Altered bilateral knee flexor synergies after total and unicompartmental knee arthroplasty resemble non-surgical osteoarthritis synergies.

Abstract

Knee osteoarthritis (KOA) alters gait biomechanics and neuromuscular control. Muscle synergy analysis has revealed characteristic changes in knee flexor activation patterns in KOA patients. In this study, we investigated whether such alterations persist after total or unicompartmental knee arthroplasty (TKA, UKA) during level walking. sEMG data from 45 participants (14 TKA, 11 UKA, 20 healthy age-matched controls) were processed using non-negative matrix factorization to extract muscle synergies. Knee flexion angles were retrieved through inverse kinematics from 3D marker trajectories using OpenSim. Clustered bilateral knee flexor synergy activation matrices and knee flexion angles were compared via separate two-way ANOVAs (Group x Side) using statistical parametric mapping. All groups exhibited four distinct muscle synergies with similar weighting- and activation matrices. Only the knee flexor synergy activation was significantly increased in TKA and UKA during loading response compared to controls. No significant differences emerged between TKA and UKA patients, nor surgical and non-surgical sides. The altered synergy activation patterns in TKA and UKA resembled those previously observed in non-surgical KOA patients. The absence of differences between prosthesis types suggests that cruciate ligament retention in UKA does not influence synergy organization during level gait. Together with the similar alterations observed in both the surgical and non-surgical limb, these consistencies might be driven by changes in whole-body gait dynamics, such as increased sagittal trunk flexion, that impose bilateral effects on gait control. Addressing these whole-body adaptations during rehabilitation may be essential for improving long-term recovery and mobility.