Transition Zone Syndrome: Iatrogenic Instability or Natural History?

Introduction: Transition zone syndrome has come to imply the radiographic and clinically significant symptoms of premature degeneration of a mobile segment adjacent to a fusion. Some have hypothesized that increased stresses transferred to the adjacent segment by the previous surgical procedure in some way precipitate the premature degeneration. Despite this general understanding, no study has looked specifically at a group of patients with transition zone syndrome to identify possible predisposing features either in the preoperative or postoperative radiographs.

Purpose: To review the plain radiographic record of a group of patients selected because of either clinical or radiographic evidence of transition zone syndrome. A detailed review of the medical records and the preop, postop, and subsequent follow–up x–rays was conducted to identify any factors common to this group.

Materials and Methods: Thirty patients were identified in a busy tertiary referral spinal practice to fit the inclusion criteria. These patients spanned a follow–up period from 1988–99. Standard demographic information was retrieved from the medical records. Radiographic information collected from pre, immediately postop, and follow–up films included degenerative disease at each lumbar level, coronal and sagittal alignment, over the entire lumbar spine and the instrumented segments and evidence of instability such as spondylolisthesis and lateral listhesis. In addition, radiographs were investigated looking for any evidence suggestive of iatrogenic injury to the adjacent levels. Data was investigated and compared using statistical analysis ANOVA and paired t–Test with accepted significance at p=0.05.

Results: There were 10 male and 20 female patients. The average age at surgery was 65.6 years (43.8–78.6). 53.8% of patients had evidence of pre–existing degenerative disease prior to the surgical procedure. 73% of patients had evidence of instability, i.e. spondylolisthesis (n=14), or lateral listhesis (n=6) on preoperative films. Five (16.7%) patients were noted to have superior endplate or disc violation on the first postop follow–up radiograph. The index procedure was decompression (n=1), posterior instrumentation and fusion (n=25), and anterior lumbar fusions with decompression (n=2). Eight patients underwent operative repair of the transition zone segment. Fourteen patients were pursuing nonoperative treatment and eight were asymptomatic requiring no treatment. In the surgical group, 37.5% improved significantly, 62.5% improved some, and no patient was made worse. In the nonoperative group, 7.1% improved significantly, 57% improved some, and 35.7% did not improve at all or got worse. Postoperative loss of sagittal alignment correlated statistically significantly (paired t–Test, p<0.05) with the development of TZS. Loss of lumbar lordosis within the instrumented levels correlated with development of TZS (ANOVA, p<0.001) Loss of lordotic disc angulation above the instrumented level correlated with the development of TZS (paired t–Test, p<0.05)

Discussion: Transition zone syndrome is a poorly understood and poorly described phenomenon. This review suggests that there are three types of “transition zone syndrome” patients. Type A (true transition zone syndrome): Consists of patients with no pre–existing preoperative disease at the level which ultimately degenerated. Type B: Consists of patients with pre–existing degenerative disease at the level which ultimately failed adjacent to the fusion. This probably represents the natural history of the degenerative lumbar disease in these patients, perhaps exacerbated by the adjacent fusion. Type C: Consists of patients who develop transition zone syndrome as a result of adjacent segment damage, either facet, endplate, or disc, during the index procedure. For the purpose of further investigation and comparison of data, the etiology of the transition zone syndrome should be identified. This study also clearly suggests that there are inciting factors that seem to be consistently associated with the development of transition zone syndrome: loss of segmental and overall sagittal alignment, particularly when the plumbline falls anterior to the sacrum; failure to restore anatomic lumbar lordosis overall and within the instrumented levels; and pre–existing degenerative disease or instability or deformity at the level adjacent to the fusion.

Conclusion: Further studies need to be conducted to prospectively analyze preop, postop, and follow–up radiographic information, including MRIs for soft tissue information and CT scans potentially to evaluate facet joints at the levels adjacent to proposed fusions. This study would best be performed in a multicenter fashion so larger patient populations can be evaluated.