What is a Dislocation?

Dislocation is defined as the complete separation of the two articulating surfaces of a joint. 

What is a Posterior Dislocation of the Shoulder?

Posterior dislocation is defined when the head of the humerus is separated from the glenoid and pushed posteriorly. One of the most missed or the late diagnosed dislocation of the shoulder is the posterior one(1).

This is because the shoulder complex is guarded posteriorly by the scapula and a thick musculature covering it. This makes the posterior dislocation less frequent with about 2 -5% of the occurrence, compared to the anterior one.

About 60 – 79% of the posterior dislocations are missed during the initial examination, hence it warrants a keen examination for a good prognosis(1,2)

Aa per the basic classification, posterior dislocations can be classified as Traumatic and Atraumatic, of which the traumatic being more common.

Posterior dislocations are classified more precisely according to the etiopathogenesis and presentation as- 

1. Acute dislocation
2. Chronic (Fixed/ Locked) dislocation
3. Recurrent Posterior subluxation (more common)

Mechanism of Injury

Trauma

Trauma is the most common mechanism of posterior dislocation. 67% of all posterior dislocations occur with a high energy force directed axially to the shoulder, with the upper extremity in an internally rotated and adducted position(3).

This may be observed in the case of grabbing a dashboard during a motor vehicle collision or falling on the hand(2).

A sudden force while guarding against an opponent in combat or high-intensity sports.

Seizures

Seizures can cause posterior shoulder dislocations. In fact, 31% of the dislocations reported were being accountable due to the seizures of all the posterior dislocations(3).

A seizure is characterised by a sudden onset of high-intensity muscle contraction.

This can cause the larger muscle mass of internal rotators, consisting of the subscapularis, latissimus dorsi, and pectorals to overpower the external rotators mainly consisting of the rotator cuff muscles to posteriorly dislocate the shoulder.

Electrocution

A sudden passage of electric current has an incidence of 2% of total posterior dislocations (3).

Posterior Instability / Microtrauma

The posterior structures of the shoulder are under tension due to repeated episodes of loading. This can be seen in line backs in American Football, goalkeepers,  weightlifters, and overhead athletes who repeatedly are subjected to posteriorly directed force (3,5). A recent study on shoulder instability in the NFL has shown a greater incidence of posterior instability in quarterbacks and linebackers compared to other instabilities(8).  The mechanism of this can be explained as the structures getting stretched. This is seen as a continuum in fact a posterior instability gives rise to frank dislocation during the season, and hence preseason screening – prevention strategies can help in managing the injuries better. 

Anterior vs Posterior Shoulder Dislocation:

The differences between anterior and posterior shoulder dislocations are shown in this table:

Shoulder Dislocation X-Ray

The images below show X-Rays of anterior and posterior shoulder dislocations.

Posterior Shoulder Dislocation MRI

MRI helps in diagnosing the associated soft-tissue injuries like rotator cuff tears , bicep tendon inflammation, extent of reverse hill sach lesion and vascular supply of the humeral head(6,7).

Hence, posterior dislocation of the shoulder, one of the trickiest shoulder instability conditions to diagnose, needs a thorough assessment, a good reason for doubt, and preventive strategies in athletic shoulders, and a series of radiology investigations.

One of the main differentials in the elderly population is frozen shoulder which can give similar signs of restriction in external rotation and abduction. If misdiagnosed as the frozen shoulder the patient loses time and the viable humeral head blood supply(1). Even reduction in more than 3 weeks old chronic cases should be only taken with an in-depth investigation and consultation with a shoulder surgeon.

REFERENCES

1. Perron AD, Jones RL. Posterior shoulder dislocation: avoiding a missed diagnosis. The American journal of emergency medicine. 2000 Mar 1;18(2):189-91.
2. Paul J, Buchmann S, Beitzel K, Solovyova O, Imhoff AB. Posterior shoulder dislocation: systematic review and treatment algorithm. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2011 Nov 1;27(11):1562-72.
3. Robinson CM, Seah M, Akhtar MA. The epidemiology, risk of recurrence, and functional outcome after an acute traumatic posterior dislocation of the shoulder. JBJS. 2011 Sep 7;93(17):1605-13.
4. Rouleau DM, Hebert-Davies J. Incidence of associated injury in posterior shoulder dislocation: systematic review of the literature. Journal of orthopaedic trauma. 2012 Apr 1;26(4):246-51.
5. Tannenbaum E, Sekiya JK. Evaluation and management of posterior shoulder instability. Sports health. 2011 May;3(3):253-63.
6. Basal O, Dincer R, Turk B. Locked posterior dislocation of the shoulder: A systematic review. EFORT Open Reviews. 2018 Jan 15;3(1):15
7. Paparoidamis G, Iliopoulos E, Narvani AA, Levy O, Tsiridis E, Polyzois I. Posterior shoulder fracture-dislocation: A systematic review of the literature and current aspects of management. Chinese Journal of Traumatology. 2021 Jan 1;24(01):18-24.
8. Anderson MJ, Mack CD, Herzog MM, Levine WN. Epidemiology of shoulder instability in the national football league. Orthopaedic Journal of Sports Medicine. 2021 Apr 27;9(5):23259671211007743.
9. Chan O, editor. ABC of emergency radiology. John Wiley & Sons; 2012 Dec 12.
10. https://www.ortho-teaching.feinberg.northwestern.edu/XRreading/shoulder/yview.html
11. Abrams R, Akbarnia H. Shoulder dislocations overview. InStatPearls [Internet] 2021 Aug 13. StatPearls Publishing.
12. https://radiopaedia.org/articles/posterior-shoulder-dislocation

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What is the difference between Shoulder Separation vs Dislocation?

