Exploring Mechanisms of Calcific Tendonitis Using a Novel Turkey Model

Calcific tendinopathy is a common musculoskeletal disorder marked by calcium deposition within tendons, often accompanied by pain, impaired mobility, and in severe cases, ossification. However, the mechanisms underlying tendon mineralization remain poorly understood. In contrast to pathological human calcification, turkeys naturally develop tendon mineralization during growth without signs of inflammation or ossification. This study had two phases: an observational phase to assess onset and progression of calcification, and an interventional phase to evaluate the role of mechanical loading. In the observational phase, flexor tendons were collected from turkeys aged 1-16 weeks in a serial sacrifice study and analyzed by Von Kossa staining and biomechanical testing. Calcification began at 7 weeks, localized within organized collagen matrices, progressed through Weeks 8-14, and peaked by 16 weeks. In the interventional phase, nine female turkeys were randomized at 4 weeks into a transection group (n = 3), sham group (n = 3), and control group (n = 3). Transection at the muscle-tendon junction eliminated mechanical loading. At 16 weeks, tendons were analyzed by histology, quantitative RT-PCR, ICP-MS, and biomechanical testing. Transected tendons showed a near-complete absence of mineralization, reduced expression of osteogenic markers (osteopontin, osteocalcin, Runx-2), and significantly lower calcium, magnesium, and phosphorus levels. Biomechanical testing indicated reduced stress relaxation, stiffness, and Young's modulus in the transected group. Tendon calcification in turkeys functioned as a mechanically regulated, nonpathological process. The study established a relevant model for early tendon mineralization and offered a basis for developing load-dependent therapies for human tendon disease.