Acromioclavicular (AC) Joint Injury

1. Anatomy

Figure: Anatomy of the acromioclavicular joint (Tintinalli's Emergency Medicine)

• Fibrocartilaginous intra-articular disc: Present in two forms - complete and partial (meniscoid). It undergoes degeneration by the fourth decade of life. - Rockwood & Green's, p.1113
• Joint inclination: The joint may be nearly vertical or inclined downward and medially, with the clavicle overriding the acromion by up to 50 degrees. Approximately 50% of joints have incongruent articular surfaces. - Rockwood & Green's, p.1113
• Nerve supply: Branches of the axillary, suprascapular, and anterolateral pectoral nerves supply the AC joint.

Stabilizing Ligaments

• Trapezoid ligament (lateral) - resists axial compression and anterior-posterior translation
• Conoid ligament (medial) - resists superior displacement most strongly

2. Epidemiology and Mechanism of Injury

Mechanism

• Direct force (most common): A fall on the point of the shoulder with the arm adducted drives the acromion downward while the clavicle remains held up by the sternocleidomastoid, creating a shearing force across the joint.
• Indirect force (less common): A fall on the outstretched hand transmits force up the arm to the AC joint.
• The scapula and shoulder complex droop inferomedially while the clavicle appears to displace superiorly. - Rockwood & Green's, p.1113

3. Rockwood Classification (Tossy-Rockwood)

4. Clinical Features

History

• Fall on the point of the shoulder or FOOSH (fall on outstretched hand)
• Pain at the top of the shoulder, localized to the AC joint
• Difficulty lifting the arm overhead or across the body

Physical Examination

• Point tenderness directly over the AC joint
• Step-off deformity (prominence of the distal clavicle) in Types III-V
• Cross-arm adduction test: Arm elevated to 90 degrees, then adducted across the chest with elbow at 90 degrees. Positive test = pain specifically at AC joint. O'Brien et al. reported 88% sensitivity for AC joint abnormalities. - Rockwood & Green's, p.1095
• Piano key sign: In acute complete dislocations, the clavicle can be pushed down and springs back up when released
• Range of motion: May be limited depending on severity; a high painful arc (last 20-30° of elevation) is common. - Bailey & Love's, p.2252
• Cross-body adduction reproduces pain in AC joint arthritis

5. Imaging

Plain Radiographs

• AC-specific views require one-third to one-half the beam penetration of standard shoulder films. Always request "AC joint" radiographs, not "shoulder" radiographs, to avoid overpenetration. - Rockwood & Green's, p.1095
• Zanca view: 10-15 degree cephalic tilt AP projection - removes the spine of the scapula from the image; the preferred view for AC joint evaluation.
• Axillary lateral view: Mandatory when posterior dislocation (Type IV) is suspected.
• Bilateral comparison views: Allow direct comparison of CC distance.

Stress Radiographs

• Weighted stress views (10 kg) were historically used to differentiate Type III from Type V injury, but are no longer routinely recommended because:
  • They have not been validated to correlate with intraoperative findings
  • They do not reliably change injury grade or treatment decision
  • They cause significant pain in the acute setting - Rockwood & Green's, p.1095

Normal Radiographic Measurements

• AC joint width: 1-3 mm (joint space)
• CC distance: 11-13 mm (conoid to trapezoid tuberosity)

• 25% side-to-side difference in CC distance = significant ligament injury

Advanced Imaging

• CT scan: For complex injuries, suspected fractures, or when plain films are inconclusive
• MRI: Useful for evaluating associated labral, rotator cuff, or soft tissue injuries
• Ultrasound: Can demonstrate joint contour and dynamic instability; less useful than CT for SC joint injuries

6. Associated Injuries

• Rotator cuff tears
• Distal clavicle fractures
• Coracoid process fractures
• Neurovascular injuries
• Pneumothorax or rib fractures in severe trauma
• Glenohumeral dislocation

