Workup for Trapezius Pain Radiating into the Armpit
Begin with plain radiographs of the shoulder (AP views in internal and external rotation plus axillary or scapula-Y view) to exclude fracture, dislocation, or bony pathology, followed by MRI without contrast if radiographs are negative and soft-tissue injury is suspected. 1
Initial Clinical Assessment
Focus your examination on:
- Mechanism of injury (traumatic vs. atraumatic onset) - this fundamentally changes your diagnostic approach 1
- Red flags: fever, weight loss, night pain, history of malignancy, neurologic deficits, or age >65 years with osteoporosis risk 1
- Pain pattern: Does the pain radiate to the temple or posterior neck (suggesting myofascial trigger points), or does it follow a dermatomal distribution (suggesting nerve root involvement)? 2
- Palpable trapezius tenderness: Severe tenderness correlates strongly with higher pain intensity and may indicate active myofascial trigger points 3, 4
Imaging Algorithm
Step 1: Plain Radiography (Initial Study)
- Obtain shoulder radiographs with at least three views: anteroposterior in internal and external rotation, plus axillary or scapula-Y view 1, 5
- Perform upright - supine films can miss shoulder malalignment 1
- Rationale: Excludes fractures (clavicle, scapula, proximal humerus), dislocations, and bony abnormalities that require immediate orthopedic referral 1, 5
- Critical pitfall: Acromioclavicular and glenohumeral dislocations can be misclassified on AP views alone - the axillary or scapula-Y view is essential 1, 5
Step 2: Advanced Imaging if Radiographs Negative
If radiographs are normal but symptoms persist, proceed with MRI without IV contrast (rating 7-8/9 appropriateness) 1, 6, 5
MRI without contrast is the preferred next step for evaluating:
Alternative: Ultrasound can evaluate tendon/ligament injuries and is appropriate if MRI is unavailable 6
MR arthrography (rating 9/9) is considered gold standard for intra-articular pathology but is typically reserved for surgical planning rather than initial workup 1, 5
When to Refer Immediately
Urgent orthopedic referral is indicated for: 1, 5
- Unstable or significantly displaced fractures
- Shoulder joint instability or dislocation
- Neurologic deficits
- Suspected vascular injury
Conservative Management Trial
If no red flags and radiographs negative, consider 4-6 weeks of conservative management before advanced imaging: 1
- Physical therapy
- NSAIDs
- Activity modification
However, proceed directly to MRI if: 1
- Significant trauma occurred
- Myelopathy suspected
- Patient has osteoporosis or chronic steroid use
- Symptoms worsen or fail to improve with initial management
Special Considerations for Myofascial Pain
If clinical examination suggests myofascial trigger points in the trapezius (palpable tender nodules, referred pain pattern to neck/temple/armpit):
- Pressure pain threshold testing can quantify hypersensitivity - active trigger points typically show PPT approximately 105 kPa lower than healthy muscle 4
- Referred pain patterns: Trapezius trigger points commonly refer to posterior-lateral neck and temple, and can mimic tension-type headache 2
- Note: Impaired microcirculation in chronic trapezius myalgia may explain persistent symptoms despite normal imaging 7, 8
What NOT to Order Initially
- CT without contrast: Inferior to MRI for soft-tissue evaluation; reserve for fracture characterization if bony abnormality seen on radiographs 1
- Bone scan: Not indicated in initial workup unless occult fracture or malignancy strongly suspected and MRI unavailable 1
- CT or MR arthrography: Not first-line; reserve for surgical planning 1