Differential Diagnoses for Acute Shoulder/Arm Pain, Swelling, and Limited Motion After Trauma
The differential diagnosis for acute traumatic shoulder pain with swelling and limited motion includes fractures (clavicle, proximal humerus, scapula), glenohumeral dislocation, acromioclavicular joint separation, rotator cuff tear, labral tear, and capsular/ligamentous injury 1, 2.
Fracture-Related Diagnoses
Bony injuries are the primary concern requiring immediate identification:
- Proximal humerus fractures - Most common in elderly patients; bimodal age distribution with young adults in high-energy trauma and older adults from falls 2, 3
- Clavicle fractures - Among the most common acute shoulder injuries, with >80% manageable conservatively 4
- Scapular fractures - Frequently missed on radiographs, especially when nondisplaced; require high-energy trauma 1
- Glenoid fossa fractures - Associated with glenohumeral instability 5
Dislocation and Instability
Joint disruptions present with obvious deformity and severe pain:
- Glenohumeral dislocation - 80% are anterior; diagnosis is straightforward with characteristic physical findings 4
- Posterior sternoclavicular dislocation - Requires urgent surgical referral due to risk of mediastinal structure compromise 3
- Acromioclavicular joint separation - Graded Types I-VI; swelling and deformity at AC joint 2, 3
Soft Tissue Injuries
Capsuloligamentous and tendinous pathology commonly coexists with or mimics fractures:
- Rotator cuff tear - Can be acute traumatic or acute-on-chronic; presents with weakness and limited active range of motion 1
- Labral tear (including SLAP lesions) - Associated with instability mechanisms; may have joint effusion acutely 1
- Capsular and ligament tears - Best assessed with MRI; contribute to instability 1, 2
- Biceps tendon pathology - Less common in acute trauma but can occur 2
Complex Injury Patterns
High-energy mechanisms produce combined injuries:
- Floating shoulder - Combined scapular neck and clavicle fractures creating unstable shoulder girdle 5
- Glenohumeral fracture-dislocation - Combination of humeral head/neck fracture with dislocation 5
- Scapulothoracic dissociation - Rare but devastating injury with neurovascular compromise 5
Critical Diagnostic Approach
The mechanism of injury and patient age narrow the differential significantly:
- High-energy trauma in young adults → Consider complex fracture patterns, dislocations, and combined injuries
- Low-energy falls in elderly → Proximal humerus fractures most likely
- Contact/collision sports → AC separations, dislocations, and rotator cuff tears predominate 3
Physical examination findings that distinguish diagnoses:
- Visible deformity → Dislocation or displaced fracture
- Point tenderness over AC joint → AC separation
- Weakness with active motion but preserved passive motion → Rotator cuff tear
- Restricted passive and active motion → Fracture, dislocation, or capsular injury
- Neurovascular compromise → Scapulothoracic dissociation or posterior sternoclavicular dislocation requiring urgent intervention 3, 5
Imaging-Guided Differential Refinement
Radiographs (AP internal/external rotation + axillary or scapular-Y view) are mandatory first-line imaging 1, 2. The axillary view is critical as AC and glenohumeral dislocations can be missed on AP views alone 2.
When radiographs are positive for fracture, the differential narrows to fracture characterization and associated soft tissue injury 1.
When radiographs are normal or indeterminate with persistent symptoms, consider occult fracture, bone marrow contusion, rotator cuff tear, labral tear, or capsular injury 1. MRI without contrast is the next appropriate study as acute trauma typically produces joint effusion sufficient for soft tissue visualization 1.
Common Pitfalls
Do not assume normal radiographs exclude significant pathology - Nondisplaced scapular fractures, occult proximal humerus fractures, and all soft tissue injuries require advanced imaging when clinical suspicion persists 1.
Do not order MR arthrography acutely - The traumatic hemarthrosis/effusion provides natural contrast; arthrography is reserved for subacute/chronic settings 1, 2.
Do not miss posterior sternoclavicular dislocations - These require urgent surgical referral due to potential mediastinal structure compression 3.