Establishing Limits of Normal for Important Muscles and Tendons of the Rotator Cuff Using Ultrasound

Ultrasound (US) is frequently used to diagnose shoulder pathology, and can be used in an office setting to quickly and cost-effectively assess the quality of the rotator cuff musculature. Diagnostic imaging of the rotator cuff muscle quality can help determine prognosis as well as appropriate management. For instance, we know that maximum cross-sectional area (CSA) of the rotator cuff muscles is closely related to that muscle’s isokinetic strength and predicts rotator cuff pathology and surgical outcomes. Fatty degeneration of the rotator cuff is predictive of deficits in strength and function, specifically for abduction, external rotation, and internal rotation. Though the thickness or CSA of a rotator cuff can easily be obtained, there is much variation in in a healthy rotator cuff muscle’s CSA based on patient age and gender, which makes it difficult to deduce whether there is pathology based on only CSA, making a ratio involving muscle size more predictive of pathology than CSA only.

Literature suggests that use of ratios of rotator cuff CSA or thickness may be predictive of rotator cuff pathology than thickness or CSA alone, and that supraspinatus and infraspinatus size can be reliably measured under ultrasound. Therefore, we propose establishing normative measurements of three different ratio involving the rotator cuff muscles: the trapezius : supraspinatus thickness ratio, the supraspinatus : infraspinatus CSA ratio, and the infraspinatus : teres minor CSA ratio.