Common shoulder conditions – Shoulder instability

event 24.04.2023.

The shoulder is the most mobile, but also the most unstable joint of the human body. Great mobility is necessary in order to be able to perform all daily tasks, be it work, recreation or sports. In order for this not to be a problem, it is necessary for the shoulder joint to be stable. Its mobility is enabled by an abundant articular capsule and a large disparity between the size of the head of the humerus and the joint socket of the scapula: the humeral head is 2-3 times larger than the socket.

The shoulder can be considered a complex consisting of four bones, four joints or articulations (with all stabilizing ligaments), two spaces, and more than 30 muscles and their corresponding tendons. The anatomy of the shoulder joint is very complex. The shoulder complex is an intricate structure that requires synchronized, “orchestral” movements to function properly. The shoulder complex requires healthy and ligamentously stable joints along with numerous muscles that work in synergy to enable movement of the upper limb into various positions that subject it to extreme forces and torque.

The shoulder girdle, in a broad sense, is composed of four separate but mutually coordinated and connected joints:

  1. sternoclavicular,
  2. acromioclavicular,
  3. glenohumeral, and
  4. scapulothoracic joint.

Their alignment allows the shoulder joint in the narrow sense – the glenohumeral joint – to have maximum mobility. Damage to one or more parts of the shoulder girdle impairs shoulder function. A thorough understanding of the anatomy and complex biomechanics of the shoulder is extremely important for clinicians to be accurate in diagnosing disorders, applying appropriate treatment methods, (conservative or surgical), as well as implementing appropriate rehabilitation protocols.

Pain in the shoulder area is usually the first indicator of a problem, and a correct diagnosis is essential so that the patient can start treatment as soon as possible.

The causes can be the result of hard physical work, injuries, excessive and/or improper exercise, but also due to working on a computer, driving, etc., wherein issues appear gradually without an obvious cause. The causes are really diverse, but they all require a clinical examination by an orthopedist in order to discover the real cause of the issues and symptoms.

In addition to the clinical examination itself, ultrasound (U/S) is extremely helpful in confirming the diagnosis. Also, it is important for the patient to bring associated diagnostic imaging tests such as X-rays (RTG) and magnetic resonance images (MRI) if they have been done previously.

The most common injuries and diseases of the shoulder are:

  • rotator cuff rupture
  • calcifying tendinitis and subacromial bursitis
  • frozen shoulder
  • shoulder arthrosis
  • luxation (dislocation) and shoulder instability.

Unfortunately, the stability of the shoulder is not ensured by a large congruence of bone joint bodies, such as in the hip joint, but by static dynamic stabilizers, among which the most important role is played by the capsulo-ligamentous system and the rotator cuff muscle system. It is precisely this great mobility of the hand in the shoulder joint and the very common weakness of the capsulo-ligamentary system that are the cause of the high frequency of traumatic shoulder dislocations in the population, especially the younger and sports-active population.

If the dislocation recurs, the shoulder joint becomes unstable, and each time less and less trauma is needed to cause a new dislocation. At the other end of the spectrum of people with unstable shoulders are people whose ligamentous system is inherently weaker, so they do not need an injury for the shoulder to become unstable. Most often, instability in these cases occurs due to repetitive sports or other movements.

Static stabilizers of the shoulder joint include the bony anatomy, the labrum, joint capsule, and glenohumeral ligaments. Although the glenoid surface is almost flat and is only a third of the surface of the humerus head, it still enables the concavity of the articular body in certain ways.

The glenoid labrum is a fibrocartilaginous structure that is attached along the periphery of the glenoid or cup of the scapula. The labrum is wedge-shaped, which increases the effective depth of the glenoid. The glenoid depression increased by the labrum contributes to the overall stability of the shoulder due to suction effects, as a result of the intra-articular vacuum created in the shoulder joint. The labrum contributes to stability and the rebound effect, i.e. returning the head of the humerus towards the center of the glenoid.

In the case of traumatic luxation of the shoulder, a very common consequence is damage to the labral complex, known as Bankart’s lesion, where the front edge of the labrum is damaged and the sleeve separates from the front edge of the glenoid.

The glenohumeral joint capsule is a bag-like structure that surrounds the shoulder joint. The capsule has several areas of thickening called the glenohumeral ligaments. Dislocation of the shoulder itself leads to an injury of the capsuloligamentous complex of the shoulder joint, which without proper treatment allows repeated popping of the shoulder.

When we talk about shoulders that are “inherently unstable”, we are talking about people whose capsulo-ligamentary structures are more elastic, weaker than usual, so the instability is not caused by a single traumatic moment, but is caused by repeated micro-traumas. Excessive activity can damage static stabilizers that are already genetically weaker. The resulting instability of the shoulder disrupts the synchronous mechanism between the scapula rotators and the rotator cuff muscles and leads to another aspect of instability – atraumatic, multidirectional, most often bilateral instability – and requires rehabilitation, in case of failure of which, surgery for arthroscopic duplication of the joint capsule is indicated.

The basic method of treatment is shoulder joint reconstruction. In our practice, we suggest surgery already after the second luxation in order to avoid major damage to the ligaments and bony structures of the shoulder joint, which significantly complicates the treatment later on.