INTRODUCTION: Posterolateral intertransverse lumbar fusion is a commonly performed procedure for stabilisation of the degenerated lumbar spine. A typical clinical scenario for which such fusions are used is the stabilisation of a degenerative spondylolisthesis after decompression. In a recent large series reported in the literature, this type of fusion was noted to have a pseudarthrosis rate of up to 45% (Fischgrund, Spine 1997).

METHODS: A pilot study was designed to evaluate the safety and efficacy of osteoinductive protein-1 (OP-1, also known as recombinant human BMP-7) in lumbar posterolateral fusion. Thirty-six patients with the diagnosis of symptomatic spinal stenosis and single level degenerative spondylolisthesis in the lower lumbar spine (L3–S1) were enrolled. The patients were randomised to either the OP-1 group or the control group. The OP-1 group received 3.5 mg of OP-1 per side in a putty carrier. The control group received iliac crest autograft alone. Outcomes were measured clinically using the Oswestry score and radiographically using dynamic radiographs evaluated independently by two blinded radiologists using digital calipers. Patients were deemed a clinical success if they showed a > 20% improvement in Oswestry score and were deemed a radiographic success if they showed bridging bone and spinal stability on flexion/ extension films.

RESULTS: At twelve months, 18/21 (85.7%) patients in the OP-1 group and 8/11 (72.7%) patients in the autograft group were considered clinical successes, while 13/18 (72.2%) of patients in the OP-1 group and 6/10 (60%) patients in the autograft group were considered radiographic successes. No adverse events related to the use of OP-1 were noted.

DISCUSSION: Despite the non-statistical number of patients enrolled in this pilot study, these preliminary results suggest that OP-1 appears to be a safe and effective replacement for iliac crest autograft in human pos-terolateral lumbar fusion. The OP-1 group had a higher radiographic fusion rate than the autograft group. This correlated well with the greater clinical success experienced by the OP-1 group, as measured by improvement in the Oswestry score. None of the previously reported device related complications related to the use of BMPs in animal studies, such as exuberant bone growth with subsequent neural impingement, ectopic ossification, or spinal stenosis, was seen in the treatment group.

CONCLUSION: OP-1 appears to be a safe and effective replacement for iliac crest autograft in human posterolateral lumbar fusion. The dose, 3.5 mg per side, and the carrier, a biodegradable putty, appear to provide a safe and effective means of delivering the bone morphogenetic protein OP-1 to the human lumbar spine.