AC joint arthritis is the wearing out of the cartilage surfaces at the joint between the acromion (the bony roof of the shoulder) and the clavicle (collarbone). It is a common source of shoulder pain in weightlifters, heavy laborers, and patients with a history of prior AC joint injury. Unlike glenohumeral arthritis, AC arthritis produces pain localized to the top of the shoulder rather than a deep joint pain, which helps distinguish it clinically.
What Is AC Joint Arthritis?
The AC joint is a small synovial joint between the lateral end of the clavicle and the acromion. It has minimal motion relative to the major joints of the shoulder but transmits load during overhead lifting, bench pressing, and any activity that engages the shoulder girdle. The joint surfaces are covered with articular cartilage. When this cartilage wears out, the exposed bone ends grind against each other, causing inflammation and pain.
AC arthritis is common well before old age because the joint has a small surface area, high load per square inch, and limited ability to repair itself. X-ray findings of AC arthritis are common in adults over 40 but do not always produce symptoms. Treatment is driven by the patient’s symptoms, not the imaging alone.
Causes and Risk Factors
- Prior injury to the AC joint, including sprain or separation, which predisposes to premature arthritis
- Heavy repetitive loading from weightlifting, overhead occupations, or manual labor
- Contact sports with repeated collision forces through the shoulder
- Age-related cartilage wear
- Previous distal clavicle fracture involving the joint surface
Symptoms
- Pain localized to the top of the shoulder, directly over the AC joint
- Tenderness to direct palpation of the joint
- Pain with overhead activity, heavy pressing, and cross-body reaching
- A visible bump or swelling over the AC joint
- Crepitus or grinding with specific movements
Diagnosis
Dr. Chudik’s evaluation includes the activity pattern, prior shoulder history, and pain location. Physical examination centers on palpation over the AC joint, cross-body adduction testing, and assessment of shoulder motion. A diagnostic lidocaine injection into the AC joint that relieves pain helps confirm the diagnosis. X-rays document joint space narrowing, osteophytes, and any pre-existing fracture deformity. MRI is added when rotator cuff disease is suspected to coexist, which is common in this patient population. The Westmont office has on-site high-field MRI and X-ray.
Treatment
Non-surgical treatment is effective for many patients and is the first line. Options include activity modification (reducing overhead pressing, bench press, and other provocative loads), anti-inflammatory medication, ice, and AC joint corticosteroid injection, which provides both diagnostic confirmation and symptomatic relief.
For patients whose symptoms do not resolve despite non-surgical treatment, Dr. Chudik performs arthroscopic distal clavicle resection. Through small incisions, he removes five to seven millimeters of bone from the damaged end of the clavicle, preventing the worn surfaces from contacting while leaving the AC ligaments intact to maintain joint stability. At the same procedure, Dr. Chudik can inspect and treat any associated pathology inside the shoulder joint, including rotator cuff tears, which are sometimes present despite a negative MRI.
Recovery and Outcomes
Recovery after arthroscopic distal clavicle resection is relatively quick. A sling is used for one to two weeks for comfort, active motion begins early, and progressive strengthening follows at two to four weeks. Return to overhead work and most sport is typically six to eight weeks. Return to heavy bench pressing and overhead lifting is typically 10 to 12 weeks.
Outcomes are good in appropriately selected patients, including heavy overhead laborers and competitive weightlifters who return to full activity without restriction.
When to See Dr. Chudik
Schedule an evaluation if pain at the top of the shoulder has persisted through activity modification, if AC joint symptoms interfere with overhead work or training, or if prior treatment has failed. Call 630-324-0402 or request an appointment online.