II. Epidemiology

  1. Incidence: 24 per 100,000 persons per year
    1. Most commonly dislocated joint (50% of all major joint dislocations)

III. Types: Dislocation

  1. Anterior dislocation (most common, 90% of dislocations)
    1. Humerus is displaced anteriorly relative to the glenoid cavity
    2. Results from fall on externally rotated, abducted and extended arm (throwing position)
    3. Humeral head lie may be subcoracoid (most common), subglenoid, subclavicular or intrathoracic
  2. Posterior dislocation (<4% of all Shoulder Dislocations)
    1. Large force at anterior Shoulder directed posteriorly against internally rotated arm, flexed Shoulder
    2. Often occurs secondary to Generalized Seizure (via forced internal rotation and adduction)
      1. Seizure is responsible for approximately one third of cases (remainder due to Trauma)
      2. May cause bilateral dislocation
    3. Some patients can posteriorly dislocate voluntarily
    4. Often missed on initial provider evaluation (50% of cases)
      1. Diagnosis has been delayed weeks to months in some cases with significant complications
  3. Multidirectional instability
    1. Lax joint capsule allows multidirectional dislocation
  4. Inferior dislocation (Luxatio Erecta): Rare (<0.5% of all Shoulder Dislocations)
    1. Variant of anterior dislocation
    2. Associated with Fracture, Rotator Cuff Injury and neurovascular injury (Brachial Plexus, axillary artery)
    3. Result of high energy mechanism with exaggerated abduction, tearing the inferior capsule and labrum
      1. Axial loading of a fully abducted arm OR
      2. Hyperabduction force to the arm
    4. Patient presents locked with Forearm to forehead position, unable to move the arm out of this position
      1. Arm is in fixed, abducted position overhead
      2. Humeral head palpable in the axilla
    5. Managed with Shoulder reduction using inferior dislocation specific techniques (see Shoulder reduction)
    6. Operative management indications (8% of cases)
      1. Neurovascular injury (Brachial Plexus Injury, axillary artery injury)
      2. ShoulderFracture Dislocation
      3. Unstable Shoulder requiring rotator cuff repair and capsular reconstruction
      4. Nambiar (2018) Eur J Trauma Emerg Surg 44(1): 45-51 [PubMed]

IV. Pathophysiology: Mechanism

  1. General
    1. The Shoulder joint is unstable by nature
    2. The shallow glenoid fossa articulates only 20-30% of the humeral head
    3. Requires ligamentous (e.g. labrum) and tendons (rotator cuff) for stability
  2. Young patient
    1. Direct Trauma or Sports Injury (Contact Sports, Bicycle accident)
  3. Older patient
    1. Results from fall (often with Fracture)

V. Pathophysiology: Mnemonic TUBS-AMBRI

  1. First Type of Shoulder Dislocation (TUBS)
    1. Traumatic mechanism of injury
    2. Unilateral Shoulder involvement
    3. Bankart and Hill-Sachs glenohumeral Fractures
      1. Bankart lesion (Glenoid fossa avulsion)
      2. Hill-Sachs Lesion (Humeral head avulsion)
    4. Surgery often required for management
  2. Second Type of Shoulder Dislocation (AMBRI)
    1. Atraumatic mechanism
    2. Multidirectional instability
    3. Bilateral Shoulder involvement
    4. Rehabilitation as primary management
    5. Inferior Capsular shift surgery
      1. Indicated for failed conservative therapy

