Most Likely Diagnosis: Acromioclavicular (AC) Joint Osteoarthritis
The most likely diagnosis in an elderly female patient with right shoulder and subclavicular aching pain and mild degenerative changes on X-ray is acromioclavicular (AC) joint osteoarthritis. 1, 2
Clinical Reasoning
Why AC Joint Osteoarthritis is Most Likely
- Location of pain: Subclavicular pain is the hallmark of AC joint pathology, as the AC joint sits directly beneath the clavicle at the superior aspect of the shoulder 1, 2
- Age and demographics: AC joint osteoarthritis is the most common disorder of the AC joint and frequently affects elderly patients, with degenerative changes being the primary pathologic process in this age group 1, 2
- Radiographic findings: Mild degenerative changes on plain X-rays are consistent with AC joint osteoarthritis, which typically shows joint space narrowing, osteophyte formation, and subchondral sclerosis 1
Key Distinguishing Features
The subclavicular location is critical here—this anatomic descriptor points away from:
- Glenohumeral osteoarthritis: Would present with deeper shoulder pain, not subclavicular 3, 4
- Rotator cuff pathology: Typically causes lateral shoulder pain and pain with overhead activities, not specifically subclavicular 5, 6
- Subacromial impingement: Presents with anterolateral shoulder pain, not subclavicular 6
Diagnostic Confirmation
Physical Examination Findings to Look For
- Tenderness to palpation directly over the AC joint (located at the superior aspect of the shoulder, just medial to the acromion) 1, 2
- Pain with cross-body adduction test (bringing the affected arm across the chest toward the opposite shoulder) 1, 2
- Pain with active forward flexion above 120 degrees (when the AC joint is maximally stressed) 1
Definitive Diagnostic Test
- Diagnostic local anesthetic injection into the AC joint: If injection of 2% lidocaine into the AC joint provides complete or near-complete pain relief, this confirms AC joint osteoarthritis as the pain generator 1, 2
- This test is essential because AC joint pathology is often overlooked, and the diagnosis requires confirmation beyond radiographic findings alone 1
Critical Pitfall to Avoid
Do not assume all shoulder pain in elderly patients with degenerative changes is glenohumeral osteoarthritis or rotator cuff disease. The AC joint is frequently neglected by clinicians despite being a common source of shoulder pain, particularly when pain is localized to the subclavicular region 1. The subclavicular location in this case is the key clinical clue that should direct attention to the AC joint rather than other shoulder structures 1, 2.