Shoulder Instability

Anatomy & Biomechanics - Anatomy's Tightrope Act

• Glenohumeral Joint (GHJ): Inherently unstable; relies on static & dynamic stabilizers.
• Static Stabilizers:
  • Glenoid: Shallow; retroversion 2-7°.
  • Labrum: Fibrocartilage, deepens glenoid.

    ⭐ Labrum increases glenoid depth by ~50%.

  • Ligaments:
    • SGHL: Resists inferior translation (adducted).
    • MGHL: Limits ER at 0-45° abd. (📌 MGHL May Go Hiding - often variable).
    • IGHLC: Main anterior stabilizer in ABER position (90° abd. + ER).
  • Negative intra-articular pressure.
• Dynamic Stabilizers:
  • Rotator Cuff (SITS): Compresses humeral head.
  • Long Head of Biceps (LHB): Depresses head.
  • Scapulothoracic rhythm.

Classification & Lesions - Decoding the Wobble

• Etiology: Traumatic, Atraumatic, Microtraumatic (repetitive).
• Direction: Anterior, Posterior, Inferior (Luxatio erecta), Multidirectional (MDI).
• Severity: Dislocation (complete) vs. Subluxation (partial).

⭐ Anterior instability is the most common type (approx. 95%).

- **Bankart Lesion**: Anteroinferior labrum & IGHL detachment.
    + Bony Bankart: Involves glenoid rim fracture.
    ![Bankart Lesion: Anterior Inferior Labral Tear](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Orthopaedics_Sports_Medicine_Shoulder_Instability/65208883-ee75-4d5f-a02a-ad846fcd87f8.jpg)
- **Hill-Sachs Lesion**: Posterolateral humeral head impaction fracture.
    ![Bankart Lesion of the Shoulder](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Orthopaedics_Sports_Medicine_Shoulder_Instability/c556102e-ee01-497a-bdd2-d17524683119.jpg)
- ALPSA: Anterior Labrum Periosteal Sleeve Avulsion.
- HAGL: Humeral Avulsion of Glenohumeral Ligament.
- SLAP: Superior Labrum Anterior-Posterior tear.

Diagnosis & Evaluation - Clinical Detective Work

• History: Mechanism (FOOSH, direct blow, overuse), prior dislocations, pain, clicking, "dead arm" sensation. Differentiate TUBS vs. AMBRI.
• Examination: Observe (asymmetry, atrophy), palpate key structures, assess active/passive ROM. Neurovascular status crucial.

• Special Tests:

  Test Category	Key Tests
  Anterior Instability	Apprehension, Relocation, Surprise
  Posterior Instability	Posterior Drawer, Jerk Test
  Inferior Instability	Sulcus Sign (Grades +1/+2/+3)
  Labral/SLAP	O'Brien's, Crank Test

• Imaging:
  • X-rays: AP, Grashey, Axillary lateral. Consider West Point (bony Bankart), Stryker Notch (Hill-Sachs).

  ⭐ The West Point axillary view is best for imaging a bony Bankart lesion.

  • MRI/MR Arthrogram: Gold standard for labral tears, capsular injury, RTC.

Management Principles - Fixing the Flux

• Goal: Restore stability & function; prevent recurrence & arthropathy.
• Conservative Management (Often first-line):
  • Immobilization (sling for comfort, brief duration).
  • Physiotherapy: Key for AMBRI. Focus on rotator cuff, deltoid, and scapular stabilizer strengthening.
  • Activity modification.
• Surgical Management (Indications vary by instability type):
  • TUBS: Often requires surgery after first dislocation in high-demand individuals or for recurrence.
    • Arthroscopic Bankart Repair: For labral tears without significant bone loss.
    • Latarjet Procedure: For significant glenoid bone loss >20-25% or failed soft-tissue repair.
  • AMBRI: Surgery (e.g., capsular shift/plication) if extensive physiotherapy fails.
  • 📌 Mnemonic (Instability Types & Treatment Bias):
    • TUBS: Traumatic, Unidirectional, Bankart lesion, Surgery often needed.
    • AMBRI: Atraumatic, Multidirectional, Bilateral, Rehabilitation (primary), Inferior capsular shift (if surgery).

⭐ Latarjet procedure is indicated for recurrent anterior instability with significant glenoid bone loss (typically >20-25%) or failed previous soft tissue repairs.

High‑Yield Points - ⚡ Biggest Takeaways

• Anterior instability (95%) is most common, from abduction & external rotation.
• Bankart lesion (anteroinferior labral tear) is pathognomonic for traumatic anterior instability.
• Hill-Sachs lesion (humeral head impaction) often co-exists with Bankart.
• Key acronyms: TUBS (Traumatic, Unidirectional, Bankart, Surgery) & AMBRI (Atraumatic, Multidirectional, Bilateral, Rehabilitation).
• Tests: Apprehension, Relocation (anterior); Sulcus sign (inferior/MDI).
• High recurrence of traumatic dislocations in young, active patients.
• Posterior instability often follows seizures/electric shock.