Knee Stability in Remnant-Preserving ACL Reconstruction: Letter to the Editor

Dear Editor:

We read with great interest the article titled “Comparing Clinical Outcomes and Knee Stability in Remnant-Preserving ACL Reconstruction Versus Standard ACL Reconstruction: A Systematic Review and Meta-analysis” by Allende et al, ¹ published in The American Journal of Sports Medicine. This comprehensive meta-analysis addresses a critical aspect of anterior cruciate ligament reconstruction (ACLR) techniques, particularly focusing on the benefits of remnant-preserving methods. The systematic review included 7 randomized controlled trials (RCTs) and 5 cohort studies, analyzing a total of 1122 patients. The study concluded that remnant-preserving ACLR provides comparable clinical outcomes and significantly improves knee stability compared to standard ACLR, without increasing the complication rate. Specifically, the meta-analysis highlighted improvements in Lysholm scores and pivot-shift test results, favoring the remnant-preserving technique.

However, we have several methodological concerns and suggestions that we believe are important for the interpretation of the results and future research directions:

First, the meta-analysis commendably integrates RCTs and prospective cohort studies to address a crucial clinical question. An I² value >40% indicates significant heterogeneity, which can affect the reliability of the meta-analysis outcomes. In this study, substantial heterogeneity was found in several outcome measures. For instance, the analysis of anterior tibial translation using KT-1000, KT-2000, or Rolimeter devices revealed an I² value of 82%, indicating high heterogeneity among the included studies. Additionally, the Lysholm scores showed moderate heterogeneity, with an I² value of 48%. This variability complicates the interpretation of the results and suggests the presence of underlying differences between studies. To enhance the robustness and reliability of such meta-analyses, we suggest adopting Bayesian methods. Bayesian approaches can better handle variability and incorporate prior knowledge, offering a more nuanced synthesis of the data. ² Additionally, standardizing data extraction procedures and considering individual patient data meta-analyses when feasible can significantly improve data quality and comparability. While Allende et al ¹ have taken substantial steps to address the challenges of combining RCTs and cohort studies, adopting these practical measures could further reduce bias and heterogeneity. These enhancements would not only strengthen the validity of their findings but also contribute to more reliable and interpretable results in future research.

Second, in this meta-analysis, the findings regarding complications and cyclops lesions prompt several considerations. Although only one study reported a higher incidence of cyclops lesions in the remnant-preserving group, this risk remains significant. Cyclops lesions, defined as localized arthrofibrosis, can lead to knee extension deficits, impacting functional recovery and overall patient satisfaction. They are among the common causes of extension loss after ACLR. Four of the original studies included in this meta-analysis reported on cyclops lesions. However, it appears that the reporting of adverse reactions and complications in the included studies was inconsistent and often lacked standardization. Some original studies failed to comprehensively report all potential adverse reactions. For example, some studies focused only on knee stability and clinical scores without detailing postoperative complications and lesions.^3,4 Additionally, because of differences in data collection and outcome reporting, this meta-analysis struggled to comprehensively synthesize adverse reaction data. These inconsistencies and limitations in data collection could affect the validity of the combined results. Therefore, future original studies need to more rigorously and uniformly report adverse reactions and complications to ensure that meta-analyses can accurately reflect the safety profiles of these techniques. Understanding the causes of cyclops lesions is crucial for improving surgical methods. Future research should explore how surgical techniques, the amount of remnant tissue preserved, and individual patient differences contribute to cyclops lesion formation. ⁶ The geometry of the intercondylar notch, including its width and shape, is associated with the risk of cyclops lesions.

Notably, there are differences in the cyclops lesion incidence between single-bundle and double-bundle reconstruction techniques. Single-bundle reconstruction, typically involving less tissue preservation, may result in a lower incidence of cyclops lesions. In contrast, double-bundle reconstruction often preserves more remnant tissue, potentially increasing the cyclops lesion risk because of more biologically active tissue and collagen within the femoral notch. ⁵ This knowledge will aid in developing preventive measures and reducing such complications. Considering the impact of cyclops lesions, postoperative follow-ups should monitor knee extension to detect and address these lesions early. Detailed postoperative monitoring and management can enhance long-term patient satisfaction and functional recovery.

In conclusion, the meta-analysis by Allende et al ¹ provides significant insights into the potential advantages of remnant-preserving ACLR. We commend the authors for their rigorous analysis and valuable contributions to the field of sports medicine. Continued research with longer follow-up periods, diverse graft types, and standardized outcome measures will further elucidate the benefits and limitations of remnant-preserving ACLR techniques. Ensuring comprehensive and standardized reporting of adverse reactions and complications will also be crucial for a thorough evaluation of these surgical methods.