There is no question but that for surgical purposes the most cost-effective material which can be used for fusion is the patient’s own bone (autograft). Bone from donors (allograft) and from animals (xenograft) is much less effective.
Where then can the surgeon find adequate autograft (autogenous bone)? The pelvic iliac crest has typically served as the source of this material. Although goodly amounts of bone are available from the pelvis the following problems have plagued these patients following surgery:
High incidence of post-fusion pain syndromes referred to the graft site.
Injuries and fractures produced in the pelvis. Pelvic deformities.
The liabilities of harvesting iliac bone are such that 75% of NASS members surveyed as of January 27, 2004 believed that it would no longer be used, in the future, as a source of autogenous bone graft for spinal stabilization procedures.
Typically spine fusions are also associated with decompressions in which local bone can be harvested. Actually, in many of the cases where fusion is done without decompression it turns out to be a bad experience for the patient because the most common reason for spine surgery failure is the fiasco of not identifying or addressing nerve compression due to lateral spinal stenosis. We will assume that the operating surgeon recognizes the nerve compression in addition to existing segmental dysfunction/ instability. When adequate decompression is performed the local bone removed (dorsal process, lamina, facet joint, etc.), typically discarded in the past, can readily be processed and used for effective autograft by the surgeon.
The harvesting of autogenous bone in general and local bone in particular has been a haphazard endeavor in the past. Some spine surgeons have now borrowed bone processing technology from their maxillo-facial reconstruction colleagues.
The Tessier bone mill shown above represents one example of a hand powered mill (Stryker Leibinger) designed to process bone chips harvested through the primary incisional site thus avoiding pelvic rim intervention. The best, and least expensive, osteogenic potentiator is autogenous bone marrow which can be easily aspirated from the ileum through a needle.
When appropriate decompression is performed the volume of processed bone is typically adequate for fusion purposes. This is, however, not always the case but a number of bone “extenders” are now available to increase the bone volume to make it adequate. As with all things the cost-effectiveness of these extenders measured against additional pelvic surgery where the “cost is right” but the liabilities are significant needs to be considered.
The need for bone-extenders has produced a new area of commercial endeavor where various additives derived from donor humans as well as manufactured substances are now in use. In addition to these substances there are a host of carriers being used to create different mixtures having different properties. The following substances are representative of substances presently in use as carriers:
Calcium sulfate (better known as “plaster of Paris”) arboxymethycellulose Glycol (infamous as a component of Depo-Medrol® and other steroid suspensions used for epidural injection) Hyaluronic Acid Lesithin
Clinical use has sown that some of the addititves presently being used have problems such as non-isotonic pH producing hemolysis of local blood and stem cells.
Autogenous bone and autogenous marrow serve well to promote William of Occam’s Razor. Which of the commercial additives will also fit this Razor remain to be determined.