CARPOMETACARPAL AND METACARPOPHALANGEAL INJURIES OTHER THAN FRACTURE
The thumb acts as a very mobile post that opposes the actions of the index, middle, ring, and small fingers. The stability of the thumb is therefore very important in hand function.
Injury To Ulnar Collateral Ligament Of The Thumb
In the metacarpophalangeal joint of the thumb, injury to the ulnar collateral ligament destroys joint stability and impairs the ability to pinch. Known as the game-keeper thumb, this injury is a common consequence of skiing, motor vehicle, and occupational accidents.
Any injury to the ulnar side of the metacarpophalangeal joint of the thumb must be evaluated with a stress test to determine the integrity of the ulnar collateral ligament. The stress test should be performed using digital block anesthesia. If the test shows joint instability, the ulnar collateral ligament should be repaired surgically.
Surgical examination often reveals the adductor tendon aponeurosis interposed between the torn ends of the ulnar collateral ligament; this condition, called the Stener lesion, prevents healing. A tear in the substance of the ligament itself is repaired with interrupted sutures. If the ligament is avulsed from the bone, repair with a pull-out wire or bone suture anchor is needed. Avulsion of a bone fragment together with the ligament requires reduction of the fragment and fixation with a small screw, a pull-out wire, or Kirschner wires.
To ensure stability, a Kirschner wire is sometimes placed across the joint to relieve the tension on the repaired ligament. After ligament repair, the thumb is immobilized in a cast for at least 4 weeks. The patient can begin guarded activity at 4 weeks, after the cast and pin are removed. Early anatomic repair of gamekeeper thumb produces quite satisfactory results.
Dislocation Of Carpometacarpal Joint
This thumb injury can also be quite disabling. Because of the configuration of the carpometacarpal joint, dislocations are inherently unstable. Although reduction of the carpometacarpal dislocation is easy, maintaining the reduction in a plaster cast is very difficult. Therefore, in most carpometacarpal dislocations, the reduction must be pinned to ensure stability. The pin is placed across the joint and maintained for 4 to 6 weeks to allow the joint capsule to heal. Chronic, undiagnosed, or recurrent dislocations of the carpometacarpal joint of the thumb can be treated either with ligament reconstruction, using the flexor carpi radialis tendon, or with arthrodesis of the carpo- metacarpal joint.
Dislocation of the carpometacarpal joint is also common in the small finger and lesser in the ring finger and is usually due to a punch against a wall in a fit of anger. Because there is significant mobility in the ring and small finger carpometacarpal joint, it remains unstable unless reduced and it often requires temporary pinning. There is also a high incidence of fracture of either the base of the metacarpal or the dorsal articular surface of the hamate that requires open reduction and internal fixation to restore the articular surface.
Dislocation Of Metacarpophalangeal Joint
Dorsal dislocation of the metacarpal phalangeal joint occurs more commonly in the thumb than the lesser fingers, and the direction of dislocation is defined by the direction of the distal bone. These can be difficult to reduce owing to the interposition of the volar plate, which makes closed reduction difficult at times. Open reduction in the thumb is often easily achieved from a dorsal incision, and then the volar plate that is reduced to the palmar position scars back down in place after immobilization of the joint in 30 degrees of flexion. If unstable, this joint can be held with a pin across the metacarpophalangeal joint for 4 weeks. A palmar approach to the metacarpophalangeal joint allows for direct repair of the volar plate to the volar neck of the metacarpal with a bone anchor.
In the lesser fingers, closed reduction becomes a challenge not only because the volar plate is trapped but also because the flexor tendons wrap around one side of the metacarpal neck and the lumbrical muscle around the opposite side and any kind of traction tightens this “noose,” preventing reduction of the palmarly displaced metacarpal head. Both dorsal and volar approaches have been described to open reduce this dislocation. More uncommonly, palmar dislocations of the thumb and lesser fingers do occur and operative reduction is usually required.