Assessment of MASTERGRAFT PUTTY as a graft extender in a rabbit posterolateral fusion model

Study Design. Randomized, controlled study in a laboratory setting. Blinded observations/assessment of study outcomes. Objective. The purpose of this study was to determine the performance characteristics of MASTERGRAFT PUTTY as a bone graft extender in a rabbit posterolateral spine fusion model. Summary of Background Data. The rabbit posterolateral fusion model is an established environment for testing of fusion concepts. It offers the opportunity to obtain radiographical, histological, and biomechanical data on novel fusion materials. Methods. Thirty-six rabbits were entered into the study with 30 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 (2.5–3.0 cc per side), 25% MASTERGRAFT PUTTY/75% autograft (3.0 cc total per side), or 50% MASTERGRAFT PUTTY and 50% autograft (3.0 cc total per side). Animals were humanely killed at 8 weeks postsurgery. Results. The autograft group had a 63% radiographical fusion rate (5 of 8) and correlated with manual palpation results (63%). The 25% MASTERGRAFT PUTTY group had a 73% radiographical fusion rate (8 of 11) and a manual palpation fusion rate of 64%. The 50% MASTERGRAFT PUTTY group demonstrated a 91% (10 of 11) radiographical fusion rate and 73% manual palpation fusion rate. Histologically, no inflammatory reactions were evident regardless of implant. The 2 MASTERGRAFT PUTTY groups had new bone in direct apposition to the MASTERGRAFT ceramic granules. Conclusion. In this commonly used rabbit posterolateral fusion model, MASTERGRAFT PUTTY in an autograft extender mode produces clinically and radiographically similar results to autograft fusion alone.