Evaluation of porous biphasic calcium phosphate ceramics for anterior cervical interbody fusion in a caprine model

Abstract

Study Design. This study compared the efficacy of characterized 50/50 hycfroxyapat ite tricalcium phosphate ceramic nf 30%, 50%, and 70% porosity and auto graft to promote interbody spinal fusion at C2-C3 and C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months, Objectives, Radiographs, histology, dual energy x-ray absorptiometry analysis, and bioTiechenical testing were used to evaluate the ability of (he 30%, 50%, and 70% porous 60/&0 hydroxyapatiteZ/f-tricalcium phosphate ceramics and autograft to promote oervical interbody fusion.Summary of Background Data. The conundrum in the use of calcium phosphates for interbody fusion is what porosity is most effective to promote ingrowth yet strong enough to resist compressive stresses found in the spine? It is known that tie ability for bone ingrowth increases and the comprcssivc strangth decreases as porosity of the ceramic is increased. Dense ceramics remain Iniact but may be surrounded by fibrous USSLJB. Porous ceramics have good ingrowth but mey fracture, Methods, Radiographs were evaluated For fusion and fracture or collapse of the ceramics or autograft. Dual energy x-ray absorptiometry was used to evaluate the fusion mass. Treated motion segments underwent biomcchanical tasting to quantify the flexibility of the segment. Undecalcified and decalcified histologic analysis were performed to evaluate the presence or absence of a bony union.Results, Thirty percent, 50%, and 70% porous ceram ics had better radiographic fusion scores than the autograft at 3 and 6 months. Incidence of ceramic fracture did not increase with porosity and was equivalent lo the collapse of autograft, although ceramics maintained disc height when fractU'O occurred No statistically significant differences were found stween autograft and the porous ceramics with biomechanical tEsting and periimplant bone mineral density values as measured by dual energy x-ray absorptiometry, At 3 months, history analysis showed a union rate of 0% for autog raft and 30% pomua ceramic, 67% for 50% porous ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate was 67% for the 30%, 50%, and 70% porous ceramics and 50% for autograft.Conclusions. Thirty percent, 50%, and 70% porous ceramics performed equal to or better than autogenous bone after 3 and 6 months. There may he promise for the use of 50/E10 hydroxyapatite tricalcium phosphate In spine surgery as the need to harvest autogr&Ft from the iliac crest is obviated, and complications and cost associated with the harvest are avoided. © 1995, Lippincot-Raven Publishers.