[Extensor tendon injuries at the level of the proximal interphalangeal joint]

Closed and open injuries of the extensor mechanism at the proximal interphalangeal (PIP) joint can involve the central slip, the lateral slips or both. They are classified as zone III injuries. All open injuries on the dorsal side of the PIP joint should raise suspicion of an extensor tendon injury that is frequently overlooked. The operative strategy consists of wound revision with extensor tendon suture or refixation of the central slip. Acute closed central slip injuries are clinically diagnosed (Elson test) after ruling out bony injuries to the joint. Nondisplaced avulsions of the central slip insertion or lacerations can be treated nonoperatively by splinting. For displaced avulsions and complex injuries the treatment is surgical. In overlooked injuries a typical deformity (buttonhole/Boutonnière deformity) develops within 1-2 weeks that is characterized by an extension lag of the PIP joint and hyperextension at the distal interphalangeal joint. In early cases, when passive extension is still complete (mobile buttonhole deformity) the central slip can be immediately reconstructed. In fixed deformities complete passive extension of the PIP joint has to be restored before surgery by hand therapeutic measures or PIP joint release. Depending on the pattern of the injury and the resulting defects, a number of reconstructive techniques have been established that are summarized in this article. The functional results can be limited by tendon adhesions, imbalance within the reconstructed extensor apparatus and stiff joints that can all restrict the range of motion. Therefore, active rehabilitation protocols are mandatory for optimal results.