Session 2a - Bones And Joints Of The Forearm

Question 1

What are the bones of the forearm?

Answer 1

The radius and ulna are the two bones of the forearm. In life, they are connected by an interosseous membrane

Question 2

What do the radius and ulna articulate with?

Answer 2

They articulate at their proximal ends with the distal humerus to form the elbow joint: the trochlea notch of the ulna articulates with the trochlea of the humerus and the radial head articulates with the capitellum of the humerus.

Question 3

What movements occur at the elbow joint?

Answer 3

Flexion and extension occur at the elbow joint.

Question 4

Where do radius and ulna articulate with each other?

Answer 4

The radius and ulna also articulate with each other at the proximal and distal radioulnar joints. These joints allow pronation and supination of the forearm and hand. The radius pivots around the ulna. These movements are achieved by muscles in the anterior arm, and the anterior and posterior forearm.

Question 5

What does the radius articulate with distally?

Answer 5

Distally, the radius articulates with two of the small bones of the wrist (the carpal bones) to form the radiocarpal joint. The radiocarpal joint is referred to as the wrist joint. Flexion, extension, abduction and adduction occur at the wrist joint. These movements are achieved by muscles in the anterior and posterior forearm.

Question 6

What does the proximal ulna form?

Answer 6

Posteriorly, the proximal ulna forms a bulky process known as the olecranon. This can be easily palpated in all individuals. The olecranon fits into the olecranon fossa on the posterior distal humerus to allow full extension.

Question 7

Where is the coronoid process? What does it do?

Answer 7

The ulna has a process that protrudes anteriorly near its proximal end called the coronoid process. The coronoid process fits into the coronoid fossa of the anterior distal humerus when we flex our elbow fully.

Question 8

Where is the radial tuberosity?

Answer 8

The radius has a roughened lump near it proximal end, but distal to the head and neck, known as the radial tuberosity. This is where the biceps brachii tendon inserts onto the radius. Distally, both the radius and ulna have a styloid process. These are distal protrusions of the radius and ulna that are often implicated in fractures in this region.

Question 9

What is the elbow joint?

Answer 9

This synovial hinge joint is formed by articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitellum of the humerus and the radial head. The trochlear notch of the ulna forms a deep recess and the trochlear of the humerus fits into it very well, providing a very stable joint. The coronoid process (distally) and the olecranon (proximally) of the ulna ‘pinch’ the trochlea of the humerus to help maintain stability. The joint capsule is reinforced by medial (ulnar) and lateral (radial) collateral ligaments.

Question 10

What are the radioulnar joints?

Answer 10

These joints are a pair of synovial, pivot-type joints between the radius and ulna. The radius rotates around the ulna when the forearm is pronated and supinated. The annular ligament of the radius, which wraps around the radial neck, is attached to the ulna and holds the radial head in place. The radial head rotates within it to produce pronation and supination.

Question 11

What is the carpus joint and radiocarpal joint (wrist)?

Answer 11

The carpus is comprised of eight small bones that articulate with each other at small joints. The bones are roughly arranged into two rows of four bones. The distal radius articulates with two of the bones in the proximal row – the scaphoid and lunate – to form the radiocarpal joint.

Question 12

What are the proximal row of carpal bones?

Answer 12

The proximal row of carpal bones comprises, from lateral to medial: the scaphoid, lunate, triquetrum and the pisiform. The pisiform is not a true carpal bone, but rather is a small bone that develops in the tendon of flexor carpi ulnaris.

Question 13

What do the carpal bone names mean?

Answer 13

‘Scaphoid’ is derived from Greek meaning ‘boat-shaped’, lunate means ‘moon-shaped’ in Latin, triquetrum means ‘three-cornered’ and pisiform means ‘pea-shaped’.

Question 14

What is the distal row of carpal bones comprised of?

Answer 14

The distal row of carpal bones comprises, form lateral to medial: the trapezium (base of the thumb), trapezoid, capitate (located centrally and is the largest carpal bone) and the hamate. The hamate bears a bony process anteriorly (the hook), which is obvious when you view the bone on a skeleton and is palpable on examination.

Question 15

What do the names of distal row of carpal bones mean?

Answer 15

o The names of trapezium and trapezoid are references to their shapes. ‘Capitate’ is derived from the Latin for ‘head’, and ‘hamate’ is derived from the Latin for ‘hook’ based on it hook-like process.

Question 16

What type of joint is the wrist?

Answer 16

The radiocarpal joint (wrist joint) is a condyloid synovial joint formed by the articulation of the distal radius with the scaphoid and lunate. It is surrounded by a joint capsule which is reinforced by ligaments. It allows flexion, extension, ulnar deviation (adduction) and a small amount of radial deviation (abduction).

