Background

Gamekeeper's thumb is a clinical instability of the first metacarpophalangeal (MCP) joint caused by an insufficiency of the ulnar collateral ligament (UCL) in the MCP of the thumb. Because the stability of the thumb is important for prehension, treatment is directed toward optimizing the healing of the ligament to restore its full function.^{[1, 2, 3, 4, 5]}

The common name for this condition, originally coined in 1955,^[6]  derived from the observation that this injury was most often associated with Scottish gamekeepers, especially rabbit keepers. In these individuals, the injury was work-related, occurring as game animals (eg, rabbits) were sacrificed. The animals' necks were broken between the ground and the gamekeeper's thumb and index fingers; this placed a valgus force onto the abducted MCP) joint, leading to UCL injury and to instability accompanied by pain and weakness of the pinch grasp.

Currently, this type of injury is typically more acute. The most common mechanism is a skier landing on the ground with his or her hand braced on a ski pole, causing a valgus force on the thumb.^[7]  The alternative term skier's thumb reflects the acute nature of the injury.^{[8, 9, 10, 11, 12, 13]}

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Anatomy

The MCP joint is a diarthrodial joint that is primarily involved in flexion and extension. The static restraints and some dynamic stabilizers provide joint stability.

The static restraints include the proper collateral ligament (mostly in flexion), the accessory collateral ligament (mostly in extension), the palmar plate (mostly in extension), and the dorsal capsule (limited, in flexion). The dynamic stabilizers include the thumb intrinsic and extrinsic muscles. The adductor mechanism is particularly important here because it inserts onto the extensor expansion through its aponeurosis, which lies superficial to the UCL.

The UCL is a 4- to 8-mm × 12- to 14-mm band that originates from the metacarpal head and inserts into the medial aspect and base of the proximal phalanx of the thumb. Occasionally, when the UCL is strained, it avulses the bone at its insertion and leads to a gamekeeper's fracture.

Pathophysiology

A Stener lesion occurs when the adductor aponeurosis becomes interposed between the ruptured UCL and its site of insertion at the base of the proximal phalanx. Thus, the distal portion of the ligament retracts and points superficially and proximally. A rupture of the proper and accessory collateral ligaments must occur for this injury to happen. The UCL no longer contacts its area of insertion and cannot heal.

Occasionally, failure of the UCL avulses a small portion of the proximal phalanx at its insertion, leading to a gamekeeper's fracture^[8] ; this injury can be subtle or obvious, and it can involve a substantial portion of the articular surface of the proximal phalanx. However, a lump or mass over the ulnar aspect of the MCP joint of the thumb does not necessarily imply a fracture; it may be the result of the Stener lesion.

Etiology

Gamekeeper's thumb is caused by a valgus force that is directed on the MCP joint of the thumb and produces a failure of the UCL. Falls on an abducted thumb and the fall of a skier against a planted ski pole are common mechanisms. (For a discussion of the anatomy of the MCP joint and the UCL, see Anatomy.)

Chuter et al, over a 10-year period, studied 127 patients who underwent surgical repair of an acute thumb UCL rupture for clinically unstable injuries or displaced avulsion fractures.^[4] Most of the injuries (≥66%) were hyperextension or abduction injuries. The most common cause was a fall (49%), followed by sports injuries (skiing injuries accounted for only 2.4% of injuries). More than 99% of patients had a UCL rupture confirmed at surgery. Other findings included avulsion fractures (21%), dorsal capsular tears (57%), and dorsal capsule infolding (29%).

Epidemiology

Gamekeeper's thumb is a common injury. The incidence is increased in skiers, but it does not depend on the type of ski pole used. No sex-related proclivity exists.

Prognosis

Failure to diagnose this injury and the patient's failure to seek medical treatment are the most common reasons for a poor outcome.

Early diagnosis is the most important determinant of functional outcome in cases of gamekeeper's thumb. In more than 90% of complete ruptures that are surgically treated within 3 weeks of the injury, a good-to-excellent result can be expected. Repair within 1 week of the injury is optimal. The prognosis for all repairs and reconstructions that are undertaken longer than 6 weeks after a complete UCL rupture is poor.

In thumbs with partial ligament injuries, nonsurgical treatment by means of immobilization yields a stable, painless thumb with nearly normal motion in most cases. In complete tears, the failure rate of treatment with bracing and early motion is 50%. If a patient is unable to tolerate or refuses surgery, the use of a brace or thumb spica splint is the treatment of choice. However, full stability of the thumb is unlikely.

Pain and stiffness can be expected to be mild or absent, and pinch and grip strength will be nearly normal. The rate of return to former activities, including recreational sports, is reported to be as high as 96%.

Clinical Presentation