The effects of internal fixation on calcium carbonate. Ceramic anterior spinal fusion in dogs.

STUDY DESIGN

An anterior interbody fusion was performed in the canine thoracic spine. Either calcium carbonate or autologous iliac crest bone graft was used to fill a surgically created spinal defect between T7 and T8. Some of the spines were stabilized intraoperatively with anterior instrumentation. Four experimental arthrodesis groups were studied: iliac crest bone graft with or without instrumentation and ceramic with or without instrumentation.

OBJECTIVE

To evaluate the effects of internal fixation on an anterior interbody fusion using calcium carbonate ceramic, and to compare this with autologous iliac crest bone grafting.

SUMMARY OF BACKGROUND DATA

Bone grafting can be associated with significant morbidity, and an acceptable substitute material is sought. In vivo analysis of ceramic as a substitute has revealed fracture and failure of the implant. Creating a stable environment with internal fixation may improve the performance of ceramic as a bone graft substitute.

METHODS

Fusions were evaluated in 20 adult beagles 8 weeks after surgery. Structural properties of the fusion segment were evaluated with biomechanical testing. Histologic analysis was performed to determine junction healing, new bone formation, and revascularization.

RESULTS

Fusion segments with iliac crest bone graft and instrumentation were significantly stiffer than the other three groups in all tested modes of angular deformation. Greater junction healing was seen when instrumentation was used with iliac crest bone graft. Greater junction healing, new bone formation, and revascularization were observed when instrumentation was used with calcium carbonate ceramic. Most of the ceramic implants without fixation demonstrated near complete isolation with no revascularization.

CONCLUSIONS

Internal fixation resulted in histologically and biomechanically superior healing of autologous iliac crest bone graft in this canine model of anterior interbody fusion. Although fixation did not statistically improve the biomechanical properties of ceramic fusion segments, it had a profound effect on the ability of the ceramic to be revascularized and remodeled. Porous ceramic bone graft substitutes appear to depend on a stable environment for incorporation.