Lumbar interbody fusion comparing allograft bone dowels with threaded titanium cages: a prospective, randomized, multicenter study

Abstract

Frank M. Phillips, MD, Chicago, IL, USA; Mark Falahee, MD, Ypsilanti, MI, USA; F. Todd Wetzel, MD, Chicago, IL, USA; Richard Rabinowitz, MD, Hoffman Estates, IL, USA; Purnendu Gupta, MD, Chicago, IL, USAPurpose: Stand alone lumbar interbody fusion has been used as a treatment for symptomatic lumbar spondylosis using both allograft bone dowels and threaded titanium cages. This paper reports findings of a randomized, prospective multicenter study that assesses results of interbody fusion using threaded bone dowels or titanium cages with autograft for the treatment of discogenic low back pain unresponsive to conservative treatment measuring both fusion parameters and patient-centered outcomes.Materials and methods: This multicenter, randomized, prospective study enrolled 60 patients at five study sites from April 1998 to July 2000. Fifty-six patients advanced beyond the enrollment period. All study patients had mechanical low back pain greater than leg pain with the disc confirmed as source of the pain by provocative discography. Patients were between 18 and 65 years old and had failed at least 6 months of conservative care. Up to grade 1 degenerative spondylolisthesis at the involved level was allowed for inclusion into the study. One- or two-level stand alone interbody fusion was performed using either threaded allograft bone dowels or threaded titanium cages with autograft with patients randomized at each study site into one of these two groups. No supplemental instrumentation was used. Fusion outcome was assessed at 12 months by anteroposterior, lateral and flexion-extension views. Patient functional outcomes were assessed by SF-36 and Oswestry scale measurements at enrollment, 6- and 12-month intervals collected independent of the physician's office.Results: A total of 28 patients completed 1-year follow-up X-ray evaluation with 35 total interbody fusion sites. Overall, 24 patients and 30 interbody sites were judged by independent radiologic assessment as fused, with 3 patients and four interbody levels judged as indeterminate and 1 patient with one interbody level judged a fusion failure. Assuming all indeterminate levels were considered nonfused, the series would have a 85.7% fusion rate for all patients and 85.7% fusion for all interbody sites. In the threaded bone dowel group of 13 patients and 15 interbody sites, all sites were judged fused. Of the 15 patients and 20 interbody sites treated with threaded titanium cages, 11 patients and 15 sites were judged fused with 3 patients and 4 interbody sites judged indeterminate, and 1 site/patient a failure to fuse.Thirty patients completed the 12-month postoperative clinical outcome survey. Statistical analysis was carried out to evaluate the Short Form (SF)-36, Oswestry and Pain scores for both groups comparing preoperative and 12-month postoperative scores. For both the threaded bone dowel group and the threaded titanium cage group, statistically significant changes indicating improvement were found for the SF-36 scores for Physical Functioning (p=.0033), Role Limitations-Physical (p=.00001), Social Functioning (p=.0009). Bodily Pain (p=.00001), Vitality (p=.00001) and PCS (p=.00001) as well as for the Oswestry Disability Index (preoperative mean, 51.78; postoperative mean, 33.05; p=.00001) and Back Pain Visual Analog Scale (preoperative mean, 7.64; postoperative mean, 4.56; p=.0001). Although both the threaded bone dowel group and the threaded titanium cage group showed statistically significant clinical improvement, there was no statistical difference that was detected in the scores for any of the outcome parameters between the threaded bone dowel and titanium cage groups.Discussion: Stand alone interbody fusion using both threaded bone dowels and threaded titanium cages was found an acceptable treatment for discogenic back pain that had failed conservative care. Clinical results showed statistically significant improvement in patient-centered outcomes using both fusion options. No significant differences in clinical outcomes were detected between the two groups. Radiological assessment of fusion was determined more definitively when threaded bone dowels were used for interbody fusion. It is unclear whether the threaded titanium cages deemed to have an indeterminate fusion status had indeed failed to fuse or if it was simply not possible to interpret the fusion on the radiographic studies.