Systemic intermittent parathyroid hormone treatment improves osseointegration of press-fit inserted implants in cancellous bone.

BACKGROUND AND PURPOSE: Intermittent administration of parathyroid hormone (PTH) has an anabolic effect on bone, as confirmed in human osteoporosis studies, distraction osteogenesis, and fracture healing. PTH in rat models leads to improved fixation of implants in low-density bone or screw insertion transcortically. MATERIAL AND METHODS: We examined the effect of human PTH (1-34) on the cancellous osseointegration of unloaded implants inserted press-fit in intact bone of higher animal species. 20 dogs were randomized to treatment with human PTH (1-34), 5 µg/kg/day subcutaneously, or placebo for 4 weeks starting on the day after insertion of a cylindrical porous coated plasma-sprayed titanium alloy implant in the proximal metaphyseal cancellous bone of tibia. Osseointegration was evaluated by histomorphometry and fixation by push-out test to failure. RESULTS: Surface fraction of woven bone at the implant interface was statistically significantly higher in the PTH group by 1.4 fold with (median (interquartile range) 15% (13-18)) in the PTH group and 11% (7-13) in control. The fraction of lamellar bone was unaltered. No significant difference in bone or fibrous tissue was observed in the circumferential regions of 0-500, 500-1,000, and 1,000-2,000 µm around the implant. Mechanically, the implants treated with PTH showed no significant differences in total energy absorption, maximum shear stiffness, or maximum shear strength. INTERPRETATION: Intermittent treatment with PTH (1-34) improved histological osseointegration of a prosthesis inserted press-fit at surgery in cancellous bone, with no additional improvement of the initial mechanical fixation at this time point.

Strontium is incorporated into the fracture callus but does not influence the mechanical strength of healing rat fractures.

Strontium ranelate (SrR) is a new agent used in the treatment of osteoporosis and is suggested to reduce bone resorption and increase bone formation. We investigated whether SrR influences the macro- and nanomechnical properties of healing fractures in rats. A closed tibia fracture model was used to study fracture healing in rats after 3 and 8 weeks of healing. Two groups of rats were treated with SrR (900 mg/kg/day) mixed into the food, while two groups served as control animals. The healing fractures were investigated by three-point bending, dual energy X-ray absorptiometry, energy-dispersive X-ray spectroscopy (EDX), and nanoindentation. There was a 100-fold increase (P < 0.001) in serum Sr after 3 and 8 weeks of SrR treatment. The callus volume was significantly higher in the SrR-treated group than in control animals (P < 0.01) after 3 weeks of healing. This was accompanied by a significant increase in callus bone mineral content (P < 0.05). However, after 8 weeks of healing, no difference was found in either callus volume or bone mineral content. SrR did not influence maximum load or stiffness of the fractures after either 3 or 8 weeks of healing. EDX showed that Sr was incorporated into the callus; however, this did not influence the nanomechanical properties. In conclusion, SrR stimulates callus formation but has no effect on callus remodeling. Sr is incorporated into the newly formed callus tissue, but this has no deteriorating effect on the mechanical properties of rat tibial fractures at either the macroscopic or nanoscopic level after 3 or 8 weeks of healing.