The shoulder consists not only of the glenohumeral joint (humeral head in the glenoid cavity) but also of the scapula joint with the thoracic wall (scapulothoracic joint), the joint between the scapula and the clavicle (acromioclavicular joint) and finally the joint between the clavicle and the sternum (sternoclavicular joint).
The movement of the shoulder means that the scapulothoracic joint should move just as the glenohumeral joint.
During this movement the glenohumeral joint moves so that the humeral head rotates in the glenoid cavity.
Using the upper extremity above the level of the head, for example at work or in sports, charges the joints that stabilize the head in the glenoid cavity.
The normal head is larger than the glenoid cavity.
This anatomy, which is similar to a golf ball in its original position before the shot, allows for the wide range of movements required for motion.
The glenoid cavity becomes wider and deeper with the help of a flexible cartilage rim around its perimeter.
This increases stability by making the glenoid cavity larger and deeper.
The cartilage also acts as a fixing point for the joints that stabilize the shoulder joint during movement.
The shoulder joints cross the space between the humeral head and the glenoid cavity and act by limiting the head over-sliding in the glenoid cavity, as well as the rotation of the head in the glenoid cavity.
The main joint called the inferior glenohumeral joint is similar to a hammock.
It protects the humeral head in the same way that a hammock protects an individual.
The role of the glenohumeral joints is to act as seat belts and airbags on the shoulder by restricting extensive rotational movements and head slides outside the glenoid cavity.
Much of the stability during normal movement is achieved by compressing the head into the glenoid cavity with the rotator cuff muscles.
The joints provide static stability as they passively restrict movement, while the rotator cuff muscles provide dynamic stability by pressing the head and the glenoid cavity together.
Normal movement is highly varied as some individuals have loose joints and ligaments although they do not have shoulder instability while others have relatively tight joints and exhibit less joint mobility.
What is shoulder instability?
Shoulder instability occurs when the humeral head moves out of the glenoid cavity during shoulder movement.
This is associated with symptoms that are typically pain and a sense of a lift.
If the head is completely out of the glenoid cavity then this is called dislocation.
If the head is partially out of the glenoid cavity then this is called subluxation.
Shoulder instability can occur as a result of just one real event such as a fall or tackling. It can also occur as a result of repetitive movements that stretch the shoulder joints allowing the head to move partially out of the glenoid cavity.
Although flexibility or looseness of the shoulder is a normal feature of its function some individuals are more likely to have shoulder instability due to the normal looseness of their joints.
Other people may have the ability to dislocate their shoulder by selectively contracting the muscles around it.
These rare cases usually have no symptoms of pain.
Some patients may have a hypoplasia of the glenoid cavity which is a congenital failure of the glenoid cavity to develop in normal shape and depth.
This is a rare condition and may not occur until the second or third decade of human life.
Shoulder instability mainly occurs on the anterior surface, although in about 10% of patients it may occur on the posterior surface.
In another 5-10% of cases instability may occur on more than one axis. This is called instability on multiple axes.
Traumatic anterior shoulder instability
Most cases of shoulder instability occur as a result of a simple traumatic event, such as a fall or a collision in sports.
The upper extremity is often out of its anatomical position, but some patients may not remember the exact position of their upper extremity.
When this happens, the patient may feel the shoulder coming out of the joint or may simply experience pain.
It is not uncommon to have the feeling of a dead upper extremity, where the patient experiences a loss of sensation and control of the upper extremity.
The shoulder may be completely out of the joint (dislocation) or may be partially moved out of the joint (subluxation).
Sometimes the head dislocation may be restored automatically or the patient may discover that it can be placed into position by shaking the shoulder.
If the shoulder remains dislocated it is necessary to refer to a hospital emergency room so that a doctor can relocate the shoulder back in place.
This is usually achieved by intravenous muscle relaxants so that the muscles relax and with gentle manipulation the humeral head is relocated in place.
What is injured when the shoulder is dislocated?
When sufficient force is applied to the shoulder and dislocation occurs, one or more injuries can occur in the ligaments or cartilage of the shoulder.
The most common injury is called Bankart rupture.
This is a separation of the cartilage from the tip of the glenoid cavity.
The result of this injury is the detachment of the adhesion point of the main (inferior) glenohumeral joint.
In addition, the cartilage that deepens the glenoid cavity is also destroyed.
In some cases the joint may be stretched separately or in combination with a Bankart rupture.
Ultimately the joint can actually be microscopically fractured.
