Multidirectional Instability of the Shoulder

Definition

  • Concept introduced by Neer & Foster in 1980
  • Instability in at least 2 planes
  • Symptomatic inferior instability with Anterior and/or Posterior instability

Aetiology

Three aetiological factors in varying combinations

  • Inherent Ligamentous Laxity > 50%
  • Microtrauma – repetitive overuse with capsular stretch
  • Macrotrauma – one or more episodes of significant trauma in < 50%

Epidemiology

  • Recognized as more common problem & often misdiagnosed
  • Most patients athletic
  • Average age 24 years
  • 15-54 year range

Anatomy

Pathology

  • Main pathology is ↑ joint volume due to enlarged inferior axillary capsular pouch
  • Collagen abnormal with ligamentous laxity
  • Attenuated, broad rotator cuff interval

Classification

History

  • Shoulder pain, fatigue
  • Feeling of shoulder “slipping down” while carrying heavy loads
  • Impingement type pain with overhead activities
  • Anterior ± Posterior instability with arm in respective provocative position
  • Transitory numbness of arm (Dead Arm Syndrome)
  • Often bilateral
  • Discomfort with the arm in forward elevation & internal rotation
    • Eg. pushing open a heavy door
    • Suggests posterior instability
  • Instability of other joints

Examination

  • Sulcus sign
  • Anterior & posterior draw
  • Jobes relocation test
  • Generalised ligamentous laxity in > 50%
    • Ruth Wynn-Davies tests for ligamentous laxity (these are passive tests)
      • Thumb can touch volar aspect forearm
      • Fingers hyperextend to lie parallel to forearm
      • Elbow hyperextension
      • Knee hyperextension
      • Ankle dorsiflexion > 45°
    • Test positive if 3 or greater

Investigations

Xray

  • Standard AP, Lateral
    • Hill Sachs lesion
  • Traction XR
    • Patient erect with 5-10kg in each hand
    • Inferior subluxation of humeral head seen

CT scan

  • anatomy of glenoid

MRI

  • Bankhart lesion
  • Size of inferior pouch
  • Capsular

Differential Diagnosis

  • Anterior Shoulder Instability
  • Causes of inferior displacement of head
    • Superior cuff tear
    • Suprascapular nerve palsy
    • Deltoid atony (eg. CVA)
    • Deltoid palsy

Treatment

Nonoperative

  • Aim
    • Improve strength & tone of shoulder
    • Without mechanical irritation of capsule & ligaments
  • Initial shoulder strengthening
    • Look at 3 parts
      • Deltoid
      • Cuff
      • Scapular stabilisers
    • Specific with therabands & pulleys
    • Combine with education program
  • 90% successful
  • Continue for at least 12 months
  • Repeated evaluation of exercises
  • Repeated assessment of patient for voluntary dislocation & psychiatric disorders
  • Repeated assessment for direction of instability

Operative

  • Principles
    • Never operate on voluntary dislocator
    • Not under age 16 years
    • Surgery for MDI less successful than for unidirectional
    • Standard surgery for unidirectional not successful
  • Neer recognised four errors
    • Surgery on voluntary dislocator
    • Shoulder loose but asymptomatic & other cause (ACJ Osteoarthritis, Cervical radiculopathy)
    • Standard surgery for unidirectional will fail
    • Incomplete surgical correction of all elements
  • Neer & Foster Inferior Capsular Shift
    • Principle
      • Detach capsule from neck of humerus
      • Shift it to the opposite side of the calcar
      • To obliterate the inferior pouch
    • Indications
      • Involuntary instability
      • Failure of non-op treatment > 12 months
      • Persisting severe pain/ instability/ paraesthesia
    • Surgical Technique: Inferior Capsular Shift
    • Outcome
      • 90% satisfied at 5 years (Bigliani)
      • No significant loss of ROM

Prognosis