Multi-Directional Instability

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Pathophysiology

• mechanisms
  • underlying mechanism includes
    • microtrauma from overuse
      • seen with overhead throwing, volleyball players, swimmers, gymnasts
    • generalized ligamentous laxity
      • associated with connective tissue disorders: Ehlers-Danlos and Marfan's
• pathoanatomy
  • hallmark findings of MDI
    • Imaging findings: patulous inferior capsule on MRI (IGHL anterior and posterior bands)
    • rotator interval deficiency

Anatomy:

• Glenohumeral stability
  • static restraints
    • glenohumeral ligaments (below)
    • glenoid labrum (below)
    • articular congruity and version
    • negative intraarticular pressure
      • if release head will sublux inferiorly
  • dynamic restraints
    • rotator cuff muscles
      • the primary biomechanical role of the rotator cuff is stabilizing the glenohumeral joint by compressing the humeral head against the glenoid
    • biceps
    • periscapular muscles

Presentation:

• Symptoms
  • pain
  • instability
  • weakness
  • paresthesias
  • crepitus
  • shoulder instability during sleep
  • signs of generalized hypermobility - generalized ligamentous laxity = Beighton's criteria >4/9
    • able to touch palms to floor while bending at waist (1 point)
    • genu recurvatum (2 points)
    • elbow hyperextension (2 points)
    • MCP hyperextension (2 points)
    • thumb abduction to the ipsilateral forearm (2 points)

Imaging:

• Radiographs
  • recommended views
    • a complete trauma series needed for evaluation (AP-IR, AP-ER, AP-True, Axillary, Scapular Y)
  • findings
    • may be normal in multidirectional instability
• MRI
  • indications
    • to fully evaluate shoulder anatomy
    • arthrogram needed to assess volume of capsule
  • findings
    • patulous inferior capsule (IGHL anterior and posterior bands)
    • Bankart lesion - may occur in conjunction with traumatic anterior instability
    • Kim lesion - may occur in conjunction with traumatic posterior instability
    • bony erosion of glenoid - following chronic anterior instability
• Arthroscopy
  • drive-through sign may be present
    • a positive drive-through sign is considered the ability to pass an arthroscope easily between the humeral head and the glenoid at the level of the anterior band of the IGHL
    • also associated with shoulder laxity

Treatment:

• Nonoperative
  • dynamic stabilization physical therapy
    • indications
      • first line of treatment
      • vast majority of patients
    • technique
      • 3-6 month regimen needed
      • strengthening of dynamic stabilizers (rotator cuff and periscapular musculature)
      • closed kinetic chain exercises are used early in the rehabilitation process to safely stimulate co-contraction of the scapular and rotator cuff muscles
• Operative
  • capsular shift / stabilization procedure (open or arthroscopic)
    • indications
      • failure of extensive nonoperative management
      • pain and instability that interferes with ADLs of sports activities
    • contraindications
      • voluntary dislocators
  • capsular reconstruction (allograft)
    • rare, described in refractory cases and patients with collagen disorders

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