Shoulder dislocations can be scary and occasionally debilitating for a short period of time. The aim of this blog post is to shed some light on what happens in a shoulder dislocation. A future post will explore what to expect when recovering after this relatively common injury. Behind bone fractures and soft tissue injuries (e.g. ‘a corky’), joint dislocation was the third most common reason for presentation to a hospital emergency department in Australia during 2011-12. The most common dislocations occur at the fingers, with the shoulder joint being a close second.
Acute shoulder dislocations usually occur as a result of impact; whether falling on an outstretched arm or direct impact to the shoulder such as what might happen during an unsafe ‘spear’ tackle and landing on the front or back of the shoulder.
A quick spot of Anatomy
The shoulder is generally thought of as the functional unit made up of the Clavicle attached to the Scapula, which is predominantly controlled by a group of muscles around the upper back/ chest, as well as the joint between upper arm and scapula; the Glenohumeral joint. It is the Glenohumeral (Glenoid of scapula to Head of Humerus) joint that is the focus here.
This joint, simply, is a ball in a socket joint, allowing a large amount of movement in many directions. It is made stable by a rubbery fibrocartilage labrum, that blends into the joint capsule and Glenohumeral ligaments. Our rotator cuff muscles are the primary contractile units that aid in stabilising the joint. Other larger muscles such as your Latissimus Dorsi and Pectorals, and to a lesser extent your Biceps and Triceps all move the Glenohumeral joint and can play a lesser stabilising role, although their primary role is large movement.
|Pic 1: Front to back view of Glenohumeral joint:bones and ligaments (courtesy Wikipedia online)||Pic 2: Back to front view of rotator cuff (courtesy Wikipedia online)|
Dislocation of the Glenohumeral joint is an injury whereby the Head of Humerus, typically sitting comfortably within the joint capsule afforded by the Glenoid rim, becomes effectively detached from this position. This creates a strain on the supporting structures and results in significant pain and often long term instability.
Anterior vs. Posterior Dislocation
The most common shoulder dislocation is the anterior shoulder dislocation, 90-95% of shoulder dislocations. Posterior dislocations make up 5-9% with Inferior dislocation being the least common form. The anterior form of dislocation most often occurs as a result of a fall, particularly with the arm being pushed up and backwards in the ‘stop-sign’ position, forcing the Humerus forwards within the joint. This strains the capsule and ligaments that otherwise provide stability at the front and lower portions of the Glenohumeral joint. There is often a popping sound and immediate pain. In severe cases, tingling or numbness in the arm and altered blood flow may occur, although this is less common.
Posterior dislocation often involves impact to the front of the upper arm, close to the shoulder, or a fall onto the outstretched arm in front and across the body, which forces the Humerus backwards within the joint.
Inferior dislocation is rare and occurs when the arm is abducted and abuts up into the acromion, thereby straining the capsule and inferior ligaments and slipping the head of the Humerus inferiorly in the joint.
Pic 3: Left anterior shoulder dislocation (free usage rights via google images)
Complications from dislocation and relocation
Clearly there is a risk of significant damage to the primary static and active stabilisers of the joint (capsule, ligaments and muscle). There is also a risk of damage to the labrum (labral tear), fracture of the scapula aspect of the joint; the Glenoid rim (Bankart Lesion), or fracture to the Humeral head (Hill-Sach’s Lesion). As mentioned earlier, there is also a risk of damage to the axillary nerve or blood vessels. Finally, it is very common for a dislocation to recur, usually being reported in approximately 2/3rds of patients who have suffered a Anterior Dislocation.
It is encouraged that when a person presents with an acute shoulder dislocation, a pre-relocation x-ray be performed, but this is often not possible. In some instances, the shoulder may relocate spontaneously, often if the person is leant forward and relaxing the arm. More commonly, a skilled professional may assist with relocation. Following the relocation, an X-ray is encouraged to rule out bony fractures and to ensure the head of the Humerus is again sitting in its appropriate place.
I would like to stress at this point that it is important that should a dislocation occur, a trip to the hospital is advised. Relocation by a skilled professional is paramount, as a simple and thought-less tug or push can compromise blood vessels and nerves, leading to long term damage.
What to do next?
If the dislocation has been relocated safely and ensured that no nerve or other major damage has occurred, the next step is to rest. These checks will have been performed in hospital. Occasionally a shoulder sling will be provided and is often recommended. There might be differences in sling and arm position depending on the injury sustained and whether a bone or labral lesion have occurred.
It will be important to check-in with your physiotherapist to start your rehabilitation within the first weeks. Engaging the damaged stabilising muscles and ensuring appropriate relative rest, as well as reducing any swelling and excess muscle tone.
1. AIHW: Kreisfeld R, Harrison JE, & Pointer S 2014. Australian sports injury hospitalisations 2011–12.Injury research and statistics series no. 92. Cat. no. INJCAT 168. Canberra: AIHW.
2. Jamali, S. (2011). Anterior shoulder dislocation: Seated versus traditional reduction technique. Australian family physician, 40(3), 133.
3. Brukner, P. (2012). Brukner & Khan’s clinical sports medicine. North Ryde: McGraw-Hill.
4. Vermeiren, J., Handelberg, F., Casteleyn, P. P., & Opdecam, P. (1993). The rate of recurrence of traumatic anterior dislocation of the shoulder. International orthopaedics, 17(6), 337-341.
Post-script: Interestingly, on the day of writing this, I was conveniently present as an opposing player at an indoor sports court happened to dislocate his shoulder by getting his hand caught on some netting surrounding the field while running… Fate? Coincidence? Never-the-less, it made for a very personally relevant first blog post!