Biocompatibility of Calcium Phosphate Bone Cement with Optimised Mechanical Properties: An In Vivo Study

This work establishes the in vivo performance of modified calcium phosphate bone cements (CPCs) for vertebroplasty of spinal fractures using a lapine model. A non-modified CPC and collagen-CPC composites with enhanced mechanical properties, utilising either bovine collagen or collagen from a marine sponge, were compared to a commercial poly(methyl methacrylate) (PMMA) cement. Conical cement samples (8 mm height x 4 mm base diameter) were press-fit into distal femoral condyle defects in New Zealand White rabbits and assessed after 5 and 10 weeks. Bone apposition and tartrate resistant acid phosphatase (TRAP) activity around cements were assessed. All implants were well tolerated, but bone apposition was higher on CPCs than on PMMA cement. Incorporation of collagen showed no evidence of inflammatory or immune reactions. Presence of positive TRAP staining within cracks formed in CPCs suggested active osteoclasts were present within the implants and were actively remodelling within the cements. Bone growth was also observed within these cracks. These findings confirm the biological advantages of CPCs over PMMA and, coupled with previous work on enhancement of mechanical properties through collagen incorporation, suggest collagen-CPC composite may offer an alternative to CPCs in applications where low setting times and higher mechanical stability are important.