Efficacy comparison of Accell Evo3 and Grafton demineralized bone matrix putties against autologous bone in a rat posterolateral spine fusion model.

Background Context: Spinal fusion procedures are intended to stabilize the spinal column for a multitude of disorders including abnormal curvature, traumatic instability, degenerative instability, and damage from infections or tumors. As an aid in the bone healing response, bone graft materials are used to bridge joints for arthrodesis and promote unions in pseudoarthrosis. Currently, the gold standard for stabilizing fusion masses in spinal procedures involves using the osteogenic, osteoinductive, and osteoconductive properties of autologous iliac crest corticocancellous bone. However, considerable morbidity is associated with harvesting the autologous graft. Donor site complications including infection, large hematomas, and pain have been reported at rates as high as 50% (Boden and Jeffrey, 1995). Biologically, the rate of bone repair dictates the rate at which the fusion mass will unite under autologous graft conditions.

Purpose: The purpose of this study is to compare the quality and rate of fusion between Accell Evo3 and Grafton demineralized bone matrix (DBM), with the gold standard iliac crest bone graft (ICBG) as the control, in athymic rat posterolateral fusion.

Study Design: This study was a randomized, controlled study in a laboratory setting at the Hospital for Special Surgery in New York City. Blinded observations were made, which created an assessment of outcomes for successful fusions between each method.

Patient Sample: Forty-eight (48) athymic rats were used in this study and underwent posterolateral lumbar fusion. They were assessed at either 3 weeks or 9 weeks to see the rate and efficacy of fusion.

Outcome Measures: Outcome measures will be the efficacy of the different bone grafts and their success rates of fusion in the rats.

Methods: A comparison of the quality and rate of fusion between Accell Evo3® (DBM A) and Grafton (DBM B), with the gold standard iliac crest bone graft (ICBG) as the control, was performed using the established posterolateral intertransverse process on an athymic rat model. Materials were evaluated for fusion by several criteria, including manual palpation, standard and high-resolution radiographic imaging, micro-computed topography, and histologic analysis. Forty-eight (48) athymic rats received a bilateral intertransverse process fusion, using either bone from the iliac crest (control group), Accell Evo3, or Grafton. Twelve (12) rats (four from each group) were sacrificed at 3 weeks postoperatively, whereas the remaining thirty-six (36) were sacrificed at 9 weeks postoperatively. Three blinded observers examined the spines after the rats were euthanized, and they blindly assessed each rat for fusion success.

Results: Manual palpation of the three different groups at 3 weeks postoperatively found successful fusion in 1 of 4 (25%) of the autologous bone graft (ABG) group and 4 of 4 (100%) of both DBM A and B groups. Manual palpation of the remaining animals that were sacrificed at 9 weeks postoperatively showed successful fusion in 4 of 12 (33%) of the ABG group, 8 of 12 (66%) of the DBM A group, and 12 of 12 (100%) of the DBM B group. Radiography found that 9 of 16 (56%) of the ABG group and 16 of 16 (100%) of both DBM Putty A and B groups had fused. Histologic analysis of the ABG group demonstrated less mature and less organized osteoid at both 3 and 9 weeks than the DBM Putty A and B groups. Nondestructive mechanical testing demonstrated increased stiffness in 4-point bending of both DBM A and B compared with ABG.

Conclusions: Both DBM-treated groups achieved a significantly higher rate of fusion than the ABG-treated group at 9 weeks in this model. Successful fusion was also demonstrated in the DBM-treated groups at 3 weeks.