Glenohumeral joint

The shoulder joint ( articulatio humeri Latin, also glenohumeral joint, in veterinary anatomy and shoulder joint ) is the head of the humerus (caput humeri ) and the shoulder blade socket ( glenoid cavity, short and glenoid ) of the shoulder blade ( scapula ) is formed. Since this joint is secured primarily by muscles and the movements are hardly restricted by bony structures, it is the most mobile joint in the human body ball. This, however, are dislocations ( dislocation ) of the shoulder is relatively common, as well as muscle and tendon rupture in the rotator cuff.

• 5.1 Special features of animals

Bony structures and joint surfaces

The spherical head of the upper arm bone ( humerus) is related to the longitudinal oval shaped articular surface of the scapula ( glenoid ) in conjunction.

The glenoid is flat and shaped like a plate. It is above ( cranial) narrow and widens downward ( caudal ). It is tilted at three-quarters of the people around average 7.4 ° from the Skapulaebenen backwards ( retroverted ). The average diameter is in the sagittal plane and 25 mm in the coronal plane average 35 mm. This articular surface is compared to the humerus head (average diameter 45-48 mm) small and therefore surrounds him is not complete as it is the case for example in the hip joint, but only to a small extent. An increase in the contact area between the two joint partners is a three to four millimeters wide fibrocartilaginous pan lip ( glenoid ), which is fixed to the joint surface, which increases the contact area to the humeral head and at the same time the origin of the long head of the biceps and the glenohumeral ligaments.

The humeral head forms with the humerus shaft form an angle of 130-150 ° and is rotated by 20-30 ° relative to a line through the epicondyle of the elbow backwards ( retroverted ).

Joint capsule

The joint capsule of the shoulder joint is relatively broad and flabby. Windwärts tail ( caudal ) is located in a relaxed position about one centimeter long reserve zone ( axillary recess ), which offers a large range of motion.

The joint capsule sends a spur to the tendon of origin of the biceps brachii and thus forms a so-called capsule tendon sheath.

Bursa

Numerous bursa ( bursae ) play an important role in the function of the shoulder joint:

• The bursa musculi subtendinea subscapularis is below the tendon of the subscapularis muscle and decreases occurring between tendon and shoulder blade friction. Through an oval opening ( foramen ovale, Weitbrecht ) to communicate with the joint cavity.
• The bursa is a subcoracoid below the raven beak -like extension of the acromion ( coracoid process ) situated reserve space of the joint. It also communicates with the joint cavity.
• The subacromial bursa and the subdeltoid bursa are also known as subacromial Xenarthra. These two bursa is in the Abspreizbewegung (abduction ) of the arm, the mobility of the large upper arm bone trochanter ( greater tuberosity of the humerus ) to the shoulder height ( acromion ) guaranteed.

Bands

The shoulder joint has seen in relation to its stress a very weakly developed ligaments, consisting of only four bands: coracohumeral ligament, ligament coracoglenoidale, coracoacromial ligament and the ligaments glenohumeralia. A guided tour of bands is therefore not given.

Musculature

The management and protection of the shoulder joint is made by manner of a sleeve surrounding muscles, called the rotator cuff. It makes a much greater contribution to stability than the bands and therefore is the main fuse the joint. In addition, the tendon of the long head of the biceps brachii muscle, the deltoid muscle, the pectoralis major muscle and other muscles contribute to the stabilization and management of the shoulder.

Through the interplay of these muscles in conjunction with the freedom of movement of the shoulder joint, the highest measured speed of the human body is achieved when throwing. The removal form the biomechanical properties of this dates back to the time of Homo erectus about two million years ago.

Degrees of freedom

Due to the construction of a ball joint, the movement of the arm in all three planes and axes. A significant contribution to make mobility in humans, the other two partial joints of the shoulder girdle ( articulatio articulatio acromioclavicularis and sternoclavicularis ). Depending on the requirements to be modified by the mobility of these joints, the positions of the key (clavicle ), and the shoulder blade.

In practice it can be assumed that almost no movement of the arm due to a sole movement of the shoulder joint. The interaction of the joint group is therefore to be considered in the assessment of movement limitations. The standard values ​​follow the instructions on the measurement sheets of the German Social Accident Insurance, which are used in medical assessments:

• Transversal Anteversion to 90 ° in the shoulder joint, an elevation in addition to 150-170 ° is possible only with the cooperation of the shoulder girdle
• Retroversion to 40 °

• Abspreizbewegung (abduction ) to 90 ° at the shoulder joint, with involvement of the shoulder girdle to 180 °
• Pre- movement ( adduction) to 20-40 °

• Pronation ( internal rotation ) to 95 ° abutting to the body and arm to 70 ° with a 90 ° abgespreiztem ( abducted ) upper arm
• Eversion ( external rotation ) to 40-60 ° abutting to the body and upper arm to 70 ° with a 90 ° abgespreiztem ( abducted ) upper arm

Peculiarities in animals

In mammals which perform more walking movements, the shoulder joint is likewise a ball joint, the arrangement of the muscle, it is so far restricted in its movement, that only diffraction (flexion ) and stretching ( extension) are possible, so the joint only is moved in a direction axis (so-called AC joint).

Diseases

A relatively common injury of the joint is the joint luxation ( dislocation of the shoulder ), the humeral head jumps out of the glenoid cavity of the scapula. The reduction ( righting ) can usually be made non-operational. Sometimes can develop a habitual dislocation from a first traumatic dislocation, when the joint has become unstable. A dislocation of the acromioclavicular joint is called the acromioclavicular dislocation.

For the treatment of osteoarthritis or injuries, there is also the shoulder joint around since 1995 artificial Gelenkersätze ( endoprostheses ). The picture shows the X-ray image of an inverse prosthesis of the shoulder joint - "inverse " because the joint head on the shoulder blade and the pan was attached to the upper arm bone.