Background: We studied the incidence, prevalence, and radiographic progression of symptomatic adjacent-segment disease, which we defined as the development of new radiculopathy or myelopathy referable to a motion segment adjacent to the site of a previous anterior arthrodesis of the cervical spine. Methods: A consecutive series of 374 patients who had a total of 409 anterior cervical arthrodeses for the treatment of cervical spondylosis with radiculopathy or myelopathy, or both, were followed for a maximum of twenty-one years after the operation. The annual incidence of symptomatic adjacent-segment disease was defined as the percentage of patients who had been disease-free at the start of a given year of follow-up in whom new disease developed during that year. The prevalence was defined as the percentage of all patients in whom symptomatic adjacent-segment disease developed within a given period of follow-up. The natural history of the disease was predicted with use of a Kaplan-Meier survivorship analysis. The hypothesis that new disease at an adjacent level is more likely to develop following a multilevel arthrodesis than it is following a single-level arthrodesis was tested with logistic regression. Results: Symptomatic adjacent-segment disease occurred at a relatively constant incidence of 2.9 percent per year (range, 0.0 to 4.8 percent per year) during the ten years after the operation. Survivorship analysis predicted that 25.6 percent of the patients (95 percent confidence interval, 20 to 32 percent) who had an anterior cervical arthrodesis would have new disease at an adjacent level within ten years after the operation. There were highly significant differences among the motion segments with regard to the likelihood of symptomatic adjacent-segment disease (p < 0.0001); the greatest risk was at the interspaces between the fifth and sixth and between the sixth and seventh cervical vertebrae. Contrary to our hypothesis, we found that the risk of new disease at an adjacent level was significantly lower following a multilevel arthrodesis than it was following a single-level arthrodesis (p < 0.001). More than two-thirds of all patients in whom the new disease developed had failure of nonoperative management and needed additional operative procedures. Conclusions: Symptomatic adjacent-segment disease may affect more than one-fourth of all patients within ten years after an anterior cervical arthrodesis. A single-level arthrodesis involving the fifth or sixth cervical vertebra and preexisting radiographic evidence of degeneration at adjacent levels appear to be the greatest risk factors for new disease. Therefore, we believe that all degenerated segments causing radiculopathy or myelopathy should be included in an anterior cervical arthrodesis. Although our findings suggest that symptomatic adjacent-segment disease is the result of progressive spondylosis, patients should be informed of the substantial possibility that new disease will develop at an adjacent level over the long term.

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Radiculopathy and Myelopathy at Segments Adjacent to the Site of a Previous Anterior Cervical Arthrodesis

Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion?

Study design A biomechanical study was performed using cadaveric cervical spine specimens. Objective To determine the effect of cervical spine fusion on adjacent-level intradiscal pressure. Summary of background data Clinical studies have reported that patients with spinal fusion are at greater risk of pathology and early disc degeneration at adjacent levels. It is hypothesized that eliminating motion at one level leads to hypermobility and increased forces at adjacent levels, thus increasing the rate of disc degeneration. Methods Six cadaveric cervical spine specimens were tested. Specimens were stabilized at T1 and loaded at C3 to 20 degrees of flexion and 15 degrees of extension. Intradiscal pressures and segmental motion at C4-C5 and C6-C7 were recorded first on intact specimens, and then after anterior cervical plating at C5-C6. Changes in intradiscal pressure and segmental motion were calculated and statistically analyzed using a paired Student t test. Results Intradiscal pressures were significantly increased during flexion at both adjacent levels. The pressure increased by 73.2% at C4-C5 (P = 0.002), and by 45.3% at C6-C7 (P = 0.006). Intradiscal pressures increased at both adjacent levels during extension, but not significantly. During flexion, segmental motion increased at both adjacent levels, with greater increases at C4-C5. During extension, segmental motion increased at both adjacent levels, with greater increases at C6-C7. Conclusions Clinical studies have reported increased rates of disc degeneration at levels adjacent to fusion. It is believed that eliminating motion through fusion shifts the load to the adjacent levels, causing earlier disc degeneration. This study has shown that significant increases in intradiscal pressure and segmental motion occur at levels adjacent to fusion during normal range of motion. These results may partially explain the mechanism of early disc degeneration at levels adjacent to cervical spine fusion.

