Bone graft substitutes for spinal fusion surgery - August 2003 update (Research article)

Osteobiologics, or the science of promoting bone growth and maturation, is probably the fastest growing segment of orthopedics and spine surgery. After several years of research, there is still much interest in developing effective bone graft substitutes—with the hope that eventually the need to harvest bone graft from the patient (usually from the pelvis) during a spine fusion surgery will be eliminated.

Significant advances in bone graft substitutes have been made in the last couple of years, and the Food and Drug Administration (FDA) has approved a number of new products, but much of the ongoing research promises to offer even more options for surgeons and patients looking for alternatives to autograft (patient’s own bone).

It recently has been estimated that the cost of harvesting a patient’s own bone is more than $4,100¹. This estimate rests on the assumption that the procedure itself creates the need for a patient to stay in the hospital an extra day after the surgery. Although this estimate is probably high, the point is well made that even a patient’s own bone is not free, and there is a significant cost to performing the procedure. In addition to the extra cost, the procedure of harvesting a patient’s bone is well known to carry inherent risks (such as postoperative pain, infection, bleeding, etc…).

Approaching the pelvic wing from the front (anterior approach) to obtain iliac crest bone graft has unique problems or morbidities (unwanted side effects) versus using a posterior (from the back) approach:

• There is a small nerve (lateral femoral cutaneous nerve) that has a variable course in the anterior approach that may potentially be injured, leading to chronic numbness in the front of the thigh and pain at the harvest site.

• Another major consideration is that the anterior procedure is often done through a separate incision, whereas the posterior incision for bone graft can be performed via the same skin incision used for posterior spinal fusion.

• After surgery, the anterior incision is readily identified by the patient, which may lead to a greater awareness of incisional pain.

When the spinal fusion procedure itself is done via an anterior approach to the lumbar spine, many surgeons believe that bone graft substitutes may be used with success in this application, eliminating the need for autograft. In the anterior fusion bed, the bone graft material is under compression which is a biochemically favorable environment for bone healing.

The types of bone graft substitutes chosen by the surgeon depends on many variables, such as cost, availability, the presence of inhibitory factors to fusion (e.g. nicotine or steroid exposure) and the location of proposed fusion (i.e. the front (anterior) or back (posterior) of the spine).

Since allograft (cadaver bone obtained from a tissue bank) is traditionally the most commonly used alternative to autograft, a review of the usefulness of allograft in various spinal fusion procedures is a good starting point for a discussion of bone graft substitutes.

Reference:

1. Shaffrey CI, Polly DW, Peterson RC, et al. Economic Analysis of rhBMP-2 vs. Autogenous Iliac Crest Bone Graft for One Level Spinal Fusions. Scientific Proceedings of the 51st Annual Congress of Neurological Surgeons Meeting, September 29-October 4, 2001, San Diego, California, pp. 131-132.