Radiographic grading of facet degeneration, is it reliable? - a comparison of MR or CT grading with histologic grading in lumbar fusion candidates

Abstract

Background context: The current interest in motion-sparing surgery highlights the need for a more accurate radiologic evaluation of the degree of facet degeneration. In the presence of severe facet degeneration, a surgeon cannot ensure a positive outcome, even after successful surgery. To the best of our knowledge, no prospective study has compared the accuracy of grading facet degeneration by computed tomography (CT) or magnetic resonance (MR) scans with that attained from a real histologic evaluation.

Purpose: The purpose of this study was to determine the accuracy and reliability of CT or MR assessments of lumbar facet degeneration by comparing it with the histologic grading of the resected facets during surgery.

Study design/setting: A prospective study of consecutive patients undergoing posterior lumbar fusion surgery.

Methods: Forty-four excised facets from 18 patients who received lumbar fusion were evaluated using radiographic and histologic techniques. All patients prospectively underwent CT scanning, routine axial T2-weighted MR scanning, and axial MR using a double echo steady state (DESS) sequence for cartilage imaging. The facets were graded radiologically using four-point scales. The inferior articular processes including the cartilage and subchondral bone of the corresponding facets were resected during surgery and evaluated histologically using a four-point grading system.

Results: Radiologic grading revealed a tendency for underestimating facet degeneration than histologic grading. The number of facets undergraded by radiologic evaluations was 24 (55%) facets by CT, 16 (36%) by routine MR, and 22 (49%) by DESS. The weighted kappa coefficients between the histologic and radiologic grading also showed a poor correlation (0.120 for CT, 0.128 for routine MR, and 0.280 for MR using DESS sequence, respectively). The false-negative rates for detecting histologic degeneration by radiologic studies were 41% to 54%. The receiver operating characteristic curve revealed MR using DESS to have a better performance.

Conclusions: The degree of facet degeneration can be underestimated by current radiologic modalities, and their ability to detect facet degeneration is quite limited. Surgeons should be aware of these limitations during a preoperative evaluation of patients considered for motion-sparing techniques in lumbar spinal surgery.