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AC Joint Arthritis: Causes, Symptoms & Treatment

Anatomy

The acromioclavicular (AC) joint is a plane synovial joint between the acromion (scapula) and clavicle. Stabilized by AC ligaments (capsular) and CC ligaments (conoid, trapezoid).

Causes

  • Primary Osteoarthritis: Age-related wear; repetitive overhead use (weightlifting, construction).
  • Post-Traumatic: AC separation (Grade III+), distal clavicle fracture.
  • Inflammatory: Rheumatoid arthritis, psoriatic arthritis, septic arthritis.
  • Osteolysis: Weightlifter's shoulder (repetitive microtrauma → distal clavicle resorption).

Symptoms

  • Top-of-shoulder pain (point tenderness over AC joint)
  • Pain with cross-body adduction, overhead reach, push-ups, bench press
  • Swelling, crepitus, visible step-off (if prior separation)
  • Night pain (advanced)

Diagnosis

  • Clinical: Cross-body adduction test, O'Brien's test, AC joint tenderness.
  • X-ray: Joint space narrowing, osteophytes, cystic changes, distal clavicle resorption.
  • MRI: Bone marrow edema, soft tissue, labral pathology.

Treatment

  1. Conservative: Activity modification, NSAIDs, PT (scapular stabilization, rotator cuff), ice/heat.
  2. Injection: Ultrasound-guided corticosteroid (diagnostic/therapeutic).
  3. Surgical: Distal clavicle excision (Mumford procedure) — open or arthroscopic. Removes 8–10 mm medial clavicle. High success for mechanical pain.

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