Subclinical knee extensor weakness predicts gait and balance impairment in degenerative cervical myelopathy.

Degenerative cervical myelopathy (DCM) is a leading cause of non-traumatic spinal cord disorders in older adults. Gait instability and balance dysfunction are common in DCM, even in the absence of clinically evident lower limb weakness. We hypothesized that subclinical weakness, measured through maximal voluntary isometric contractions (MVICs) of the knee extensors and ankle plantar flexors, is associated with impaired gait and balance in individuals with DCM. Pre-surgical DCM participants with symptoms of DCM and MRI evidence of cervical spinal cord compression were prospectively enrolled in this observational study. Knee extensor and ankle plantar flexor MVICs of the self-reported most-affected leg were measured using a Biodex system. Berg Balance Scale (BBS) scores, gait speed and spatiotemporal gait parameters, and the modified Japanese Orthopedic Association score (mJOA) were recorded. Multivariable regression assessed associations between MVICs and gait/balance outcomes, controlling for age and sex. Data from 32 DCM participants (11 females; mean age 59.1 ± 10.7 years) were analyzed. Knee extensor MVICs showed significant positive correlations with gait speed (r = 0.38, p = 0.001), mJOA lower extremity scores (r = 0.41, p = 0.019), and BBS scores (r = 0.44, p = 0.007). These associations remained significant in multivariable linear regression models adjusted for age and sex. Ankle plantar flexor MVICs were not significantly associated with any outcomes (p > 0.05). Knee extensor MVICs reflect subclinical lower extremity weakness and are associated with impaired gait and balance in DCM. MVIC is a promising objective method to quantify motor impairment in DCM.