Understanding traumatic shoulder instability

Traumatic shoulder instability is the term for dislocating your shoulder with force, creating damage to the structures of your shoulder joint.

A traumatic shoulder dislocation occurs when the head of your upper arm bone (humerus) pops out of your shoulder joint due to the force of a trauma. The shoulder joint is especially prone to dislocation as it is a ball and socket joint with a very shallow socket. This allows for greater movement but also increases the risk of dislocation. 

In over 95% of shoulder dislocations, the humerus pops forward out of the joint (anterior shoulder dislocation) while in a minority of cases it pops backwards (posterior shoulder dislocation). 

In either case, the shoulder joint is damaged, normally injuring the bumper around the shoulder joint (labrum) and sometimes the bone of the joint socket as well, along with creating a ‘dent’ in the head of the humerus. This damage makes it more likely that the shoulder will dislocate in the future — this is known as traumatic shoulder instability. 

Causes of traumatic shoulder instability

Traumatic shoulder instability commonly occurs in sports, particularly contact sports (eg rugby, boxing) and sports involving forceful overhead arm movements (eg throwing sports, basketball, gymnastics, tennis). 

In traumatic anterior shoulder instability, the shoulder tends to dislocate when force is applied that drives the arm into an abduction external rotation position (ie the high-five position). This could occur in a tackle in rugby, a block in basketball or when a punch is blocked in boxing. Shoulder dislocations can occur whether you are an elite athlete or an amateur. 

Common causes of traumatic posterior shoulder instability, where posterior shoulder dislocation occurs, are, once again, contact sports, eg during rugby if a player is carrying the ball in one hand and is either tackled hard or hits the ground hard in that position, forcing the humerus bone backwards out of the socket. 

Epileptic fits are also associated with posterior shoulder dislocations, although they still more frequently cause anterior shoulder dislocations. Uncontrolled epilepsy can create significant challenges in the management of traumatic shoulder instability.

In addition to sports and epilepsy, due to the inherent vulnerability of the shoulder to dislocation, any significant trauma, such as road traffic accidents can also lead to traumatic shoulder instability, with anterior or posterior dislocation occurring depending on the forces directed on the shoulder at the time of the accident.

Who is at risk of traumatic shoulder instability?

The under 30 years old age group, particularly if they play contact or overhead sports or have epilepsy, are most at risk of traumatic shoulder instability. In these individuals, after an initial traumatic shoulder dislocation, the chances of a future dislocation are around  60% or higher. If they play contact sports, that risk may rise to 90% or higher. 

The highest risk group of all is adolescence. A first-time traumatic anterior shoulder dislocation in a promising young rugby player, for example, can be considered a career-threatening injury. Young individuals with hypermobile joints, colloquially referred to as being ‘double-jointed’, are also at greater risk of traumatic shoulder instability.

The situation is different in older individuals. Traumatic shoulder dislocations often occur due to a simple fall but can occur in individuals still competing in contact sports. In most cases, unlike the younger age group, they are not subsequently at greater risk of another shoulder dislocation in the future. However, they are at risk of sustaining a rotator cuff tear during their fall, which can cause weakness in the arm, soreness and an inability to elevate their arm. This rotator cuff injury can often be missed in A&E departments as this damage can’t be seen on X-ray. Consequently, the British Elbow & Shoulder Society has published guidance that all individuals aged between 40–60 years should be offered an MRI scan or ultrasound scan of their shoulder after traumatic dislocation of the shoulder. 

Older individuals are also at greater risk of small fractures of the head of the humerus from a dislocation. 

When to seek help

It is important to get your humerus back into your shoulder joint as soon as possible, so you should go to A&E where a doctor can treat your dislocated shoulder. You may also need an X-ray to check if you have sustained a fracture.

Treating traumatic shoulder instability

Physiotherapy and surgery both play an important role in traumatic shoulder instability. 

Physiotherapy helps individuals gain greater control and strengthen the shoulder to make further dislocations less likely. 

Ultimately, when you seek a specialist opinion about traumatic shoulder instability, you will undergo a risk assessment. Your surgeon may suggest shoulder stabilisation surgery, based on your risk of re-dislocation. However, often your doctor will still recommend physiotherapy to restore your range of movement first and improve your confidence in moving your shoulder before and certainly after your surgery. 

What does stabilisation surgery involve?

