Anterior extraperitoneal exposures to the lumbar spine are being increasingly used owing to the expanding use of novel technologies to treat degenerative disc disease. Lumbar plexus injuries are potential, albeit uncommon, complications of such exposures and can lead to significant perioperative morbidity. In this report, we present three patients with thoracolumbar fractures who sustained isolated femoral nerve palsies after a mini-open extraperitoneal approach to the midlumbar spine was undertaken to perform a partial corpectomy. To further understand the pathophysiology of this nerve injury, we conducted a cadaveric experiment to evaluate the effect of performing this approach and the effect of hip positioning on linear displacement of the femoral nerve. The displacement of the femoral nerve during the anterolateral extraperitoneal exposure through a 4- to 6-cm incision was equal to 6.6% of the full femoral nerve length. Relaxation of the femoral nerve was equal to 25% of the full nerve length when the hip was flexed to 90 degrees in neutral abduction-adduction. We conclude that the anterolateral extraperitoneal exposure of the midlumbar spine can potentially stretch the femoral nerve beyond its physiologic limits, particularly in trauma cases where exposure of the lateral vertebral body necessitates substantial retraction of the psoas muscle. The avoidance of self-retaining retractors for prolonged periods of time and the positioning of the hip in flexion may help to avoid such nerve injuries.