Summary

ACL graft elongation during downhill running after double-bundle ACL reconstruction were evaluated using a biplane radiographic system and MRI. ACL graft elongation after double-bundle ACL reconstruction doesn’t change so much during downhill running after over a 10-year follow-up and graft elongation closely replicates contralateral native ACL elongation over 10 years after ACL reconstruction.

Abstract

Introduction

There is a lack of evidence of the anterior cruciate ligament (ACL) graft length change at long-term follow-up after ACL reconstruction (ACLR). The purpose of this ongoing study is to evaluate long-term changes in ACL graft length during downhill running. This analysis tests the hypotheses that ACLR graft elongation doesn’t change over time and it is not different compared to the contralateral native ACL over a 10-year follow-up.

Methods

Written informed consent has been obtained from five patients who underwent anatomic double-bundle (DB) ACLR at least 10 years ago with a quadriceps tendon autograft with a patellar bone block (4 males). Both knees were imaged within a biplane radiography imaging system (150 images/sec, 1ms exposure) for three trials per knee during downhill running (10° slope) at 3 m/s. Tibiofemoral motion was tracked using a previously validated volumetric model-based tracking process. Knee kinematics during the stance phase of the gait cycle were calculated following standard conventions. The same coordinate system was used at all test dates. In the contralateral side, the ACL insertions were divided into the anteromedial bundle (AMB) and posterolateral bundle (PLB) at the midpoint (50/50%) of the entire ACL insertion as identified on 3T MRI. Then, the ACL or graft length was measured as the distance between the femoral and tibial ACL attachment points or apertures of the bone tunnels for each bundle. Biplane radiography was collected at 6 and 24 months, and at least 10 years after ACL. ACL graft length in the affected side at final follow-up was compared to 6 months and 24 months after ACLR and to the contralateral side at final follow-up at 5° increments of tibiofemoral flexion. Linear mixed effects model analysis was performed to compare changes over time in the affected knee and to compare the affected versus contralateral knee at long-term follow-up, with significance set at p < 0.05.

Results

Participant’s average age at the time of surgery was 22.8±6.6 years and the mean follow-up period was 12.9±0.3 years. Regarding the length change over time, both AMB and PLB showed similar relative elongation patterns during knee flexion at 6 months, 24 months, and over 10 years after ACLR, Although the mean relative elongation at 6 months was consistently less than at 24 months and over 10 years, no statistically significant differences were found. Over a 10-year follow-up, both AMB and PLB showed similar relative elongation patterns on the affected and contralateral side during downhill running, with no significant differences detected.

Discussion

In our cohort of 5 patients, no difference in ACL graft length relative elongation could be detected between 6 months, 24 months or 10 years after ACLR, nor was there a difference detected between the affected and contralateral side over a 10-year follow-up, with our hypotheses supported. This analysis suggests that during downhill running anatomic DB ACL graft elongation does not change even after over a 10-year follow-up and AMB and PLB graft elongations closely replicate contralateral native AMB and PLB elongation over 10 years after ACLR.