A Comparative Evaluation of Commercially Available Cell-Based Allografts in a Rat Spinal Fusion Model

Background: To evaluate the comparative abilities of commercially available, viable, cellular bone allografts to promote posterolateral spinal fusion. Methods: Human allografts containing live cells were implanted in the athymic rat model of posterolateral spine fusion. Three commercially available allogeneic cellular bone matrices (Trinity Evolution, Trinity ELITE and Osteocel Plus) were compared with syngeneic iliac crest bone as the control. All spines underwent radiographs, manual palpation, and micro-computed tomography (CT) analysis after excision at 6 weeks. Histological sections of randomly selected spines were subjected to semiquantitative histopathological scoring for bone formation. Results: By manual palpation, posterolateral fusion was detected in 40% (6/15) of spines implanted with syngeneic bone, whereas spines implanted with Trinity Evolution and Trinity ELITE allografts yielded 71% (10/14) and 77% (10/13) fusion, respectively. Only 7% (1/14) of spines implanted with Osteocel Plus allografts were judged fused by manual palpation (statistically significantly less than ELITE, P < .0007, and Evolution, P < .0013). The mineralized cancellous bone component of the allografts confounded radiographic analysis, but Trinity Evolution (0.452 +/- 0.064) and Trinity ELITE (0.536 +/- 0.109) allografts produced statistically significantly higher bone fusion mass volumes measured by quantitative micro-CT than did syngeneic bone (0.292 +/- 0.109, P < .0001 for ELITE and P < .003 for Evolution) and Osteocel Plus (0.258 +/- 0.103, P < .0001). Semiquantitative histopathological scores supported these findings because the total bone and bone marrow scores reflected significantly better new bone and marrow formation in the Trinity groups than in the Osteocel Plus group. Conclusions: The Trinity Evolution and Trinity ELITE cellular bone allografts were more effective at creating posterolateral fusion than either the Osteocel Plus allografts or syngeneic bone in this animal model.