79 patients with osteoporosis scheduled for instrumented posterior lumbar interbody fusion due to single-level degenerative spondylolisthesis were randomized to be postoperatively administered either zoledronic acid or saline. The purpose of this study was to compare groups based on fusion status, the incidence of a subsequent vertebral compression fracture, clinical outcome, serum biomarkers of bone metabolism, and femoral neck bone mineral density over the first year after surgery. Results demonstrated a higher rate of complete or partial fusion at 3, 6, and 9 months in the ZOL group compared to the control group. The incidence of subsequent VCF was 0% in the ZOL group and 17% in the control group. Significant differences in favour of the ZOL group compared to the control group were also observed for disability scores at 9 and 12 months, as well as bone resorption, formation biomarkers and femoral neck BMD throughout follow-up.