The arm consists of 3 bones: the humerus or shoulder, scapula and clavicle. The upper part of the humerus (head of the humerus) connects to the Glena, part of the scapula, to form the shoulder joint (glenohumeral). Glena has a fairly flat surface. Around the joint pan, the rim is attached circumferentially, which resembles a rubber gasket. The ligaments that connect the head of the humerus to the pelvis attach to this vertebra and together with it provide stability of the shoulder.
Because the Glena is flat as a plate and not as deep as a bowl, just like the hip in the hip, the shoulder joint will be much more mobile than any other joint in the body – the ball moves more easily when placed on the hip . the plate than when it is inside the cup. However, this freedom of movement puts the shoulder at risk of dislocations and instability.
Shoulder instability is a condition in which the head of the humerus leaves the surface of the acetabulum and exits the joint. The head of the humerus, usually completely leaving the surface of the acetabulum, is pushed out of its edge and thus the dislocation of the shoulder occurs. Sometimes the head of the humerus can only partially protrude from the acetabulum and then there is a dislocation of the shoulder.
What are the causes of shoulder instability?
Fall injuries leading to shoulder dislocations. During a fall, we usually extend our hand to soften the fall. When the hand touches the ground, the force of the impact will be transferred to the arm and will be pushed out of the body. When this happens, the head of the humerus can completely leave the surface of the acetabulum and move. The vertebra and ligaments attached to the vertebra are detached from the edge of the acetabulum when the head of the humerus leaves the joint. If the vertebra and ligaments have ruptured at the time of the dislocation, they will no longer heal properly in their original position. This will lead to repeated dislocation and instability of the shoulder.
Multidirectional instability: some patients, especially young women and adolescents, have generalized ligament weakness. These patients have a peculiarity, namely: they can move the joints beyond the normal limit. At shoulder level, they may feel that the joint easily leaves its place when performing simple actions, such as trying to get something from behind.
Some sports that involve lifting the arm up, such as swimming and volleyball, can lead to progressive stretching of the ligaments and an increased sense of instability of the shoulder. These patients may experience joint dislocations or total joint dislocations. In shoulder suspensions, the vertebra is usually not detached from the edge of the joint capsule, but the ligaments will be partially torn or stretched when the head of the humerus repeatedly leaves the surface of the joint capsule.
How is shoulder instability diagnosed?
In general, in patients with symptoms of shoulder instability, an orthopaedic consultation is recommended to establish a correct diagnosis. Initially, a short history will be collected from the patient, followed by a clinical examination.
It is important to determine whether the episodes of instability occurred as a result of injury or not!
In the first part of the test, the mobility of the shoulder will be checked. The arm will be positioned in different positions and it will be observed if the arm becomes unstable. The head of the humerus will be pushed into the joint in several directions to see which ligaments are stretched or which is the main direction of displacement of the shoulder.
An imaging diagnosis is also performed. An X-ray will show if there are injuries to the shoulder bones. MRI will show us detailed information about the vertebrae, tendons, ligaments and other soft parts of the shoulder.