Anterior and Posterior Arm

Question 1

What are the two heads of biceps brachii? Give the origins, insertions and action.

Answer 1

The long head originates from the supraglenoid tubercle of the scapula.

The short head originates from the coracoid process of the scapula.

The tendon of the long head passes through the shoulder joint and intertubecular groove of the humerus to meet the short head. At the level of the humeral shaft, the two heads combine to form the muscle belly.

Distally, the biceps attaches to the radial tuberosity.

The main action of the biceps brachii is supination of the forearm. It also flexes the arm at the elbow and at the shoulder.

Question 2

Give the origins, insertion and action of corachobrachialis

Answer 2

The coracobrachialis muscle lies deep to the biceps brachii in the arm.

It originates from the coracoid process of the scapula. The muscle passes through the axilla, and attaches the medial side of the humeral shaft, at the level of the deltoid tubercle.

The coracobrachialis is a flexor of the arm at the shoulder

Question 3

Give the origins, insertion and action of the brachialis muscle

Answer 3

The brachialis muscle lies deep to the biceps brachii, and is found more distally than the other muscles of the arm. It forms the base of the cubital fossa.

It originates from the medial and lateral surfaces of the humeral shaft, and inserts into the tuberosity of ulna just distal to the elbow joint.

The brachialis muscle is the main flexor at the elbow.

Question 4

How are the biceps, brachialis and coracobrachialis muscles innervated?

Answer 4

Muscolocutaneous Nerve. However, note that a small lateral portion of the brachialis muscle is innervated by the radial nerve.

Question 5

Give the origins and insertions of the three heads of Triceps Brachii. Also, what is the innervation and action?

Answer 5

The medial head of the triceps lies deeper than the other two, which cover it. The medial head is therefore not visible unless the other two heads are dissected away.

The three heads:

Long head – Originates from the infraglenoid tubercle

Lateral head – Originates from the humerus, superior to the radial grove

Medial head – Originates from the humerus, inferior to the radial groove.

The three heads combine to make one muscle, they converge to a tendon, which then attach to the olecranon of the ulna.

The triceps brachii performs extension of the arm at the elbow.

It is innervated by the radial nerve (C6, C7, C8, mainly C7). A tap on the triceps tendon tests spinal segment C7.

Question 6

Describe the articulations of the humerus

Answer 6

The proximal region articulates with the scapula and clavicle, forming part of the shoulder joint. Distally, the humerus articulates with the forearm bones (radius and ulna), to form the elbow joint.

Question 7

Describe important anatomical features of the proximal head of the humerus

Answer 7

The important anatomical features of the proximal humerus are the head, anatomical neck, surgical neck, greater and lesser tubercles and intertubercular sulcus. A tubercle is a round nodule, and signifies an attachment site of a muscle or ligament.

Separating the two tubercles is a deep depression, called the intertubercular sulcus, or groove. The tendon of the long head of biceps brachii runs through this groove. The edges of the intertubecular sulcus are known as lips.

The surgical neck runs from the tubercles to the shaft of the humerus.

Question 8

Describe important anatomical features of the distal end of the humerus

Answer 8

The lateral and medial borders of the humerus form medial and lateral supraepicondylar ridges. The lateral supraepidcondylar ridge is more roughened, as it is the site of attachment for many of the extensor muscles in the posterior forearm.

Immediately distal to the supraepicondylar ridges are the lateraland medial epicondyles –projections of bone. Both can be palpated at the elbow (the medial more so, as it is much larger). The ulnar nerve passes into the forearm along the posterior side of the medial epicondyle, and can also be palpated there.

The trochlea articulates with the ulna. It is located medially, and extends onto the posterior of the bone. Lateral to the trochlear is thecapitulum, which articulates with the radius.

Also found on the distal portion of the humerus are three depressions, known as the coronoid, radial and olecrannon fossae. They accommodate the forearm bones during movement at the elbow.

Question 9

Describe important anatomical features of the humerus shaft

Answer 9

On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.

The radial groove is shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery lie in this groove.

