Foot drop is difficulty lifting the front part of the foot, leading to dragging while walking. It is a known, though uncommon, complication after back surgery. The impairment stems from nerve issues controlling foot movement. Understanding its contributing factors after spinal procedures helps.
Understanding Drop Foot
Drop foot describes weakness or paralysis in muscles lifting the front of the foot and toes. Individuals with this condition often develop a characteristic high-stepping gait, lifting their thigh higher to prevent toe dragging. The foot may also slap the ground. Patients might also experience numbness, tingling, or reduced sensation on the top of the foot or along the shin.
Damage to nerves controlling dorsiflexion (upward foot movement) causes the condition. This prevents proper signaling to foot-lifting muscles, causing weakness or paralysis. The most frequently affected nerves are the common peroneal nerve and the L5 spinal nerve root. Foot drop is a symptom of an underlying problem, not a disease, with effects ranging from temporary to long-term.
Direct Surgical Causes
Direct nerve trauma during back surgery can cause foot drop. Surgeons manipulate structures close to nerve roots, and accidental contact, stretching, or nicking of nerves (e.g., L5 spinal nerve root, common peroneal nerve) impairs their function. For instance, procedures like laminectomies, discectomies, and spinal fusions work near these delicate nerve pathways. Misplaced surgical tools or implants (e.g., pedicle screws) can directly compress or injure nerve roots, particularly the L5 nerve root at L5-S1.
Prolonged nerve compression can also result from patient positioning during long procedures. Incorrect positioning can place sustained pressure on nerves, causing reduced blood flow (ischemia). Unrelieved pressure damages nerve fibers due to lack of oxygen and nutrients, causing dysfunction and potential foot drop. For example, improper leg positioning can compress the peroneal nerve at the fibular head, a common site of injury.
Hematoma (blood clot) formation after surgery is another direct cause of nerve compression. Bleeding around the surgical site can accumulate and exert pressure on nearby nerves, impeding signal transmission. This compression can manifest as foot drop immediately or develop days or weeks later if unnoticed.
Inflammatory responses also contribute to nerve impairment. Surgical manipulation induces swelling and inflammation around nerve roots. This inflammation can compress or disrupt nerve function, causing foot drop. While some inflammation is a natural part of the healing process, excessive or prolonged swelling detrimentally affects nerve integrity.
Contributing Factors and Vulnerabilities
Pre-existing spinal conditions increase susceptibility to foot drop after back surgery. Conditions like severe spinal stenosis, where the spinal canal narrows and already compresses nerve roots, make them more fragile and prone to injury during surgery. Similarly, large disc herniations that exert pressure on nerves pre-surgery can leave them compromised, making them more vulnerable to trauma or inflammation. Patients with pre-existing compressions may experience foot drop more readily with minimal surgical disturbance.
The specific type of back surgery performed influences foot drop risk. Procedures like lumbar fusion, discectomy, and laminectomy carry inherent risks due to proximity to nerve pathways. Lumbar disc surgery, for instance, has resulted in foot drop in up to 8.8% of patients. More complex procedures, like those correcting high-grade spondylolisthesis, can have higher rates, sometimes up to 30%.
Individual patient vulnerabilities also contribute to foot drop risk. Systemic conditions like diabetes, especially with peripheral neuropathy, make nerves more susceptible to injury and slower to recover. Diseased nerves are less resilient to surgical stresses, including compression or stretching. Older age is another factor, as older patients may have neurological complications increasing foot drop chances.