal instability complex

Dorsal Intercalated Ligament Instability or DISI

Dorsal intercalated segment instability is said to occur when the lunate slips into fixed extension >10 degrees. This occurs when radial ligamentous stability is broken.

The condition is also termed as dorsal instability.

Massive ligament disruption at the time of injury, as may occur in perilunate or lunate dislocations, or gradual attrition of the secondary extrinsic stabilizers leads to an abnormal extension of the lunate and carpal collapse after scapholunate dissociation.

The combined effects of an extension moment and dorsal translation of the capitate force puts the lunate into extension and exacerbate the abnormal posture of the scapholunate joint.

Capsular contracture may serve to fix the deformity.

So all these means is that in DISI, the lunate is angulated dorsally. The relative alignment of the scaphoid to the lunate forms angle of 45 degrees. When the scapholunate angle is more than 70 degrees, ligaments between the scaphoid and lunate become nonfunctional. In such situations, the lunate becomes extended and maintains the position even during radial deviation.

This does not allow normal rotation and the spatial adaptability of the proximal row. A DISI deformity is seen in

• Scaphoid fractures
• Scapho-lunate dissociation
• Perilunate dislocation

Instability Based on Motion Patterns

Patterns of the instability can be further described based on the normal patterns of motion. Both the proximal and distal carpal rows have particular patterns of motion within the rows (ie, relationship of the scaphiod relative to the lunate).

This normal motion has been termed “associative.”

• A disruption of the normal kinematic within a row is a dissociative instability. Dissociative carpal instabilities any result from a disruption of any of the bony or ligaments components of the wrist.
• Disruption between rows, while the alignment within each row remains normal, is a nondissociative instability.

Nondissociative carpal instability [CIND]

Carpal instability, nondissociative (CIND), includes instability patterns that occur between a carpal row and the adjacent transverse osseous structures.

It is defined as an alteration in the articular relationship between the two carpal rows, while the individual joints between the skeletal elements of each row are maintained.

In these patterns, there is no dissociation within the carpal rows (ie, competent interosseous ligaments). These instability patterns include

• Midcarpal instabilities
• Ulnar translocations [ the carpus moves ulnar wards. Seen in Rheumatoid arthritis and Madelung deformity.]
• Capitolunate instability – Palmar subluxation of the capitate on the lunate.
• Proximal carpal row instabilities.

Midcarpal Instability

Type I- Palmar midcarpal instability

• Secondary to an injury to the palmar midcarpal ligaments [Scaphotrapeziotrapezoid, triquetrohamate and triquetrocapitate ligaments
• Palmar subluxation

Type II- Dorsal Midcarpal instability

• Type I instability+ injury to the radioscaphocapitate ligament.
•  Dorsal subluxation is dorsal.

Type III

• Hyperlaxity of midcarpal and radiocarpal ligaments.
• Dorsal or palmar subluxation

Type IV – Extrinsic midcarpal instability

• Often due to malunited radius
  • Dorsal  angulation
  • Progressive stretching of the radiocapitate ligaments.
• Dorsal subluxation

CIND can occur secondary to fractures, disruption or laxity of extrinsic ligaments, or both.

The most frequent reasons for nondissociative carpal instability are the collapse of the capsule and that of the intercarpal ligaments mostly following rheumatoid arthritis. Trauma is another cause.

Dissociative Carpal Instability

Dissociative carpal instability is present when there is instability between individual bones of a carpal row.

Most common causes are fracture or ligament disruption.

Dorsal intercalated segment instability and Volar intercalated segment instability are included in dissociative instability. This is because there is disruption of the ligament bond or the bone structure between the lunate and one or both of the adjacent carpal bones.

Examples of dissociative carpal instability are

• Scapholunate instability
• Lunotriquetral dissociation

Complex Carpal Instability[CIC]

Carpal instability, combined or complex (CIC), is a combination of two or more specific CID or CIND patterns. Example of the complex instability includes perilunate dislocations, radiocarpal instability with axial instability, and scapholunate dissociation with ulnar translocation.

Adaptive Carpal Instability [CIA]

The instability does not reside in the carpus but is due to sequelae of radial fractures with dorsal displacement in the epiphyseal region.

Adaptive carpal instability results from the repositioning of the carpus in response to a change into bony architecture.

One of the more common etiologies of an adaptive instability is the dorsally angulated distal radius malunion, which result in a compensatory DISI of the secondary to scaphoid nonunions, lunate malunions, or Madelung’s deformity.

Clinical Presentation and Evaluation of Wrist Instability

The history of presentation would range from high-energy polytrauma to low-energy mechanisms that cause mild, protracted symptoms. Wrist ligament injuries can range from subtle instability patterns as the result of attrition to acute and chronic injuries. Evaluation for wrist ligament injuries and resultant instability is mandatory in all patients with wrist symptoms, whether or not a recent traumatic event is identified.

Even gross carpal malalignment may be overlooked or misdiagnosed at the time of initial injury and radiographic examination.

The most devastating of these injuries, lunate or perilunate dislocations, comprise only 10% of all carpal injuries and usually occur as a result of high-energy injuries. of these, transscaphiod perilunate fracture-dislocations are the most common, representing 61% of all perilunate dislocations in one study.

The patient may present with pain and/or clunking Some patients present quite late with deformity already present. Most of the patients present with painful clunking on the ulnar side of the wrist during activities that involve active ulnar deviation.

There would be a history of asymptomatic wrist clunking for many years. There could be a history of hyperextensive injury or there could be the absence of any significant trauma.

Ligamentous laxity and a hypermobility should be ruled out.

Being subtle the deformity patterns may be difficult to detect in early stages.

