The metacarpo-phalangeal (MCP) joint is located at the base of the thumb where it joins the hand and is the most common site for injuries of the thumb. A capsule surrounds the joint with thickenings along each side known as the radial and ulnar collateral ligaments (UCL).

These injuries may be classified as mild, moderate or severe (grade I, II or III). Any injury to the ulnar collateral ligament may be accompanied by a fracture, especially in immature athletes who are still growing. Initially, the injured athlete should be checked for obvious deformity. If he/she is comfortable the athlete may be allowed to complete competition with the MCP joint taped and the thumb taped to the hand. All athletes with suspected UCL injuries should be evaluated with x-rays following competition to rule out any associated fractures.

Treatment for partial tears of the UCL consists of immobilization in a thumb splint for 3-4 weeks. Rehabilitation is started after this period and includes range of motion exercise with splinting between exercise sessions. The splint is discontinued between 4-8 weeks depending on the severity of the injury except for sports participation. A brace is used for 3 months following the injury during sports to allow the ligament to heal and prevent re-injury.

Surgical repair of UCL injuries is recommended for most complete tears. Severe bruising and laxity of the joint without an endpoint on stress examination usually help to identify complete tears. Fractures that involve more than one third of the joint surface or those which are displaced should be stabilized surgically. Immobilization after surgery is the same as for conservative management.

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