Recurrent Posterior Instability

Aetiology

  • Similar to MDI (Multidirectional Instability)
  • Ligamentous laxity > 50%
  • Repetitive microtrauma is common
  • Macrotrauma is uncommon
  • Commonly associated with MDI
  • Direction
    • Posterior only 20%
    • Posterior & Inferior 20%
    • Posterior, Inferior & Anterior 60%

Pathogenesis

  • Capsular laxity
  • Reverse Bankart lesion
  • Reverse Hill-Sach’s lesion
  • Increased humeral head retroversion
  • Posterior glenoid deficiency

History

  • Pain or instability with arm in
    • Forward flexion
    • Adduction
    • Internal Rotation
  • Baseball, Swimming & Rowing typically involved
  • Any dislocations or subluxations spontaneously reduced

Examination

  • Positive Posterior Apprehension Test
    • Stabilise the medial border of scapula
    • Posterior directed force to 90° flexed humerus, adducted & internally rotated
    • Positive test is
      • Subluxation or dislocation with pain
      • Discomfort that reproduces patient’s symptoms
  • Sulcus Sign (posteroinferior instability)
  • Joint line tenderness
    • 2/3 have posterior joint line tenderness
  • Anterior drawer
  • Anterior apprehension
  • Ligamentous laxity common

Investigations

X-ray

  • AP in Internal, External & Neutral rotation
  • Axillary view
  • Transcapular view

CT

  • Retroverted glenoid
  • Glenoid hypoplasia
  • Posterior Bankart lesion

MRI

  • Labral tears
  • More difficult than anterior probably due to capsular redundancy
  • Arthroscopy & EUA
  • Useful to confirm diagnosis & exclude MDI

Treatment

Non operative

  • Recommended prolonged initial treatment for all patients
  • Patients with posterior instability fared much better than anterior instability with rehabilitation
  • 50% failure with surgery in posterior instability
  • Rehabilitation
    • Rotator cuff & Periscapular stabilisers strengthening
    • Infraspinatus & Teres Minor with external rotation exercises
    • Avoid adducted, flexed position (bench press etc)

Operative

  • Indications
    • Failed nonoperative management
    • Moderate-Severe Disability
  • Divided into
    • Bony procedures
    • Soft tissue procedures
  • 1. Soft Tissue Procedures
    • Posterior Capsular Shift
      • Neer first described
      • T capsulotomy with vertical limb laterally
      • Inferior capsular shift performed
      • 12-6 o’clock
      • Posteroinferior capsule shifted superiorly
      • If reverse Bankart found (10-15%) then reattachment performed
      • 80% satisfactory results
      • Bigliani 1984 22 out 25 good results
  • 2. Bony Procedures
    • Posterior Bone Block
      • Hindenach 1947
      • Iliac crest graft applied to scapular neck so it projects 1/3” past glenoid margin laterally
      • Can combine with capsular shift
      • No impingement with the humeral head as lead to arthritic changes
      • Indications
        • Glenoid hypoplasia
        • Posterior capsular shift failed
    • Glenoplasty
      • Scott 1967
      • Opening wedge osteotomy of the glenoid neck with bone graft insertion
      • Indications
        • Excessive glenoid retroversion
        • Unidirectional traumatic posterior dislocation
        • Poor results if MDI present
      • Complications
        • Fracture
        • Non-union
        • Loss of graft position
        • Glenoid AVN
          • 30 – 40 %
    • Humeral Osteotomy
      • Osteotomy close to head in cancellous bone
      • Rotated the humeral shaft externally through 30° & position maintained with AO plate
      • Indications
        • Excessive humeral retroversion
        • Good results with change in the ER/ IR arc with loss of IR & gain of ER