The examination should ascertain hand dominance, loss of motion, prior hand or wrist conditions, and past medical history.

These components would affect treatment decisions.

In the acute high-energy injury, physical examination may reveal gross deformity, swelling, ecchymosis, or lacerations. The carpal injury may be overlooked or considered a low priority in this setting because of the presence of other more demanding injuries. Median nerve examination should be particularly done as up to 25% of the cases of acute carpal tunnel syndrome.

Palpation for specific sites of tenderness, and a careful neurologic/vascular examination, especially with sensory testing, are mandatory.

Point tenderness over specific carpal ligaments, such as the scapholunate interosseous ligament or the lunotriquetral interosseous ligament may represent injuries to those ligaments.

Patients with injuries caused by subacute or chronic processes may present with pain, popping catching, or symptoms of secondary degenerative changes.

In these patients, a more detailed examination of the carpus is performed. The active and passive range of motion is assessed and recorded. Direct palpation over the scapholunate, lunotriquetral, triangular fibrocartilage complex and midcarpal joints may greatly narrow the differential diagnosis.

Specific maneuvers or Special Tests

These are done to check for ligamentous disruption of the wrist may also help determine the extent of the injury. These should be done in sytematic way, beginning on radial side Watson’s scaphoid shift test, followed by the midcarpal shuck test and the lunotriquetral ballottement test.

Watson Scaphoid Shift Test for Scapholunate Instability

Watson test or Scaphoid shift test is a wrist provocative stress test done for Scapholunate instability.

The examiner’s thumb is placed on the scaphoid tuberosity of the volar aspect of the wrist. Pressure is applied to the tuberosity as the wrist is passively brought from ulnar to radial deviation. This pressure attempts to block normal scaphoid flexion.

A combination of pain and a palpable clunk when the wrist is brought from ulnar deviation into radial deviation while pressure is applied to the palmar aspect of the scaphoid tubercle.

[In theory, it indicates torn a scapholunate ligament and scapholunate instability which leads to the proximal scaphoid subluxating over the rim of the radius. A painful clunk indicates a reduction of scaphoid into the radial scaphoid fossa.]

A false positive result can also be obtained in individuals with lax ligaments.

Here is a video demonstration of the test

For lunatotriquetral instability

Shuck Test or Ballottement Test

Shuck test or Shear test, also called Ballottement test is done for lunatotriquetral instability.

The examiner’s thumb and index finger grasp the whole pisotriquetral unit. The contralateral thumb and index finger hold the lunate.  The test is performed by applying a dorsally directed pressure to the pisiform  and a palmarly directed pressure to the lunate [Lunate can be palpated beyond  dorsal and ulnar corner of the radius.]

The maneuver results in a shearing stress on lunatotriquetral joints and vector across the lunotriquetral joint.
A crepitation or clicking associated with reproduction of pain is indicative of lunotriquetral dissociation.

The triquetrum is displaced dorsally and palmarly on the lunate. The test may be false negative in cases of ligamentous laxity.

Here is a nice demonstration of Shuck test.

The diagnosis is aided by the midcarpal stress test which is performed by applying an axial load to a pronated and slightly flexed wrist, which then is brought into ulnar deviation. A painful clunk  is a sign of  instability [ 50% of patients with MCI may also have a clunk in the normal contralateral wrist and should always be examined]

Linscheid Compression Test

The examiner uses a thumb to apply a load in the radial direction at the ulnar border of the triquetrum.
The loading results in a compression force across the lunotriquetral joint. If this results in pain, the result is considered positive.

For Midcarpal Instability

Lichtman’s Pivot Shift Test

It is done for midcarpal instability. This test is a combination of ulnar deviation, axial compression, and pronation of the wrist. A positive result is obtained when this maneuver results in a painful wrist click.

Dorsal-displacement stress test

Under fluoroscopic control, a positive result is obtained when the capitate subluxates dorsally on dorsal stress as compared with the lunate and when the patient experiences a painful snap or click. Indicates capitolunate instability.

Without fluoroscopy, apprehension is taken as a positive sign.

Imaging

X-rays are the basic investigations. These are most helpful when there is bony injury fractures or diagnosing ligament disruption with associated fractures. The use of other modalities must be based on the particular clinical scenario.

Plain Xrays

Radiographic examination of the wrist is mandatory for all suspected wrist ligament injuries and instabilities.

Posteroanterior (PA) view in neutral rotation, as well as lateral views, should be enough to evaluate static deformities.

A comparison with the opposite wrist should be done for better assessment.

For evaluating dynamic stability, additional radiographs (eg, PA grip, PA maximum radial deviation, PA maximum ulnar deviation, lateral maximum flexion, and lateral maximum extension views) can be obtained..

On PA view,  disruption of one of the Gilula arcs suggests either a fracture or subluxation from a ligamentous injury.

Increased distance between the scaphoid and lunate may indicate scapholunate interosseous ligament disruption.

In patients with acute, gross malalignment of the carpus, a PA radiograph with 5 to 10 Ib of traction frequently aids in the assessment of intracarpal ligament disruptions or fractures.

Lateral radiographs should be carefully evaluated to make sure that the capitate reduces in the lunate and the lunate is reduced in the fossa of the radius.

Many patterns of instability can be identified.

In many acute carpal ligament disruptions, the initial plain radiographs are normal, with instability patterns recognized only as a late finding.

Specific instability views may be indicated to accentuate more can subtle instabilities.

For example, a PA clenched fist view can demonstrate dynamic scapholunate widening.

Fluoroscopy examination with provocative motion or maneuvers can demonstrate dynamic instability.

