What could be causing pain in the deltoid muscle of the shoulder and trapezius muscle that worsens with arm elevation?

Shoulder and Trapezius Pain with Arm Elevation

Your pain pattern strongly suggests rotator cuff tendinopathy or impingement syndrome, and you should start with plain radiographs (X-rays) followed by musculoskeletal ultrasound or MRI to evaluate the rotator cuff and subacromial structures. 1

Most Likely Diagnoses

Rotator Cuff Tendinopathy/Impingement (Primary Consideration)

• Pain worsening with arm elevation is the hallmark of subacromial impingement syndrome, where the supraspinatus tendon becomes compressed beneath the coracoacromial arch during abduction between 70-120 degrees 1, 2
• The deltoid pain you're experiencing occurs because the deltoid muscle works to elevate the arm while the inflamed rotator cuff structures underneath are being compressed, creating a painful arc of motion 2
• Trapezius pain suggests scapular dyskinesis - poor coordination of the shoulder blade muscles that commonly accompanies rotator cuff problems and contributes to the impingement mechanism 1, 2, 3
• This combination of deltoid and trapezius involvement indicates both the primary rotator cuff pathology and secondary compensatory muscle dysfunction 3

Rotator Cuff Tear (Must Rule Out)

• In patients over 35-40 years, rotator cuff tears become increasingly common and present identically to tendinopathy initially 1
• Chronic massive rotator cuff tears can even cause secondary deltoid muscle tears, though this is uncommon (0.3% prevalence) 4
• The deltoid may be compensating for a weakened or torn rotator cuff, leading to overuse pain in the deltoid itself 5, 4

Subacromial Bursitis

• Inflammation of the subacromial bursa frequently coexists with rotator cuff tendinopathy as part of the impingement syndrome spectrum 1
• Bursal fluid accumulation increases pressure in the subacromial space, worsening pain with elevation 6

Recommended Imaging Algorithm

Step 1: Plain Radiographs (Initial Study)

• Start with plain X-rays including AP, Grashey, axillary, and/or scapular Y projections to evaluate bony structures, rule out fractures, assess for acromial morphology abnormalities, and identify calcific tendinitis 1
• This is the mainstay initial imaging recommended by the American College of Radiology 1

Step 2: Advanced Imaging (Choose One)

Musculoskeletal Ultrasound (Preferred if local expertise available):

• Ultrasound is excellent for depicting rotator cuff and biceps tendon pathology with sensitivity of 85% and specificity of 90% 2
• Can visualize tendon tears, tendinopathy, bursal fluid, and allows dynamic assessment during arm movement 7
• The American College of Radiology states ultrasound is equivalent to MRI for rotator cuff evaluation when performed by experienced operators 2
• Cost-effective and immediately available in many settings 7

MRI Without Contrast (Alternative/Definitive):

• MRI is the preferred imaging for rotator cuff disorders in patients over 35 years with suspected tendinopathy or tears 1
• Sensitivity of 90% and specificity of 80% for subacromial impingement syndrome 2
• Better for evaluating muscle atrophy, bone marrow edema, and labral pathology 1
• Choose MRI if ultrasound expertise is unavailable or if surgical planning is anticipated 1

Key Physical Examination Findings to Confirm

Before imaging, your clinician should perform:

• Neer's test (passive forward flexion with internal rotation) - 88% sensitive for impingement 1, 2
• Hawkins' test (forcible internal rotation with arm flexed forward at 90 degrees) - 92% sensitive for impingement 1, 2
• Empty can test for supraspinatus weakness 1
• Assessment of passive versus active range of motion - preserved passive motion with painful/weak active motion confirms rotator cuff pathology rather than adhesive capsulitis 1
• Evaluation for scapular dyskinesis during arm elevation 1, 2, 3

Critical Pitfalls to Avoid

• Do not overlook scapular dyskinesis - the trapezius pain indicates this is present and must be addressed in treatment, as it's both a cause and consequence of rotator cuff pathology 1, 3
• Do not assume absence of trauma means absence of serious pathology - chronic rotator cuff tears can occur from repetitive stress without a specific injury event 1
• In patients over 35-40 years, always consider rotator cuff tear rather than just tendinopathy, as management may differ 1
• Deltoid tears can occur secondary to chronic massive rotator cuff tears, so if imaging shows severe rotator cuff pathology, specifically evaluate the deltoid muscle for tears 4

Initial Management While Awaiting Imaging

• Complete rest from aggravating activities (especially overhead movements and arm elevation) 1
• NSAIDs for acute pain management 1
• Ice application to reduce inflammation 1
• Avoid overhead pulley exercises which can worsen rotator cuff pathology 1