MRI Diffusion Tensor Tractography to Monitor Peripheral Nerve Recovery After Severe Crush or Cut/Repair Nerve Injury

Although nerve transfers can reduce the length of axonal growth required, failures still occur and revisions are rarely an option due to the aforementioned delays in detection. Current neurodiagnostics \[e.g., electromyography (EMG), nerve conduction studies (NCS)\] are of limited utility in severely damaged nerves, providing an incomplete picture of nerve microstructural features until target reinnervation occurs. Thus, physicians are limited to a "wait and watch" approach based on qualitative measures obtained from patient history and/or physical exam. This leads to a suboptimal management of peripheral nerve injuries, which in turn can lead to increased instances of irreversible muscle atrophy, paralysis, and/or formation of painful traumatic neuroma. In terms of the military, extremity injuries accounted for 54% of combat wounds in Operation Iraqi Freedom and Operation Enduring Freedom and recent review of service member injuries during Operation Enduring Freedom noted significant increases in brachial plexus, ulnar, and radial nerve injuries attributable to modern warfare. In addition, symptomatic neuroma occurs in 13% to 32% of amputees, causing pain and limiting or preventing the use of prosthetic devices. Take the example of a wounded warrior with a shrapnel injury to his/her elbow, resulting in the loss of an ulnar nerve segment. Even if nerve grafting is performed, true recovery (motor and/or sensory innervation of the hand) could take up to a year under typical circumstances. If the repair fails, which occurs in up to 40% of patients the failure is typically not truly recognized until that year expires using current management protocols. By that time, revisional surgery is typically not a viable option due to the aforementioned onset of irreversible muscle atrophy. In additional to an inability to effectively monitor nerve recovery after repair, diagnosis of peripheral nerve injuries is difficult using the currently available methods. For example, neurotmesis is a common, but difficult to distinguish, diagnosis following traumatic or iatrogenic extremity injury. Current electrodiagnostic and clinical examinations are invasive, time consuming, and painful. In addition, they cannot perfectly discriminate a severe axonotmetic laceration from a self-resolving neurapraxic injury in the acute setting. This is particularly important in penetrating injuries, or after iatrogenic nerve injuries resulting from nerve blocks, or from intraoperative positioning or external compression, because the degree of axonal injury is unknown.