7. Treatment

Non-Operative Management

• Acute (0-2 weeks): Rest, ice, analgesics, sling immobilization. A simple sling is the most convenient and effective initial treatment.
• Subacute (2-6 weeks): Gradual return to range-of-motion exercises starting at 7-14 days for Types I and II.
• Return to sport: As early as 10-15 days for low-grade (Type I/II) injuries in competitive athletes, though pain-free return may take longer.
• Local anesthetic injections at the AC joint are an accepted adjunct for competitive athletes (Australian Rules football and rugby data show mean of 5.7 games using injections). - Rockwood & Green's, p.1118

Operative Management

• Types IV, V, and VI (operative treatment is the standard of care)
• Type III failing 3-6 months of supervised rehabilitation
• Specific Type III subgroups: young overhead athletes, manual laborers, polytrauma patients
• Chronic symptomatic instability

Surgical Techniques

1. Hook Plate Fixation

• Currently the preferred acute surgical technique according to Rockwood & Green's
• Plate body secured to superior distal clavicle with cortical screws; hook portion passes beneath the acromion
• Supported by retrospective studies and biomechanical data
• Reliable for preventing loss of reduction in the acute setting
• Requires secondary surgery to remove the hook plate to avoid subacromial impingement - Rockwood & Green's, p.1124

2. Coracoclavicular Suspensory Fixation (Button/Loop Techniques)

• Uses high-strength suture or synthetic ligament (e.g., TightRope, Surgilig) through bone tunnels in the clavicle and around/through the coracoid process
• Advantages: minimally invasive; avoids need for hardware removal
• Disadvantages: risk of coracoid/clavicle fracture at tunnels; loss of reduction in 10-30% of cases

3. CC Ligament Reconstruction (Weaver-Dunn and Modifications)

• Involves transfer of the coracoacromial ligament to reconstruct the CC ligament
• Often combined with graft augmentation (e.g., gracilis or semitendinosus autograft) for chronic reconstructions

4. Historical Techniques (largely abandoned or used selectively)

• K-wire fixation across the AC joint: Significant risk of pin migration, breakage, and neurovascular injury - no longer recommended
• Bosworth screw: CC fixation with a large screw; risk of hardware failure and need for removal
• Phemister technique: Temporary Kirschner wire fixation

5. Arthroscopic-Assisted Reconstruction

• Gaining popularity for chronic AC joint instability
• Allows concurrent intra-articular procedures (labral repair, etc.)
• Techniques include arthroscopic-assisted coracoclavicular loop fixation

8. Complications

Post-Operative Complications - Rockwood & Green's, p.1141

Non-Operative Complications

• Posttraumatic osteolysis of the distal clavicle: Seen after repetitive stress or single acute injury
• Persistent horizontal instability: Particularly after Type II injuries with unrecognized posterior capsular disruption
• AC joint arthritis: Common long-term sequela requiring corticosteroid injection or distal clavicle excision

9. AC Joint Arthritis (Chronic/Late Presentation)

• Common in males aged 20-50 years
• Inferior osteophytes can impinge on the underlying rotator cuff
• Symptoms: pain worse with overhead activity and cross-body adduction; high painful arc (last 20-30°)
• Treatment: Intra-articular corticosteroid injection (diagnostic and therapeutic); surgical excision of the lateral 0.5-1 cm of the distal clavicle (Mumford procedure) - arthroscopic or open - gives reliable pain relief

10. Summary - Treatment Algorithm

AC Joint Injury
     │
     ├── Type I & II ──► Conservative (sling, analgesia, early ROM)
     │
     ├── Type III ──► Conservative first (3-6 months)
     │                    │
     │                    └── Failure / young overhead athlete ──► Surgery
     │
     ├── Type IV ──► Surgery (open reduction)
     │
     ├── Type V ──► Surgery (preferred: hook plate or CC reconstruction)
     │
     └── Type VI ──► Surgery (assess and treat associated injuries)

