Contribution of neuromuscular impairment to physical functional status in patients with lumbar spinal stenosis.

OBJECTIVE To evaluate the relationship between neuromuscular impairment and physical functional status in patients with lumbar spinal stenosis. METHODS Cross sectional analysis of 217 consecutive patients with lumbar spinal stenosis referred to 3 teaching hospitals. Physical functional status was measured with the physical dimension of the Sickness Impact Profile (P-SIP). Physical and radiological findings were abstracted from clinical records. The neuromuscular findings included pin sensation, strength, deep tendon reflexes and vibration. They were aggregated in a neuromuscular impairment index (NMI). Univariate relationships of the P-SIP and the NMI were analyzed with nonparametric methods. The determinants of physical functional status were evaluated using multiple linear regression models. RESULTS In 148 patients with complete clinical data, objective weakness of the lower extremity as measured at rest was not related to physical functional status in univariate analyses. Decreased vibration was common and was associated with balance disturbance and reduced physical functional status, reflecting the importance of proprioception loss. In the multivariate regression analysis, neuromuscular deficit explained only 2.5% of the variance in physical functional status. The primary determinants of physical functional status were pain, depression, comorbid conditions and work status. CONCLUSION While neuromuscular impairment is an indispensable feature of the diagnostic evaluation, its value in assessing outcome is limited. The decision whether to intervene surgically in patients without cauda equina syndrome or rapidly progressive neurological deficits should therefore be driven by pain and physical disability rather than the degree of neuromuscular impairment.