10/11/2025
𝗘𝘅𝗮𝗺𝗶𝗻𝗶𝗻𝗴 𝘁𝗵𝗲 𝗔𝗻𝗮𝘁𝗼𝗺𝘆, 𝗣𝗮𝘁𝗵𝗼𝗽𝗵𝘆𝘀𝗶𝗼𝗹𝗼𝗴𝘆, 𝗮𝗻𝗱 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗣𝗿𝗲𝘀𝗲𝗻𝘁𝗮𝘁𝗶𝗼𝗻 𝗼𝗳 𝗟𝗼𝘄𝗲𝗿 𝗘𝘅𝘁𝗿𝗲𝗺𝗶𝘁𝘆 𝗡𝗲𝘂𝗿𝗼𝗹𝗼𝗴𝗶𝗰 𝗗𝗲𝗳𝗶𝗰𝗶𝘁𝘀: 𝗔 𝗚𝘂𝗶𝗱𝗲 𝘁𝗼 𝗙𝗼𝗼𝘁 𝗗𝗿𝗼𝗽 🦶
🦶 Foot drop, defined as weakness or paralysis of the ankle dorsiflexor muscles, represents a frequent clinical challenge associated with considerable impairment in gait and quality of life. The underlying cause may occur anywhere along the motor pathway extending from the cerebral cortex to the peripheral nerves or the leg musculature itself. Foot drop is a multifactorial condition requiring a comprehensive diagnostic approach (https://pubmed.ncbi.nlm.nih.gov/18502948/, https://pubmed.ncbi.nlm.nih.gov/31288916/).
📘 In a brand-new review, Swiatek et al. (2025, https://pubmed.ncbi.nlm.nih.gov/40911727/) present an in-depth analysis of the anatomy, pathophysiology, and clinical manifestations of lower extremity neurologic deficits, offering a structured framework to improve evaluation and management.
💡 𝗔𝗽𝗽𝗹𝗶𝗲𝗱 𝗔𝗻𝗮𝘁𝗼𝗺𝘆 𝗮𝗻𝗱 𝗣𝗮𝘁𝗵𝗼𝗽𝗵𝘆𝘀𝗶𝗼𝗹𝗼𝗴𝘆
🩻 The authors emphasize that a precise understanding of the relevant neuroanatomy is fundamental to localizing the etiology of foot drop. At the spinal level, the L4 and L5 nerve roots join to form the lumbosacral trunk, which contributes to the sacral plexus (s. illustration). These roots are most often implicated in cases of foot drop due to degenerative spinal changes, disc herniation, iatrogenic surgical trauma, postoperative hematoma, infection, or tumor formation. Their anatomical course makes them particularly vulnerable during spinal procedures (https://pubmed.ncbi.nlm.nih.gov/17036418/; https://pubmed.ncbi.nlm.nih.gov/17445735/). The L5 nerve root is involved in ankle inversion, eversion, dorsiflexion, great toe extension, and hip abduction.
✅ As the sciatic nerve travels from the pelvis into the thigh, the peroneal division is more susceptible to injury than the tibial division, consistent with the law of Laplace, which relates fiber diameter to wall tension. Consequently, the peroneal fibers are at greater risk during total hip arthroplasty, especially with improper retractor placement, traction, or postoperative hematoma formation. Sciatic nerve palsy following hip replacement surgery may occur in up to three percent of cases and can cause isolated peroneal dysfunction (https://pubmed.ncbi.nlm.nih.gov/1123010/; https://pubmed.ncbi.nlm.nih.gov/1874771/).
✅ Below the knee, the common peroneal nerve—winding superficially around the fibular head—is the most frequent peripheral site of injury leading to foot drop. Compression during surgery, prolonged kneeling, leg crossing, or direct trauma are well-documented causes. Extraneural masses such as Baker’s cysts or schwannomas may also exert pressure on the nerve (https://pubmed.ncbi.nlm.nih.gov/26700629/). The common peroneal nerve divides into the superficial and deep branches, innervating the ankle evertors and dorsiflexors respectively. Selective lesions of these branches produce characteristic patterns:
▶️ isolated dorsiflexion weakness in deep peroneal neuropathy and
▶️isolated eversion weakness in superficial peroneal neuropathy.
🧠 Although peripheral lesions account for many cases, the review stresses that central causes must not be overlooked. Lesions affecting the pyramidal tract within the brain or spinal cord—such as those arising from tumors, stroke, multiple sclerosis, or thoracic disc herniation—may also result in foot drop (https://pubmed.ncbi.nlm.nih.gov/17385271/; https://books.google.de/books/about/Textbook_of_Clinical_Neurology.html?id=rU2mQgAACAAJ&redir_esc=y).
Such lesions produce upper motor neuron signs, including 👉hyperreflexia, 👉 clonus, and a 👉 positive Babinski reflex.
