Adjacent segment degeneration after lumbar spinal posterolateral fusion with instrumentation in elderly patients.

This retrospective study investigated adjacent segments radiologically and clinically after posterolateral fusion of the lumbar spine with instrumentation. Thirty-two patients over 60 years old with a postoperative follow-up of at least 4 years were included. These patients all met the criteria of a postoperative symptom-free period of over 2 years, evident fusion mass seen on plain radiographs, and no implant breakage or loosening. There was 81.3% excellent and good clinical results (26/32). For all patients, flexion and extension views of the lumbar spine were done preoperatively and postoperatively. Adjacent segments below the fusion, above the fusion, and cranial to the above adjacent segment were examined. Three patients each with translation >4 mm in adjacent segments were found in both the short and long (≥3 segments) fusion groups. The incidence was 16.7% (3/18) in the short fusion group and 21.4% (3/14) in the long fusion group. However, no statistically significant difference (p=0.7878) was found according to the Fisher exact test. Comparing the effect of different types of instruments, there still was no statistically significant difference (p=0.1161) between the VSP plate and Isola rod groups in inducing degeneration of adjacent segments after posterolateral fusion of the lumbar spine. After measuring the mobility of degenerated adjacent segments, relative hypermobility was more likely responsible for the accelerated degeneration rather than the absolute increase of mobility.