Relationship between shear modulus and passive tension of the posterior shoulder capsule using ultrasound shear wave...

Although shear wave elastography (SWE) has been used to indirectly measure passive tension in muscle tissues, it is unknown whether SWE can adequately evaluate passive tension in capsule tissues. This study investigated the relationship between the shear modulus and passive tension in the posterior shoulder capsule using SWE. Ten posterior middle and ten posterior inferior shoulder capsules were dissected from ten fresh-frozen cadavers; humeral head-capsule-glenoid specimens were created from each capsule. The humeral head and glenoid were immobilized with clamps in a custom-built device. Loads (0-400 g, in 25-g increments) were applied to each capsule via a pulley system; elasticity was simultaneously measured using SWE. The elasticity-load relationship of each tested capsule was analyzed by fitting a least-squares regression line to the data. Elasticity change due to creep or hysteresis effects was evaluated by comparing the elastic modulus for a 100-g load during and after the stepwise application of the loads. The observed relationship between the shear modulus and passive capsule tension was highly linear for all twenty tested capsules (p < 0.01). The mean coefficient of determination was 0.882 ± 0.075 and 0.901 ± 0.050 for the posterior middle and posterior inferior capsules, respectively. There was no difference in the shear modulus between the two 100-g load assessments for both the posterior middle (p = 0.205) and posterior inferior capsules (p = 0.161). Thus, SWE is a valid and useful method for indirectly evaluating the change in the passive tension under loading in specific posterior shoulder capsule.