The Effect of Knee Extension Limitation on Lumbar Intervertebral Disc Compression Force During Walking: A 3D Musculoskeletal Analysis

Knee-spine interactions suggest that limited knee extension may elevate spinal loading during ambulation in older adults. This study aimed to estimate lumbar intervertebral disc loads during walking in patients with knee extension limitations using a 3D musculoskeletal model and examine their relationship with sagittal alignment. Seventeen adults with radiographic knee osteoarthritis (Kellgren-Lawrence ≥ 2) underwent whole-spine lateral radiography and 3D gait analysis with force plates. A patient-scaled AnyBody model was used to compute intervertebral disc compression forces (T12/L1-L5/S1). Participants were categorized into two groups based on knee extension angle (KEA): a limitation cohort (deficit ≥ 10°) and a non-limitation cohort (<10°). Peak compression force (PCF) and mean compression force were normalized to body weight. The limitation group showed a smaller pelvic incidence and a larger sagittal vertical axis. PCF was significantly increased at the thoracolumbar and upper lumbar levels (T12/L1, L1/2, L2/3, and L3/4), whereas the mean forces remained unchanged. Knee extension limitation is associated with higher peak upper lumbar disc loading during gait, supporting the targeted management of knee extension in older adults at risk of spinal degeneration.