The shoulder is the most mobile of all joints in the body and is regarded as the ‘most unstable of all major joints’ due to the relatively small articulation surface. The shoulder is a synovial joint that consists of 3 bones; the humerus, scapula, and clavicle. It has 4 connections (a.k.a. articulations or joints) – these are namely (i) the acromioclavicular (AC) joint, where the acromion (the top part of the scapula) meets the collarbone or clavicle; (ii) the glenohumeral (GH) joint, where the humerus joins the glenoid; (iii) the sternoclavicular (SC) joint, where the clavicle meets the sternum; and (iv) the scapulothoracic (ST) articulation where the scapula meets the chest wall.

Both “static and dynamic restraints” are used to achieve shoulder stability. In a ‘normal’ shoulder, the humeral head stays in the centre of the glenoid fossa (a socket formed by a hollow at the superolateral edge of the scapula), which allows joint surfaces to line up perfectly. Unlike the hip, the shoulder socket is shallow and therefore requires specific positioning of the 3 bones to maintain its stability. As long as the scapula is in a good position, this wonderful ‘centring’ phenomenon occurs even when launching a cricket ball or baseball exceeding speeds of 100mph! (see the laws of stability below). The arc of the glenoid is instrumental here by containing the glenohumeral joint response force.

The Laws of Glenohumeral Stability:

1. As long as the net humeral joint reaction force (see figure 1 below) is directed within the effective glenoid arc (footnote 2), the glenohumeral joint will not dislocate (see figures 2 and 3).
2. If the glenoid and humeral joint surfaces are parallel and the net humeral joint reaction force is directed within the effective glenoid arc, the humeral head will remain centred in the glenoid fossa.

 

 

 

 

 

Is shoulder dislocation the same as a shoulder separation?

No! Commonly confused, but very different in their nature of injury, speed required for treatment, diagnosis and rehab treatment methods used.

 

What is shoulder dislocation?

A shoulder dislocation is when the humerus is pulled or pushed out of the shoulder socket, or glenohumeral joint. Shoulder dislocations represent 50% of all major joint dislocations, with anterior (forward) dislocation accounting for 97% of all types of shoulder dislocations.

 

 

What is shoulder separation?

A shoulder separation when the ligaments of the AC joint (connects collarbone to shoulder blade) are damaged, and the bones on either side can move excessively. There are 6 different types or grades given to a shoulder separation injury, then segmented into 3 main treatment routes.

 

 

Shoulder Dislocation Symptoms, Causes, Treatment

Here are the symptoms, causes and treatment of shoulder dislocation

Shoulder Dislocation Symptoms

• Deformity – Your arm appears to be out of place
• Severe shoulder pain
• Numbness in your arm, neck, hand, or fingers
• Swelling and bruising of your shoulder or upper arm
• Weakness or pain preventing you from moving your arm
• Muscle spasms in your shoulder

Shoulder Dislocation Causes

• A direct force to the shoulder from behind and at the side, often caused by sports injuries
• Falling on your shoulder or an outstretched arm
• Accidents (including traffic incidents).
• Individuals may also put their arm in a position of high risk that predisposes them to a dislocation. In this case, the muscles are “unprepared”, and the force “overwhelms” the muscle causing a dislocation.

Shoulder Dislocation Treatment

1. Relocation of the shoulder (if no contraindications) – medically called a ‘closed reduction’. Medication can relieve the pain and relax your shoulder muscles. Once the joint is back in place, the severe pain should end.
2. Use a sling (3 days to 3 weeks) – to help reduce pain, and allow muscles to relax and ligaments to heal.
3. Physiotherapy to help improve range of motion, shoulder strength and function – to improve quality of life and prevent future dislocations.

Surgery may be required if damage has been caused to the socket, tissues or nerves around the shoulder or if you get repeated dislocations.

Shoulder Separation Symptoms

• Intense pain immediately
• Tenderness of shoulder and collarbone
• Swelling
• Bruising
• Deformity

Shoulder Separation Causes

• A fall onto the shoulder.
• High impact to the shoulder, through sports such as rugby.

Shoulder Separation Treatment

1. Type I-II injuries are treated non-operatively with Physiotherapy and advice.
2. Type III injuries vary on their management depending upon factors including age, level of sporting ability, time of season, and if the individual doesn’t mind altering their activities.
3. Types IV-VI require surgery to restore function, and generally have a high success rate in returning function, when combined with Physiotherapy rehabilitation following surgery.

 

How to tell the difference between separation and dislocation?