X-ray Measurements

Following angles should be measured

• Radiolunate angle- 15 degree palmar to 15 degrees dorsal
• Capitolunate angle- 30⁰ dorsal to 30⁰ palmar)
• Scapholunate angle – 38⁰ – 60⁰
• Lunotriquetral angles – 14 degrees dorsal

[In scapholunate instability, the scaphoid tends to assume a volarly flexed posture and scapholunate angle is> 70º.

Conversely, in lunotriquetral instability, the lunate is usually palmarly flexed, and the scapholunate angle can be less than 30º.

DISI  and VISI can be defined by these values (see the classification)

Scapholunate gap can be measured on PA and PA grip radiographs. [> 3 mm. is generally considered pathologic but comparison with opposite wrist should be done.]

Determine ulnar translocation on PA x-ray – The distance between the center of the capitate and a line extending from the intermedullary axis of the ulna is divided by the length of the third metacarpal. [Normal is  0.30±0.03]

Arthroscopy

Arthroscopy remains the standard for diagnosing specific ligament injuries in the wrist. Both radiocarpal and midcarpal joints should be evaluated.

Arthroscopy is a very sensitive diagnostic test, and frequently clinically silent lesions may be detected

Computed Tomography

CT provides more detailed evaluation and may be indicated for subtle intra-articular fractures, to assess the degree of displacement, or to check for union of a fracture. Dynamic 4D CT imaging technique generates images with high spatial and temporal resolution and could be deployed to assess joint instability using this technique.

Bone Scintigraphy

These studies may be helpful to identify radiographically occult fractures, most commonly those of the scaphoid..

Arthrography

Arthrography has historically been the gold standard diagnostic test. Contrast medium is injected into the radiocarpal, midcarpal, and radiolunate compartments, with dye flow between any two indicating a tear.

Arthrography lacks specificity and is an invasive procedure.

Its most common use tends to be for evaluation of subacute or chronic wrist symptoms.

MRI

MRI has gained has the potential to provide diagnostic evaluation of intrinsic and extrinsic carpal ligaments as it has the advantage of provides better soft tissue images.

Treatment of Wrist Instability

Milder forms of instabilities in not so active patients can be considered as well to for nonoperative management.

Conservative measures that can be taken are

• External support
• Musculotendinous exercises
• Analgesics
• Steroid Injections
• Change or modification of profession/employment

Failure of conservative treatment can be considered for the cases where conservative treatment has failed.

To simplify the discussion, treatment is summarized below under the headings of the following specific types of instabilities:

Scapholunate instability

Partial tears of the scapholunate interosseous ligament (SLIL) are thought to represent occult or predynamic instability. For these injuries, most recommend an initial trial of splinting, casting, or both.

Arthroscopic debridement with or without pinning can be an option in these patients in whom initial conservative treatment is unsuccessful.

With complete scapholunate tears, options are

• Direct repair with or without dorsal capsulodesis
• Arthroscopic debridement, reduction, and pinning

In acute cases (<6 weeks), direct repair is indicated if sufficient SLIL remnant is present.

In patients with unrepairable SLIL but a reducible scapholunate interval and without degenerative changes, an indirect or direct ligament reconstruction has been advocated for stabilizing the scaphoid and to prevent the rotatory subluxation that often occurs in scapholunate instability.

Blatt dorsal capsulodesis is indirect ligament reconstruction using a flap of the dorsal capsule to tether the scaphoid tuberosity to retard scaphoid flexion. Wrist flexion is significantly reduced by this surgery. Limitation of flexion can be overcome by not tethering the scaphoid to the radius.

Direct ligament reconstruction can be considered when  SLIL is not repairable,  scapholunate dissociation is reducible, and no degenerative arthritis is observed.  A  tendon to reconstruct the SLIL or a bone-ligament-bone construct may be used. They require a long period of wrist immobilization and result in some loss of final wrist motion.

Brunelli and Brunelli technique uses a strip of the flexor carpi radialis (FCR) and weaves it through the scaphoid. The tendon is also sutured across the scapholunate interval.

Limited intercarpal fusions are indicated in presence of DISI and degenerative changes at the radiocarpal joint.

Fusions that have been described involve the scaphocapitolunate,  the scaphotrapezial trapezoid, the scaphocapitate, and the scapholunate fusion.

When arthritic changes are present(advanced scapholunate collapse) or a wide, irreducible scapholunate gap is present following are the available options

• Proximal row carpectomy
• Scaphoid excision and fusion of the lunate, triquetrum, capitate, and hamate (four-corner fusion
• Total wrist fusion [In pan carpal arthritis]

Lunotriquetral instability

A period of immobilization for acute injuries is recommended.

Failure of conservative treatment demands direct repair with or without augmentation [capsulodesis]. The goal of capsulodesis is to prevent excessive flexion of the proximal row by imbricating the dorsal radiotriquetral ligament.

Late-presenting patients can be considered for

• Capsulodesis
• Ligament reconstruction
• Arthrodesis
• Ulnar shortening
  • Removes ulnar impaction
  • Tightens the volar ulnotriquetral and ulnolunate ligament
• Lunotriquetrohamate or triquetrohamate

Midcarpal instability

• Tightening the radiocapitate ligament
  • In patients who had a positive result on fluoroscopic dorsal-displacement stress testing.
  • Tethering the middle portion of the radiocapitate ligament to the radiotriquetral ligament to close the space of Poirier.
  • Slight extension of the wrist is lost after this procedure.

Radius opening wedge osteotomy usually also corrects the carpal instability.

Ulnar translocation

Total wrist fusion is probably the best option if significant midcarpal arthrosis is present as well.

