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Anatomy of shoulder joint-Bones-Muscles-Ligaments

In this article, we will discuss about the anatomy of shoulder. Shoulder complex consist of number of joints, bones and ligaments. So to understand the anatomy  and movements of shoulder joint it is important to know about the structures of the joint. Details of these structures is discussed below.

Bones of shoulder joint

Scapula

Second name of scapula bone is shoulder blade.

Location:

It is a flat triangular bone that is located on the back of the shoulder.

Articulation:

  • It articulates with the humerus, the long bone of the upper arm, at the glenohumeral joint.
  • The scapula also articulates with the clavicle, at the acromioclavicular joint.

Structure of Scapula:

Borders:

The scapula has three borders:

  1. Superior border
  2. Medial border
  3. Lateral border
Angles:

It also has three angles:

  1. Superior angles
  2. Inferior angle
  3. Lateral angle
Surfaces:

The scapula has two surfaces:

The anterior surface

This surface is smooth and concave. It faces the chest and is covered by muscles.

The posterior surface.

The posterior surface of the scapula is rough and convex. It faces the back and muscles and ligaments cover the posterior surface .

Landmarks

The scapula has several important landmarks, including:

Glenoid fossa

This is a shallow depression on the lateral surface of the scapula. It articulates with the head of the humerus to form the glenohumeral joint.

Acromion process of scapula

This is a large, hook like process that projects from the superior border of the scapula. It articulates with the clavicle to form the acromioclavicular joint.

The coracoid process

This is a small, beak-like process it is present on the anterior surface of the scapula. It serves as an attachment point for several muscles.

Humerus

It is the long bone present in upper arm. It articulates with scapula to form glenohumeral joint and at the elbow joint it articulates with the ulna and radius.

Humerus has two main parts:

Shaft of humerus

The shaft is the long, cylindrical part of the bone.

Two ends

The ends of the humerus are the proximal end and the distal end.

Proximal end

The proximal end of the humerus has two large, rounded processes:

  • The head

It articulates with the glenoid fossa of the scapula to form the glenohumeral joint.

  • The greater tubercle.

The greater tubercle is a large, roughened area on the lateral side of the proximal end of the humerus. It serves as an attachment point for several muscles.

Distal end

The distal end of the humerus has two condyles:

  • Medial condyle
  • Lateral condyle.

The condyles are rounded, smooth areas that articulate with the ulna and radius at the elbow joint.

Clavicle

Clavicle is also known as the collarbone. It is a long, S-shaped bone that connects the scapula to the sternum. The clavicle has two ends:

Medial end

The medial end of the clavicle is attached to the manubrium of the sternum.

Lateral end

This end of the clavicle is attached to the acromion of the scapula.

Functions

The clavicle helps to stabilize the shoulder joint and to protect the brachial plexus.

Joints of shoulder complex

Glenohumeral Joint

  • The glenohumeral joint is the major joint of the shoulder complex.
  • It is a ball-and-socket joint that allows for a wide range of motion.
  • Humerus, articulates with the glenoid fossa of the scapula.
  • Humerus is held in place by the joint capsule, a thin, fibrous membrane that surrounds the joint.
  • The joint capsule is reinforced by ligaments, which are bands of tissue that connect bones to each other.

Functions

The glenohumeral joint is the most mobile joint in the body. It allows for flexion, extension, abduction, adduction, internal rotation, and external rotation of the arm. The glenohumeral joint is also responsible for overhead activities, such as throwing and reaching.

Acromioclavicular Joint

  • The acromioclavicular joint is a small joint that connects the acromion with the clavicle.
  • It is a gliding joint that allows for a small amount of movement.

Sternoclavicular Joint

  • Sternoclavicular joint connects the clavicle with the sternum.
  • It is a saddle joint that allows for a small amount of movement in all directions.

Ligament of shoulder 

Glenohumeral Ligaments

Glenohumeral ligaments provide stability to the glenohumeral joint. There are three GH ligament:

The superior glenohumeral ligament

It is the strongest of the three ligaments. It runs from the superior edge of the glenoid fossa to the anterior and inferior aspects of the humeral head.

The middle glenohumeral ligament

This ligament runs from the middle of the glenoid fossa to the anterior and inferior aspects of the humeral head.

The inferior Glenohumeral ligament

The inferior ligament runs from the inferior edge of the glenoid fossa to the anterior and inferior aspects of the humeral head.

Functions of gelnohumeral ligament

This ligaments help to prevent the humeral head from subluxating (partially dislocating) or dislocating from the glenoid fossa.

Coracohumeral Ligament

The coracohumeral ligament is a short, thick ligament that runs from the coracoid process of the scapula to the greater tubercle of the humerus.

Functions

Mainly helps to stabilize the humeral head in the glenoid fossa and to prevent the humeral head from being pulled upward by the biceps tendon.

Acromioclavicular Ligaments

The acromioclavicular ligaments connect the acromion process to the clavicle.

Functions

It acts to stabilize the acromioclavicular joint and to prevent the clavicle from being displaced upward or downward.

Muscles and Tendons of the shoulder joint

Rotator Cuff Muscles

The rotator cuff is a name given to group of four muscles that surround the shoulder joint. Abbreviations used for rotator muscles is SITS. The rotator cuff muscles are

  • supraspinatus
  • Infraspinatus
  • Teres minor
  • Subscapularis

These muscles help to stabilize the shoulder joint and to move the arm.

ROTATOR CUFF MUSCLES ORIGIN INSERTION FUNCTIONS

Supraspinatus

Location:

The supraspinatus muscle is located above the spine of the scapula.

Function:

Helps to abduct (move away from the body) the arm.

Infraspinatus

Location:

The infraspinatus muscle is located below the spine of the scapula.

Function:

It helps to externally rotate (turn outward) the arm.

Teres minor

Location:

The teres minor muscle is located below the infraspinatus muscle.

Function:

Along with the infraspinatus muscle it also helps to externally rotate the arm.

Subscapularis

Location:

The subscapularis muscle is located on the front of the scapula.

Function:

Main function of this muscle is to internally rotate (turn inward) the arm.

Deltoid

Location:

Deltoid muscle is a large muscle that covers the shoulder joint.

Function:

This muscle helps to abduct, flex, extend, and internally rotate the arm.

Biceps Tendon

The biceps tendon is a long, thick tendon that attaches the biceps muscle to the shoulder joint.

Function:

It helps to flex the elbow and to supinate (turn upward) the forearm.

deltoid, biceps, triceps muscles of shoulder joint anatomy, origin, insertion, functions nerve supply

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