Effects of Metal Fragments on Nerve Healing in Extremity Injuries Using a Rat Peroneal Nerve Model

Abstract

On the modern battlefield, the majority of injuries currently seen are to the extremities, often involving a large number of metallic fragments. Although they are typically left in place, the effects of these retained metal fragments on nerve healing have not been studied. In a rat model, the right peroneal nerve was surgically sectioned and reanastomosed (control group). In the study group, metal fragments from an artillery casing were placed around the reanastomosed peroneal nerve. Functional recovery in both groups was evaluated over a 4-week period by measuring maximum ankle dorsiflexion captured on video as the animals walked through a tunnel. Morphologic analyses included distal and proximal axon counts, measurement of nerve fiber and axon diameter ratios, and myelin thickness. A significant decrease (p < 0.05) in return toward baseline for the rats' ankle angle in the nerves exposed to metal fragments was noted at weeks 2 through 4. Distal axon counts were significantly less (p < 0.05) in the metal fragment group for weeks 1 through 4. Proximal axon counts were increased in both groups, with a greater (p < 0.05) increase in the metal fragment group. Functional recovery after rat peroneal nerve transection and repair is decreased when metal fragments are placed in and around the injury site. Select histologic indicators of nerve regeneration showed decreased healing when exposed to metal fragments. Further studies of functional recovery in patients sustaining penetrating injuries from bullets or explosive devices are indicated.