Extensor Mechanism Injuries At The Metacarpophalangeal Joint

Subluxation of Extensor Digitorum Communis

Traumatic dislocation or subluxation of the extensor tendon apparatus at the MCP joint is less common than other extensor injuries but can occur in the athlete. The injury has been reported by Elson84 and described in detail by Kettelkamp et al85 and Harvey and Hume.86 The injury may be due to a direct blow to the flexed MCP joint or by a flexion ulnar deviation force exerted over the involved digit. The lesion involves tearing of the sagittal band of the extensor hood, usually on the radial side of the extensor tendon. The sagittal fibers function to keep the extensor tendons centered over the metacarpal head, and when a rupture occurs, the tendon dislocates or subluxates into the valley between metacarpal heads.86 The long finger is the most commonly involved digit.

On physical examination, the athlete presents with swelling about the MCP joint and inability to fully extend the digit at this joint. Once the MP joint is passively extended, the patient may maintain this position because it usually reduces the tendon. This helps differentiate the lesion from a radial neuropathy or extensor rupture.71

Treatment of this lesion in acute cases may involve simple splinting in extension for 4 weeks and intermittent splinting and ROM exercises for another 4 weeks.87 If reduction cannot be maintained or there is a delay in diagnosis, primary suture of the defect in the radial sagittal band is indicated.85 In late cases in which primary repair is not possible or the tissue is of poor quality, reconstruction of the radial retinaculum may be indicated.88,89

Boxer's Knuckle

Another extensor injury at the MCP joint has been described by Melone90 and termed boxer's knuckle. This refers to a longitudinal tear in the extensor digitorum communis tendon or the sagittal bands overlying the metacarpal head, usually arising from a single event or repetitive direct trauma to this area such as seen in boxing. The long finger is most commonly involved due to its prominence in the fisted position, although the lesion may occur in other digits. The athlete presents with pain over the metacarpal head and frequently a defect is palpable in the extensor mechanism. There may be some weakness to full extension or an extensor lag. Melone90 has found that disruption occurs with equal frequency in the ulnar and radial sagittal bands with splits in the central tendon being less common.

Once diagnosed, treatment usually involves exploration and side-to-side repair of the tear. In the boxer, care must be taken to place the incision in such a location as to avoid the prominence of the knuckle. The capsule should not be closed so that full flexion may be obtained postoperatively.

Following surgery, splinting is maintained for 6 weeks followed by an aggressive rehabilitation program. If the injury occurs in a boxer, he or she does not return to punching until full ROM and normal strength is obtained, which usually requires 4 months.

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