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http://upload.orthobullets.com/topic/3052/images/mdi_scope1_moved.jpg
http://upload.orthobullets.com/topic/3052/images/sulcus sign.jpg
Introduction
  • Also referred to as AMBRI
    • Atraumatic
    • Multidirectional
    • Bilateral (frequently)
    • Rehabilitation (often responds to)
    • Inferior capsular shift (best alternative to nonop)
  • Epidemiology
    • incidence
      • peaks in second and third decades of life
  • 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 
        • patulous inferior capsule (IGHL anterior and posterior bands)
        • rotator interval deficiency
      • labral lesions or glenoid erosion can still occur from traumatic events
        • Bankart lesion is anteroinferior labral tear
        • Kim lesion is posteroinferior labral avulsion
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
  • Complete Glenohumeral anatomy  
Presentation
  • Symptoms
    • pain
    • instability
    • weakness
    • paresthesias
    • crepitus
    • shoulder instability during sleep
  • Physical exam 
    • tests
      • sulcus sign 
        • assesses rotator interval
      • apprehension/relocation test
      • load and shift test (posterior instability)
      • Neer and Hawkins test
        • impingement or rotator cuff tendonitis in <20 year old signals possible MDI
    • signs of generalized hypermobility
      • able to touch palms to floor while bending at waist
      • genu recurvatum
      • elbow hyperextension
      • MCP hyperextension
      • thumb abduction to the ipsilateral forearm
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
    • findings
      • patulous inferior capsule (IGHL anterior and posterior bands)
      • Bankart lesion
      • Kim lesion
      • bony erosion of glenoid
  • Arthroscopy
    • drive through sign may be present
Differential Diagnosis
  • Unidirectional instability
  • Cervical spine disease
  • Brachial plexitis
  • Thoracic outlet syndrome
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
Techniques
  • Capsular shift / stabilization procedure (open or arthroscopic)
    • approach
      • arthroscopic approach to shoulder 
    • stabilization
      • must address capsule +/- rotator interval
      • inferior capsular shift (capsule shifted superiorly)
      • plication of redundant capsule in a balanced fashion
      • rotator interval closure (open or arthroscopic)
        • produces the most significant decrease in range of motion in external rotation with the arm at the side 
      • address any anterior or posterior labral pathology if present
      • thermal capsulorrhaphy (historical)
        • is contraindicated because of complications including capsular thinning/insufficiency and attenuation, and chondrolysis
    • post-operative rehabilitation
      • 4-6 weeks: shoulder immobilizer or sling
      • 6-10 weeks: ADL's with 45 degree limit on abduction and external rotation
      • 10-16 weeks: gradual range of motion
      • >16 weeks: strengthening
      • >10 months: contact sports
      • patient should resume sports activities only after normal strength and motion have returned
Complications
  • Subscapularis deficiency
    • more common after open anterior-inferior capsular shift
    • may be caused by injury or failed repair
    • postop physical exam will show a positive lift off test and excessive external rotation
  • Loss of motion
    • may be due to asymmetric tightening or overtightening of capsule
    • leads to loss of ER
    • treat with Z-lengthening of subscapularis
    • rare
  • Axillary nerve injury
    • iatrogenic injury with surgery (abduction and ER moves axillary nerve away from glenoid)
    • usually a neuropraxia that can be observed postoperatively
    • can occur with anterior dislocation of shoulder
  • Late arthritis
    • usually wear of posterior glenoid
    • may have internal rotation contracture
    • historically seen with Putti-Platt and Magnuson-Stack (non-anatomic) procedures
  • Recurrence
    • high rate following thermal capsulorrhaphy
      • open revision indicated (not arthroscopic)
 

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