40 osteoporosis patients undergoing single-level posterior lumbar interbody fusion were randomized to receive alendronate or vitamin D (alfacalcidol) to determine the impact of bisphosphonates on the spinal fusion recovery process. Following clinical, radiographic, and biochemical evaluations over a 12 month period, the results indicated that greater solid fusion, less cage subsidence, and no vertebral compression fractures were observed in the alendronate group, although bone formation and bone resorption markers were decreased with alendronate therapy.