Question 10

Explain the clinical relevance of humerus shaft fractures in different positions

Answer 10

Surgical Neck Fracture:

• this occurs by a direct blow to the area, or by falling on an outstretched hand.
• the key structures of concern is this scenario are the axillary nerve and posterior circumflex artery.
• damage to the axillary nerve will result in paralysis to the deltoid and teres minor muscles; the patient will not being able to abduct their arm.
• the axillary nerve also innervates the skin over the lower deltoid (known as the regimental badge area), and so sensory innervation here could be lost.

Midshaft Fracture:

• a mid-shaft fracture could easily damage the radial nerve and profunda brachii artery, as they are tightly bound in the radial groove.
• the radial nerve innervates the extensors of the wrist. In the event of damage to this nerve, the extensors will be paralysed. This results in unopposed flexion of the wrist occurs, known as ‘wrist drop’.
• There is also some sensory loss over the dorsal (posterior) surface of the hand, and the proximal ends of the lateral 3 and a half fingers dorsally.

Distal Humeral Fracture:

• Supracondylar fractures and medial epicondyle fractures are common fracture types of the distal humerus. A supraepicondylar fracture occurs by falling on a flexed elbow. It is a transverse fracture, spanning between the two epicondyles
• Direct damage, or swelling can cause interference to the blood supply of the forearm from the brachial artery. The resulting ischaemia can cause Volkmann’s ischaemic contracture – uncontrolled flexion of the hand, as flexors muscles become fibrotic and short. There also can be damage to the medial, ulnar or radial nerves.
• A medial epicondyle fracture could damage the ulnar nerve, a deformity known as ulnar claw is the result. There will be a loss of sensation over the medial 1 and 1/2 fingers of the hand, on both the dorsal and palmar surfaces.

Question 11

What is the role of the ulna?

Answer 11

The ulna is a long bone in the forearm. It lies medially and parallel to the radius, the second of the forearm bones. The ulna acts as the stabilising bone, with the radius pivoting to produce movement.

Question 12

How does the ulna articulate?

Answer 12

Proximally, the ulna articulates with the humerus at the elbow joint. Distally, the ulna articulates with the radius, forming the distal radio-ulnar joint.

Question 13

Describe important anatomical features of the proximal end of the ulna

Answer 13

Olecranon – A large projection of bone that extends proximally, forming part of trochlear notch. It can be palpated as the ‘tip’ of the elbow. The triceps brachii muscle attaches to its superior surface.

Coronoid Process – This ridge of bone projects outwards in a anterior manner, forming part of the trochlear notch.

Trochlear Notch – Formed by the olecrannon and coronoid process. It is wrench shaped, and articulates with the trochlea of the humerus.

Radial Notch – Located on the lateral surface of the trochlear notch, this area articulates with the head of the radius.

Tuberosity of Ulna – An roughening immediately distal of the coronoid process. It is where the brachialis muscle attaches.

Question 14

Describe the shaft of the ulna

Answer 14

The three surfaces:

Anterior – Site of attachment for the pronator quadratus muscle distally.

Posterior – Site of attachment for many muscles.

Medial – Unremarkable.

The three borders:

Posterior – Palpable along the entire length of the forearm posteriorly

Interosseous – Site of attachment for the interosseous membrane, which spans the distance between the two forearm bones.

Anterior – Unremarkable.

Question 15

Describe important anatomical features of the distal end of the ulna

Answer 15

t is mostly unremarkable, terminating in a rounded head, with distal projection – the ulnar styloid process.

The head articulates with the ulnar notch of the radius to form the distal radio-ulnar joint.

Question 16

What is the clinical relevance of fractures of the ulna?

Answer 16

The forearm is a common site for bone fractures.

A fracture of the ulna alone (not involving the radius) usually occurs as a result of the ulna being hit by an object. The shaft is the most likely site of fracture. In this situation, the normal muscle tone will pull the proximal ulna posteriorly.

Less commonly, the olecrannon process can be fractured. This is caused by the patient falling on a flexed elbow. The triceps brachii can displace part of the fragment proximally.

The ulna and the radius are attached by the interosseous membrane. The force of a trauma to one bone can be transmitted to the other via this membrane. Thus, fractures of both the forearm bones are not uncommon.

There are two classical fractures:

Monteggia’s Fracture – Usually caused by a force from behind the ulna. The proximal shaft of ulna is fractured, and the head of the radius dislocates anteriorly at the elbow.

Galeazzi’s Fracture – A fracture to the distal radius, with the ulna head dislocating at the distal radio-ulnar joint.

