The relationship between strength and width of the supraspinatus: An isokinetic and ultrasonographic study

Quantitative assessment of supraspinatus (SSp) strength can add substantially to the understanding of the underlying pathomechanics and recovery status of this critically important shoulder joint muscle. Since strength measurement of the SSP is an involved procedure which at times could be contraindicated, obtaining indirect but well correlated evidence in the form of muscle dimensional size may be an alternative method. The objective of this study was therefore to examine the relationship between SSp size and strength in a group (n = 16) of asymptomatic normal male adults. Strength during rotations, external (ER) and internal (IR), of the shoulder joint was measured using isokinetic dynamometry. The representative morphological dimension of the SSp was its width as calculated from ultrasonographic imaging of the longitudinal cross section. The main findings indicated a moderate to strong correlation with ER strength (r = 0.65 to 0.85). In contrast, no parallel association was indicated with respect to IR. Similar patterns were found for the right and left shoulders. It is concluded that ultrasonography of the SSp can furnish valuable information about the strength of this muscle in asymptomatic subjects. However, clinical studies are essential for vindication of this technique with respect to symptomatic shoulders affected mainly with rotator cuff dysfunction.