Comprehensive Overview of Humerus Anatomy, Ossification, and Clinical Implications

HUMERUS

The arm's bone is called the humerus. It is the upper limb's longest bone. It has a shaft, a lower flattened end, and an upper rounded end.

Determination of the Side

1. The head is formed by rounding the top end. The bottom end is enlarged in both directions and backwards and flattened from before.
2. The head is turned back, upward, and medially.
3. The intertubercular sulcus, also known as the bicipital groove, limits the smaller tubercle's lateral growth as it extends from the front of the top end.

Features

Upper End

1. The head is turned upward, rearward, and medially. It forms the shoulder joint by articulating with the scapula's glenoid cavity. The head is significantly bigger than the glenoid cavity, making up around one-third of a sphere.
2. The term "anatomical neck" refers to the boundary that divides the head from the remainder of the upper body.
3. An elevation on the anterior face of the upper end is known as the smaller tubercle, or Latin lump.
4. The lateral portion of the higher end is formed by an elevation called the larger tubercle. There are three impressions that identify its upper and posterior aspects: upper, middle, and lower.
   
5. The lesser tubercle medially and the anterior portion of the bigger tubercle are divided by the intertubercular sulcus, also known as the bicipital groove. The smaller and greater tubercles are represented by the medial and lateral lips of the sulcus, which are downward prolongations of them.
6. The surgical neck is the thin region that divides the humerus's shaft from its upper end.
7. The surgical neck is 11.5 cm above the morphological neck. It displays the epiphyseal line's location.

Shaft

The shaft has a triangular lower half and a rounded upper half. It features three surfaces as well as three boundaries.

Limitations

1. The lateral lip of the intertubercular sulcus is formed by the upper third of the anterior border. It forms the front edge of the deltoid tuberosity in its middle section. The front border's lower portion is rounded and smooth.
2. Only at the lower end, where it creates the lateral supracondylar ridge, is the lateral boundary noticeable. It is hardly noticeable in the upper region all the way to the larger tubercle's posterior surface. It is broken up in the middle by the spiral or radial groove.
3. The medial lip of the intertubercular sulcus is formed by the upper portion of the medial border. It has an uneven strip across its midsection. It and the medial supracondylar ridge are connected below.

Surfaces

1. The anterior and lateral margins define the anterolateral surface. The deltoid covers the upper portion of this surface. It is distinguished by a V-shaped deltoid (Greek triangular-shaped) tuberosity just above the middle. The radial groove traverses the surface back and forth behind the deltoid tuberosity.
2. Between the anterior and medial boundaries is the anteromedial surface. The narrow upper portion of it forms the intertubercular sulcus floor. Below its center section, close to the medial border, is a nutrient foramen.
3. The lateral and medial margins define the posterior surface. Its upper portion is identified by an angled ridge. The radial groove crosses the center one-third.

Lower end

The lower end of the humerus forms the condyle which is stretched from side-to-side, and has articular and non-articular components. The following are included in the articular portion.

• A rounded projection that articulates with the head of the radius is called the capitulum, or small head in Latin.
• This pulley-shaped surface is called a trochlea (Greek pulley). It articulates with the ulna's trochlear notch. The carrying angle is formed when the trochlea's medial edge protrudes 6 mm farther downward than its lateral edge.

The following are included in the non-articular portion.

1. On the medial side of the lower end, the medial epicondyle is a noticeable bony projection. It is subcutaneous and readily palpable on the elbow's medial side.
2. Compared to the medial epicondyle, the lateral epicondyle is smaller. There is a muscular imprint on its anterolateral portion.
3. The term "lateral supracondylar ridge" refers to the acute lateral border directly above the lower end.
4. On the medial side, a comparable ridge is the medial supracondylar ridge.
5. The anterior aspect of the trochlea is somewhat above the coronoid fossa, a depression. As the elbow is flexed, it makes room for the ulna's coronoid process.
6. Directly above the anterior part of the capitulum is a dip called the radial fossa. When the elbow is flexed, it makes room for the radius head.
7. Directly above the posterior part of the trochlea is the olecranon fossa, also known as the Greek ulna head. When the elbow is extended, it takes up the ulna's olecranon process.

