The Normal Anatomy of the Shoulder Joint by Dr. Vivek Bansal in Chandigarh and Mohali

The shoulder joint, a marvel of human anatomy, is one of the most complex and flexible joints in the body. It allows a wide range of motion, making it essential for various daily activities and athletic endeavors. To understand shoulder-related injuries or conditions, it is crucial to first have a clear understanding of its normal anatomy.

Bones of the Shoulder Joint

The shoulder is composed of three main bones:

1. Humerus: The upper arm bone, which fits into the socket of the shoulder blade.
2. Scapula: Also known as the shoulder blade, this flat, triangular bone provides the socket for the humerus to fit into.
3. Clavicle: Commonly referred to as the collarbone, the clavicle connects the scapula to the sternum (breastbone), acting as a strut that helps stabilize the shoulder.

Joints of the Shoulder

The shoulder involves several joints that work together to enable its wide range of motion:

1. Glenohumeral Joint: This is the ball-and-socket joint where the head of the humerus fits into the glenoid cavity of the scapula. It allows for rotational movement and a broad range of arm movements.
2. Acromioclavicular (AC) Joint: The AC joint is where the clavicle meets the acromion, a bony projection on the scapula. This joint plays a crucial role in the upward and downward motion of the shoulder.
3. Sternoclavicular Joint: The connection between the clavicle and the sternum, this joint supports the shoulder’s overall stability and movement.

Muscles and Tendons

The shoulder’s remarkable flexibility is made possible by a group of muscles and tendons known as the rotator cuff. This group includes four primary muscles:

1. Supraspinatus
2. Infraspinatus
3. Teres Minor
4. Subscapularis

These muscles are responsible for stabilizing the shoulder joint and facilitating various arm movements. The biceps tendon also plays a vital role, particularly in lifting and rotating the arm.

Ligaments and Labrum

Ligaments are strong bands of tissue that connect bones to each other, providing stability to the joints. In the shoulder, the glenohumeral ligaments are essential for maintaining the stability of the glenohumeral joint.

The labrum is a ring of cartilage that surrounds the glenoid cavity, deepening the socket and helping to stabilize the head of the humerus within the joint. It acts as a cushion and provides additional stability to prevent dislocations.

Bursae

Bursae are small, fluid-filled sacs that reduce friction between the bones, tendons, and muscles around the shoulder. The most notable in the shoulder is the subacromial bursa, which helps the rotator cuff tendons glide smoothly under the acromion.

Nerves and Blood Vessels

The shoulder is richly supplied with nerves and blood vessels, ensuring that it functions effectively and efficiently. The brachial plexus is a network of nerves that supplies the shoulder and arm with motor and sensory signals. Additionally, arteries such as the axillary artery and subclavian artery provide blood flow to the shoulder region.