Bone Land Markings of Radius

Bone Land Markings of Radius/The radius is the thicker and shorter of the two long bones in the forearm. It is located on the lateral side of the forearm parallel to the ulna (in anatomical position with arms hanging at the sides of the body, palms facing forward) between the thumb and the elbow. The radius and ulna pivot around one another to allow rotation of the wrist. Together, along with the humerus, they create the elbow joint.

The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is shorter and smaller than the radius. It is a long bone, prism-shaped and slightly curved longitudinally.

Proximal radius (head, neck, and tuberosity)

The head can be found proximally and is known as the caput radii, which articulates with the capitulum of the humerus as part of the compound joint of the elbow and is concave to look at. The radius also communicates with the head of the ulna by articulating with the ulna’s radial notch via its own circumference.
The neck is the area of the bone that narrows in between the head and the radial or bicipital tuberosity. Just below the head and neck of the radius is the radial tuberosity, which is an oval-shaped convexity upon which the biceps brachii inserts.

Radial Shaft

The shaft of the radial bone is the long, wide column of bone that is convex on its lateral side but enlarges towards the wrist. It has three borders (anterior, posterior, and interosseous) and three surfaces (anterior, posterior and lateral). There are several anatomical landmarks upon its surfaces, which allows for the origin and insertion of tendons.

Laterally we can find the attachment of two muscles:

Supinator muscle (radial head) attaches to the lateral aspect of the radius, covering a large area of it.
Pronator teres muscle also adheres to the radial shaft (below the supinator’s attachment) and inserts on the pronator tuberosity, which is a well-demarcated, rough area.

Medially, in between the invagination created by the two laterally attaching muscles, we can see the origins of another two muscles, as follows:

Flexor digitorum superficialis.
Flexor pollicis longus (just inferior to the origin of Flexor digitorum superficialis).

The larger of the two muscular attachments that cover the distal end of the shaft on its medial surface is that of pronator quadratus muscle. Slightly inferior to it on the opposite side sits the insertion of the brachioradialis muscle, which is just above the styloid process – an extrusion of the suprastyloid crest. This is a projection of the lateral aspect of the distal end of the radial bone that margins the carpal articular surface superiorly. Meanwhile, The posterior surface of the radius is the origin of two more muscles:

Abductor pollicis longus which originates just below the posterior margin of the attachment of the supinator muscle.
Extensor pollicis longus which can be found distally still.

Distal Radius

The last two landmarks of note are not, however, muscle attachments, but bony developments. The dorsal tubercle protrudes on the posterior aspect of the distal head of the radius and is seated between the grooves for the tendons of the extensor carpi radialis longus and brevis as well as the tendon of the extensor pollicis longus. The ulnar notch of the radius is a medial concavity upon the distal head of the bone which directly contacts the distal ulna at the same level.

Borders

The volar border (margo volaris; anterior border; palmar😉 – extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is prominent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the flexor digitorum superficialis muscle (also flexor digitorum sublimis) and flexor pollicis longus muscle; the surface above the line gives insertion to part of the supinator muscle.
The dorsal border (margo dorsalis; posterior border) – begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. is indistinct above and below, but well-marked in the middle third of the bone.
The interosseous border (internal border; crista interosseous; interosseous crest;) – begins above, at the back part of the tuberosity, and its upper part is rounded and indistinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch.

Surfaces

This end of the bone has three non-articular surfaces – volar, dorsal, and lateral.

The volar surface – rough and irregular, affords attachment to the volar radiocarpal ligament.
The dorsal surface – is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side:
- The first groove is broad, but shallow, and subdivided into two by a slight ridge – the lateral of these two, transmits the tendon of the extensor carpi radialis longus muscle; the medial, the tendon of the extensor carpi radialis brevis muscle.
- The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward and transmits the tendon of the extensor pollicis longus muscle.
- The third is broad, for the passage of the tendons of the extensor indicis proprius and extensor digitorum communis.
The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the brachioradialis, and by its apex to the radial collateral ligament of wrist joint. The lateral surface of this process is marked by a flat groove, for the tendons of the abductor pollicis longus muscle and extensor pollicis Brevis muscle.

Muscle Attachment of Radius

Muscles Of Anterior Compartment Of Arm (Flexors Of Arm)

Biceps brachii

Function: Major flexion of forearm, supination of the forearm, resists dislocation of the shoulder
Origin: Short head originates from the coracoid process. The long head is from the supraglenoid tubercle of the scapula
Insertion: Radial tuberosity and forearm fascia (as bicipital aponeurosis)
Innervation: Musculocutaneous nerve (C5, C6)

Brachialis

Function: Flexion of forearm
Origin: Distal anterior humerus
Insertion: Coronoid process and ulnar tuberosity
Innervation: musculocutaneous nerve (C5, C6, C7 small contribution)

Coracobrachialis

Function: Flexion and adduction of the arm
Origin: Coracoid process
Insertion: Middle of the humerus, on its medial aspect
Innervation: Musculocutaneous nerve (C5, C6, C7)

Muscles Of Posterior Compartment Of Arm (Extensors Of Arm)

Triceps brachii

Function: Major extensor of the forearm, resists dislocation of the shoulder
Origin: Lateral head: above the radial groove, medial head: below the radial groove, long head: infraglenoid tubercle of the scapula
Insertion: Olecranon process of ulna and forearm fascia
Innervation: Radial nerve (C6,C7,C8)

