Effects of parathyroidectomy and vitamin D on fracture healing. Fracture biomechanics in rats after parathyroidectomy and treatment with 1,25-dihydroxycholecalciferol.

Fracture healing was studied in male, adult Sprague-Dawley rats. Closed bilateral tibial fractures were observed to be clinically stable after 3 weeks. Parathyroidectomy (PTX) resulted in impaired fracture healing and several delayed unions. Fracture tensile strength, elastic stiffness and failure energy were significantly lower at the beginning of the healing period compared to that of control fracture rats. Treatment with low doses (60 ng/kg/day) of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) increased early fracture bone formation and mineralization. However, these events did not result in a corresponding increase of tensile strength or failure energy compared with that of the controls. Increased bone turnover seemed to be the dominant characteristic and resulted in early resorption of periosteal callus. Toward the end of the healing period, fracture strength measured as tensile strength and failure energy actually decreased compared to that of the control rats. Elastic stiffness initially rose above control values due to increased mineralization, but declined later to control values.