Question 17

Describe the articulations of the radius

Answer 17

The radius articulates in four places:

Elbow Joint – Partly formed by an articulation between the head of the radius, and the capitulum of the humerus.

Proximal Radioulnar Joint – An articulation between the radial head, and the radial notch of the ulna.

Wrist Joint – An articulation between the distal end of the radius and the carpal bones.

Distal Radioulnar Joint – An articulation between the ulnar notch and the head of the ulna.

Question 18

Describe important anatomical features of the proximal end of the radius

Answer 18

Head of Radius – A disk shaped structure, with a concave articulating surface. It is thicker medially, where it takes part in the proximal radioulnar joint.

Neck – A narrow area of bone, which lies between the radial head and radial tuberosity.

Radial Tuberosity – A bony projection, which serves as the place of attachment of the biceps brachii muscle

Question 19

Describe important anatomical features of the distal end of the radius

Answer 19

In the distal region, the radial shaft expands to form a rectangular end. The lateral side projects distally as the styloid process. In the medial surface, there is a concavity, called the ulnar notch, which articulates with the head of ulna, forming the distal radioulnar joint.

The distal surface of the radius has two facets, for articulation with the scaphoid and lunatecarpal bones. This makes up the wrist joint.

Question 20

Describe important anatomical features of the shaft of the radius

Answer 20

In the middle of the lateral surface, there is a small roughening for the attachment of the pronator teres muscle.

Question 21

What is the clinical relevance of radius fractures?

Answer 21

The forearm is a common site for bone fractures. Here, we shall look at the common fracture types involving the radius:

Colles’ Fracture – The most common type of radial fracture. A fall onto an outstretched hand causing a fracture of the distal radius. The structures distal to the fracture (wrist and hand) are displaced posteriorly. It produces what is known as the ‘dinner fork deformity’.

Fractures of the radial head – This is characteristically due to falling on an outstretched hand. The radial head is forced into the capitulum of humerus, causing it to fracture.

Smith’s Fracture – A fracture caused by falling onto the back of the hand. It is the opposite of a Colles’ fracture, as the distal fragment is now placed anteriorly.

The radius and the ulna are attached by the interosseous membrane. The force of a trauma to one bone can be transmitted to the other via this membrane. Thus, fractures of both the forearm bones are not uncommon.

Question 22

Describe the proximal radioulnar joint

Answer 22

The proximal radioulnar joint is located immediately distal to the elbow joint, and is enclosed with in the same articular capsule. It is formed by an articulation between the head of the radius and the radial notch of the ulna.

The radial head is held in place by the annular radial ligament, which forms a ‘collar’ around the joint. The annular radial ligament is lined with a synovial membrane, reducing friction during movement.

Movement is produced by the head of the radius rotating within the annular ligament. There are two movements possible at this joint; pronation and supination.

Pronation: Produced by the pronator quadratus and pronator teres.

Supination: Produced by the supinator and biceps brachii.

Question 23

Describe the distal radioulnar joint

Answer 23

This distal radioulnar joint is located just proximally to the wrist joint. It is an articulation between the ulnar notch of the radius, and the ulnar head.

In addition to anterior and posterior ligaments strengthening the joint, there is also a fibrocartilaginous ligament present, called the articular disk. It serves two functions:

• Binds the radius and ulna together, and holds them together during movement at the joint.
• Separates the distal radioulnar joint from the wrist joint.

Like the proximal radioulnar joint, this is a pivot joint, allowing for pronation and supination. The ulnar notch of the radius slides anteriorly over the head of the ulnar during such movements.

Pronation: Produced by the pronator quadratus and pronator teres

Supination: Produced by the supinator and biceps brachia

Question 24

What is the interosseous membrane?

Answer 24

The interosseous membrane is a sheet of connective tissue that joins the radius and ulna together between the radioulnar joints.

It spans the distance between the medial radial border, and the lateral ulnar border. There are small holes in the sheet, as a conduit for the forearm vasculature.

This connective tissue sheet has three major functions:

• Holds the radius and ulna together during pronation and supination of the forearm, providing addition stability.
• Acts as a site of attachment for muscles in the anterior and posterior compartments of the forearm.
• Transfers forces from the radius to the ulna.