The Anatomy of the Pectoral Girdle

The pectoral girdle, also known as the shoulder girdle, is the set of bones that connects the arm to the rest of the skeleton. It provides support and stabilization to allow the shoulder to move. The joints of the pectoral girdle can become damaged after injury or repetitive overuse of the shoulder.

Anatomy

The pectoral girdle provides the main structural support for the shoulder joint. The pectoral girdle consists of two bones:

• Clavicle or collar bone
• Scapula or shoulder blade

These bones of the pectoral girdle form several joints, including:

• Acromioclavicular (AC) joint: The acromioclavicular joint forms between the acromion of the scapula and the clavicle at the top of the shoulder.
• Sternoclavicular joint: The sternoclavicular joint forms between the sternum (breastbone) and clavicle at the front of the chest.
• Scapulothoracic joint: The scapulothoracic joint forms between the medial border (inner edge) of the scapula and the thoracic vertebrae of the upper spine.

Function

The pectoral girdle connects the arm to the rest of the skeleton and provides support and stabilization to allow the shoulder to move.

The scapula provides the primary structural support for the shoulder and can move in six different directions. These are protraction and retraction (forward and backward movement) elevation and depression (up and down movement) and upward rotation and downward rotation.

Without proper movement of the scapula, the ball in the socket of the shoulder joint cannot move properly, which can result in disorders like shoulder impingement and bursitis.

Muscles that attach to the scapula and control proper movement include the trapezius (upper, middle, and lower fibers), rhomboids (major and minor), levator scapulae, serratus anterior, and pectoralis minor.

The scapula also serves as an attachment site for muscles that move the shoulder and arm, including the four rotator cuff muscles (subscapularis, supraspinous, infraspinatus, and teres minor), deltoid, biceps brachii, triceps brachii, teres major, coracobrachialis, and latissimus dorsi.

The omohyoid muscle that controls the hyoid bone of the neck also attaches to the scapula. There are a total of 17 different muscles that attach to the scapula.

The clavicle is an elongated bone with a slight S-shaped curve that sits in between the shoulder and sternum at the top of the ribcage. It is the most frequently fractured bone in the body.

The clavicle provides structural support between the shoulder and rest of the skeleton, and has a small degree of movement into elevation and depression, protraction and retraction, and rotation. The deltoid, trapezius, sternocleidomastoid, pectoralis major, and subclavius muscles all attach to the clavicle for support.

Associated Conditions

The bones and joints of the pectoral girdle can become damaged from injury or repetitive overuse of the shoulder. Common conditions associated with the pectoral girdle include:

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 Collarbone)

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, formed between the clavicle and sternum, or breast bone, 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 the 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

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

Winged Scapula

A winged scapula occurs when the medial border, or inner edge, lifts up away from the scapulothoracic joint. This produces an extrusion of the shoulder blade on the back of the body that becomes more prominent when lifting the arm overhead.

A winged scapula can result from weakness of the serratus anterior muscle that holds the scapula in place against the thoracic spine or from injury to the long thoracic nerve, and can result in arm weakness and decreased range of motion.

Rehabilitation

Depending on the extent of your condition, rehabilitation for conditions associated with the pectoral girdle include the following:

• Medications: Pain-relieving and anti-inflammatory medications can temporarily be used to manage symptoms after injury to the pectoral girdle.
• 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 pectoral girdle 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 the joints of the pectoral girdle 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.
• Physical therapy: Physical therapy can help rehabilitate the pectoral girdle 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.