Figure 1. Sagittal MRI view of the lumbar spine.
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Figure 2. Axial MRI view of the lumbar spine.
A 43-year-old man presents to the office with pain in his right leg and foot drop on the right side, both of which have been present for 3 weeks. Magnetic resonance imaging (MRI) of the lumbar spine in sagittal and axial planes is performed (Figures 1 and 2) and reveals a foraminal herniated nucleus pulposus at L5-S1.
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A foraminal disc herniation at the L5-S1 level usually causes nerve impingement and L5 radiculopathy, as seen in this patient. The L5 nerve controls motor function to the ankle dorsiflexors including the tibialis anterior and the extensor hallucis longus muscles. Weakness of the ankle dorsiflexors may cause foot drop, in which the foot drags while walking. Foot drop can be temporary or permanent.
Significant motor weakness is an indication for surgery such as laminectomy or discectomy. The overall prognosis for acute foot drop is favorable for return of function after surgery. A study by Bhargava et al found complete improvement in 61% of patients, some improvement in 27% of patients, and no improvement in 12% of patients with foot drop treated by discectomy with or without laminectomy.1 The majority of patients should expect to see significant improvement in their foot drop within 3 months following surgery.
All of the patients who recovered completely in the Bhargava study had symptoms of foot drop for <4 weeks. Severe weakness lasting >6 months and advanced age are predictors of poor functional recovery.1 The ideal time for surgery is unclear as there is no improved prognosis with urgent vs delayed surgery. In general, patients who present with foot drop are usually treated with surgery within 4 to 6 weeks from the onset of symptoms.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. Bhargava D, Sinha P, Odak S, Tyagi A, Towns G, Pal D. Surgical outcome for foot drop in lumbar degenerative disease. Global Spine J. 2012;2(3):125-128.
2. Girardi FP, Cammisa FP Jr, Huang RC, Parvataneni HK, Tsairis P. Improvement of preoperative foot drop after lumbar surgery. J Spinal Disord Tech. 2002;15(6):490-494.