Response Letter to the Editor regarding ‘Increased contralateral dynamic valgus in female athletes following ACL reconstruction’

We would like to thank the authors for their thoughtful and constructive letter regarding our article, ‘Increased contralateral dynamic valgus in female athletes following ACL reconstruction’. We appreciate the interest in our work and welcome the opportunity to further clarify our findings and put them into context. First, we fully agree that statistical power and sample size are critical considerations when interpreting biomechanical studies. As transparently stated in our manuscript, the subgroup analysis of female athletes did not reach the a priori calculated sample size required to detect an 8° difference in valgus angle with 80% power. This limitation was explicitly acknowledged, and our conclusions were deliberately worded with caution, particularly regarding non-significant findings. We therefore concur with the authors that negative results, especially in underpowered subgroup analyses, should be interpreted carefully. With regard to the Hamstrings-to-Quadriceps (H/Q) ratio, we agree with the authors that the borderline p value (p = 0.051) should be interpreted with caution, particularly in the context of the limited sample size. As outlined in our manuscript, the corresponding effect size was moderate to large, suggesting that the absence of statistical significance may, at least in part, reflect limited statistical power and an increased risk of a Type II error rather than the absence of a physiological effect. Importantly, strength parameters were explored as secondary outcomes and were not defined as primary endpoints. In line with the authors' interpretation, we agree that valgus movement patterns are likely caused by a complex interplay of neuromuscular factors that goes beyond the isolated strength of the thigh muscles. We concur that proximal neuromuscular control, including hip and trunk stability, plays an important role in valgus mechanics. Our findings support the view that functional movement analysis provides complementary information to conventional strength testing, particularly in the return-to-sport phase following anterior cruciate ligament (ACL) reconstruction. Regarding the clinical implications, we welcome the authors' emphasis on the contralateral limb and concur that this aspect is often underrepresented in standard return-to-sport criteria. The timing of our assessment coincided with a clinically vulnerable phase for secondary injury, and our results support the notion that contralateral biomechanics should receive more attention in both rehabilitation and injury prevention strategies. We agree that future multi-centre studies with larger sample sizes are needed to further validate these observations and to establish clinically meaningful thresholds. In summary, we appreciate the authors' constructive critique and view their comments as complementary to our own interpretations. We believe that our study contributes to the growing body of evidence supporting sex-specific and movement-based approaches to secondary ACL injury prevention, while highlighting the need for adequately powered, multi-centre biomechanical research. All authors contributed to the drafting and revision of the response and approved the final manuscript. ChatGPT (OpenAI, GPT-5.2) was used for language editing. Wolf Petersen: Royalties or licences: Karl Storz, Tuttlingen, Germany; Consulting fees: OPED, Valley, Germany; Arthrex, Munich, Germany; Payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events: Plasmaconcept, Cologne, Germany; Arthrex, Munich, Germany; OPED, Valley, Germany; Otto Bock, Duderstadt, Germany; Leadership or fiduciary role in other board, society, committee or advocacy group (unpaid): Vice president of GOTS (Society of Orthopedics and Trauma in Sports), Board member if the German Knee Society (DKG). The remaining authors declare no conflicts of interest. The authors have nothing to report. The authors have nothing to report.