Effect of wrist position on extensor mechanism after disruption separation.

A cadaveric study was performed on extensor tendon separation and excursion after extensor zone I (distal interphalangeal [DIP]) joint and III (proximal interphalangeal [PIP]) level lacerations and treatment. An average 1.5 mm tendon gap with 30 degrees lag following laceration at the DIP joint level and a 1.1 mm average tendon gap with 18 degrees (10 degrees-25 degrees) extension loss at the PIP level was demonstrated. Splinting zone I injuries with the DIP joints in 5 degrees hyperextension and zone III injuries with the PIP joint in 0 degrees extension eliminated tendon separation in all passive joint positions except when the wrist and metacarpophalangeal joints were placed in flexion. This position produced a 0.9 mm gap with a laceration at the DIP level and 1.0 and 2.0 mm gap at the PIP level, with a central slip and central slip and lateral band laceration, respectively. The tendon gaps were eliminated by placing the wrist in extension. This suggests that splinting of the wrist in neutral to mild extension and the joint underlying the tendon injury in full extension, while leaving the other joints free to move, would optimize treatment results.