Experimental Tibial Plateau Fractures Augmented With Calcium Phosphate Cement or Autologous Bone Graft

BACKGROUND: Depression fractures of the tibial plateau are often managed with use of internal fixation and autologous bone-grafting to maintain an anatomical reduction. Bone-grafting, however, provides only limited stability. As calcium phosphate cements have appropriate mechanical properties, they may provide a more suitable alternative. The objective of this study was to compare the effect of a calcium phosphate cement with that of impacted cancellous autograft for maintaining an anatomical reduction in an experimental model of a tibial plateau fracture. METHODS: Standardized cylindrical subchondral defects that were 8 mm in diameter and 10 mm deep were created bilaterally beneath the subchondral bone of the articular cartilage in the lateral tibial plateau of goats. An osteotome was used to fracture the overlying subchondral plate and articular cartilage. The plateau fracture fragment was completely depressed into the subchondral defect and then was anatomically reduced. The defects were randomly filled with either calcium phosphate cement or cancellous autograft. No internal fixation was used. The tibiae were harvested at varying time-periods that ranged from twenty-four hours to eighteen months. The stiffness of the healing augmented plateau fractures was determined. Histological specimens were assigned a score for degenerative changes. Loss of anatomic reduction was demonstrated in photomicrographs, and the amount of subsidence of the osteochondral fragment was measured in whole-mount histological sections. RESULTS: The prevalence and degree of fracture subsidence was significantly reduced at all time-points in the defects treated with calcium phosphate cement compared with those filled with autograft (p < 0.05). There were no significant differences in fracture stiffness between the two treatment groups at any of the time-points examined. The calcium phosphate cement was rapidly resorbed, and the volume fraction of the calcium phosphate cement was decreased to 4% at six months. The trabecular bone volume in the defects was restored to that of the intact controls at six months in both treatment groups. CONCLUSIONS: Cancellous autograft did not maintain an anatomical reduction of the tibial plateau fractures in this model. In contrast, augmentation with calcium phosphate cement prevented subsidence of the fracture fragment and maintained articular congruency as the fracture healed. The improved articular congruency reduced the prevalence and severity of degenerative changes in the joint.