Objectives. This study was conducted to investigate the course of incorporation of coralline hydroxyapatite in human spine.

Summary of Background data. Conventional techniques for surgical treatment of spine have a substantial failure rate and associated morbidity. Bone graft substitutes are an alternative technique to enhance fusion rates and limit the morbidity associated with spine fusion using autologous iliac crest bone graft. There are some experimental studies supporting the use of hydroxyapatite in spine surgery.

Material & Methods. During revision surgery specimens derived from the fusion mass from 15 operations in 13 patients, who received spinal instrumentation and fusion in cervical, thoracic, and lumbar spine and addition of coralline hydroxyapatite. The age of patients at the time of revision surgery was 46+20 years. The time lapsed from the implantation of coralline hydroxyapatite and revision surgery was 11+9 months. The indication for revision surgery was infection, pseudarthrosis, technical error, and pain related to bulky hardware. The diagnosis for the primary fusion was degenerative disease, trauma and scoliosis, and the material of instrumentation used was composed from titanium alloy. The coralline hydroxyapatite was applied on the decorticated posterior elements of the instrumented spine. Material from ten different places from the fusion mass was intraoperatively taken in all patients and was sent for histological evaluation using the Hematoxylin-eosin histological stain technique and photomicroscope.

Results: Under photomicroscope there was a remarkable concentration of foreign-body like giant cells & development of inflammatory granulation tissue around hydroxyapatite, which was gradually replaced by dense connective collagen tissue. Both inflammatory granulation and collagen tissue showed areas with foreign body reaction. In the cases, where bone has developed, the most initial finding was the presence of osteoblasts & apposition of osteoid in contact to hydroxyapatite granules. In a later phase, cancellous and lamellar bone has developed as a result of secondary ossification. Bone formation was observed in 11/15 cases and was related with the patient’s age in favor of young patients (R=0.56, PO.05), while there was no correlation with time lapsed from operation.

Conclusion: Coralline hydroxyapatite conducts bone formation in spine surgery because in the vast majority of the operated cases for different spinal disorders bone and osteoid has developed around the implanted coralline hydroxyapatite.