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Shoulder Instability

SHOULDER STABILISERS (Also see Shoulder Anatomy)

Static restraints

These keep the shoulder in joint when at rest

1.       Intracapsular pressure: normally the intracapsular pressure of the shoulder is negative

2.       Suction effect: glenoid labrum acting on humeral head like a “plunger”

3.       Adhesion-cohesion: between 2 wet smooth surfaces

4.       Glenoid version: may have bearing on a few cases with recurrent posterior dislocation but exception is in patient with congenital glenoid dysplasia

5.       Humeral retroversion: normal 21-30º, some studies have shown a significant reduction in patients with recurrent anterior dislocation  

6.    Labrum: “chock block” to humeral head movement, increases depth of the glenoid by 50%

7.    Ligaments

  1. Coracohumeral ligament
  2. Superior glenohumeral ligament (SGHL)
  3. Middle glenohumeral ligament (MGHL)
  4. Inferior glenohumeral ligament complex (IGHLC)
  5. Posterosuperior capsule

Dynamic constraints

Keep the shoulder in joint during activity

1.       Rotator cuff

2.       Proprioception

·         Lephart et al 1994 studied proprioception in three groups of patients: Normal, Unstable, Reconstructed shoulders.  Study found that proprioception was significantly reduced in unstable shoulders but returned to near normal in reconstructed shoulders

3.       Long head of biceps: biceps is much more active in patients with recurrent dislocation



TUBS and AMBRI (Matsen)

TUBS or “Torn Loose”

Traumatic aetiology

Unidirectional instability

Bankart lesion is the pathology

Surgery is required

AMBRI or “Born Loose”

Atraumatic: minor trauma

Multidirectional instability may be present

Bilateral: asymptomatic shoulder is also loose

Rehabilitation is the treatment of choice

Inferior capsular shift: surgery required if conservative measures fail

Voluntary Dislocator

Often associated with a psychiatric condition or alternative gain

The desire to voluntarily dislocate the shoulder cannot be treated surgically.


Multi-directional Instability (MDI)

Definition = Abnormal amount of excursion of the humeral head on the glenoid in all directions

 Classification - Neer

Group I 

Antero-inferior dislocation

Posterior subluxation

Group II

Postero-inferior dislocation

Anterior subluxation

Group III           

Global dislocation

 MDI presents as primary instability which is most obvious in one direction

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Brachial plexus Injury
Clavicle fractures
Dislocations of the Acromioclavicul...
Frozen Shoulder
Os acromiale
Rotator Cuff Disease
Scapula fractures
Shoulder biomechanics
Shoulder anatomy
Shoulder Arthroscopy
Shoulder Instability
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