Shoulder

AC Joint Arthritis

Acromioclavicular (AC) joint arthritis is a common source of shoulder pain, causing pinpoint discomfort at the top of the shoulder with overhead activities and cross-body movements. Whether from prior injury or age-related wear, Maryland Orthopedic Specialists offers targeted treatments (from diagnostic injection to minimally invasive surgical resection) to provide lasting relief.

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What is ac joint arthritis?

The acromioclavicular joint is a small diarthrodial joint between the distal clavicle and the acromion of the scapula, separated by a fibrocartilaginous disc. Despite its small size, it is subjected to high loads during overhead and cross-body activities. It is one of the most common joints to become arthritic.

The acromioclavicular joint is a small diarthrodial joint between the distal clavicle and the acromion of the scapula, separated by a fibrocartilaginous disc. Despite its small size, it is subjected to high loads during overhead and cross-body activities.

AC joint arthritis develops through two main mechanisms:

Post-traumatic OA: Cartilage and disc damage sustained during an AC joint separation (any grade) accelerates degenerative change. Even minor Grade I–II injuries can lead to symptomatic arthritis years later.
Primary (idiopathic) OA: Age-related degeneration, particularly in overhead athletes (weightlifters, throwing athletes) and manual laborers. Distal clavicle osteolysis (stress-related resorption of the distal clavicle) is a specific variant seen in weightlifters.

AC joint arthritis is frequently discovered as a coexisting diagnosis in patients presenting for shoulder impingement, rotator cuff tears, or biceps pathology. Superior osteophytes from the AC joint can contribute to subacromial impingement and rotator cuff abrasion.

Symptoms — do you recognize these?

Localized pain at the top of the shoulder, directly over the AC joint
Pain with cross-body adduction (reaching across the chest — the most provocative movement)
Pain with overhead reaching, pressing, or lifting
Tenderness to direct palpation over the distal clavicle and AC joint
Possible swelling or visible osteophyte prominence at the AC joint
Night pain when lying on the affected side

Call us at (301) 515-0900. Same-day appointments available at our Bethesda and Germantown locations.

How we diagnose it

Physical Examination

Direct palpation over the AC joint reproduces pain and is the most specific finding. The cross-body adduction test (bringing the arm horizontally across the chest) stresses the AC joint and typically provokes pain localized to the AC joint in AC joint arthritis. This distinguishes it from glenohumeral OA and impingement, which produce more diffuse or lateral pain.

O'Brien's test, performed for SLAP pathology, also loads the AC joint and may produce AC-joint-specific pain (pain on top of the shoulder rather than deep inside). This is a useful differentiating point during examination.

A diagnostic AC joint injection of local anesthetic (if it reliably abolishes the cross-body pain) confirms the AC joint as the primary pain source and also represents the first therapeutic intervention.

Imaging

X-rays (Zanca view, 10° cephalic tilt): Optimizes visualization of AC joint space narrowing, osteophyte formation, subchondral sclerosis, and distal clavicle osteolysis.
MRI: Identifies joint effusion, marrow edema, osteophytes encroaching on the subacromial space, and concurrent rotator cuff or labral pathology.

Treatment options

Corticosteroid Injection (Diagnostic and Therapeutic)

An AC joint corticosteroid injection is simultaneously the best diagnostic test and initial therapeutic intervention. Ultrasound guidance is preferred to ensure accurate intra-articular placement in this small joint. Most patients achieve meaningful pain relief for weeks to months, and many are managed long-term with periodic injections.

Activity Modification and Physical Therapy

Reducing heavy overhead and cross-body loading (particularly heavy bench press and wide-grip exercises) decreases symptoms. PT focuses on periscapular strengthening and shoulder mechanics rather than directly treating the joint.

Surgical Procedure

Distal Clavicle Excision

Arthroscopic removal of the distal 5–8 mm of the clavicle to eliminate bone-on-bone contact causing AC joint arthritis pain. Frequently performed alongside rotator cuff repair or other shoulder procedures at the same sitting.

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Recovery & rehabilitation

Injection alone: Return to activity within days; relief lasts weeks to months
Arthroscopic Mumford: Sling 1–2 weeks; return to overhead activity 6–8 weeks; return to overhead sport or heavy lifting 3–4 months

Frequently Asked Questions

Is AC joint arthritis the same as a shoulder separation?

No. A shoulder separation is an acute ligament injury. AC joint arthritis is the degenerative sequel that can develop years later, either as a result of a prior separation or as primary age-related wear.

Can I wait to have surgery?

Yes. Surgery is entirely elective. Many patients manage AC joint arthritis long-term with activity modification and periodic injections, delaying or avoiding surgery indefinitely.

Will removing the end of the collarbone affect my shoulder strength?

No. The small amount of bone removed (5–10 mm) does not affect the structural integrity of the shoulder. Strength is preserved because the critical CC ligaments and muscle attachments remain intact.

How long does recovery take after distal clavicle resection?

Most patients begin gentle range-of-motion exercises within one to two weeks after surgery. Strength training progresses over the following six to eight weeks, and full return to overhead activities and sport typically occurs by three to four months. Recovery after arthroscopic surgery is generally faster than open surgery. Your MOS surgeon will provide a detailed rehabilitation protocol tailored to your shoulder and activity goals.

How is AC joint arthritis different from glenohumeral (main shoulder joint) arthritis?

AC joint arthritis affects the small joint at the top of the shoulder where the collarbone meets the shoulder blade, while glenohumeral arthritis affects the larger ball-and-socket joint. AC joint arthritis typically causes pain with cross-body movements and overhead reaching, and the pain is localized to the top of the shoulder. Glenohumeral arthritis tends to produce deeper, more global shoulder pain with rotation. Both conditions can coexist, and your MOS surgeon will evaluate each joint separately to determine which is responsible for your symptoms.