Foot drop due to lumbar degenerative conditions: mechanism and prognostic factors in herniated nucleus pulposus and lumbar spinal stenosis.

OBJECT: The aim of this study was to analyze the mechanism and prognostic factors of foot drop caused by lumbar degenerative conditions.

METHODS

The authors retrospectively reviewed the charts of 28 patients with foot drop due to a herniated nucleus pulposus (HNP) or lumbar spinal stenosis (LSS), scoring between 0 and 3 on manual muscle testing for the tibialis anterior muscles. They analyzed the mechanism of foot drop and whether the duration before the operation, preoperative tibialis anterior and extensor hallucis longus strength, age, gender, and diabetes mellitus were all found to be prognostic factors for postoperative tibialis anterior recovery. They also investigated whether the diagnosis had any influence on the prognosis.

RESULTS

The compression of double roots and a sequestrated fragment were observed, respectively, in 9 and 13 of 16 patients with HNP. Multiple levels including the L4-5 segment were decompressed in 8 of 12 patients with LSS. Analysis did not demonstrate any prognostic factor in surgically treated HNP, but significant associations with prognosis were observed with respect to preoperative tibialis anterior (p = 0.033) and extensor hallucis longus (p = 0.020) strength in patients with LSS. In addition, the postoperative muscle recovery in patients with HNP was significantly superior to that in patients with LSS (p = 0.011).

CONCLUSIONS

Double root compression was the most common condition associated with foot drop due to HNP. The diagnosis and preoperative tibialis anterior and extensor hallucis longus strength in LSS were factors that influenced recovery following an operation.