Acromioclavicular (AC) joint injury is a term used to describe an injury to the top of the shoulder, where the front of the shoulder blade (acromion) attaches to the collarbone (clavicle). It can be caused by a traumatic event, such as a fall directly on the outside of the shoulder, or by repetitive overuse. AC joint injuries are most common in individuals younger than 35 years of age, with males sustaining 5 times more traumatic AC joint injuries than females. Because younger athletes are most likely to participate in high-risk and collision activities, such as football, biking, snow sports, hockey, and rugby traumatic AC joint injuries occur most often in this population. AC joint injuries can be identified and effectively treated by a physical therapist, often avoiding the need for surgery.
What Are Acromicioclavicular (AC) Joint Injuries?
There are 4 ligaments holding the 2 bones of the AC joint (the acromion and the clavicle) together. When an AC joint injury occurs, these ligaments are stressed, resulting in some degree of joint separation. There are 2 types of injuries that can occur at the AC joint:traumatic and overuse injuries.
A traumatic AC joint injury occurs when there is a disruption of the joint due to damaged ligaments holding the 2 bones of the joint together. This injury is called a shoulder separation (in contrast to a shoulder dislocation, it involves the ball-and-socket joint of the shoulder).
Traumatic AC joint injuries are most common in individuals who sustain a fall and land on the outside of the shoulder or onto a hand (eg, a football player who is tackled, a bicyclist who crashes, or a manual laborer who falls off a ladder.
Traumatic AC joint injuries are graded from mild to severe based on the amount of separation of the joint. Treatment of mild cases likely will be provided by a physical therapist; more severe cases may require surgery followed by physical therapy.
An overuse AC joint injury occurs over time as repeated, excessive stress is placed on the joint. Cartilage at the ends of the acromion and clavicle bones protects the joint from daily wear and tear. Over time, the demand placed on this cartilage may be more than it is capable of enduring, resulting in an overuse injury. Significant wearing of the cartilage is known as arthritis. Overuse AC joint injury is most common in individuals who perform tasks, such as heavy weight lifting (bench and military presses), or jobs that require physical labor with the arms stretched over the head.
How Does an AC joint injury Feel?
With an AC joint injury, you may experience:
- General shoulder pain and swelling
- Swelling and tenderness over the AC joint
- Loss of shoulder strength
- A visible bump above the shoulder
- Pain when lying on the involved side
- Loss of shoulder motion
- A popping sound or catching sensation with movement of the shoulder
- Discomfort with daily activities that stress the AC joint, like lifting objects overhead, reaching across your body, or carrying heavy objects at your side
How Is an AC Joint Injury Diagnosed?
Diagnosis of an AC joint injury starts with a thorough review of the patient’s medical history, including specific questions regarding when the pain began, and what aggravates and relieves the pain.
Your physical therapist will examine your shoulder and assess different measures, such as sensation, motion, strength, flexibility, tenderness, and swelling. Your physical therapist will perform several tests specific to the shoulder joint to examine the structures located there. The therapist may also ask you to briefly demonstrate the activities or positions that cause your pain. Other nearby areas, such as your neck and upper back will also be examined to determine whether they, too, might be contributing to your shoulder condition.
While an AC joint injury can usually be identified through a shoulder examination, diagnostic imaging, such as ultrasound, x-ray, or MRI is often used to confirm the diagnosis and determine the severity of the injury.
How Can a Physical Therapist Help Treat an AC Joint Injury?
Once other conditions have been ruled out and an injury to the AC joint is diagnosed, your physical therapist will work with you to develop an individualized plan tailored to your specific shoulder condition and your goals. There are many physical therapy treatments that have been shown to be effective in treating this condition. Your physical therapist may focus on:
Range of Motion. An injury to the AC joint, whether traumatic or overuse, causes the joint to be irritated, often resulting in swelling and stiffness, causing loss of normal motion. Motions that are usually most difficult after an AC joint injury are reaching across your body and lifting your arm directly overhead. While it is important to regain your normal shoulder motion, it is also important to allow your injury to heal without placing excessive stress on the healing joint. Your physical therapist will assess your motion and the degree of your injury, and establish a plan that will balance joint protection and motion restoration.
Strength Training. After an injury, the surrounding muscles demonstrate weakness. All of the muscles near the shoulder and elbow as well as those of the upper back, work together to allow for normal, coordinated upper-body motion. Therefore, balancing the strength of all the upper-body muscles is crucial to making sure the shoulder joint is protected and moves efficiently. Your physical therapist will design an individualized exercise program to strengthen the muscles at and around the shoulder, so that each muscle is able to properly perform its job.
Manual Therapy.Physical therapists are trained in manual (hands-on) therapy. If needed, your physical therapist will gently move and mobilize your shoulder joint and surrounding muscles as needed to improve their motion, flexibility, and strength. These techniques can target areas that are difficult to treat on your own.
Pain Management.Your physical therapist may recommend therapeutic modalities, such as ice and heat to aid in pain management.
Functional Training. The AC joint is a relatively small joint that is often asked to bear a significant load. In order to successfully meet this demand, there is a need for functional training, teaching your entire shoulder to work best in different positions. For example, when lifting overhead, poor coordination places undue stress on the shoulder. Physical therapists are experts in assessing movement quality. Your physical therapist will be able to point out and correct your movements to help you maintain a pain-free shoulder.
Education. The first step to addressing your shoulder pain is rest. The amount of rest required varies, and largely depends on the degree of your injury. Your physical therapist will create a personalized plan for your rehabilitation, so you can safely return to your desired daily and recreational activities.
Can an AC Joint Injury be Prevented?
It may be difficult to prevent many traumatic AC joint injuries, such as bicycle crashes, falls to the ground, etc. Accidents do happen. Fortunately, however, much can be done to prevent the cascade of events that lead to overuse injuries to the AC joint, including:
- Learning about the risks of pushing through pain.
- Monitoring work and weight-lifting activities, particularly repetitive overhead lifting.
- Avoiding repetitive overhead lifting when possible.
- Maintaining adequate general shoulder strength and motion to safely perform desired tasks.
- Consulting with a physical therapist if symptoms are persistent or worsening despite rest.
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