Thursday, 16 September 2010

Shoulder Complex (Part II) - The Unstable Shoulder

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

No comments:

Post a Comment