The acromioclavicular (AC) joint is a joint located between the acromion, a bony projection on the shoulder blade, and the clavicle, the collarbone. It is a vital joint in the shoulder, as it helps to provide stability and support for the upper limb.
Structure
Acromioclavicular joint is a synovial joint, which means it is surrounded by a capsule that contains synovial fluid to lubricate and nourish the joint.
Ligaments
The AC joint is held together by several strong ligaments, including the acromioclavicular ligament, the coracoclavicular ligament, and the trapezoid and conoid ligaments. These ligaments work together to keep the clavicle in place and provide stability to the shoulder.
The acromioclavicular ligament is a flat, triangular ligament that spans across the top of the AC joint. It helps to keep the clavicle in place and prevent it from moving too far upward.
The coracoclavicular ligament is a pair of ligaments that connects the clavicle to the coracoid process, a bony protrusion on the shoulder blade. These ligaments provide additional stability to the AC joint by limiting the movement of the clavicle.
The trapezoid and conoid ligaments are located below the coracoclavicular ligaments and help to hold the clavicle in place. They also play a role in absorbing shock and distributing weight when the arm is in use.
Muscles
In addition to the ligaments, the AC joint also has several muscles that help to support and move the joint. These muscles include the deltoid, the pectoralis major, and the trapezius.
The deltoid is a large muscle that covers the shoulder and helps to lift the arm. It is divided into three sections: the anterior, middle, and posterior deltoid. Each section works together to lift and rotate the shoulder.
The pectoralis major is a chest muscle that helps to move the arm forward and inward. It is a large, triangular muscle that covers the upper chest and connects to the humerus, the bone of the upper arm.
The trapezius is a muscle in the upper back that helps to lift and rotate the shoulder. It is a large, triangular muscle that extends from the base of the skull to the lower back.
Location
The AC joint is located at the top of the shoulder, where the clavicle meets the acromion. It is an important joint for the movement of the upper limb, as it allows the arm to lift, rotate, and reach out to the side. The joint also helps to absorb shock and distribute weight when the arm is in use.
Functions of the Acromioclavicular Joint
The acromioclavicular (AC) joint is a vital joint in the shoulder that helps to provide stability and support for the upper limb. Its strong ligaments and muscles work together to allow for a wide range of motion and protect the joint from injury.
Support and stability
The Acromioclavicular joint helps to provide stability to the shoulder by keeping the clavicle in place and preventing it from moving too far upward. This is achieved through the action of the acromioclavicular ligament, the coracoclavicular ligament, and the trapezoid and conoid ligaments, which work together to hold the clavicle in place.
The muscles around the AC joint also contribute to the stability of the shoulder. The deltoid, pectoralis major, and trapezius muscles work together to lift and rotate the shoulder, providing support for the upper limb during movement.
Range of motion
The Acromioclavicular joint allows for a wide range of motion in the shoulder, including lifting, rotating, and reaching out to the side. This is made possible by the diarthrosis (freely movable) nature of the joint, as well as the action of the muscles that surround it.
Absorption of shock
The AC joint plays a role in absorbing shock when the arm is in use. The trapezoid and conoid ligaments, in particular, help to distribute weight and absorb shock when the arm is lifted or moved. This helps to prevent injury to the joint and surrounding structures.
Clinical significance
Injuries to the Acromioclavicular joint can occur due to falls, car accidents, or sports-related activities. These injuries can range from sprains to complete dislocation of the joint. The most common type of AC joint injury is a sprained AC joint, which occurs when the ligaments around the joint are stretched or torn. This can cause pain and swelling in the shoulder, as well as difficulty moving the arm.
AC joint dislocations are less common, but can occur due to high-impact injuries or falls. A dislocated Acromioclavicular joint occurs when the clavicle is forced out of its normal position, causing severe pain and difficulty moving the arm.
Treatment for Acromioclavicular joint injuries will depend on the severity of the injury. In mild cases, treatment may include rest, ice, and physical therapy to help strengthen the muscles around the joint. More severe injuries may require surgery to repair or reconstruct the damaged ligaments or to realign the clavicle.
It is important to seek medical attention if you suspect that you have an Acromioclavicular joint injury. Early treatment can help to reduce the risk of long-term complications and ensure a full recovery.
