RT Book, Section A1 Breed, Meghan A1 Fitch, Robert Warne A2 Knoop, Kevin J. A2 Stack, Lawrence B. A2 Storrow, Alan B. A2 Thurman, R. Jason SR Print(0) ID 1181041989 T1 Boutonnière and Swan-Neck Deformities T2 The Atlas of Emergency Medicine, 5e YR 2021 FD 2021 PB McGraw-Hill PP New York, NY SN 9781260134940 LK accessemergencymedicine.mhmedical.com/content.aspx?aid=1181041989 RD 2024/03/29 AB 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.