Letter to the Editor regarding ‘Anterior cruciate ligament primary repair revision rates are increased in skeletally mature patients under the age of 21 compared to reconstruction, while adults (>21 years) show no significant difference: A systematic review and meta-analysis’

We read with great interest the recent article by Rilk et al. addressing the critical influence of age on the outcomes of anterior cruciate ligament (ACL) repair techniques [9]. The authors should be commended for their rigorous methodology and thought-provoking findings, particularly identifying the age of 21 years as a key age threshold for ACL repair efficacy. This finding holds significant promise in guiding personalised treatment strategies. However, we believe that certain limitations warrant further discussion to enhance the clinical applicability of the conclusions.

First, the methodological constraints of the study deserve attention. The limited number of included studies (12), which were predominantly retrospective, led to a relatively low level of evidence. The small sample size may have affected the robustness of the effect size estimation, increasing the risk of false-positive or false-negative results. Consequently, the current evidence may be insufficient to definitively support the 21-year age cutoff. Moreover, significant heterogeneity existed among the included studies regarding ACL reconstruction techniques, graft types, and fixation methods. The lack of adequate subgroup analysis or adjustment during meta-analysis may have affected the reliability of the results. Additionally, the included populations varied in age, sex, and preoperative activity level, with only 30% of the non-randomised studies performing cohort matching, making it difficult to exclude the influence of selection and confounding biases. Future meta-analyses should expand the literature search, including more high-quality prospective studies, and employ meta-regression, Egger's test, and sensitivity analyses to explore the sources of heterogeneity and assess the impact of bias [8].

Second, the authors' interpretation of certain unexpected findings lacks depth. Regarding the higher revision rate of repair techniques compared to reconstruction in patients aged ≤21 years, the authors speculate that this may be related to the higher risk of re-injury in young individuals. However, they did not thoroughly explore the potential mechanisms underlying the age-efficacy relationship. Based on the literature, we propose the following hypotheses for the authors' consideration: (1) younger individuals may have more severe ACL degeneration at the time of injury, hindering repair; [5, 12] (2) higher postoperative weight-bearing and activity levels in younger patients may increase early stress, leading to re-injury at the repair site; [1, 13, 14] and (3) although younger individuals have more robust ligament cell metabolism, metabolic derangements after repair may affect tissue healing quality [2, 7]. These factors could collectively influence the repair outcomes and increase the risk of revision.

Similarly, the authors attributed the higher reoperation rate of dynamic intraligamentary stabilisation (DIS) compared with ACL reconstruction to complications caused by the fixation of foreign bodies. However, this analysis might have been incomplete. In addition to foreign body-related complications, factors such as selection bias in DIS indications (predominantly proximal avulsion injuries) and the surgeon's learning curve may also be contributing factors [3, 4, 6, 10, 11].

In conclusion, while this meta-analysis employed rigorous literature inclusion criteria and statistical methods, offering valuable insights into the critical role of age in ACL repair outcomes, the generalisability of the conclusions may be influenced by limitations such as the level of evidence and heterogeneity among the included studies. Future research should focus on large-scale, long-term, prospective cohort studies with expanded sample sizes, extended follow-up, and balanced baseline characteristics. Additionally, in-depth investigations into the mechanisms and risk factors of ACL repair failure, optimisation of indication selection and surgical techniques, and multidisciplinary collaboration are crucial for overcoming the current challenges. Only through the continuous accumulation of evidence-based medicine and refinement of treatment strategies can we ultimately achieve precise and individualised ACL injury management that benefits patients. This endeavour requires concerted efforts of basic research, clinical practice, and rehabilitative guidance, working hand-in-hand to advance the field of sports medicine.

We appreciate the valuable contributions of the authors to the evolving landscape of ACL injury treatment and look forward to further research that builds on these findings, driving the development of personalised and evidence-based care.

The authors declare no conflict of interest.