# Lower body kinematic changes induced by anterior cruciate ligament transection: an in vivo three-dimensional analysis in rats

## TL;DR

This study examines how ACL injuries in rats affect lower body movement, revealing compensatory changes in the hip joint.

## Contribution

The study provides new insights into 3D kinematic changes and compensatory hip joint responses following ACLT in a rat model.

## Key findings

- Hip range of motion was significantly reduced in ACLT rats at 8 weeks compared to controls.
- Hip flexion range correlated positively with knee valgus and knee flexion range in ACLT rats.
- Compensatory hip joint responses were observed, similar to those in humans with ACL injuries.

## Abstract

Gait disturbance is readily recognized as a disruption in walking performance, and gait analysis offers insight into the functional impairment of all lower leg joints. However, limited information is available on three-dimensional (3D) kinematic analysis of the lower leg following anterior cruciate ligament transection (ACLT) in rodent models. This information obtained using animal models contributes to the establishment of effective interventions with a view to clinical application. This study aimed to clarify the 3D kinematic alterations and compensatory actions of joints adjacent to the knee, as well as their correlations, in a rat model.

Forty male Wistar rats were assigned to either the control (Ctrl) or ACLT group. Three-dimensional motion analysis was conducted at 1, 2, 4, and 8 weeks post-surgery. Two types of assessment parameters were analyzed based on the plane of assessment: sagittal (2D) and other (3D). Lower limb joint angles during gait were measured, and the relationship between knee joint changes and alterations in other joints was analyzed.

An interaction between group and time was observed not only in knee range of motion (ROM), but also in adjacent hip ROM. Hip ROM was significantly reduced in the ACLT group compared with the Ctrl group at 8 weeks (p < 0.05). Additionally, a correlation between hip ROM and knee parameters was noted at 8 weeks. Among them, hip flexion range was positively correlated with knee valgus and knee flexion range (r = 0.87, p = 0.03; r = 0.84, p = 0.03, respectively). No interaction was observed in the 3D parameters.

The findings of this study demonstrate a compensatory response in the hip joint of rats after ACLT, which parallels observations in individuals with anterior cruciate ligament injuries. This may offer further insight into the impact of ACL injuries on adjacent joints and inform rehabilitation strategies.