Key Teaching Points

1. The AC joint is stabilized by two separate ligament systems: the AC ligaments (horizontal stability) and the CC ligaments (vertical stability). Each must be assessed independently.
2. The Rockwood classification (Types I-VI) drives treatment decisions. The critical distinction is Type III vs Type V, determined by whether the deltotrapezial fascia is stripped.
3. AC-specific radiographs are mandatory - standard shoulder technique overpenetrates and misses subtle fractures. The Zanca view (10-15° cephalic tilt) is preferred.
4. Weighted stress views are no longer routinely recommended.
5. Type III injuries remain controversial: current evidence supports a trial of nonoperative management for most patients.
6. Types IV, V, and VI are surgical injuries. Hook plate fixation is currently the preferred acute technique per Rockwood & Green's.
7. Loss of reduction (10-30%) is the most common surgical complication.

Radiographic Images - Rockwood Classification

AP stress radiographs illustrating Rockwood Types I, II, III, and V injuries

Rockwood Type III AC joint separation with superior clavicular displacement

Rockwood Type V injury: complete disruption of all stabilizing structures with 200-300% increase in CC distance

Shoulder (Glenohumeral) Dislocation

1. Anatomy and Biomechanics of Glenohumeral Stability

Static Stabilizers

Dynamic Stabilizers

• Rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis): Provide stability via three mechanisms: (1) concavity-compression - compressing the humeral head into the glenoid; (2) coordinated contraction to guide the head onto the glenoid center; (3) dynamization of the GHL through their attachments. A 50% reduction in rotator cuff forces increases anterior displacement by 46% and posterior displacement by 31%. - Rockwood & Green's, p.1272
• Long head of biceps: Contributes to anterior stability, particularly in the ABER position
• Scapulothoracic musculature: Positions the scapula to optimize glenohumeral stability; scapulothoracic dyskinesia is especially important in MDI

2. Epidemiology

• GH dislocation is the most common dislocation in the body - accounts for approximately 50% of all dislocations
• Incidence: ~17 per 100,000 person-years
• Anterior dislocations account for 95-97% of all GH dislocations
• Peak incidence in males aged 20-30 years (sports-related) and in the elderly (falls)
• Recurrence rate after first-time anterior dislocation approaches 80% in males under 20 years old - Rockwood & Green's, p.1262

3. Classification Systems

A. Matsen & Thomas Classification (TUBS / AMBRII) - Rockwood & Green's, p.1267

• Traumatic
• Unidirectional
• Bankart lesion present
• Surgery usually required for recurrent instability

• Atraumatic
• Multidirectional
• Bilateral laxity
• Rehabilitation is first-line treatment
• If surgery necessary, tighten the Inferior capsule and rotator Interval

B. Bailey & Love Classification - Bailey & Love's, p.2323

1. Traumatic: Unidirectional, involuntary - surgery usually successful
2. Atraumatic: Multidirectional, painful, involuntary - responds to surgery
3. Habitual: Voluntary, ligament laxity, painless - surgery usually contraindicated

C. FEDS Classification (Kuhn) - Rockwood & Green's, p.1265

• Frequency (solitary / occasional / frequent)
• Etiology (traumatic / atraumatic)
• Direction (anterior / inferior / posterior)
• Severity (subluxation / dislocation)

D. OTA Classification

• 10-A1: Anterior dislocation
• 10-A2: Posterior dislocation
• 10-A5: Inferior dislocation (luxatio erecta)

E. Stanmore Triangle Classification - Rockwood & Green's, p.1267

• Polar Type 1: Traumatic, structural (acute / persistent / recurrent)
• Polar Type 2: Atraumatic, structural (recurrent)
• Polar Type 3: Muscle patterning, non-structural (no labral damage, abnormal EMG)

