Abstract
Adjacent segment disease and pseudarthrosis are common complications of cervical spine fusions. Adjacent segment disease occurs in up to 30% of patients 10 years after surgery. Pseudarthrosis rates in the cervical spine can be as high as 18% for a three level fusion. Both these incidences can be reduced with surgical techniques.
Keywords
adjacent segment disease, pseudarthrosis, cervical spine fusion
Highlights
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Adjacent segment disease occurs in up to 30% of patients 10 years after surgery.
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Pseudarthrosis rates for a one-, two-, and three-level anterior cervical fusion with allograft and a plate are approximately 4%, 9%, and 18%, respectively.
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Adjacent segment disease and pseudarthrosis rates can be reduced by surgical techniques.
Background
The use of fusion procedures to treat a variety of spinal pathologies in the United States is increasing as the population ages. However, all spinal fusions carry a risk of pseudarthrosis and adjacent segment disease. Increased knowledge in spinal biomechanics, bone fusion biology, preoperative optimization, and spinal balance may help lower the rates of these problems.
Anterior cervical discectomy and fusion (ACDF) is one of the preferred treatments for degenerative cervical stenosis. The pseudarthrosis rate for this procedure ranges from 4% to 18%, and the rates for adjacent segment disease have been reported at 3% to 30%, depending on the follow-up length. Given the large volume of these cases done every year, neurosurgeons are likely to see these issues in their practices. We review the relevant literature on these issues in cervical spine surgery as well as their treatments here.
Anatomic Insights
Adjacent Level Disease
The pathophysiology of adjacent segment disease is still debated. The predominant theory postulates that when fusing previously mobile segments in the spine, forces that would have been absorbed by that segment are transmitted to the adjacent joints. This has been shown in cadaveric studies and using fluoroscopy in patients. However, some studies have failed to replicate these findings and instead postulate that adjacent segment disease is merely the progression of a preexisting spondylitic process.
Regardless the cause of adjacent level disease, segments adjacent to a fusion often degenerate to the point of requiring repeat surgery. A study by Hilibrand et al. reviewed 374 patients and found a 2.9% annual incidence of adjacent level disease, with survivorship analysis estimating that 25% of patients will develop adjacent level disease within a decade. Bydon et al. found a rate of 31% at 10 years and determined that the level or length of fusion did not change the incidence. A study by Ishihara et al. found that adjacent level disease is more prevalent in levels that previously showed degeneration.
Pseudarthrosis
Pseudarthrosis, or the failure to achieve bony fusion, can cause pain from continued motion at an arthritic joint. It can eventually lead to mechanical instability and hardware failure. The rates have declined with modern graft and plating technologies. The rates for a one-, two-, and three-level anterior cervical fusion with allograft and a plate are 4%, 9%, and 18%, respectively. The pseudarthrosis rate of four-level anterior cervical discectomies and fusions remains unacceptably high, and those cases should probably be accompanied with posterior cervical fixation.
Background
The use of fusion procedures to treat a variety of spinal pathologies in the United States is increasing as the population ages. However, all spinal fusions carry a risk of pseudarthrosis and adjacent segment disease. Increased knowledge in spinal biomechanics, bone fusion biology, preoperative optimization, and spinal balance may help lower the rates of these problems.
Anterior cervical discectomy and fusion (ACDF) is one of the preferred treatments for degenerative cervical stenosis. The pseudarthrosis rate for this procedure ranges from 4% to 18%, and the rates for adjacent segment disease have been reported at 3% to 30%, depending on the follow-up length. Given the large volume of these cases done every year, neurosurgeons are likely to see these issues in their practices. We review the relevant literature on these issues in cervical spine surgery as well as their treatments here.
Anatomic Insights
Adjacent Level Disease
The pathophysiology of adjacent segment disease is still debated. The predominant theory postulates that when fusing previously mobile segments in the spine, forces that would have been absorbed by that segment are transmitted to the adjacent joints. This has been shown in cadaveric studies and using fluoroscopy in patients. However, some studies have failed to replicate these findings and instead postulate that adjacent segment disease is merely the progression of a preexisting spondylitic process.
