Assessment of the Rotator Cuff Muscles: State-of-the-Art MRI and Clinical Implications.

Rotator cuff (RC) tears are a common cause of shoulder pain and, depending on the tear pattern, can substantially limit daily activities and affect quality of life. After a tendon tear, the RC muscle undergoes degenerative changes, including fatty degeneration and volume atrophy. The extent of fatty muscle degeneration has been associated with poorer functional and surgical outcomes after RC reconstruction, and the evaluation of the RC muscles is one of the most important factors for deciding whether to perform an RC repair. A variety of qualitative and quantitative methods are available to assess RC fatty muscle degeneration and volume atrophy based on MRI. This review provides a detailed overview of the RC muscle assessment, including qualitative measurements to assess the RC muscles, such as Goutallier grading, tangent sign, and fish backbone sign. Another focus is state-of-the-art quantitative MRI techniques, including chemical shift-based techniques such as single-voxel MR spectroscopy, multipoint water-fat separation, and MR relaxometry. Furthermore, the clinical relevance of qualitative and quantitative intramuscular fat assessment is addressed, and its potential importance for treatment planning and patient outcomes is discussed.