Facet joint osteoarthritis is considered a consequence of the aging process; however, there is evidence that it may be associated with degenerative changes of other structures. The goal of this study was to investigate the correlation between lumbar multifidus muscle features and facet joint osteoarthritis. This retrospective study included 160 patients who had acute or chronic low back pain and were diagnosed with facet joint osteoarthritis on computed tomography scan. Morphometric parameters, including cross-sectional area, muscle-fat index, and percentage of bilateral multifidus asymmetry at L3-L4, L4-L5, and L5-S1, were evaluated with T2-weighted magnetic resonance imaging. Patients with facet joint osteoarthritis had a smaller cross-sectional area and a higher muscle-fat index than those without facet joint osteoarthritis (P<.001). In multivariate regression analysis, older age and higher muscle-fat index were independently associated with facet joint osteoarthritis at all 3 spinal levels (P<.001). Smaller cross-sectional area was independently associated with facet joint osteoarthritis only at L4-L5 (P=.005). Asymmetry of the bilateral multifidus cross-sectional area was independently associated with facet joint osteoarthritis at L5-S1 (P=.009), but did not seem to be responsible for asymmetric degeneration of the bilateral facet joints. A higher multifidus muscle-fat index was independently associated with facet joint osteoarthritis, and bilateral multifidus size asymmetry was associated with the development of facet joint osteoarthritis at L5-S1. It seems more accurate to consider facet joint osteoarthritis a failure of the whole joint structure, including the paraspinal musculature, rather than simply a failure of the facet joint cartilage. [Orthopedics. 2017; 40(5):e793-e800.].
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