Shoulder Complex (Part II) - The Unstable Shoulder

SHOULDER INSTABILITY

Glenohumeral instability is the inability to maintain the humeral head in the glenoid fossa.

Classification Scheme:

1. Degree

2. Frequency

3. Etiology

4. Direction

1. Degree

• Dislocation = Complete loss of humeral articulation from the glenoid fossa
• Subluxation = Partial loss of humeral articulation within the glenoid
• Laxity = Generalised hypermobility of the glenohumeral joint and other joints; asymptomatic

2. Frequency

• Primary = Initial incident (95% traumatic, 5% atraumatic)
• Recurrent = Subsequent occurrence, complication of primary dislocation (70% of primary dislocations --> recurrent dislocation within 2 years of initial injury)

Primary vs Recurrent Dislocation

Highest rates of primary shoulder dislocation in people aged 11-20yo and 51-60yo.

Highest recurrence rates in adolescents aged 20 years or less

       Why the higher recurrence rates in adolescents - Collagen vs Age:

• Collagen type I fibres are tough, non-elastic and more stable
• Collagen type III fibres are more supple and elastic
• The ratio of collagen type I : III changes with age
• Adolescents: Type III > Type I
• Adults: Type I > Type III
• Higher content of stretchy collagen in younger people explains for the increased recurrence rates

3. Etiology

• Traumatic = Injury from direct blow to the proximal humerus, forceful collision, fall on an outstretched arm or sudden wrenching movement; sporting injuries
• Atraumatic = Minor incidents (eg. raising the arm or moving during sleep)

4. Direction

• Unidirectional = Anterior (most common); posterior
• Multidirectional = Instability in two or more planes; generalised laxity

TWO main types of Shoulder Dislocation: TUBS vs AMBRI

1. TUBS

• T = Traumatic mechanism
• U = Unilateral involvement
• B = Bankart and Hill-Sachs lesions (B - Anterior glenoid labrum avulsion; H-S - Humeral head avulsion)
• S = Surgery

2. AMBRI

• A = Atraumatic
• M = Multidirectional
• B = Bilateral
• R = Rehabilitation (as primary management)
• I = Inferior capsular shift surgery (indicated if failed conservative management)

Examination of the Unstable Shoulder

1. History:

• Traumatic or atraumatic?
• Direction of dislocation/instability
• Type of sport, throwing or overhead activity
• Voluntary subluxation?
• "Clunk" or knock
• History of primary and/or recurrent dislocations and direction of force
• Previous injury to capsule, rotator cuff, labrum, glenoid, humerus
• Painful movements

2. Observation

• Signs of dislocation/subluxation?
• Wasting of shoulder complex (esp. supraspinatus, infraspinatus)
• Scapular winging?
• Active range of motion (ROM) / Passive ROM (NB: pain and abnormal scapulohumeral rhythm)
• Hypermobility

3. Special tests and assessments

• Anterior instability tests (anterior drawer, apprehension)
• Posterior instability tests (posterior drawer, push-pull)
• Multidirectional instability tests (load & shift, sulcus)
• Clunk test (labral tear)
• Strength tests
• Xrays (identify Bankart, Hill-Sachs lesions), MRI