Summary

This study evaluates the knee's functional biomechanics in adolescent patients 8-12 months post-ACLR, highlighting how standard return-to-sport tests may overlook deficits in the operated leg at the end of the rehabilitation phase, and showing that a comprehensive biomechanical analysis could improve return-to-sport decision-making.

Abstract

Introduction

To reduce the risk of ACL re-injury, standardized rehabilitation and return-to-sport (RTS) processes are used, focusing on more than just the time since surgery. RTS tests generally include strength measurements and horizontal hop tests to assess functional symmetry between limbs. These methods are widely used due to their simplicity and inexpensive equipment. However, they have been found to be poor predictors of successful RTS outcomes one year after injury. Recent studies have shown the need to assess lower limb biomechanics to better understand knee functional deficits that may be masked by the functional limb symmetry calculated during jumping performance (1). Therefore, the purpose of this study was to assess lower limb biomechanics to identify deficits in knee function and respective compensatory strategies in young patients after ACLR. We hypothesized that despite nearing the end of their rehabilitation, patients would still exhibit altered lower limb biomechanics affecting the RTS decision.

Methods

A total of fourteen patients (5 women, 9 men, mean age: 17.6±1.5 years) who underwent primary ACLR (3 isolated, 11 with meniscal repairs) using two different graft types (10 Quadriceps tendon, 4 Semitendinosus/Gracilis tendon), were evaluated at 8-12 months after surgery, nearing the end of their rehabilitation process. Patients were invited for biomechanical testing if the inter-limb isokinetic knee strength was >80%. Kinematic (10 Miqus cameras, 100Hz, Qualisys AB, Sweden and Theia Markerless. Patch 14, HAS Motion, Canada) and kinetic (1kHz, Arsalis 800 × 500; Arsalis SPRL; Louvain-la-Neuve, Belgium) data were recorded during treadmill running, bilateral counter movement jump (CMJ) and single-leg CMJ. Ankle, hip and knee joint angles, moments and power were calculated using Visual3D (HAS Motion, Canada) for the operated and contralateral limbs in addition to the vertical ground reaction force vectors. Between-limb differences (at midstance for running, during propulsion and landing phases for the jumps) were evaluated using paired T-tests or Mann Whitney-U tests after assessing the data for normal distribution using the Shapiro-Wilk test. Significance was set at p<0.05.

Results

For running and jumping, we found significant decreases in knee flexion angle, knee extension moment and knee landing power in the operated limb compared to the contralateral limb. The operated leg also showed a significant reduction in power generation and absorption during the bilateral jumps, suggesting a possible strength or function deficit. When looking at the adjacent joints, only a significant decrease in ankle flexion was seen in the operated leg for all the exercises, whereas no significant differences were found at the level of the hip.

Conclusion

During running and vertical jumps, patients at RTS still exhibit knee biomechanical deficits characterized by stiffer knee movements which could be a risk for re-injury. Our study highlights that despite achieving standard rehabilitation milestones, significant biomechanical asymmetries are still present 8-12 months post-ACLR. These findings suggest that current RTS criteria may not fully account for underlying deficits, emphasizing the need for more comprehensive biomechanical evaluations to better identify patients at risk of secondary injury and ensure a safer RTS.
Acknowledgements: The financial support of the Fondation André Losch is greatly appreciated.
References:
1- Kostifaki et al. (2022), British Journal of Sports Medicine, 56:490-498.