F. ABC Classification (Posterior Instability - Moroder & Scheibel)

• A: First-time (A1 = subluxation, A2 = locked dislocation)
• B: Dynamic recurrent (B1 = functional, B2 = structural with Bankart/bone loss)
• C: Chronic static (C1 = constitutional, C2 = acquired)

4. Anterior Shoulder Dislocation

Mechanism

• Arm raised in abduction + external rotation (throwing, tackling)
• Fall on outstretched hand (FOOSH) with arm abducted

Subtypes of Anterior Dislocation (by position of humeral head)

1. Subcoracoid - most common; head lies inferior to coracoid process
2. Subglenoid - head lies inferior to glenoid
3. Subclavicular - rare; head lies medial to coracoid, under clavicle
4. Intrathoracic - very rare; head displaced into chest between ribs

Clinical Features

• Severe shoulder pain and inability to use the arm
• Arm held in slight abduction and external rotation
• Shoulder has a "squared off" appearance - loss of normal rounded deltoid contour
• Humeral head palpable anteriorly below the coracoid
• Hollow beneath the acromion (empty glenoid)
• Patient resists adduction and internal rotation
• Cannot touch contralateral shoulder with the affected hand (Dugas test positive)
• Neurovascular examination is mandatory - axillary nerve is most commonly injured (test sensation over deltoid patch)

Associated Pathological Lesions

MRI showing the classic "kissing lesions": Hill-Sachs lesion posterolaterally on the humeral head, and Bankart lesion at the anterior-inferior glenoid labrum

CT coronal and axial views showing bipolar bone loss: bony Bankart lesion (anterior glenoid) and large Hill-Sachs deformity (posterolateral humeral head)

5. Posterior Shoulder Dislocation

Key Points

• Accounts for only 2-4% of all GH dislocations but is the most commonly missed dislocation in clinical practice - Bailey & Love's, p.2414
• Often initially missed on an AP radiograph, which may appear deceptively near-normal

Mechanism

• Electric shock or epileptic seizure (massive simultaneous contraction of internal rotators)
• "Half-Nelson" position (forced internal rotation with arm behind the back)
• Direct anterior blow to the shoulder
• Heavy fall with arm across the body

Clinical Features

• Arm held in adduction and internal rotation (opposite of anterior dislocation)
• Shoulder appears flattened anteriorly, prominent posteriorly
• Loss of external rotation (a key diagnostic sign - patient cannot externally rotate past neutral)
• AP radiograph may appear near-normal to the unwary; requires high clinical suspicion

Radiographic Signs of Posterior Dislocation

• "Light bulb sign" (or "drum-stick sign"): On AP view, the humeral head appears symmetrically rounded due to fixed internal rotation, lacking the normal convex/biconcave shadow of the lateral head - Bailey & Love's, p.2460
• "Trough line sign": A vertical line of cortical compression (reverse Hill-Sachs / McLaughlin lesion) on the anteromedial humeral head, visible on AP view
• Widening of the joint space >6 mm
• Axillary or scapular Y view confirms the dislocation and is mandatory - Tintinalli's

Associated Lesions

• Reverse Hill-Sachs (McLaughlin) lesion: Impaction fracture of the anteromedial humeral head against the posterior glenoid rim
• Reverse Bankart lesion: Posterior labral tear
• If >20-40% of the articular surface is involved, the head locks on the posterior glenoid rim ("locked posterior dislocation")

CT axial view: posterior GH dislocation with reverse Hill-Sachs lesion (arrow) on anteromedial humeral head

6. Inferior Dislocation (Luxatio Erecta)

• Extremely rare; arm is locked in full abduction overhead (patient cannot bring arm down)
• Mechanism: hyperabduction forcing the humeral head inferiorly, levering the neck against the acromion
• Associated with high rates of neurovascular injury (brachial plexus, axillary artery)
• Classified as OTA 10-A5
• Treatment: Traction in the direction of the arm (upward), then adduction

