BACKGROUND: Structural characteristics of calcium phosphate cement (CPC) offer substantial mechanical integrity for fracture stabilization and fixation during the healing process, with particular applications in mechanically compromised osteoporotic bone.OBJECTIVE: To investigate the mechanism of the augmentation to fixation with CPC, comparing with screw fixation augmented by polymenthymethacrylate (PMMA) bone cement or with unaugmented screw fixation for femoral neck fractures in sheep by histological evaluation.DESIGN: Randomized controlled, duplicated observation and opening study.SETTING: Departments of Orthopeadics and General Surgery, the First Hospital of Jilin University; Department of Pathology, Basic Medical College of Jilin University; Department of Plastic Surgery, Aichi Medical University of Japan.MATERIALS: The experiment was completed in the Taonan Municipal Hospital of Jilin, Jilin University and Aichi Medical University of Japan from January 1999 to January 2004. A total of 45 adult sheep with mean age of 12.5 months were divided into three groups: unaugmentation group,CPC augmentation group and PMMA augmentation group with 15 in each group. Five sheep from each group were selected at 3, 6 and 12 weeks after operation. CPC was consisted of 75% α-tricalcium phosphate (α-TCP),18% tetracalcium phosphate (TeCP), 5% dicalcium phosphate dihydrate (DCPD) and 2% hydroxyapatite (HA). The solidify liquid was consisted of 5% sodium chondroitin sulphate, 12% sodium succinate and 83% water.The ratio between powder and water was 3:1. PMMA bone cement was combined with 97.4% methylmethacrylate, 2.6% N dimethyl-para-toluidine and hydroquinone.METHODS: ① Sheep from each group were anaesthetized by intravenous injection of pentobarbital sodium. The surgical steps were steotomy, drill,tap and fixation. An osteotomized bone at the base of right femoral neck of all groups was fixed by two cancellous bone screws of the diameter 4 mm through femoral neck at the site below great trochanter region. The cement material was filled into the screw hole before the screw insertion. ② CPC was injected into wells in CPC augmentation group, PMMA was injected into wells in PMMA augmentation group, but wells in unaugmentation group was not give any materials. ③After the maximum, compressive load was tested to detect intensity of healing bone, the specimens were fixed in 40%, 70%, 90% and 100% ethanol, dehydrated and stained, in the end embedded in PMMA resin. Serial histological specimens of 150-200 μm thickness were sliced along the long axis of the femoral neck with the microtom. The histological specimens also were taken for contact microradiography. The changes of the host bone and the new bone formation at the interface between cement and bone would be evaluated histologically until 3, 6 or 12 weeks after surgery.MAIN OUTCOME MEASURES: Changes of the host bone and the new bone formation in each group at various time points after operation.RESULTS: All 45 mature Chinese sheep were involved in the final analysis without any loss. Changes of the host bone and the new bone formation in each group at various time points after operation: ① Unaugmentation group: By 3 weeks after surgery, the thin fibrous tissue was found around the screw, and the host bone had micro-destruction. By 6 or 12 weeks after surgery, the micro-destruction of host bone was repaired. ② CPC augmentation group: By 3, 6 or 12 weeks after surgery, the most of gap between the screw and the host bone was occupied by this material, and the new bone connected directly to the material surface, and there was no intervening fibrous tissue between new bone and the material. Especially by 12weeks after surgery, a large quantity of the new bone was formed, and new bone was matured with many bone canals. ③ PMMA augmentation group:By 3 weeks after surgery, the thick fibrous tissue Between PMMA bone cement and the host bone, and the remarkable bone atrophy of host bone were found. By 6,12 weeks after surgery, the fibrous tissue and the bone atrophy were developed.CONCLUSION: CPC provide long-term beneficial augmentation of femoral neck fractures in sheep because of a good biocompatibility, good osteoconduction and capability of remodeling.