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Updated: May 17 2023

Multidirectional Shoulder Instability (MDI)

Images sign.jpg
  • summary
    • Multidirectional shoulder instability (MDI) is a condition characterized by generalized instability of the shoulder in at least 2 planes of motion (anterior, posterior, or inferior) due to capsular redundancy. 
    • Diagnosis is made clinically with presence of increased anterior and posterior humeral translation, a sulcus sign, and overall increased external rotation.
    • Treatment is a trial of prolonged physical therapy focusing on dynamic stabilization and periscapular muscle training. Arthroscopic stabilization with capsular shift is indicated for patients with persistent instability who fail an extensive course of physical therapy. 
  • Epidemiology
    • Incidence
      • peaks in second and third decades of life
  • Etiology
    • 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
        • labral lesions or glenoid erosion can still occur from traumatic events
          • Bankart lesion is anteroinferior labral tear
          • Kim lesion is posteroinferior labral avulsion
      • MDI is also referred to as AMBRI
        • Atraumatic
        • Multidirectional
        • Bilateral (frequently)
        • Rehabilitation (often responds to)
        • Inferior capsular shift (best alternative to nonop)
  • 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 - must have instability in 2 or more planes (anterior, posterior, or inferior) to be defined as MDI
        • sulcus sign (2+ or more)
          • assesses rotator interval
          • laxity of rotator interval presents as increased external rotation with the arm fully adducted and at 90 degrees abduction
        • apprehension/relocation test
        • anterior and posterior load and shift test (2+ or more)
        • Neer and Hawkins test
          • impingement or rotator cuff tendonitis in <20 year old signals possible MDI
      • 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
  • Differential Diagnosis
    • Anterior shoulder instability
    • Posterior shoulder 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
        • deltopectoral approach for open
          • subscapularis tenotomy versus subscapularis split
      • 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
      • late finding - humeral head anterior sublaxation on axillary radiograph
    • 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 (capsulorraphy induced arthritis)
      • usually wear of posterior glenoid with posterior humeral head subluxation and significant retroversion of the glenoid
      • may have internal rotation contracture (severe lack of external rotation on exam)
      • historically seen with Putti-Platt and Magnuson-Stack (non-anatomic, historical) procedures
    • Recurrence
      • most common complication following arthroscopic or open capsulorraphy
      • high rate following thermal capsulorrhaphy (historical) due to capsular insufficiency
        • open revision indicated (not arthroscopic)
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