Patient-Centered Outcomes After Minimally Invasive Internal Splinting Versus Open Achilles Tendon Repair: Comparable Clinically Meaningful Recovery at 12 Months

Background/Objectives: Comparative studies evaluating minimally invasive surgery (MIS) and open repair for acute Achilles tendon rupture have predominantly relied on mean-based statistical comparisons, which may not adequately capture whether outcomes are clinically meaningful from the patient perspective. This study aimed to compare 12-month outcomes between MIS using the internal splinting technique and open repair, establish anchor-based minimal clinically important difference (MCID) thresholds, and compare patient-centered responder outcomes between techniques. Methods: This retrospective non-randomized comparative cohort study included 70 patients allocated to MIS (n = 35) or open repair (n = 35). Outcomes were assessed using VAS, AOFAS, ATRS, and Thermann score. Anchor-based MCID thresholds were determined via ROC curve analysis using the Global Rating of Change (GROC) scale as the external anchor. Patient Acceptable Symptom State (PASS) was assessed using a dichotomous anchor question. Results: Both groups demonstrated significant improvements across all outcome measures at 12 months (p < 0.001). No significant between-group differences were observed in mean functional scores, MCID achievement rates, PASS rates, or GROC-defined clinical success (p > 0.05 for all). AUC values ranged from 0.975 to 0.984. The MCID threshold for pain relief was identified as a VAS reduction > 4.8 points (AUC: 0.975, 95% CI: 0.906–0.998), while ROC-derived functional MCID thresholds were identified as an AOFAS increase >38 points (AUC: 0.984, 95% CI: 0.920–0.999), an ATRS increase >38 points (AUC: 0.984, 95% CI: 0.920–0.999), and a Thermann score increase >37 points (AUC: 0.984, 95% CI: 0.920–0.999). These thresholds should be considered exploratory and require validation in larger independent cohorts. MCID achievement rates were 42.9% for VAS in both groups, whereas MCID achievement for functional outcome measures (AOFAS, ATRS, and Thermann scores) was 62.9% in the MIS group and 57.1% in the open repair group. PASS-positive rates were 85.7% and GROC-defined clinical success 71.4% in both groups. Complication rates were low in both groups; however, the small number of events limits the strength of this conclusion, and larger studies are needed to evaluate potential between-group differences. Conclusions: Both techniques were associated with substantial clinically meaningful recovery at 12 months, and neither approach demonstrated a clear clinical advantage in patient-centered outcomes. The population-specific MCID thresholds derived in the present cohort may provide clinically interpretable benchmarks for future research, although external validation is required before broader application. Surgical decision-making may rely on surgeon expertise and patient factors rather than anticipated differences in patient-centered outcomes.