References

• Pulos N, Bozentka DJ. Carpal Ligament Anatomy and Biomechanics. Hand Clin. 2015 Aug. 31 (3):381-7.
• Lee DJ, Elfar JC. Carpal Ligament Injuries, Pathomechanics, and Classification. Hand Clin. 2015 Aug. 31 (3):389-98.
• Watson HK, Weinzweig J, Zeppieri J. The natural progression of scaphoid instability. Hand Clin. 1997 Feb. 13(1):39-49.
• Kuo CE, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. J Hand Surg [Am]. 2008 Jul-Aug. 33(6):998-1013.
• Whipple TL. The role of arthroscopy in the treatment of scapholunate instability. Hand Clin. 1995 Feb. 11(1):37-40.
• Kozin SH. The role of arthroscopy in scapholunate instability. Hand Clin. 1999 Aug. 15(3):435-44, viii.
• Ruch DS, Poehling GG. Arthroscopic management of partial scapholunate and lunotriquetral injuries of the wrist. J Hand Surg [Am]. 1996 May. 21(3):412-7.
• Weiss AP, Sachar K, Glowacki KA. Arthroscopic debridement alone for intercarpal ligament tears. J Hand Surg [Am]. 1997 Mar. 22(2):344-9.
• Garcia-Elias M. Treatment of scapholunate instability. Ortop Traumatol Rehabil. 2006 Apr 28. 8(2):160-8.
• Kirschenbaum D, Coyle MP, Leddy JP. Chronic lunotriquetral instability: diagnosis and treatment. J Hand Surg [Am]. 1993 Nov. 18(6):1107-12.
• Shin AY, Battaglia MJ, Bishop AT. Lunotriquetral instability: diagnosis and treatment. J Am Acad Orthop Surg. 2000 May-Jun. 8(3):170-9.
• Chaudhry T, Shahid M, Wu F, Mishra A, Deshmukh S. Soft tissue stabilization for palmar midcarpal instability using a palmaris longus tendon graft. J Hand Surg Am. 2015 Jan. 40 (1):103-8.

Perilunate injuries which include perilunate dislocations and perilunate fracture-dislocations are the most devastating closed injuries of the wrist that involve traumatic rupture of the radioscaphocapitate ligament, the scapholunate interosseous ligament, and the lunotriquetral interosseous ligament.

 Because the lunate is strongly bound to the radius and ulna by the palmar capsular ligaments, in severe injuries the lunate often remains reduced to the distal radius while the remainder of the carpus is dislocated. These injuries are commonly referred to as perilunate dislocations.

Perilunate dislocations purely ligamentous injuries or associated with fractures [fracture dislocations].When these injuries are associated with fractures the fractured bones are denoted by prefix trans. So the injuries become transscaphoid, transradial-styloid, transscaphoid-trans-capitate-perilunate injuries.

Lunate dislocations occur when the lunate rotates palmarly on these strong capsular ligaments and the remainder of the carpus and remains relatively aligned with the distal radius and ulna. Both injuries lie within the spectrum of the fracture-dislocations of the carpus.

Perilunate dislocations and lunate dislocations may represent a stage of a common spectrum of injury and are typically considered together [see classification].  For a purpose of this discussion, both patterns generally will be considered as perilunate injuries. [The term perilunate instability is also used interchangeably]

These injuries are high energy injury and associated with poor functional outcomes.

Periluate injuries are often missed at initial presentation In up to 25 percent of the cases.

Anatomy of Wrist

[Read detailed anatomy of wrist]

The carpus is composed of two rows of bones, as follows 

• Proximal carpal row  scaphoid, lunate, triquetrum and pisiform
• Distal carpal row – trapezium, trapezoid, capitate, and hamate

Wrist Ligaments

Intrinsic

Stabilize adjacent carpal bones.

Extrinsic

Span the carpal rows and origin from radius or ulna proximally.

Read more about Intrinsic and Extrinsic ligaments

• Scapholunate interosseous ligament binds the scaphoid to the lunate and comprises of proximal, distal and volar part, with dorsal part being the strongest stabilizing factor of scapholunate articulation.
• Lunotriquetral interosseous ligament secures the articulation of the lunate and the triquetrum.
• Interosseous ligaments
  • Interosseous ligaments are types of intrinsic ligaments that are within the joint only.
  • These hold the carpal bones tightly but do allow relative motion between the scaphoid and lunate and between the lunate and the triquetrum.

The distal carpal row is also stabilized by intrinsic ligaments like capitohamate ligament.

Caphotrapeziotrapezoidal  joints are stabilized by scaphotrapezial ligament, scaphocapitate capsular ligament and dorsal and palmar scaphotrpeziotrapeziodal capsular ligaments.

Extrinsic carpal ligaments provide integrity for the articulations of the proximal and distal carpal rows.

Radioscaphocapitate ligament originates from the radial styloid, crosses the waist of the scaphoid, and inserts on the volar waist region of the capitate.

Ulnar to the radioscaphocapitate ligament is the radiolunotriquetral ligament, which originates from the radial styloid, sends an attachment to the volar aspect of the lunate, and then terminates on the triquetrum.

The short radiolunate originates from the most ulnar aspect of the distal radial articular surface and inserts on the proximal volar aspect of the lunate.

Ulnotriquetral ligament origin from ulnar styloid and insert on triquetral.

Ulnocapitate ligament origins from ulnar styloid and insert on the waist of the capitate and join the radioscaphocapitate ligament, forming an inverted V confluence known as the arcuate ligament.

Just proximal to the base of the V is a soft spot, the space of Poirier which is a weak open space.

Dorsally, dorsal intercarpal ligament [from waist of the scaphoid across the carpus, inserting onto the dorsal aspect of the triquetrum] and dorsal radiocarpal ligament[ radial styloid to the dorsal aspect of the triquetrum].

Together, these two ligaments form a V, with the base of the V on the triquetrum and there is less substantial dorsal wrist capsule between the V.

