What is the likely diagnosis and first‑line management for a patient with localized acromioclavicular (AC) joint pain and a positive Empty‑Can (Jobe) test?

Acromioclavicular Joint Osteoarthritis with Supraspinatus Tendinopathy

A positive Empty-Can test with localized AC joint pain most likely indicates concurrent AC joint osteoarthritis and supraspinatus tendinopathy, requiring initial conservative management with NSAIDs, activity modification, and physical therapy focused on rotator cuff strengthening, with diagnostic AC joint injection reserved for persistent symptoms after 6–12 weeks. 1, 2

Understanding the Clinical Picture

The Empty-Can (Jobe) test primarily evaluates supraspinatus tendon integrity and function, not the AC joint itself. 1, 2 When this test is positive alongside localized AC joint pain, you are dealing with two distinct but commonly coexisting pathologies:

• Supraspinatus tendinopathy/impingement causes the positive Empty-Can test through weakness or pain during resisted abduction at 90° with internal rotation 1, 2
• AC joint osteoarthritis produces the localized AC joint tenderness and pain with cross-body adduction 3, 4

This combination is extremely common in patients over 35–40 years, where degenerative changes affect both the rotator cuff and the AC joint simultaneously. 1, 2, 3

Critical Diagnostic Steps

Physical Examination Maneuvers

• Palpate directly over the AC joint (superior shoulder, approximately 2–3 cm medial to the lateral acromion) to confirm localized tenderness distinct from subacromial pain 3, 4
• Perform cross-body adduction test: passively bring the affected arm across the chest—reproduction of AC joint pain confirms AC pathology 3, 4
• Hawkins and Neer impingement signs should also be assessed; these will likely be positive given the supraspinatus involvement suggested by the Empty-Can test 1, 2
• Assess active abduction strength: roughly 4/5 strength suggests tendinopathy without complete tear, while marked weakness (<3/5) raises concern for full-thickness rotator cuff tear 1, 2

Initial Imaging Protocol

• Plain radiographs are mandatory as the first imaging study: obtain AP views in internal and external rotation plus an axillary or scapular-Y view 1, 2
• AC joint-specific radiographic findings include joint space narrowing, subchondral sclerosis, osteophyte formation, and distal clavicle erosion 3, 5, 4
• Important caveat: Radiographic AC joint degeneration is present in up to 50% of asymptomatic individuals over age 50, so imaging findings alone cannot establish the diagnosis 4

Diagnostic Injection

• A diagnostic local anesthetic injection into the AC joint is the gold standard for confirming that AC joint pathology is the pain generator, particularly when clinical findings are equivocal 3, 6, 4
• This injection should be image-guided (ultrasound or fluoroscopy) to ensure accurate intra-articular placement 3
• Perform this injection only after 6–12 weeks of failed conservative therapy, not as an initial diagnostic step 3, 6

First-Line Management Algorithm

Phase 1: Initial Conservative Treatment (Weeks 0–6)

For the supraspinatus component:

• Complete rest from aggravating activities (overhead movements, pushups, cross-body activities) until pain-free 1, 2
• NSAIDs for acute pain control during the initial inflammatory phase 1, 2, 3
• Ice application to the shoulder for 15–20 minutes, 3–4 times daily 1, 2

For the AC joint component:

• Activity modification is paramount: avoid cross-body movements, bench press, and overhead pressing exercises 3, 6, 7
• Oral NSAIDs or analgesics provide symptomatic relief but do not alter disease progression 3
• Physical therapy has limited benefit for isolated AC joint osteoarthritis, as therapeutic exercise and range-of-motion work play only a minor role 3

Phase 2: Rehabilitation (Weeks 6–12)

• Begin rotator cuff and scapular stabilizer strengthening once pain-free motion is achieved 1, 2
• Focus on eccentric strengthening exercises for the supraspinatus, which are specifically recommended for tendinopathy healing 2
• Stretching and mobilization to improve range of motion, particularly external rotation and abduction, preventing secondary adhesive capsulitis 1, 2
• Avoid overhead pulley exercises, which encourage uncontrolled abduction and can worsen rotator cuff pathology 2

Phase 3: Persistent Symptoms (After 12 Weeks)

If AC joint pain persists despite adequate conservative therapy:

• Diagnostic AC joint injection with local anesthetic to confirm the AC joint as the primary pain generator 3, 6, 4
• If diagnostic injection provides relief, consider corticosteroid injection into the AC joint for short-term pain relief (typically 3–6 months) 3, 4
• Important limitation: Corticosteroid injections do not alter the natural progression of AC joint osteoarthritis 3

If supraspinatus symptoms persist:

• MRI without contrast is indicated after 3–6 months of failed conservative therapy to evaluate for full-thickness rotator cuff tear, tendon retraction, muscle atrophy, or fatty infiltration 1, 2
• MRI is also appropriate earlier if there is clinical suspicion for full-thickness tear (marked weakness, age >60 years, positive drop-arm test) 1, 2

Surgical Considerations

• For AC joint: Distal clavicle resection (open or arthroscopic) is indicated after minimum 6 months of unsuccessful conservative treatment 3, 6, 4
• For rotator cuff: Surgical referral is appropriate if MRI demonstrates full-thickness tear with tendon retraction, muscle atrophy, or fatty infiltration 1, 2
• Only 9% of patients with subacromial impingement ultimately require surgery after appropriate conservative management 2

Common Pitfalls to Avoid

• Do not assume the positive Empty-Can test means the AC joint is the sole problem—this test evaluates the supraspinatus, not the AC joint 1, 2
• Do not proceed directly to MRI without obtaining plain radiographs first—you may miss fractures, dislocations, or significant arthritis that fundamentally change management 1, 2
• Do not diagnose AC joint osteoarthritis based on radiographic findings alone—asymptomatic degenerative changes are extremely common and require clinical correlation 4
• Do not perform AC joint corticosteroid injection as a first-line treatment—reserve this for patients who have failed 6–12 weeks of conservative therapy and have confirmed diagnosis via diagnostic injection 3, 6
• Do not overlook cervical radiculopathy in the differential, particularly if there are neurological symptoms or dermatomal pain patterns 8, 9