Acromioclavicular (AC) Joint Arthritis

By: Emily Barton, PT, DPT

Where is the AC Joint? 

The AC (acromioclavicular) joint is located at the front of the shoulder where the collar bone (clavicle) and the shoulder complex connect. It is the only joint that attaches the upper limb to the rest of the body, all other attachments are connected via muscles! This makes the AC joint a critical area for force transmission from the arm to the rest of the body (I.e., lifting, throwing, carrying tasks).  

While there are not any specific muscular attachments to the AC joint, there are several ligaments surrounding and attached to the area that help to support the stability of the joint. These ligaments include the Coracoclavicular and acromioclavicular ligaments. The acromioclavicular ligament is the primary source of restraint at the AC joint.  

Image of the shoulder anatomy with labels for AC or acromioclavicular joint, acromioclavicular ligament, and coracoacromial ligament

What is Arthritis of the Acromioclavicular Joint?

Arthritis occurs when there is degeneration of the cartilage around the joint. This is most common in middle-aged populations or those where frequent overhead lifting is required such as athletes or construction workers.  

What does Acromioclavicular Joint Arthritis feel like?

Common symptoms of Acromioclavicular Joint Arthritis include:

  • pain at the top of the shoulder
  • decreased shoulder range of motion especially overhead
  • popping or clicking with certain movements
  • pain with bringing arm across the body 
  • sleeping on the involved sign. 

Pain with AC arthritis will more likely be experienced at end available ranges versus pain in the middle of movement.  

How is AC Joint Arthritis Diagnosed?

Your doctor can diagnose you based on symptoms and imaging including x-rays.  

Other Causes of Pain at the Front of the Shoulder:

  • AC Joint Separation- Occurs where the clavicle and the scapular separate due to tearing of ligaments around the AC joint. This typically occurs from trauma to the shoulder including a fall or direct blow. Depending on the severity of the separation, you might see a “step-off” deformity at the AC joint. Treatment includes use of a sling or surgery if severe.  
  • Clavicular (collarbone) fracture- One of the most fractured bones in the body, this typically will occur from trauma or injury including a direct blow or a fall. There will be noticeable swelling at the front of the chest, anywhere between the sternum and the shoulder joint. Immobilization or use of a sling is the most common treatment approach.  

X-ray image of a clavicle fracture with labels and red arrows to show location of fracture and SC joint or Sternoclavicular joint

  • Shoulder impingement- the narrowing of joint space between the top of the shoulder (acromion) and the humerus. This can be caused by a bony deformity or irritation of soft tissues, such as the rotator cuff, that compress within the shoulder joint. Symptoms of shoulder impingement are similar to AC arthritis with pain at the front of the shoulder and with overhead or across body reaching. However, AC arthritis pain is typically more centralized. Shoulder impingement will be more diffuse, or throughout shoulder, including activities such as reaching behind the back. 

How do you Treat AC Joint Arthritis? 

AC joint arthritis is typically non-operative and can be managed with a combination of conservative treatments including physical therapy, activity modifications, anti-inflammatories (NSAIDs) or injections to the AC joint.  

How Should I Sleep with AC joint pain? 

If you have pain from Acromioclavicular joint arthritis, It is best to sleep on your back with the involved side propped or sleeping on the uninvolved side with a pillow underneath the involved arm. 

Related Links:

In Acromioclavicular joint arthritis (AC Jt) is causing you pain, the Jacksonville Orthopaedic Institute can schedule an appointment with a JOI shoulder specialist, call (904)JOI-2000, schedule online, or click the link below. To see a JOI Rehab Therapist in 1 of our 12 locations, call (904) 858-7045.

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