AC Joint

An Overview of the AC Joint

The acromioclavicular joint, also known as the AC joint, is located where the clavicle (collarbone) meets the highest point of the acromion (shoulder blade). The shoulder AC joint is small and has a limited range of motion, unlike the shoulder joint. The AC joint is a critical structure within the shoulder since it is the main connection between the arm and the axial skeleton. Dr. Peter Millett, orthopedic shoulder specialist, is well-trained and highly experienced at treating orthopedic injuries and sports injuries associated with the acromioclavicular joint.

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AC Joint Function

The AC joint is classified as a synovial joint. Located where the collarbone meets the shoulder blade, the shoulder AC joint allows the arm to raise above the head. It also allows the transmission of forces from the upper arm to the rest of the skeleton. The joint itself does not have its own musculature, so movement is initiated elsewhere. For instance, when the arm is raised or rotated, the AC joint moves to accommodate the action.

AC Joint Anatomy

The acromioclavicular joint’s articular surfaces are lined with fibrocartilage, much like those of the sternoclavicular joint. The cavity of the AC joint is partially divided by an articular disc that is classified as a wedge of fibrocartilage suspended from the capsule’s upper portion.

The shoulder AC joint capsule is composed of a loose fibrous layer which encloses the two articular surfaces. As a synovial joint, the joint capsule is lined by a synovial membrane that releases synovial fluid into the joint cavity.

The acromioclavicular joint is stabilized by three ligaments and two sets of muscles. The acromioclavicular ligament runs horizontally from the shoulder blade to the collarbone. The two coracoclavicular ligaments connect the coracoid process, portion of the scapula, to the collarbone. The two sets of muscles responsible for assisting with the support of the AC joint include the trapezius muscle and deltoid muscle.

Injuries related to the AC joint are fairly common and often result from a hard fall or other trauma. Some examples of these injuries include:

Dr. Millett will perform a thorough physical examination to assess a patient’s shoulder AC joint injury, and then will discuss appropriate treatments that are available for patients from Vail, Aspen and the surrounding Denver, Colorado communities.

For additional resources on the AC joint, please contact the orthopedic practice of Dr. Peter Millett.

Are you suffering from an AC joint injury?

There are two ways to initiate a consultation with Dr. Millett:

You can provide current X-rays and/or MRIs for a clinical case review ($250).

You can schedule an office consultation with Dr. Millett.

Request Case Review or Office Consultation

Peter Millett, MD

Average rating:

39 reviews

Alexandra Thompson

Mar 23, 2024

by Alexandra Thompson on Peter Millett, MD

110%

Dr. Millett and his team did a SLAP tear repair and bicep tenodesis on my left shoulder. I use my arms as an artist, and love to swim in the ocean, surf, paddle, and telemark ski. So regaining full use of my shoulder and keeping my bicep attached was very important to me. Now, over two years later, my shoulder has the equivalent range of motion as my other arm and as before the injury, and no pain. After the first three months it felt so good and was so strong that - to my horror - I completely forgot my six-month follow-up.

Not only did Dr. Millett and his team make my arm as good as new, but having had the experience of such kindness and expertise throughout the process of surgery and recovery is like an added shoulder superpower.

Thank you Rita, Brooke, Jason, Sarah, Camille, Olivia, Dr. Millett and everyone! And see you soon when my husband comes in for his knee...

Jeff Chandler

Jan 31, 2022

by Jeff Chandler on Peter Millett, MD

Flawless procedure, Easy recovery

Dr. Millet's repaired my knee and tibia, following a botched operation by a different surgeon. That procedure was virtually pain free and I was weight bearing within a few days. That was 18 years ago and the knee is still strong. A few years after the knee incident, Dr Millet repaired my shoulder. My insurance company approved me for 3 months of disability following that surgery. I was off pain medication in 2 days and had 90% range of motion within a week. I withdrew my disability claim and returned to work within two weeks of surgery. I’m not a famous athlete—just a regular guy. Nonetheless, I was treated like an NFL at the Steadman clinic. Most notable was the time for recovery. Other surgeons perform their hour-long task in the OR and don’t involve themselves in the other functions. Peter and his team manages the entire process from diagnosis, anesthesia, nursing care, and therapy. He takes a holistic approach to patient care and doesn’t skip any steps.

Jenn West

Jul 2, 2021

by Jenn West on Peter Millett, MD

Saved My Life

I went to Dr. Millett after 7 knee surgeries (6 on my right and 1 on my left) and had seen 11 different surgeons who all refused to remove femur metal from my right leg. I am highly allergic to metal and the chronic pain was leaving me bedridden for 3.5wks out of a month. He personally wrote me back on my inquiry, listened to my concerns, scheduled my surgery within a week (due to insurance issues) and personally followed up with my recovery. The level of patient care from Dr. Millett and his ENTIRE team is above any care I have ever received in my 20 years of dealing with orthopedic surgeons. There are not enough words to describe the level of care, dedication and professionalism you receive from Dr. Millett and his staff.
My only disappointment is that I did not find him sooner!!!

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An Overview of the AC Joint

AC Joint Function

AC Joint Anatomy

Are you suffering from an AC joint injury?

About the Author: Peter Millett, MD