7. Imaging Protocol

Plain Radiographs (Minimum Three Views)

1. AP (True AP / Grashey view): Standard; 35-40° oblique to the plane of the scapula
2. Axillary lateral view: Gold standard for confirming direction of dislocation; mandatory when posterior dislocation is suspected
3. Scapular Y view ("Y view"): Useful when axillary view cannot be obtained

Advanced Imaging

• CT scan: Best for quantifying glenoid bone loss and Hill-Sachs lesion size; used for surgical planning. 3D CT reconstruction with en-face glenoid view allows measurement of bone defect using the "circle method"
• MRI / MR arthrogram: Best for soft tissue lesions - labral tears (Bankart, ALPSA, HAGL), IGHL damage, rotator cuff tears, cartilage lesions. MRI circle method accuracy is within 1.3% of 3D CT for glenoid bone loss calculation. - Rockwood & Green's, p.1263

Critical Glenoid Bone Loss - "The 25% Rule"

• Loss of >25-27% of the anterior-inferior glenoid width = inverted pear glenoid
• This amount of bone loss exceeds the critical threshold and predicts failure of soft-tissue repair (Bankart) alone
• Requires a bony augmentation procedure (Latarjet or bone block) - Rockwood & Green's, p.1263

8. Reduction Techniques - Anterior Dislocation

1. Stimson (Hanging-Weight) Method

• Patient prone, affected arm hanging off the table, 5-10 kg weight attached
• Gravity and muscle fatigue allow spontaneous reduction over 15-30 minutes
• Gentle and atraumatic; useful when patient cooperation is good

2. Cunningham (Muscle Massage) Technique

• Patient seated, examiner massages the deltoid, biceps, and trapezius while guiding the arm into adduction and external rotation
• No analgesia required in many cases; high success rate

3. External Rotation Method (Leidelmeyer / Eachempati)

• Patient supine, elbow flexed to 90°, arm slowly externally rotated in the plane of the body without traction
• Gentle; avoids forceful manipulation; success rate ~80-90%

4. Milch Technique

• Arm abducted overhead with simultaneous external rotation; thumb pressure on humeral head guides it back into the glenoid
• Can be done without sedation

5. Kocher Method (historical; now used cautiously)

• Elbow flexed 90°; traction then external rotation, adduction across chest, internal rotation
• Risk of humeral fracture with forceful application; no longer the first choice in most centres
• Contraindicated if fracture suspected

6. Hippocratic Method

• Operator places foot in axilla as counter-traction while applying longitudinal traction on the arm
• Risk of axillary nerve/vessel injury with the foot in the axilla; largely superseded

7. FARES (Fast, Reliable, Safe) Method

• Patient supine; longitudinal traction applied with oscillatory vertical movements as arm is progressively abducted to >90°; external rotation applied at approximately 90°
• High success rates without sedation in multiple studies

Posterior Dislocation Reduction

• Gentle traction on the adducted, internally rotated arm with anteriorly directed pressure on the posterior humeral head
• If locked (reverse Hill-Sachs engages the posterior glenoid), closed reduction under general anesthesia is required; locked lesions >20-40% articular involvement need open surgery - Bailey & Love's, p.2444
• Post-reduction: immobilize in external rotation brace to allow stretched posterior structures to heal

Post-Reduction Protocol

• Neurovascular check immediately after reduction
• Postreduction radiographs to confirm reduction and identify any new fractures
• Sling immobilization for comfort; early ROM exercises
• Physical therapy focused on rotator cuff strengthening

9. Natural History and Recurrence Risk

10. Surgical Treatment

Indications for Surgery

• Acute: First-time dislocation in young athletes with high recurrence risk (relative indication); locked or irreducible dislocations; associated displaced fracture; neurovascular injury
• Recurrent instability: After failed conservative management; most common indication
• Significant bone loss: Inverted pear glenoid (>25% loss) mandates bony procedure

