Definition shoulder joint
The shoulder joint (Articulatio humeri) connects the upper arm (humerus) with the shoulder blade (scapula). It is enclosed by a joint capsule, has few ligaments and is mainly secured by the strong musculature (rotator cuff).
Function
The shoulder joint, also known as the humeroscapular joint, is a ball and socket joint with three degrees of freedom. Firstly, the arm can be moved forward or backward in the shoulder. This is called anteversion or retroversion.
In addition, the arm can be spread out or put on the body (abduction/adduction) and turned inwards or outwards (internal rotation/external rotation). The sternoclavicular joint (Articulatio sternoclavicularis), the acromioclavicular joint (Articulatio acromioclavicularis) and two secondary joints (subacromial secondary joint and shoulder blade thorax joint) are also involved in the range of motion of the shoulder. However, the shoulder joint contributes by far the largest share to the range of motion. The triangular muscle (deltoid muscle) and the rotator cuff, consisting of the supraspinatus, infraspinatus, subscapular and teres minor muscles, are the most important muscles of the shoulder.
Anatomical structure
The shoulder joint is formed by the head of the upper arm (caput humeri) and the elongated joint portion of the shoulder blade (scapula), which is also called cavitas glenoidalis and forms a concave surface. At the lower edge of this surface there is a lip of fibrous cartilage (Labrum glenoidale), which serves to enlarge the cavitas. The head of this ball joint is many times larger than the socket. This disproportion allows a large range of motion, but at the expense of stability. This is ensured by a fixed muscle belt (rotator cuff).
Joint capsule and ligament protection of the shoulder joint
The joint capsule of the shoulder joint originates at the humerus, encloses the humeral head and the joint space and attaches to the outer surface of the shoulder blade. It is relatively wide and, when the arm is hanging down, has a bulge in the armpit area called the axillary recessus. This bulge serves as a reserve fold, which is used especially during spreading movements. Since the joint capsule is very thin, it is reinforced in the anterior region by three ligament structures (Ligamenti glenohumeralia superius, medial and inferius) and in the upper region by the Ligamentum coracohumerale. These ligaments extend from the humeral head to the shoulder blade.
All articles in this series:
