Arm Bone diagram: Radius, Proximal, Function, Humerus

The humerus, ulna, and radius are the three bones that make up an arm.The arm of the human body is a critical portion that permits movement along the shoulder, elbow,helpful wrist and fingers for day-to-day activities.

Humerus

• The humerus, which resembles the femur bone found in the legs, is the longest bone in the human arm.

• From the shoulder to the elbow, it is extended.

• The body, the lower extremities, and the upper extremity make up its three main components.

• The upper extremity features a slender neck, a hemispherical head, and two processes that extend from it.It moves across the shoulder by articulating with the scapula (shoulder bone).

• Overall cylindrical in shape, the body's bottom has a prism-like appearance.

• The elbow joint is made up of two depressions or fossae, two smooth articular surfaces (trochlea and capitulum), and two projections (epicondyles) on the lower extremity.

• The radius and ulna, respectively, and the capitulum and trochlea articulate.

• The ulna bone projects into the two depressions of the fossae.

• The forearm and finger muscles join to the bones at the epicondyles, which are found on either side of the bones.

Proximal Landmarks

The head, anatomical neck, surgical neck, greater and lesser tuberosity, and intertubercular sulcus are the distinguishing features of the proximal humerus.

The head is located at the top of the humerus. The anatomical neck divides this from the bigger and lesser tuberosities, and it faces medially, upward, and backward.

The larger tuberosity has an anterior and a posterior surface and is situated laterally on the humerus. Three of the rotator cuff muscles, the supraspinatus, infraspinatus, and teres minor, attach to the superior, middle, and inferior aspects of the greater tuberosity, respectively.

The lesser tuberosity is situated further medially on the bone and is significantly smaller. Only the anterior surface is present. Here is where the subscapularis, the last rotator cuff muscle, attaches.

The intertubercular sulcus, a deep groove, divides the two tuberosities. In this groove, the tendon of the long head of the biceps brachii emerges from the shoulder joint.

Lips are the designation for the intertubercular sulcus' margins. The lips of the intertubercular sulcus are inserted by the pectoralis major, teres major, and latissimus dorsi muscles. The phrase "a woman between two majors" can help you recall this since the latissimus dorsi attaches between the pectoralis major laterally and the teres major on the medial lip.

The surgical neck runs from the tuberosities immediately distal to the humeral shaft. Here, the circumflex humeral arteries and the axillary nerve rest against the bone.

Shaft

Several muscles attach to the humerus' shaft at this location. It is seen to be round proximally and flattened distally in cross section views.

On the lateral side of the humeral shaft is a roughened area where the deltoid muscle attaches. The deltoid tuberosity is the name given to this.

The radial (or spiral) groove is a small depression that extends parallel to the deltoid tuberosity down the posterior surface of the humerus. In this groove are the profunda brachii artery and radial nerve. Along the humerus' shaft, the following muscles are connected to it:

Coracobrachialis, deltoid, brachialis, and brachioradialis are located anteriorly.

Lateral and medial heads of the triceps are located in the back (the spiral groove demarcates their respective origins).

Distal Region

The lateral and medial margins of the distal humerus form medial and lateral supraepicondylar ridges. The lateral supraepicondylar ridge is more roughened, indicating the region of common origin of the forearm extensor muscles.

The lateral and medial epicondyles are extracapsular bone projections that are immediately distal to the supraepicondylar ridges. At the elbow, both can be felt. The medial is the largest and farther-reaching of the two. It is possible to feel the ulnar nerve as it passes through a groove on the medial epicondyle's backside.

The trochlea is situated medially and reaches onto the back of the bone distally. The capitulum, which articulates with the radius, is located lateral to the trochlea.

Three depressions called the coronoid, radial, and olecranon fossae are also seen on the distal part of the humerus. When the elbow is flexed or extended, they allow room for the forearm bones.

Articulations

The glenohumeral joint is created when the proximal area of the humerus articulates with the glenoid fossa of the scapula (shoulder joint).

Distally, at the elbow joint, the trochlea of the humerus articulates with the trochlear notch of the ulna and the capitulum of the humerus with the head of the radius.

Body Features

The humerus's body has three surfaces and three edges.

Borders

1. Anterior

2. Lateral

3. Medial

Surfaces

1. Antero-lateral

2. Antero-medial

3. Posterior

Function

The upper limb's function depends on 13 muscles that are attached to the humerus and which help move the hand, elbow, and other upper limb-related joints.

Radius

The radius is the name of the lateral forearm bone.It is a long bone with a proximal end, shaft, and distal end as its main structural components. The distal end articulates with the carpal bones at the wrist and the head of the ulna, while the proximal end's head articulates with both the distal humerus and the proximal ulna. The interosseous membrane, a thick connective tissue, holds the shaft (body) securely to the ulna.

Proximal radius

The head, neck, and radial tuberosity are carried by the proximal end of the radius. The complex elbow joint is made up of the capitulum of the humerus and the concave superior surface on the disc-shaped head of the radius. The proximal radioulnar joint is created by positioning the radial head's periphery, also known as the articular circumference of the head of the radius, inside the radial notch of the ulna and wrapping it in the annular ligament.

