A comparative study of the behaviors of normal and frozen shoulder: A finite element study

Frozen shoulder is a common condition characterized by a stiff shoulder. Thickening of an axillary pouch and a coracohumeral ligament, which are the passive stabilizers of the shoulder joint, is widely known as a manifestation of frozen shoulder. In this study, the effect of frozen shoulder on the shoulder behavior was investigated by using five finite element shoulder models. Finite element analysis was performed for the shoulder motions. The rotational angle, strain distribution, and the stress distribution were assessed relatively. The mean rotational angle was 54.9 ± 4.5° in external rotation, 35.9 ± 2.8° in internal rotation, 21.2 ± 6.0° in adduction, and 28.2 ± 2.1° in abduction. The resultant angle was decreased 4.1° in external rotation, 4.6° in internal rotation, 1.5° in adduction, and 2.3° in abduction from the normal shoulder to frozen shoulder respectively. The thickening of the AP had more effect on the rotational motions and abduction, on the other hand, the thickening of the CHL had more effect on adduction. The overall strain distribution was similar between the normal and frozen shoulder, however, the high-strain area and the strain value were reduced in frozen shoulder.