In Brief:
Twenty-four sheep underwent noninstrumented, single-level posterolateral fusion and were implanted bilaterally with (n = 6): 1) autograft, 2) tricalcium phosphate (TCP) alone, 3) TCP with bone marrow, and 4) osteoprogenitor-enriched TCP. At 6 months, cell-enriched TCP yielded 33% fusion, autograft: 25%, TCP with whole bone marrow: 8%, and TCP alone: 0%.