Effect of segmental lordosis on early-onset adjacent-segment disease after posterior lumbar interbody fusion

OBJECTIVE Although several reports have described adjacent-segment disease (ASD) after posterior lumbar interbody fusion (PLIF), there have been only a few reports focusing on early-onset ASD occurring within 3 years after primary PLIF. The purpose of this study was to investigate the prevalence and postoperative pathologies of early-onset ASD and its relation with radiological parameters such as segmental lordosis (SL). METHODS The authors reviewed a total of 256 patients who underwent single-segment PLIF at L4-5 for degenerative lumbar spondylolisthesis (DLS) and were followed up for at least 5 years. The definition of ASD was a symptomatic con- dition requiring an additional operation at the adjacent fusion segment in patients who had undergone PLIF. ASD occur-ring within 3 years after primary PLIF was categorized as early-onset ASD. As a control group, 54 age-and sex-matched patients who had not suffered from ASD for more than 10 years were selected from this series. RESULTS There were 42 patients with ASD at the final follow-up. ASD prevalence rates at 3, 5, and 10 years postop- eratively and at the final follow-up were 5.0%, 8.2%, 14.1%, and 16.4%, respectively. With respect to ASD pathologies, lumbar disc herniation (LDH) was significantly more common in early-onset ASD, while lumbar spinal stenosis and DLS occurred more frequently in late-onset ASD. Significant differences were detected in the overall postoperative range of motion (ROM) and in the changes in ROM (AROM) at L3-4 (the cranial adjacent fusion segment) and changes in SL (ASL) at L4-5 (the fused segment), while there were no significant differences in other pre-and postoperative param- eters. In stepwise logistic regression analysis, ASL was identified as an independent variable (p = 0.008) that demon- strated significant differences, especially in early-onset ASD (control 1.1 degrees vs overall ASD -2.4 degrees, p = 0.002; control 1.1 degrees vs early-onset ASD -6.6 degrees, p = 0.00004). CONCLUSIONS The study results indicated that LDH was significantly more common as a pathology in early-onset ASD and that ASL was a major risk factor for ASD, especially early-onset ASD.