✅ Furthermore, several neuromuscular disorders, such as Charcot–Marie–Tooth disease, Lambert–Eaton syndrome, and myasthenia gravis, can produce distal weakness, generalized muscle atrophy, and diminished deep tendon reflexes (https://pubmed.ncbi.nlm.nih.gov/27704495/).
🩺 Clinical Examination
A comprehensive neurological examination remains central to accurate diagnosis.
𝗧𝗵𝗲 𝗺𝗼𝘁𝗼𝗿 𝗲𝘅𝗮𝗺𝗶𝗻𝗮𝘁𝗶𝗼𝗻 𝗲𝗻𝗮𝗯𝗹𝗲𝘀 𝗽𝗿𝗲𝗰𝗶𝘀𝗲 𝗹𝗲𝘀𝗶𝗼𝗻 𝗹𝗼𝗰𝗮𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻
▶️ Weakness in hip abduction, mediated by the superior gluteal nerve, suggests L5 nerve root pathology,
▶️ while preserved hip abduction accompanied by dorsiflexion weakness indicates a more distal, peripheral lesion.
▶️ Weakness in the short head of the biceps femoris, uniquely innervated by the peroneal division of the sciatic nerve, points toward a lesion proximal to the common peroneal nerve.
▶️ The presence or absence of ankle inversion is equally significant: Normal inversion strength of the tibialis posterior implies intact tibial nerve and L5 function, ruling out isolated radiculopathy. Tibialis posterior strength can be accurately examined by asking the patient to invert the foot in full plantarflexion, whereas the clinician pushes laterally against the medial border of the foot.
𝗦𝗲𝗻𝘀𝗼𝗿𝘆 𝘁𝗲𝘀𝘁𝗶𝗻𝗴 𝗽𝗿𝗼𝘃𝗶𝗱𝗲𝘀 𝗮𝗱𝗱𝗶𝘁𝗶𝗼𝗻𝗮𝗹 𝗰𝗹𝘂𝗲𝘀
▶️ Dermatomal sensory deficits support a spinal root origin (but rememder…often, you can`t trust the dermatomes, https://www.youtube.com/watch?v=BZYtAR4zUpg),
▶️ whereas patchy or diffuse sensory loss without clear dermatomal correlation suggests peripheral neuropathy or systemic disease.
𝗥𝗲𝗳𝗹𝗲𝘅 𝘁𝗲𝘀𝘁𝗶𝗻𝗴 𝗿𝗲𝗳𝗶𝗻𝗲𝘀 𝘁𝗵𝗶𝘀 𝗹𝗼𝗰𝗮𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 𝗳𝘂𝗿𝘁𝗵𝗲𝗿
▶️ reduced ankle reflexes imply lower lumbar root compromise,
▶️ while an asymmetric medial hamstring reflex strongly correlates with L5 radiculopathy (sensitivity and specificity of 76% and 85%, https://pubmed.ncbi.nlm.nih.gov/23087820/).
▶️ By contrast, hyperreflexia, clonus, or bilateral presentation favor a central etiology.
🩻 Diagnostic Modalities
Swiatek et al. (2025) underscore the complementary roles of magnetic resonance imaging (MRI) and electrodiagnostic studies. MRI remains essential for detecting compressive lesions in the spine, knee, or brain, depending on the suspected level of pathology. Electromyography (EMG) and nerve conduction studies are invaluable for distinguishing radiculopathy from peripheral nerve injury and for assessing prognosis. EMG evidence of conduction block in the tibialis anterior without axonal loss predicts rapid recovery, whereas findings of extensive axonal degeneration portend a prolonged or incomplete recovery (https://pubmed.ncbi.nlm.nih.gov/36070242/).
👫Illustrative Case Studies
Two clinical cases in the review demonstrate the practical application of these principles.
1️⃣ In the first case, a woman developed left-sided foot drop following a fall onto her buttock. She exhibited preserved hip abduction and lacked spinal compression on MRI. EMG revealed L5 radiculopathy with concurrent peroneal neuropathy. These MRI and EMG findings, along with a physical examination demonstrating 5/5 hip abductor strength, led the clinician to believe that this patient’s foot drop was likely due to a peripheral lesion, potentially peroneal or sciatic nerve contusion from her injury. The symptoms resolved with conservative physical therapy and gait training.
2️⃣ The second case described an elderly man who developed postoperative left foot drop after lumbar fusion. Despite correct implant positioning, he displayed normal inversion and eversion strength, consistent with compressive peroneal neuropathy at the fibular head due to postoperative immobility. Non-surgical management led to full recovery. Both cases underscore the importance of considering peripheral and central etiologies alongside spinal causes.
Illustration: Nerves of the sacral plexus, https://books.google.de/books/about/Human_Anatomy_Media_Update_Books_a_la_Ca.html?id=Go0-XwAACAAJ&redir_esc=y
Summary (infographic) in comments!
