The shoulder has two main joints that are prone to osteoarthritis, and one of them is the acromioclavicular (AC) joint.
We recently added a new video to our video library that illustrates where and how AC joint arthritis forms and progresses.
When arthritis occurs in the AC joint, it causes pain, stiffness, and weakness in the front of the shoulder.
The AC joint is located where the clavicle, or collar bone, meets the acromion, the highest part of the shoulder blade.
This joint doesn’t move much, but it does enable some specific movements, such as raising the arm above the head or across the body.
The AC joint’s movement is protected by cartilage on the ends of the bones, but wear and tear, overuse, or a previous injury can cause the cartilage to become inflamed.
As the inflamed cartilage wears away, the space between the bones narrows and the bones may come into direct contact, grinding against each other.
This irritation to the bone surface can trigger the growth of osteophytes, or bone spurs, that can interfere with joint movement. The osteophytes can also irritate or impinge on nearby soft tissues like shoulder tendons and rotator cuff muscles. This is referred to as shoulder impingement syndrome.
The pain, swelling, and tenderness of AC joint arthritis affect the front and top of the shoulder. It can make activities like reaching up, swinging a golf club, or putting on a seat beat painful or impossible.
Osteoarthritis can also affect the glenohumeral joint of the shoulder, which is the main ball-and-socket joint that connects the shoulder and upper arm.