Quantitative evaluation of natural progression of fatty infiltration and muscle atrophy in chronic rotator cuff tears without tear extension using magnetic resonance imaging

Abstract

BackgroundThe pathology of and mechanisms underlying muscle degeneration remain unclear. We aimed to quantitatively evaluate the natural changes in fatty infiltration and muscle atrophy in patients with chronic rotator cuff tears using 3-dimensional 2-point Dixon magnetic resonance imaging (MRI). MethodsThirty patients with nonoperatively observed rotator cuff tears without tear extension were evaluated using multiple MRI examinations with a minimum interval of 2 years. The fatty infiltration ratio (%fat) and muscle volume of the rotator cuff muscles were compared between the two examinations in those with supraspinatus tear <2 cm (<2 cm SSP group), supraspinatus tear ≥2 cm (≥2 cm SSP group), and massive tear (massive group). The supraspinatus (SSP), infraspinatus and teres minor (ISP+TM), and subscapularis (SSC) muscles were evaluated. ResultsThe massive group showed a significantly greater %fat than the <2 and ≥2 cm SSP groups in the SSP (P=0.002) and ISP+TM muscles (P<0.001). The total muscle volume did not differ among the three groups for all rotator cuff muscle components. The %fat values did not change in any rotator cuff components during the follow-up period in all groups. The total muscle volume in the massive group significantly decreased in the SSP (P=0.018) and ISP+TM muscles (P=0.013). ConclusionThe present results indicate that fatty infiltration of the torn muscle occurs in the early phase after a rotator cuff tear, whereas muscle atrophy appears to progress gradually in chronic rotator cuff tears. Early intervention before muscle degeneration should be considered if the tear involves the infraspinatus tendon.