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Causes of AC Joint Impingement

To understand the causes and nature of AC joint syndrome, it may be helpful to cover the basics of shoulder anatomy. 

In particular, the acromioclavicular joint is the joint that connects the bony tip of the outer edge of the shoulder blade (acromion) to the collar bone (clavicle). The joint is located at the top of the shoulder and covers the essential role of stabilizing the shoulder joint. 

Just below the AC joint sits the bursa (a thin, fluid-filled sac in charge of keeping the joint lubricated) and the rotator cuff (a band of muscles and tendons that connect the shoulder to the humerus).

When the bursa or portions of the rotator cuff get pinched by or caught on the AC joint, you may start suffering from shoulder impingement syndrome.

This condition often arises when the space below the AC joint is restricted and the muscles, tendons, and other soft tissues in the shoulder don’t have enough space to move freely. Risk factors that may lead to this include the following: 

Inflammatory Conditions (i.e.: Bursitis)

Inflammatory conditions such as tendonitis may increase the risk of AC joint impingement. This is because the high levels of inflammation may cause the swelling of soft tissues which, in turn, reduce the space below the AC joint and make it more likely for areas of the bursa to become “impinged” by the above joint. 

Thickening of the Rotator Cuff Tendons

Inflammation may also cause the tendons around the rotator cuff to become thicker and swollen, which reduces the space into which they can move freely. This can cause the surrounding bones to start pressing on them, which leads to further irritation, inflammation, irritation, and pain. Some of the main causes of thickened shoulder tendons are repetitive stress and overuse. 


Shoulder impingement may be the result of an injury or traumatic event that pushes the soft tissue around the rotator cuff closer to the surrounding bones and joints. Some injuries that may lead to this condition include falling onto the shoulder or onto an outstretched arm. 

Repeated Stress

AC joint impingement syndrome is particularly common among athletes who regularly perform overhead rotational movements with their arms. Some activities that increase the risk of this condition include swimming, throwing, and playing baseball, tennis, or volleyball. 

Some occupational activities like window washing and painting may also cause repeated and excessive stress. 

Age-Related Bone Spurs

Another cause of AC joint impingement is age-related bone spurs. Bone spurs are bony growths that the body produces when attempting to replenish the cartilage (or soft cushioning) between the joints, which often declines or degenerates as we age. 

Bone spurs change the structure of the shoulder and reduce the space below the AC joint, thus making impingement syndrome more likely. 

Anatomic Factors

Some anatomic and hereditary anatomic abnormalities may lead to shoulder impingement syndrome. For example, if you were born with an acromion (the pointy bone at the top end of the shoulder blade) that is curved or not flat, it can press on the tendons and muscles underneath it. Malpositioning of the bones and structural changes related to injuries such as fractures may also lead to this condition.

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Symptoms of AC Joint Impingement

The symptoms of AC joint impingement may vary in nature and intensity from one patient to another. Because of this, healthcare providers often use a combination of physical examination and imaging tests to determine whether your shoulder pain is caused by impinged tendons, muscles, or bursa. 

Below are some of the common symptoms of this condition. 

Shoulder and Arm Pain

One of the most common symptoms of shoulder impingement is pain that radiates from the top or front of your shoulder through your arm. The painful sensations may intensify when lifting or extending your arms above your head, or when lying on the affected side of the body.

Difficulty Raising Your Arm Overhead

The impingement – or the portion of tendons and soft tissue caught on the bones or joints – may worsen when lifting your arms. This can make it difficult to raise your arms or carry out overhead movements. 

Nighttime Discomfort and Sleep Disturbances

Shoulder pain deriving from an AC joint impingement may intensify at nighttime. This is because, before going to sleep, you’ll have fewer distractions, thus making the painful sensations more noticeable. Additionally, laying on or rolling onto the affected side while you are asleep can cause painful flare-ups. This leads to sleep disturbances which, according to a 2015 study, affect the majority of people with shoulder disorders. 

Shoulder Stiffness and Reduced Range of Motion 

The impingement of tissue in and around the rotator cuff can lead to severe inflammation and progressive irritation. Swelling and the buildup of fluids are part of the body’s inflammatory response. In turn, the excessive swelling can prevent you from moving your shoulder freely, which leads to sensations of stiffness or reduced range of motion.

Regenerative Treatment Options for AC Joint Impingement

AC joint impingement syndrome is a long-term condition that may cause symptoms lasting from six months to a year. In some cases, conservative therapies take two years or longer to offer satisfactory results and, for some people, shoulder impingement is a recurring or chronic disorder that will accompany them throughout life. 

Unfortunately, most patients dealing with shoulder impingement are prescribed one of two equally-undesirable lines of treatment: taking pain-relieving medications (such as steroids)  daily or undergoing surgery. 

However, thanks to today’s progress in orthopedic regenerative medicine, there are other, non-invasive and non-surgical options available. Below, we’ll look at the procedures used in combination at Orthagenex to create treatment programs for patients with AC joint impingement.

Super-Concentrated PRP for AC Joint Impingement 

Platelet-rich plasma (PRP) refers to autologous blood samples that have been processed to have platelet concentrations that are 10-30 times higher than baseline levels using lab setting. The use of PRP in regenerative medicine has received significant interest, due to its ability to deliver high concentrations of growth factors precisely and non-invasively to an area in need.

PRP procedures involve injecting the body’s own healing factors (platelets) into the injured tissue using image guidance with fluoroscopy and MSK ultrasound. This procedure can be used to treat a variety of orthopedic conditions, including joint instability, minor arthritis, ligament, and tendon injuries, and strains.

More than 30 randomized controlled trials have been carried out on the effectiveness of PRP to support the body’s ability to heal naturally by stimulating the stem cells within the targeted area.

Bone Marrow Concentrate Stem Cell Injections for AC Joint Impingement 

Stem cells are an essential component of the human body and play an important role in the repair of injured bones, ligaments, tendons, and other tissues. However, when we age or suffer an injury, the body may become unable to deliver enough stem cells to the area in need.

To help with this, bone marrow concentrate procedures at Orthagenex use imaging guidance to deliver concentrated bone marrow containing stem cells to the area in need. This encourages the body’s inherent ability to heal itself by replenishing cell population in the injured area.

In practice, bone marrow concentrate procedures are carried out by cannulating the bone near the pelvis with a trocar, a sharp-tipped device. This provides a narrow tunnel that can be used to collect samples of the bone marrow’s liquid component, which is rich in stem cells.

BMC procedures can assist patients in improving their shoulder health and mobility without the lengthy and painful rehabilitation periods associated with surgery.


Skip the Shoulder Replacement Surgery

If you have received a diagnosis of AC joint impingement, the chances are that you are facing one of two prospects: having to take medications every day to deal with the pain or undergoing invasive surgical procedures. 

Luckily, Orthagenex treatments provide non-surgical and non-invasive treatment options for those suffering with shoulder pain. If you are ready to take the first step towards improving your shoulder health, Orthagenex can help!

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