Methods: Retrospective study.

Objective: The purpose of this study was to clarify (1) the overall prevalence of radiologic and clinical adjacent segment disease (ASD), (2) the prevalence of radiologic ASD at cranial versus caudal adjacent segments, and (3) preoperative risk factors and preoperative radiologic features associated with radiologic disc degeneration of the cranial and caudal adjacent segments.

Methods: A total of 154 patients who underwent posterior lumbar interbody fusion and screw-rod fixation at the L4-L5 level were retrospectively evaluated more than 2 years after surgery. We analyzed demographic factors and radiographic features. Special focus was preoperative radiographic features of patients who required additional surgery. These patients were studied to detect risk factors for clinical deterioration.

Results: Of 154 patients, 103 (66.8%) showed radiologic degeneration at an adjacent segment after surgery-92 (59.7%) at the cranial adjacent segment and 61 (39.6%) at the caudal adjacent segment-and 10 patients (6.4%) required second operation because of radicular pain as well as severe back pain or spinal instability with back pain and neurologic deficits. Age, body mass index (BMI), and preexisting stenosis at the cranial adjacent segment were identified as important risk factors for clinical ASD requiring second operation.

Conclusions: Age, BMI, and preexisting stenosis at the cranial adjacent segment were the most important risk factors for clinical ASD requiring a second operation. Careful consideration is warranted when these risk factors are present.