Radiographic Adjacent Segment Degeneration at Five Years After L4/5 Posterior Lumbar Interbody Fusion With Pedicle Screw Instrumentation: Evaluation by Computed Tomography and Annual Screening With Magnetic Resonance Imaging.

STUDY DESIGN: Retrospective clinical study.

OBJECTIVE: To investigate adjacent segment degeneration (ASD) at 5 years after L4/5 posterior lumbar interbody fusion (PLIF) with pedicle screw instrumentation and L4/5 decompression surgery using plain radiographs, CT and MRI, with 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 PLIF 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. Disc height, vertebral slip, intervertebral angle, and intervertebral range of motion were examined on plain radiographs. Facet joint degeneration on CT, and disc 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 decompression procedures.

RESULTS: The radiographic changes observed in the study were defined as radiographic ASD (R-ASD) without reoperation, since no patient required reoperation. R-ASD was rarely detected by radiography. At the L3/4 and L5/S1 levels, the incidences of facet joint degeneration, MRI-detected disc degeneration, and spinal stenosis were 21% and 23%, 27% and 17%, and 35% and 4%, respectively. Progressive disc 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 disc 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 to those who received bilateral fenestration at L4/5 (P<0.01).

CONCLUSION: R-ASD was detected more frequently by CT and MRI than radiography. Preoperative facet joint degeneration and morphology were not always related to progressive disc 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.