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Injury to the Ulnar Collateral Ligament of the Thumb
Wednesday, 13 March 2013 00:00

By: Tom Gocke, MS, ATC, PA-C, DFAAPA

The thumb is a unique structure of the hand and allows us to perform many tasks daily. Injury to the collateral ligaments will prohibit apposition and opposition of the thumb with the ulnar four (4) fingers. Injuries to the ulnar collateral ligament can occur acutely (Skier's thumb) or from repetitive actions (Gamekeeper's thumb). My blog today will discuss the differences between skier's and gamekeeper's thumb injuries.

General Anatomy Review

The thumb Metacarpal Phalangeal (MCP) is a diarthrodial joint with a primary function is to allow flexion and extension. The MCP joint support structures are divided into static (ligament) and dynamic (muscle/tendon) stabilizers. The static stabilizers are comprised of the collateral ligaments (radial/ulnar), accessory collateral ligaments, the volar plate (aka: palmer plate) and the dorsal capsular ligament. The collateral ligaments restrict in flexion, accessory collateral ligaments restrict in extension, the volar plate limits extension and the dorsal capsular ligament limits in flexion. The ulnar collateral ligament originates at the metacarpal head and inserts at the base of the proximal phalanx. Dynamic stabilizers of the MCP joint include the extensor hood, intrinsic/extrinsic muscles of the thumb and the adductor musculature of the thumb. Remember, that the adductor tendons will attach at the level of the ulnar collateral ligament. The dorsal sensory branch of the radial nerve traverses near the ulnar aspect of the thumb.

Gamekeeper's Thumb

A true gamekeeper's thumb injury involves attenuation of the ulnar collateral ligament (UCL) of the MCP joint at the thumb. It is a recurrent injury that results from a constant or frequently recurring stress placed on the ulnar collateral ligament. This long-term stress allows for the collateral ligament to stretch or loose integrity over time. This chronic laxity allows for instability and arthritic changes to occur at the MCP joint. The gamekeeper's injury is frequently used to describe acute and recurrent injuries to the ulnar collateral ligaments at the thumb MCP joint. However, it more accurately describes the work related injury suffered by European game keepers. The gamekeeper would sacrifice small animals breaking their neck by forcing the neck between the thumb and index finger. This repetitive mechanism would lead to an initial valgus injury and then repeated valgus stress that would force the collateral ligament to heal in an elongated fashion. This would ultimately lead to instability, pain and weakness with the pinch motion (grasp).

Skier's Thumb

A more accurate description of an acute injury to the ulnar collateral ligament would be to call it a "skier's thumb". In this case, the ulnar collateral ligament is injured when a patient falls while grasping a pole (or any other cylindrical object) and has an acute forced valgus stress to the thumb MCP joint. Skier's thumb is a fairly common injury. A variant of the acute ulnar collateral ligament sprain is a Stener lesion. This occurs when the UCL (and accessory ligaments) rupture and a portion of the adductor aponeurosis becomes interposed between the UCL and its insertion point on the base of the proximal phalanx. This will prevent the UCL from making bone contact and will impede healing. This lesion can also occur when an avulsion fracture impacts the MCP joint and prevents anatomic bone healing. This fracture can present with acute swelling and a palpable lump or deformity in the ulnar side of the thumb. Radiographs will show an intra-articular fracture in the ulnar base portion of the thumb metacarpal.

Evaluation & Treatment

The hallmark of treatment is recognition of the injury. For injuries to the UCL, recognizing the mechanism of injury will be a key component in evaluation. Differentiating the difference from a repetitive mechanism vs. an acute injury will guide long-term treatment. The major difference in the recurrent vs. acute UCL injury is the presence of swelling. The acute inflammatory response is activated when soft tissue is injured thus resulting in swelling. This will be localized in the area of the thumb MCP but may extravasate into the thenar hand space. Ecchymosis is an indication of acute injury but does not quantify the extent of injury. Range of motion (ROM) will be limited 2nd to swelling in the acute injury or bone block in an avulsion fracture at the base of the proximal phalanx. Arthritic changes in the recurrent injury may limit ROM as well. The amount of pain and laxity at the UCL on stress test will determine the extent of injury. Keep in mind that pain and patient apprehension maybe a limiting factor in the initial assessment of injury. In the gamekeeper's injury, the amount of associated arthritic pain may be a contributing factor. Keep in mind that an associated Stener lesion or bony avulsion fracture will affect your initial assessment of laxity of the UCL.

Radiographs will reveal any avulsion fracture or other bony injury. The amount articular surface involvement in an avulsion fracture will dictate whether surgical repair is warranted. With some variability, fracture fragments that occupy > 25% of the articular surface and have > 3mm of displacement should be surgically repaired. Likewise, UCL laxity that has the clinical appearance of a soft tissue block (Stener lesion) that prevents the anatomic alignment of the MCP joint will necessitate surgical exploration and repair of tissue injuries.

Initial immobilization in a well padded thumb spica splint is desirable. This allows the acutely painful and/or arthritic painful joint to rest and limit ROM which can contribute to pain. In non-Stener lesions and the absence of fracture, these acute injuries will heal in about 6 weeks. There is considerable variability in immobilization preferences. These range from forearm based thumb spica cast, hand based thumb spica cast, forearm or hand based custom molded thermoplastic splint, to commercial thumb based splints. In the more chronic UCL laxity, the immobilization device is more for rest and reduction of pain symptoms. Adherence to splint wear is more flexible since acute ligament healing is not a concern.

Conclusion

Injuries to the UCL can be from acute injury or from recurrent stressors placed on the thumb. Recognition of injury mechanisms will aid the clinician in determining the amount of injury to the UCL. In acute injury, most UCL sprains will heal in 6 weeks with adequate immobilization. In more chronic UCL injuries or in the case of acute injury that is associated with a Stener lesion or bony avulsion fractures, surgical correction maybe necessary. Having a working knowledge of the differences between acute (Skier's thumb) and chronic (Gamekeeper's thumb) UCL thumb injuries will help the clinician treat their patients in a more comprehensive fashion.

To learn more about hand injuries and other ortho-related injuries, go to www.orthoedu.com.

 

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