A 20-yr-old male right-hand dominant collegiate boxer at a military academy presented to the team physician with several weeks of pain over the dorsal (extensor) aspect of his right small finger MCP joint. He denied any specific injury but did train daily for 8 months each year for over 3 yr. His training regimen included between 20 and 40 min of bag punching per session, and frequent sparring sessions. He had no other history of injury to the hand.
Examination showed mild swelling and tenderness over the dorsal aspect of his right small-finger MCP joint. The involved joint had full active range of motion and normal grip strength. With active MCP flexion, the extensor tendon appeared to subluxate to the ulnar aspect of the MCP joint. Plain radiographs of his hand were normal.
Diagnosis and treatment
The initial diagnosis was radial sagittal band disruption. The trainer was instructed to pad the interspace between the ring and small finger under his wraps, and the subject was allowed to finish the season. He competed with pain, but successfully defended his national collegiate championship. Immediately after the season, he was taken to the operating room, where his sagittal bands were found to be intact. His extensor digitorum communis and the extensor digiti minimi tendons, however, were separated into two divergent strands (Fig. 1). A tear in the capsular tissue on the ulnar side of the tendon deep to the extensor digiti minimi tendon was also noted, exposing the underlying metacarpal head. The capsular rent was repaired with nonabsorbable suture in a running fashion. The extensor tendons were then centralized in a side-to-side fashion with a running suture (Fig. 2). After the repair, flexion and extension of the MCP joint produced no subluxation of the tendons.
Postoperatively, the patient was treated for 4 wk in an ulnar gutter splint followed by 4 wk in a removable ulnar gutter splint. He progressed with active and passive range of motion exercises and returned to boxing at 4 months postsurgery. He noted no further pain or swelling in hand. He successfully defended his third national championship 10 months after surgery.
Direct trauma to the dorsal aspect of the MCP joint of the fingers is a common occurrence in sports. Boxers and martial artists sustain repetitive forceful trauma to the clenched fist. There have been reports of isolated injuries in football players as a helmet struck a clenched fist (7). The MCP joint may sustain contusions, synovitis, articular fractures, collateral ligament damage, or extensor mechanism disruption (1–9). Traumatic soft tissue injury to the extensor hood has been coined “boxer’s knuckle” and can be a devastating injury to the elite athlete (4,5,7).
The extensor mechanism of the MCP joint is comprised of the longitudinal extensor digitorum communis (EDC) tendon and the transverse peripheral fibers, termed the sagittal bands. Intact sagittal bands prevent subluxation of the EDC tendon (4,5,7,8). The extensor tendons are also stabilized by the juncturae tendinum, which are fibrous connections between the tendons proximal to the MCP joints. Beneath the extensor hood is the thick dorsal capsule, which contributes to protection of the MCP joint (7). These structures are maximally stretched over the metacarpal head as a fist is made, making them more susceptible to injury (4). The index and small fingers each have two extensor tendons crossing the MCP joint. The index finger has the extensor indicis proprius and the small finger has the extensor digiti minimi each lying on the ulnar side of the common extensor tendon (4).
Closed direct trauma may produce a contusion of the capsule, which normally heals within 1–2 wk without sequelae (7). More forceful trauma may injure the sagittal bands, allowing tendon subluxation. The radial sagittal bands are more commonly injured, producing ulnar subluxation of the tendon. Further force may rupture the dorsal capsule. In the index or small finger, the extensor hood may be ruptured between the two tendons, creating a divergent dislocation of the two tendons (1,2,6). With an acute sagittal band rupture, the athlete usually displays swelling and tenderness over the radial or ulnar aspect of the MCP joint. Occasionally, there is a palpable defect at the site of the rupture. There may be decreased joint extension due to pain and tendon subluxation. The athlete usually can demonstrate the “popping” or “catching” of the tendon as it subluxates while he makes a fist (8). Plain radiographs should be performed to rule out bony pathology. Arai et al. (2) have recommended arthrography of the MCP joint to assess capsular integrity.
Some authors have recommended nonoperative treatment for sagittal band rupture (4,6,8). This does not appear to be a viable option in athletes who require repetitive hand use as the tendon will continue to subluxate and the capsule will remain inflamed. Occasionally, as in our case, the boxer can finish the season and undergo repair in the off-season. Ideally, however, surgery is performed relatively soon after recognition. During surgery, the tendon is centralized and the capsular tear is repaired. The sagittal bands are then repaired (3–8). Tendons in the small or index finger that have dislocated divergently are reapproximated side to side (Fig. 2). The MCP joint is immobilized at 60° for approximately 4–6 wk, followed by a period of protected motion and strengthening exercises. Punching is allowed when there is pain-free full range of motion.
MCP joint injuries can be prevented with appropriate equipment and specific training. Boxers, trainers, and coaches must be knowledgeable with the application of wraps and gloves. Appropriate punching techniques should be used to avoid awkward or unnecessary blows. Punching should only be allowed if the hand is pain-free. Boxers should be encouraged to seek medical attention if the hand becomes painful or swollen. The trainers and treating physicians must be aware of the perils of “boxer’s knuckle” and be prepared for prompt treatment or referral.
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