Incidence of Carpal Bone Fractures
Following is a rough approximate incidence of carpal bone fractures
Source: Gelberman RH et al. J Hand Surg 1983
Mechanism of Injury To Carpal Bones
Most of the carpal bones fractures occur due to falling on outstretched hand concentrating the body weight and external forces on the wrist. Other mechanisms include palmar flexion, a motorcycle accident, or twisting injuries in sports.
Axial compression force applied with the wrist in hyperextension places palmar ligaments under tension and the dorsal joint surfaces put under compression and shear stresses.
For example, a scaphoid injury appears to occur if the wrist is dorsiflexed past 95 degrees and radially deviated by 10 degrees. The proximal pole of the scaphoid is held by the radius and the proximal radioscaphocapitate ligament in this position, while the distal pole of the bone is carried dorsally by the trapeziocapitate complex.
The fracture can be transverse, oblique, or comminuted depending on the direction of the load.
High-energy forces result in carpal bone fractures or ligamentous disruptions whereas low energy forces result in sprains.
Following article discusses carpal bone fractures other than scaphoid.
Fractures of Lunate
Lunate is the fourth most fractured carpal bone after the scaphoid, triquetrum, and trapezium.
Acute fractures of the lunate are classified into five types-
- Frontal fractures of the palmar pole with the involvement of the palmar nutrient arteries.
- Osteochondral fractures of the proximal articular surface without substantial damage to the nutrient vessels.
- Frontal fractures of the dorsal pole.
- Transverse fractures of the body.
- Transarticular frontal fractures of the body of the lunate.
Fresh fractures of the lunate include dorsal and palmar horn avulsion fractures that occur more often in the radial corner than in the ulnar corner. Fractures of the body are usually transverse in the coronal plane. The more common of these is between the middle and palmar thirds of the body.
Lunate fractures are difficult to visualize early due to superimposed structures. Therefore, if the routine radiographs fail to show fractures, further investigations should be sought if there is a clinical suspicion of the lunate fracture.
Available investigations are bone scan, CT or MRI.
In fractured lunate, technetium 99m bone scan will be positive within 24 hours of injury.
A CT scan would show the fracture clearly. Osteonecrotic changes are also more easily seen on CT and would also help to identify whether the fracture is primary or secondary [Secondary fractures of lunate occur in Kienboch disease]
MRI not only shows a fracture but also can assess the blood supply. It is able to pick osteonecrosis in early stage and in a healing stage can help to asses revascularization.
Most fractures of the lunate can be treated by immobilization in the cast for four weeks.
All fractures of the lunate need to be followed up by regular x-rays and MRIs when required to look for osteonecrosis.
Nonunion of a lunate body fracture is rare because of most progress to Kienbock Disease.
Fractures of Triquetrum
The triquetrum is the second most commonly fractured carpal bone, first being scaphoid. Most of these fractures are avulsion injuries and the most common cause is impingement of the ulnar styloid [Occurs with the wrist in extension and ulnar deviation] or hamate.
There is pain and tenderness on the ulnar side of the proximal carpal row.
Fractures of the triquetral body are identified on the AP view
CT scan and MRI may help to detect missed fractures and associated injuries.
For undisplaced fractures, immobilization in a forearm plaster cast for 4 weeks is sufficient.
Displaced fractures are treated by closed reduction and immobilization after reduction is successful.
If closed reduction cannot be achieved, open reduction and internal fixation is done.
Fractures of Trapezium
Fractures of the trapezium comprise approximately 3% to 5% of all carpal bone fractures and it is the third most common fractured bone.
They are very important fractures to detect because of its involvement in the first carpometacarpal joint in actions such as grip and pinch.
Fractures of trapezium usually result from high energy trauma.
They are of two main types
- Ridge fractures
- Body fractures
Most of these fractures are vertical body split fractures.
Ridge fractures are mostly avulsion fractures caused by the capsular ligaments can occur during forceful deviation, traction, or rotation.
Fractures of the tuberosity of the trapezium may be associated with fractures of the hook of the hamate or with dislocation of the hamate.
