A 69-year-old hospitalized woman is evaluated for new-onset weakness of the right foot. The patient has a history of chronic hip pain due to osteoarthritis and underwent left total hip arthroplasty under general anesthesia while in the right lateral decubitus position 2 days ago. Since the surgery, she has had difficulty moving her right foot. Other medical conditions include lumbar spinal stenosis, hypertension, type 2 diabetes mellitus, and a small ischemic stroke with no residual deficit. On examination of the right lower extremity, the patient is unable to dorsiflex or evert the foot or extend the toes. Sensation is decreased over the dorsum of the right foot. The rest of the neurologic examination of the right lower extremity is normal. Injury to which of the following structures is the most likely cause of this patient's current symptoms?

Question

A 69-year-old hospitalized woman is evaluated for new-onset weakness of the right foot.  The patient has a history of chronic hip pain due to osteoarthritis and underwent left total hip arthroplasty under general anesthesia while in the right lateral decubitus position 2 days ago.  Since the surgery, she has had difficulty moving her right foot.  Other medical conditions include lumbar spinal stenosis, hypertension, type 2 diabetes mellitus, and a small ischemic stroke with no residual deficit.  On examination of the right lower extremity, the patient is unable to dorsiflex or evert the foot or extend the toes.  Sensation is decreased over the dorsum of the right foot.  The rest of the neurologic examination of the right lower extremity is normal.  Injury to which of the following structures is the most likely cause of this patient's current symptoms?

Quizplus · Accepted Answer

11ec160b_35bf_db95_9249_877dadd9f519_MD0001_00 The common fibular (peroneal) nerve originates in the popliteal fossa as the lateral branch of the sciatic nerve. From there, it courses laterally around the head and neck of the fibula before dividing into the deep and superficial fibular nerves. Because of its proximity to the lateral neck of the fibula, the common fibular nerve is particularly susceptible to compression from a leg cast or during prolonged time in the lateral decubitus position (eg, during surgical procedures). Common fibular neuropathy characteristically presents with deficits involving both the deep fibular (eg, weakness in foot dorsiflexion and toe extension) and the superficial fibular (eg, weakness in foot eversion, sensory loss over the dorsal foot) nerves (Choice B). In an ambulatory patient, gait examination typically shows foot drop due to loss of dorsiflexion, with the affected foot lifted high off the ground to compensate (ie, steppage gait). (Choice C) Although the femoral nerve is rarely injured during hip replacement, this injury would result in weakness on hip flexion and knee extension along with loss of sensation over the anterior thigh. (Choice D) The lateral sural cutaneous nerve is a branch of the common fibular nerve that provides sensory innervation to the posterolateral leg; it does not provide motor innervation. (Choice E) Irritation of the lumbosacral spinal nerve roots can cause variable sensorimotor deficits due to the involvement of multiple myotomes and dermatomes. This patient's sensorimotor findings are specific for common fibular nerve injury. (Choice F) The most common cause of proximal sciatic nerve injury is trauma or surgery involving the hip joint. However, sciatic nerve injury causes deficits in the fibular, tibial, and sural nerve distributions, with loss of sensation over the posterior leg and weakness involving the hamstrings and most of the muscles of the lower leg. (Choice G) The tibial nerve can be injured at the knee by trauma or compression (eg, Baker cyst in the popliteal fossa). Proximal tibial neuropathy usually causes weakness in foot plantar flexion and decreased sensation over the sole of the foot. Educational objective: The common fibular nerve is susceptible to injury at the lateral neck of the fibula due to compression (ie, prolonged lying on the affected side) or fracture. Patients typically have weakness in foot dorsiflexion, foot eversion, and toe extension along with sensory loss over the lateral leg and dorsal foot. __________ References: Entrapment neuropathies of the lower extremity. (http://www.ncbi.nlm.nih.gov/pubmed/23542774)

A 69-Year-Old Hospitalized Woman Is Evaluated for New-Onset Weakness of the Right