Overview
Acromioclavicular joint arthritis is wear-and-tear arthritis affecting the AC joint, the small joint at the top of the shoulder where the collarbone meets the highest part of the shoulder blade. Over time, the joint cartilage can thin and become rough, and the joint lining may become irritated, which can produce pain and stiffness. Because the AC joint plays a key role when you lift your arm and move it across your body, inflammation and bone changes can limit comfort and function. Symptoms are often most noticeable at the top of the shoulder and with certain reaching activities.
Symptoms
Pain is usually felt at the very top of the shoulder near the AC joint, and it can worsen when reaching across your body, lifting the arm, or lying on that side. Some people notice a clicking, grinding, or catching sensation with shoulder movement. Stiffness and reduced ability to comfortably reach overhead or behind the back can develop, usually because pain limits motion rather than true numbness from nerve injury. In flare-ups, the area may feel more tender and sore with everyday tasks like dressing, driving, or carrying items.
Causes
Most cases develop from degeneration, where repeated mechanical stress gradually wears down the joint cartilage and irritates the joint lining. Prior trauma is also common, including an AC joint separation or repeated minor impacts that leave the joint biomechanically irritated. As arthritis progresses, bone spurs can form and the joint can become more inflamed, which amplifies pain during motion.
Risk Factors
Risk increases with age and with jobs or sports that involve frequent overhead reaching, heavy lifting, or repetitive cross-body motions. Prior shoulder or AC joint injuries, including clavicle injuries, can leave the joint more susceptible to long-term degeneration. Genetics and overall joint wear patterns may also contribute. Smoking and poor conditioning can indirectly affect tissue health and recovery from flare-ups.
Prevention
You can lower flare-ups by reducing repetitive high-load shoulder motions that provoke symptoms and by using good lifting and reaching mechanics. Building and maintaining shoulder strength, especially the rotator cuff and shoulder blade stabilizers, can reduce abnormal forces at the AC joint. A gradual progression of activity and appropriate rest during symptom flares helps prevent ongoing irritation. Maintaining healthy overall fitness and body weight can also reduce chronic joint stress over time.
How the Diagnosis Is Evaluated
Clinicians usually start with a focused history about where the pain is located and what movements make it worse, especially reaching across the body. A physical exam often includes pressing over the AC joint and performing shoulder maneuvers that reproduce pain from the AC joint. Imaging typically begins with X-rays to look for joint space narrowing, bone spurs, and other arthritis changes, though not every patient needs advanced imaging. If symptoms suggest other causes like rotator cuff or labral problems, additional imaging or tests may be considered based on exam findings.
Nonsurgical Treatment Options
Treatment usually starts with activity modification to avoid movements that strongly trigger AC joint pain while keeping the shoulder gently moving. Anti-inflammatory strategies such as oral NSAIDs, topical NSAIDs, and ice during flares can help reduce pain and irritation. Physical therapy focuses on maintaining shoulder mobility and improving strength and control of the rotator cuff and scapular stabilizers, which can unload the AC joint. If pain remains significant, a clinician may offer an ultrasound-guided corticosteroid injection into or around the AC joint to rapidly calm inflammation. Some patients ask about biologic or regenerative options such as PRP or platelet-rich plasma injections or hyaluronic acid injections, which may be considered on a case-by-case basis depending on local practice and response to standard care.
When to Seek Medical Attention
Seek prompt medical attention if you have sudden severe shoulder pain after a fall or injury, visible deformity, or you cannot lift your arm at all. Get urgent evaluation for fever, rapidly increasing swelling or redness around the joint, or feeling unwell with shoulder symptoms. Contact a clinician soon if pain is persistent despite home care, if night pain is worsening, or if you develop new neurologic symptoms like numbness, progressive weakness, or loss of hand function. If pain is accompanied by significant chest symptoms, shortness of breath, or other concerning systemic signs, seek emergency care.
Frequently Asked Questions
Yes, it commonly causes aching or sharp pain directly over the AC joint, often worse with reaching across your body or lifting your arm.
For many people, guided physical therapy plus short-term anti-inflammatory measures help, and an image-guided corticosteroid injection can provide faster symptom relief when pain is limiting.
Next Steps
If your pain is localized to the top of the shoulder and is triggered by reaching across your body, schedule a clinical evaluation to confirm the source and start targeted conservative care. Early guidance from a physical therapist can help you choose safe exercises and activity modifications to reduce flare-ups. If symptoms are severe or worsening, ask about image-guided injection options and confirm whether X-rays are appropriate.