Foot Drop

Excerpt

Foot drop is characterized by the inability to dorsiflex the forefoot due to weakness in the dorsiflexor muscles. This condition can lead to an unsteady, compensatory gait and increase the risk of falls. The underlying causes are diverse and may include muscular, neurological, spinal, autoimmune, and musculoskeletal disorders. Treatment approaches vary based on the underlying etiology; therefore, understanding the pathophysiology is essential before formulating an appropriate treatment plan. The etiology, clinical features, diagnostic approaches, and treatment options for foot drop are examined, emphasizing that it is not always a straightforward case of simple L5 radiculopathy.

Anatomy of the Lumbar and Sciatic Nerve Structures

Lumbar nerve roots: The lumbar spine consists of 5 vertebrae. The lumbar nerve roots emerge from the lateral spinal recess, which is formed by the inferior facet of the rostral vertebra and the superior facet of the caudal vertebra. The L5 nerve root exits between the L5 and S1 vertebrae.

Lumbar plexus: The lumbar plexus is formed by the anterior rami of the L1 to L4 spinal nerves. Several vital nerves arise from this plexus. The iliohypogastric and ilioinguinal nerves innervate the transverse abdominis and internal oblique muscles. The obturator nerve supplies the thigh's adductor muscles. The femoral nerve, one of the largest branches, innervates the quadriceps femoris group and continues as the saphenous nerve, which provides sensory innervation to the medial aspect of the leg.

Sciatic nerve: The sciatic nerve, the largest branch of the lumbosacral plexus, arises from the L4 to S4 nerve roots. This nerve travels through the posterior thigh and reaches the popliteal fossa, where it divides into 2 major branches—the tibial nerve and the common fibular nerve. The tibial nerve innervates the hamstring muscles, as well as the plantar flexors and invertors of the foot.

Common fibular nerve: The common fibular nerve is the lateral terminal branch of the sciatic nerve. This nerve courses laterally across the lateral head of the gastrocnemius muscle, then wraps around the neck of the fibula, where it becomes subcutaneous and vulnerable to compression. As it passes between the fibula and the fibularis longus muscle, it bifurcates into 2 branches—the deep fibular nerve and the superficial fibular nerve. The deep fibular nerve innervates the ankle and toe extensors and provides sensory innervation to a small area in the first web space between the first and second toes. Please see StatPearls' companion resource, "Anatomy, Bony Pelvis and Lower Limb: Leg Anterior Compartment," for more information.

Historically, the common fibular nerves were referred to as the peroneal nerves. The superficial fibular nerve innervates the primary evertors of the foot—the fibularis longus, fibularis brevis, and fibularis tertius muscles. Its sensory branch provides sensation to the dorsum of the foot and the lateral aspect of the calf.