Parathyroid hormone 1-34 enhances extracellular matrix deposition and organization during flexor tendon repair

Parathyroid hormone (PTH) 1-34 is known to enhance fracture healing. Tendon repair is analogous to bone healing in its dependence on the proliferation and differentiation of mesenchymal stem cells, matrix formation, and tissue remodeling.(1,2,3) We hypothesized that PTH 1-34 enhances tendon healing in a flexor digitorum longus (FDL) tendon repair model. C57Bl/6J mice were treated with either intraperitoneal PTH 1-34 or vehicle-control (PBS). Tendons were harvested at 3-28 days for histology, gene expression, and biomechanical testing. The metatarsophalangeal joint range of motion was reduced 1.5-2-fold in PTH 1-34 mice compared to control mice. The gliding coefficient, a measure of adhesion formation, was 2-3.5-fold higher in PTH 1-34 mice. At 14 days post-repair, the tensile strength was twofold higher in PTH 1-34 specimens, but at 28 days there were no differences. PTH 1-34 mice had increased fibrous tissue deposition that correlated with elevated expression of collagens and fibronectin as seen on quantitative PCR. PTH 1-34 accelerated the deposition of reparative tissue but increased adhesion formation.