VI. Signs

  1. Acromion much more prominent
  2. Humeral head fullness absent under deltoid
    1. Leaves prominent cavity
    2. Dimpling at lateral Shoulder (inferior to acromion)
  3. Severe pain with any range of motion
    1. Arm "locked" in place (may be cradled by other hand)
    2. Patient refuses to move arm
  4. Anterior dislocation
    1. Affected Shoulder has squared off appearance
    2. Arm held externally rotated, and slightly abducted
    3. Anterior Shoulder appears full with anterior bulge
    4. Space below acromion appears empty
    5. Internal rotation painful
  5. Posterior dislocation
    1. Arm held in internal rotation and adduction
    2. Forearm rests on Abdomen
    3. Anterior Shoulder flat with loss of contour
    4. Prominent coracoid process anteriorly
    5. Posterior Shoulder rounded and full
    6. External rotation painful and limited
    7. Assess neurovascular structures
      1. Check axillary nerve with deltoid Sensation (lateral shoulder Sensation)
  6. Inferior dislocation (luxio erecta)
    1. Arm held fixed, abducted overhead with Forearm pronation (Luxatio Erecta)
      1. Humeral head palpable in the axilla
      2. Flexed elbow and pronated Forearm
    2. Evaluate carefully for associated neurovascular injury, Fracture or tendon/ligament injury
      1. Axillary artery injury (39% of cases)
      2. Brachial Plexus Injury (60% of cases)
      3. Labral and joint capsule injury
      4. Humerus Fracture
      5. Rotator Cuff Tear
  7. Other evaluation
    1. Evaluate for neurovascular injury with distal pulses, motor and Sensation (esp. posterior dislocation)
    2. Evaluate for Axillary Nerve Injury (shrugging Shoulder)

VII. Differential Diagnosis

  1. Acromioclavicular Separation (or AC Sprain)
  2. Distal Clavicle Fracture
  3. Humeral Neck Fracture

VIII. Imaging: Shoulder XRay

  1. Precautions: Posterior Shoulder Dislocation
    1. Easily missed on XRay since the humeral head will be roughly in proximity to glenoid (on AP film)
      1. However, Scapular Y View XRay should identify the dislocation (esp. with comparison views)
      2. Velpeau orthogonal view also visualizes a posterior dislocation
    2. Humeral head will have rounded appearance (lightbulb sign, gun barrel sign, drumstick sign)
      1. Results from internal rotation of the arm
      2. Loss of visibility of the greater tuberosity and lesser tuberosity contours
      3. Rim sign (increased distance between anterior glenoid fossa and humeral head)
      4. Decreased half moon overlap of glenoid with humeral head
    3. Consider CT Shoulder Imaging
      1. Defines articular surface defects, humeral head and glenoid Fractures not seen on xray
      2. May direct surgical management
  2. Precautions: Inferior Dislocation
    1. Humeral head is parallel to Scapular spine
    2. Consider CT Angiography for suspected associated vascular injury (axillary artery)
  3. Pre-reduction Shoulder XRay
    1. Not needed if low force mechanism with findings consistent with uncomplicated Anterior Shoulder Dislocation
      1. Especially on sideline (if no obvious signs of Fracture) or recurrent dislocator with atraumatic mechanism
      2. Early relocation without delay allows for an easier relocation prior to development of spasm
    2. Imaging Indications
      1. Age over 40 years or other risks for pathologic Fracture
      2. First-time Shoulder Dislocation
      3. Traumatic mechanism suggests risk for more significant injury (suspected Fracture)
      4. Unclear diagnosis
      5. Emond (2004) Acad Emerg Med 11(8): 853-8 [PubMed]
  4. Post-reduction Shoulder XRay
    1. Obtain in all cases
  5. Standard Views
    1. Anteroposterior (AP)
    2. Lateral Shoulder XRay (Transaxillary lateral often easiest)
    3. Scapular Y Xray
  6. Other XRay Views
    1. West Point View (glenoid cavity)
    2. Stryker View (Hill-Sachs Fracture)
  7. References
    1. Mallon (2013) Shoulder disorders, EM Bootcamp, Las Vegas

