Intra-operative monitoring of the common peroneal nerve during total knee replacement.

We present a method allowing intra-operative monitoring of the common peroneal nerve during total knee arthroplasty using a magnetic stimulator. Previous reports have shown no pre-operative method successful in selecting those patients prone to develop a post-operative palsy. The device, placed beneath the lumbar spine, stimulates the cauda equina; common peroneal nerve function is assessed via the response in extensor digitorum brevis. There is a loss of signal from the nerve with the use of a tourniquet 25 min following its application. The protocol therefore requires that a tourniquet is used at least only for fixation of the prosthetic components. The method is quick, safe, non-invasive and reproducible, and is of use both in at-risk patients and in research work.