Introduction. Successful spinal fusion with a solid bone bridge between the vertebrae is traditionally achieved by grafting with autologous iliac bone. However, the disadvantages of autograft and unsatisfactory fusion rates have prompted the exploration of alternative bone grafts. This study investigates a slowly resorbable biphasic Calcium Phosphate bone graft with submicron microporosity (BCP<μm) as an alternative for autograft.
Methods. Adults indicated for lumbar posterolateral fusion (PLF; one to six levels) were enrolled at five participating centers. After bilateral instrumentation and fusion-bed preparation, the randomized allocation side (left or right) was disclosed. Per segment 10cc of BCP<μm granules (1-2 mm) was placed in the posterolateral gutter on one side and 10cc autograft on the contralateral side. Fusion was systematically scored on one-year follow-up CT scans. The study was powered to detect >15% inferiority with binomial paired comparisons of the fusion performance score per treatment side. At segment level, a Generalized Estimating Equations (GEE) model was used accounting for clustering of fusions within segments and within patients.
Results. Out of 100 patients (57 ±12.9 years, 62% female), 91 subjects and 128 segments were analyzed. The overall posterolateral fusion rate per segment (left and/or right) was 83%. For the BCP<μm side the fusion rate was 79% vs. 47% for the autograft side (difference 32 percentage points, 95% CI = 23 to 41). The estimated odds ratio was 4.2 (95% CI = 2.7 to 6.8) in favor of the BCP<μm. Analysis of the primary outcome confirmed the non-inferiority of BCP<μm with an absolute difference in paired proportions of 39.6% (95% CI = 26.8 to 51.2%, p<0.001).
Conclusion. This clinical trial demonstrates non-inferiority and even superiority of BCP<μm as a standalone ceramic compared to autograft for posterolateral spinal fusion. Further studies are needed to confirm these findings, but these results challenge the belief that autologous bone is the optimal graft material.