The dorsal ligaments are thinner and weaker, but they appear to play an important role in the final stages of carpal instability when static deformity occurs. The dorsal intercarpal ligament appears to play the most significant role in controlling carpal motion.

Causes and Pathomechanics Perilunate Injuries

These injuries are usually traumatic, high energy injuries which occur when wrist extended and ulnarly deviated. The force causing injury leads to intercarpal supination. The angle of hyperextension determines the extent of injury.

Fractures of the radial styloid, the scaphoid, the trapezium, the capitate, and the triquetrum also may be associated with the dorsal or the volar perilunate dislocation.

These injuries occur as the final stage of a spectrum of injuries progressing around the wrist in a radial-to-ulnar direction.

Motor vehicle accidents falls from heights, and sports accident are the most common causes of these injuries. The typical mechanism is believed to be hyperextension and ulnar deviation.

Pure ligamentous perilunar injuries of the wrist are classified as lesser arc injuries, whereas the transosseous variants [through the bone] are regarded as greater arc injuries. The mechanism of perilunate dislocations has been described as a four-stage process, as follows as given by Mayfield and associates.

Mayfield and Associates Classification of Perilunate Injuries

The classification is, in fact, the sequence of the events in what is called progressive perilunate instability.

The four stages of the progressive ligamentous damage occur with the wrist hyperextended and with variable degrees of ulnar deviation and forearm supination.

It is also called Mayfield classification of carpal instability or perilunate instability classification or Perilunar Carpal dislocations Classification.

Stage I- Scapholunate dissociation [Rotatory subluxation of the scaphoid]

• The radioscaphocapitate ligament and the scapholunate interosseous ligament rupture.
• Terry Thomas sign present and is exacerbated in clenched fist views

Stage II – Lunocapitate disruption [ Perilunate dislocation]

• The lunate remains normally aligned with the distal radius, and the remaining carpal bones are dislocated (almost always dorsally)
• Dislocation of the capitolunate joint occurs as the injury progresses through the space of Poirier
• The lunate projects through the space of Poirier
• 60% are associated with scaphoid fractures

Stage III – Lunotriquetral disruption, “perilunate”

• The lunotriquetral interosseous ligament ruptures or triquetral fracture
• Neither the capitate or the lunate is aligned with the distal radius

Stage IV – Lunate Dislocation

• Dorsal radiolunate ligament injury
• dislocation of the lunate in a palmar direction
• Often associated with median nerve compression
• Tipped teacup appearance

Clinical Presentation

Most patients present acutely after a fall from a height onto a dorsiflexed wrist. Patients with perilunate dislocations and perilunate fracture dislocations may demonstrate deformities and marked swelling.

The presentation may also be rather subtle like complain of a sprained wrist.

In the dorsal perilunate fracture-dislocations, the carpus is dislocated dorsally, and the radius is prominent volarly.

However, in the pure lunate dislocation, the lunate alone is prominent volarly.

These injuries are diagnosed late in as many as 25% of cases.

Often these injuries are high energy injuries and assessment of other parts [trauma survey] for injuries of the head, thorax, and extremities is imperative.

Median nerve gets often damaged in these injuries and should be assessed.

Tenting of the skin by volar radius may cause ischemia of skin.

In old cases, arterial compromise or established compartment syndromes may be present.

Chronic cases typically have mild deformity and signs of median nerve involvement.

Imaging

Perilunate injuries may be subtle even on x-rays and could be even missed.

Therefore x-rays of wrist injuries need to be studied with great attention with due diligence to subtle findings.

PA and lateral views are generally sufficient but if needed additional views may be sought.

PA view/AP View

Normally, On the PA view, the space between individual carpal bones should be uniform throughout.

An uneven gapping between the carpal bones indicates disruption of the ligamentous connections.

The articular surface of the proximal and distal carpal rows should form smooth arcs [gilula arcs] at the radiocarpal and midcarpal articulations.

With perilunate dislocations, these arcs are disrupted and unusual overlap of adjacent bones is seen.

There may be an increased overlap of lunate and capitate.

Lateral Radiograph

In the uninjured wrist, the radius, lunate, and the capitate should be relatively collinear, with the proximal convex surface of the lunate seated on the distal radius and the head of the capitate seated in the concavity of the distal lunate.

The dislocation is more easily appreciable on the lateral view. Following observations would indicate an injury

• The capitate would not be found sitting within the distal articular ‘cup’ of the lunate
• Line drawn through radius and lunate fails to intersect capitate
• The majority of cases involve dorsal dislocation of the capitate and carpus relative to the lunate which remains in near-normal alignment with the radius. Volar perilunate dislocation is rare.
• In a trans-scaphoid perilunate dislocation the proximal scaphoid maintains its lunate relationship, and the distal scaphoid and remainder of the carpal bones displace dorsally.
• Abnormal scapholunate angle
  • Normal 30-60 degrees
  • Reduced in dorsal perilunate dislocation
• Abnormal capitolunate angle
  • Normal 0-30 degrees
  • Increased in dorsal perilunate dislocation)
• Associated Fractures
  • Scaphoid ( 60% of cases)
  • Radial styloid
  • Trapezium
  • Capitate
  • Triquetrum

CT

CT plays an important role in assessing for associated occult fractures; the most common and important being scaphoid fracture.

Treatment of Perilunate Injuries

Definitive treatment of perilunate injuries is surgical. For optimal treatment results, all perilunate dislocations and all perilunate fracture dislocations must undergo open reduction and internal fixation as soon after the injury as possible.

Conservative treatment has no role as loss of reduction has been reported in 59% of wrists where the initial anatomic closed reduction was achieved and a cast was applied.

