When Bones Refuse to Fuse: Dr. Anderson Researches Successful Bone Fusion

Dec. 4, 2018

Clear Skull model

Take a moment to appreciate the freedom of movement your head likely enjoys. (Really—go “a-head”!) For most people, the neck allows the head remarkable range of motion. It can swivel left and right, nod up and down, tilt side to side and “roll” around from shoulder to shoulder. Much of that motion is due to the anatomy of just the top two joints in the neck: the joint between the skull and the first bone of the spine, and the joint between the first and second bones in the spine.

But neurosurgeons, including Dr. Richard Anderson at Columbia University Irving Medical Center/NewYork-Presbyterian Hospital, sometimes need to permanently immobilize one or both of these joints, using a procedure called a spinal fusion. This can be crucial for certain patients with conditions such as spine injury, spinal tumor, degenerative arthritis, spinal deformity and others.

A successful fusion at the top of the neck and the skull does restrict some of that incredible range of motion. But far more important, it keeps the bones of the head and neck in safe, strong alignment. In a fusion procedure, doctors introduce a bone graft that encourages the separate bones to fuse (grow together). When the procedure goes well, the graft fuses into a “bone bridge” between the bones. Where there had once been a joint, there is now a single, strong bone.

Sometimes, though, the bones refuse to fuse. This is called a fusion failure. And it can be a big problem when doctors and patients are depending on that strong fusion to provide long-term stability for the bones of the skull and neck. When there is a fusion failure, patients generally must receive another round of surgery to once again encourage the bones to fuse.

Nobody wants a fusion failure and a second round of surgery—not patients, and not surgeons—and so spinal surgeons like Dr. Anderson are interested in maximizing the safety and effectiveness of fusion surgeries. In a recent paper, Dr. Anderson and other researchers* examined the rates of successful fusion at the top of the neck and skull, based on the type of graft material doctors used.

The two basic choices for a bone graft are autograft and allograft. Autograft is bone harvested from the patient’s own body—often from a bone in the pelvis or rib. Allograft, by contrast, is donated bone taken from a bone bank.

The reason the researchers were interested in looking at these two types of grafts is that when fusing bones at the head and neck, an addition surgical incision is required to harvest a patient’s own bone (autograft). This results in a longer overall time under anesthesia. While most people do fine, surgeons are always aware that any additional surgery time puts patients at risk for more complications.

But the risks are not large, especially compared with the risk of fusion failure, which generally requires an entire second fusion surgery. If autografts create more successful fusions at the top of the neck and skull, they would probably still be the best option, even though they mean a little more surgery at the beginning. But researchers weren’t 100 percent sure that autografts do, in fact, create more successful fusions in this area.

To find out, the authors combed through two large insurance databases. And we mean large: The databases contain information on more than 80 million patients, de-identified for privacy. Such a huge pool was exactly what the researchers needed: they wanted to look at a large enough number of patients that the results of the study would be meaningful, wanted to look at enough different kinds of patients that they could see how each “bridge” performed under many circumstances, and wanted to use exactly the same criteria to examine each case.

So the researchers looked for patients who had had a spinal fusion at the top of the neck and/or skull, either with autograft or allograft. That came to about 500 of those 80 million. Then the researchers analyzed which of those patients required a repeat spinal fusion due to a fusion failure.

The authors found that autograft and allograft were equally successful in these surgeries. There was no difference between the two in rate of fusion or need for a second surgery.

This finding offers more information that surgeons can use when planning their patients’ procedures and deciding on which graft type is best for each patient.

And that’s something that can make us all—whether we have a full range of motion or are restricted by a (hooray) successful fusion—nod in approval.

Find out more about Dr. Anderson on his bio page here.

* Full list of authors: Robinson LC, Anderson RCE, Brockmeyer DL, Torok MR, Hankinson TC; Pediatric Craniocervical Society.

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