Comparing autograft, allograft, and tricalcium phosphate ceramic in a goat instrumented posterolateral fusion model

The most common application of bone grafts is spinal fusion surgery, in which the use of iliac crest autograft is the gold standard. Harvesting of autograft, however, requires an extra surgical procedure, which is associated with additional morbidity. Allograft is the well-known alternative, but it is generally considered less effective in posterior fusions. Therefore, the need for an effective alternative remains. Recently, it was shown that ceramics can be endowed with biologically instructive properties by changing the basic parameters of the material. In this study, we compared a novel tricalcium phosphate ceramic (TCP) to iliac crest autograft and allograft, in instrumented posterolateral fusions in a goat model. A total of nine goats were included, who underwent a two-level lumbar fusion. Each side of the spine was randomized into one type of graft: iliac crest autograft; fresh-frozen allograft; TCP alone; or TCP combined with local autograft (50:50). The fusion rates after 16 weeks were comparable between the groups (autograft 3/8, allograft 4/8, TCP 4/8, and TCP/local autograft 5/8). Calculation of the fusion volume on computed tomography images, showed significantly greater volume in the control groups (autograft 7.8 mL and allograft 8.9 mL) compared with the groups with TCP (TCP 6.1 mL and TCP/local autograft 6.0 mL). No adverse tissue response was seen on histological analysis and TCP was almost completely resorbed. The results demonstrate that TCP is capable of achieving fusion at a similar rate to iliac crest autograft in posterolateral fusions, while almost completely resorbing within 16 weeks. Despite the lower fusion volume, the TCP is a promising alternative circumventing the disadvantages of autograft and allograft.