Anterior deltoid muscle tension quantified with shear wave ultrasound elastography correlates with pain level after reverse shoulder arthroplasty.

INTRODUCTION: Reverse shoulder arthroplasty (RSA) leads to medialization and distalization of the centre of rotation of the shoulder joint resulting in lengthening of the deltoid muscle. Shear wave ultrasound elastography (SWE) is a reliable method for quantifying tissue stiffness. The purpose of this study was to analyse if deltoid muscle tension after RSA correlates with the patients' pain level. We hypothesized that higher deltoid muscle tension would be associated with increased pain. MATERIAL AND METHODS: Eighteen patients treated with RSA were included. Constant score (CS) and pain level on the visual analogue scale (VAS) were analysed and SWE was performed on both shoulders. All three regions of the deltoid muscle were examined in resting position and under standardized isometric loading. RESULTS: Average patient age was 76 (range 64-84) years and average follow-up was 15 months (range 4-48). The average CS was 66 points (range 35-89) and the average pain level on the VAS was 1.8 (range 0.5-4.7). SWE revealed statistically significant higher muscle tension in the anterior and middle deltoid muscle region in patients after RSA compared to the contralateral non-operated side. There was a statistically significant correlation between pain level and anterior deltoid muscle tension. CONCLUSION: SWE revealed increased tension in the anterior and middle portion of the deltoid muscle after RSA in a clinical setting. Increased tension of the anterior deltoid muscle portion significantly correlated with an increased pain level. SWE is a powerful, cost-effective, quick, dynamic, non-invasive, and radiation-free imaging technique to evaluate tissue elasticity in the shoulder with a wide range of applications. LEVEL OF EVIDENCE: Diagnostic study, Level III.

The application of ultrasound elastography in the shoulder.

Ultrasound elastography (EUS) is a recently developed method for the assessment of tissue elasticity by applying mechanical stress and subsequently analyzing tissue displacement with ultrasound. To date, mainly two different techniques are used in clinical practice: strain (compression) EUS and shear wave EUS. However, shear wave EUS has been shown to be more examiner independent and more reliable as this technique allows a quantitative measurement of tissue elasticity. There is increasing evidence that EUS can be used to evaluate mechanical properties of musculoskeletal tissue. Thus, it might be a powerful tool to detect and to monitor pathologic processes affecting the shoulder girdle. As ultrasound is an essential clinical tool for the examination of the shoulder, this review describes the two most important EUS techniques available for clinical use, presenting the published evidence on the applications of EUS for the evaluation of pathologic processes affecting the shoulder joint. In addition, technical issues, limitations, and future perspectives of these methods for the assessment of the shoulder are outlined.