Scapular Waist: Definition, Joints, Movements, Strengthening, Bones and Muscles That Compose It

It is the group of bones that manage to connect the arm and the appendicular skeleton of each side.

The shoulder belt or better known as the shoulder girdle, is the bony ring used for the fixation and support of the upper extremities.

The scapular waist is the one that connects the upper extremity with the axial skeleton on the left and right sides of the body.

The anatomical connection joins the anterior sternoclavicular joints, the axial skeleton, and the scapular waist.

There is no anatomical articulation between each scapula and the thoracic cage; on the other hand, the muscular connection or the physiological expression between the two allows excellent mobility of the scapular waist compared to the tight pelvic girdle.

The shoulder girdle consists mainly of the actual shoulder joint (glenohumeral joint) and the joint between the shoulder blade and the thorax (scapulothoracic joint).

Joints of the shoulder girdle

The scapular waist is a complex of five joints that can be divided into two groups.


Three of these are accurate anatomical joints, while two are physiological joints.

Within each group, the joints are mechanically linked so that both groups simultaneously contribute to the different movements of the shoulder in varying degrees.

  1. In the first group, the scapulohumeral or glenohumeral joint is the anatomical joint mechanically linked to the subdeltoid or superhumeral physiological joint so that movements in the latter result in the former.
  2. In the second group, the scapulocostal or scapulothoracic joint is the essential physiological joint that can not function without the two anatomical joints of the group, the acromioclavicular and sternoclavicular joints; that is, they unite both ends of the clavicle.

Glenohumeral joint

The glenohumeral joint is located between the head of the humerus and the glenoid cavity of the scapula.

It is a ball and socket synovial joint with three rotational degrees of freedom and three translational degrees; it allows abduction, adduction, lateral and medial rotation, extension, and flexion of the arm.

Acromioclavicular joint

It is a flat type of synovial joint located between the scapula’s acromion and the clavicle’s lateral end.

The acromion rotates on the acromial end of the clavicle.

Sternoclavicular joint

The articulation of the manubrium of the sternum and the first costal cartilage with the medial end of the clavicle is the sternoclavicular joint.

It is a type of synovial joint mount, but it functions as a flat joint and can be raised to a 60º angle and adapts to many movements of the scapula.

Scapulocostal joint

The scapulocostal joint is a physiological joint formed by articulating the anterior scapula and the posterior thoracic cage.

It is musculotendinous and is formed preponderantly by the rhomboid, serratus anterior, and trapezius muscles.

The pectoralis minor also plays a role in their movements.

The sliding movements in this joint are elevation, depression, retraction, protraction, and upper and lower rotation of the scapula.

Disorders of the scapulocostal joint are not very frequent and, in general, are limited to the rupture of the scapula.

Suprahumeral articulation

The supramental joint is formed by an articulation of the coracoacromial ligament and the head of the humerus; it is a physiological joint formed by the gap between the humerus and the acromion process of the scapula.

In this area, there is the subacromial pocket and the supraspinatus tendon.


The shoulder girdle is the anatomical mechanism that allows the entire arm and shoulder movement.

From its neutral position, the scapular waist can be rotated around an imaginary vertical axis at the medial end of the clavicle (the sternoclavicular joint).

Throughout this movement, the scapula is rotated around the wall of the thorax so that it moves 15 centimeters laterally, and the glenoid cavity is rotated from 40 to 45 degrees in the horizontal plane.

When the scapula moves medially, it is in a frontal plane with the glenoid cavity facing directly to the sides.

In this position, the lateral end of the clavicle is rotated backward so that the angle in the acromioclavicular joint opens slightly.

When the scapula moves laterally, it is in a sagittal plane with the glenoid cavity facing anteriorly.

In this position, the lateral end of the clavicle is rotated forward so that the clavicle is in a frontal plane.

While this slightly closes the angle between the clavicle and the scapula, it also widens the shoulder.

From its neutral position, the scapular waist can be rotated around an imaginary vertical axis at the medial end of the clavicle.

Throughout this movement, the scapula is rotated around the wall of the thorax so that it moves 15 centimeters laterally, and the glenoid cavity is rotated from 40 to 45 degrees in the horizontal plane.

The scapula can be raised and pressed from the neutral position to a full range of 10 to 12 centimeters; in its highest position, the scapula is always tilted so that the glenoid is facing up.


The shoulder girdle is the shoulder region that joins the upper arm with the axial skeleton. Therefore, it is closely associated with the upper extremity.

It consists of two bones that form the shoulder and are responsible for providing essential structural support. As it does not have a posterior attachment, it has a wide range of motion.

Bones of the shoulder girdle


The scapula, also known as the scapula, is the bone that connects the humerus (upper arm bone) to the clavicle.

The scapula forms the back of the scapular waist in humans. It is a flat bone that has an approximately triangular shape.

It is placed on the posterolateral aspect of the rib cage. Its ventral surface has a broad concavity, known as the subscapular fossa.

The scapula is a vital bone, as it provides fixation to several muscles of the head, neck, and back region.


The clavicle is a small S-shaped bone that forms the scapular waist and the scapula, which connects the arm to the body, and is located above the first rib.

The clavicle helps in the function of the chest belt to keep the arm away from the thorax and the central skeleton, which ensures that the component can perform a wide range of movements with relative ease.

It also acts as a rigid support, where the upper extremity and the scapula are suspended.

Scapular girdle muscles

The scapular girdle consists of five muscles that join the clavicle and the scapula, allowing movement of the sternoclavicular joint (the connection between the sternum and the clavicle) and the acromioclavicular joint (relationship between the clavicle and the scapula).

The five muscles that comprise the function of the scapular waist are the trapezius muscle (upper, middle, and lower), the levator scapula muscle, and the rhomboid muscles (major and minor), the serratus anterior muscle, and the pectoral muscle.

Pectoral Mayor

This is one of the main muscles involved with the pectoral waist.

Its origin is found in the clavicular head and the sternocostal head.

When these two parts of the muscle act together, the central pectoral adducts rotate the humerus medially at the shoulder joint.

The lateral and medial pectoral nerves innervate this muscle.

Pectoral minor

It is widely covered by the pectoralis major and is innervated by the medial pectoral nerve.

It is attached to the ribs near the costal cartilages and is also connected to the coracoid process of the scapula.

Serrato anterior

It is a large muscle located very close to the thorax on its side.

It is attached proximally to all the ribs and is attached distally to the medial border of the scapula.

The long thoracic nerve innervates it.

This is the muscle responsible for the scapula’s protraction and holds it and fixes it against the chest wall.

Some muscles are indirectly involved with the scapular waist; they are attached to the scapula or the clavicle but only partially help their movement.

These include the subclavian, the scapulae elevator, the rhomboid, and the trapezius muscle.