Posterior lumbar interbody fusion using recombinant human bone morphogenetic protein type 2 with cylindrical interbody cages

Abstract

Background context

In a large series of human patients undergoing open anterior lumbar interbody fusion with a tapered titanium fusion cage, recombinant human bone morphogenetic protein type 2 (rhBMP-2) on an absorbable collagen sponge carrier has been shown to decrease operative time and blood loss, to promote osteoinduction and fusion and to be a safe and effective substitute for iliac crest harvesting.

Purpose

The purpose of the study was to determine the clinical and radiographic outcomes in patients treated for single-level degenerative lumbar disc disease with a posterior interbody fusion, using stand-alone cylindrical threaded titanium fusion cages with either autogenous bone graft or rhBMP-2 and an absorbable collagen sponge carrier.

Study design/setting

A prospective, randomized, nonblinded, 2-year pilot study at 14 investigational sites.

Patient sample

Between March 1999 and December 1999, 67 patients with symptomatic, single-level degenerative lumbar disc disease of at least 6 months' duration underwent a single-level posterior lumbar interbody fusion using two paired cylindrical threaded titanium fusion devices. Patients were randomly assigned to one of two groups: one (n=34 patients) received rhBMP-2 on a collagen sponge carrier; the other (n=33 patients) autogenous iliac crest bone graft.

Outcome measures

Clinical outcomes were measured using low back and leg pain numerical rating scales, the Short Form (SF)–36, Oswestry Low Back Pain Disability Questionnaire and work status. Plain radiographs and computed tomographic scans were used to evaluate fusion at 6, 12 and 24 months after surgery.

Methods

In this prospective nonblinded study, 67 patients were randomly assigned to one of two groups who underwent interbody fusion using two cylindrical threaded fusion cages: the investigational group (34 patients), who received rhBMP-2 on an absorbable collagen sponge, and a control group (33 patients), who received autogenous iliac crest bone graft. Clinical data were collected and analyzed by a commercial entity.

Results

The mean operative time and blood loss for the investigational rhBMP-2 group was 2.6 hours and 322.8 ml, respectively. For the autograft control group, these values were 3.0 hours and 372.7 ml. The differences were not significant. Although not statistically different, at 24 months, the investigational group's fusion rate of 92.3% was higher than the control's at 77.8%. At all postoperative intervals, the mean Oswestry, back and leg pain scores and physical components of the SF-36 improved in both treatment groups compared with preoperative scores, but no significant differences were found between groups. A statistically significant difference in the change in back pain was found at 24 months for the investigational group. In the control group, two adverse events related to harvesting of the iliac crest graft occurred in two patients (6.1%).

Conclusions

This small multicenter, randomized, nonblinded trial showed few statistically significant differences between the study groups. Both groups showed comparable improvements on outcome scores. Overall results show that the use of rhBMP-2 can eliminate the need for harvesting iliac crest graft and may be an equivalent replacement for autograft for use in successful posterior lumbar interbody fusions. Further studies of the use of rhBMP-2 in posterior lumbar interbody fusion cage procedures are needed.

Introduction

Posterior lumbar interbody fusion (PLIF) is an effective treatment for patients with symptomatic degenerative disc disease, spondylolisthesis and other painful discogenic syndromes. Fusion of the degenerative and unstable lumbar spinal motion segment can give significant relief from this disabling and often progressive condition [1], [2], [3], [4]. PLIF limits the extent of posterolateral soft tissue exposure, muscle stripping and injury. With this technique, the surgeon uses the traditional posterior approach to the lumbar spine; however, dissection is limited laterally to the facet joints. Through this approach, direct neural decompression can be completed, disc space height and sagittal balance can be restored [2], [3], [4], [5], [6] and intervertebral grafts can be placed in a biomechanically advantageous position.

Lumbar spine stabilization procedures that limit the extent of posterior spinal muscle exposure have some significant advantages. With PLIF surgical techniques, the fusion bed is within the disc space, which eliminates the exposure of the transverse processes. The PLIF approach to the lumbosacral spine enables the surgeon to reestablish the normal anatomic alignment and the relationships of the spinal motion segment while avoiding excessive injury to the posterior paravertebral muscles [2], [3], [4], [5], [6].

Cloward [1] presented his technique for this innovative procedure in 1953. In his surgical technique, he described using a wide laminectomy and facetectomies that would allow for the placement of large structural bone grafts in the denuded and meticulously prepared disc space. Later, Lin et al. [2] modified this intervertebral grafting technique of structural grafts. This modified PLIF technique involves filling the disc space with cancellous bone strips, allowing for preservation of a portion of the posterior elements and avoiding the complication of insertion of large structural grafts. Additional modifications of the bone graft technique and bone graft materials have been made. Kuslich et al. [3] and Ray [4] introduced the idea of using threaded interbody fusion cages inserted through a PLIF approach as a means of stabilizing the lumbar motion segment, increasing rates of fusion and improving clinical outcomes.

Recombinant human bone morphogenetic protein type 2 (rhBMP-2) [7] applied to an absorbable collagen sponge carrier has been shown to promote osteoinduction and fusion in the lumbar spine [8], [9], [10], [11]. In a large series of patients who underwent stand-alone anterior lumbar interbody fusion with fusion cages, rhBMP-2 was shown to enhance rates of fusion, reduce surgical time and improve clinical outcomes [12], [13]. To further evaluate this method of bone graft replacement, we evaluated the clinical and radiographic outcomes at 24 months of 67 patients who underwent a single-level PLIF. We compared the outcomes in the investigational patients (rhBMP-2) with those in the control patients (autogenous bone).