A. Arthroscopic Bankart Repair (ABR) - Standard for Soft Tissue Instability

• Patient in lateral decubitus or beach chair position with arm in traction
• Posterior portal entry (2 cm below, 1 cm lateral to posterolateral acromion edge)
• Two anterior portals: anterolateral (near supraspinatus) and anteroinferior/5:30 portal (above subscapularis) for drilling and suture passing
• Diagnostic arthroscopy evaluates all intra-articular structures
• Bankart lesion elevated and mobilised; anterior glenoid rim prepared with burr
• Minimum 3 suture anchors (2.9-mm or 3-mm) placed along anterior glenoid rim
• Labral tape shuttled and loaded onto knotless PushLock anchors creating a "bumper" effect
• Associated posterior tears repaired via accessory posterolateral portal

B. Open Bankart Repair

• Beach chair position; deltopectoral approach
• Superior half-to-two-thirds subscapularis tenotomy (1 cm from bicipital groove)
• T-capsulotomy
• Bankart lesion elevated; anterior glenoid rim abraded
• Anchors placed on glenoid rim; capsule shifted and repaired with arm at 30° flexion and 30° external rotation
• Subscapularis tenotomy repaired

C. Latarjet Procedure - For Significant Glenoid Bone Loss

1. Bony block: Coracoid transfer restores the anterior glenoid arc
2. Sling effect: The conjoined tendon (coracobrachialis + short head biceps) acts as a dynamic sling across the anterior capsule in the ABER position
3. Capsular reinforcement: The coracoacromial ligament is repaired to the anterior capsule

• Deltopectoral approach (incision over coracoid to axilla)
• Cephalic vein identified; retracted laterally with deltoid
• Pectoralis minor released from medial coracoid; coracoacromial ligament resected from acromion and preserved
• Coracoid osteotomy at base; inferior surface flattened
• Horizontal subscapularis split; anterior capsule exposed
• Coracoid fixed to anterior glenoid neck with two screws (5-6 mm medial to glenoid surface)
• Coracoacromial ligament repaired to capsule; subscapularis split closed

D. Remplissage Procedure - For "Engaging" Hill-Sachs Lesion

• Indication: Large Hill-Sachs lesion that "engages" the anterior glenoid rim in the ABER position (off-track lesion), performed in conjunction with ABR
• Capsulotenodesis of the infraspinatus tendon into the Hill-Sachs defect using suture anchors
• Fills the defect, preventing engagement
• Results in slight loss of external rotation (~10°) - Rockwood & Green's, p.1281

E. Posterior Labral Repair (for Recurrent Posterior Instability)

• Repair of posterior Bankart lesion with anchor fixation
• Posterior capsular tightening/plication
• McLaughlin procedure or modified McLaughlin (subscapularis transfer into reverse Hill-Sachs lesion) for locked posterior dislocation with <40% articular involvement
• Humeroplasty or humeral head arthroplasty when >40% articular surface involved

F. Inferior Capsular Shift (Neer & Foster) - for MDI

• Open procedure addressing the patulous inferior capsule
• Can also be performed arthroscopically (capsular plication + rotator interval closure)

11. Complications

Early

• Axillary nerve injury: Most common nerve injury (~9-18%); transient neuropraxia is common; test sensation over deltoid patch
• Axillary artery injury: Rare (<1%); more common in elderly; presents with expanding hematoma or absent radial pulse
• Brachial plexus injury: Traction injury; most recover spontaneously
• Rotator cuff tear: Especially in patients >40 years; incidence increases with age (up to 30-35% in patients >40 years)
• Greater tuberosity fracture: ~15% of anterior dislocations
• Recurrence: Most common complication overall, especially in young males

