Frontal plane movement of the pelvis and thorax during dynamic activities in individuals with and without anterior cruciate ligament injury

BACKGROUND: For elite athletes with anterior cruciate ligament (ACL) reconstruction, reducing pelvis and trunk obliquities is a common goal of rehabilitation. It is not known if this is also a suitable goal for the general population. This study aimed to quantify pelvis and thorax obliquities during dynamic activities in individuals from the general population with and without history of ACL injury. METHODS: Retrospective analysis of cross-sectional data from 30 participants with ACL reconstruction, 28 participants with ACL deficiency (ACLD), and 32 controls who performed overground walking and jogging, single-leg squat, and single-leg hop for distance. Pelvis and thorax obliquities were quantified in each activity and compared across groups using one-way ANOVA. Coordination was quantified using cross covariance. RESULTS: In the stance phase of walking and jogging, pelvis and thorax obliquities were within ±10° of neutral and there was a negative correlation between the two segments at close to zero phase lag. In single-leg squat and hop, range of obliquities varied across individuals and there was no consistent pattern of coordination. Eight ACLD participants felt unable to perform the single-leg hop. In the remaining participants, range of pelvis (p = 0.04) and thorax (p = 0.02) obliquities was smaller in ACLD than controls. CONCLUSIONS: In challenging single-leg activities, minimal frontal plane motion was not the typical movement pattern observed in the general population. Coordination between the pelvis and thorax was inconsistent within and across individuals. Care should be taken when considering minimising pelvis and thorax obliquities in patients with ACL injury.