472 - Comparison of Fusion Rates of Anterior and Posterior Fusion, Using FRA...

#472 Comparison of Fusion Rates of Anterior and Posterior Fusion, Using FRA Supplemented with Posterior Pedicle Screw Instrumentation, with and without rhBMP-2 with a Minimum of 2 Year Follow-up

Oral Posters: Lumbar

Presented by: R. Rabbani

Author(s):

R. Rabbani (1)
J.G. Bendetson (1)
G. Tepper (1)

(1) Miracle Mile Medical Center, Los Angeles, CA, USA

Abstract

Introduction: Recombinant human bone morphogenetic protein-2 (rhBMP-2) is an osteoinductive protein that has been approved for the lumbar interbody space through an anterior approach. High fusion rates have been reported with its use in threaded interbody allograft dowels and cages, stand-alone anterior interbody devices, and femoral ring allografts (FRA) supplemented with posterior pedicle screw instrumentation. Poor results have been reported with its use in stand-alone FRAs secondary to graft resorption. Previous prospective studies of anterior lumbar interbody fusion (ALIF) using FRAs supplemented with posterior pedicle screw instrumentation and rhBMP-2 have demonstrated fusion rates up to 100% at 12 and 24 months.

Purpose: To compare the fusion rates of anterior and posterior fusion, using FRA supplemented with posterior pedicle screw instrumentation, with and without rhBMP-2 with a minimum of 2 year follow-up.

Methods: This was a retrospective study conducted over a 6 year period from 2004 to 2010 consisting of 112 consecutive patients who underwent a one, two, or three-level circumferential fusion through the anterior retroperitoneal and posterior approach. Group 1 consisted of 68 patients who underwent ALIF with FRA and posterior pedicle screw instrumentation. Group 2 consisted of 44 patients who underwent ALIF with FRA and posterior pedicle screw instrumentation with 4.2 mg/level rhBMP-2. 64 slice CT Scan and/or flexion-extension radiographs were used by the primary investigators at a minimum of 24 months to evaluate for fusion. Molinari-Bridwell grading system was used to assess fusion on CT Scan. Criteria, used previously in the literature, for fusion on flexion-extension radiographs included the presence of all four of the following: 1) Bridging bone connecting the adjacent vertebral bodies either through the FRA or around the FRA 2) Less than 5 degrees of angular motion 3) Less than 3 mm of translational motion 4) Absense of radiolucent lines around more than 50% of the allograft. The primary investigators were blinded to the use of rhBMP-2 and one another's determination at the time of evaluating imaging studies for fusion.

Results: In Group 1 (no rhBMP-2), 7 of the 68 patients (10.3%) had a pseudarthrosis. In Group 2 (rhBMP-2), 1 of the 44 patients (2.3%) had a pseudarthrosis (p=0.14). Analyzed per interbody level, Group 1 had 6.3% pseudarthrosis rate; Group 2 had 1.6% pseudarthrosis rate (p=0.26). Interobserver reliability was high in this study, with the primary investigators disagreeing on only 1 of the 112 cases (κ=0.98).

Conclusions: The addition of rhBMP-2 in the FRA with posterior pedicle screw instrumentation trends toward an increase in fusion rate from 89.3% to 97.3%. Analyzed per interbody level, the addition of rhBMP-2 in the FRA with posterior pedicle screw instrumentation trends toward an increase in fusion rate from 93.7% to 98.4%. A larger sample size is required to demonstrate statistical significance between the two groups.