Three-Dimensional gait biomechanics in patients with mild knee osteoarthritis.

Knee osteoarthritis (KOA) is a common degenerative joint disease in older adults that causes pain and functional impairment. Gait biomechanics in early-stage KOA (Kellgren-Lawrence grades I-II) are understudied. This study aimed to examine differences in three-dimensional gait biomechanics and muscle activation in mild KOA to inform early detection and intervention. Twenty-four patients (aged 55-70 years) with unilateral mild KOA and twelve age- and sex-matched healthy older adults were recruited for evaluation. Participants were instructed to walk at a self-selected, comfortable speed along a 6-meter walkway, and at least five valid gait trials were collected for each individual. Three-dimensional gait analysis was conducted using a motion capture system synchronized with force plates to measure spatiotemporal parameters (gait cycle, step width, walking speed), joint kinematics (ROM, peak angular velocity), and joint kinetics (peak joint moments). Muscle activation levels (normalized to %MVIC) and muscle onset times were recorded using a 16-channel wireless surface electromyography system. Between-group differences were assessed using independent-samples t-tests (p < 0.05), with effect sizes calculated using Cohen's d. Mild KOA patients had a significantly longer gait cycle (1.12 ± 0.13 vs. 1.10 ± 0.07 s, p = 0.04, d = 0.18) and a wider step width (0.09 ± 0.03 vs. 0.07 ± 0.04 m, p < 0.01, d = 0.60) than healthy controls, while walking speed remained similar between groups. They exhibited reduced knee and ankle range of motion and lower peak angular velocities at the hip and knee joints compared to controls. For example, sagittal-plane knee flexion-extension ROM was 61.5°±5.1 vs. 65.1°±2.8 (KOA vs. control, p < 0.01, d = 0.85), and ankle plantarflexion-dorsiflexion ROM was 53.4°±8.1 vs. 59.1°±6.5 (p < 0.01, d = 0.77). Peak knee angular velocity was also lower in KOA patients (372 ± 58 vs. 399 ± 72 °/s, p = 0.01, d = 0.41). KOA patients also generated lower peak flexion and extension moments at the hip and knee joints compared to controls, along with a higher external rotation moment at the affected knee. Muscle activation patterns differed between the groups. The KOA group showed reduced activation of the gluteus medius and medial gastrocnemius (GMed: 27% ± 23 vs. 38% ± 19; MG: 41% ± 24 vs. 62% ± 16; both p < 0.01) but higher activation of the biceps femoris and tibialis anterior. Furthermore, the gluteus maximus on the affected side activated later in the gait cycle, whereas the semimembranosus and the contralateral gluteus maximus activated earlier than in controls. Even at a mild stage, KOA is associated with distinct gait and neuromuscular alterations. These findings underscore the importance of early gait assessment and targeted interventions to improve dynamic stability and potentially slow the progression of osteoarthritis.