MRI-based degeneration grades for lumbar facet joints do not correlate with cartilage mechanics

Background: Lumbar facet joint arthritis is characterized by degeneration of articular cartilage, loss of joint spacing, and increased boney spur formation. These signs of facet joint degeneration have been previously measured using destructive biochemical and mechanical analysis. Nondestructive clinical evaluation of the facet joint has also been performed using MRI scoring, which ranks the health of the facet joint using the Fujiwara scale. However, nondestructive clinical evaluation of facet joint arthritis using standard MRI scoring provides low resolution images which result in high interobserver variability. Therefore, to assess the accuracy of nondestructive MRI analysis with regard to the health of the facet joint, this study determined whether any correlations existed between lumbar facet joint articular cartilage mechanics, facet articular cartilage biochemical signatures, and Fujiwara scores. Materials and Method: To accomplish this aim, human cadaveric lumbar spines were obtained and imaged using T1 MRI, then independently scored by three spine researchers. An osteochondral plug from each of the L2 thru L5 facet joints was obtained and loaded under unconfined compression. Results: The experiments showed no trends between histological images and changes in the Fujiwara score. The mechanical properties of articular cartilage (thickness, Young's modulus, instantaneous modulus, and permeability) also had no correlations with the Fujiwara score. Conclusions: These results show that the current Fujiwara score cannot accurately describe the biomechanics or biochemical composition of facet joint articular cartilage.