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What are AC joint injuries?

The AC (acromioclavicular) joint is located at the top of the shoulder where the collarbone (clavicle) meets the shoulder blade (scapula). The acromion, a section of the scapula next to the clavicle, helps stabilize the shoulder.

AC joint injuries are a common source of shoulder pain.

In children and adolescents, the most common type of AC joint injury is clavicle fracture. Other types of AC joint injuries include separation and arthritis.

Clavicle fracture

Clavicle fractures (broken collarbones) are fairly common in growing children. Like all bones in a child’s body, collarbones are soft until a child reaches their adult height. They become solid bone later than many other bones, around age 18 and are prone to fracture until they do.

Clavicle fractures typically occur in children and adolescents as the result of a fall on their shoulder or onto an outstretched arm. Playing contact sports like lacrosse or football, or falling while biking, skiing, or skateboarding, increase the risk of clavicle fracture.

AC joint separation

This type of injury occurs when the AC joint is separated, the ligaments connecting the acromion and collarbone are damaged, and the two structures no longer line up correctly. AC joint separations are graded depending upon which ligaments are torn and how badly they are torn.

  • Grade I injury: The ligaments that support the AC joint are strained but the bones still line up.
  • Grade II injury: The ligaments that reinforce the AC joint are damaged. These ligaments are stretched but not entirely torn. When stressed, the AC joint becomes painful and unstable.
  • Grade III injury: The AC and secondary ligaments are completely torn, and the collarbone is no longer connected to the shoulder blade, resulting in a visible deformity.

AC joint arthritis

Arthritis is a condition that develops when cartilage that surrounds and cushion a joint breaks down and the bones begin to rub against each other. It is most common in older adults, however some childhood injuries can increase the risk of arthritis in early adulthood.

  • Friction between bones causes pain and swelling, especially with activity. Reaching across the body toward the other arm may be particularly painful.
  • Arthritis can lead to formation of spurs around the joint. These spurs are a symptom of arthritis and not the main cause of pain.

AC Joint Injuries | Symptoms & Causes

What are the symptoms of AC joint injury?

Symptoms of an AC injury may be different, depending on whether the injury is a fracture, dislocation, or arthritis. Symptoms may include:

  • shoulder pain at the front or top of the shoulder
  • swelling, bruising, or tenderness around the collarbone
  • pain or difficulty moving the affected arm or shoulder

Your child should be seen by a doctor or sports medicine specialist if they have any of these symptoms.

What causes AC joint injuries?

Most clavicle fractures and AC joint separations are the result of a fall or collision.

Arthritis of the AC joint mainly affects adults. Weightlifters are at increased risk, mainly from bench press and, to a lesser degree, military press. People with rotator cuff problems may also develop AC joint arthritis.

The following injuries or characteristics increase the risk for future arthritis of the AC joint:

AC Joint Injuries | Diagnosis & Treatments

How are AC joint injuries diagnosed?

To diagnose the cause of your child’s shoulder pain, their doctor may conduct a complete medical history and physical exam. Diagnostic testing may include:

  • x-ray: images of internal tissues, bones, and organs
  • magnetic resonance imaging (MRI): detailed images of organs and structures within the body (to rule out any associated abnormalities of the spinal cord and nerves)

How are AC joint injuries treated?

Your child’s treatment will depend on the type and severity of their injury. Our doctors in the Orthopedic and Sports Medicine Center are committed to repairing AC joint injuries in the least invasive manner possible, including pain medication and physical therapy. Surgery is only used in the most severe cases of AC joint injury.

Clavicle fracture treatment

Your child may need to wear a sling or brace to keep their arm immobile while the collarbone heals. At a certain stage of healing, your child’s doctor may recommend physical therapy to help restore range of motion in the shoulder.

Children can typically return to sports after eight weeks of treatment and healing from a clavicle fracture. If their fracture is minor, they may be able to return to sports sooner.

AC joint separation treatment

An AC joint separation can be very painful, so the initial treatment focuses on decreasing pain. This typically includes:

  • immobilizing the arm in a sling and placing an ice pack to the shoulder for 20 to 30 minutes every two hours, as needed
  • taking anti-inflammatory medications, such as Advil or Tylenol, as directed

As pain starts to decrease, it is important for your child to begin moving their fingers, wrist, elbow, and eventually their shoulder to prevent their shoulder from becoming stiff or frozen. Your child’s doctor, physical therapist, or trainer will give you instructions on when and how much your child should move their shoulder.

The length of time needed to regain full motion and function depends on the severity or grade of the injury.

  • Recovery from a Grade I AC separation usually takes 10 to 14 days.
  • Recovery from a Grade III separation may take six to eight weeks.

AC joint arthritis treatment

There is currently no way to replace cartilage damaged by arthritis. The primary way to control the symptoms of arthritis is to avoid or modify activities that aggravate the condition. For temporary pain relief, patients with arthritis can:

  • put an ice pack on the joint for 20 to 30 minutes at a time
  • take medication including aspirin, Tylenol, and non-steroidal anti-inflammatory drugs (NSAIDs)
  • take a shot of cortisone — temporary pain relief for serious cases only

When is surgery recommended for AC joint injuries?

Most AC joint injuries can be repaired without surgery, however, there are some exceptions.

Your child’s doctor may recommend surgery for clavicle fracture if your child’s bone doesn’t heal despite treatment (a condition called nonunion). However, clavicle fractures almost never require surgery.

Surgery for Grade I and II separations is also rare. If your child has a Grade III injury, they may have a painful lump near the collarbone. Minimally invasive surgery called partial clavicle excision can be very successful in such cases. But as always, the benefits must be weighed against potential risks.

When it comes to arthritis, surgery may be recommended if nonsurgical measures fail. Since arthritis pain is caused by friction between the ends of the bones, the treatment is removal of a portion of the end of the clavicle. This outpatient surgery can be performed through a small incision about one inch long or arthroscopically using several small incisions.

Regardless of the technique used, most patients who have surgery for AC joint arthritis have full motion by six weeks and return to sports by 12 weeks.

How we care for AC joint injuries at Boston Children’s Hospital

As the largest and most experienced pediatric and young adult sports medicine practice in the country, the Sports Medicine Division at Boston Children's combines personalized care with innovative treatment for each athlete we treat.

Our Sports Medicine team consists of sports medicine physicians, orthopedic surgeons, physical therapists, podiatrists, athletic trainers, sports psychologists, dietitians, and many others who collaborate in every aspect of our patients’ care and their recovery.

The Micheli Center for Sports Injury Prevention, part of the Sports Medicine Division, is dedicated to the prevention of sports injuries. Through research and clinical training, we offer practical strategies that help young athletes reduce their risk of injury while enhancing their sports performance. Our rehabilitation and strength training programs help injured athletes return to play stronger and healthier.

Whether injury prevention or recovery is your goal, we have the skills and dedication to help your child remain active in the sports they love.

AC Joint Injuries | Programs & Services