Arthritis can be very challenging to live with and may affect any joint of the body. One common joint affected by arthritis is the acromioclavicular (AC) joint. But how do you know if you are experiencing AC joint arthritis? Keep reading to learn more about what AC joint arthritis is, current treatment options for this condition, and which exercises are best to improve your shoulder mobility.
The acromioclavicular joint (AC joint) is a small joint at the top of your shoulder, joining the tip of your shoulder blade or scapula (the acromion process) and your clavicle (the collarbone). The joint is fairly flat with a lining of cartilage to reduce friction and improve joint motion.
The function of the AC joint is to produce a gliding movement that assists with movement of the scapula. It is especially important for facilitating the end ranges of shoulder flexion (raising your arm overhead, in front of your body) and shoulder abduction (raising your arm overhead, away from your body). When movement of the joint becomes limited, motion of the entire shoulder complex can be affected.
Like many other joints in the body, the AC joint is susceptible to many types of injury. However, because of its shape and location, it is a particularly vulnerable part of the shoulder complex.
Repetitive use of the shoulder can cause irritation in the AC joint, especially during overhead and cross-body movements of the shoulder. Those who repeatedly perform these motions during work activities, exercise, or sports may be at an increased risk of developing overuse injuries and AC joint pain (1).
One of the most common forms of injury to the AC joint is ligament sprains. The acromioclavicular joint is held together by the acromioclavicular ligament, which provides stability and limits separation of the two bones. When the ligament is placed under excessive load, either during a sudden movement or slowly over time, it will overstretch and become partially torn.
Symptoms of AC joint sprains vary depending on the degree of the sprain. First-degree sprains typically involve shoulder joint pain, tenderness in the shoulder, and sometimes pain with reaching or carrying. Second-degree sprains are characterized by reduced stability and strength of the AC joint with presence of a “bump” due to laxity of the ligament, usually with pain during reaching and carrying. Third-degree sprains are the most severe and involve total rupture of the ligament, leading to severe instability and weakness of the shoulder joint.
However, one of the most common causes of shoulder pain in older adults is AC joint arthritis.
The term arthritis describes pain and inflammation within a joint. While there are many forms of arthritis, osteoarthritis (OA) is the most common variety in older adults. During the development of OA, cartilage lining the joint is gradually broken down, leading to increased stress and friction between bones. In response to stress, the bones become rough and progressively deformed.
The acromioclavicular joint or AC joint is located at the top of your shoulder and is where your shoulder blade (scapula) meets the end of your collarbone (clavicle). Arthritis occurs when the smooth glistening cartilage that lines the joint wears away. AC Joint arthritis is not the same as shoulder arthritis. Doctors usually refer to glenohumeral joint arthritis as ‘shoulder arthritis’.
Most people will develop OA in small amounts throughout their lifetime due to repetitive stress and wear on the joints of the body, so older adults are especially prone to experiencing OA. However, significant accumulation of OA in a single joint can lead to dysfunction.
In the case of AC joint arthritis, cartilage lining the joint becomes progressively thinner and the ends of the joint become rough. As a result, motion at the joint becomes stiffer and more limited (2). Additionally, motions that compress the AC joint, such as crossing the arm to the opposite side of the body, may be painful due to compression of the sensitive joint.
The specific shape of your acromioclavicular joint, determined by your unique genetics, may increase likelihood of developing arthritis. However, AC joint shape only accounts for a fraction of OA incidence, leaving the remainder of cause to specific activities and stressors on the AC joint (3).
Because the AC joint is involved in achieving the end ranges of overhead shoulder motion, these motions may become limited and painful as the severity of arthritis progresses. This may affect your ability to perform activities like reaching for a high shelf, throwing a ball, or swinging a racquet.
There are many treatments available for AC joint arthritis, although some are more popular than others. Because OA involves permanent changes to bone, most treatments focus on slowing the progression of arthritis, minimizing pain, and maximizing function.
In many cases, physical therapy will be the first choice for treatment. Your physical therapist will likely help you find exercises that improve your strength and range of motion while limiting stress on your AC joint during your daily activities or sports. Additionally, manual therapy may be performed to reduce pain and improve tolerance for exercise (4).
Your doctor may also prescribe medications to manage your arthritis symptoms. In many cases, oral analgesics (painkillers) are prescribed to help manage persistent aches and pains due to arthritis. Non-steroidal anti-inflammatories (NSAIDs) may also be prescribed to help limit inflammation and swelling around the joint. Your doctor may also recommend a variety of topical creams or patches to help manage symptoms of arthritis, which may be the best option for those with poor tolerance for oral medications.
While mild cases of AC joint arthritis respond well to physical therapy, more severe cases may require injection therapy to improve symptoms. One of the most common types of injection therapy is a steroid injection, which aims to reduce joint inflammation temporarily. A steroid injection typically improves tolerance for joint movement, which can improve the response to other AC joint arthritis treatment.
Very severe cases of AC joint arthritis may require surgical treatment. A commonly performed surgery is a distal clavicle resection, where the tip of the clavicle is removed to eliminate contact between the rough edges of bone within the AC joint (5). In many cases, AC joint surgery will be followed with physical therapy to restore motion and strength of the shoulder.
As the severity of AC joint arthritis progresses, shoulder mobility (the ability to move into and control certain positions) will generally decrease. It’s important to have a selection of safe physical therapy exercises that help improve mobility of your shoulder to minimize your pain and maximize your function. Although there are many potential AC joint exercises for improving shoulder motion, these examples are commonly used:
Start by lying on your back with your knees bent while holding a dowel in both hands. Slowly raise both arms overhead, using your mobile shoulder to assist your stiff shoulder. Pause at the end of the comfortable range of motion and return to the starting position.
Start by standing in a doorway or at a wall while holding a towel in your hand. Place the towel in front of you, against the wall at shoulder level. Slowly slide the towel up the wall within a comfortable range of motion, then return to the starting position.
Start by leaning with one arm on the edge of a counter or table with knees slightly bent. Gently relax your opposite arm and allow it to hang towards the floor. Slowly rock your hips back and forth while keeping your arm relaxed to create a pendulum motion and repeat, attempting to maintain smooth and comfortable motion.
Stand in an open doorway. Raise each arm up to the side, bent at 90 degree angles with palms forward. Rest your palms on the door frame or wall. Slowly step forward with one foot. Feel the stretch in your shoulders and chest. Stand upright and don’t lean forward. Hold for 30 seconds. Step back and relax.
Although these AC joint exercises are generally safe, you should always consult your doctor before participating in a new exercise program.
Menge, T. J., Boykin, R. E., Bushnell, B. D., & Byram, I. R. (2014). Acromioclavicular osteoarthritis: a common cause of shoulder pain. Southern medical journal, 107(5), 324–329. https://doi.org/10.1097/SMJ.0000000000000101
UC Davis Health Department of Orthopaedic Surgery: AC joint rehabilitation protocol
Candela, V., Villani, C., Preziosi Standoli, J., Scacchi, M., & Gumina, S. (2021). AC joint osteoarthritis: The role of genetics. An MRI evaluation of asymptomatic elderly twins. Journal of anatomy, 238(4), 1023–1027. https://doi.org/10.1111/joa.13340
Choose PT: Physical Therapy Guide to Osteoarthritis of The Shoulder
Link To Resource
Bigliani, L. U., Nicholson, G. P., & Flatow, E. L. (1993). Arthroscopic resection of the distal clavicle. The Orthopedic clinics of North America, 24(1), 133–141.
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