The brachial plexus is a nerve cluster that runs through the anterior surface of the shoulder and when the femoral head is dislocated, it can exert pressure on the nerves of the brachial plexus.
This can lead to weakness and a lack of sensitivity (numbness).
This can affect one or more nerves of the grid.
The most common mesh affected is the axillary, which provides sensation along the lateral surface of the shoulder and also carries electrical impulses to contract the deltoid and to raise the upper extremity above head height.
In about 80% of these cases, nerve injuries recover completely, but recovery can last for months.
Rotator Cuff Injuries
Rotary pedal ruptures can occur in patients over 40 years of age following a traumatic event.
However, such ruptures are rare in younger people.
The reason for this is that along with aging the tendon of the rotator cuff weakens and can actually be ruptured when stretched, as in the case of shoulder dislocation.
It is very important for the doctor to carefully evaluate the strength of the rotator cuff muscles after a dislocation and if a tendon injury is suspected a magnetic resonance imaging should be performed.
In some cases of serious injury, the tip of the glenoid cavity may be fractured or the insertion of the rotator cuff on the greater tubercle of the humeral head may be dislocated.
In the event of multiple recurrences of the shoulder dislocation and especially if one or more failed fixation procedures have been preceded, an injury on the rim of the glenoid cavity may occur, as well as a protrusion on the back of the head of the humeral head. This injury is called Hill-Sachs injury.
Treatment of traumatic anterior shoulder instability
Conservative therapy with physiotherapy:
If an acute dislocation occurs, the shoulder is immobilized on a splint for a period of time, so that pain and inflammation may subside.
The length of time that the upper extremity should be held stationary has been a subject of controversy.
Although some surgeons suggest 3 weeks of immobilization, which will reduce the likelihood of relapse, more recent studies have shown that this is not entirely the case.
In addition, the period of immobilization does not affect the risk of future relapse.
So, the treatment we recommend consists of immobilization for 1 or 2 weeks, followed by physiotherapy program to repair the muscles around the muscle ring.
If the patient is an athlete, the physiotherapy program continues until muscle strength is restored and there is no pain or concern for the patient regarding the dislocation when the upper extremity exits immobilization period.
The athlete’s return to sports is then allowed and considered safe.
However, there is a risk of relapse of instability, especially in young male athletes.
Immobilization can be used to create a feeling of security in the athlete, but there is no evidence that this will prevent another episode of instability.
The probability of relapse is mainly related to age so that a patient who is 40 years old has less than a 50% chance of relapse while a 17 year old patient may have a probability of more than 90%.
Surgical stabilization of shoulder instability
Surgical stabilization is indicated when instability recurs and becomes a chronic problem.
The decision to undergo surgery after an initial episode must be assessed with a number of indications in mind.
If there has been a fracture of the glenoid cavity, which remains dislocated, then the surgery is indicative of restoring the stability and continuity of the joint.
In the absence of a fracture, the individual risk of instability and how it affects the patient’s sport or activity in general should be taken into account.
If an athlete is young and involved in physical contact, such as in a combat sport, it should be made clear that conservative rehabilitation may increase the risk for a second dislocation and if this happens during the racing season then this may mean the end of the racing season for the athlete.
An alternative option in this case could be to schedule a surgery out of the racing season, thereby ensuring a lower risk of instability in the following racing season.
Arthroscopic versus open method of rehabilitation
When there is no bone injury, the goal of surgery is to restore stability by repairing the Bankart rupture and any other joint extension or rupture.
In most cases this can be performed with arthroscopic surgery, which involves the placement of anchors (plastic, metal or absorbable) on the rim of the glenoid cavity.
The stitches from these anchors are then arthroscopically inserted into the cartilage and the articular fibrous capsule.
This restores the tension of the joints and restores the lost depth of the glenoid cavity caused by the bancart rupture.
Advantages of arthroscopic restoration over open surgery
Modern techniques and technology allow the results to be equivalent in both methods.
However, there are great advantages for the arthroscopic method.
These include less pain than open surgery and the ability to perform surgical operations under local anesthesia.
In arthroscopic surgery there is no need to disrupt normal tissues such as the rotator cuff, which may not be possible in open surgery.
In addition, the risk of infection is theoretically lower in the arthroscopic than in the open method.
When is open surgery indicated?
In more than 90% of cases, arthroscopic surgery is possible.
In the remaining 10% of cases, open surgery may be needed when dealing with bone loss or a ligament injury (rarely).
In the case of bone loss along the anterior wall of the glenoid cavity a bancart-type restoration of soft tissue is highly likely to fail.
Instead, open surgery should be attempted.