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NEED TO KNOW
Traumatic anterior shoulder dislocations generally occur because of an anterior force to the abducted, externally rotated arm; this may lead to recurrent anterior shoulder instability, particularly in young athletes.
Diagnosis is made clinically, with the presence of positive apprehension tests and confirmed with MRI studies; the latter may reveal labral and / or bony injuries of the glenoid and proximal humerus( Hill – Sachs lesion).
Reduce acute shoulder dislocations as early as possible to minimise the damage to surrounding neurovascular structures.
Shoulder dislocation in those older than 40 may be associated with a rotator cuff tear or an avulsion fracture.
In young, active populations, surgery is often offered after a single dislocation event.
Atraumatic multidirectional instability is usually treated non-operatively with scapular stabilisation physical therapy.

Shoulder instability

Dr Sami Al Badwi( left) Sports medicine and shoulder surgery fellow, Sydney, NSW.
Professor George AC Murrell( right) Orthopaedic surgeon specialising in shoulder surgery; conjoint professor of orthopaedic surgery at UNSW Sydney and director of the Orthopaedic Research Institute at the St George Hospital Campus, UNSW Sydney, NSW.
Copyright © 2025 Australian Doctor All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means without the prior written permission of the publisher. For permission requests, email: howtotreat @ adg. com. au.
This information was correct at the time of publication: 16 May 2025
BACKGROUND
SHOULDER instability is a common
musculoskeletal condition that is characterised by excessive movement of the humeral head within the shoulder joint. Shoulder dislocations account for about 50 % of all major joint dislocations; anterior dislocation is the most common. 1 The shoulder is an unstable joint because of a shallow glenoid that only articulates with a small part of the humeral head. The shoulder joint relies on soft tissue restraints, especially the capsule and ligaments for stability. Contact sports injuries are often the cause of shoulder dislocation, with young athletes who compete in contact sports at high risk of recurrent instability.
This How to Treat covers the normal anatomy of the shoulder and the pathoanatomy of shoulder dislocation. It aims to ensure GPs can diagnose and manage these common disorders.
SHOULDER ANATOMY
THE shoulder is a complex joint that
consists of articulations between the clavicle and the sternum, the clavicle
and the acromion, and the scapula and the ribcage, as well as the glenohumeral articulation( see figure 1). The glenohumeral articulation provides the greatest range of motion of any joint in the body. It is stabilised by a shoulder capsule and ligaments, that can get torn when the shoulder dislocates, and by a set of muscles, the rotator cuff, that helps secure the humeral head in the glenoid and allows overhead function.
The humeral head normally articulates with the glenoid and is held there by several static and dynamic restraints. The static stabilisers are the glenohumeral ligaments, glenoid labrum and the negative intra-articular pressure. The dynamic stabilisers are the rotator cuff muscles.
AETIOLOGY
Shoulder instability can be broadly categorised into traumatic( see box 1) and atraumatic types. Traumatic instability often results from a significant injury, such as a dislocation or a forceful impact to the shoulder joint. Up to 96 % of shoulder dislocations are traumatic in origin. 2 Traumatic dislocation is often caused by
Box 1. Types of traumatic dislocation
• Anterior dislocation is the most common, accounting for up to 95 % of all shoulder dislocations: 3— The mechanism of injury is usually a force to an abducted, externally rotated and extended extremity( see figure 2).
• Posterior dislocations account for 2-4 % of shoulder dislocations: 3— The injury may be caused by a hit to the anterior shoulder and an axial loading of the adducted internally rotated arm( see figure 3).
— A posterior shoulder dislocation may also be a result of violent muscle contractions( seizures, electrocution).
contact sports injuries with damage to the shoulder stabilisers.
Atraumatic instability, on the other hand, is secondary to ligament laxity and is usually multidirectional. When an atraumatic
shoulder dislocation occurs, consider an underlying connective tissue disease such as Ehlers-Danlos syndrome, or a bony abnormality such as glenoid hypoplasia or excessive glenoid deformity.
EPIDEMIOLOGY
SHOULDER instability is one of the most common serious shoulder injuries. It is common in young males( 20-30 years of age) with a male-tofemale ratio of 9:1. 4 Around 95 % of shoulder dislocations are anterior and only 2-4 % of shoulder dislocations are posterior.
PATHOPHYSIOLOGY
FOLLOWING a traumatic shoulder dislocation, there is usually a capsulolabral injury or a chondral or osteochondral lesion. A Bankart lesion is an avulsion of the anterior labrum in anterior shoulder dislocation. A posterior labrum injury occurs in posterior shoulder dislocation. A superior labrum from anterior to posterior tear / lesion( SLAP tear) can result from excessive load through the long head of biceps( eg, falling while hanging onto scaffolding, see figures 4 and 5).