Posterior Instability & Posterior Dislocation

Topic updated on 07/06/16 3:29pm
  • Axillary lateral of posterior shoulder dislocationPosterior shoulder dislocations are less common than anterior dislocations, but more commonly missed
    • 50% of traumatic posterior dislocations seen in the emergency department  are undiagnosed
  • Epidemiology
    • incidence
      • 2% to 5% of all unstable shoulders
    • risk factors
      • bony abnormality
        • glenoid retroversion or hypoplasia is a less common cause of instability
      • ligamentous laxity
  • Pathophysiology
    • mechanism
      • trauma
        • 50% of cases that present for evaluation
      • microtrauma
        • may lead to a labral tear, incomplete labral avulsion, or erosion of the posterior labrum
        • leads to gradual stretching of capsule
        • common in lineman, weight lifters, overhead athletes 
      • seizures and electric shock
        • tetanic muscle contraction pulls the humeral head out 
    • biomechanical forces
      • flexed, adducted, and internally rotated arm is a high-risk position
  • Associated conditions
    • see table below
Lesions Associated with Posterior Instability
Avulsion of posterior band of IGHL Associated with acute subluxations
Posterior Bankart lesions Characterized by detachment of posterior inferior capsulolabral complex
Reverse Hill-Sachs lesions Associated with nonreducible and difficult to reduce dislocations
Posterior labral cyst Associated with chronic reverse Bankart lesion
Posterior glenoid rim fracture Associated with chronic reverse Bankart lesion
Lesser tuberosity fracture Associated with posterior dislocation
Large capsular pouch Can see with MRI with contrast
  • Glenohumeral anatomy
  • Primary stabilizers of the posterior shoulder
    • posterior band of IGHL
      • primary restraint in internal rotation 
    • subscapularis
      • primary dynamic restraint in external rotation
    • superior glenohumeral ligament and coracohumeral ligament 
      • primary restraint to inferior translation of the adducted arm and to external rotation
      • primary stabilizer to posterior subluxation with shoulder in flexion, adduction, and internal rotation
  • Static restraint
    • labrum deepens the glenoid
  • Acute versus chronic
  • Voluntary versus involuntary
  • History
    • trauma with the arm in a flexed, adducted, and internally rotated position
  • Symptoms
    • pain with flexion, adduction, and internal rotation of the arm
  • Physical exam
    • inspection
      • prominent posterior shoulder and coracoid
    • motion
      • limited external rotation
      • shoulder locked in an internally rotated position common in undiagnosed posterior dislocations 
    • provocative tests
      • posterior load & shift test
        • place patient supine with arm in neutral rotation with 40 to 60° abduction and forward flexion, load humeral head and apply anterior and posterior translating forces noting subluxation
      • Jerk test
        • place arm in 90° abduction, internal rotation, elbow bent
        • apply an axial force along axis of humerus and adduct the arm to a forward-flexed position
        • a ‘clunk’ is positive for posterior subluxation 
        • 97% sensitive for posterior labral tear when combined with a Kim test  
      • Kim test 
        • performed by having the patient seated, arm at 90° abduction, followed by flexing the shoulder to 45 forward flexion while simultaneously applying axial load on the elbow & posterior-inferior force on the upper humerus. 
        • test is positive when pain is present
      • posterior stress test
        • stabilize scapula and look for posterior translation with a posterior direct force
        • pain is elicited often, but this is not a specific finding
Posterior Load & Shift Grading
1+ apparent translation but not to rim
2+ translation to glenolabral rim
3+ translation over glenolabral rim
4+ translation with complete dislocation
  • Radiographs
    • recommended views
      • AP
        • unreliable
        • may show a 'lightbulb' sign
      • axillary lateral
        • best view to demonstrate a dislocation  
    • optional
      • Velpeau view if patient is unable to abduct arm for axillary view 
  • CT
    • indications
      • analyze the extent and location of bone loss in a chronic dislocation (>2 to 3 weeks)
  • MRI
    • indications
      • evaluate for suspected associated rotator cuff tear
      • may show Kim lesion (concealed avulsion of the deep posteroinferior labrum, with apparently intact superficial labrum)
  • Nonoperative
    • acute reduction and immobilization in external rotation for 4 to 6 weeks
      • indications
        • should be initially attempted for all acute traumatic posterior dislocations
      • most dislocations reduce spontaneously
      • technique
        • immobilize in 10-20 degrees of external rotation with elbow at side
        • after 6 weeks advance to physical therapy (rotator cuff strengthening and periscapular stabilization) and activity modification (avoid activities that place arm in high-risk position)
  • Operative
    • open or arthroscopic posterior labral repair (Bankart)  and capsular shift 
      • indications
        • recurrent posterior shoulder instability
        • continued pain with loading of arm in forward flexed position (bench press, football blocking)
      • outcomes
        • 80% to 85% success at 5- to 7-year follow-up after open repair
        • similar outcomes with arthroscopic repair after shorter follow-ups 
    • open reduction with subscapularis and lesser tuberosity transfer to the defect (McLaughlin) 
      • indications
        • chronic dislocation < 6 months old
        • reverse Hill-Sachs defect < 50%
    • hemiarthroplasty
      • indications
        • chronic dislocation > 6 months old
        • severe humeral head arthritis
        • collapse of humeral head during reduction
        • reverse Hill-Sachs defect > 50% of articular surface 
    • total shoulder arthroplasty
      • indications
        • significant glenoid arthritis in addition to one of the hemiarthroplasty indications
Surgical Techniques
  • Open or arthroscopic posterior labral repair (Bankart)  and capsular shift  
    • goal is to repair any labral detachment or capsular tears, and/or reduce the posterior capsule volume
    • approach 
      • arthroscopic approach to shoulder 
        • high lateral portal is better than standard portal for posterior labral work
        • lateral decubitus position allows for improved visualization for arthroscopic stabilization
    • posterior capsular shift
      • most common treatment
      • up to 50% failure rate
    • closure of rotator interval
      • augments posterior capsular shift
      • controversial
    • thermal shrinkage of capsule
      • contraindicated due to complications
      • mechanism
        • breaks collagen cross links
        • critical temp (65 to 75° C)
    • complications
      • recurrence
      • capsular necrosis
      • axillary nerve injury
    • postoperative care
      • rigid immobilizer with arm abducted to 30 degrees in neutral internal rotation and elbow posterior to the plane of the body
      • early range of motion and strengthening
      • full heavy labor and contact sports after 6 month
  • Open reduction with subscapularis and lesser tuberosity transfer to defect (McLaughlin)
    • approach
      • deltopectoral approach 
    • technique to repair defect
      • subscapularis and lesser tuberosity transfer
        • used by most (modified McLauglin procedure)
      • iliac crest bone graft
        • can be used for any glenoid bone loss
      • disimpaction and bone grafting of the defect
        • if < 3 weeks the surgeon can try disimpaction and bone grafting of the defect
      • opening wedge glenoplasty
        • may be indicated with glenoid hypoplasia
    • complications
      • stiffness
      • AVN
      • osteoarthritis
  • Recurrence
    • most common (7% to 50%)
  • Adhesive capsulitis
  • Generalized stiffness
  • Overtightening of posterior capsule
    • may lead to anterior subluxation or coracoid impingement
  • Nerve injury
    • axillary or suprascapular


