Effect of Mesenchymal Stem Cell-Derived Secretome Injection on Functional Outcomes After Anterior Cruciate Ligament Reconstruction Using Peroneus Longus Tendon Autograft: A Double-Blind Randomized Controlled Trial

<title>Abstract</title> <p> <bold>Introduction</bold> : Graft healing after anterior cruciate ligament (ACL) reconstruction remains challenging, as inadequate ligamentization and tendon–bone integration can lead to graft failure. Mesenchymal stem cell (MSC)-derived secretome, a cell-free conditioned medium containing bioactive factors, has demonstrated promising regenerative potential in preclinical studies. This study compared six-month functional outcomes of ACL reconstruction using a peroneus longus tendon (PLT) autograft with and without adjuvant secretome injection. <bold>Methods</bold> : A double-blind randomized controlled trial enrolled 24 participants undergoing arthroscopic single-bundle ACL reconstruction with a PLT autograft, randomly assigned to receive intralesional secretome injection into the graft (secretome group, n = 12) or saline placebo (control group, n = 12). Functional outcomes were assessed preoperatively and at six months using the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form and Tegner–Lysholm Knee Scoring Scale. Between-group comparisons used the independent-samples t-test or Mann–Whitney U test, with significance at p &lt; 0.05. <bold>Results</bold> : Baseline IKDC scores were comparable (secretome 48.57 ± 4.91 vs. control 47.51 ± 4.45; p &gt; 0.05). At six months, the secretome group showed significantly higher IKDC scores (86.89 ± 5.11 vs. 78.27 ± 3.91; p &lt; 0.01) and Tegner–Lysholm scores (87.08 ± 5.16 vs. 79.33 ± 2.67; p &lt; 0.01). Post hoc power analysis confirmed adequate statistical power (0.85 for IKDC; 0.89 for Tegner–Lysholm). No major adverse events occurred; transient swelling and mild pain resolved spontaneously. <bold>Conclusion</bold> : Adjuvant MSC-derived secretome injection during PLT autograft ACL reconstruction yielded significantly superior six-month functional outcomes. Secretome may serve as a promising cell-free biologic adjuvant to enhance graft healing and early recovery following ACL reconstruction. Level of evidence Level 1 Registry: ClinicalTrials.gov, NCT07723625, Registration date: 19 July 2026. </p>