Anatomical Description of the Upper Arm and Shoulder

The upper arm and shoulder form a complex network of bones, muscles, ligaments, and joints that provide structure and allow for a wide range of motion.

The structure of the upper arm and shoulder allows for a wide range of movements, including lifting, pulling, and pushing. However, this area can be prone to injury and conditions such as rotator cuff tears, shoulder impingement, and biceps tendonitis.

Here’s a breakdown of the key components:

Bones: The humerus is the long bone of the upper arm, extending from the shoulder to the elbow. The shoulder joint is formed where the humerus fits into the scapula (shoulder blade) in a socket called the glenoid fossa. The clavicle (collarbone) also plays a crucial role in the shoulder, connecting the scapula to the sternum (breastbone).

The shoulder is a complex joint system that includes three bones:

  1. Humerus: This is the long bone of the upper arm that extends from the shoulder to the elbow.
  2. Scapula: Also known as the shoulder blade, it’s a flat bone that sits on the back of the rib cage.
  3. Clavicle: Known as the collarbone, it’s a slender, S-shaped bone that connects the scapula to the sternum (breastbone).

Muscles: The shoulder is composed of several muscles that provide movement and stability:

  1. Rotator cuff: This group of muscles and their tendons stabilize the shoulder. They include the supraspinatus, infraspinatus, teres minor, and subscapularis.
  2. Deltoid: This large muscle covers the shoulder joint and enables lifting of the arm and gives the shoulder its rounded contour.
  3. Pectoralis major: This large muscle on the front of the chest allows for forward movement and inward rotation of the arm.
  4. Latissimus dorsi: This wide muscle on the back helps move and rotate the arm.
  5. Trapezius and rhomboid muscles: These muscles in the upper back and neck help position the shoulder blade for various movements.

Ligaments: Ligaments are tough bands of tissue that connect bones to each other, providing stability to the joints. In the shoulder, the joint capsule is a group of ligaments that surround the shoulder joint. The rotator cuff tendons are particularly important for shoulder movement and stability. The biceps tendon attaches the biceps muscle to the shoulder and the elbow, allowing it to control arm rotation and flexion.

Several ligaments contribute to the stability of the shoulder:

  1. Coracoclavicular ligament: This connects the clavicle to a part of the scapula known as the coracoid process.
  2. Acromioclavicular ligament: This connects the clavicle to the acromion, another part of the scapula.
  3. Glenohumeral ligaments (superior, middle, and inferior): These three small ligaments on the front of the shoulder help prevent dislocation.

Nerves: The brachial plexus is a network of nerves that originates from the neck and provides sensation and motor control to the shoulder, arm, and hand.

Blood Supply: The axillary artery, a continuation of the subclavian artery, and its branches supply blood to the shoulder and upper arm.

Fascial Compartments: The shoulder does not have true anatomical compartments like the lower limbs. However, it is divided into an anterior and posterior region by the scapula, with each region containing specific muscles.

Joint Anatomy:

The shoulder comprises three joints:

  1. Glenohumeral joint: This is a ball-and-socket joint where the head of the humerus fits into the glenoid fossa of the scapula. This joint allows for a wide range of motion, including flexion, extension, abduction, adduction, internal rotation, and external rotation.
  2. Acromioclavicular joint: This is where the acromion process of the scapula and the clavicle meet. This joint helps with overhead and across-the-body movements.
  3. Sternoclavicular joint: This is where the sternum and the clavicle meet. It allows the shoulder to move in three planes.

Bursa Sacs: The primary bursa in the shoulder is the subacromial bursa, located under the acromion. It reduces friction between the acromion and the rotator cuff tendons.

Kinesiology: The kinesiology of the shoulder involves a wide range of movements:

  1. Flexion and extension: Lifting the arm up in front of the body and moving it back down.
  2. Abduction and adduction: Lifting the arm out to the side and moving it back down.
  3. Internal (medial) rotation and external (lateral) rotation: Rotating the arm towards the body and away from the body.
  4. Circumduction: Moving the arm in a circular motion, which involves a combination of flexion, extension, abduction, and adduction.
  5. Scapular motion: Includes elevation, depression, protraction, retraction, upward rotation, and downward rotation. These movements are essential for full shoulder range of motion.

Understanding the anatomy and kinesiology of the shoulder is critical in diagnosing and treating shoulder pathologies, designing rehabilitation programs, and in preventing injuries.