Does lower-limb osteoarthritis alter motor cortex descending drive and voluntary activation? A systematic review and meta-analysis.

Purpose: The aim of the study was to quantify motor cortex descending drive and voluntary activation (VA) in people with lower-limb OA compared to controls. Methods: A systematic review and meta-analysis according to the PRISMA guidelines was carried out. Seven databases were searched until 30 December 2022. Studies assessing VA or responses to transcranial magnetic stimulation (TMS; i.e. motor evoked potential, intracortical facilitation, motor threshold, short-interval intracortical inhibition, and silent period) were included. Study quality was assessed using Joanna Briggs Institute criteria and evidence certainty using GRADE. The meta-analysis was performed using RevMan inverse variance, mixed-effect models. Results: Eighteen studies were included, all deemed low-quality. Quadriceps VA was impaired with knee OA compared to healthy controls (standardised mean difference (SMD) = 0.84, 95% CI = -1.12-0.56, low certainty). VA of the more symptomatic limb was impaired (SMD = 0.42, 95% CI = -0.75-0.09, moderate certainty) compared to the other limb in people with hip/knee OA. As only two studies assessed responses to TMS, very low-certainty evidence demonstrated no significant difference between knee OA and healthy controls for motor evoked potential, intracortical facilitation, resting motor threshold or short-interval intracortical inhibition. Conclusions: Low-certainty evidence suggests people with knee OA have substantial impairments in VA of their quadriceps muscle when compared to healthy controls. With moderate certainty we conclude that people with hip and knee OA had larger impairments in VA of the quadriceps in their more painful limb compared to their non-affected/other limb.