Augmentation of spinal arthrodesis with autologous bone marrow in a rabbitposterolateral spine fusion model

Study Design. Posterolateral spinal fusion with autologous bone marrow aspi rate in addition to autograft iliac crest bone graft in a rabbit model. Objective. To demonstrate that the addition of autologous bone marrow can h ave positive effects on bone formation and spinal fusion. Summary of Background Data. Bone marrow has been shown to contain osteoprog enitor cells. A number of studies have demonstrated that bone formation is possible with autologous marrow injection into orthotopic sites such as tha t performed in femur fracture models. Methods. A bone paucity model of posterolateral spine fusion was developed. The control animals received 0.8 g of morselized autogenous iliac crest bo ne graft harvested from a single iliac crest. The graft was mixed with 2 mt of clotted peripheral blood. In the experimental group, 2 mt of bone marro w aspirated from the opposite iliac crest was substituted for the periphera l blood clot. All rabbits were killed at 12 weeks, and the specimens were s ubjected to evaluation by posteroanterior radiography for the presence of f usion, computed tomography for bone volume, and biomechanical testing for s tiffness. Results. Successful fusion was achieved in 61% of the animals in the experi mental group verses 25% in the control group (P < 0.05). The fusion mass in the experimental group had a mean volume of 919 +/- 387 mm(3) verses 667 /- 512 mm(3) for the control group, as measured from computed tomography im ages. The results of the biomechanical testing validated the radiographic s coring system. The stiffness in specimens, graded as having a radiographic score of 4, was significantly greater than in specimens with radiographic s cores of 1 and 2. Conclusion. In cases for which an adequate quantity of autogenous bone graf t is not available, addition of bone marrow may facilitate greater bone for mation and successful fusion.