Following thoracolumbar scoliosis surgery, this 48-year-old man presented with pain on the right thigh and around the right hip. He had weakness of right hip flexion and leg extension, sensory impairment over the anteromedial thigh and leg, and an absent right patellar reflex. There was no adductor weakness. There was no Tinel sign over the right inguinal ligament. The video obtained weeks after surgery also showed wasting and atrophy of the distal right quadriceps.

The femoral nerve, the largest branch of the lumbar plexus, is a mixed sensory and motor nerve. The femoral nerve arises from the posterior division of the ventral rami of L2, L3, and L4 within the psoas muscle and courses onward laterally, reaching the inguinal ligament (Poupart ligament) lateral to the femoral artery. Under the inguinal ligament, the femoral nerve divides into anterior and posterior division. Branches within the pelvis supply the iliacus and psoas muscles. The anterior division supplies motor innervation to the pectineus and sartorius muscles and cutaneous innervation to the anteromedial thigh. The posterior division provides motor innervation to the quadriceps femoris and cutaneous innervation to the medial aspect of the leg and foot.

Our patient had thoracolumbar scoliosis with coronal and sagittal deformity. He was placed in the left lateral decubitus position, and underwent a transthoracic approach with osteotomies of T5-6, T6-7, T7-8, T8-9, with excision of a calcified and partially ossified anterior longitudinal ligament and loosing of the patient’s coronal deformity. An inferior vena cava (IVC) filter was placed. Following this, the patient was returned to the full prone position and underwent a posterior thoracolumbar decompression.

Our patient had a postoperative painful right femoral neuropathy proximal to the origin of the branches to the iliacus and psoas muscles. Electromyography (EMG) showed electrodiagnostic findings consistent with a right femoral neuropathy, with decreased recruitment of slightly large amplitude motor unit action potentials (MUAPs) in the right vastus lateralis and vastus medialis. Needle EMG of lumbar paraspinals was normal. Computed tomography (CT) of the pelvis showed asymmetric enlargement of the right iliacus and distal iliopsoas muscle consistent with an intramuscular hemorrhage. Magnetic resonance imaging/magnetic resonance angiography (MRI/MRA) of the pelvis showed muscle edema of the right iliacus, distal iliopsoas, and proximal sartorius (Fig. 9.1). There was no evidence of pseudoaneurysm, dissection, or arterial or venous thrombosis. A follow-up study showed improving soft tissue edema abnormalities of the right iliacus, psoas, and sartorius.