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
Stabilize adjacent carpal bones.
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
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.
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.
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
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
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.
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.
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.
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.
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