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The shoulder joint is the largest joint in the upper limb that connects the humerus with the shoulder girdle. As a spherical joint it allows a very wide range of motion in all planes. Damage to the shoulder joint may, on the one hand, generate pain and limit mobility in the joint, and, on the other hand, cause instability associated with excessive relaxation and stretching of the structures surrounding it.
The shoulder joint is prone to injury and injuries because it is used quite intensively and often overused by athletes. This, combined with the large range of motion in all directions and the multitude of structures surrounding it, makes it easy to damage.
Shoulder joint - anatomy
The articular surfaces formhumeral headandscapular acetabulum . The edges of the acetabulum are surrounded by a fibrous ring - the so-calledarticular limbmade of fibrous cartilage and about 4-6 mm thick. The articular limb enlarges the acetabular surface, thus preserving the movements in the joint.
The head of the joint(i.e. the head of the humerus) is almost half of the sphere with a radius of about 2.5 cm. The border of the joint head is formed by the anatomical neck and the cartilage that covers the articular surface extends to it (this line is crossed only within the intercubular sulcus).
Due to the large difference in size between the head and the acetabulum, as well as the wide range of motion -articular capsulecreates a loose, long and voluminous bag that guides into the armpit while the arm is lowered. After visiting the limb, the loose fold is not visible, because the bag is tightening at this point.The bag is protected and strengthened by the musclesthat surround it and stick to it:
- m. podopatkowy;
- m. supraspinatus;
- m. sub-ridge;
- m. rounder smaller.
The tendons of the muscles that fuse with the articular capsule can be considered the so-called active ligaments. Apart from them, the shoulder joint capsule also hasproper ligaments , which also strengthen it, but acting passively:
- coro-brachial ligament- starts at the coccyx process of the scapula and ends at both tubercles of the humerus. It strengthens the top wall of the purse, inhibits itadduction and lifts the arm in its normal, lowered position, thus preventing the head of the humerus from sliding off the acetabulum;
- the labrum-humeral ligament- attaches, just like the bag itself, to the neck of the anatomical humerus and to the edge of the labrum. It strengthens the deep layers of the bag, mainly at the front and top. It inhibits, among others external rotation movement;
- corvoid-brachial ligament- It connects the raven's process of the scapula and the shoulder end of the collarbone. During the ascent by bending and abducting the arm above 60 degrees, it causes the blade to move (the so-called rotation of the blade).
Forvascularizationof the shoulder joint there are articular branches:
- suprascapular artery(from subclavian artery),
- anterior and posterior artery surrounding the arm ,
- subscapular artery(from the axillary artery).
The surrounding arteries fuse together to form a ring around the neck of the surgical humerus, from which numerous ascending branches feed the lower part of the joint.
The nerves are responsible for the innervation of the shoulder joint:
- superscapular ,
- podopatkowy ,
- axillary .
They all depart from the brachial plexus. These are the same nerves that supply the shoulder muscles.
Shoulder joint - functions
The shoulder joint is a free, multi-axis spherical joint. It owes its great mobility to the fact that the acetabulum is relatively small in relation to the head of the joint, and the joint capsule is spacious and loose. According to Adam Bochenek and Michał Reicher, multilateral movements in the joint can be reduced tofour basic movements :
- abduction and adduction movement- during abduction, the axillary fossa opens and the muscles work: supraspinatus, medial deltoid and long head of the two-headed arm. During adduction, the armpit closes and the muscles are activated: the greater pectoral, the long head of the triceps and the broadest spine. Abduction above the level is not possible because the adductors and the lower wall of the articular capsule tighten and the greater tubercle of the humerus rests against the shoulder of the shoulder. Raising the limb to about 150-160 degrees takes place in the collarbone joints, and the further vertical movement of the arm is taken over by the chest and spine;
- flexion and extension movement- in other words, forward and backward lifting of the limb, i.e. swinging movements. The shoulder is raised forwards mainly by the biceps muscles of the shoulder, corpus-brachial muscles and the collarbone part of the deltoid and thoracicbigger. The lifting back is performed by the muscles of the larger, broadest spine, the posterior part of the deltoid and the long head of the triceps;
- circumferential movements in the shoulder joint- is a combination of flexion and extension movements with abduction and adduction. The free end of the humerus follows a transversely oval ellipse. Circumferential movements in the shoulder joint are combined with corresponding movements in the collarbone joints, significantly increasing the range of all motion;
- rotational movements- these are movements in relation to the long axis of the humerus, i.e. inward rotation (turning) and outward rotation (inversion) of the arm. The following muscles are responsible for the rotation inwards (turning): the sub-scapular, the greater pectoral, the widest spine, the greater rounder, the biceps and the anterior deltoid muscles. Rotation outwards is performed by the muscles of the infraspinatus, the polygon lesser muscles, the supraspinatus (very slightly) and the posterior part of the deltoid.
The causes of shoulder pain and shoulder pain are as varied as the range of motion in the shoulder joint is wide. They are most often referred to aspainful shoulder syndrome ,frozen shoulderor related areadamage to the rotator cuff , which injuries and methods of their treatment you will learn from the following articles:
- Bochenek A., Reicher M., Human Anatomy, Volume I, PZWL Medical Publishing, Warsaw 2012.
- Wiszomirska I., Anatomy of the human locomotor system, AlmaMer Publishing House, Warsaw 2009.