The nature of the dislocation of the shoulder joint
Everyone knows that the shoulder joint is the loosest of the joints of the human body and no other can be compared with it in mobility. At the same time, its structure is very unstable – basically, this joint is supported by soft tissues that control its movements and at the same time limit them. Due to such high mobility, the shoulder joint is susceptible to various injuries, especially if the load falls on it at the moment when it is in an unfavorable position from the point of view of biomechanics of movements.
One of these injuries is a dislocation of the shoulder joint, that is, the exit of the head of the humerus from the articular cavity of the scapula. With a dislocation, the soft tissues of the shoulder supporting the joint cannot hold the joint in an anatomically correct position, which leads to a significant decrease in the stability of the shoulder joint.
Another type of injury, subluxation, also leads to loss of stability of the shoulder joint and interferes with the normal movement of the head of the humerus in the articular cavity. With subluxation, a partial displacement of the head of the humerus from the articular cavity occurs. A subluxation can also be called a situation in which the head of the bone first leaves its position in the joint, and then returns.
The shoulder joint is essentially spherical – the head of the humerus rotates freely in the articular cavity. The problem is that if we pay attention to the structure of the articular cavity of the scapula, we will see that it is very small and, most importantly, flat – it does not encircle the head of the humerus. That is why this head can very easily come out of the cavity – a special effort is not required for this.
The joint lip of the shoulder joint, which is a ring of fibrous cartilage, joins the edge of the articular fossa of the scapula. This cartilage slightly deepens the articular cavity, which should protect the joint from dislocations, but they still happen.
In practice, doctors most often encounter anterior dislocation of the shoulder joint. With such an injury, the head of the humerus moves forward relative to the articular cavity of the scapula. The combination of such movements as abduction and rotation of the humerus outward most often leads to an anterior dislocation.
The shoulder joint is surrounded by many ligaments – they work together to form a kind of joint capsule. The tissue of the joint capsule is often indistinguishable from the tissue of the ligaments surrounding the shoulder joint. However, in anatomy, some of these ligaments have separate names. One of the most important structures of the shoulder joint that impede the anterior dislocation of the shoulder is the lower joint-brachial ligament. With anterior dislocation of the shoulder, this ligament is excessively stretched or stretched.
The lower joint-brachial ligament is attached to the lower border of the joint lip of the shoulder joint. If this ligament is subjected to excessive stretching, it can stretch the articular lip from the edge of the articular cavity of the scapula. Such an injury is called Bankrat damage. It is often accompanied by anterior dislocation of the shoulder joint, and you need to work with it after the dislocation is repaired.
Another structure consisting of soft tissues and playing a crucial role in holding the humeral head from the anterior dislocation is the tendon of the long head of the biceps of the shoulder. This tendon is attached to the superarticular tubercle of the scapula, and some of its fibers are attached to the upper portion of the joint lip of the shoulder joint. Since this tendon passes through the front of the humeral head, it helps keep it from moving forward, that is, the front dislocation.
With anterior dislocation of the shoulder, the biceps tendon can pull the upper part of the joint lip of the shoulder joint so that it completely moves away from the upper part of the joint fossa of the scapula. Such an injury is called SLAP damage or SLAP syndrome (from the English Superior Labrum Anterior Posterior, anteroposterior damage to the upper joint lip of the shoulder joint). Behind this acronym is the separation of the upper part of the joint lip of the shoulder joint and its movement anterior and posterior. With such an injury, the normal functioning of the biceps muscle of the shoulder and its tendon is disrupted – it no longer holds the head of the humerus in the correct position. Therefore, the stability of the joint is violated, which in the future can lead to dislocation.
So, we figured out the nature of the dislocation of the shoulder joint, and tomorrow we will analyze the main methods of diagnosing this problem and the key factors that increase the risk of injuries of this kind.