Adjacent segment disease after anterior cervical interbody fusion.

BACKGROUND CONTEXT

There have been many follow-up studies on anterior interbody fusion for cervical nerve root and spinal cord compression, and excellent neurological outcomes have been reported. However, postoperative degenerative changes at adjacent discs may lead to the development of new radiculopathy or myelopathy. In the previous reports, the incidence of symptomatic adjacent segment disease has ranged from 7% to 15%.

PURPOSE

The present study was undertaken to investigate the incidence of symptomatic adjacent segment disease after anterior cervical interbody fusion (ACIF) and to identify the factors that are related to the development of this disease.

STUDY DESIGN/SETTING: This is a retrospective cohort study.

PATIENT SAMPLE

A total of 112 patients were followed up clinically and radiologically for more than 2 years.

OUTCOME MEASURES

Follow-up evaluation was primarily by means of clinical visits. The postoperative course of any symptoms, the findings of neurological examination and serial follow-up radiographs were performed in all patients.

METHODS

The diagnosis of symptomatic adjacent segment disease was based on the presence of new radiculopathy or myelopathy symptoms referable to an adjacent level, and the presence of a compressive lesion at an adjacent level by magnetic resonance imaging or myelography. We evaluated the correlation between the incidence of symptomatic adjacent segment disease and the following clinical parameters (age at operation, sex, number of the levels fused) and radiological parameters (preoperative cervical spine alignment, preoperative range of motion of C2-C7 cervical spine, anteroposterior spinal canal diameter, preoperative existence of an adjacent segment degeneration on plain radiograph, myelography and magnetic resonance imaging [MRI]).

RESULTS

Symptomatic adjacent segment disease developed in 19 of 112 patients (19%) followed. A Kaplan-Meier survival analysis was performed in order to follow the disease-free survival of the entire series of patients. The disease-free survival rates were 89% at 5 years, 84% at 10 years and 67% at 17 years. The incidences of indentation of dura matter on preoperative myelography or disc protrusion on MRI at the adjacent level were significantly higher in disease cases (p=.0087, .0299, respectively; chi-squared test). However, the other parameters did not show a statistically significant difference. There were seven cases (37%) who had failure of nonoperative treatment and additional operations were performed.

CONCLUSIONS

The incidence of symptomatic adjacent segment disease after ACIF was higher when preoperative myelography or MRI revealed asymptomatic disc degeneration at that level regardless of the number of the levels fused, preoperative alignment, spinal canal diameter or fusion alignment.