Evaluation of OP-1 as a Graft Substitute for Intertransverse Process Lumbar Fusion

Study Design. An established rabbit intertransverse process lumbar fusion model was used to evaluate osteo genic protein (OP)-1 as a potential graft substitute. Objectives. To determine whether OP-1 is effective in producing intertransverse process lumbar fusion in a rab bit model. of Background Data. Autogenous iliac crest bone is the gold standard in grafting material for inducing intertransverse process fusion. However, bone graft sub stitutes are being considered as supplementary or alter native means to achieve such fusion with less morbidity Relatively little research has been undertaken to investi gate the efficacy of OP-1 in this role. Methods, Single-level intertransverse process lumba fusions were performed at L5-L6 of 31 New Zealand White rabbits. These were divided into three study groups: autograft, carrier alone, and carrier with OP-1 The animals were killed 5 weeks after surgery. Resultan fusion masses were evaluated by manual palpation, radi ography, biomechanical multidirectional flexibility test ing, and histology. Results. Seven rabbits (23%) were excluded because of complications. Of the remaining 24 rabbits, 5 (63%) o the 8 in the autograft group had fusion detected by man ual palpation, none (0%) of the 8 in the carrier-alone group had fusion, and all 8 (100%) in the OP-1 group had fusion. Radiographs were 55% sensitive and 92% specific for determining fusion. Biomechanical testing results cor related well with those of manual palpation. Histologi cally, autograft specimens were predominantly fibrocar tilage, OP-1 specimens were predominantly maturing bone, and carrier-alone specimens did not show signifi cant bone formation. Conclusions. OP-1 was found to reliably induce solic intertransverse process fusion in a rabbit model at 5 weeks.