In vivo evaluation of coralline hydroxyapatite and direct current electrical stimulation in lumbar spinal fusion

Study Design. An animal model of posterolateral intertransverse process lum bar spinal fusion using autologous bone, coralline hydroxyapatite, and/or d irect current electrical stimulation. Objectives. To evaluate the effect of an osteoconductive bone graft substit ute and direct-current electrical Stimulation on the rate of pseudarthrosis in a rabbit spinal fusion model. Summary of Background Data. Conventional techniques for the surgical treatm ent of degenerative conditions in the lumbar spine have a substantial failu re rate acid associated morbidity. Bone graft substitutes and electrical st imulation are alternative techniques to enhance fusion rates and limit the morbidity associated with posterolateral intertransverse process fusion usi ng autologous iliac crest bone graft. Methods, Fifty-three adult female New Zealand White rabbits underwent singl e-level lumbar posterolateral intertransverse process fusion. Animals were assigned to one of four groups using either autologous bone (Group I), cora lline hydroxyapatite with autologous bone marrow aspirate (Group II), coral line hydroxyapatite with a 40-mu A implantable direct current electrical st imulator and bone marrow aspirate (Group III), or coralline hydroxyapatite with a 100-mu A implantable direct current electrical stimulator and bone m arrow aspirate (Group IV). Animals were killed at 8 weeks, and fused motion segments were subjected to manual palpation, mechanical testing, and radio graphic and histologic analysis to assess the fusion mass. Results, Successful fusion was achieved in 57% (8/14) of animals in Group I , 25% (3/12) in Group 11, 50% (6/12) in Group III, and 87%(13/15) in Group IV. Mean stiffness and ultimate load to failure were significantly higher i n Group IV than in all other groups (P < 0.05), Histologic analysis demonst rated a qualitative increase in fusion mass in Group IV Versus all other gr oups. Conclusions, Direct-current electrical stimulation increased fusion rates i n a dose-dependent manner in a rabbit spinal fusion model. Coralline hydrox yapatite is an osteoconductive bone graft substitute, and thus requires an osteoinductive stimulus to ensure reliable fusion rates. Furthermore, coral line hydroxyapatite and direct current electrical stimulation can be used t ogether to increase fusion rates in a rabbit spinal fusion model while avoi ding the morbidity associated with harvesting iliac crest bone.