Late

• Recurrent instability: Natural history; surgical stabilization required
• Glenohumeral arthritis: Hovelius found ~2/3 of patients had arthritis at mean 25-year follow-up - Rockwood & Green's, p.1262
• Distal clavicle/glenoid osteolysis: Posttraumatic
• Bankart repair failure: Loss of reduction; often related to bone loss not addressed at initial surgery
• Stiffness: Particularly after overly tight capsular repair; loss of external rotation

Surgical Complications

• Loss of reduction (10-30%)
• Anchor pullout or anchor-related complications
• Coracoid nonunion (Latarjet)
• Coracoid screw complications: Neurovascular proximity (musculocutaneous nerve at risk during Latarjet)
• Subscapularis failure after open procedures

12. Apprehension Test (Key Clinical Examination Finding)

Figure 38.23: Apprehension test for anterior instability - forced abduction and external rotation produces a sensation of impending dislocation (Bailey & Love's)

• Sulcus sign: Inferior traction on the humerus creates a sulcus under the acromion (inferior laxity/MDI)
• Load-and-shift test: Translates the humeral head anteriorly/posteriorly while in the glenoid; grades translation
• O'Brien's active compression test: 88% sensitivity for AC joint and labral pathology

13. Atraumatic Instability (MDI)

• No history of an initiating injury
• Multidirectional - instability in >1 direction
• Associated with generalised ligament laxity (Beighton score)
• Sulcus sign positive; apprehension tests positive in multiple directions - Bailey & Love's, p.2484
• Initial treatment: Supervised rehabilitation - rotator cuff and scapular stabiliser strengthening, proprioception training. Most patients respond without surgery.
• Surgery (inferior capsular shift / arthroscopic plication) reserved for failures after a dedicated 6-month rehabilitation program

14. Summary Treatment Algorithm

SHOULDER DISLOCATION
│
├── ACUTE DISLOCATION
│    ├── Pre-reduction X-ray (rule out fracture)
│    ├── Closed reduction (method depends on clinical factors)
│    ├── Post-reduction X-ray
│    ├── Neurovascular check
│    └── Immobilize → supervised rehabilitation
│
├── RECURRENT ANTERIOR INSTABILITY
│    ├── No significant bone loss (<25%) ──► Arthroscopic Bankart Repair
│    │                                       ± Remplissage (if engaging Hill-Sachs)
│    └── Significant bone loss (>25%) ──────► Latarjet Procedure
│         or failed prior repair
│
├── RECURRENT POSTERIOR INSTABILITY
│    ├── Conservative (rehab) first
│    └── Structural lesion / failure ──────► Posterior Bankart Repair
│         Locked posterior (McLaughlin) ──► McLaughlin / Open Reduction
│
└── MDI (MULTIDIRECTIONAL)
     ├── Rehabilitation (6 months) first
     └── Failure ──────────────────────────► Inferior Capsular Shift / Plication

Key Teaching Points

1. The GH joint sacrifices bony constraint for mobility. Only 25-30% of the humeral head contacts the glenoid at any time; stability depends primarily on the IGHL complex and rotator cuff.
2. Anterior dislocation accounts for 95-97% of cases; the arm is held in abduction and external rotation.
3. Posterior dislocation is easily missed - key clue is the history (seizure, electric shock, half-Nelson). The "light bulb sign" and loss of external rotation are diagnostic hints.
4. The Bankart lesion (anteroinferior labral avulsion) is the primary pathological lesion in traumatic anterior instability. A Hill-Sachs lesion (posterolateral humeral head impaction) accompanies it in up to 80%.
5. Recurrence risk is highest in young males in contact sports (~80%). Age is the single biggest predictor.
6. Critical glenoid bone loss (>25%) requires a bony procedure (Latarjet). Soft-tissue repair alone will fail.
7. The Latarjet procedure provides a triple blocking mechanism: bone, sling effect (conjoined tendon), and capsular reinforcement.
8. The remplissage is added for "engaging" (off-track) Hill-Sachs lesions to prevent engagement with the glenoid rim.