Anconeus

Function: Extension of the forearm, stabilization of elbow joint
Origin: Lateral epicondyle of humerus
Insertion: Olecranon process and posterior ulna
Innervation: Radial nerve (C7, C8, T1)

Muscles Of Anterior Compartment Of Forearm (Flexors Of Forearm)

Superficial layer

Pronator teres

Function: Pronation of radio-ulnar joint
Origin: Coronoid process and medial epicondyle of humerus
Insertion: Lateral surface of the radius
Innervation: Median nerve (C6, C7)

Flexor carpi radialis

Function: Flexion and adduction at the wrist
Origin: Medial epicondyle of humerus
Insertion: Base of the second metacarpal
Innervation: Median nerve (C6, C7)

Palmaris longus

Function: Flexion at the wrist, tensing of the palmar aponeurosis
Origin: Medial epicondyle of humerus
Insertion: Flexor retinaculum
Innervation: Median nerve (C7, C8)

Flexor carpi ulnaris

Function: Flexion and adduction at the wrist
Origin: Medial epicondyle of humerus and olecranon
Insertion: Pisiform, the hook of hamate and fifth metacarpal
Innervation: Median nerve (C7, C8)

Intermediate Layer

Flexor digitorum superficialis

Function: Flexion of the proximal interphalangeal joint of the second, third, fourth, and fifth fingers. Also has a weaker flexion action on the metacarpophalangeal joints of the same fingers
Origin: Medial epicondyle, coronoid process, and anterior radius
Insertion: Second, third, fourth, and fifth middle phalanges
Innervation: Median nerve (C7, C8, T1)

Deep Layer

Flexor digitorum profundus

Function: Flexion of the distal interphalangeal joint of the second, third, fourth, and fifth finger
Origin: Medial and the anterior surface of the proximal ulna and interosseous membrane
Insertion: Second, third, fourth, and fifth distal phalanges
Innervation: Ulnar nerve (C8, T1) for the medial part, anterior interosseous nerve (C8, T1) for the lateral

Flexor pollicis longus

Function: Flexion of the interphalangeal joint of the thumb
Origin: Anterior aspect of radius as well as interosseous membrane
Insertion: Base of distal phalanx of thumb
Innervation: Anterior interosseous nerve (C7, C8)

Pronator quadratus

Function: Pronator of the forearm
Origin: Anterior aspect of distal ulna
Insertion: Anterior aspect of the distal radius
Innervation: Anterior interosseous nerve (C7, C8)

Brachioradialis

Function: Weak flexor of the forearm
Origin: Proximal supracondylar ridge on the humerus
Insertion: Lateral surface of the distal end of radius
Innervation: Radial nerve (C5, C6, C7)

Muscles Of Posterior Compartment Of Forearm

Superficial

Extensor carpi radialis longus

Function: Extension and abduction of the wrist
Origin: Proximal supracondylar ridge on the humerus
Insertion: Dorsal base of the second metacarpal
Innervation: Radial nerve (C6, C7)

Extensor carpi radialis brevis

Function: Extension and abduction of the wrist
Origin: Lateral epicondyle of humerus
Insertion: Dorsal base of the third metacarpal
Innervation: Deep branch of the radial nerve (C7, C8)

Extensor digitorum

Function: Extension of the proximal interphalangeal joint of the second, third, fourth, and fifth fingers. Also has a weaker extension action on the metacarpophalangeal joints of the same fingers
Origin: Lateral epicondyle of humerus
Insertion: Extensor expansions on the dorsal aspect of second, third, fourth, and fifth middle and distal phalanges
Innervation: Posterior interosseous nerve (C7, C8)

Extensor digiti minimi

Function: Extension of the little finger at the metacarpophalangeal joint and interphalangeal joint
Origin: Lateral epicondyle of humerus
Insertion: Extensor expansion on the dorsal aspect of the fifth phalanx
Innervation: Posterior interosseous nerve (C7, C8)

Extensor carpi ulnaris

Function: Extension and adduction of the wrist
Origin: Lateral epicondyle of the humerus and posterior ulna
Insertion: Fifth metacarpal base
Innervation: Posterior interosseous nerve (C7, C8)

Deep Layer

Extensor indices

Function: Extension of the index finger
Origin: Dorsal surface of the distal ulna and interosseous membrane
Insertion: Extensor expansion of the second finger
Innervation: Posterior interosseous nerve (C7, C8)

Supinator

Function: Supination of the forearm
Origin: Lateral epicondyle and supinator crest of the ulna
Insertion: Lateral surface of radius
Innervation: Deep branch of the radial nerve (C7, C8)

Abductor policies longus

Function: Abduction of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
Origin: Dorsal aspects of the proximal radius, ulna, and interosseous membrane
Insertion: Base of the first metacarpal
Innervation: Posterior interosseous nerve (C7, C8)

Extensor pollicus longus

Function: Extension of the thumb by acting on the carpometacarpal joint, the metacarpophalangeal joint, and the interphalangeal joint.
Origin: Dorsal aspects of the middle ulna and interosseous membrane
Insertion: Distal phalanx of 1st finger
Innervation: Posterior interosseous nerve (C7, C8)

Extensor pollicus brevis

Function: Extension of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
Origin: Dorsal aspects of middle radius and interosseous membrane
Insertion: Distal phalanx of 1st finger
innervation: Posterior interosseous nerve (C7, C8)

References

[bg_collapse view=”button-orange” color=”#4a4949″ expand_text=”Show More” collapse_text=”Show Less” ]

[/bg_collapse]