Acromioclavicular (AC) Joint Injury

The shoulder is one of the most complex joints in your body and allows your arm to rotate and move in many different directions. The shoulder joint is described as a “ball and socket” joint, however, the socket is very shallow and is similar to a golf ball resting on a tee. The shoulder is made up of three bones: the humerus (upper arm bone), the clavicle (collarbone), and the scapula (shoulder blade). The outer portion of the scapula bone is called the glenoid and is the golf tee where the ball of the humeral bone rests to make up the shoulder joint. The shoulder joint is also called the glenohumeral joint and you may see it referred as this in test results.

Two smaller joints complete the “shoulder girdle” and are the acromioclavicular joint (AC) and the sternoclavicular (SC) joints. The AC joint is the connection between the acromion (a bony protrusion from the shoulder blade) and the clavicle (collarbone). The SC joint is the connection between the sternum of your chest and the clavicle.

An AC joint injury occurs when the acromion and clavicle bones separate from each other, injuring the sets of ligaments (AC and CC ligaments) that hold them together. This can occur with a fall onto the shoulder and is seen in patients who participate in contact sports, skiing, or snowboarding.

AC joint injuries are very common and make up 10% of all shoulder injuries. The majority of injuries can be treated without surgery.

Types of AC Joint Injury

AC joint injuries are divided based on the degree of injury to the surrounding ligaments that hold the bones together.

• Type I – Sprain of the AC ligaments. Patients can have pain with use of the shoulder, but normal X-Rays. These injuries can be treated without surgery.

• Type II – Tear of the AC ligaments but the CC ligaments remain intact. Patients can have pain with use of the shoulder and X-rays will show a small vertical movement of the clavicle with relation to the acromion. These injuries can be treated without surgery.

• Type III – Tear of the AC and CC ligaments. Patients can have pain with use of the shoulder and can see a bump at the top of the shoulder. X-Rays will show the clavicle has moved vertically and sits above the acromion. The majority of patients are successfully treated without surgery, but a subset of patients will continue to have pain that affect their ability to return to activities and ultimately need surgery.

• Type IV – Tear of the AC and CC ligaments with the collarbone abnormally positioned backward. This is an uncommon injury but generally requires surgery.

• Type V – Tear of the AC and CC ligaments, along with a tear of the deltotrapezial fascia (a thick tissue around the muscles) that results in a collarbone that is positioned directly under the skin. X-rays will show significant vertical displacement of the clavicle relative to the acromion. This generally requires surgery.

• Type VI – This is a rare injury where the clavicle is positioned under the bones of the front of the shoulder. This injury requires surgery.

Symptoms & Diagnosis

Patients with AC joint injuries of all types typically have pain with movement of the shoulder, localized to the top of the shoulder. The top of the shoulder with be painful to the touch. Patients may feel a click when they move their arm over their head. With more severe injuries, patients may see a bump on the top of the shoulder.

AC joint injuries are diagnosed using physical examination and imaging studies to confirm the diagnosis. The physical examination is used to identify areas of pain, weakness, and changes in range of motion of the shoulder. X-rays of both shoulders help evaluate the severity of the injury and allow comparison to the uninjured shoulder. MRI (magnetic resonance imaging) allows us to evaluate the soft tissue and non-bony parts of your shoulder and specifically look at the ligaments that stabilize the AC joint and to evaluate for other injuries to the shoulder.

Treatment

Treatment of AC joint injuries can be done with non-surgical or surgical means, depending on the severity of the injury. The goal of treatment is to reduce pain and regain function of the shoulder. Non-surgical treatment is used for patients with type I, II, or III injuries. These therapies are used to reduce inflammation associated with injury and allow you to strengthen the shoulder, decrease inflammation, and regain function. Non-surgical treatment options include:

• Rest: A sling can be used for 1-2 weeks to protect the shoulder while inflammation decreases.

• Change in activities: Avoiding activities that irritate the shoulder, specifically overhead motions

• Non-steroidal anti-inflammatory medications (NSAIDs) can help decrease inflammation

• Injections: Steroid injections can help decrease inflammation in the AC joint. Steroid injections can be used if rest, activity modification, and NSAIDs do not improve the symptoms.

• Physical therapy: This is an important tool to help you strengthen and retrain the muscles of the rotator cuff to work better together

Surgery is used to treat those with Type IV, V, and VI injuries, as well patients with Type III injuries who continue to have symptoms after trying non-surgical treatment.

• Arthroscopic reconstruction of the AC joint: This minimally invasive procedure uses small incisions around the shoulder and a larger incision in the front of the shoulder to restabilize the AC joint. A small camera and specialized instruments are used to clean out inflammation and scar tissue from the AC joint. Restabilization of the AC joint can be accomplished by reconstructing the ligaments by using a graft to stabilize the joint.  Surgical reconstruction is most effective when post-operative instructions are carefully followed, including completion of a physical rehabilitation program. Most patients can expect full recovery to normal daily activities in 4-6 months after surgery.