Asian Journal of Orthopaedic Research

A 30-year-old man, morbid obesity (BMI 36 ), with no pre-existing neurological deficits underwent corrective osteotomy and fusion for severe thoracic kyphoscoliosis, cobb angle 85 degree. The patient was positioned prone utilizing dome-shaped gel pads onto the chest wall and iliac crest. Although the baseline Motor Evoked Potential (MEP) obtained post-positioning revealed a mild preoperative reduction (20%) in the left vastus medialis, this finding was deemed insignificant given that it did not meet the >50% criterion for a meaningful change. Progressive signal loss, with a final amplitude reduction of more than 50%, occurred in both vastus medialis muscles at the end of the corrective maneuver after approximately five hours of surgery. Despite adherence to consensus-based guidelines for managing intraoperative neuromonitoring changes, MEPs remained reduced at closing. Postoperatively, the patient exhibited weakness in bilateral hip flexion and knee extension, accompanied by numbness consistent with femoral nerve distribution. Acute spinal cord injury was ruled out via immediate MRI. While nerve conduction study (NCS) proved inconclusive, the patient achieved full recovery within 6 weeks following a dedicated rehabilitation program.   

Bilateral femoral nerve palsy is an exceptionally rare complication following spinal surgery. This case highlights the critical role of optimal patient positioning, particularly in obese patients undergoing lengthy procedures, to minimize the risk of such complications. It underscores the importance of considering possibility peripheral nerve injury especially when small IONM signals reduction immediately after patient positioning. Conservative management is proved a viable option for such case.