Neuromuscular Characteristics Associated with Knee Instability in Osteoarthritis and After Total Knee Replacement: A...

Background/Objectives: Knee joint instability is frequently reported in individuals with knee osteoarthritis (OA) and may persist after total knee replacement (TKR), where it represents a leading cause of revision. However, neuromuscular factors associated with knee instability remain poorly understood. This systematic review and meta-analysis aimed to compare neuromuscular characteristics between individuals with stable and unstable knees in OA and TKR populations. Methods: PubMed, CENTRAL, Scopus, and EMBASE were searched from inception to 10 January 2025. Studies comparing neuromuscular outcomes between stable and unstable knees were included. Neuromuscular parameters included: muscle strength, muscle power, muscle activation pattern, and joint stiffness. Where appropriate, pooled standardized mean differences (SMD) were calculated using random-effects models. Certainty of evidence was evaluated using the GRADE approach. Results: Nineteen studies (16 OA, 3 TKR; n = 7369 participants) were included, with eleven studies eligible for meta-analysis. OA individuals with unstable knees demonstrated significantly lower limb muscle strength compared with stable counterparts (SMD = -0.49, 95% CI -0.81 to -0.16, p = 0.003). Muscle co-contraction did not differ significantly between groups (SMD = 0.12, 95% CI -0.70 to 0.94, p = 0.77). The overall certainty of evidence was rated as very low. Conclusions: Knee instability in OA populations is associated with reduced lower limb muscle strength, although evidence quality is limited and findings regarding neuromuscular control strategies remain inconclusive. Evidence in TKR populations is scarce. Future studies should investigate muscle activation patterns and dynamic joint stabilization during functional tasks to clarify the neuromuscular mechanisms underlying knee instability.