A dislocation is an emergency and should be reduced as soon as possible as an emergent procedure and splinted. The extremity is elevated and iced until the definitive procedure is performed.

A well-padded plaster splint is applied once the carpus is reduced, to maintain the reduction. The patient should be observed carefully for skin or neurovascular compromise.

Often the patient will have sustained other severe injuries that will take priority and delay the surgical treatment.

The timing of the definitive treatment depends on the patient’s overall condition, swelling of the wrist and hand, or the need for appropriate surgical assistance.

Failure to achieve closed reduction mandates immediate open reduction and fixation.

Before the procedure, neurovascular examination should be assessed.

The strength of abductor pollicis brevis and two-point discrimination determination over the median nerve distribution of the hand should be particularly assessed.

Allen test or doppler Allen test should be performed to assess the integrity of the radial and ulnar arteries at the wrist.

The dorsal and volar skin must be carefully examined.

Approaches to Wrist

The wrist is approached by a single dorsal approach or the combined dorsal-volar approach to the wrist.

The combined dorsal-volar approach provides superior exposure. The volar approach enables repair of the transverse capsular/ligamentous rupture, a uniformly seen result of these injuries.

The arthroscopic approach may be a reliable therapeutic approach either alone or in conjunction with a dorsal miniopen approach.

Options for Surgical Treatment

Acute Cases

Closed Reduction in emergency

Tavernier’s maneuver for closed reduction

The traction is applied to the wrist and it is brought in extension. The surgeon’s thumb is placed on the lunate volarly to prevent creating a volar lunate dislocation. Then, the wrist is flexed with traction still maintained.

This should result in an audible or palpable clunk signifying a reduction of the capitate on the lunate and restoration of normal bony alignment.

Definitive Treatment

Surgical Treatment includes the following

• Open reduction, Ligament repair, Fixation with or without Carpal Tunnel Release

This is the treatment of choice in all acute injuries or presentation < 8 weeks. K-wires, intraosseous wiring are used for fixation.

Open reduction and repair of the scapholunate and lunotriquetral ligaments is indicated in all perilunate and lunate dislocations.

Acute reduction leads to a decreased risk of median nerve damage and cartilage damage.

However return to full function unlikely.

After the procedure, the hand should be elevated for 48 hours, and the patient is monitored for neurologic and vascular status.

The dressing is removed after 3-5 days and wound examined. Sutures are removed after 10-14 days short arm cast is applied for 3 months. Radiographs are obtained periodically to ensure maintenance of midcarpal and radiocarpal reduction.

Upon cast removal, the patient is placed in a removable splint, and gentle ROM exercises are begun. Splinting is continued until 6 months after surgery. Full activity is not renewed until 8 months after surgery.

A  patient with delayed onset of median nerve symptoms should undergo decompression of the carpal tunnel.

Most authors recommend ligament repair at the time of open reduction.

Delayed Presentation  of  Perilunate Injuries

Some patients may have minimal symptoms at the time of presentation but the long-term outcome is typically poor. Pain, weakness, and loss of motion are common, with posttraumatic arthrosis, carpal tunnel syndrome, and attritional flexor tendon rupture reported.

Late treatment options include open reduction and internal fixation, lunate excision, proximal row carpectomy, and wrist fusion.

Open reduction should be considered, even if the injury occurred long ago as reduction offers the greatest potential for restoring more normal wrist biomechanics.

Proximal row carpectomy is a reasonable option if reduction cannot be achieved and the head of the capitate has not been significantly injured.

Arthrodesis is also effective in relieving pain and improving strength.

Complications of Perilunate Injuries

In untreated patients, pain, loss of motion, and median nerve dysfunction can occur.

Unreduced dislocations the initial significant deformity can cause skin ischemic pressure necrosis.

In long-term stiffness, weakness, and osteoarthritis can occur in spite of the treatment.

Carpal instability may develop.

Perilunate fracture dislocations can also be complicated by fracture non-union. For example, scaphoid fracture non-union.

Prognosis

The outcome for untreated perilunate injuries is generally poor.

With treatment, maximal recovery of motion and strength typically occurred between 12 and 18 months.

The incidence of carpal instability and subsequent posttraumatic arthritis is believed to be reduced with open reduction and internal fixation.

References

• Krief E, Appy-Fedida B, Rotari V, David E, Mertl P, Maes-Clavier C. Results of Perilunate Dislocations and Perilunate Fracture Dislocations With a Minimum 15-Year Follow-Up. J Hand Surg Am. 2015 Nov. 40 (11):2191-7.
• Herzberg G, Burnier M, Marc A, Merlini L, Izem Y. The role of arthroscopy for treatment of perilunate injuries. J Wrist Surg. 2015 May. 4 (2):101-9.
• Souer JS, Rutgers M, Andermahr J, et al. Perilunate fracture-dislocations of the wrist: comparison of temporary screw versus K-wire fixation. J Hand Surg [Am]. 2007 Mar. 32(3):318-25.
• Muppavarapu RC, Capo JT. Perilunate Dislocations and Fracture Dislocations. Hand Clin. 2015 Aug. 31 (3):399-408.
• Budoff JE. Treatment of acute lunate and perilunate dislocations. J Hand Surg Am. 2008 Oct. 33(8):1424-32.
• Forli A, Courvoisier A, Wimsey S, Corcella D, Moutet F. Perilunate dislocations and transscaphoid perilunate fracture-dislocations: a retrospective study with minimum ten-year follow-up. J Hand Surg Am. 2010 Jan. 35(1):62-8.
• Stanbury SJ, Elfar JC. Perilunate dislocation and perilunate fracture-dislocation. J Am Acad Orthop Surg. 2011 Sep. 19(9):554-62.
• Kannikeswaran N, Sethuraman U. Lunate and perilunate dislocations. Pediatr Emerg Care. 2010 Dec. 26(12):921-4.
• Capo JT, Corti SJ, Shamian B, Nourbakhsh A, Tan V, Kaushal N, et al. Treatment of dorsal perilunate dislocations and fracture-dislocations using a standardized protocol. Hand (N Y). 2012 Dec. 7(4):380-7.
• Haase SC, Berger RA, Shin AY. Association between lunate morphology and carpal collapse patterns in scaphoid nonunions. J Hand Surg [Am]. 2007 Sep. 32(7):1009-12.
• Yasuda M, Ando Y, Masada K. Treatment of scaphoid nonunion using volar biconcave cancellous bone grafting. Hand Surg. 2007. 12(2):135-40.

