The main shoulder joint is the most mobile joint in the human body, with a range of motion of almost 360°. It consists of the humeral head and the glenoid. The shoulder joint is primarily guided and stabilized by soft tissues, including the labrum, ligaments, and rotator cuff. While this allows for an exceptional range of motion, it also makes the joint more susceptible to instability and/or dislocation. Unlike other joints, such as the hip, the shoulder joint has relatively little bony stability.

Following a dislocation or subluxation, additional injuries to the soft tissues and bony structures may occur. The ligaments, labrum, or tendons may be affected. Bony structures, such as the glenoid or humeral head, may show abrasions or defects. Depending on the extent of these associated injuries, surgical treatment may be considered.

With so many terms, it can be easy to lose track. Here, we briefly explain all the key terms related to shoulder instability:

Shoulder Instability: The inability to maintain the humeral head in a centered position within the glenoid.

Subluxation: The humeral head and the glenoid partially lose contact under load. Spontaneous reduction is possible.

Shoulder Dislocation: The humeral head and the glenoid lose contact completely.

Recurrent Shoulder Dislocation: A condition resulting from a previous traumatic shoulder dislocation.

Voluntary Dislocation: The main shoulder joint can be deliberately and controlledly dislocated and then reduced by the individual.

Laxity:Normal and physiological joint mobility required to perform normal physiological movements.

Hyperlaxity (Hypermobility): Increased joint mobility beyond the normal physiological range, which may lead to clinical symptoms.

Shoulder instability is a broad and complex topic, as the appropriate treatment and follow-up care must be selected and tailored according to the type of instability.

A commonly used classification of shoulder instability is the Gerber classification. It distinguishes between instability and hyperlaxity (hypermobility), as well as, indirectly, between traumatic (unidirectional) and atraumatic (multidirectional) instability. Hyperlaxity may be associated with instability but, in itself, is not considered a pathological condition.

There are three main types of post-traumatic shoulder instability:

• static

• dynamic

• voluntary

Static Instability means that the humeral head is not centered within the glenoid. It may have shifted upward, backward, forward, or downward. Since this does not involve a complete dislocation, it is also referred to as a subluxation.

Dynamic Instability refers to a completely dislocated shoulder joint that has not been reduced. In some cases, patients may experience pain while still retaining a limited range of motion. This can sometimes be observed in older patients who have, for example, suffered a fall.

Following a dislocation, instability may tend to occur in a specific direction, such as anteriorly, posteriorly, superiorly, or inferiorly. People who are particularly hypermobile may be more prone to subluxations.

" Voluntary Instability " refers to the controlled dislocation of the main shoulder joint. Some people are able to dislocate and relocate their shoulder at will, such as contortionists in the circus.

Younger people have a higher risk of recurrent dislocations because their connective tissue is generally more flexible than that of older people. Older individuals are less prone to recurrent dislocations, but injuries may more frequently result in damage to the surrounding tissues, such as the rotator cuff, ligaments, tendons, and cartilage.

A dislocation is often very painful for those affected. The deformity is usually clearly noticeable. Following professional reduction, the pain generally subsides relatively quickly. After reduction, the most common symptom is a feeling of insecurity during certain movements due to possible instability. If the shoulder has dislocated anteriorly, for example, a feeling of instability may occur during throwing or swimming movements. In general, the pain is caused by the associated injuries, such as injuries to the muscles, nerves, ligaments, tendons, cartilage, or bones, rather than by the instability itself.

In the acute phase, the first and most important diagnostic procedure is an X-ray to rule out any bone injuries. It shows the position of the humeral head within the shoulder joint and the extent of the dislocation. During a dislocation, bone surfaces may come into contact and rub against each other, potentially causing so-called impaction defects or “dents” in the affected bones. These can also be detected on an X-ray. 

Assessment of Instability

Arthrography (CT arthrography) can be used to assess the extent of the injury. This is particularly important when evaluating chronic instability. The labrum, ligaments, and tendons, as well as the size and location of any damage, can be assessed. In addition, the size of any possible bone fragments caused by contact between the involved joint surfaces (the humeral head and glenoid) can be determined more precisely.

Following non-surgical reduction, the patient wears a sling for two weeks to immobilize and stabilize the shoulder. During the follow-up examination, the physician determines whether any further treatment is required.

If, following a dislocation, for example, only the labrum is damaged and there are no injuries to the bony structures, purely functional treatment measures may be initiated depending on the extent of the injury. Soft-tissue injuries do not always require surgery. Treatment may include physiotherapy, mobilization, joint-stabilizing measures, muscle strengthening, and much more.

If shoulder instability cannot be adequately treated with physiotherapy and targeted exercises, surgery may be considered. In general, there are two types of surgical procedures that may be performed to treat instability, depending on the extent of the injury:

• Bankart Procedure

• Latarjet Procedure

The Bankart Procedure involves reattaching the labrum using anchors and sutures. This procedure is performed arthroscopically.

The joint surface remains largely unchanged.

Latarjet Procedure may be performed when repairing the labrum alone is not sufficient to provide adequate shoulder stability or when the extent of bone loss is too significant. As this procedure involves altering bony structures, it is more complex than a Bankart procedure and cannot always be performed arthroscopically.

In this procedure, part of the coracoid process is detached and secured to the anterior rim of the glenoid with screws. This provides additional stabilization of the humeral head within the glenoid. The “joint surface” is enlarged by transferring the coracoid process to the glenoid rim.

The choice of procedure varies from person to person. The decision depends on factors such as the individual’s activity level, bone loss, flexibility, and other considerations. The risk of recurrence is generally slightly higher following a Bankart procedure than after a Latarjet procedure.