L2: The Arm and Elbow

Question 1

What is the brachial plexus?

Answer 1

The brachial plexus is a braid of nerve that arises from the spinal cord and located in the neck and axilla. It gives rise to the 5 major branches. It gives rise to 5 major branches that provide the motor and sensory innervation of the upper limb.

Question 2

Give the roots of the Brachial plexus.

Answer 2

C5-T1

Question 3

What roots make up the trunks of the brachial plexus?

Answer 3

C5 and C6 form the superior trunk.

C7 forms the middle trunk

C8 and T1 form the inferior trunk.

Question 4

What trunks make up the divisions of the brachial plexus?

Answer 4

The superior, middle and inferior trunk split into anterior and posterior divisions.

Question 5

What divisions make up the cords of the brachial plexus?

Answer 5

The Lateral Cord: Formed by the anterior division of the superior and middle trunk.

The Posterior Cord: formed by the posterior divisions of all 3 trunk.

The Medial Cord: formed by the anterior division of the inferior trunk.

These cords are named according to their position around the axillary artery.

Question 6

Give the 5 terminal branches of the brachial plexus with their roots and the areas they supply.

Answer 6

Musculocutaneous nerve (C5-C7) - supplies the anterior upper arm muscles and the skin of the arm.

Axillary Nerve (C5 and C6) - supplies the deltoid, teres minor and the skin over the upper lateral arm.

Median nerve (C5-T1) - innervates the muscles of the anterior forearm, muscles of the thumb and skin of the arm.

Radial Nerve (C5-T1) - supplies the triceps and forearm muscles and the region of the skin on the hand.

Ulnar Nerve (C8 and T1) - anterior forearm muscles, most small muscles of the hand and muscles on the skin of the arm.

The M shape of nerve overlying the axillary artery helps us to trace backwards and identify the nerves.

Question 7

Briefly, how does the humorous articulate with the shoulder and forearm.

Answer 7

The humorous articulates with the glenoid fossa of the scapula at the shoulder and the ulna and radius at the elbow.

Question 8

What are the distal anterior anatomical landmarks of the humorous?

Answer 8

The lateral and medial epicondyle; the capitulum; the trochlea and the coronoid fossa. There is also the lateral and medial supracondylar ridges.

Question 9

What are the distal posterior anatomical landmarks of the humorous?

Answer 9

The radial nerve runs posteriorly quick close to the radial groove.

Olecranon fossa is found posteriorly. The capitulum cannot be seen on the posterior surface. The trochlea however can be seen.

Question 10

How does the humorous articulate with the forearm?

Answer 10

The capitulum articulates with the radial head.
The trochlea articulates with the ulna.
The coronoid process of the ulna articulates with the coronoid fossa.

The olecranon (proximal ulna) in full extension fits into the olecranon fossa.

Question 11

How is the joint capsule reinforced?

Answer 11

• Reinforced laterally the radial collateral ligament
• reinforced medially by the ulnar collateral ligament

The capsule is thin and loose anteriorly and posteriorly.

Question 12

What other joint is contained in the capsule of the elbow joint?

Answer 12

The radial-ulnar joint proximally and radially. It allows for supination and pronation.

Question 13

What movements are allowed at the elbow joint?

Answer 13

Flexion and extension. It is a hinge joint.

Question 14

How is the elbow joint described?

Hint: In terms of stability

Answer 14

Very congruent

Question 15

What are the muscles of the anterior arm?

Answer 15

Biceps
Brachialis
Corocobrachialis

Question 16

What nerves innervate the muscles of the anterior arm?

Answer 16

Musculocutanous nerve (C5-C7)

Question 17

What are the muscles of the posterior arm?

Answer 17

Triceps

Question 18

What nerves innervate the muscles of the posterior arm?

Answer 18

The radial nerve

Question 19

What are the attachments of the muscles of the anterior arm?

Answer 19

Biceps: The long head attaches to the supraglenoid tubercle. The short head attaches to the coracoid process. Distally the biceps attaches to the radial tuberosity. It is capable of moving both joints as it spans them both.

Brachialis: The origin is at the shaft of the humorous. Distally its attaches to the ulna tuberosity. It is therefore only able to move the elbow joint.

Corocobrachalis: It’s origin is at the coracoid process. Distally it attaches to the proximal humeral shaft. It is able to weakly flex the shoulder.

Question 20

What are the attachments of the muscles of the posterior arm?

Answer 20

Origin:
The long head of the triceps: attaches to the infraglenoid tubercle on the scapula, so contributes to shoulder extension as its spans the shoulder joint.
The lateral head: attaches proximally to the posterior shaft of the humorous.
The medial head: deep to the long and lateral heads, attached to the shaft of the humorous.

They join together to form a common tendon which attaches at the olecranon of the ulna. Its attachment on the infraglenoid fossa on the scapula, means the triceps can have an extension effect on the shoulder.

Question 21

What nerves run close to the bone and so are in danger in the case of rupture?

Answer 21

4 of the terminal branches of the BP are found in the arm: musculocutaneous (heading into the anterior compartment), median (towards the forearm), radial (posterior compartment behind the humorous) the and ulnar (travelling on the medial aspect of the arm towards the forearm).

Question 22

How can a pulled elbow occur in children?

Answer 22

The radial head subluxes (dislocates) from the annular ligament. This is very painful, the child is unable to move their arm. The radial head can be palpated.

Question 23

What is at risk in a humeral supracondylar fracture?

Answer 23

May injure the median nerve. This leads to impaired function of the forearm muscles and sensory disturbance in the skin innervated by the median nerve.

Question 24

What is a risk of posterior dislocation?

Answer 24

May injure the ulnar nerve. This leads to impaired function if the muscles and sensory disturbance in the skin innervated by the ulnar nerve.

Question 25

What is the produnda brachii? What does it supply?

Answer 25

In the arm the axillary artery continues as the brachial artery. Brachial artery gives rise to the deep artery of the arm (profunda brachii). This supplies the into the posterior compartment. It travells behind the humorous.

Question 26

What prevents hyperextension?

Answer 26

The olecranon fossa is the bony limitation that prevents hyperextension.