Anterior lumbar interbody fusion (ALIF) is an effective treatment for patients with chronic low back pain resulting from single level arthritic conditions. Lumbar spine fusion procedures that do not interfere with the posterior spinal muscles have some significant advantages in the surgical treatment of low back pain. The anterior approach to the lumbosacral spine enables the surgeon to expand the disc space and re-establish the normal anatomic alignment and relationships of the lumbar vertebra while at the same time avoiding injury to the lumbar spinal muscles. The anterior approach also avoids scarring of the nerve roots.
Stand-alone ALIF procedures using autogenous bone grafts alone have been associated with a high rate of non-union and poor positioning of the spinal elements. Addition posterior fusion surgery has been advocated to stabilize interbody grafts and increase rates of fusion. Recently, cylindrical threaded intervertebral fusion cages have been shown to stabilize a lumbar vertebra and promote fusion. The use of fusion cages has lead to high rates of fusion and to improved clinical outcomes.
In animal studies, recombinant human bone morphogenetic protein 2 (rhBMP-2) applied to an absorbable collagen sponge carrier (INFUSE® Bone Graft) has been shown to promote fusion after ALIF. Recently, this technique was used in a small series of human patients who underwent stand-alone ALIF with tapered fusion cages. In these patients, the use of rhBMP-2 applied to a collagen sponge was also shown to promote fusion. To further evaluate this method, the clinical and radiographic outcomes at two years of 279 patients who underwent a single level ALIF were studied.
In a multi-center, 2-year study, 279 patients who underwent a single-level anterior lumbar interbody fusion with the LT-CAGE® fusion device were evaluated. These patients were place into two groups by random selection.
One group (136 patients) received autogenous iliac crest bone graft. The other group (143 patients) received recombinant human bone morphogenetic protein-2 (rhBMP-2) on a collagen sponge carrier (INFUSE®). The objective of the study was to determine the clinical and radiographic outcomes in patients treated for single-level degenerative lumbar disc disease with a stand-alone anterior interbody fusion using tapered threaded titanium fusion cages with autogenous bone graft or rhBMP-2 and an absorbable collagen sponge carrier.
The patients' clinical outcomes were assessed by their neurologic status, work status, back pain, leg pain and disability questionnaires. Plain radiographs and computed tomographic scans were used to evaluate the progress of the patients' fusion.
Mean operative time (1.6 hours) and blood loss (109.8 mL) was less in the rhBMP-2 group than in the autograft group (2.0 hours and 153.1 mL). At 24 months, the rhBMP-2 group's fusion rate of 94.5% remained higher than the autograft's at 88.7%. New bone formation occurred in all patients treated with rhBMP-2. At all postoperative intervals, the average disability, back pain, and leg pain and neurologic status were improved in both treatment groups compared with the preoperative status. In the autograft group, 8 adverse events related to harvesting of the iliac crest graft occurred in 8 patients (5.9%). At 24 months after surgery, 32% patients still reported graft site discomfort and 16% were bothered by the appearance of graft site. Of course, no patients in the rhBMP-2 INFUSE® group had any graft site pain of complications.
The rhBMP-2 INFUSE® treated patients had shorter operative times and less blood loss. At 24 months, this group of patients had a fusion rate that was nearly 6 percentage points greater than the autograft group. Overall results show that the use of rhBMP-2 can eliminate the need for harvesting iliac crest graft for successful lumbar fusions.
Key Points From the Study
· Fusion rates for both treatment groups were high at all studied intervals. At 24 months, the average rate of fusion for patients treated with rhBMP-2 was nearly 6 percentage points higher (94.5% vs. 88.7%) than for patients treated with autograft.
· The average operative time was 1.6 hours for patients treated with rhBMP-2 compared with 2.0 hours in the autograft group. This difference was statistically significant.
· Blood loss was less for patients treated with rhBMP-2 than for patients who underwent iliac crest bone graft harvesting.
· At all postoperative assessment intervals, patients in both treatment groups showed improvement in disability scores, in neurologic status, and in relief of back and leg pain.
· The use of rhBMP-2 in anterior lumbar interbody fusion procedures eliminates the complications of iliac crest bone harvesting including postoperative pain and scarring.
rhBMP-2 has recently received clearance from the Food and Drug Administration (FDA) for specific uses. Consult your surgeon to learn if you are a candidate.