Effects of altered crystalline structure and increased initial compressive strength of calcium sulfate bone graft substitute pellets on new bone formation.

A new, modified calcium sulfate has been developed with a different crystalline structure and a compressive strength similar to many calcium phosphate materials, but with a resorption profile only slightly slower than conventional surgical-grade calcium sulfate. A canine bilateral defect model was used to compare restoration of defects treated with the modified calcium sulfate compared to treatment using conventional calcium sulfate pellets after 6, 13, and 26 weeks. The modified calcium sulfate pellets were as effective as conventional calcium sulfate pellets with regard to the area fraction and compressive strength of newly formed bone in the treated bone defects. Mechanical testing demonstrated that the initial compressive strength of the modified material was increased nearly three-fold compared to that of conventional surgical-grade calcium sulfate. This increase potentially allows for its use in a broader range of clinical applications, such as vertebral and subchondral defects.

An injectable calcium sulfate-based bone graft putty using hydroxypropylmethylcellulose as the plasticizer.

The addition of a plasticizer to synthetic bone graft substitutes can improve handling characteristics, injectability, and the ability to uniformly fill defects. Restoration of large medullary bone defects using an injectable calcium sulfate-based putty using hydroxypropylmethylcellose as the plasticizer was compared to conventional calcium sulfate paste in a canine model. Beginning 2 weeks following implantation, serial clinical and specimen radiographs demonstrated a similar progressive resorption of the implanted materials and replacement with new bone for both the putty and paste forms of calcium sulfate. The area fraction of new bone and remaining implant material in bone defects treated with the putty were not significantly different from defects treated with conventional calcium sulfate paste after 13 and 26 weeks. In addition to its handling characteristics, the putty was biocompatible and as effective as conventional calcium sulfate paste in achieving substantial bony restoration of a large, critical-size bone defect.