Biomechanical link between knee osteoarthritis and lumbar spine loading: An experimental and simulation-based analysis

Knee osteoarthritis (KOA) and low back pain (LBP) frequently co-occur, yet their biomechanical link remains unclear. This exploratory study investigated whether KOA gait is associated with altered trunk muscle forces and lumbar loading. Motion-capture and ground-reaction-force data were collected from eight individuals with mild-to-moderate medial KOA and ten healthy controls. Participant-scaled OpenSim models were used to estimate trunk muscle forces and lumbar joint reaction forces (JRFs). Between-group comparisons used Mann-Whitney U tests with false-discovery-rate correction. Walking speed did not differ between groups, whereas stride length was shorter in KOA (q = 0.033). Proximal kinematic differences were limited: no pelvic variable remained significant after correction, and only mean thoracic lateral bending differed (q = 0.032), with a small absolute magnitude. Mean knee angle differed between groups (q = 0.014), with additional differences in peak knee and ankle kinematics (q ≤ 0.006). Model-predicted mean and peak multifidus, longissimus, and iliocostalis forces were greater in KOA, whereas internal oblique forces were lower (all q < 0.05). Mean and peak lumbar compression were greater in KOA at all six levels from T12-L1 to L5-S1 (all raw p < 0.001; q < 0.05), and anterior-posterior JRFs were greater at selected levels. These higher muscle forces and JRFs, despite limited group-level proximal kinematic differences, may reflect attenuation or cancellation of heterogeneous individual gait adaptations during averaging, even though these adaptations may still influence internal mechanical demands.