Wrist biomechanics and function of the human wrist joint are unique.

The wrist joint is a diarthrodial joint composed of two rows of carpal bones. The proximal row articulates with the distal articular surface of the radius, which consists of the scaphoid fossa and the lunate, fossa.

The distal surface of the scaphoid, lunate, and triquetrum articulate with the distal carpal row, comprised of the trapezium, trapezoid, capitates, and hamate. The proximal articulation of the wrist is the radiocarpal joint, the distal articulation is the midcarpal joint. Six major articulations are

• Radiocarpal
• Midcarpal
• Pisotriquetral
• Trapeziometacarpal
• Common carpometacarpal
• Distal radioulnar joints. Each has multiple subarticulations.

The intrinsic ligaments hold the bones of the proximal and distal carpal rows together.

Each of the carpal bones is unique in its mechanics and possesses a unique center of rotation. The overall motion in the wrist is, essence, the sum of the carpal bones moving on each other, influenced by their articulations, ligamentous attachments, and indirect actions of adjacent tendons.

An understanding of the normal biomechanics helps in to assess the mechanisms of wrist injuries better and determine the appropriate treatment.

Normal Carpal Biomechanics

Wrist motion occurs at radiocarpal and intercarpal or midcarpal joints.

There are three axes of motion

• Flexion-extension
• Radial-ulnar deviation
• Prono-supination

Different movements of the wrist are

• Flexion is about 65-75 degrees. 40%  of the movement is at radiocarpal joint and 60% is at midcarpal joint.
• Extension is also about same degrees and the amount of movement contribution differs. 66%  is radiocarpal and 33% is midcarpal
• Normal radial deviation is about 15-25 degrees and 90% movement is midcarpal
• Ulnar deviation is about 35-50 degrees and is equally divided in radiocarpal and midcarpal joints.

The carpus is biaxial in nature and maintains a constant carpal height ratio during radial and ulnar deviation.

[This ratio is the distance from the base of the third metacarpal to the distal subchondral plate of the radius, divided by the length of the third metacarpal. This normal carpal height ratio is 0.54+_ 0.03.]

The proximal carpal row is an intercalated segment with no tendon attachments. All the tendons that influence wrist motion insert distally, either

• Base of the metacarpals
  • Flexor carpi radialis
  • Extensor carpi radialis longus and brevis
  • Extensor carpi ulnaris
• Onto the pisiform
  • Flexor carpi ulnaris

Thus, wrist motion in any plane must be initiated at the distal carpal row. Motion in the proximal carpal row begins only when the extrinsic ligaments crossing the midcarpal joint become taut and the force exerted on the proximal carpal row becomes greater than the frictional forces of the intervening articular segments and the resistance of the antagonistic muscular forces.

In spite of some motion between the individual bones of the distal carpal row, these bones function as a single unit with the index and middle metacarpals.

Wrist motion produces multiplanar motion of the distal carpal row because of geometry.

During flexion of the wrist

• Distal carpal row flexes and deviates slightly ulnarly.

During extension

• the distal carpal row extends and deviates radially.

With radial deviation

• the distal carpal row deviates radially, extends and supinates.

With ulnar deviation

• The distal carpal row deviates ulnarly, flexes, and pronates.

Thus,  the relationship between the distal carpal row and the index and middle metacarpals is maintained throughout all directions and magnitudes of motion.

But the proximal carpal row cannot be considered a single functional unit as a significant motion occurs between the bones.

There is coordinated motion between the distal and proximal carpal rows.

As the distal carpal row flexes, the proximal carpal row also flexes. Similarly, when the distal carpal row extends, the proximal carpal row extends.

Radial or ulnar deviation involves a complex reciprocating motion of the proximal and distal carpal rows.

Distal carpal row inclines radially and extends and supinates whereas proximal carpal bones principally flex and translate ulnarly.

With ulnar deviation, the opposite occurs. The distal carpal row inclines ulnarly and flexes and pronates, whereas the proximal carpal bones extend and translate radially. These complex motions are required to maintain the carpal congruency and spatial consistency in all wrist positions.

The scaphoid, because of its position, has the potential energy for flexion, while the triquetrum, because of its articulation with the hamate, has potential energy for the extension. This potential energy created in the proximal carpal row is facilitated by a scapholunate interosseous ligament, which stabilizes the scaphoid and the lunate, and the lunotriquetral interosseous ligament, which stabilizes the lunate and the triquetrum.

The result is a dynamic, balanced lunate within the proximal carpal row. During radial deviation, the proximal carpal row translates toward the ulna, while the distal carpal row inclines toward the radius. Additionally, the scaphoid must flex to avoid impinging on the radial styloid, and the entire proximal row is pulled into flexion as long as there is an integrity of the scapholunate interosseous ligament.

