2015 ISAKOS Biennial Congress ePoster #2112

Posterior Shoulder Capsules Elasticity Negatively Correlates with Glenohumeral Internal Rotation

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Abstract:

Introduction

During the follow-through phase of pitching, the posterior rotator cuff and capsule endures significant distraction forces (1). Repetitive microtrauma, due to overhead throwing and subsequent tissue healing, are thought to thicken the posterior shoulder capsules (2). Thomas et al. reported that the posterior capsule was thicker on throwing shoulders than on non-throwing shoulders and a negative relationship existed between hypertrophied posterior capsules and the loss of glenohumeral internal rotation (2). However, the hardness of the thickened capsules was unknown. The purpose of this study was to investigate the elasticity of the posterior shoulder capsules and its relationship between glenohumeral internal rotation.

Methods

Forty-five male collegiate baseball players (mean age, 19.7 year) were examined during the off-season. There were thirteen pitchers and thirty-two field players. One orthopaedic surgeon obtained all sonograms using Aixplorer® (SuperSonic Imagine, Aix-en-Provence, France), which can measure the tissue elasticity quantitatively without probe compression.
The subjects were seated upright on a stool with the shoulders in the same neutral position used by other ultrasonographic researches (2). The linear array transducer was placed on the posterior aspect of their shoulder. The thickness and elasticity of the posterior capsule were measured at a location 5-mm laterally from the edge of the labrum.
Then the subjects were placed in the supine position and glenohumeral internal rotation at 90 degrees abduction was measured with the scapula being stabilized by the tester’s hand.
For statistical comparisons between the throwing and non-throwing shoulders, a paired t test was performed with significance set at P < 0.05. The relationship between the posterior capsule thickness/elasticity and glenohumeal internal rotation was analyzed by Pearson’s Correlation Coefficient. All data are reported as the mean±standard deviation.

Results

The average thickness and elasticity of the posterior capsules were 1.34±0.20 mm and 40.0±5.5 kilopascals on the throwing side and 1.04±0.09 mm and 32.2±5.7 kilopascals on the non-throwing side. Glenohumeral internal rotation was 41.7±11.7 degrees on the throwing side and 67.6±9.0 degrees on the non-throwing side. Both the thickness and elasticity of the posterior capsules were significantly greater and internal rotation was significantly smaller (P < 0.01) on the throwing side than on the non-throwing side.
Significant negative correlations were found between glenohumeral internal rotation and posterior capsule thickness/elasticity (-0.53, P < 0.001; -0.61, P < 0.001, respectively)

Discussion

Shear-wave ultrasound elastography (SWUE) is a relatively new real-time diagnostic imaging technique. Besides thyroid and abdominal organs, the elasticity of muscle and tendon has been measured using SWUE in healthy populations (3).
The present study demonstrated that the posterior capsule was thicker and harder on the throwing shoulder than on the non-throwing shoulder. Moreover, the elasticity correlated more strongly with the loss of glenohumeral internal rotation than the thickness of the posterior capsules.

References:
1. Burkhart SS, et al. Arthroscopy. 2003; 19: 404-420.
2. Thomas SJ, et al. J Shoulder Elbow Surg. 2011; 20: 708-716.
3. Arda K, et al. Am J Roentgenol. 2011; 23: 532-536.