A 68-year-old woman is evaluated for right lower extremity weakness while hospitalized. The patient was admitted after sustaining a right femoral neck fracture and underwent total hip arthroplasty. Her operative course was uncomplicated, but the patient experienced right leg weakness postoperatively. Since the surgery, she has had difficulty with physical therapy and reports numbness of the right leg. The patient's other medical conditions include hypertension, type 2 diabetes mellitus, a prior transient ischemic attack, and osteoarthritis. Right lower extremity examination shows weakness in dorsiflexion, plantar flexion, and knee flexion. Hip flexion and knee extension are normal. Sensation to light touch is decreased on the dorsum of the right foot and posterolateral aspect of the right calf. Ankle reflex is absent on the right. Which of the following is the most likely cause of this patient's current findings?
Show Explanatory Sources
This patient underwent total hip replacement following a right femoral neck fracture and developed right lower extremity neurological deficits across the sciatic nerve (L4-S3) and its main branches:
Sciatic nerve: weakness in knee flexion
Common peroneal nerve: weakness in dorsiflexion, numbness on dorsal foot and posterolateral calf
Tibial nerve: weakness in plantar flexion and inversion, absent ankle reflex
These deficits are characteristic of a proximal sciatic nerve injury. The sciatic nerve is particularly susceptible to injury in patients with femoral head dislocation, hip fracture, and/or arthroplasty due to its proximity to the hip joint and femur. Injury to the nerve can be caused by direct mechanical trauma (caused by the surgery or initial fracture), compression of the nerve (due to hematoma or swelling), or local inflammation.
(Choice A) Diabetic neuropathy often manifests as peripheral sensory loss (eg, stocking-glove numbness). However, the deficits are typically bilateral and develop chronically with loss of distal sensory axons first, followed by motor deficits in advanced cases.
(Choice B) L5 radiculopathy is typically caused by disc herniation or degenerative vertebral changes and can result in unilateral lower extremity motor and sensory loss. However, patients typically have significant radicular back pain with a normal ankle reflex and lateral foot sensation (both derived from the S1 nerve root).
(Choice C) Lacunar strokes occur in deep brain arteries in patients with chronic hypertension and typically cause unilateral sensorimotor deficits without cortical signs (eg, aphasia, hemineglect). However, these lesions typically result in more complete hemiparesis/hemisensory loss (eg, affecting face, arm, and leg); sensorimotor deficits localized to the sciatic distribution are more suggestive of peripheral nerve damage.
(Choice D) Compression of the common peroneal nerve against the neck of the fibula can occur in the setting of prolonged immobilization (eg, surgery, bed rest) and cause weakness in foot dorsiflexion and eversion. However, this patient also has deficits involving the sciatic and tibial nerves, indicating a more proximal lesion.
Educational objective:
Sciatic neuropathy is a common complication of hip fracture and/or arthroplasty because of the proximity of the sciatic nerve to the hip joint. Injury to the sciatic nerve in the pelvis causes neurological deficits across the sciatic nerve (knee flexion), common peroneal nerve (dorsiflexion, numbness of the calf and dorsal foot), and tibial nerve (plantar flexion, ankle reflex).