Attachments

1. The smaller tubercle is penetrated by the multipennate subscapularis.
2. The supraspinatus is placed into the larger tubercle's topmost imprint.
3. The bigger tubercle's center impression is where the infraspinatus is placed.
4. The bigger tubercle's lower imprint is used to place the teres minor.
5. The lateral lip of the intertubercular sulcus receives the insertion of the pectoralis major. A bilaminar insertion is made.
6. The intertubercular sulcus floor is where the latissimus dorsi is placed.
7. The intertubercular sulcus' medial lip receives the insertion of the teres major.
8. The tendon of the long head of the biceps brachii and its synovial sheath are the contents of the intertubercular sulcus. b. The anterior circumflex humeral artery's ascending branch.
9. The deltoid is placed inside the tuberosity of the deltoid.
10. In the center of the medial border, the coracobrachialis is inserted into the rough area.
11. The lower half of the shaft's anteromedial and anterolateral surfaces give rise to the brachialis. A portion of the region touches the back side.
12. The upper two-thirds of the lateral supracondylar ridge give rise to the brachioradialis.
13. The lower portion of the lateral supracondylar ridge is where the extensor carpi radialis longus originates.
14. The lower third of the medial supracondylar ridge gives birth to the pronator teres, or humeral head.
15. The anterior aspect of the medial epicondyle serves as the common ancestor of the forearm's superficial flexor muscles. We refer to this as the common flexor origin.
16. The lateral epicondyle is the common ancestor of the forearm and supinator superficial extensor muscles. We refer to this as the common extensor origin.
17. The posterior surface of the lateral epicondyle gives rise to the anconeus, or Greek elbow.
18. The triceps brachii's medial head emerges from the posterior surface beneath the radial groove, whereas its lateral head originates from an oblique ridge on the top portion of the posterior surface above the groove.
19. The shoulder joint's capsular ligament is attached to the anatomical neck, with the exception of the medial side, where a little portion of the shaft inside the joint cavity is included when the line of attachment dips down by about two millimeters. The tendon of the long head of the biceps brachii exits the joint cavity through an aperture created by the interruption of the line at the intertubercular sulcus.
20. The olecranon fossa and the radial and coronoid fossae reside within the joint cavity, and the capsular ligament of the elbow joint is joined to the lower end along a line that reaches these fossae's upper limits. The trochlea and medial epicondyle are separated medially by the line of attachment. It travels between the capitulum and the lateral epicondyle on the lateral side.
21. The axillary nerve at the surgical neck, the radial nerve at the radial groove, and the ulnar nerve at the medial epicondyle are three nerves that are directly related to the humerus and may be injured as a result.

OSSIFICATION

One primary center and seven subordinate centers form the ossification of the humerus. During the eighth week of development, the major center emerges in the center of the diaphysis. The head (first year), the bigger tubercle (second year), and the lesser tubercle (fifth year) are the three secondary centers from which the upper end ossifies. In the sixth year, the three centers unite to form a single compound epiphysis, which unites with the shaft in the twentieth year. At the level of the head's lowest border, the epiphyseal line encircles the bone. This is the bone's developing end. (Remember that the growing end is always the direction in which the nutrient foramen is directed.) the final ossities from two epiphyses and four centers. The centers are located in the first year of the trochlea's capitulum and lateral flange, the ninth year of the trochlea's medial flange, and the twelfth year of the lateral epicondyle. After all three combine to produce a new compound epiphysis in the fourteenth year, the shaft and the epiphysis unite at about years. The medial epicondyle center originates during the first four to six years of life, separates into an epiphysis, and unites with the shaft in the twentieth year.

MEDICAL ANATOMY

A humerus fracture frequently occurs in the surgical neck, shaft, and supracondylar area. Young people frequently sustain supracondylar fractures, which are caused by falls onto the outstretched hand. When the elbow joint dislocates, the lower fragment is primarily moved backwards and the elbow becomes excessively prominent. The median nerve may be harmed by this fracture. It could also result in brachial artery blockage, which would produce Volkmann's ischemic contracture. When the elbow is flexed, the three bony points of the typical elbow create the equilateral triangle, and when the elbow is extended, they form a single line.