Effects of zoledronic acid on bone fusion in osteoporotic patients after lumbar fusion

Treatment with zoledronic acid in osteoporotic patients with spinal fusion shortens the duration of time to fusion, improves the fusion rate, prevents the subsequent adjacent vertebral compression fractures, improves the clinical outcomes, and prevents immobilization-induced bone loss in the hip. The objective of the study was to explore the effects of zoledronic acid on the healing process in osteoporotic patients following spinal fusion in a randomized, placebo-controlled, and triple-blinded study. Seventy-nine osteoporotic patients with single-level degenerative spondylolisthesis were randomly assigned to receive either zoledronic acid infusion (zoledronic acid group) or saline infusion (controls) after spinal fusion. Functional radiography and CT scans were used to evaluate fusion status. Bone formation was graded into three categories: Grade A (bridging bone bonding with adjacent vertebral bodies), Grade B (bridging bone bonding with either superior or inferior vertebral body), or Grade C (incomplete bony bridging). A solid fusion was defined as less than 5A degrees of angular motion with Grade A or B bone formation. Adjacent vertebral compression fractures (VCF) were assessed on MRI at 12 months after surgery. Serum level of carboxy terminal cross-linked telopeptide of type I collagen (beta-CTX) and amino-terminal propeptide of type I procollagen (PINP) was measured. Bone mineral density (BMD) was measured by DXA. Oswestry Disability Index (ODI) was used to assess the clinical outcomes. Grade A or B bridging bone was more frequently observed in zoledronic acid group at 3, 6, and 9 months post-operation compared to the control group (p < 0.05). At 12 -months post-operation, bridging bone and solid fusion were not significantly different between groups. No patients in zoledronic acid group showed aVCF, whereas six patients (17 %) in the control group did (p < 0.05). Both beta-CTX and PINP were suppressed in zoledronic acid group. BMD at the femoral neck decreased rapidly and did not return to the preoperative level in the controls at 3 (-1.4 %), 6 (-2.5 %), and 12 (-0.8 %) months after surgery. Zoledronic acid prevented this immobilization-induced bone loss and increased BMD. ODI showed the improved clinical outcomes compared with controls at 9 and 12 months post-surgery. Treatment with zoledronic acid in osteoporotic patients with spinal fusion shortens the time to fusion, improves the fusion rate, prevents subsequent aVCFs, and improves clinical outcomes.