Summary

No detectable change in dynamic knee kinematics was found between short-term and long-term follow-up using biplane radiography during downhill running 10+ years after anatomic anterior cruciate ligament reconstruction and no difference between limbs could be detected at 10+ years postoperative.

Abstract

Introduction

Substantial evidence from biomechanical studies shows that anterior cruciate ligament (ACL) reconstruction (ACLR) improves anterior-posterior and rotatory stability. However, previous in-vivo studies have reported that ACLR fails to fully restore physiological kinematics within 24 months, leaving unclear how knee kinematics are affected in the long-term. This study aims to investigate knee kinematics after anatomic ACLR with quadriceps autograft, utilizing dynamic biplane radiography at a minimum of 10-year follow-up. It was hypothesized that knee kinematics remain unchanged between short- and long-term follow-up after ACLR and that the surgical knee 10+ years after ACLR has similar kinematics compared to the contralateral healthy knee.

Methods

This study enrolled patients from a previous randomized controlled trial in which patients underwent primary anatomic single- or double-bundle ACLR with a quadriceps tendon (QT) autograft. In vivo knee kinematics were previously measured at 6 and 24 months postoperatively. Exclusion criteria for the current study included ACL revision surgery or knee arthroplasty. At a minimum of 10-years follow-up, synchronized biplane radiographs of both knees were obtained in the same laboratory. Participants performed downhill running at 3 m/s. A dual belt instrumented treadmill recorded ground reaction forces at 900 Hz with a threshold of 50N to identify foot strike and toe off. Volumetric and surface models of the femur and tibia were obtained previously by segmentation of CT scans (Mimics, Materialize, Inc.). A validated model-based tracking system was used for three-dimensional (3D) positioning and orientation of the tibia and femur, allowing the calculation of 3D motions of the tibia and femur. Analyzed kinematic parameters were tibiofemoral flexion, internal rotation, abduction, and anterior translation, analyzed at 0%, 20%, and 40% of the stance phase. Linear mixed effects models were created to compare joint kinematics at 6 months, 24 months, and 10+ years and between limbs within each individual, with significance set at p<0.05. Clinical outcome parameters collected included the International Knee Documentation Committee Subjective Knee Form (IKDC SKF).

Results

Seven subjects of the initial randomized controlled trial have been tested (mean age at surgery 27.4 ± 10.5 years; 1 (14%) female; 1 (14%) single-bundle ACLR) at a follow-up of 12.5 ± 0.6 years. None of the assessed kinematic parameters within subject showed significant differences among the three time points in the surgical knee. No significant differences were identified between surgical and contralateral limb kinematics at 10+ years after surgery. Mean IKDC SKF at the latest follow-up was 85.7 ± 14.7.

Conclusion

There was no detectable change in knee kinematics after anatomic ACLR from short-term to long-term follow-up in this cohort of seven patients. Additionally, there were no differences in knee kinematics between the surgical and contralateral knee at long-term follow up. However, the small sample size is not sufficient to statistically conclude that knee kinematics are unchanged over time and results are limited to subjects without ACLR revision. Enlarging the sample size bears the potential to further assess whether anatomic ACLR effectively restores and maintains joint kinematics similar to the native contralateral limb over the long-term.