Methods: Randomized, controlled study in a laboratory setting. Blinded observations/assessment of study outcomes. Objective: The purpose of this study is to determine the performance characteristics of Progenix(®) DBM putty as a bone graft extender, enhancer, and substitute in a rabbit posterolateral spine fusion model.

Background: The rabbit posterolateral fusion model is an established environment for testing of fusion concepts. It offers the opportunity to obtain radiographic, histological, and biomechanical data on novel fusion materials.

Methods: Forty rabbits were entered into the study with 37 used for analysis. Bilateral posterolateral lumbar intertransverse fusions were performed at L5-L6. the lateral two thirds of the transverse processes were decorticated and covered with graft material: autograft only (1.5 or 3.0 cc/side), a combination of Progenix(®) (1.5 cc) + autograft (1.5 cc), Progenix(®) (1.5 cc) + autograft (3.0 cc), or Progenix(®) only (3.0 cc/side).

Results: RADIOGRAPHIC FUSION: At 8 weeks the 3.0 cc autograft group had a 67% fusion rate and the 1.5 cc autograft group fused in 25%. the extender group (1.5 cc autograft + 1.5 cc Progenix(®)) had an 88% fusion rate at 8 weeks. In the enhancer group (3.0 cc autograft + 1.5 cc Progenix(®)) 86% of the spines were fused. the substitute group (Progenix(®) only) had a fusion rate of 38%. Manual Palpation: the 3.0 cc autograft group had a 67% fusion rate and the 1.5 cc autograft group fused in 38%. the extender group had an 88% fusion rate. In the enhancer group 86% of the specimens fused. the substitute group had a 50% fusion rate.

Conclusions: In a rabbit posterolateral fusion model, Progenix(®) DBM Putty in an autograft extender or enhancer mode produced manual palpation and radiographic fusion rates equivalent or slightly better than autograft fusion (3 cc) alone. the results from the two autograft groups demonstrate the need for adequate graft volume to achieve high radiographic and mechanical fusion rates.