In vitro osteoblast proliferation as a predictor for spinal fusion mass

BACKGROUND CONTEXT: The biological factors determining a successful spinal fusion have not yet been fully determined. PURPOSE: To determine the influence of graft cell vigor on fusion rate and fusion mass using in vitro osteoblast proliferation as a predictor. STUDY DESIGN: Animal study randomizing to posterolateral fusion with autograft with or without pedicle-screw instrumentation. PATIENT SAMPLE: Twenty adult Gottingen mini-pigs. OUTCOME MEASURES: Fusion rate measured both with X-ray and computed tomography (CT) as well as amount of fusion mass determined with three-dimensional CT. METHODS: Animals underwent posterolateral fusion with autograft either with or without pedicle-screw instrumentation. Additional graft was harvested for osteoblastlike cell culture. Cells were counted after 3 weeks, and their proliferative capacity was correlated to fusion rate and fusion amount. RESULTS: Cell count was significantly higher in the fused animals (p CONCLUSIONS: The achievement of a solid spinal fusion using autograft is related to properties of the bone-forming cells in the graft and fusion bed. Most likely it is the number of cells and not their proliferative capacity that is the most important factor.