The acromioclavicular (AC) joint in the shoulder is very important to support the shoulder girdle. It also assists with providing shoulder strength, motion, and maintaining shoulder joint position. The joint is stabilized by various ligaments and a capsule, which can cause pain and affect normal joint function if damaged.
Anatomy of the AC Joint
The AC joint is located at the highest point of the shoulder, where the acromion, a bony projection on the shoulder blade, connects to the clavicle or collarbone. This joint assists with enabling you to lift your arm above your head and is important for overall shoulder control, motion, and strength.
The AC joint is stabilized by the following structures:
- Capsular ligaments: These ligaments are called the acromioclavicular ligaments. They have upper and lower components and resist separation of the joint in the horizontal direction.
- Extracapsular stabilizers: These are ligaments extending from the bony process of the scapula called the coracoid process to the clavicle (coracoclavicular ligaments) and the acromion (coracoacromial ligaments). These ligaments resist vertical forces from separating the joint.
- Muscular attachments: The deltoid muscle on the outside of the shoulder and the trapezius muscle in the upper back and neck also help stabilize the acromioclavicular joint.
Any injury to the AC joint, particularly to the ligaments, can result in instability or separation of the AC joint (shoulder separation), causing pain and discomfort and limiting shoulder function.
Causes of AC Joint Injuries
Injuries to the AC joint commonly occur due to:
- Falling onto the point of the shoulder
- Lifting heavy objects or weights
- A direct blow over the top of the shoulder
- Repetitive overhead use of the arm
Various situations which can result in an AC joint injury include:
- Participating in contact and collision sports
- Participating in activities that increase your risk of falls, such as skiing, biking, or skating.
- Physically strenuous jobs, especially those that involve overhead use of the arm
Symptoms of AC Joint Injuries
Signs and symptoms of AC joint injuries include:
- Pain over the AC joint at the top of the shoulder
- Tenderness over the AC joint at the top of the shoulder
- A bump over the shoulder
- Pain with lifting the arm above shoulder height
- Pain with lying on the affected side
Treatment for AC Joint Injuries
In most cases, conservative treatment methods are effective in treating AC joint injuries:
- Resting the joint for prolonged periods
- Application of an ice pack at regular intervals to reduce pain and swelling
- Use of anti-inflammatory medications
- Targeted injections of local anaesthetic and cortisone into the AC joint
- Physical therapy to help strengthen the shoulder muscles and improve range of motion.