Ring avulsion injuries: A biomechanical study

The biomechanics of ring avulsion injuries was studied in a cadaveric simul ation model. Custom-fitted metal rings attached to a rigid frame were place d over the proximal phalanx of fresh or thawed fresh-frozen specimens. Ring avulsion injuries in 44 fingers were produced with a standardized force ap plied to the proximal ulna. The progress of injury was evaluated with simul taneous high-speed cinematography and continuous force measurements. The in jured digits were x-rayed and categorized according to Urbaniak's classific ation. Continuous force measurements produced similar curves for all classe s of injuries. The average maximum force resulting in class I injuries was 80 N. The average maximum force producing amputation in class III injuries was 154 N, a force much lower than expected. Force measurements for class I I injuries were nearly identical to those of class Ill. This surprisingly m inimal force resulting in digit amputation was explained by high-speed cine matography, which showed that the rings tilt on the digits concentrating di sruption forces as a result of ring angulation on the finger. Incomplete am putations were due to loss of ring purchase by skin flap eversion. Finally, comparison of high-speed cinematography with force curves suggests that sk in rupture rather than skeletal or tendon disruption accounted for the maxi mum force during ring avulsion injury. (J Hand Surg 1999;24A:1249-1253. Cop yright (C) 1999 by the American Society for Surgery of the Hand.)