Shoulder Pain

1. THE 2-MINUTE PHYSIOLOGY

Glenohumeral (GH) Dislocation: Anterior dislocations account for >90% of shoulder dislocations and occur when an external force (often a fall with the arm externally rotated and abducted) overcomes the dynamic and static stabilizers of the glenohumeral joint, tearing the joint capsule and ligaments.
Posterior Sternoclavicular (SC) Dislocation: A severe mechanical displacement of the medial clavicle posteriorly into the superior mediastinum. This is a true orthopedic emergency because the displaced bone directly compresses life-sustaining intrathoracic structures (trachea, great vessels, esophagus, brachial plexus).
Rotator Cuff / Impingement Syndrome: Repetitive mechanical friction of the supraspinatus tendon under the acromion leads to localized inflammation, tendon thickening, subacromial bursitis, and eventual micro-tearing or full-thickness rupture of the tendinous insertion.
Biceps Tendon Rupture: Tensile overload leads to complete mechanical failure of the proximal long head of the biceps, often exacerbated by underlying tendinopathy or the use of specific medications (e.g., fluoroquinolones) that degrade collagen integrity.

2. THE BEDSIDE ACTION PLAN

• Immediate Stabilization: Assess for airway or vascular compromise immediately if a posterior sternoclavicular dislocation is suspected. For glenohumeral dislocations, support the arm in the position of comfort (usually adduction and internal rotation for anterior dislocations).
• Procedural Analgesia & Sedation: Before closed reduction of a dislocated shoulder, consider intra-articular lidocaine injection or a regional suprascapular nerve block as highly effective alternatives to systemic procedural sedation. These methods are particularly useful in the elderly or those with cardiovascular comorbidities.
• Reduction Techniques: For anterior shoulder dislocations, utilize single-operator, low-force techniques such as the Milch technique or scapular manipulation. These can often be performed without systemic procedural sedation.
• Immobilization: For biceps tendon ruptures and proximal humerus fractures, immobilize the arm in a sling with the elbow in 90 degrees of flexion and provide standard NSAID/acetaminophen analgesia.

3. THE DIAGNOSTIC GRID

• Posterior Sternoclavicular Dislocation: Can present with dysphagia, stridor, or vascular compromise. This is a life-threatening "can't-miss" diagnosis.
• Posterior Glenohumeral Dislocation: Often missed on standard AP views. Requires high clinical suspicion, particularly after seizures, electrocution, or awkward falls.
• Acute Full-Thickness Rotator Cuff Tear: Suspect in patients with severe pain and inability to abduct the arm following acute trauma.
• Diagnostic Imaging Workup:
• Plain Radiography (The 3-View Trauma Series): Mandatory for evaluation. Includes a True Anteroposterior (AP) view (45-degree lateral), a trans-scapular lateral ("Y" view), and an axillary lateral view. The True AP view is superior to a standard AP view because it profiles the glenohumeral joint without bony overlap.
• Non-Contrast CT: Indicated if there is high suspicion for a posterior glenohumeral dislocation but the patient's pain prevents obtaining an axillary lateral view.
• MRI: The definitive confirmatory outpatient test for rotator cuff and biceps tendon tears; cross-sectional imaging is not indicated in the ED for simple impingement.

4. THE VISUAL BOARD

• Anterior Dislocation Appearance: The patient's shoulder will appear "squared off" with a prominent acromion and loss of the normal rounded contour of the deltoid.
• Biceps Rupture: Look for the classic "Popeye" deformity—a visible bunching of the biceps muscle in the distal upper arm and bruising at its insertion.
• Point-of-Care Ultrasound (POCUS):
• Dislocations: Highly accurate for diagnosing glenohumeral dislocations prior to X-ray.
• Impingement/Bursitis: Look for thickening of the supraspinatus tendon and associated anechoic fluid in the subacromial bursa.
• Biceps Rupture: Look for an empty bicipital groove and fluid collection within the tendon sheath.
• X-Ray Interpretation: On the trans-scapular Y view, the humeral head should be perfectly centered over the center of the "Y" (the glenoid). Anterior displacement indicates anterior dislocation; posterior displacement indicates posterior dislocation.

5. THE SCORING MATRIX

• Rotator Cuff Clinical Pathway: An inability to abduct the shoulder above 90 degrees combined with a positive small finger resistance test identifies >90% of acute full-thickness rotator cuff injuries (with ~70% specificity).
• Acromioclavicular (AC) Joint Separation Grading: The goal of the ED physician is to differentiate mild injuries (Types I and II) which require conservative management, from severe displacements (Types IV, V, and VI) which require emergency orthopedic consultation. Note: Early AC joint stress radiographs are not recommended as they are often falsely negative due to muscle splinting and do not change acute ED management.

6. THE DANGER ZONE

• The Posterior Dislocation Trap: Failing to obtain orthogonal radiographic views (trans-scapular Y or axillary lateral views). A posterior glenohumeral dislocation cannot be excluded with a single AP view. Missing this leads to a locked posterior dislocation that will ultimately require operative reduction under general anesthesia.
• The Outdated Reduction Trap: Utilizing archaic, high-complication reduction techniques such as the Hippocratic method (foot in the axilla) or the Kocher maneuver (forceful leverage, adduction, and internal rotation). These are strictly no longer recommended due to the high risk of causing iatrogenic humeral shaft/neck fractures, capsular damage, and axillary nerve injuries.
• The "Incomplete Exam" Trap: Failing to document a specific neurovascular exam before and after any joint manipulation. You must explicitly test and document axillary nerve function (sensation over the lateral deltoid) and musculocutaneous nerve function (sensation over the anterolateral forearm).
• Critical Action: Immediate recognition and expedited reduction of a posterior sternoclavicular dislocation due to the catastrophic risk of great vessel laceration, pneumothorax, or tracheoesophageal fistula.

7. MCQ MASTERCLASS

• Buzzword: "Prominent acromion," "loss of rounded deltoid contour," or "squared-off shoulder" = Anterior Glenohumeral Dislocation.
• Buzzword: Arm held in "adduction and internal rotation" after a fall on an externally rotated arm = Anterior Glenohumeral Dislocation.
• Buzzword: Patient taking "fluoroquinolones" presents with an acute "pop" in the arm and muscle "bunching" = Biceps Tendon Rupture.
• Distractor Trap: An exam question presents an elderly patient with a minimally displaced proximal humerus fracture and good radial pulses, offering "emergent orthopedic consultation for operative repair" or "emergent vascular surgery consult" as options. These are distractors. Minimally displaced proximal humerus fractures respond well to conservative care (sling, pain control, outpatient orthopedics) and rarely cause vascular injury.

8. THE BOARDROOM SCRIPT

"This is a 25-year-old male presenting with severe right shoulder pain after a fall on an outstretched, externally rotated arm. On inspection, he has a squared-off shoulder with a prominent acromion, consistent with an anterior glenohumeral dislocation. Prior to any imaging or manipulation, I will perform and strictly document a neurovascular exam, specifically assessing the axillary nerve by testing sensation over the lateral deltoid, as well as the musculocutaneous nerve. I will order a true AP, trans-scapular Y, and axillary lateral radiographic series to confirm the anterior dislocation and rule out any associated fracture. For analgesia and reduction, I will perform an intra-articular lidocaine injection or suprascapular nerve block to avoid the risks of systemic sedation, and subsequently perform a gentle reduction utilizing the Milch technique or scapular manipulation. Post-reduction, I will re-assess his neurovascular status, place the arm in a sling, and obtain post-reduction films."