The safety of OP-1 for lumbar fusion with decompression - a canine study

OBJECTIVE: Bone morphogenetic proteins can serve as adjuncts to autologous bone to achieve bony fusion, and recombinant BMPs such as osteogenic protei n-1 (OP-1) have the potential to replace autologous bone altogether as fusi on substrate. However, relatively little is known about the safety of OP-1 for spinal fusion procedures. This study examined the effects of OP-1 inten tionally placed in the subarachnoid space following thecal sac decompressio n, and used as graft substrate in a canine dorsolateral lumbar spine fusion model. METHODS: Lumbar decompression with dorsolateral fusion was performed on 30 canines. The dura was opened to simulate an intraoperative rent and OP-1 wa s placed in the subarachnoid space and in the fusion bed. Animals were sacr ificed after 16 weeks and the spines were examined manually, radiographical ly and pathologically. RESULTS:. All animals treated with OP-1 developed new bone in the subarachn oid space. This bone compressed the spinal cord, but no clinical or patholo gical features of neurotoxicity were noted. Mild spinal stenosis was noted at the site of dural decompression in the OP-1 treated animals. Over 80% of animals treated with OP-1 developed fusion as assessed by palpation (52% b y CT criteria), while only 25% of control animals fused. CONCLUSIONS: Recombinant human OP-1 is effective at promoting fusion in a c anine dorsolateral lumbar spine fusion model. However, bone growth can occu r over exposed, decompressed dura, and it can form in the subdural and suba rachnoid spaces. The use of OP-1 as an adjunct to spinal fusion appears to have merit, but its use must be carefully controlled to avoid unwanted bone formation and subsequent neural compression.