Courtesy: Prof Young Lae Moon MD, Seoul, South Korea

Anterior Glenohumeral Instability

Anatomy, Evaluation, Imaging & Management

Basic Anatomy & Biomechanics

• The glenoid fossa is a shallow, dish-like structure

• At any given time, only ~25% of the humeral head articulates with the glenoid

• The glenoid labrum:

  • Deepens the socket

  • Increases humeral head contact area by ~70%

• Shoulder stability depends on a balance between:

  • Static stabilizers (capsule, ligaments, labrum)

  • Dynamic stabilizers (muscles)

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Static Stabilizers of the Shoulder

Superior Glenohumeral Ligament (SGHL)

• Origin: Glenoid rim near labral apex

• Inserts with the long head of biceps onto the anatomic neck of humerus

• Function: Prevents inferior subluxation of the humeral head

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Middle Glenohumeral Ligament (MGHL)

• Origin: Anterior glenoid margin

• Insertion: Anatomic neck of humerus

• Function:

  • Primary stabilizer at ~45° of abduction

  • Works with anterosuperior fibers of the IGHL

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Inferior Glenohumeral Ligament Complex (IGHL)

• Components:

  • Anterior band

  • Posterior band

  • Axillary pouch

• Origin: Anterior, inferior, and posterior glenoid

• Insertion: Anatomic and surgical neck of humerus

• Key role:

  • Primary static anterior stabilizer of the shoulder, especially in abduction and external rotation

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Dynamic Stabilizers

Extrinsic Muscle

• Deltoid

  • Main extrinsic stabilizer

  • Tends to translate the humeral head superiorly

Intrinsic Muscles

• Provide compressive stabilization

• Subscapularis

  • Principal anterior dynamic stabilizer

  • Most effective in lower ranges of abduction and external rotation

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Clinical Evaluation

History

• Timing and mechanism of injury

• Sport or activity level

• Number of instability episodes

• Voluntary vs involuntary instability

• Previous treatment (operative or non-operative)

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Physical Examination Tests

Anterior Instability Drawer Test

• Patient standing or supine

• One hand stabilizes the glenoid

• Other hand translates humeral head anteriorly and posteriorly

• Assesses degree of translation and overriding

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Crank (Apprehension) Test

• Patient supine

• Shoulder placed in abduction and external rotation

• Positive test:

  • Patient shows apprehension

  • Points to anterior shoulder pain

• If positive ? proceed to relocation test

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Jobe’s Relocation Test

• Examiner applies posterior force over humeral head

• Relief of apprehension indicates anterior instability

• Sudden release reproduces pain/apprehension

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Sulcus Sign

• Inferior traction applied to arm

• Observe sulcus under lateral acromion

• Grading:

  • <1 cm: normal / 1+

  • 1–2 cm: 2+

  • 2 cm: 3+

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Ligamentous Laxity Assessment

Beighton Score (0–9)

• Palms to floor with knees straight

• Thumb hyperflexion

• MCP hyperextension

• Elbow recurvatum

• Knee recurvatum

Score >/=4 suggests generalized ligamentous laxity

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Classification of Shoulder Instability

By Degree

• Subluxation

• Dislocation

By Chronology

• Acute

• Recurrent

• Chronic (fixed)

• Locked

By Etiology

• Traumatic

• Repetitive microtrauma

• Voluntary / involuntary

• Congenital

• Neuromuscular

• Seizure-related

By Direction

• Anterior

• Posterior

• Inferior

• Multidirectional

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Imaging Evaluation

Plain Radiographs

• AP view

  • Acute dislocation

  • Glenoid rim fractures (bony Bankart)

• Scapular Y view

  • Confirms reduction

• Axillary view

  • Confirms reduction

  • Detects:

    • Anterior glenoid deficiency

    • Hill-Sachs lesion

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CT Scan

• Gold standard for bipolar bone loss

• Quantifies:

  • Glenoid bone loss (GBL)

  • Size and orientation of Hill-Sachs lesion

• Critical for surgical planning

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MRI

• Evaluates soft-tissue injuries:

  • Labral tears

  • Rotator cuff tears

  • Biceps pathology

  • HAGL / reverse HAGL

  • ALPSA lesions

  • GLAD lesions

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Glenoid Bone Loss (GBL)

• Commonly measured using the best-fit circle method

• Critical thresholds:

  • >13.5% – increased failure of soft-tissue repair

  • >20% – osseous augmentation usually required

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Glenoid Track Concept

• Glenoid track around 83% of glenoid width

• Represents area of humeral head contact with glenoid

On-Track vs Off-Track

• On-track Hill-Sachs

  • Defect smaller than glenoid track

  • Lower risk of engagement

• Off-track Hill-Sachs

  • Defect larger than glenoid track

  • High risk of engagement and instability

Calculations

• Glenoid track = (0.83 × D) – d

• Hill-Sachs interval = Hill-Sachs defect + bone bridge

• Distance to Dislocation (DTD) = Glenoid track – Hill-Sachs interval

• DTD = 0 -> On-track lesion

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Management

Non-Operative Treatment

• Suitable for:

  • Older patients

  • Low-demand individuals

  • Non-contact sports

  • First-time dislocation

  • No critical bone loss or cuff tear

• Shared decision-making in young low-risk patients

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Surgical Management

Indications

• Age <20 years

• Contact or collision sports

• Male sex

• Recurrent instability

• Osseous Bankart lesion

• Bipolar bone loss

• Failed non-operative treatment

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Arthroscopic Bankart Repair

Key Recommendations

• Use 4 anchors, appropriately spaced

• Restore labral concavity

• Optimize anchor trajectory

Technical Pearls

• Anterosuperior viewing portal

• Avoid anchor placement above 3 o’clock

• Capsular plication with labral repair

• Posteroinferior capsular stitches for balance

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Remplissage Procedure

• Fills Hill-Sachs defect with infraspinatus tendon and capsule

• Converts lesion to extra-articular

• Prevents engagement

Indications

• Off-track Hill-Sachs with GBL <25%

• Contact athletes or hyperlaxity

• Near-track lesions

• Failed Bankart repair without critical bone loss

Recurrence rates reported as low as ~5%

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Coracoid Transfer Procedures

Bristow / Latarjet

• Restores glenoid bone stock

• Provides:

  • Bony augmentation

  • Dynamic sling effect from conjoined tendon

  • Capsular reinforcement

• Effective for:

  • Critical bone loss

  • High-risk recurrent instability

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Postoperative Rehabilitation

Phase 1: Immobilization

• Sling protection

Phase 2: Passive & Active-Assisted Motion

• Gradual ROM restoration

Phase 3: Strengthening

• Rotator cuff

• Scapular stabilizers

• Sport-specific training

Return to sport/work: 4–6 months, depending on goals
Criteria-based testing recommended before return

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Key Take-Home Messages

• Shoulder stability is multifactorial

• Bone loss assessment is critical

• Glenoid track guides treatment

• Young, active patients have high recurrence risk

• Procedure selection must be individualized