Summary
In vivo knee kinematics was evaluated by an electromagnetic measurement system before and after the ACL reconstruction in isolated ACL injury cases to test the effect of the ACL on pure axial rotation. Isolated ACL injury increased the angle of axial rotation, and the abnormal axial rotation was restored simply by ACL reconstruction.
Abstract
Introduction
Anterior cruciate ligament (ACL) injuries result in an anterolateral rotatory instability (pivot-shift), a combined movement of abnormal anterior-posterior translation and axial rotation. While pivot-shift in ACL-injured knees is routinely evaluated and heavily used for diagnosis and follow-up in our clinical practice, axis rotation has been rarely assessed in clinical setting due to lack of accurate evaluation systems. Recently, axial rotation has been increasingly tested in basic biomechanical studies especially for ACL reconstruction with or without extraarticular procedures. However, there is no consensus as to how ACL injuries effect knee joint kinematics. The purpose of this study was to quantitatively evaluate the effect of ACL injury and reconstruction on axial rotation angle in response to simple axial rotation stress.
Methods
Subjects were 30 patients with unilateral ACL injuries who underwent ACL reconstruction between 2017~2021, who were followed up for more than one year, excluding cases with concomitant meniscus or other ligament injuries. Both knees were flexed under 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 difference in internal/external rotation angle was defined as d-R. Comparisons of d-R and comparisons of tibial translation under internal/external rotation stress were conducted between ACL-injured or reconstructed knee and contralateral knee. Additionally, the correlation between d-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
Preoperatively, d-R was significantly greater in ACL-injured knees at 30° and 60° knee flexion (p<0.05), but no significant difference at 90° (p>0.05). There was no difference in the amount of tibial translation under internal and external rotation stress (p>0.05). The d-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). d-R did not correlate with the acceleration of posterior tibial translation during the pivot-shift test (p>0.05). After the ACL reconstruction at around one year follow-up, there was no significant difference of d-R between ACL reconstructed knees and contralateral intact knees at all flexion angles (p>0.05). d-R did not correlate with the postoperative IKDC subjective score (p>0.05).
Discussion
The axial rotation angle was correlated with anteroposterior mobility in the Lachman test, but was not correlated with the acceleration of posterior tibial translation during pivot-shift. Axial rotation angle had little effect on anterolateral rotation instability and clinical scores of the knee joint. ACL reconstruction could solely restore abnormal axial rotation dur to ACL insufficiency.
Conclusion
Isolated ACL injury increased the angle of axial rotation, and the abnormal axial rotation could be restored by ACL reconstruction without any additional procedures.