Pectoral (Shoulder) Girdle: Names of Bones, Functions, & Diagram

Contents

Definition of the Shoulder Girdle
Bones in the Shoulder Girdle and Their Anatomy
Connections of the Shoulder Girdle
Muscle Attachments
Functions
Frequently Asked Questions
References

Definition of the Shoulder Girdle

The human skeleton comprises the axial skeleton, the body’s central axis, and the appendicular skeleton, which forms the limbs. The shoulder girdle, also known as the pectoral girdle, is a curved bony structure that links the appendicular skeleton to the axial skeleton at the shoulder, thereby connecting the arms to the body trunk.

Bones in the Shoulder Girdle and Their Anatomy

The shoulder girdle is composed of the clavicle and scapula, which articulate to create the half-circular structure at the shoulder. There are two shoulder girdles in the human body, each capable of functioning independently, allowing for the separate use of both shoulders and arms.

The following are the two bones comprising the structure:

1. Collarbone (Clavicle)

It is the elongated bone situated horizontally at the front of the body, one on each side. The clavicles are the only horizontally positioned bones in the human body. They articulate with the scapula to support the shoulder and facilitate rotation and other arm movements.

The clavicle is divided into the following parts, facilitating its connection of the upper arm to the axial skeleton:

Medial end: Also known as the sternal end, this triangular end articulates with the sternum, a bone of the axial skeleton, anteriorly.
Lateral end: The pointed end toward the lateral side articulates with the acromion of the scapula, forming the shoulder’s pointed tip. It is often referred to as the acromion end.
Shaft: The middle part or the body of the bone.

2. Shoulder Blade (Scapula)

These are the large, triangular bones on both sides of the back. The scapula, also known as the shoulder blade, serves as a primary attachment point for several muscles that facilitate arm and shoulder movements.

In addition to articulating with the clavicle at the acromion, the scapula articulates with the humerus at the glenoid cavity to form the shoulder joint.

It has three borders, named according to the direction they face:

Medial or vertebral border
Lateral or axillary border
Superior border

The scapula has two angles — the inferior and the lateral angles.

Connections of the Shoulder Girdle

Sternoclavicular (SC) Joint: The junction of the clavicle and the manubrium, the thickest and uppermost part of the sternum. This joint, positioned at the center of the chest, lies just over the first rib and is the only connection between the axial and appendicular skeletons in the upper body.
Scapulothoracic Joint: Not a genuine synovial joint, it is a connection between the front surface of the scapula and the back of the ribcage. The ‘joint’ relies on multiple muscles to sustain and control the connection, allowing the scapula to glide over the ribcage.
Acromioclavicular (AC) Joint: As the name implies, it is the joint between the acromion and the clavicle. The semicircular or V-shaped joint is the attachment point for various back and neck muscles.
Glenohumeral Joint: One of the most vital ball-and-socket joints, it is the joint between the shallow depression on the scapula, known as the glenoid cavity, and the head of the humerus. The loose joint is held in place by the rotator cuff, a strong muscular band formed by the shoulder muscles supraspinatus, infraspinatus, teres minor, and subscapularis.

Muscle Attachments

The key muscles that attach to the shoulder girdle and act on it are the pectoralis minor, and subclavius at the front, and the elevator scapulae, trapezius, and rhomboids (major and minor) at the back.

Functions

As previously mentioned, the primary role of the shoulder girdle is to secure the limbs (appendicular skeleton) to the body trunk (axial skeleton).
Another important function is facilitating a wide range of motion for the shoulder, particularly the mobility allowed at the scapulothoracic and sternoclavicular joints.
As the main attachment point for numerous small and large neck, shoulder, back, and chest muscles, it assists in arm and upper body movement.

Frequently Asked Questions

Q.1. Why is the shoulder girdle an incomplete ring?

Ans. The left and right shoulder girdles form an incomplete ring because the two scapulas do not meet at the back. The space between the two scapulas allows passage to muscles that attach to the spinal column.

Q.2. What are the differences between the shoulder girdle and shoulder joint?

Ans. As discussed above, the shoulder girdle is a bony structure constituting the clavicle and scapula to connect the axial and appendicular skeletons. On the other hand, the shoulder joint is the connection between the upper arm and the shoulder, consisting of two different joints, the glenohumeral and acromioclavicular joints.

Q.3. What are the differences between the shoulder and pelvic girdles?

Ans. The shoulder girdle is the connection between the axial and appendicular skeletons in the upper body. In contrast, the pelvic girdle is the connection between the two in the lower body.

The pelvic girdle is formed of the three pelvic bones, the ilium, ischium, and pubis. It is stronger than the shoulder girdle as it is the primary bony structure supporting body weight and locomotion, connecting the legs to the trunk.