Regardless the cause of adjacent level disease, segments adjacent to a fusion often degenerate to the point of requiring repeat surgery. A study by Hilibrand et al. reviewed 374 patients and found a 2.9% annual incidence of adjacent level disease, with survivorship analysis estimating that 25% of patients will develop adjacent level disease within a decade. Bydon et al. found a rate of 31% at 10 years and determined that the level or length of fusion did not change the incidence. A study by Ishihara et al. found that adjacent level disease is more prevalent in levels that previously showed degeneration.
Pseudarthrosis
Pseudarthrosis, or the failure to achieve bony fusion, can cause pain from continued motion at an arthritic joint. It can eventually lead to mechanical instability and hardware failure. The rates have declined with modern graft and plating technologies. The rates for a one-, two-, and three-level anterior cervical fusion with allograft and a plate are 4%, 9%, and 18%, respectively. The pseudarthrosis rate of four-level anterior cervical discectomies and fusions remains unacceptably high, and those cases should probably be accompanied with posterior cervical fixation.
Prevention
Adjacent Level Disease
A few studies have attempted to find interventions that decrease the rate of adjacent level disease. Hwang et al. found that, in cadavers, the amount of motion transmitted to adjacent segments was mitigated by the use of a larger lordotic cage. Some surgeons advocate for matching the cage height to that of normal levels in the same patient. However, there are no large prospective trials to prove that this method works. The only intervention that has thus far been shown to decrease adjacent level disease in patients is the use of cervical arthroplasty. A review by Upadhyaya et al. examined the three cervical arthroplasty trials approved by the U.S. Food and Drug Administration (FDA) at the time. By combining the data from three FDA trials and using a fixed effects model, they found that the use of arthroplasty instead of fusion reduced the rate of adjacent level surgery, with a relative risk of 0.46. Five-year follow-up data from one of those trials showed a reoperation rate of 11% in ACDF compared with 3% in arthroplasty. This would favor the theory that adjacent level disease is at least partially caused by the fusion. Given these data, the authors typically counsel patients extensively about the possibility of accelerated spondylosis after cervical fusion.
The cervicothoracic junction (CTJ) deserves special mention because this level is especially prone to adjacent segment disease. Terminating a long segment cervical fusion at C7 creates a large lever arm that transmits force to the junction, theoretically accelerating degeneration there. A study by Steinmetz et al. showed that fusions terminating at C7 trended toward more fusion failures in patients. Yang et al. did not find that rod size had any effect on pseudarthrosis rate across the CTJ.
Pseudarthrosis
It has long been known that smoking decreases fusion rates in the lumbar spine and cervical spine. Use of steroids has been shown to decrease fusion rates in rabbits. Postoperative NSAID use has been shown to increase pseudarthrosis in the lumbar spine, but these studies have not been performed in cervical fusion models. Postoperative infections impede wound healing and decrease fusion rates. Lau et al. showed that two-level corpectomies and three-level ACDFs have equivalent pseudarthrosis rates.
The risk of pseudarthrosis can be decreased with patient optimization. This can be done by counseling regarding tobacco cessation and NSAID avoidance. A multidisciplinary approach is needed if patients have comorbid conditions that are actively being treated with steroids because cessation of steroids is optimal but may not be possible. If osteoporosis is suspected, a preoperative dual-energy x-ray absorptiometry scan should be obtained. If low bone density is confirmed, teriparatide treatment has been shown to increase bone formation over bisphosphonates in spinal fusions. Nutritional status should also be addressed. Although poor nutrition may not lead directly to a higher pseudarthrosis rate, it can adversely affect wound healing, which indirectly increases the pseudarthrosis rate. Decreased vitamin D levels have also been shown to impede bony fusion. Levels should be measured and supplemented if needed. See Table 47.1 for a list of risk factors and how they can be addressed.
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