Biomechanical Study on the Effect of Cervical Spine Fusion on Adjacent-Level Intradiscal Pressure and Segmental Motion

Background A primary concern after posterior lumbar spine arthrodesis is the potential for adjacent segment degeneration cephalad or caudad to the fusion segment There is controversy regarding the subsequent degeneration of adjacent segments, and we are aware of no long-term studies that have analyzed both cephalad and caudad degeneration following posterior arthrodesis A retrospective investigation was performed to determine the rates of degeneration and survival of the motion segments adjacent to the site of a posterior lumbar fusion Methods Two hundred and fifteen patients who had undergone posterior lumbar arthrodesis were included in this study The study group included 126 female patients and eighty-nine male patients The average duration of follow-up was 67 years Radiographs were analyzed with regard to arthritic degeneration at the adjacent levels both preoperatively and at the time of the last follow-up visit Disc spaces were graded on a 4-point arthritic degeneration scale Correlation analysis was used to determine the contribution of independent variables to the rate of degeneration Survivorship analysis was performed to describe the degeneration of the adjacent motion segments Results Fifty-nine (274%) of the 215 patients had evidence of degeneration at the adjacent levels and elected to have an additional decompression (fifteen patients) or arthrodesis (forty-four patients) Kaplan-Meier analysis predicted a disease-free survival rate of 835% (95% confidence interval, 775% to 895%) at five years and of 639% (95% confidence interval, 540% to 738%) at ten years after the index operation Although there was a trend toward progression of the arthritic grade at the adjacent disc levels, there was no significant correlation, with the numbers available, between the preoperative arthritic grade and the need for additional surgery Conclusions The rate of symptomatic degeneration at an adjacent segment warranting either decompression or arthrodesis was predicted to be 165% at five years and 361% at ten years There appeared to be no correlation with the length of fusion or the preoperative arthritic degeneration of the adjacent segment Level of Evidence Prognostic study, Level IV (case series) See Instructions to Authors for a complete description of levels of evidence

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Adjacent Segment Degeneration in the Lumbar Spine

Object The authors report the results of a prospective randomized multicenter study in which the results of cervical disc arthroplasty were compared with anterior cervical discectomy and fusion (ACDF) in patients treated for symptomatic single-level cervical degenerative disc disease (DDD). Methods Five hundred forty-one patients with single-level cervical DDD and radiculopathy were enrolled at 32 sites and randomly assigned to one of two treatment groups: 276 patients in the investigational group underwent anterior cervical discectomy and decompression and arthroplasty with the PRESTIGE ST Cervical Disc System (Medtronic Sofamor Danek); 265 patients in the control group underwent decompressive ACDF. Eighty percent of the arthroplasty-treated patients (223 of 276) and 75% of the control patients (198 of 265) completed clinical and radiographic follow-up examinations at routine intervals for 2 years after surgery. Analysis of all currently available postoperative 12- and 24-month data indicated a two-point...

Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial

Study design A retrospective review of all patients surgically treated for adjacent segment disease of the cervical spine over a 20-year period. Objectives To determine the clinical and radiographic success of discectomy with interbody grafting and corpectomy with strut grafting in the treatment of adjacent segment disease of the cervical spine. Summary of background data Up to 25% of all patients undergoing anterior cervical fusion have new disease due to degeneration of an adjacent segment within 10 years. The success of surgical treatment in these patients with adjacent segment disease has not been reported. Methods Thirty-eight patients were surgically treated for adjacent segment disease by discectomy with interbody grafting or corpectomy with strut grafting. Arthrodesis was evaluated by flexion-extension lateral radiographs and clinical outcomes were assessed using Robinson's criteria at least 2 years after surgery. Fusion rates were compared by Fisher's exact test, and outcomes were compared by rank-sum analysis. Results The rate of arthrodesis was significantly lower in the 24 patients treated by discectomy with interbody grafting at one or more levels (63%) than in the 14 patients treated by corpectomy with strut grafting (100%; P = 0.01). Clinical outcomes were similar for the corpectomy and discectomy groups (P = 0.55). There was a trend toward better outcomes in patients who achieved a solid arthrodesis (P = 0.13). Conclusions Achieving fusion is more difficult when anterior cervical arthrodesis is performed adjacent to a prior fusion. Strut grafting resulted in a significantly higher rate of arthrodesis than interbody grafting.

Gregory D. Carlson

Papers

Radiculopathy and Myelopathy at Segments Adjacent to the Site of a Previous Anterior Cervical Arthrodesis

The success of anterior cervical arthrodesis adjacent to a previous fusion.

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