[Neurophysiological changes after correction of valgus deformity with total knee artrhoplasty]

we aimed to search for a correlation between neurophysiological changes in the anatomic distribution of the common peroneal nerve (CPN) and the degrees of valgus deformity correction after total knee arthroplasty (TKA).

a prospective cohort study of 23 patients was conducted. A preoperative and at one and six months postoperative neurophysiological studies of the CPN were performed. Subsequently, the association between the pathologic neurophysiological findings found (polyphasicity, motor unit loss, low amplitude of evoked potentials) with the degrees of deformity correction and the limb length difference after TKA was analyzed.

sixteen of 23 patients completed the study. The mean valgus deformity correction was 9.3°, and the mean lower limb length difference was +10,1 mm. One-month postoperative electromyogram (EMG) was normal in seven patients while the other nine patients showed some findings that normalized at six months. In three patients, mild findings remained. As to electroneurogram (ENG), in all cases there were normal sensory and motor conduction velocities even though thirteen patients showed changes compatible with neurapraxia in different degrees of severity. At six months all patients showed normal values, except one. In any case, there was no clinical sign of major sensory or motor loss in the distribution of the CPN. No statistical correlation could be found between neurophysiological findings and the degrees of valgus deformity correction.

we could not find a correlation between neurophysiological changes and the degrees of valgus deformity correction or leg length difference. A threshold of valgus deformity correction indicating prophylactic common peroneal nerve decompression could not be established.