Induction of fracture healing using fibrous calcium phosphate composite spherulites

The healing of large fractural defects is a difficult clinical problem, especially if it occurs in elderly or otherwise debilitated patients. The objective of this study is to determine if a new formulation of fibrous calcium phosphate crystals would induce fracture healing in vivo. Fibrous calcium phosphate (FCP) can be grown with unique size, shape, and surface area characteristics as a resorbable or nonresorbable, osteoconductive or osteoinductive material. In comparison with other conventional calcium phosphate particulates, FCP particles possess approximately x 100 to x 1000 more surface area. One-and-one-half centimeter sections were removed from the ulnas of 12 rabbits. Three groups had fibrous calcium phosphate spherulites (4-8 microns, 150-300 microns, 400-600 microns) mixed with collagen and a growth factor-bonding agent injected into the ulnar defect. One site per group was not treated. X-rays were obtained during the study and the percentage of the ulna defect filled in by callous was measured. The percentage was recorded as the amount of fracture healing for each site. Histologic examination of the ulnas was performed following sacrifice at 12 weeks. Fracture sites treated with fibrous calcium phosphate showed significantly greater healing (0.79 +/- 0.3) than control animals (0.36 +/- 0.1) (P less than .05, unpaired t-test) radiographically. Histologic examination showed that the spherulites remain in situ and become embedded within the new growth of fibrous tissue, collagen and new bone. Radiographically and histologically, FCP preparations appear to accelerate fracture healing by inducing new bone formation, into which they often become embedded.