Evaluation of a resorbable, in situ setting bone substitute in a sheep model

The gold standard for bone substitution is the autologous bone graft, but because of its limited supply and the associated morbidity, the search for synthetic alternatives is necessary. A new in situ setting tricalcium phosphate cement was implanted in a trepanation defect (9.4 mm diameter, 10 mm depth) in the distal femoral epiphysis of sheep. Empty cavities and autologous bone graft were used as controls. Histologic and histomorphometric examinations were carried out after 12 weeks. Nearly 90% of the implanted cement was resorbed and replaced by ingrown bone with close contact between surrounding bone, new bone, and remaining cement particles. The amount of bone in the defect area was significantly higher in defects filled with cement relative to defects filled with autologous bone graft (mean 27 vs. 21%, 95% confidence intervals 23 to 31 and 18 to 23, p = 0.026). In conclusion, this new in situ setting cement is bioactive, resorbable, and osteoconductive. It will be useful as an alternative to autologous bone graft to fill stable defects.