- Tenderness and swelling at the base of the thumb
- Painful pinch
Routine views for detecting injury are standard PA, lateral and oblique views of the wrist. Special views include
The beam is directed toward trapeziometacarpal joints with wrist pronated and hypothenar eminence resting on the cassette.
Carpal Tunnel view
Consider getting comparison views of the normal wrist, or CT scan if the diagnosis is not definitive on plan films.
If the x-rays do not help to reach the conclusion, computerized tomography [CT] or bone scintigraphy can be done.
Stability of the joint is evaluated before carrying out before carrying out the treatment. Rupture of the surrounding ligaments and the dorsal joint capsule may result in instability and they need to be repaired.
Fractures involving an articular surface require accurate reduction and in displaced fractures, open reduction and internal fixation are recommended.
Undisplaced fractures can be managed by below elbow cast immobilization.
Fractures of Trapezoid
Trapezoid fractures represent 0.4% of all carpal injuries and rarely occur as an isolated fracture. The trapezoid, being located between the first and second ray may be exposed to fewer forces
Injury to the trapezoid generally occurs when force is applied through the second metacarpal.
The patient usually presents after injury with pain and swelling in the wrist in the second metacarpal area. There would also be a loss in the range of motion of the wrist
Routine wrist views including oblique views are done. Loss of the normal relationship between the second metacarpal base and the trapezoid may indicate injury to the trapezoid.
A computed tomography scan with 3-D reconstruction may help in confirmation of diagnosis where the diagnosis cannot be made on routine imaging.
Because of the rarity of isolated trapezoid fractures, a standard treatment has not been established. Recommended treatments in undisplaced fractures include cast immobilization.
Open reduction and internal fixation with or without excision of small fragments can be done for displaced fractures.
Fractures of Capitate
The capitate is the largest carpal bone. Capitate fractures of the wrist which initially were thought to be rare are being reported more commonly and it is thought that they were missed quite often earlier.
Two injury mechanisms are postulated:
- Direct blow
- A fall on outstretched hand with the wrist in dorsiflexion.
The patient would present with a swelling after the injury to the wrist in the line of the third and fourth metacarpal. Tenderness may be present
Fractures of the capitate can usually be identified on standard scaphoid views. CT scans and MRI may be necessary to detect occult capitate fractures.
Recommended treatment of capitate fractures includes early immobilization for 6 to 12 weeks. Excision of very small proximal fragments has also been described.
Herbert screw fixation may be needed in displaced fragments.
Hamate fractures are rare though a recent increase in the incidence has been noticed following rising of sports activities.
Fractures of Hamate
Hamate fractures are thus classified as type I fractures involving the hook and type II fractures involving the body. Type I fractures are more common than type II fractures.
Most of the hamate hook fractures are seen in individuals who participate in sports involving a racquet, bat, or club or in individuals who have a history of falling on an outstretched hand.
Hamate body fractures may be caused by direct trauma.
Hamate body fractures are commonly associated with dislocation of the fourth and fifth fingers. ally require internal fixation because of the high incidence of instability in these injuries.
The usual complaint is of pain in the wrist in the line of fourth and fifth metacarpal. The pain is aggravated by grasp, pain with dorso-ulnar deviation.
Physical examination reveals tenderness on palpation over the hook of the hamate. There would be a decrease in grip strength. Sometimes, ulnar nerve my get involved [Compression in Guyon’s canal] and paresthesia may be present in the fourth and fifth fingers.
Few of the cases are completely asymptomatic when an acute injury occurs and only present when chronic condition develops.
Many authors recommend carpal tunnel but the view may be difficult to obtain due to positioning problems.
CT is considered a better method for detection of these fractures. MRI may aid in the detection of associated soft tissue injuries.
A study of the literature shows that conservative treatment which was common in the past might have resulted in nonunion rates greater than 50% and as high as 80-90%.
Therefore there is an increasing trend to operate these fractures.
Two types of surgeries are commonly performed for hamate hook fractures.
- Excision of the hook itself.
- Open reduction and internal fixation
One of the important complications is entrapment of the ulnar nerve and requires decompression of Guyon’s canal.
Other reported complications of ununited hook fractures include-
- Carpal tunnel syndrome
- Ulnar artery compromise
- Partial or complete flexor tendon ruptures involving the fourth, fifth fingers.
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