What is pseudarthrosis? The surgeon tells me this is what is causing my back pain after I had spinal fusion surgery. I thought my pain was going to be better but instead it's worse and pseudarthrosis is the reason why.

Pseudarthrosis is another word for false joint and refers to movement that occurs at the fused site. It can occur without symptoms so the patient doesn't even know he or she has it. Or it can cause back and leg (or arm) pain, depending on whether the fusion is at the cervical (neck) or lumbar (low back) level.

There can be many causes of failed spinal fusion such as the hardware coming loose or infection and poor wound healing. Pseudarthrosis occurs as a result poor health from smoking, diabetes, and/or heart disease. It accounts for almost one-fourth of all revision fusion surgeries.
Patients who do not follow the guidelines for movement restriction during the post-operative period are also at risk of failed fusion.

How does the physician diagnose pseudarthrosis? It can be discovered in the patient who doesn't have any real symptoms when dynamic imaging studies are done. Dynamic means the X-rays are taken as the patient is moving. But this method isn't very reliable and wouldn't be done routinely after surgery if the patient wasn't having any problems.

When it comes to diagnostic imaging, there just isn't a good way to tell if the fusion failed. When reading dynamic radiographs, the radiologist knows that just because there isn't any obvious motion doesn't mean the fusion is complete. And just how much motion constitutes a failed fusion remains fuzzy. There's a lot of debate about what is and what isn't a solid fusion. Some experts think there's a difference in springiness between a fusion with and without hardware to hold it together during the healing phase.

Thin-slice CT scans have been used to assess the fusion site. But the results don't really add anything more than what is seen on the X-rays. The one exception to this is in the case of locked pseudoarthrosis. Thin-cut CT scans help show this problem more clearly than dynamic radiographs. Locked pseudoarthrosis describes a situation in which the top and bottom of the cage inserted between the two vertebrae has fused solid but the middle (inside the cage) has not filled in with bone and solidified.

MRIs can be a bit iffy in patients with hardware in place because the implants cause artifacts (unexplained shadows and altered densities). Those changes interfere in judging whether or not the fusion is completed. There has been some question about the use of ultrasound and bone scans to help diagnose pseudarthrosis. Not enough study has been done to clear up any questions about these modalities. When imaging studies do not aid in the diagnosis, the surgeon can rely on a follow-up surgical procedure to confirm any diagnostic suspicions. Only patients with painful, disabling symptoms would undergo a second (diagnostic) procedure.

Reference: 

Noah M. Raizman, MD, MFA, et al. Pseudarthrosis of the Spine. In Journal of the American Academy of Orthopaedic Surgeons. August 2009. Vol. 17. No. 8. Pp. 494-503.

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