Adjacent Segment Instability after Posterior Lumbar Fusion: Comparison Between Subtotal Laminectomy and Total Laminectomy

Abstract

Objective: Whereas fusion with pedicle screw fixation has shown satisfactory clinical results, solid fusion has been reported to accelerate degenerative changes in adjacent unfused levels. The purpose of this study was to evaluate the effect of bone/ligament/bone integrity after subtotal or total laminectomies on the development of adjacent segment instability(ASI). The hypothesis that total laminectomy would increase ASI more than would subtotal laminectomy was analyzed. Material and Methods: This is a retrospective study of 316 patients who were treated with posterior fusion and pedicle screw fixation between 1996 and 2001. After attempts to review all 316 patients and radiologic files, 36 patients who were diagnosed with ASI were carefully reviewed, including follow-up periods of 2-8 years. The medical records were carefully reviewed for recurrence of low back pain or neurologic symptoms after a period of postoperative relief, and the radiologic files were evaluated to determine instability. All patients had undergone single-level or multilevel instrumented posterior lumbar interbody fusion for intractable pain related to degenerative conditions of the spine. Results: Patients over the age of 60 were at a higher risk of developing clinical ASI however,fusion length, level and gender were not associated with ASI. The ASI was noted to occur most commonly in the cranial segment prior to fusion. Conclusions: This study revealed more frequent ASI after total laminectomy than after subtotal laminectomy, especially in elderly patients. The ideal procedure will be one combining maximal canal and foraminal decompressions with minimal resection of bony structures and supporting ligaments.