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Qbank (13 Questions)

(OBQ11.164) Which of the following patients may benefit from a lesser tuberosity transfer (modified McLaughlin procedure)? Topic Review Topic

1. A kidney transplant recipient with AVN of the humeral head
2. A patient with severe rheumatoid arthritis
3. A young man with a locked posterior dislocation following an electric shock injury at work
4. A patient with a history of previous shoulder surgery that now has subscapularis insufficiency
5. A patient with a large Hill-Sachs defect following an anterior shoulder dislocation

(OBQ10.102) A 26-year-old football offensive lineman presents with shoulder pain which is affecting his ability to block effectively. On exam, he has a positive jerk test and a positive Kim test. What is his most likely diagnosis? Topic Review Topic

1. SLAP tear
2. ALPSA lesion
3. Hill-Sachs lesion
4. Posterior labral tear
5. PASTA tear

(OBQ09.7) An acute posterior shoulder dislocation should be suspected in a patient with pain and the shoulder locked in what position? Topic Review Topic

1. Internal rotation
2. External rotation
3. Forward elevation
4. Abduction
5. Retraction

(OBQ09.106) A football player subluxates his shoulder while blocking with his arm forward flexed and internally rotated. The “Jerk” test is positive. What is his most likely pathology? Topic Review Topic

1. Bankart lesion
2. Kim lesion
3. Hill-Sachs lesion
4. Glenohumeral internal rotation deficit
5. Acromioclavicular separation

(OBQ08.117) Posterior glenohumeral dislocations are as common as anterior dislocations in which of the following patient groups? Topic Review Topic

1. Football players
2. Marfan's syndrome patients
3. Renal failure patients
4. Epilepsy patients
5. Women

(OBQ08.161) A 35-year-old man awoke following a night of heavy drinking with severe right shoulder pain and inability to raise his arm above his head. A radiograph from the emergency room is provided in Figure A. He was treated with a sling for a diagnosis of rotator cuff tear. Six weeks later, he complains of continued pain and difficulty using the arm. Which of the following is the next best step in management? Topic Review Topic
FIGURES: A          

1. Physical therapy for range of motion followed by rotator cuff and deltoid strengthening exercises
2. Axillary radiograph of the shoulder
3. EMG to evaluate the suprascapular and axillary nerves
4. Arthroscopic rotator cuff repair
5. Open subacromial decompression and latissimus dorsi transfer for massive cuff tear

(OBQ08.270) A football linemen has posterior shoulder pain after making a block with his arm in forward flexion and internal rotation. What is the most likely diagnosis? Topic Review Topic

1. Bankart lesion
2. Posterior labral tear
3. Superior labral tear
4. Humeral avulsion of the glenohumeral ligament (HAGL)
5. Acromioclavicular separatation

(OBQ06.15) A 63-year-old diabetic female complains of left shoulder pain and decreased range of motion 7 months after a fall onto her left side. On physical examination she has marked decrease in external rotation. A radiograph obtained earlier that day at her primary care office is displayed in Figure A. What is the next step in management? Topic Review Topic
FIGURES: A          

1. Physical therapy for adhesive capsulitis secondary to chronic 2-part humeral head fracture
2. Proximal humeral arthroplasty
3. Obtain further radiographic studies
4. Open reduction and internal fixation of the chronic 2-part humeral head fracture
5. Sling immobilization for 10-14 days then begin physical therapy for chronic 2-part humeral head fracture

(OBQ06.156) A 25-year old female with a seizure disorder complains of persistent left shoulder pain after sustaining a seizure 1 week ago. She was placed in a sling in the ER and is following up in your office. Figure A shows the radiograph taken in the ER. On examination, her range of motion is limited and is only able to externally rotate to neutral. What is the next step in management? Topic Review Topic
FIGURES: A          

1. Sling use for comfort and follow-up in 2 weeks
2. Repeat True AP radiograph
3. Axillary lateral radiograph
4. MRI of the shoulder
5. Intra-articular cortisone injection with range of motion exercises

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