The Anatomy of the Clavicle

The clavicle, also referred to as the collar bone, is an elongated, S-shaped bone that sits between the shoulder and sternum at the top of the ribcage. It provides structural support between the shoulder and the rest of the skeleton, and is one of the most frequently fractured bones in the body.

Structure

The clavicle joins the scapula, or shoulder blade, and sternum to form two joints on either end of the bone, which are:

• Acromioclavicular (AC) joint: The acromioclavicular joint forms between the acromion of the scapula and clavicle at the top of the shoulder, held together by the acromioclavicular ligament.
• Sternoclavicular joint: The sternoclavicular joint forms between the sternum and clavicle at the front of the chest, and is supported by the costoclavicular ligament.

The relative size of the clavicle leaves it particularly susceptible to fracture. Fracture of the clavicle can occur from a fall landing on an outstretched hand or through a direct blow to the shoulder. The middle third of the clavicle is most commonly fractured, accounting for about 80% of all cases of clavicle fractures.

The clavicle and scapula together are collectively referred to as the pectoral girdle, or shoulder girdle.

Function

The clavicle connects the shoulder to the rest of the skeleton. Its positioning allows for increased range of motion of the shoulder away from the body and helps protect the arm by dispersing force transmitted through direct contact.

The clavicle has a small degree of movement in elevation and depression (upward and downward movement), protraction and retraction (forward and backward movement), and rotation.

The subclavius, which means “beneath the clavicle,” is the primary muscle that controls the clavicle. It originates at the first rib, and attaches to the underside of the clavicle. When contracted, the subclavius, controlled by the subclavian nerve, causes the clavicle to depress, or move downwards.

The anterior deltoid, trapezius, sternocleidomastoid, and pectoralis major muscles all attach to the clavicle for support, and cause a small degree of multidirectional movement as well.

The midclavicular line, a vertical line drawn down the body from the midpoint of the clavicle, serves as an important anatomical landmark for locating other structures, including the apex of the heart, where a stethoscope can be placed to listen to the heartbeat.

Associated Conditions

The clavicle and associated joints can become damaged from injury or repetitive overuse of the shoulder. Common conditions associated with the clavicle include the following.

Acromioclavicular (AC) Joint Sprain or Separation

Trauma to the acromioclavicular joint, such as a direct blow to the front of the shoulder or falling and landing on an outstretched hand, can injure the ligaments holding the acromion and clavicle together. This can result in either an acromioclavicular joint sprain or separation of the joint. Symptoms include pain localized specifically at the acromioclavicular joint at the top of the shoulder.

Clavicle Fracture (Broken Collar Bone)

Injury to the shoulder, especially direct trauma to the front of the shoulder, can cause the clavicle to fracture. Symptoms include pain at the clavicle and shoulder, as well as pain and difficulty with moving the arm.

Sternoclavicular Joint Sprain or Dislocation

The sternoclavicular joint, between the clavicle and sternum, can become dislocated with injury to the front of the shoulder, causing pain and swelling around the injured area.

Distal Clavicle Osteolysis (Weightlifter’s Shoulder)

The end of the clavicle, or distal portion, that forms the acromioclavicular joint can become irritated and inflamed. Osteolysis, or bone degeneration, can easily occur at the end of the clavicle due to the high degree of stress and repetitive forces placed through the small surface area of the acromioclavicular joint, especially with heavy lifting such as bench press or military press. The bone begins to break down at a faster rate than it is able to heal and form new bone cells. Sharp pain commonly occurs with overhead and pushing movements of the arm and shoulder with a dull ache at rest.

Acromioclavicular (AC) Joint Arthritis

Aging and repetitive overuse of the shoulder can lead to degeneration of the cartilage and the development of arthritis within the acromioclavicular joint, causing inflammation within the shoulder and pain with arm movements.

Rehabilitation

Depending on the extent of your condition, rehabilitation for conditions associated with the clavicle or associated joints include the following:

• Medications: Pain-relieving and anti-inflammatory medications can temporarily be used to manage symptoms after injury.
• Cortisone injections: Cortisone can be injected into the acromioclavicular joint to help decrease pain and inflammation.
• Rest: Avoiding activities that cause increased symptoms for associated conditions of the clavicle is often necessary to allow time for inflammation to decrease and for injured joints to heal. Overhead movements and pulling, pushing, and lifting should be avoided.
• Immobilization: It may be necessary to wear a shoulder sling to protect your clavicle after an injury. For acromioclavicular and sternoclavicular joint sprains or dislocations, you may need to wear a shoulder sling for two to six weeks, depending on the severity of the injury. For a clavicle fracture, you may need to wear a shoulder sling for six to eight weeks until the bone heals.
• Physical Therapy: Physical therapy can help rehabilitate the structures surrounding the clavicle after injury to decrease pain, restore range of motion and proper joint mobility, and strengthen the muscles around the shoulders and shoulder blades.
• Arthroscopic surgery: Arthroscopic surgery of the shoulder is commonly performed for active patients with distal clavicular osteolysis who wish to resume weightlifting and athletic activities without pain. A distal clavicle resection is often performed, where a small portion of the end of the clavicle that has become inflamed is removed to increase the space in the acromioclavicular joint and reduce joint compression and degeneration. Arthroscopic surgery may also be performed to manage symptoms of acromioclavicular joint arthritis when other treatment methods have failed to relieve pain.
• Surgical Repair: Surgical repair may be necessary for a significant fracture of the clavicle. An open reduction internal fixation (ORIF) is most commonly performed, during which the broken pieces of the clavicle are repositioned back together, or reduced, and then held together with metal hardware, or internally fixated.