In ulnar deviation of the carpus, the triquetrum is forced into extension by its helicoid articulation with the hamate. This pushes the remainder of the proximal carpal row into extension by virtue of the force transmission through the LTIL. in contrast, the distal carpal row has negligible intracarpal motion, being generally bound together by very short, stout ligaments with broad insertions.³⁴

Ligaments, in general, are composed of 90% type I collagen and 10% type III collagen and  function primarily as viscoelastic structures

The relatively greater strength and viscoelastic nature of the interosseous ligaments reflect their functional characteristics and anatomy. The complex, intercalated movements of the proximal carpal row are facilitated by the interosseous ligaments, which are strong and particularly accommodating to shear stress. The extrinsic wrist ligaments, by contrast, are much weaker and stiffer because there is little need for these structures to have dynamic capabilities.

In spite of knowing the movements, the principle or theory of carpal motion is not fully elucidated.

Following theories have been floated.

Column theory of carpal kinematics

The column theory was first proposed by Navarro in 1935. It divides the wrist into the following three columns:

• Radial column, consisting of the scaphoid, the trapezium, and the trapezoid. The scaphoid is center of motion and it  is mobile
• Central column, including the lunate and the capitates and participate in flexion-extension motion
• Ulnar column or medial column, consisting of the triquetrum and the hamate and the motion is rotation.

Row theory of carpal kinematics [Link Theory]

• Comprises proximal and distal rows
• Scaphoid is a bridge between rows
• Motion occurs within and between rows
• Muscle contractions impart rotational moments to the proximal row through the distal row, and carpal motion is governed by a combination of ligamentous and articular constraints.
• The scaphoid, lunate, and triquetrum rotate in the same primary direction, albeit to different magnitudes, during any movement of the hand.

Combined column-row theory of carpal kinematics

Some have theorized that an individual’s carpal kinematic behavior can be explained by some combination of the columnar theory with the row theory.

It is found that the amount of scaphoid shortening and ulnar translation of the scaphoid varies in a normal distribution.

Also, if the scaphoid shortens more, it translates less. Some authors attribute it to the difference in individual laxity.

In radial-ulnar deviation, the scaphoid of very lax wrists moved preferentially in the sagittal plane (flexion-extension), whereas in the more rigid wrists, the scaphoid moved preferentially in the frontal plane (radioulnar deviation).

Oval-ring theory of carpal kinematics

The oval-ring theory functionally depicts the carpus as a transverse ring formed by proximal and distal rows and joined by two physiologic links, one radial and the other ulnar.

The radial link is the mobile scaphotrapezial joint, and the ulnar link is the rotatory triquetrohamate joint.

Mechanism of Wrist Injuries

Radial-Sided Carpal Instabilities

These occur following injury caused by compressive force across a hyperdorsiflexed wrist.

The spectrum of injuries has a common mechanism

• Hyperdorsiflexion of the wrist
• Forearm pronation
• Ulnar deviation of the hand
• Axial loading of the wrist through the radial palm and thenar eminence

Four distinct Patterns of injury are collectively called progressive perilunate instability.

That progression occurs in four stages.

Stage I

Disruption of the scapholunate and radioscaphocapitate ligament

Stage II

The capitates and scaphoid separate from the lunate and the triquetrum.

Stage III

Injury continues ulnarly and separates the triquetrum from the lunate. Carpus is completely separated from the lunate resulting in a perilunate dislocation.

Stage IV

Complete lunate dislocation. The perilunate and the lunate dislocations may occur in a dorsal or palmar direction.

Pure perilunate dislocation, without fractures, is termed lesser arc injury.

Perilunate dislocations with fractures are called t greater arc injuries and are prefixed with trans.  The pure greater arc injury propagates in a transscaphiod, transcapitate, and transtriquetral fashion. Typically, these injuries occur secondary to high-energy trauma, and the position of the wrist at the time of injury will determine the fracture-dislocation pattern

They are thought to result from high-energy three-dimensional loading of the wrist with axial and torsional forces applied to any combination of hyperextension, hyperflexion, and radial or ulnar deviation.

Ulnar-Sided Wrist Ligament Injuries

Some perilunate wrist injuries initiate on the ulnar side of the wrist.

These are lunotriquetral ligament injuries along with a spectrum, beginning with simple ligament tears and progressing to static ventral intercalated segment instability.

Progressive perilunate disruption is a three-stage injury mechanism.

Stage I

Tear of the lunotriquetral ligament

Stage II

• Disruption of the palmar ulnar leash complex
• Dorsal radiotriquetral and the dorsal scaphotriquetral ligaments

Stage III

• Tear of the scapholunate ligament

Axial Disruptions

[Also longitudinal disruption capitohamate diastasis and columnar dislocations.]

Axial disruption of the wrist are and usually occur secondary to high-energy crush or blast injuries as derangement of the carpus that is oriented parallel to the long axis of the forearm.

In axial carpal disruption, the normal convexity of the metacarpal arch is flattened, rotational deformities of the fingers occur, and the carpometacarpal junction is widened.

The typical mechanism of the injury of axial carpal disruptions a crush[most common], twisting, or blast injury.

The spectrum ranges from acute traumatic fracture dislocations with severe soft-tissue trauma to chronic dynamic instability between the axial components.

Three groups have been defined according to the direction of the instability

• Axial-ulnar disruptions
• Axial-radial disruptions
• Combined axial-radial-ulnar disruptions.

In axial-ulnar disruptions, the carpus splits into two columns, with the radial column stable with respect to the radius and the ulnar column with the metacarpals is displaced ulnarly and proximally.

In axial-radius disruptions, the ulnar column is stable with respect to the radius, and the radial column including the metacarpals displaces proximally and radially.

A combination of the ulnar and radial displacement of the column is classified as an axial-radial-ulnar disruption.