A composite bone graft substitute for anterior cervical fusion -: Assessment of osseointegration by quantitative computed tomography

Study Design. An ongoing prospective nonrandomized trial was conducted with 146 patients who underwent anterior cervical fusion with a bone graft substitute. The results for 78 patients followed up a minimum of 2 years are reported by an independent observer. Objective. To investigate the clinical efficacy and osseointegration of the implant. Summary of Background Data. Most of the cervical cages provide an immediate load-bearing capacity, but not necessarily a solid fusion. The bony ingrowth can hardly be evaluated by flexion-extension plain radiographs, especially if a part of the implant is made of titanium. Methods. The composite bone graft substitute consists of a rectangular fenestrated titanium cage filled with a highly porous hydroxyapatite cylinder soaked with bone marrow aspirated from a vertebra. Altogether, 102 implants were inserted for anterior cervical fusion. The bone ingrowth was measured in 50 patients by quantitative computed tomography of the implant and the adjacent vertebrae after 1 week, then 6 and 12 months after surgery, The investigation was repeated in 24 randomly selected patients 24 months after surgery. Results. The surgery benefited 42 of 48 patients with myelopathy, 27 of 28 patients with radiculopathy, and both patients with anterior horn cell syndrome. No graft substitute-related complications were observed, and no revision surgery was performed. Six months after surgery, quantitative computed tomography showed up to a 14% increase in the hydroxyapatite mass in the core of the implant,which was statistically significant (P<0.001). At 1 year, the newly formed hydroxyapatite mass increased to 23%, and in 2 years reached 24%. Conclusions. The composite implant is effective as a bone graft substitute, providing immediate load-bearing capacity, an osteoconductive scaffold, and osteoinductive potency. After surgery, the increase in hydroxyapatite radiodensity was apparent in plain computed tomography scans and confirmed to be significant by quantitative computed tomography.