The neck is formed by the thin section of the radius that is distal to the head. The biceps brachii muscle attaches onto the medially directed, oval-shaped radial (bicipital) tuberosity that is located just below the neck

Radial shaft

The shaft of the radius is a lengthy segment of bone that continues distally from the neck and radial tuberosity. It is thin proximally but enlarges towards the wrist, when it broadens to create the distal end of radius. The radial shaft has a modest lateral curve and is triangular in cross-section for much of its length.Anterior, posterior, and interosseous boundaries make up its three borders.

On the medial side of the bone, the anterior boundary is located. It begins immediately distal to the radial tuberosity and passes diagonally to the side of the shaft. The middle of the shaft is where the posterior boundary is most noticeable as it is located on the posterior face of the radius. The acute interosseous boundary faces the ulna medially. The middle radioulnar joint is created when this border connects to the ulna's interosseous border via the fibrous interosseous membrane.

An anterior, posterior, and lateral surface are also present on the radial shaft. While its rear surface is located between the interosseous and posterior borders, its anterior surface is located between the anterior and interosseous borders. The anterior and posterior borders are separated by the lateral surface, which is slightly convex.

Distal radius

The radius's shaft enlarges to create a wide, rectangular distal end with a four-sided cross-section that extends beyond the ulna's distal end.

The distal radius's front surface is smooth, concave, and anteriorly angled. The distal radioulnar joint is formed by the ulnar notch, a concavity on the medial surface that receives the head of the ulna. On the other hand, the lateral surface of the distal radius is rough and extends inferiorly as the radial styloid process.

Two facets on the inferior surface, also known as the carpal articular surface, are in contact with the scaphoid and lunate carpal bones. The dorsal tubercle (also known as Lister's tubercle), a large bony projection on the distal radius's posterior surface, is located between the grooves that transmit the tendons of the forearm muscles.

Ulna

The longer of the two parallel forearm bones, the ulna is the medial bone of the forearm. Similar to the radius, the ulna is composed of a proximal end, a shaft, and a distal end. The distal humerus and the head of the radius are articulated with the proximal end. On the other hand, the distal end has a head that joins with the distal radius. The shaft (body) of the ulna and the shaft of the radius are connected by the interosseous membrane.

Proximal ulna

The distal humerus and the head of the radius interact with the proximal ulna, a huge hook-shaped bone. It has the ulnar tuberosity, sublime tubercle, radial notch, coronoid process, olecranon, and trochlear notch.

The triceps brachii muscle inserts at the olecranon, a conspicuous, proximal projection from the posterior portion of the proximal ulna. When the elbow joint extends, its uppermost section bends anteriorly like a beak and fits into the olecranon fossa of the distal humerus to prevent hyperextension. The c-shaped trochlear notch is formed by the concave anterior surface of the olecranon. Similar to the jaws of a wrench, this notch is covered in articular cartilage and articulates with the trochlea of the distal humerus to form a hinge that allows flexion and extension movements at the elbow.

The coronoid process, which is accommodated by the coronoid fossa on the anterior face of the distal humerus during flexion, projects anteriorly as the lower lip of the trochlear notch. The sublime tubercle, a little tubercle on the proximal part of the medial border of the coronoid process, is where the anterior band of the ulnar collateral ligament attaches. The proximal ulna carries the ulnar tuberosity, where the brachialis muscle inserts, just distal to the coronoid process.

The shallow, rounded depression known as the radial notch is located directly distal to the trochlear notch on the lateral surface of the proximal ulna. The proximal radioulnar joint is created when the radial notch articulates with the radial head's circumference.

Ulnar shaft

The ulna's shaft is wider near its proximal end and narrows distally as it approaches its head. The ulnar shaft has three boundaries and, like the radius, has a triangle cross-section for the majority of its length (anterior, posterior and interosseous).

The front border is smooth and rounded. It starts immediately medially to the ulna's tuberosity and descends along the anteromedial shaft. The anterior border terminates distally on the posterior side of the shaft, not far from the styloid process' base. The entire length of the forearm can be palpated subcutaneously to feel the posterior boundary, which extends from the styloid process to the posterior aspect of the olecranon. The medially protruding interosseous border of the ulna, which joins the ulna to the radius, is pointed, similar to the radial shaft, and acts as a place of attachment for the fibrous interosseous membrane.

The anterior, posterior, and medial surfaces of the ulnar shaft are all present. With the exception of slight roughening at its distal end, which indicates where the pronator quadratus muscle is attached, the anterior surface, which is located between the interosseous and anterior borders, is essentially smooth. The posterior surface of the ulnar shaft is the area between the interosseous and posterior borders. This surface has linear marks that show the many places where muscles attach. Between the anterior and posterior boundaries of the ulnar shaft, the medial surface is smooth and transversely convex.

Distal ulna

A tiny, rounded head and an ulnar styloid process make up the distal ulna. The distal radioulnar joint is formed by the lateral convex articular surface of the head of the ulna and the ulnar notch of the distal radius. The triangular fibrocartilage (TFC), an articular disc that separates the head of the ulna from the carpal bones, articulates with the inferior surface of the ulna. As a result, the head of the ulna has no direct role in the development of the wrist joint. The dorsomedial portion of the wrist can feel the short, rounded ulnar styloid process, which extends distally from the posteromedial aspect of the distal ulna.