In vivo bundle-specific anterior cruciate ligament length changes during overground walking

The purpose of this study was to characterise in vivo bundle-specific anterior cruciate ligament (ACL) length changes during level overground walking and evaluate synchrony between the anteromedial (AM) and posterolateral (PL) bundles. We hypothesised that bundle length changes during overground walking would be phase-dependent and that the AM and PL bundles would exhibit distinct but highly coordinated patterns throughout the gait cycle.

Thirty healthy young adults underwent gait analysis during level overground walking at a self-selected speed. An image-integrated motion analysis system combining optical motion capture (250 Hz) and fluoroscopy-based three-dimensional bone registration was used to reconstruct femoral and tibial motion. ACL bundle lengths were defined as centroid-to-centroid distances between anatomically identified attachment regions. Bundle length waveforms were expressed as relative changes referenced to initial heel contact. Phase-specific bundle length changes (Δ length) were analysed during stance and swing and within four stance subphases. Synchrony between bundles was assessed using Spearman's correlation analysis.

Both bundles demonstrated greater length changes during swing than stance. Mean AM bundle length change was 7.1 ± 1.9 mm during stance and 10.6 ± 3.6 mm during swing (p < 0.001), while mean PL bundle length change was 9.1 ± 2.4 and 14.8 ± 4.1 mm, respectively (p < 0.001). During stance, bundle length changes remained small from loading response to terminal stance and increased markedly during pre-swing. The PL bundle showed greater geometric length-change amplitude than the AM bundle across most gait phases, except terminal stance. AM and PL bundles exhibited highly synchronised length-change waveforms throughout the gait cycle (Spearman's ρ = 0.95, p < 0.001).

ACL bundle length changes during overground walking were phase-dependent, with greater geometric length-change amplitude in the PL than AM bundle and highly synchronised behaviour. These findings provide reference data for bundle-specific ACL mechanics during gait.

Level IV.