The intercarpal joints between the carpal bones are synovial joints, which are also reinforced by ligaments, but they do not allow much movement.

Question 17

What is the hand composed of?

Answer 17

The hand is composed of many small bones and joints.
• The metacarpals are located distal to the carpus.
• The bones of the digits are phalanges; there are three phalanges in each finger and two phalanges in the thumb.

Question 18

What is the cubital fossa?

Answer 18

The cubital fossa is the region anterior to the elbow joint. In clinical practice it is often referred to as the antecubital fossa and abbreviated in medical notes to ‘ACF’.

Question 19

What are the borders of the ACF?

Answer 19

The cubital fossa is a triangular-shaped region with three borders:
• the lateral border is formed by brachioradialis, a posterior forearm muscle.
• the medial border is formed by pronator teres, an anterior forearm muscle.
• the superior border (or base) is formed by an imaginary line drawn between the medial and lateral epicondyles of the humerus.
• The apex is most distal, ‘pointing’ towards the forearm and hand.

Question 20

What are the contents of the cubital fossa?

Answer 20

• The tendon of biceps brachii can be traced into the cubital fossa as it travels to its insertion point on the radial tuberosity. The tendon is easily palpated with the elbow flexed.
• The bicipital aponeurosis is a fascial extension of the biceps tendon. It is continuous with the fascia on the surface of the anterior forearm muscles, and it separates the superficial veins from deeper structures in the fossa: the brachial artery and the median nerve.
• The brachial artery is medial to the biceps tendon, and it can be palpated here. The brachial artery bifurcates into its terminal branches – the radial and ulnar arteries – deep in the cubital fossa. Great care must be taken during venepuncture and cannulation to avoid puncturing the brachial artery. Deep veins accompany the arteries.
• The median nerve is medial to the brachial artery. The median nerve does not innervate any muscles in the arm, but travels through the anterior compartment of the arm and the cubital fossa on its journey to the anterior forearm and hand.
• The radial nerve also passes through the lateral aspect of the cubital fossa. It is deep to brachioradialis here.

Question 21

What is the venous drainage of the ACF?

Answer 21

The superficial veins that are located in the subcutaneous tissue over the cubital fossa include the cephalic, basilic and median cubital veins. They are of clinical importance as they are commonly accessed for venepuncture (taking blood) and intravenous access (i.e. placing a cannula for administering fluids or drugs). It is important to understand the anatomy of this region to perform these procedures safely – the median nerve and brachial artery must not be mistakenly punctured or cannulated.

Question 22

What is the venous drainage of the ACF?

Answer 22

The superficial veins that are located in the subcutaneous tissue over the cubital fossa include the cephalic, basilic and median cubital veins. They are of clinical importance as they are commonly accessed for venepuncture (taking blood) and intravenous access (i.e. placing a cannula for administering fluids or drugs). It is important to understand the anatomy of this region to perform these procedures safely – the median nerve and brachial artery must not be mistakenly punctured or cannulated.

Question 23

What must you remember about the veins in the ACF?

Answer 23

Although the anatomy of the superficial veins in the region of the forearm and cubital fossa is represented similarly across anatomy images, the arrangement of these veins is highly variable between individuals.

Question 24

What is a radial head subluxation? (Pulled elbow)

Answer 24

This is seen in young children and is often caused by the child being pulled upwards by their arm. The annular ligament is partially torn, and the radial head moves distally out of the ligament (subluxation). It is painful and when assessing children in whom you suspect this injury, you may only notice that are not using the affected limb. The subluxed head can be reduced with relative ease using a simple manoeuvre.

Question 25

What is a scaphoid fracture?

Answer 25

The scaphoid forms from two bones, each with its own blood supply, that fuse together. With fusion, the artery to the proximal end degenerates, and the bone is supplied from its distal end. When the scaphoid fractures, the proximal part of the bone may be disconnected from the blood supply and death of the proximal segment results – this is called avascular necrosis.

Avascular necrosis is a serious problem because the proximal scaphoid articulates with the distal radius at the wrist joint. For this reason, fractures must not be missed. However, scaphoid fractures are not always evident on X-rays taken soon after the fracture has occurred. If a fracture is suspected but not seen on X-ray, patients are still followed-up.

Question 26

What is a fracture of the distal radius?

Answer 26

A fracture of the distal radius is very common in older people, especially females (in whom osteoporosis is more common). It is usually caused by a Fall Onto an OutStretched Hand (FOOSH). Simple distal radius fractures can be manipulated into an acceptable position for healing in the emergency department, but more complex fractures may require surgery.