Calcium sulfate used as bone graft substitute in acetabular fracture fixation

The purpose of this study was to determine the natural history of calcium sulfate pellets implanted during acetabular fracture surgery. The study group consisted of patients sustaining an acetabular fracture with intraarticular comminution or marginal impaction or both in whom calcium sulfate pellets were implanted in lieu of autologous bone graft. Between 1997 and 1999, 32 fractures were treated. Followup adequate to delineate pellet outcome, including radiographs and computed tomography, was obtained in 31 patients. Evaluation of plain radiographs showed that the calcium sulfate pellets became undifferentiated from the surrounding bone at an average of 7 weeks postoperatively. In no case was a residual bony deficit seen. Computed tomography analysis showed that in 22 patients, the pellets essentially had been (> 90%) replaced by bone and in four patients, the majority (> 50%-90%) of the pellets had been replaced by bone. However, in five patients, less than 50% of the pellets had been replaced by bone, including one showing no bony replacement. The common finding in patients with an extensive residual deficit was direct communication of the pellets with the joint space shown on the postoperative computed tomography scan. Patients with the best results had complete containment of the pellets within bone. Therefore, it seems that implanted calcium sulfate pellets in contact with joint synovial fluid are at risk for resorption without significant bony response. If calcium sulfate pellets are to be implanted in a periarticular location, complete bony containment is desirable. Evaluation of the periacetabular bony response requires computed tomography scans, as plain radiographs are inadequate for this purpose.