Growth hormone treatment promotes guided bone regeneration in rat calvarial defects

This study evaluated the biomechanical strength and bone formation in calvarial critical size bone defects covered with expanded polytetrafluoroethylene (e-PTFE) membranes in rats treated systemically with recombinant human growth hormone (rhGH). A full-thickness bone defect, 5 mm in diameter, was trephined in the central part of each parietal bone in 40 one-year-old female Wistar rats, which were randomly assigned to two groups of 20 animals each. The bone defects were covered with an exocranial and an endocranial e-PTFE membrane. From the day of operation, the rhGH-treated animals were given 2.7 mg rhGH/kg/day and the placebo-injected rats were given isotonic sodium chloride. The animals were killed 28 days after operation. The biomechanical test was performed by a punch out test procedure placing a 3.5-mm diameter steel punch in the centre of the right healed defect. After mechanical testing, the newly formed tissue inside the defect was removed and the dry and ash weights were measured. The left healed defects were used for three-dimensional (3D) reconstruction by means of micro-computer tomography (micro-CT). Ultimate load, ultimate stiffness, and energy absorption at ultimate load were significantly increased in the rhGH-treated group (P < 0.003). Also, tissue dry and ash weights were significantly augmented in the rhGH-treated group (P < 0.001). The 3D reconstruction of newly formed bone showed that there was almost twice as much bone volume present in the rhGH-treated defects compared with the placebo group. The experiment demonstrated that rhGH administration enhances bone deposition and mechanical strength of healing rat calvarial defects, covered with e-PTFE membranes.