A novel biomechanical measure to determine knee instability after ACLR: variability at knee rotational axis.

INTRODUCTION

Hop distance tests are commonly used to determine when it is safe to return to sports (RTS), but symmetrical test results do not necessarily indicate the absence of biomechanical deficiencies. Three-dimensional motion analysis may quantify ongoing lower extremity instability following anterior cruciate ligament reconstruction (ACLR).

MATERIALS AND

METHODS

We estimated the instantaneous knee rotation axis during the landing phase of the triple hop test. The angular deviation in the orientation of the knee rotation axis between two successive instants was computed and used as a variability measure at the knee joint rotation in three dimensions.

RESULTS

Knee flexion was less, the duration of the landing interval was shorter, and the variation at the knee rotation axis orientation over landing duration was higher on the operated side. We then classified the participants into two groups due to the threshold (above versus below 90%) defined at the Range of Motion-Limb Symmetry Index. Significantly shorter landing intervals and higher variation at the knee rotation axis orientation over the landing period at the operated side persisted in the below-threshold group only.

CONCLUSION

We suggest an assessment of the variation in the orientation of the knee rotation axis over the hop test landing duration, which has the potential to be utilized for decisions in RTS at ACLR.