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

## TL;DR

This study shows that limited knee extension increases peak spinal disc forces in older adults during walking, suggesting that managing knee extension could help prevent spinal degeneration.

## Contribution

The study introduces a 3D musculoskeletal model to quantify how knee extension limitations affect upper lumbar disc loading during walking.

## Key findings

- Peak compression forces at upper lumbar discs are significantly higher in patients with knee extension limitations.
- Mean compression forces across the gait cycle remain unchanged despite knee extension limitations.
- Knee extension limitations are linked to altered spinal alignment and increased thoracolumbar disc loading.

## Abstract

What are the main findings?
Peak compression force at the upper lumbar intervertebral discs during walking is significantly increased in patients with knee extension limitations.Mean compression forces across the gait cycle remain unchanged in patients with knee extension limitations.

Peak compression force at the upper lumbar intervertebral discs during walking is significantly increased in patients with knee extension limitations.

Mean compression forces across the gait cycle remain unchanged in patients with knee extension limitations.

What are the implications of the main findings?
The findings underscore the heightened risk of disc overload during everyday activities in patients.Clinically assessing and managing knee extension can potentially mitigate adverse upper lumbar loading and reduce the risk of degenerative progression.

The findings underscore the heightened risk of disc overload during everyday activities in patients.

Clinically assessing and managing knee extension can potentially mitigate adverse upper lumbar loading and reduce the risk of degenerative progression.

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.