Determinants of initial bone graft volume loss in posterolateral lumbar fusion

Bone graft volume decreases postoperatively without known etiology. We sought to determine the bone graft volume over time in 15 consecutive patients undergoing a single-level, instrumented, posterolateral lumbar fusion for degeneration causing mechanical pain or spondylolisthesis, and to identify factors associated with bone graft resorption. Following Institutional Review Board approval, a retrospective analysis was performed. Immediate and 3-month postoperative lumbar spine CT scans were imported into imaging software for volumetric analysis. We found that the 15 patients averaged approximately 11% graft volume loss at 3 months postoperatively. All patients exhibited volumetric graft loss on each side (range, 0.3-45%). A paired t-test revealed that immediate postoperative graft volume on a patient's left or right did not reflect graft volume on that side 3 months postoperatively (p=0.0008). Gender, age, history of prior operation, history of regular exercise, body mass index, level fused, operative time, initial graft volume, and laterality did not influence percentage volumetric loss (p=0.1-0.5). Interestingly, people who smoked cigarettes (range, 10-40 pack-years) exhibited 27% graft loss, compared to 7% in those who did not (Spearman p=0.009 graft loss versus pack-years smoked). We concluded that bone graft exhibited resorption 3 months postoperatively on both sides of all patients in this series, and that smoking was significantly associated with increased bone graft resorption.