Tendon overuse models have different effects on tissue mechanical properties in ex vivo bovine tendons

Tendinopathy is an overuse injury that occurs in high load bearing tendons, causing decreased function and increased pain. Current tendinopathy treatments produce inconsistent outcomes, creating a need for novel treatments. It is unclear whether current tendinopathy models used to develop new treatments replicate the mechanical effects of the injury. We aim to compare the mechanical properties of 2 established tendinopathy models - collagenase injection and mechanical overload - in ex vivo bovine tendons. Eighteen bovine tendons were split into 3 groups, including: uninjured, collagenase injection (0.5 mL collagenase and 0.5 mL fibrin gel), and mechanical overload (5 cycles of tensile loading/unloading). Mechanical testing of samples was performed. Stiffness, maximum force at failure, and ultimate tensile stress (UTS) were computed, then compared across groups using 1-way ANOVA with significance set at p < 0.05. Results showed maximum force and UTS were reduced for the mechanical overload group (402.1 ± 232.3 N; 9.1 ± 5.3 MPa) versus uninjured (1222.9 ± 270.8 N; 28.9 ± 4.6 MPa) and collagenase injection groups (1309.0 ± 242.1 N; 25.0 ± 8.2 MPa) (all p < 0.001). Stiffness was not different across groups (all p > 0.33). Findings suggest that ex vivo mechanical overload better represents the mechanical properties of tendinopathy than collagenase injection.