Quantitative assessment of thinning of the subscapularis tendon in recurrent anterior dislocation of the shoulder by use of magnetic resonance imaging

It is known that thinning and lengthening of the subscapularis tendon occur in shoulders with recurrent anterior dislocation. However, no studies have been performed to quantify the morphologic changes of the subscapularis tendon under such conditions. We retrospectively measured the thickness and cross-sectional area of the subscapularis tendon by use of magnetic resonance imaging in 22 shoulders in 11 patients with unilateral recurrent anterior dislocation of the shoulder. The contralateral shoulder in each patient served as a control. The thickness and cross-sectional area of the subscapularis on the affected side were smaller than those on the normal side (6.5 ± 1.7 mm vs 8.0 ± 1.9 mm, P = .001, and 388.6 ± 120.0 mm² vs 547.9 ± 128.5 mm², P = .0001, respectively). We conclude that the subscapularis tendon undergoes an 18.7% decrease in thickness and a 29.1% decrease in cross-sectional area in shoulders with recurrent anterior dislocation.