Key points

Introduction

Spinal surgery has been increasingly used over the last several decades in order to correct structural compression of neural elements. The goal of spinal surgery is 2-fold: to decompress neural elements and to fuse the bony elements surrounding the spine to prevent future instability.

In particular, there are 2 methods used to promote bony fusion across adjacent vertebral elements. The first method is referred to as “instrumentation-induced fusion (IIF).” In this method, hardware is affixed to the bony elements of the spine to immobilize them relative to each other. Fusion then results over several months as bone formation occurs across these immobilized bony elements.

Another method involves the placement of material adjacent to the vertebrae to enhance bone growth, which is referred to as “material-induced fusion (MIF).” Importantly, MIF is completely independent of IIF, and each of these methods can be performed separately from or simultaneously with the other. As an example, “on-lay fusion” techniques represent MIF performed separately from IIF. However, placing pedicle screws and rods in conjunction with iliac bone autograft for lumbar spinal fusion represents the simultaneous use of MIF and IIF techniques. Importantly, the gold standard of MIF is the use of iliac bone autograft to enhance bony fusion. However, iliac bone autograft has been associated with a relatively high morbidity and leads to often unacceptable levels of postoperative pain that can impede recovery and prolong hospital length of stay.

The use of bone morphogenic protein (BMP) has thus been proposed to replace iliac bone autograft to enhance bony fusion. It is important to view the use of BMP within the broad goals of spine surgery: it is one method to enhance arthrodesis. In that context, it is not important to determine if BMP enhances bone growth, but instead it is important to determine if BMP promotes arthrodesis at a higher rate than other MIF and IIF approaches within an acceptable safety profile.

BMP itself is a salient topic in spine surgery, primarily because it has gained widespread use. Indeed, many spine surgeons across both neurosurgery as well as orthopedic surgery use BMP as a method of MIF despite the fact that BMP has not gained general US Food and Drug Administration (FDA) approval for this purpose. As a result, most surgeons have adopted the practice of adding the off-label use of BMP to the consenting process for surgery. With such widespread adoption by the spine community without the express sanctioning by the FDA, it remains the responsibility of those in the field of spinal surgery to continuously weigh the risks and benefits of BMP. Such heightened scrutiny is especially needed because BMP has an unclear safety profile, and it is argued to be a nontrivial cause of various numbers of postoperative complications and adverse events.

In this review, the authors first review the development of BMP. Then, they cover the controversy surrounding the role of BMP in the development of bony cancers. Finally, the authors summarize the current state of affairs regarding the use of BMP in spinal surgery.

Introduction

Spinal surgery has been increasingly used over the last several decades in order to correct structural compression of neural elements. The goal of spinal surgery is 2-fold: to decompress neural elements and to fuse the bony elements surrounding the spine to prevent future instability.

In particular, there are 2 methods used to promote bony fusion across adjacent vertebral elements. The first method is referred to as “instrumentation-induced fusion (IIF).” In this method, hardware is affixed to the bony elements of the spine to immobilize them relative to each other. Fusion then results over several months as bone formation occurs across these immobilized bony elements.

Another method involves the placement of material adjacent to the vertebrae to enhance bone growth, which is referred to as “material-induced fusion (MIF).” Importantly, MIF is completely independent of IIF, and each of these methods can be performed separately from or simultaneously with the other. As an example, “on-lay fusion” techniques represent MIF performed separately from IIF. However, placing pedicle screws and rods in conjunction with iliac bone autograft for lumbar spinal fusion represents the simultaneous use of MIF and IIF techniques. Importantly, the gold standard of MIF is the use of iliac bone autograft to enhance bony fusion. However, iliac bone autograft has been associated with a relatively high morbidity and leads to often unacceptable levels of postoperative pain that can impede recovery and prolong hospital length of stay.

The use of bone morphogenic protein (BMP) has thus been proposed to replace iliac bone autograft to enhance bony fusion. It is important to view the use of BMP within the broad goals of spine surgery: it is one method to enhance arthrodesis. In that context, it is not important to determine if BMP enhances bone growth, but instead it is important to determine if BMP promotes arthrodesis at a higher rate than other MIF and IIF approaches within an acceptable safety profile.

BMP itself is a salient topic in spine surgery, primarily because it has gained widespread use. Indeed, many spine surgeons across both neurosurgery as well as orthopedic surgery use BMP as a method of MIF despite the fact that BMP has not gained general US Food and Drug Administration (FDA) approval for this purpose. As a result, most surgeons have adopted the practice of adding the off-label use of BMP to the consenting process for surgery. With such widespread adoption by the spine community without the express sanctioning by the FDA, it remains the responsibility of those in the field of spinal surgery to continuously weigh the risks and benefits of BMP. Such heightened scrutiny is especially needed because BMP has an unclear safety profile, and it is argued to be a nontrivial cause of various numbers of postoperative complications and adverse events.

In this review, the authors first review the development of BMP. Then, they cover the controversy surrounding the role of BMP in the development of bony cancers. Finally, the authors summarize the current state of affairs regarding the use of BMP in spinal surgery.