IX. Management

  1. Acute Management
    1. See Shoulder Dislocation Management
      1. Includes Post-Reduction Management of Shoulder Dislocation (e.g. sling, range of motion)
    2. Do not attempt to reduce a Chronic Shoulder Dislocation present for >3-4 weeks (>1 week in elderly)
      1. Prolonged dislocations form adhesions between Humerus and axillary artery
      2. Risk of axillary artery rupture on relocation maneuvers
      3. Relocation should be by orthopedic surgery typically in the operating room
      4. Herbert and Webley in Herbert (2015) EM:RAP 15(3): 1
      5. Verhaegen (2012) Acta Orthop Belg 78(3): 291-5 [PubMed]
      6. Sahajpal (2008) J Am Acad Orthop Surg 16(7): 385-98 [PubMed]
    3. Emergent orthopedic Consultation indications
      1. Neurovascular Injury
      2. Inferior Shoulder Dislocation
      3. Concurrent Proximal Humerus Fracture (e.g. surgical neck Fractures)
      4. Bankart fracturs >20% of inferior glenoid
      5. Articular defects >25% in Posterior Shoulder Dislocations
      6. Failed emergency department reduction
        1. Soft tissue (long head biceps, subscapularis tendon) may block Shoulder relocation
  2. Chronic Management and prevention of recurrence
    1. See Shoulder Instability

X. Course: Primary Dislocation

  1. Anterior Shoulder Dislocation in under 25 years (even first episode)
    1. Surgical management results in fewer future dislocations
    2. Surgery also offers less risk of longterm instability and Traumatic Arthritis
  2. Age under 30 years
    1. Recurrence rate: 50%
    2. Surgery indicated for recurrent dislocation or Hill-Sachs Lesion
      1. Restrict rotation
      2. Reinforce joint capsule
  3. Age over 40 years
    1. Shoulder stiffness common
    2. Dislocation recurs less frequently
  4. Age over 50 years
    1. Risk of concurrent Rotator Cuff Rupture: 50%

XI. Complications

  1. Hill-Sachs Deformity (35-40% of cases)
    1. Cortical depression of proximal humeral head
    2. Impaction Fracture where humeral head contacted the anterior glenoid rim
  2. Bony Bankart lesion (esp. younger patients)
    1. Glenoid Fracture (and labral tear) at anterior inferior Scapula
    2. Associated with persistent pain, instability and recurrent dislocation
  3. Rotator Cuff Injury
    1. Age over 40 years old predicts Rotator Cuff Tear in 35% of dislocation cases
    2. Greater tuberosity Fracture predicts Rotator Cuff Tear in 40% of dislocation cases
    3. Axillary Nerve Injury predicts Rotator Cuff Tear in 100% of dislocation cases
  4. Neurovascular injury (esp.in elderly, inferior dislocation)
    1. Axillary Nerve Injury
    2. Brachial Plexus Injury
      1. Terrible Triad (dislocation, Rotator Cuff Injury, Brachial Plexus) is associated with worse outcomes
  5. Shoulder Labral Tear
    1. Anterior glenoid labral tear is most common
  6. Shoulder Instability
    1. Recurrent Shoulder Dislocation or Shoulder Subluxation
  7. Missed Posterior Shoulder Dislocation
    1. Humeral Head Avascular Necrosis
    2. Glenohumeral joint degeneration, articular cartilage injury and Arthropathy
    3. Chronic Shoulder Pain and Disability
  8. Adhesive Capsulitis
    1. Highest risk in Diabetes Mellitus and older patients
    2. Early Shoulder mobilization is preventive

XII. References

  1. Chan and Huang (2022) Crit Dec Emerg Med 36(2): 16-7
  2. Dolbec (2019) Crit Dec Emerg Med 33(1): 17-25
  3. Kiel and Koneru (2019) Crit Dec Emerg Med 33(9): 17-27
  4. Huang (2021) Crit Dec Emerg Med 34(7): 24-5
  5. Hendey (2000) Ann Emerg Med 36:108-13 [PubMed]
  6. Hovelius (1996) J Bone Joint Surg 78-A: 1677-84 [PubMed]
  7. Monica (2016) Am Fam Physician 94(2): 119-27 [PubMed]

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