Testosterone Therapy and Tendon Injury: Clinical Evidence, Biological Mechanisms, and Sports Medicine Implications.

Testosterone therapy increases lean mass and can improve muscle strength in men with hypogonadism. This review examines the relationship between testosterone therapy, tendon adaptation, and tendon injury, including the possibility of a mismatch between changes in muscle strength and tendon capacity. This narrative review critically evaluates the clinical and experimental evidence relating testosterone exposure to tendon injury. The present review focuses specifically on tendon-related safety and is not intended to assess the overall benefit-risk profile of testosterone therapy. Prescription-based studies have identified associations with distal biceps, rotator cuff, quadriceps, patellar, and Achilles tendon injuries. The magnitude of association varies considerably, with modest elevations in broad analyses and larger relative estimates in some site-specific studies. Absolute event rates are generally low, and the available studies cannot establish causation. Important limitations include incomplete information about treatment indications, testosterone concentrations, dosage, adherence, formulation, physical activity, pre-existing tendinopathy, and undisclosed anabolic-androgenic steroid use. Evidence from supraphysiologic androgen exposure provides greater biological plausibility but cannot be directly extrapolated to physiologic testosterone replacement. Potential biological mechanisms involving collagen synthesis, matrix remodelling, and tendon mechanical properties are also examined. No clinical evidence establishes a dose-response relationship or demonstrates that topical treatment, smaller injections, or more frequent dosing reduces tendon risk. Testosterone improves bone mineral density and estimated bone strength, but fracture prevention has not been demonstrated. Overall, a small increase in tendon injury risk with testosterone therapy is plausible, particularly in highly active individuals undergoing rapid increases in loading, but the evidence remains observational and substantially confounded. Clinicians should provide proportionate counselling without discouraging appropriately indicated treatment.