Study design: Retrospective clinical study.
Objective: To investigate adjacent segment degeneration (ASD) at 5 years after L4/5 posterior lumbar interbody fusion with pedicle screw instrumentation and L4/5 decompression surgery using plain radiographs, computed tomography (CT), and magnetic resonance imaging (MRI), with the evaluation of annual changes on MRI.
Summary of background data: Methods of evaluation have been inconsistent among studies of ASD. There is no report that ASD in the lumbar spine after posterior lumbar interbody fusion at the same level is thoroughly evaluated on radiographs, CT, annual MRI changes, and the impact of decompression procedures.
Methods: ASD was evaluated in 52 patients. Disk height, vertebral slip, intervertebral angle, and intervertebral range of motion were examined on plain radiographs. Facet joint degeneration on CT and disk degradation and spinal stenosis on MRI were classified into categories, and facet sagittalization and tropism were measured on CT. The incidence of ASD was compared between the decompression procedures.
Results: The radiographic changes observed in the study were defined as radiographic ASD (R-ASD) without reoperation, as no patient required reoperation. R-ASD was rarely detected by radiography. The incidences of facet joint degeneration, MRI-detected disk degeneration, and spinal stenosis at the L3/4 and L5/S1 levels were 21% and 23%, 27% and 17%, and 35% and 4%, respectively. Progressive disk degeneration at L3/4 was found significantly more frequently in patients with aggravation of facet degeneration (P<0.01); however, the severities of preoperative facet degeneration, facet sagittalization, and tropism were not associated with progressive disk degeneration or spinal stenosis. In annual MRI, most R-ASD cases were detected within 3 years after surgery. Patients who underwent L4 total laminectomy had significantly more frequent R-ASD compared with those who received bilateral fenestration at L4/5 (P<0.01).
Conclusions: R-ASD was detected more frequently by CT and MRI compared with radiography. Preoperative facet joint degeneration and morphology were not always related to progressive disk degeneration or spinal stenosis. Annual MRI suggested that accelerated degeneration was due to lumbar spine fusion, rather than aging degeneration. Decompression with preservation of posterior connective components is recommended to prevent R-ASD.