Magnetic resonance image-based morphological predictors of single photon emission computed tomography-positive facet arthropathy in patients with axial back pain.

OBJECTIVE

A major barrier to understanding facetogenic low back pain has been the lack of radiographic diagnostic criteria. This study investigates the correlation between radiographic findings on magnetic resonance imaging (MRI) scans and single photon emission computed tomographic (SPECT) scans in patients clinically found to have facetogenic axial back pain.

METHODS

Thirty-one patients with severe axial back pain underwent lumbar MRI and SPECT scans. Two hundred thirty facets were identified and were graded from 1 to 4 using synovial area, size, cartilaginous discontiguity, osteophytic overgrowth, and joint space obliteration. Twenty-nine "hot" joints were identified on SPECT scans. MRI features of 230 lumbar facets were correlated with SPECT results.

RESULTS

Four basic morphological patterns were identified on the basis of synovial appearance on MRI scans, light, mottled, narrowed, and obliterated, and formed the basis for the grading 1 to 4, respectively (sensitivity for "hot facet", 0.93). The mottled group had 0.90 specificity (P = 0.0001). Osteophytic overgrowth demonstrated 0.94 specificity (P = 0.0004). Facet hypertrophy was not associated with increased tracer uptake.

CONCLUSION

We identify four types of synovial architecture on T2-weighted MRI scans with overall high sensitivity for predicting SPECT positivity. These four grades likely represent a continuum of facet degeneration, from a normal to obliterated joint. One particular subtype, Grade 2, demonstrated a high specificity for SPECT and synovial fluid increase suggestive of inflammation. Facet hypertrophy was not predictive of bone scan positivity, perhaps suggesting the protective nature of a hypertrophied facet. Synovial abnormalities correlate with SPECT findings and a grading scale is proposed delineating the degeneration of a lumbar facet over time. A subtype of SPECT(+) inflamed joint is proposed. Further studies will be needed to improve our understanding of the natural history of the lumbar facet.