The boutonnière deformity results from injury to the central slip insertion of the extensor hood on the dorsal surface of the middle phalanx. After a tear of the central slip, the flexor tendon is unopposed at the PIP and the lateral bands of the extensor tendon contract. With time, these displace volarly, resulting in additional PIP joint flexion and DIP joint extension. The central slip rupture may result from forceful flexion of the PIP joint during full extension, a dorsal PIP joint laceration, or a palmar PIP joint dislocation. The deformity may not be immediately apparent as it takes time for the lateral bands to slide down to create extension of the DIP joint. Pain and swelling over the dorsal PIP joint, tenderness over the PIP central slip, inability to extend the PIP, and possible DIP joint hyperextension are common. Radiographically, a small bone fragment may be seen at the proximal portion of the dorsal middle phalanx.
The swan-neck deformity occurs because of the contracture of intrinsic hand muscles secondary to systemic diseases such as rheumatoid arthritis and systemic lupus erythematosus. The digit is contorted with hyperextension of the PIP and flexion of the DIP and MCP joints.
Management and Disposition
For a closed boutonnière deformity, immobilization of the PIP joint in extension for 4 weeks is adequate, followed by active range of motion. Open injuries must be carefully explored and repaired. If the deformity is associated with a bony fragment, surgical repair may be necessary. Swan-neck deformities should be splinted and referred as an outpatient. Both require outpatient referral to a hand specialist.
Boutonnière Deformity. Avulsion or laceration of the central extensor mechanism results in a flexion deformity at the PIP joint and hyperextension of the DIP joint—the boutonnière, or buttonhole, deformity. (Modified with permission from Way LW. Current Medical Diagnosis & Treatment. 10th ed. Norwalk, CT: Appleton & Lange; 1994.)
Boutonnière Deformity. Fourth digit flexion of the PIP joint and extension of the DIP joint. (Photo contributor: E. Lee Edstrom, MD.)
Boutonnière deformity generally develops weeks after the initial injury as the lateral bands contract.
The Elson test is the most reliable way to diagnose a central slip injury before the deformity is present. Have the patient bend the PIP joint to 90 degrees over the edge of the table and extend the middle phalanx against resistance. If a central slip injury is present, there will be weak PIP extension, and the DIP will become rigid. If the central slip tendon remains intact, the DIP remains floppy because all force is applied to extension of the PIP joint and the lateral bands are not activated.
Surgical repair ...