Summary

ACL injury increased the angle of axial rotation irrespective of anterior-posterior translation, and increase of axial rotation angle had little relationship with pivot-shift instability and clinical scores of the knee joint.

Abstract

Introduction

Anterior cruciate ligament (ACL) injury induces an anterolateral rotatory instability (pivot-shift), a combined movement of abnormal anterior-posterior translation and axial rotation. Quantitative evaluation of the pivot-shift is recommended for the ACL research. While tibial anterior translation during the pivot-shift in ACL-injured knees is evaluated independently and is heavily used for diagnosis and follow-up, there is no consensus as to whether ACL injury affects pure axial rotation of knee joint. The purpose of this study was to quantitatively evaluate the effect of ACL injury on axial rotation angle in response to simple axial rotation stress and to examine the relationship with pivot-shift grade and clinical score.

Methods

Subjects were 32 patients with unilateral ACL injuries who underwent ACL reconstruction between 2017~2021, excluding cases with concomitant meniscus or other ligament injuries. Both knees were flexed while applying simple internal/external rotation stress under general anesthesia prior to ACL reconstruction, and the 6 degrees of freedom of the knee joint were measured using the electromagnetic sensor (JIMI Kobe). The range between maximum internal and external rotation angle was defined as delta R. Comparisons of delta R between ACL intact knee and ACL-injured knee and comparisons of tibial translation under internal/external rotation stress between ACL intact knee and ACL-injured knee were performed using t-tests. The correlation between delta R and anterior tibial translation during the Lachman test, acceleration of posterior tibial translation during pivot-shift, and IKDC subjective score at one year postoperatively were also examined using Pearson's correlation analysis.

Results

Delta R was significantly greater in ACL-injured knees at 30° and 60° knee flexion (30°: injured knee 33.2±9.4°, healthy knee 28.1±8.9°; 60°: injured knee 29.5±7.5°, healthy knee 25.5±6.1°, p<0.05), but no significant difference at 90° (injured knee 28.1±6.0°, intact knee 26.6±4.8°, p>0.05). There was no difference in the amount of tibial translation under internal and external rotation stress (p>0.05). The delta R at 30° and 60° correlated positively with the amount of anterior tibial translation during the Lachman test (30°r=0.57, 60°r=0.54, p<0.05). ?R did not correlate with the acceleration of posterior tibial translation during the pivot-shift test or with the postoperative IKDC subjective score.

Discussion

The main finding of this study was that the ACL injured knee had larger axial rotation range under pure axial rotational stress than the contralateral knee. Meniscus condition might affect the knee rotation. Therefore, we investigated ACL injury cases excluding meniscus injury. The axial rotation angle was correlated with anteroposterior laxity in the Lachman test, but was not correlated with the acceleration of posterior tibial translation during pivot-shift. Increase of axial rotation angle in the ACL injured knees is irrelevant to dynamic pivot-shift instability and clinical scores of the knee joint.

Conclusion

ACL injury increased the angle of axial rotation irrespective of anterior-posterior translation, and increase of axial rotation angle had little relationship with pivot-shift instability and clinical scores of the knee joint.