Shoulder Instability

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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.

Shoulder Joint Ligaments and Tendons

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%).

FeatureTUBSAMBRI
EtiologyTraumaticAtraumatic
DirectionUnidirectional (usually Anterior)Multidirectional
PathologyBankart lesionOften bilateral, capsular laxity
TreatmentSurgery (often required)Rehabilitation (primary), Inferior capsular shift (if surgery)
📌 MnemonicTorn Loose, Bankart, SurgeryAtraumatic, Multidirectional, Bilateral, Rehabilitation, Inferior capsular shift
- **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 CategoryKey Tests
    Anterior InstabilityApprehension, Relocation, Surprise
    Posterior InstabilityPosterior Drawer, Jerk Test
    Inferior InstabilitySulcus Sign (Grades +1/+2/+3)
    Labral/SLAPO'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).

Bankart vs. Latarjet: Patient-reported outcomes over 2 years

⭐ 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.

Practice Questions: Shoulder Instability

Test your understanding with these related questions

A patient received an electric shock and fell down. He cannot do external rotation of shoulder and cannot move arm. What is the diagnosis:-

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Flashcards: Shoulder Instability

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The "unhappy triad" presents with acute _____ and signs of joint injury/instability.

TAP TO REVEAL ANSWER

The "unhappy triad" presents with acute _____ and signs of joint injury/instability.

knee pain

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