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Shoulder joint

Synonyms: glenohumeral joint, articulatio humeri articulatio humeroscapularis, articulatio glenohumeralis
German: Schultergelenk

1 Definition

In the shoulder joint the head of the humerus (caput humeri) articulates with the joint surface (cavitas glenoidalis) of the shoulder blade (scapula). The shoulder joint is the most mobile ball joint of the body.

2 Construction

The spherical head of the humerus articulates with the longitudinally oval shaped glenoid cavity cavitas glenoidalis. The glenoid cavity compared to the humeral head is small, and thus does not surround the humeral head completely as is the case for example in the hip. An increase in the contact area between the two joint partners is achieved by the 3-4 mm wide glenoid labrum labrum glenoidale (pan lip) formed aound the glenoid. The glenoid labrum (labrum glenoidale) is made of fibrocartilage and is attached to the glenoid cavity.

The joint capsule of the shoulder joint is relatively spacious and loose. Caudally in a relaxed position there exists a reserve zone about 1 cm long which is referred to as the axillary recess recessus axillaris. If the arm is fixed too long in this position, the lower capsule fold shrinks and movement limitation results. For this reason, the shoulder joint in an instance of prolonged immobilisation is fixed in an abducted and slightly anteverted position.

The capsule extends cranially to the coracoid process processus coracoidus) and encloses the tendon of the long head of the musculus biceps brachii as well. The tubercles of the humerus are in contrast found outside the capsule.

3 Ligament structure

The shoulder joint, considered in relation to that demanded of it, has a very poorly developed ligament apparatus. Control via the ligaments is therefore not present. The ligaments of the shoulder joint are:

The ligaments strengthen the thin capsule cranially and ventrally. Traumatic shoulder dislocation usually occurs in a forward downward direction.

4 Muscle control

The management and protection of the shoulder joint is performed by the sleeve-like enclosing muscles - the so-called rotator cuff. It delivers a much greater contribution to stability than do the ligaments.

5 Bursa (bursae)

Numerous bursae play an important role in the functions of the shoulder joint.

The bursa subtendinea musculi subscapularis decreases friction manifested beneath the tendon of the musculus subscapularis between the tendon and scapula. Through an oval opening it links up with the joint cavity. The bursa subcoracoidea is a reserve space of the joint situated beneath the processus coracoideus. It also links up to and works with the joint cavity.

The bursa subacromialis and bursa subdeltoidea are sometimes referred to in some parts of the world as an accessory joint. However, this designation is not correct from an anatomical point of view, since there is no cartilage-covered joint surface here and thus it does not qualify as a joint. The two bursae ensure mobility of the greater tuberosity of the humerus tuberculum majus beneath the acromion with abduction of the arm.

6 Mechanics

Due to the form of construction of the ball-and-socket joint, movement of the arm is possible within limits in all 3 axes. A significant contribution to this mobility comes from the accessory joints of the shoulder girdle (articulatio acromioclavicularis, articulatio sternoclavicularis). Depending on requirements, the positions of the clavicle clavicula and scapula are modified by the mobility of the joints.

In practice, it can be assumed that hardly any movement of the arm is accounted for solely by movement of the shoulder joint. The interaction of the joint group should therefore be considered in the evaluation of movement limitations.

The ranges of motion in the different axes are indicated as follows starting in the neutral zero position:

  • transversal
    • anteversion to 90° in the shoulder joint, elevation above this (up to a maximum 170 °), assisted by the joints of the shoulder girdle, full elevation (180°) is made possible by stretching of the spine
    • retroversion to a maximum of 50°
  • sagittal
    • abduction to 90° in the shoulder joint, with involvement of the shoulder girdle and the spine to 180°
    • adduction up to 45°

See also: shoulder joint luxation, impingement, Bankart lesion, Hill-Sachs lesion

This page was last edited on 19 May 2016, at 10:11.

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