Shoulder joint
The shoulder joint (medical: acromioclavicular joint , AC joint ; anatomical ( Latin ) articulatio acromioclavicularis ; also lateral clavicle joint) is the articulated connection between the outer end of the collarbone ( clavicle ) and the upper end of the shoulder blade ( scapula ), the so-called shoulder height ( Acromion ). The acromioclavicular joint (ACG) belongs to the real joints (diarthrosis), that is, it has a joint space, joint cartilage and a connective tissue joint capsule as a stabilizing cover .
anatomy
The right and left collarbones are anchored to the sternum ( sternum ) via the sternoclavicular joint ( articulatio sternoclavicularis ) and connected to the shoulder blade via the acromioclavicular joint. These two V-shaped parts are symmetrical and are combined to form the shoulder girdle , which rests on the upper thoracic wall . The entire upper extremity is connected to the trunk via the shoulder girdle and must therefore absorb all forces that occur between the arm and trunk (e.g. when climbing , serving in tennis ).
The acromioclavicular joint has the stability to withstand these forces, but still supports the lifting of the arm above shoulder height. However, movements in the ACG are always carried out synchronously with the sternoclavicular joint and the scapulothoracic joint ( articulatio scapulothoracalis ). The collarbone and shoulder blade are mechanically linked to one another due to the transverse tension of the ligaments. Horizontal stability is achieved primarily through the acromioclavicular ligament ( ligamentum acromioclaviculare ). Coracoclavicular ligaments ( ligamentum coracoclavicular ) provide vertical stability . A distinction is made between an anterior ( trapezoidal ligament ) and a posterior ( ligamentum conoideum ). With regard to the tear resistance , it is described that the coracoclavicular ligament is somewhat more stable. The force that is necessary to provoke a complete demolition is given as approx. 1000 N.
The two articulating joint surfaces are covered with hyaline cartilage , but do not fit exactly together. This incongruence is usually compensated for by an intermediate joint disk ( discus acromioclavicularis , Weitbrecht cartilage, named after the anatomist Josias Weitbrecht ) to protect against abrasion. However, from the age of 20, this is already worn out by everyday stress, so that no intermediate disc can be found in the majority of those over 40 years of age. Osteoarthritis of the acromioclavicular joint can be found in almost everyone over 50 years of age. This makes the shoulder joint one of the joints most frequently affected by osteoarthritis . However, the majority of patients do not experience any symptoms as a result.
Diseases of the shoulder joint
The most common injury to the ACG is an ankle joint dislocation or ACG dislocation . According to Tossy (I-III), three different degrees of severity are distinguished. Usually, a fall on the shoulder leads to overstretching or tearing of one or more ligaments, which can lead to instability of the joint. In the majority of cases, brief immobilization in a Gilchrist bandage is recommended as therapy.
A painful restriction of movement can also be an indication of osteoarthritis , but more rarely of a cyst near the joint. The therapy of ACG osteoarthritis is usually in physiotherapy and physical applications such as cold and electrotherapy . If this is unsuccessful, a resection of the shoulder joint can also be considered, for this purpose the joint surfaces are milled off on both sides of the joint and then a kind of meniscus made of the body's own material is placed between these joint surfaces to fill the gap. If everything goes well, the results are impressive, after approx. 2 months the shoulder is fully resilient and largely pain-free. This method can be minimally invasive , but this operation is often carried out openly. The chances of success are higher with the open method, but the disadvantage is the higher risk of infection and wound pain.