CORR Insights®: Variations in Knee Kinematics After ACL Injury and After Reconstruction Are Correlated With Bone Shape Differences.

Abstract

Where Are We Now? In their study, Lansdown and colleagues examine the relationship between bone morphology and knee kinematics in patients with ACL injured knees that are subsequently surgically reconstructed. The authors identify four bone-shape features associated with abnormal knee kinematics after ACL injury and ACL reconstruction: (1) Medial femoral condyle height, (2) medial femoral condyle sphericity, (3) length of lateral tibial plateau, and (4) slope of medial tibial plateau. By identifying these features, researchers can better determine how bone morphology relates to kinematics in the ACL injured knee, possess a greater understanding of why the impact of ACL injury on knee function varies between patients, and perhaps even predict the response of the knee and/or the patient to ACL injury, which could guide initial management. Where Do We Need To Go? Further investigation is needed to verify and clarify the relationship of the four bone morphology variables to knee kinematics and clinical outcomes in patients with ACL injured knees. For example, if certain morphology predicts that a knee with an ACL tear is likely to be stable with activities of daily living, less active patients with that morphology may be ideal candidates for initial nonsurgical management. Conversely, if the presence of certain morphology predicts instability with activities of daily living, earlier surgical intervention may be ideal. Understanding the relationship of bone morphology to kinematics in the post-ACL reconstructed knee may be even more important for its potential relationship to two clinically important issues: (1) The risk for recurrent ACL graft breakdown, and (2) the risk of developing postsurgical osteoarthritis. Recurrent injury to the reconstructed ACL is a well-known risk, particularly in younger, more-active patients [2, 6]. There is a lack of well-defined risk factors to further stratify the likelihood of ACL reinjury in these patients. If bony morphology is a predictor of reinjury risk, the information could be used to identify subpopulations who may benefit from surgical modifications for ACL reconstruction or optimized rehabilitation and return to play protocols to ameliorate their increased risk. Similarly, it is well-established that patients who tear their ACL have an increased risk of knee osteoarthritis, with or without surgical reconstruction [1, 3-5]. Identifying the factors associated with osteoarthritis is necessary to develop alternative approaches for potentially reducing the risk for that sequelae. Studies to assess whether bony morphology at the time of ACL injury is associated with the future risk of osteoarthritis in patients who undergo surgical and nonsurgical treatment are necessary. Additionally, identifying the predictive information based on bone morphology could be used to guide treatment choices. How Do We Get There? Longer-term followup involving the current cohort could help determine whether abnormal kinematics persist over time or whether they relate to clinical outcomes, risk of graft reinjury, or the development of osteoarthritis. A large, prospective cohort could possibly confirm initial baseline findings, associate bony morphology features with abnormal kinematics, and develop more predictive power for clinical and radiographic outcomes. Once there is evidence of the prognostic value of bone morphology in patients with ACL tears, the next step would be to develop randomized treatment protocols to assess the effectiveness of variable interventions, such as operative versus nonoperative treatment or variable graft choice for reconstruction based on bone morphology.