Clinical Outcomes of Injectable Porcine Collagen in Diabetic Patients with Achilles Tendinopathy: A Retrospective Study

Background/Objective: Achilles tendinopathy (AT) is a disabling condition, and treatment options are limited in patients in whom corticosteroid injections are discouraged or contraindicated, including individuals with diabetes. Collagen injections have been proposed as a conservative option; however, clinical evidence in diabetic populations remains limited. This study aims to describe pain and functional outcomes after peritendinous collagen injections in diabetic patients with chronic Achilles tendinopathy. Methods: Twenty-two diabetic patients with ultrasound-confirmed degenerative Achilles tendinopathy refractory to conservative management were retrospectively included and split into two groups according to AT type: insertional (IAT) and non-insertional/midportion (NIAT). All patients received five weekly ultrasound-guided peritendinous collagen injections. Outcomes included VAS assessed at baseline, after the second injection, at 1 month, and at 6 months; VISA-A at baseline and 6 months; return-to-work (RTW) time; and adverse events. Baseline variables included BMI, HbA1c, symptom duration, and previous treatments. Analyses were based on descriptive statistics and within-group comparisons over time. Results: All patients completed the treatment protocol, and no adverse events were recorded. Pain significantly improved over follow-up in both subgroups. Mean VAS decreased from baseline to 6 months (mean ΔVAS: 5.1 in IAT and 4.4 in NIAT; p = 0.001 for within-group change). VISA-A also improved at 6 months (mean ΔVISA-A: 32.78 in IAT and 38.97 in NIAT; p < 0.0001). Median RTW was 37 days in IAT and 35 days in NIAT (p > 0.05). No significant between-group differences were observed for VAS or VISA-A changes (p > 0.05). Conclusions: In this uncontrolled retrospective case series, peritendinous collagen injections were feasible and well-tolerated in diabetic patients with Achilles tendinopathy and were associated with clinically relevant improvements in pain and functional outcomes at 6 months. These findings are hypothesis-generating and warrant confirmation in prospective controlled studies.