The type of stabilisation surgery, certainly for traumatic anterior shoulder instability, will depend on a number of factors, which are quite well summarised by a clinical measure called the Instability Severity Index Score. This includes: 

• Age
• Whether you play contact or overhead sports
• The level at which you play these sports 
• Whether you have hypermobile joints
• Whether you have significant damage to the bony edge of the socket
• How big the ‘dent’ in the head of the humerus bone is

For posterior shoulder instability, similar factors are considered, but how much your socket points backward and therefore your susceptibility to posterior dislocation (medically known as the version) is also very important.

Arthroscopic versus open soft tissue stabilisation surgery

When the appropriate type of surgery is selected, there is no difference in the outcomes between arthroscopic (keyhole) versus open stabilisation surgery for soft tissue problems ie when your shoulder labrum is knocked off and needs to be reattached to the bone. Soft tissue stabilisation surgery reduces the chances of future dislocation from 60–90% to around 8%. 

Surgery for dislocations associated with damage to the bony rim of the shoulder socket

If you have lost a significant amount of bone from the rim of your socket, soft tissue stabilisation is much more likely to fail. In these cases, it is important to replace this lost bone from the front of the socket, along with reattaching the labrum. 

Broadly speaking, bone can be replaced in one of two ways: the Latarjet procedure or a free bone graft.

The Latarjet procedure involves transferring a bit of bone from part of your shoulder blade called the coracoid to the area where bone has been lost. In transferring part of this bone, the tendons attached to it and the nerves running through and/or close to this, are also moved.

A free graft involves transferring a piece of bone from elsewhere in your body, most often from the pelvis or alternatively from the end of your collarbone, to where the bone has been lost. This bone can be attached, just as in the Latarjet procedure, by using screws or endobuttons (titanium buttons attached to strong stitches). 

These procedures can be done via traditional open surgery or arthroscopically by making small holes in your shoulder. There may be potential benefits to the arthroscopic techniques, as well as the use of endobuttons. 

Arthroscopic techniques tend to cause less damage to the surrounding soft tissues in the area and this may speed up recovery, but more importantly may make further surgery, if required, a bit easier. 

Further surgery may be required due to re-dislocation and in certain cases, if a person has dislocated their shoulder many times before their stabilisation surgery, they may go on to develop arthritis in their joint, which could require shoulder replacement in the future. 

Fixation of bone grafts with screws has risks including lysis (resorption of bone around the screws) and poor healing of the bone graft. Endobuttons with sutures may be a solution to this problem.

Surgery for posterior shoulder instability

Traumatic posterior shoulder dislocation can often be treated without surgery. However, if you continue to experience pain or posterior shoulder dislocations, surgery may be recommended. It can be performed in the same way as for anterior shoulder soft tissue shoulder stabilisations. Similarly, in the case of bone loss from the posterior rim of the socket ie the labrum, the lost bone can be replaced as required.

Individuals who have significant retroversion of their socket ie where the socket faces more backward making them more susceptible to posterior shoulder dislocation, along with traumatic posterior instability, may be recommended to have posterior glenoid osteotomy surgery. This involves creating a break on one side parallel to the socket and then inserting a bone graft to wedge it open and therefore correct the retroversion of the socket. The labrum is then also repaired.

Risks of stabilisation surgery

Every surgery comes with risks, such as bleeding, infection and nerve damage as well as that 8% risk of re-dislocation.

Risks specific to stabilisation surgery will depend on the type of surgery you have. For example if you have a bone graft, it may not fully heal, or there can be complications with the metalwork used to fix the graft.

There is also a chance of developing a frozen shoulder post-operatively. This can occur with open or arthroscopic surgeries, but in arthroscopic surgery research has quantified this risk as being in the region of 5%. To relieve this, you will most likely need a special type of high-volume injection, physiotherapy and possibly further surgery to restore your range of movement. 

Recovering from stabilisation surgery

Physiotherapy after stabilisation surgery is essential to restore your confidence in moving your shoulder joint, as well as to improve its strength, stability and range of movement. Your physiotherapist will sometimes provide you with a programme of exercises for both of your shoulders, even though only one has been dislocated.

Generally, in the first six weeks after surgery, when you’re outside, you should wear a sling to help protect your shoulder and prevent you from placing your shoulder in positions where an injury is more likely. However, when you are in a safe environment at work or at home, it is important to keep your shoulder and arms moving to prevent stiffness and engage the important muscles around the shoulder.