The shoulder joint is stabilised by the shoulder labrum and capsule (as well as the surrounding muscles).
The labrum is a cartilage-like ring surrounding the glenoid (see below).
The capsule is a series of ligaments that connects the humerus to the glenoid.
When the labrum and/or ligaments stetch or tear, the shoulder has a greater tendency to dislocate. This is known as instability, which can lead to greater and more painful shoulder conditions, especially dislocation and subluxation.
Dislocation and subluxation are the telltale signs of instability .
The shoulder may dislocate either out the front (anterior), out the back (posterior) or out the bottom (inferior - subluxio erecta). The images below show an anterior dislocation, which is the most common. For information on posterior instability and dislocations click here.
Animation of a shoulder joint dislocating anteriorly (head of humerus dislocates from glenoid).
A Bankart lesion (below) is a tearing of the labrum off the glenoid bone with an anterior dislocation:
Shoulder instability means your shoulder can dislocate or subluxate repeatedly during active movement or exercise. Subluxate means the joint moves more than it should do in normal circumstances but doesn't actually come out of joint. There can be a number of reasons for this and this will determine the type of treatment you will receive.
Shoulder instability is divided into three main categories (this is largely dependant on the first episode of dislocation).1. Traumatic dislocation.
This when the shoulder has undergone an injury with enough force to pull the shoulder out of joint such as being tackled in a football or rugby game, a road traffic accident etc. Usually this is the first episode and it would need reducing in A&E. You would be put into a sling for a period of time and then in some cases would undergo a course of physiotherapy.
Due to the amount of force that is associated with such an injury the labrum can be torn from the bone (creating a Bankart lesion .) and this can result in an unstable shoulder which may lead to further episodes of dislocation. This would be an indication for a surgical procedure called an Anterior Stabilisation where the torn part of the labrum ( Bankart lesion ).For more information Click Here
A Bankart lesion is the most common injury sustained with traumatic dislocation, but other injuries can occur. These may alter the surgery and rehabilitation. These injuries can usually be diagnosed on an MR-Arthrogram or CT-Arthrogram.
These injuries are:
- ALPSA lesion - (Anterior Labral Periosteal Sleeve Avulsion) a displacedBankart tear, where the labrum has displaced around the glenoid neck. This is associated with a higher risk of recurrent instability than an undisplacedBankart tear. - ALPSA lesion at arthroscopy
- HAGL tear - (Humeral Avulsion of Glenohumeral ligament)
- Bony Bankartt - a fragment of bone breaks off with the Bankart tear - Bony Bankart at arthroscopy
- Hill-Sachs lesion - a dent in the back of the humeral head which occurs during the dislocation as the humeral head impacts against the front of the glenoid.
- SLAP Tear - a tear at the top of the labrum
2. Atraumatic dislocation.
This occurs when the shoulder dislocates with minimal force such as reaching up for an object or turning over in bed. Usually it will 'pop' back in itself or with a little help. Normally this type of dislocation does not need reducing in A&E. It can occur regularly throughout the day and will be associated with certain positions the arm is placed into. This type of dislocation is associated with people that have 'lax' joints, for example people who hyper-extend their knees and elbows and can get the palms of both hands onto the floor with ease. This joint laxity is normal for these people and the onset of dislocation can be associated with a change in how the muscles around the shoulder are interacting with each other or a change in posture/ position of the arm. This can produce an imbalance in the control of the joint. Referral for appropriate physiotherapy is the initial form of management. The physiotherapist should look at the way in which the muscles and shoulder joint is moving and posture aiming to restore the balance. Treatment can 'cure' the problem as long as the exercises and advice is continued, but in some cases there is only minimal or nil benefit. At this point surgical intervention is indicated.
For more information Click Here
3. Positional Non-traumatic dislocations.
This group of people can dislocate their shoulders without any form or history of trauma. Some may have started out dislocating their shoulder as a party trick; others may have always had shoulders that just 'fall' out of joint. This type of dislocation is usually painless and can be put back in easily. Both shoulders are typically involved. The cause of this type of dislocation is usually a result of what we call 'abnormal muscle patterning' which means the strong muscles around the shoulder joint are not working in the correct order causing them to pull the shoulder out of joint with active movement in the particular direction such as lifting the arm forward above the head or out to the side and above the head. The main treatment for this is physiotherapy that looks at re-sequencing the muscles in order to prevent further dislocations. Occasionaly surgery in the form of thermal capsular shrinkage or plication may be neccessary.
Physiotherapy - to train the shoulder muscles to control the shoulder correctly and prevent further instability
Surgery - A number of procedures are available to remedy chronic instability, depending on the causes and findings on investigations.
Types of Surgery:
- Arthroscopic Procedures - through keyhole surgery.
- Open Shoulder Procedures - depending on the problems found, such as the Latarjet procedure for glenoid bone loss or open capsular repair for HAGL lesions.
Strong shoulder muscles remain the best defence against shoulder dislocation, subluxation, and, thus, instability. Exercises that build up these muscles around the shoulder should be done. The key is to balance the muscles around the shoulder and ensure not only the 'mirror' muscles are exercises (those that you can see when looking in the mirror). Good core stability and posture are also important.
Adequate warm-up before activity and avoidance of high-contact sports will help prevent instability-causing injuries.
For more information see Shoulder Injury Prevention.