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Graft Resorption With the Use of Bone Morphogenetic Protein: Lessons From Anterior Lumbar Interbody Fusion Using Femoral Ring Allografts and Recombinant Human Bone Morphogenetic Protein-2

Pradhan, Ben B., MD, MSE*; Bae, Hyun W., MD*; Dawson, Edgar G., MD*; Patel, Vikas V., MA, MD; Delamarter, Rick B., MD*

doi: 10.1097/01.brs.0000216442.12092.01
Clinical Case Series

Study Design. This is a prospective cohort study examining the results and radiographic characteristics of anterior lumbar interbody fusion (ALIF) using femoral ring allografts (FRAs) and recombinant human bone morphogenetic protein-2 (rhBMP-2). This was compared to a historical control ALIF using FRAs with autologous iliac crest bone graft (ICBG).

Objective. To determine whether the use of rhBMP-2 can enhance fusion ALIF with stand-alone FRAs.

Summary of Background Data. ALIF is a well-accepted procedure in reconstructive spine surgery. Advances in spinal surgery have produced a multitude of anterior interbody implants. The rhBMP-2 has promoted fusion in patients undergoing ALIF with cages and threaded allograft dowels. The FRA still remains a traditional alternative for anterior support. However, as a stand-alone device, the FRA has fallen into disfavor because of high rates of pseudarthrosis. With the advent of rhBMP-2, the FRA may be more attractive because of its simplicity and remodeling potential. It is important to understand the implications when rhBMP-2 is used with such structural allografts.

Methods. A total of 36 consecutive patients who underwent ALIF with stand-alone FRAs by a single surgeon (E.G.D.) at 1 institute were included. A cohort of 9 consecutive patients who received FRAs filled with rhBMP-2 was followed prospectively. After noticing suboptimal results, the senior author terminated this method of lumbar fusion. A total of 27 prior consecutive patients who received FRAs filled with autogenous ICBG were used for comparison. Analyzing sequential radiographs, flexion-extension radiographs, and computerized tomography with multiplanar reconstructions determined nonunions. Minimum follow-up was 24 months.

Results. Pseudarthrosis was identified in 10 of 27 (36%) patients who underwent stand-alone ALIF with FRAs and ICBG. Nonunion rate was higher among patients who received FRAs with rhBMP-2 (i.e., 5 of 9 [56%]). Statistical significance was not established because of the early termination of the treatment group (P > 0.3). Of interest, radiographs and computerized tomography revealed early and aggressive resorption of the FRAs when used with rhBMP-2. This preceded graft fracture and even disintegration, resulting in instability and eventual nonunion.

Conclusion. The use of rhBMP-2 did not enhance the fusion rate in stand-alone ALIF with FRAs. In fact, the trend was toward a higher nonunion rate with rhBMP-2, although this was not significant with the numbers available. This result appears to be caused by the aggressive resorptive phase of allograft incorporation, which occurs before the osteoinduction phase.

The Food and Drug Administration has approved recombinant human bone morphogenetic protein-2 for use in lumbar interbody fusion with cages. With interest in cages declining and the advent of bone morphogenetic protein, the traditional allograft alternative is regaining popularity. However, recombinant human bone morphogenetic protein-2 is not a panacea for spinal fusion. It can cause enhanced graft resorption and induce nonunion with inadequate stabilization.

From the *Spine Research Foundation, The Spine Institute at Saint John's Health Center, Santa Monica, CA and †Department of Orthopaedic Surgery, The University of Colorado Health Sciences Center, Denver, CO.

Acknowledgment date: March 17, 2005. First revision date: August 11, 2005. Acceptance date: October 7, 2005.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Ben B. Pradhan, MD, MSE, The Spine Institute at Saint John's Health Center, Suite 400, 1301 20th Street, Santa Monica, CA 90404; E-mail: benpradhan@yahoo.com

© 2006 Lippincott Williams & Wilkins, Inc.