Function
The musculus subscapularis originates on the inside of the shoulder blade, the fossa subscapularis. It starts at the small hump (tuberculum minus) of the humerus and at the bony structure below (crista tuberculis minoris). The main task of the muscle is the internal rotation of the upper arm in the shoulder.
The muscle also brings the upper arm closer to the body (adduction) and can also lead it away from the body (abduction). Some muscle fibers are fused with the capsule of the shoulder joint, thereby tensioning and stabilizing the joint capsule. Since the end tendon of the subscapular muscle is very broad, it provides important protection against anterior shoulder dislocation.
If the subscapular muscle is injured in the course of a rotator cuff rupture, the usual symptoms of a rotator cuff rupture may initially occur. These include severe pain and, in the case of the subscapularis muscle, significantly restricted internal rotation of the arm. However, it is also possible that the shoulder is simultaneously “dislocated” (luxated) as part of the course of the accident.
Typical is a counter-impact on a lifted (abducted) and externally rotated arm, for example when playing handball. In such a case, the patient suffers severe pain and holds the arm slightly away from the body and supports it on the side. The mobility in the shoulder is blocked and the normal contour of the shoulder is missing.
In the X-ray examination in 2 planes, the head of humerus is no longer visible in the socket. In a magnetic resonance imaging (MRI) or magnetic resonance imaging of the shoulder, the tear of the subscapular muscle is noticeable. The function of the subscapular muscle can also be limited by paralysis of the supplying nerve (subscapular nerve).
In this case the internal rotation is also severely restricted. As a result, the palm of the hand can only be moved to the back with great effort and with the help of the other muscles.