There are multiple was that you can tell the difference between shoulder separation and shoulder dislocation:

• Clinical information – Knowing how the injury occured, and what happened immediately afterwards.
• Visual observation – Bruising, swelling, or obvious dislocation (arm abducted and externally rotated) or deformity/bump seen at the shoulder end of the collarbone.
• Palpation/Touching – Knowing normal joint position can enable a clinician to feel what is where.
• Imaging – X-rays, CTs or MRIs will all show clearly if the humerus is dislocated from the joint space, or indeed if the collarbone is separated from the shoulder blade.

Conclusion 

A shoulder separation is when the acromioclavicular ligament detaches partially or fully causing a deformation of the collarbone, due to lack of connectedness. Commonly occurring in impact sports such as rugby.

A shoulder dislocation is when the humeral head leaves the safety of the glenoid fossa a.k.a the shoulder socket and is essentially ‘not in location’. Often caused by high velocity trauma or car accidents.

If you are more of an auditory, and visual learner, then this short video explains the difference between shoulder dislocation and shoulder separation in 2 minutes. If you have any questions at all, then please do reach out and we would love to help answer them.

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Patients with prior shoulder dislocation are more prone to redislocation as the tissues have not healed properly and the shoulder complex is weaker than normal.

Younger patients have a much higher frequency of redislocation; most likely due to higher activity levels. 

What is a shoulder dislocation?  

If you have a shoulder dislocation, it means that your upper arm bone (the humerus) has shifted out from its normal position in the shoulder joint.

Medically, a dislocation is defined as a total loss of contact between the two ends of bones .

What are the 3 types of shoulder dislocations?The shoulder can dislocate in three directions:

1. Anterior dislocation (forwards) 
2. Posterior dislocation (backwards)
3. Inferior dislocation (downwards)

• The most common dislocation is the anterior dislocation, accounting for up to 97% of the cases.

ICD 10 – Shoulder dislocation 

The World Health Organisation (WHO) published the ICD-10 which stands for International Classification of Diseases. Medical terms are coded according to ICD form the main basis for health recording and statistics on disease in a primary, secondary, and tertiary care.

In the ICD 10 codes, S40-S49 represent injuries to the shoulder and upper arm.

Out of these codes, S43 is a code indicative of subluxation or dislocation of the shoulder joint. To enable the assignment of correct ICD-10 codes, the documentation ideally specifies the positioning, location of the dislocation including laterality (right or left), joint involved, the extent of the dislocation, and encounter.

However, a note must be made that the ICD-11, was adopted by the 72^nd World Health Assembly in 2019 and came into effect on 1^st January 2022. 

Treatment for a Dislocated Shoulder

The treatment for shoulder dislocations depends on the patient’s age, symptoms, the severity of dislocation, patient’s level of fitness, and patient’s goals.

Both conservative (non-surgical) and surgical management are options for treating shoulder dislocation, which attempts to restore a fully functional, pain-free, and stable shoulder. Closed reduction of the dislocation is generally performed before conservative or surgical treatment.

(closed= the surgeon won’t cut your shoulder open, reduction=put your shoulder back in place). Which is then followed by physiotherapy and a rehabilitation regimen.

However, if the dislocations are severe and recurrent, there is no role of conservative management. Operative care may entail open or arthroscopic surgery and is typically followed by a monitored physical therapy programme.

How long does a dislocated shoulder take to heal?

• After a closed reduction under general anaesthesia is done, the shoulder is immobilized in a sling. 
• Ideally, the immobilization period is for 3 to 6 weeks.
• However, this can depend on a plethora of factors namely- age, presence of co-morbidities like diabetes, addictions like smoking, etc. that can delay wound healing.

Dislocated Shoulder Range of Motion 

If you are, let’s say, at the gym and hear your shoulder pop out, – do not try to stretch it, do not apply traction, do not rotate, twist, or turn the shoulder.

Shoulder dislocations can be associated with labral tears (labrum = a thick layer of tissue around your shoulder joint that keeps the joint intact), rotator cuff injury (the shoulder muscles you were probably trying to strengthen in the gym when this pop occurred), humeral fractures (humerus = the upper arm bone), nerve damage, etc.

All of these associated injuries don’t always happen, but you will not know that until you visit a healthcare professional.

How long does it take to get the full range of motion with a dislocated shoulder? 

There is no one correct answer for this. Multiple patient factors govern the treatment plan and also determine the time it would take to gain the full range of motion (ROM) back.

For a young healthy active adult who was treated non-operatively,

• Phase 1 (up to 6 weeks) 

Since the shoulder is in a sling, the focus is on the elbow, wrist, and finger ROM. Gentle strengthening without movement (isometric) exercises for the muscles around the shoulder can be started towards the end of this. 

• Phase 2 (6-12 weeks)

Ideally, this is the time when the full ROM of the shoulder should return to normal. Strengthening of the shoulder muscles can be started depending upon the patient’s symptoms and wound-healing capacity.

• Phase 3 (12- 24 weeks)

A high level of exercise (plyometric) training can be started for athletes wanting to return to sports. 

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