Glenoid Bone Deficiency in Recurrent Anterior Shoulder Instability -

Reviewed by

Dr David Shepherd MBBS | Accredited Orthopaedic Registrar

Glenohumeral anatomy

Stability conferred by
- Joint congruity/ anatomy
- Passive stabilisers
- Muscle force and coordination
Glenoid
- 5 cm2
- 5-15 degrees retroverted to scapula
Humeral head
- 30-50 degrees retroverted
- 15 cm2

Bone lesions

Hill-Sachs
- Posterolateral in anterior dislocation
- Anteromedial in posterior dislocation
Bankart
- Bony / soft tissue

Anatomy

SGHL
- Protects anterior instability in outstretched arm
- Prevents inferior translation in adduction
IGHL
- Tight in abduction, ER
- Labral lesion without IGHL injury
  - Not unstable anteriorly
- IGHL injury without Labral injury
  - Anterior instability
- Posterior band
  - Prevents inferior translation in IR
- Multidirectional instability
  - Entire IGHL complex and capsule laxity

Instability

Direction
- Anterior dislocation
  - 96-98%
  - Indirect trauma to Abducted, extended, ER arm
- Posterior dislocation
  - Axial, posterior force on an IR adducted arm
- Inferior (luxatio erecta)
Mechanism of Injury
- 96% traumatic
Associated Nerve lesions
- Axillary 42%
- Suprascapular 14%
- Musculocutaneous 12%

Management

Immobilise 3 weeks
- Early use
Goals
- Strengthen dynamic stabilisers
- Regain ROM
- Avoid provocative positions
- Muscles
  - RC, Deltoid, Pec major, Latissimus
    - Resistive exercises, isometric progressing to isokinetic
- Proprioception

Recurrence

Age
- <20
  - 95%
- 20-40
  - 40-75%
- >40
  - 0-20%

Management Recurrent Instability

Anterior instabilty
- Open
  - Bone anchor/trans-osseos sutures of Bankart
    - 2-8% recurrence rate
  - Putti-Platt, Capsular shift alone
    - poor results
- Arthoscopic
  - 4-49% recurrence
  - Range of techniques – sutures, bony anchors, bioabsorable tacks
Posterior instability
- No consensus, poorer outcomes up to 80% unsatisfactory
- Open with bony augmentation + capsular shift
- Arthroscopic
  - aim for capsular shift + labral repair
Multidirectional
- Open Inferior Shift ( Neer) – 97% satsifactory

Epidemiology of Bone loss.

Lack of uniform measure for bone loss accounts for lack of consistency in literature
Bone deficiency
- 22% initial dislocations
- Up to 90% recurrent instability
- Up to 89% failed stabilisation procedures
Nature of defect (recurrent anterior instability)
- Fracture fragments
- Attritional bone loss
- Combination
Most common location
- Anterior to glenoid face
- Majority between 2:30 – 4:20
Mechanism
- Dislocation with greater axial load (rugby) vs rotational ( avulsion by inferior GH ligament)
Defects may
- Occur at injury
- Develop with recurrent instability
Natural History
- Acute recurrence
  - Fracture fragments often present
- Delayed recurrence (15/12)
  - Attritional pattern – no identifiable fragment
  - Fragments have partially resorbed
Biomechanics
- Gleno-humeral mismatch
  - Decreased concavity to prevent dislocation
  - Smaller area to resist axial force, increasing the shear forces to a repaired capsulo-labral interface
Pertinent History
- Preinjury activity level
- Details of dislocation
  - High energy, axial load
- Recurrent instability
  - in mid-range 20 – 60 deg
  - Low energy events
- Previous surgery

Examination findings

Routine examination
- Deformity, scars, RC atrophy
- ROM (active, passive), Cuff strength
- Provocative labral signs
- Stability
  - Direction, magnitude of laxity
- Early and midrange apprehension, unidirectional suggestive of bony deficiency.

Imaging

Xray

AP
axillary views
Apical oblique
Didiee
West Point
Angles relative to glenoid face – higher yield

CT

Estimate bone loss
detect rim fracture fragments
Quantified as percentage of normal inferior glenoid surface area
- Best fit circle on inferior 2/3 of glenoid
- Degree of bone loss as a percentage of area of circle

Arthroscopic Quantification of Bone Loss

Normal Glenoid average diameter 24mm
Bare area = centre of glenoid
% bone loss = Distance to Post rim – Distance to Anterior rim
Defect often has a posterior slope, creating a narrower inferior glenoid

Critical Limit of Bone loss

Several studies
- Sequential removal of 9%, 21%, 34%, 46%
- Osteotomy at 45 degrees to long axis
- Significant instability at defects> 21%
- Bone loss of 6 -7mm of the inferior glenoid circle are significant
Inverted Pear appearance
- Range from 7.5mm (28%) – 8.6 mm (36%) of bone
- high rate of failure of labral repairs in inverted pear appearance

Management

Non-Operative

Goal
- maintenance of shoulder stability during functional activity
Methods
- Strengthening of Dynamic stabilisers – periscapular muscles and RC.
- No role for external rotation bracing in presence of bone loss
Indications
- Low demand patient
- Small defect < 20%

Operative managment

Considerations
- patient activity level
- degree of bone loss
Bone Loss < 15%
- Majority of patients with recurrent anterior instability
- Results
  - Bigliani –Open repair case series – 10-15%
    - 94% of fractures remained stable
    - 72% normal post-op stability
    - If bone fragment ignored – 40% recurrence
Bone Loss 15 -25%
- Increased failure of soft tissue only repair
- Consider open glenoid augmentation
- Results
  - Sugaya –case series 42 shoulders. 6/12 of instability
    - Arthroscopic reduction and suture anchor fixation
    - 34 month follow up. 93% good/excellent, 95% return to sport
    - Post operative CT scans in 12 patients – union of fragment
  - Mologne
    - 14.2 % failure rate of arthroscopic repair if attritional bone loss and no fragment to repair
  - Burkhart & DeBeer – 89% failure rate in overhead athletes in soft tissue only repair
Bone Loss >25%
- Acute
  - open fracture repair
- Chronic
  - More commonly – arthroscopically deficient glenoid – inverted pear
    - Bone fragment is absent (attritional loss) or resorbed
- Glenoid augmentation required
  - Options
    - Corocoid to transfer to anterinferior glenoid
      - Bristow
        Corocoid osteotomised transversely and fixed perpendicular to glenoid at base
      - Laterjet
        Long axis parallel to anterior glenoid rim
        Cuff of coracoacromial ligament for capsulolabral attachment
        More anatomic restoration of arc
      - Results
        Hovelius
        118 patients with recurrent instability, 15 year follow up
        3.4% redislocation, 10% subluxation
        Good/Excellent in 86%
        Arthropathy
        14 % moderate to severe,
        35% mild
    - Iliac Crest autograft
      - High rates of arthrosis and 18% recurrent instability

Take home message

High frequency of traumatic recurrent anterior instability cases involve glenoid bone loss
Xray, CT scan and Arthroscopy to assess extent of bone loss
Bone Loss
- <15%
  - Soft tissue bankart repair
- 15-30%
  - patient activity denotes bony procedure
  - Repair of fragment or augmentation
- >30%
  - Anatomical fiaxtion or augmentation.

References

Glenoid bone deficiency in recurrent anterior shoulder instability: diagnosis and management.
- Piasecki DP, Verma NN, Romeo AA, Levine WN, Bach BR Jr, Provencher MT.
- J Am Acad Orthop Surg. 2009 Aug;17(8):482-93. Review