Study design: A prospective randomized clinical study was conducted.
Objective: To determine whether the dose and carrier that were successful in rhesus monkeys could induce consistent radiographic spine fusion in humans.
Summary of background data: Preclinical studies have demonstrated that recombinant human bone morphogenetic protein-2 (rhBMP-2), an osteoinductive bone morphogenetic protein, is successful at generating spine fusion in rabbits and rhesus monkeys.
Methods: For this study, 25 patients undergoing lumbar arthrodesis were randomized (1:2:2 ratio) based on the arthrodesis technique: autograft/Texas Scottish Rite Hospital (TSRH) pedicle screw instrumentation (n = 5), rhBMP-2/TSRH (n = 11), and rhBMP-2 only without internal fixation (n = 9). On each side, 20 mg of rhBMP-2 were delivered on a carrier consisting of 60% hydroxyapatite and 40% tricalcium phosphate granules (10 cm /side). The patients had single-level disc degeneration, Grade 1 or less spondylolisthesis, mechanical low back pain with or without leg pain, and at least 6 months failure of nonoperative treatment.
Results: All 25 patients were available for follow-up evaluation (mean, 17 months; range 12-27 months). The radiographic fusion rate was 40% (2/5) in the autograft/TSRH group and 100% (20/20) with rhBMP-2 group with or without TSRH internal fixation ( = 0.004). A statistically significant improvement in Oswestry score was seen at 6 weeks in the rhBMP-2 only group (-17.6; = 0.009), and at 3 months in the rhBMP-2/TSRH group (-17.0; = 0.003), but not until 6 months in the autograft/TSRH group (-17.3; = 0.041). At the final follow-up assessment, Oswestry improvement was greatest in the rhBMP-2 only group (-28.7, < 0.001). The SF-36 Pain Index and PCS subscales showed similar changes.
Discussion: This pilot study is the first with at least 1 year of follow-up evaluation to demonstrate successful posterolateral spine fusion using a BMP-based bone graft substitute, with radiographs and CT scans as the determinant. Consistently, rhBMP-2 was able to induce bone in the posterolateral lumbar spine when delivered at a dose of 20 mg per side with or without the use of internal fixation. Patients with spondylolisthesis classified higher than Meyerding Grade 1 or with more than 5 mm of translational motion may still require internal fixation. Some patients did smoke during the postoperative period, and all in the rhBMP-2 groups still obtained solid fusions.
Conclusions: Consistently, rhBMP-2 with the biphasic calcium phosphate granules induced radiographic posterolateral lumbar spine fusion with or without internal fixation in patients whose spondylolisthesis did not exceed Grade 1. Statistically greater and quicker improvement in patient-derived clinical outcome was measured in the rhBMP-2 groups.