Shoulder acromioclavicular (AC) joint osteoarthritis
What is the AC joint?
The acromioclavicular joint, the AC joint, is located at the top of the shoulder where the collarbone and shoulder blade meet. The AC joint is one of many small plane joints our bodies have and which permit sliding/gliding movement between articular surfaces. This joint gives the arm extensive range of motion, allowing to raise the arm above the head and glide it across the shoulder plane.
What is AC joint osteoarthritis and what causes it?
AC joint degeneration is more rapid than other joints and is more common than shoulder (glenohumeral joint) osteoarthritis. It is the second most common shoulder pathology in adults 40 years and older (after rotator cuff pathology). AC joint arthrosis refers to asymptomatic patients with X-ray evidence of degenerative changes. Signs of osteoarthritic change are often present in asymptomatic patients in their mid-40s. Evidence of degeneration of the AC joint include narrowing of the joint space, hardening and cystic changes of surrounding cartilage tissue, and bone spur formation. These changes may develop sooner following trauma or repetitive stress. Many people may develop AC joint arthritis as they age, but several risk factors do increase the chance of development such as joint trauma, repetitive joint stress and chronic injury, congenital defects, and advanced age.
What are the signs and symptoms?
Do you find it painful when crossing your arm to buckle your seat belt or when reaching for the top shelf, such examples may be signs that you may have developed arthritis of the AC joint. Some signs that patient's with AC joint arthritis frequently describe are pain at the top of the shoulder, or pain when the arm of the affected side moves horizontally across the shoulder plane (i.e. reaching for the seat belt) or when raising it above the head. Pain may be vague or sharp, and may awaken the patient during sleep when patient rolls on the affected shoulder. Swelling around the joint is also seen in patients with arthritis. Clicking, popping, snapping, or crunching, which physicians refer to as crepitus, may also be noticed when applying stress to the joint.
Symptomatic patients may feel pain or tenderness with direct palpation of the AC joint. Pain may also radiate to the shoulder, base of the neck, or down the arm. Passive motion of the arm horizontally across the shoulder plane which compresses the joint also may illicit pain and discomfort, this is known as the cross-body adduction test. In most cases, symptoms of AC joint osteoarthritis come and go, but progressively get worse and more frequent over the years. Flare ups may occur commonly after high-intensity activities, such as weightlifting or heavy labor work.
How do we diagnose AC joint osteoarthritis?
Diagnosis of AC joint osteoarthritis or any other form of osteoarthritis consists mainly of patient history, physical exam findings, and radiographic imaging. Imaging is commonly performed to evaluate the anatomic integrity of the joint. X-rays allows us to visualize some of the degenerative changes related to arthritis, such as narrowing of the joint space which may indicate loss of cartilage tissue, or the growth and progression of any bone spur present. Still, there are patients that have no symptoms but show significant arthritic changes on X-ray and there are patients that report pain with few or any changes present on X-ray.
Other imaging techniques, like MRI, can give us further details if X-rays are inconclusive or if the physician suspects pain is due to other causes, such as damage of the rotator cuff. If there is inflammation present around the AC joint, MRI imaging can detect the excess fluid and swelling which are not appreciated in an ordinary X-ray.
Other diagnostic approaches such as injecting a local anesthetic (i.e. lidocaine) directly into the joint with immediate relief may confirm diagnosis, but if not, then another shoulder problem may be the source of pain. Blood work can also be performed to rule out other causes of arthritic pain (i.e. rheumatoid arthritis).
How do we treat AC joint osteoarthritis?
Remember, AC joint osteoarthritis as well as all other types of osteoarthritis are chronic degenerative conditions that progress over time. Most patients respond well to a combination of activity modification, physical therapy, medication, including steroid injections. The best way to slow progression is with activity modification, such as decreasing cross-body motion (i.e. golf, tennis) and overhead activities (i.e. bench pressing). Physical therapy helps decrease pain and improve function with the goal of improving strength and range of motion. Medical therapy is mostly reliant on acetaminophen or NSAIDs (i.e. ibuprofen), if pain persists with these first-line options, corticosteroid injections may be considered. Corticosteroid injections provide acute pain relief and are useful when more conservative options fail, but are not curative and chronic use has its adverse effects such as weakening or destruction of soft tissue surrounding the joint. Other additional therapies like acupuncture or glucosamine supplements may help, but are not definitive treatments.
If patient's symptoms fail to improve or continue to worsen, or shoulder does not regain adequate function and/or has poorly controlled pain with conservative therapy, surgical options should then be considered. Surgery is indicated only if no symptomatic improvement is observed with conservative treatment options after at least 3 months. Surgery mainly consists of decompression of the space below the AC joint (subacromial space) and distal clavicle resection; surgery is often curative. Arthroscopic approaches are often recommended because they are associated with better pain relief in a shorter recovery window (at 3 months), lower risk of infection, and faster gain of function.
