The acromion is a bony projection that extends laterally from the scapula (shoulder blade). It is a key anatomic structure in the shoulder joint, as it forms the top portion of the shoulder girdle and helps to support and stabilize the arm.
Structure
The acromion has a number of important features, including its shape, size, and location. It is triangular in shape and has three surfaces: a superior surface, an inferior surface, and a lateral surface. The superior surface of the acromion faces upwards and is flat, while the inferior surface is concave and faces downwards. The lateral surface is curved and faces outwards.
The acromion also has several borders, including a superior border, an inferior border, and a lateral border. The superior border of the acromion is the highest point of the acromion and marks the junction between the acromion and the spine of the scapula. The inferior border is the lowest point of the acromion and marks the junction between the acromion and the glenoid cavity (the socket of the shoulder joint). The lateral border of the acromion marks the junction between the acromion and the clavicle (collarbone).
There is some variation in the shape and size of the acromion among individuals. Some people have a flat acromion, while others have a curved or hooked acromion. This variation can affect the function of the acromion and may lead to certain conditions, such as impingement syndrome, in which the acromion rubs against other structures in the shoulder joint and causes pain and inflammation.
Where is Acromion located?
The acromion is located at the top of the shoulder joint and is connected to the clavicle and the scapula. It helps to support and stabilize the arm, particularly when lifting and carrying heavy objects. It also helps to protect the rotator cuff muscles and tendons, which are responsible for rotating and lifting the arm.
Function
Supporting and stabilizing the arm
The acromion helps to support the weight of the arm and maintain its position within the shoulder joint. This is particularly important when lifting and carrying heavy objects.
Protecting the rotator cuff muscles and tendons
The rotator cuff muscles and tendons are responsible for rotating and lifting the arm. They pass underneath the acromion and are vulnerable to injury, particularly in people who perform repetitive overhead movements or engage in sports such as tennis or throwing. The acromion helps to protect these structures by providing a bony barrier.
Providing attachment points for muscles and ligaments
The acromion serves as an attachment point for several muscles and ligaments, including the supraspinatus muscle and the coracoclavicular ligament. These structures help to support and stabilize the shoulder joint.
Participating in joint movement
The acromion is involved in several joint movements, including flexion, extension, abduction, and rotation of the arm. It moves in conjunction with the scapula and the clavicle to allow these movements to occur.
Clinical significance
Impingement syndrome
Impingement syndrome, also known as shoulder impingement, occurs when the acromion rubs against other structures in the shoulder joint, such as the rotator cuff muscles and tendons, and causes pain and inflammation. This condition is more common in people who perform repetitive overhead movements or engage in sports such as tennis or throwing. Impingement syndrome can be treated with physical therapy, rest, and anti-inflammatory medications. In severe cases, surgery may be necessary to remove the bony spur or portion of the acromion that is causing the impingement.
Fractures
The acromion can fracture, or break, due to trauma such as a fall or a direct blow to the shoulder. Fractures of the acromion can be treated with immobilization (wearing a sling), physical therapy, and in severe cases, surgery.
Arthritis
Arthritis, a condition characterized by inflammation and degeneration of the joints, can affect the acromion and cause pain and stiffness in the shoulder joint. Osteoarthritis, a type of degenerative arthritis, is more common in the acromion due to its weight-bearing function. Treatment options for arthritis of the acromion include physical therapy, medications, and in severe cases, joint replacement surgery.
Shoulder separation
A shoulder separation, also known as an acromioclavicular joint separation, occurs when the acromion becomes separated from the clavicle due to trauma such as a fall. This injury is treated with immobilization, physical therapy, and in severe cases, surgery.
