Abstract
Purpose of the Study: To assess the use of synthetic hydroxyapatite for postero-lateral spinal fusion using a new classification system
Methods: This is a prospective study on 30 patients who underwent bilateral postero-lateral spinal fusion between October 2002 and January 2004. The sides were randomised to synthetic phase pure Hydroxyapatite (Apapore® 70) mixed with bone marrow and autologus bone on one side and Apapore® 70 with bone marrow on the other. Plain Antero-posterior and Lateral x-rays were done in the immediate post-operative period and at 3, 6, 12 and 24 months. Two independent observers assessed the Antero-posterior films using a new classification system. Spine was considered fused when either or both sides showed good evidence of bone formation between the graft particles and graft and transverse process.
Results: In 6 patients x-rays were lost and 2 did not have two year follow-up. Twenty of the remaining 22 patients (90.9%) showed evidence of fusion as documented by both the observers. Good evidence of bone formation was noted as early as 6 months on the side where Apapore was used with bone marrow with 90.9 % achieving fusion at 2 years as against 57.1 % on the opposite side. The inter-observer agreement was good (mean 81.6%) with kappa score of 0.736.
Conclusion: The Hydroxyapatite based bone graft substitutes behave differently than autologus bone graft and poses difficulty in assessing fusion according to the radiographic classification systems described. The classification described above is useful in such situations and has shown to have good inter-observer reliability. With the increasing use of bone substitutes this classification system may be valuable in assessment of fusion and inter-study correlation.
Correspondence should be addressed to: Mr N. J. Henderson, BASS, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
