Motor-evoked potential analysis of peroneal nerve status during lateral closed wedge high tibial osteotomy.

Introduction: Common peroneal nerve (CPN) palsy has been reported as an intraoperative complication during lateral closed wedge high tibial osteotomy (CWHTO). However, various intraoperative iatrogenic causes have been reported, the specific cause of CPN palsy has not been clearly established. The present study aimed to clarify the effects of retractors on CPN status in CWHTO.

Materials and methods: 23 knees of 18 patients underwent CWHTO with transcranial motor-evoked potential (MEP) analysis. The CPN integrity was tested at four time-points: preoperatively as a control (first period); just after retractor placement on the fibula for fibular osteotomy in the middle portion (second period); just after retractor placement on the posterior tibia to pull the tibialis anterior muscle (third period); and after the procedure (fourth period). Postoperative CPN damage was evaluated by the presence of paralysis and a manual muscle test (MMT) for strength of ankle dorsiflexion.

Results: There was no significant difference in the mean amplitude of the CPN between the first (100 %) and 92.6 % (range, 64-100 %) in the second periods (p = 0.53); however, the amplitude was significantly reduced from the second period to 59.0 % (range, 15-100 %) in the third period (p < 0.01), and then significantly improved to 77.4 % (range, 20-100 %) in the fourth period (p < 0.01). In 20 knees (87.0 %), the amplitude of the CPN in the third period was reduced. All 18 patients had postoperative MMT grade of 5 without paralysis of the CPN.

Conclusion: 20 of 23 knees (87.0 %) revealed a significant reduction of the CPN amplitude by the retractor on the posterior tibia. Therefore, the posterior retractor should be carefully placed on the common peroneal nerve in CWHTO.