The acromial process, commonly called the acromion, is a bony projection extending from the shoulder blade, or scapula. This structure forms the highest point of the shoulder and is easily felt beneath the skin. The acromion is a central component of the shoulder girdle, fundamental to the shoulder’s wide range of motion and stability. Its health directly influences the function of underlying muscles and tendons, often making it a site of pain and dysfunction.
Anatomy and Location
The acromion is a continuation of the spine of the scapula, projecting laterally and forward. It creates a bony roof that arches over the glenohumeral joint, the main ball-and-socket joint of the shoulder. This process is flattened, defining the outer contour of the shoulder.
The underside of the acromion forms the superior boundary of the subacromial space. This narrow area contains the rotator cuff tendons, particularly the supraspinatus tendon, and the subacromial bursa. The superior surface of the acromion is rough and serves as an attachment site for large muscles.
Role in Shoulder Stability
The acromion provides stability by serving as a major articulation and attachment point for soft tissues. At its medial edge, the acromion meets the collarbone (clavicle) to form the acromioclavicular (AC) joint. This joint allows the scapula to move and rotate, which is necessary for full overhead arm movement.
The acromion anchors several muscles involved in arm and shoulder movement. The deltoid muscle originates partially from the acromion’s lateral border, while the trapezius muscle inserts onto its medial border. The acromion also connects to the coracoid process via the coracoacromial ligament, forming the coracoacromial arch. This arch acts as a mechanical barrier, protecting the rotator cuff structures that glide beneath it.
Common Acromial Injuries and Conditions
Shoulder impingement syndrome is a frequent issue, occurring when the space beneath the acromion narrows. This narrowing causes friction and pinching of the underlying rotator cuff tendons and the bursa, leading to pain and inflammation. The shape of the acromion can predispose individuals to this condition; a hooked or curved shape reduces the subacromial space more than a flat one.
Another common problem is an AC joint separation, an injury to the ligaments connecting the acromion and the clavicle. These injuries often result from a direct blow or a fall onto the shoulder, causing the ligaments to stretch or tear. Severity is graded based on which ligaments are damaged and the degree of bone displacement.
Acromial fractures can result from significant trauma to the shoulder. The AC joint is also susceptible to arthritis, a degenerative condition marked by cartilage breakdown. This wear and tear can be aggravated by activities like weightlifting, sometimes leading to distal clavicle osteolysis.
Management of Acromial Pain and Dysfunction
Initial treatment for most acromial pain, such as mild impingement or AC joint sprains, involves conservative methods. Rest and non-steroidal anti-inflammatory drugs (NSAIDs) reduce pain and inflammation. Physical therapy focuses on strengthening the rotator cuff muscles and improving posture to increase the space beneath the acromion.
If conservative treatments fail, a corticosteroid injection into the subacromial space delivers medication directly to the irritated tissues. This reduces pain, allowing the patient to participate in rehabilitation. Surgery becomes an option when non-surgical management fails to relieve symptoms after several months.
A common surgical procedure for chronic impingement is acromioplasty, where bone from the underside of the acromion is reshaped to create more clearance for the tendons. For severe AC joint separations or complex fractures, surgical repair may be necessary to realign and stabilize the joint. Recovery is extended, often requiring a gradual return to full activity.