What is the likely diagnosis and immediate management for acute shoulder pain radiating down the arm after a fall?

Acute Shoulder Pain Radiating Down Arm After Fall

The most likely diagnosis is a rotator cuff injury with possible associated brachial plexus neuropraxia, and immediate management should begin with standard three-view shoulder radiographs (AP internal rotation, AP external rotation, and axillary or scapular-Y view) to exclude fracture or dislocation, followed by neurovascular assessment and conservative treatment with sling immobilization and pain control. 1

Immediate Diagnostic Priorities

Rule Out Fracture and Dislocation First

• Obtain plain radiographs immediately with minimum three views: anteroposterior in internal rotation, anteroposterior in external rotation, and either axillary lateral or scapular-Y view 1
• The axillary or scapular-Y view is mandatory because standard AP views alone miss up to 50% of glenohumeral and acromioclavicular dislocations 1
• Radiographs effectively demonstrate fractures, dislocations, and shoulder malalignment that require urgent orthopedic intervention 2, 1

Critical Neurovascular Examination

• Palpate radial and ulnar arterial pulses bilaterally; absence of pulse after trauma requires immediate vascular imaging with CT angiography 1
• Document any numbness, tingling, weakness, or radiation pattern down the arm, as neurological symptoms suggest cervical radiculopathy or brachial plexus injury 2, 1
• Brachial plexus injuries occur in 5.4-55% of shoulder dislocations, with the axillary nerve most commonly affected 3
• The infraclavicular portion of the brachial plexus is most frequently injured, and neurapraxia or axonotmesis predominates over complete nerve disruption 3

Most Likely Diagnoses Based on Mechanism

Rotator Cuff Tear (Primary Consideration)

• Falls onto an outstretched arm or direct shoulder trauma commonly cause acute rotator cuff tears, particularly in patients over 35-40 years 2, 1
• Pain radiating down the arm with weakness during abduction and external rotation suggests rotator cuff pathology 2
• Perform empty can test and external rotation resistance testing to assess rotator cuff integrity 2, 4
• Most acute shoulder injuries from falls involve rotator cuff pathology and can be managed conservatively 5, 6

Shoulder Dislocation (Must Exclude)

• Eighty percent of shoulder dislocations are anterior and typically result from falls or direct trauma 6
• Posterior shoulder dislocations are frequently missed (1-4% of all dislocations) and require high clinical suspicion, as symptoms may mimic rotator cuff injury or shoulder contusion 7
• Diagnosis requires careful radiographic evaluation including axillary view, as standard AP views can miss posterior dislocations 7

Fractures Requiring Different Management

• Clavicle fractures are among the most common acute shoulder injuries, with more than 80% managed conservatively 6
• Proximal humerus fractures occur more commonly in elderly patients, with 85% managed nonoperatively 6
• Unstable or significantly displaced fractures require prompt orthopedic referral 1, 4

Immediate Management Algorithm

Pain Control Strategy

• Start acetaminophen 650-1000 mg every 6 hours (maximum 4 grams daily) as first-line therapy 2, 4
• Consider topical agents (methyl salicylate, capsaicin cream, or menthol) as second-line for mild-moderate pain 2
• Avoid prolonged NSAID use given gastrointestinal, renal, and cardiovascular risks, especially in elderly patients 4

Immobilization and Activity Modification

• Use sling for comfort and to rest the injured shoulder 5
• Complete avoidance of aggravating movements (overhead activities, abduction, internal rotation) until pain-free 1
• Most patients with acute shoulder injuries can be treated conservatively with sling and targeted musculoskeletal rehabilitation 5

When to Obtain Advanced Imaging

• MRI without contrast is indicated if radiographs are negative but clinical suspicion for rotator cuff tear remains high, particularly in patients over 35 years 1
• In the acute trauma setting, noncontrast MRI is preferred over MR arthrography because acute pathology produces joint effusion that aids soft-tissue assessment 8
• Ultrasound with appropriate local expertise is excellent for depicting rotator cuff pathology with 85% sensitivity and 90% specificity 1

Red Flags Requiring Urgent Orthopedic Referral

• Unstable or significantly displaced fractures on radiographs 1, 4
• Neurological deficits that do not improve within initial assessment period 4
• Suspected massive rotator cuff tears in younger active patients 2
• Shoulder joint instability with recurrent dislocations 2
• Types IV, V, and VI acromioclavicular joint injuries 5
• Posterior sternoclavicular dislocations require urgent surgical referral 5

Expected Natural History and Follow-Up

• Brachial plexus injuries from shoulder trauma resolve spontaneously in the majority of patients, with only 13-18% requiring operative treatment 3
• Operative treatment for persistent neurological deficits should be performed within 3-6 months when no signs of recovery are present 3
• Most soft-tissue shoulder injuries can undergo 6-12 weeks of conservative management before considering surgery 2
• Elective orthopedic referral is indicated for failure of 6-12 weeks of appropriate conservative treatment or progressive functional decline 2

Common Pitfalls to Avoid

• Do not assume absence of severe trauma means absence of fracture, especially in elderly patients where osteoporotic fractures occur with minimal or unrecognized trauma 1
• Posterior shoulder dislocations are frequently missed because symptoms mimic rotator cuff injury; always obtain axillary view 7
• Pain radiating down the arm may represent cervical radiculopathy rather than shoulder pathology; distinguish by examining neck range of motion and performing Spurling's test 2
• Older patient age, higher energy trauma, and longer period from dislocation to reduction are risk factors for brachial plexus injury 3