SHOULDER INSTABILITY

The glenohumeral joint is the most movable in our body, with a range of motion of almost 360°. It is composed of the humeral head and the glenoid cavity. The shoulder joint is mainly guided and stabilized by soft tissues (labrum, ligaments, rotator cuff), which on the one hand, allows this extraordinary range of motion, but on the other hand, makes it more prone to instability and/or dislocation. Unlike other joints, such as the hip joint, it is relatively little ‘secured’ by bony structures.

Once dislocation or subluxation has occurred, it can often be accompanied by other soft tissue and bone structure injuries. Ligaments, labrum, or tendons may be involved. Bony structures, such as the glenoid cavity or humeral head, may show abrasions. Depending on the extent of the associated injuries, surgical intervention may be considered.

With so many different terminologies, it can be easy to lose track of what’s going on. Therefore, all essential terms concerning shoulder instability are briefly explained here:

Shoulder instability: The inability to keep the humeral head centered in the socket.

Subluxation: The head of the humerus and the glenoid cavity have partial loss of contact under load. Spontaneous reduction is possible.

Shoulder luxation: the humeral head and glenoid cavity permanently lose contact.

Chronic-recurrent shoulder dislocation: the sequential condition following an initial traumatic shoulder dislocation.

Voluntary dislocation: The glenohumeral joint can be dislocated at will and in a controlled manner and repositioned by itself.

Laxity: The regular and physiological joint mobility required to perform physiological movements

Hyperlaxity (hypermobility): The increased mobility of a joint beyond the physiological level, which can lead to clinical symptoms

Shoulder instability is a broad issue because therapies and follow-up treatments must also be selected and adapted accordingly depending on the type.

A common classification for shoulder instability is that according to Gerber. Here, a distinction is made between instability and hyperlaxity (hypermobility) and indirectly between traumatic (unidirectional) and atraumatic (multidirectional) instability, whereby hyperlaxity may be combined with instability but primarily has no pathological value.

Here, I will essentially discuss the types of instabilities (cat. 2 Unidirectional instability without hyperlaxity), which can occur after a traumatic event.

Basically, 3 types of post-traumatic shoulder instability can be distinguished:

static

dynamic

voluntary

Static instability means that the humeral head is not centered in the glenoid cavity. It may have migrated either upward, backward, forward, or downward. Since it is not a complete dislocation, this is also called a subluxation.

Dynamic instability is a completely dislocated shoulder joint that has not been repositioned. Sometimes, affected individuals may perceive pain, but a limited range of motion is still present. Something like this can be observed in older patients who have had experienced, for example. 

There are instabilities after a dislocation that tend in one direction (anterior, posterior, superior, inferior). Especially people who are hyperflexible can be prone to subluxations.

Voluntary instability is understood to be the controlled dislocation of the shoulder joint. Some people can dislocate and retract the shoulder at will (e.g., contortionists in the circus).

Younger people have an increased risk of recurrent dislocation because the connective tissue is usually more flexible than older people. Although older people are not as susceptible to recurrent dislocation, damage to the surrounding tissues (rotator cuff, ligaments, tendons, cartilage, …) may occur after injury.

Dislocation is commonly very painful for the affected person. The malposition is often clearly perceived as such. After professional realignment, the pain subsides relatively quickly. After repositioning, the most common problems are described as insecurity during specific movements due to possible instability. If the shoulder is dislocated anteriorly, feelings of instability may be perceived, for example, during throwing or swimming movements. Basically, the accompanying dislocation injuries are perceived as painful (muscle, nerve, ligament, tendon, cartilage, or bone injuries) and not the instability itself.

Clarification in case of dislocation

In the acute phase, the most critical and first procedure for clarification is an X-ray to rule out injuries to the bone. This shows the position of the humeral head in the shoulder joint and the extent of the dislocation. Bone parts may rub against each other during a dislocation, whereby so-called dents can form on the bone structures involved.  These can also be seen in the X-ray.

Clarification in case of instability

Arthrography (arthro-CT) can show the extent of the injury. This is particularly important to clarify chronic instability. Here the labrum, ligaments, and tendons and the size and localization of the damage can be assessed. In addition, the size of possible bone fractures caused by the joint partners involved (humeral head and glenoid cavity) rubbing against each other can be determined even more precisely.

After a non-surgical reposition, the patient is given a sling for 2 weeks for immobilization and stabilization. During the follow-up examination, the physician determines whether further follow-up treatment is necessary.

If, for example, ‘only’ the labrum was injured after dislocation, and no bone structures were damaged, purely functional measures can be initiated depending on the extent of the injury. In the case of soft tissue injuries, surgery does not always have to be performed. Physiotherapy, mobilization, joint stabilization measures, muscle strengthening, etc., are applied in such cases. If the shoulder instability cannot be eliminated using physiotherapy and exercises, then surgery can provide relief. There are generally two types of surgery performed for instability, depending on the extent of the specific trauma:

Bankart surgery

Latarjet surgery

Bankart surgery involves using anchors and springs to reattach the labrum of the joint. This surgery is performed arthroscopically.

Practically nothing is changed on the joint surface here. Latarjet surgery can be performed when fixation of the labrum alone is insufficient for shoulder stability, or the extent of bone loss is too significant. Because bone structures must be altered in this case, the procedure is more complex than Bankart surgery, which means that this type cannot always be performed using arthroscopy.

Here, part of the coracoid process is separated and fixed to the anterior edge of the glenoid cavity with the help of screws to stabilize the humeral head in the glenoid cavity. The ‘articular surface’ is increased by the addition of the coracoid process.

Which procedure is used varies from individual to individual. Depending on the person’s activity, bone loss, flexibility, and others, the choice of procedure is decided. The recurrence of the condition is usually slightly greater with Bankart surgery than with Latarjet surgery.