Intraoperative threshold hunting for monitoring of common peroneal nerve function during high tibial osteotomies

Using a computer-assisted threshold hunting paradigm the motoric threshold of the common peroneal nerve was monitored in 18 patients during a high tib ial osteotomy (HTO). The exposed nerve (lateral approach) was stimulated pr oximal to the osteotomy area and the surface EMG of the M. tibialis anterio r was used to guide a threshold hunting device. Motoric threshold as a sens itive indicator of nerve function was found to be almost unaffected by seve ral surgical steps of HTO. Only forceful rotation of a subperiostal Hohmann device during high peroneal osteotomy evoked a slight threshold shift that was fully reversible with device repositioning. The tourniquet, however, a ffected the threshold significantly. In 10 of the 18 patients the nerve bec ame completely inexcitable after an average time of 59 min. The inexcitabil ity was reversible after opening of the tourniquet. On the other hand, the eight patients maintaining an excitability throughout the entire ischemic p eriod had tourniquet times that did not exceed 60 min. There are several fa ctors that may be responsible for the observed inexcitability after long is chemic periods and we conclude that tourniquet time minimization appears ap propriate to avoid neurological deficits during a high tibial osteotomy.