Clinically Relevant Anatomy
The hamate bone is one of eight carpal bones, it is a triangular bone, composed of a body and a hook, located on the ulnar side of the distal carpal row. The hamate is bordered proximally by the pisiform and the lunate in the proximal carpal row, radially by the capitate, and distally by the bases of the fourth and fifth metacarpals.. The Guyon canal carries the ulnar artery and nerve, for this reason hook fractures should suggest a high probability of ulnar artery and nerve damage. Hamate fractures constituted about 2% of all carpal fractures. They are classified as:
- Type I fractures involving the hook - more common than type II fractures.
- Type II fractures involving the body.
Mechanism of Injury / Pathological Process
Hamate fractures are most often seen in racket, club or bat sports. Racket sports, like tennis, cause impact of the grip against the hook of the hamate of the dominant hand where as in golf, baseball and hockey the club will impact against the hamate in the non-dominant hand. Type I fractures involving the hook of the hamate can occur via several different mechanisms:
- Repeated micro trauma
- Direct trauma
- Indirect trauma
Repeated micro trauma to the hook in sports involving swinging clubs, bats, or rackets can result in a hook stress fracture. These usually occur in the non-dominant hand. Direct trauma can occur during sports when the butt of the club rests on the hamate and the force of the swing is then transmitted directly to the bone. A fall onto an outstretched hand or a fall on the hand while holding an object is also seen in certain sporting activities. Indirect trauma can be applied to the hook through its muscular and ligamentous attachments. This can occur either when falling on a hyperextended wrist or during power grips. Type II fractures involving the body of the hamate always requires a direct force. These fractures are typically associated with high-energy, direct-force trauma or contusion injuries.
Point tenderness on the hypothenar and weak grip are characteristics of hamate fractures. Patients typically present with pain and tenderness over the hamate. Ulnar and median neuropathy can also be seen, as well as rare injuries to the ulnar artery. Displaced hamate fragments and haematoma as well as nonunion of the hook of the hamate can lead to neuropathy of the deep branch of the ulnar nerve, lesion of the median nerve, or even rupture of deep flexor tendons IV and V. Decreased sensation or weakness may be due to ulnar or median nerve injury. The fracture fragments may injure the nerves directly or swelling and inflammation may injure them indirectly. With a fracture of the hook of the hamate there might be pain on the dorso-ulnar aspect of the wrist.
An oblique x-ray view or a carpal tunnel view should be considered as part of the initial diagnostic investigations. It can help with diagnosis and give further important information to aid appropriate management. Usually they are negative, a CT scan of the wrist in the “praying position” is the imaging modality of choice. A high density CT scan with the wrists in the “praying position” allows comparison between the two wrists. It is reported to have a sensitivity of 100%, specificity of 98.4%, and accuracy of 97.2% and is the radiographic technique of choice in the diagnosis of hook of the hamate fractures.
Fractures of the body of the hamate are difficult to diagnose. AP (anteroposterior), lateral and oblique views are more useful for diagnosis of body fractures than for hook fractures. The oblique and lateral views are the most useful. When routine films are negative and when a fracture is highly suspected, a CT scan should be taken. Assessments of the degree of angulations, reduction and articular incongruence or subluxation are the important imaging findings.
The hook of the hamate pull test (HPPT) is a clinical test for diagnosing a hook of hamate fracture.
Management / Interventions
Conservative option for nondisplaced fractures is a short-arm cast. The cast should immobilize the metacarpophalangeal joints of the fourth and fifth fingers and be a thumb spica to decrease micrononuinion at the hook. The cast should be worn for 6-8 weeks to prevent nonunion. If pain is still present after cast removal, then excision for nonunion is the treatment of choice. In the most studies, surgical treatment (fragment excision and open reduction and internal fixation (ORIF)) of a hamate fracture has a higher success rate than after conservative treatment.
Depending on the injury passive and active exercises are explained and exercised. As the healing of the tissue progresses and the function of the involved joint improves, coordination exercises, exercises against resistance and exercises to restore strength are incorporated into the exercise program.
During the first days after injury edema in the hand may be evident, usually located on the dorsum of the hand. As a result, the function of the hand is negatively affected. In extreme swelling positioning the hand above the elbow can assist in reducing the swelling. In an intra-articular injury ice will immediately be applicated after the trauma, surgery or exercise to the involved joint to avoid post-traumatic arthritis
During the rehabilitation physiotherapist uses passive mobilizations to normalize the ROM and the rolling and sliding motion of the involved joint. These mobilizations may include traction, translation and angular mobilizations. In intra-articular lesions tractions can be performed to obtain pain relief. If in the last phase of the revalidation there is still capsular retraction, traction and translations can be carried out. During rehabilitation after plaster immobilization of the wrist there will be some stiffness of the capsule in the wrist. Here, traction and translations are performed. The patient is also encouraged to mobilize as much as possible the affected joints to improve function and return to activity as quickly as possible. Patients are encouraged to actively mobilize the adjacent joints to avoid stiffening.
After an injury, the balance between phasic and tonic muscles restored. In the hand wrist and finger flexors are tonic muscles. With a hand or wrist injury these muscles show an elevated tone and have the tendency to shorten. The flexors of the hand should be stretched and (as pain and swelling allows) excentric trained.
To start building progressive resistance exercises, the fracture has to be sufficiently consolidated. The exercises consist of concentric and eccentric muscle activity, closed and open chain exercises. Resistance exercises are necessary to regain a good functionality of the hand.
Low-intensity ultrasound has been reported to be useful in promoting fracture healing, it accelerates the normal fracture repair process.
Ultrasound treatment might be useful for nonunion caused by a repeated stress, the ultrasound is a treatment for nonunion of the hook of the hamate and is an option in various treatment methods.
Differential diagnosis includes:
- Flexor/extensor carpi ulnaris tendon injury
- Metacarpal/carpal bone fracture or contusion
- Triangular fibrocartilaginous complex tear
- Ulnar artery thrombosis
- Ulnar nerve neuropathy
- Carpal tunnel syndrome
Decision between casting and surgery is based on the lifestyle demands of the patient. The athlete who does not want to risk healing a nonunion after casting may opt for surgery to minimize the time away from sport. Similarly, a patient with a job that requires repetitive grabbing, gripping or lifting may elect for excision to reduce the risk of an extended period of time away from work.
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