A spinal fusion is a solid bone bridge between two areas of the spine which at one time moved freely or independently from one another. In very simple terms, imagine a metal link chain. Each link, when you sway or move the chain, moves a little bit in respect to the adjacent links. If you were to weld two links together, then the chain could still move, but each link would move just a little bit more to make up for the loss in motion across the welded links. A spinal fusion is a little like welding links in a chain, instead of links, in the spine, the vertebrae are fused together.

There are many types of spinal problems that are treated by spinal fusion. Additionally, there are different techniques for spinal fusion and sometimes instrumentation is used to assist in obtaining a solid fusion (screws, hooks, rods, wires, cages...). (Read more about Spinal Fusion in the Tutorial) In the very simplest case, a fusion might include just placing some bone across two vertebrae and letting those two vertebrae form a solid bone bridge. Unfortunately, obtaining a solid fusion is not always easy and even in the best of hands a fusion may not form as intended and a suboptimal or poor result may develop.

Some of the common reasons for poor result after spinal fusion include:

1. Poor bone healing leading to a pseudarthrosis (failed fusion). This may be due to the patient tissues that do not heal bone well, inadequate bone placed into the fusion area, excessive motion across the fusion area limiting healing, infection, and suboptimal alignment or fusion technique…




2. Poor alignment of the fusion. If the spine is not optimally aligned then the forces across the intended fusion area are such that the bone may not heal, the adjacent areas of the spine degenerate/fail and the muscles are strained to maintain overall balance. This can all lead to pain and significant disability.




3. Suboptimal strategy. Despite a thorough evaluation and diagnosis, the optimal treatment for complex spinal conditions remains a challenge. Even experienced specialists may not achieve good results in certain cases. Identifying the source(s) of pain can be difficult, effectively carrying out a surgical plan, and considering the many subtle parameters involved in pain and deformity are an enormous challenge in certain cases. Even when all goes as planned, there may be unpredictable results.




4. Chronic nerve injury/irritation. Assuming a source of pain has been clearly identified, a surgical strategy has been outlined and technically the surgery has been a success, clinical failure may result. For unclear reasons, chronic pain may persist even with what appears to be surgical success (good fusion, freed nerves…) and excellent radiographic findings (clear spinal canal, good alignment, solid bone healing). It appears that chronic nerve type pain, and back pain with muscle spasms can persist even in the setting of what would otherwise seem to be a surgical success. In some cases this may be due to some element of permanent injury or inflammation to nerves or a deregulation of pain control.

Learn more about Revision Surgery in our Revision Surgery Tutorial.