Can rhBMP-2 (InFuse) Enhance Fusion Rates in Anterior Lumbar Interbody Fusion Using Stand-alone Femoral Ring Allografts?**

Introduction: Anterior lumbar interbody fusion (ALIF) is a well-accepted procedure, and plays and important role in reconstructive spine surgery. Advances in spinal surgical technology has produced a multitude of anterior interbody implants, but the femoral ring allograft (FRA) remains a simple and adequate alternative for anterior structural support. As a stand-alone device however, like most other impacted allografts, the FRA has fallen into disfavor because of high rates of pseudarthrosis.

Purpose: To determine whether the use of rhBMP-2 (InFuse) applied to an absorbable collagen sponge (ACS) can enhance fusion rates in ALIF with stand-alone FRAs.

Methods: This is a retrospective study of 36 consecutive patients who underwent ALIF surgery with standalone FRAs. A single surgeon at the same institution performed all surgeries using identical technique. Minimum follow-up length was 20 months. All patients included in the study had symptomatic degenerative disc disease diagnosed by symptoms of intractable back/ and leg pain with positive diagnostic imaging findings. The first 27 consecutive patients received FRAs with autologous bone graft packed inside the intramedullary cavities. In an attempt to increase fusion rates, the next 9 patients received FRAs containing InFuse (BMP)-soaked ACS. Nonunion was diagnosed using flexion-extension radiographs, computed tomography scans, and confirmed during revision surgical procedures. The stand-alone FRA technique was no longer used after it was apparent that the use of BMP was not improving fusion rates.

Results: S: Nonunions were identified in 7 of 27 (26%) patients who underwent ALIF with stand-alone FRAs and autologous bone graft. In an effort to improve fusion rate, the surgeon then switched to adding BMP instead of autologous bone graft to the FRAs. However, nonunions were identified in 5 of 9 (56%) patients who underwent this surgery, a clear trend toward a higher nonunion rate (although not significant with the numbers available).

Conclusions: The use of rhBMP-2 soaked ACS instead of autologous iliac crest bone graft (ICBG) did not increase fusion rates in ALIFs with stand-alone FRAs. Rather, there was a non-significant trend toward increased nonunion. With BMP, CT scans showed increased absorption and remodeling of the FRA, which often fragmented and went on to nonunion. Variables which may be important when comparing FRAs containing ICBG to those containing only BMP include presence of osteoconductive material in the fusion compartment (endplate-FRA-endplate), exposure to blood supply, and fenestrations in the graft. These have implications on the optimal environment for BMP to enhance graft fusion.

**The FDA has not cleared a drug and/or medical device the use described in this presentation (i.e., the drug or medical device is being discussed in an “off-label use).