The Arm And Brachial Plexus Flashcards
What is the long bone of the arm
Humerus
Proximal parts of the humerus
Head
Anatomical neck
Surgical neck
Greater tubercle
Lesser tubercle
Deltoid tuberosity
Radial groove
Shaft of humerus
Expands distally to form bony prominences - medial and lateral epicondyles
Trochlea and capitellum
Prominences on the distal humerus which articulate with the trochlear notch of the ulna and the head of the radius at the elbow joint
What prominence of the distal humerus articulates with the trochlear notch of the ulna at the elbow joint
Trochlea
What prominence of the distal humerus articulates with the head of the radius at the elbow joint
Capitellum
What separates the arm into anterior and posterior compartments
Intermuscular septa - which extend from the deep brachial fascia which surrounds the arm
How many muscles does the anterior compartment of the arm contain
3
3 muscles in the anterior compartment of the arm
Biceps brachii
Brachialis
Coracobrachialis
Role of muscles in the anterior compartment of the arm
Flexors
What nerve innervates the 3 muscles in the anterior compartment of the arm
Musculocutaneous nerve
What is the most superficial muscle in the anterior compartment of the arm
Biceps brachii
What do the 2 heads of the biceps brachii attach to
The scapula-
Long head = supraglenoid tubercle
Short head = coracoid process
2 heads of biceps brachii
Long and short head
What does the long head of the biceps brachii attach to
Supraglenoid tubercle of scapula
What does the short head of the biceps brachii attach to
Coracoid process of scapula
Tendon of the long head of the biceps brachii
Pierces the capsule of the shoulder joint- helps to stabilise the joint
Common tendon of biceps brachii
2 muscle bellies converge to their insertion via a common tendon into the radial tuberosity of the radius
Function of biceps brachii
Flexor of elbow and shoulder joint
Supinator of the forearm when the elbow is flexed
Order of muscles from superficial to deep in anterior compartment of the arm
Biceps brachii
Brachialis
Coracobrachialis
What does the Brachialis attach to
Anterior aspect of distal half of shaft of humerus
Crosses the elbow joint to insert upon the ulna tuberosity
Function of Brachialis
Flexor of elbow joint
Why is the biceps brachii capable of contributing to flexion of the shoulder joint
Crosses the shoulder joint
Attachment of the Coracobrachialis
Coracoid process of the scapula and medial aspect of middle part of humerus
Function of Coracobrachialis
Weak flexor of the shoulder joint
What muscle is located in the posterior compartment of the arm
Triceps brachii
3 muscle bellies of triceps brachii
Converge via a common tendon onto a single insertion point- the olecranonof the ulna
Olecranon of the ulna
Where the common tendon of the triceps brachii inserts
Number of muscle bellies of the triceps brachii
3
Number of muscle bellies of the biceps brachii
2
3 muscle bellies of triceps brachii names
Long head
Lateral head
Medial hewd
Origin of long head of triceps brachii
Infraglenoid tubercle of scapula
Origin of lateral head of triceps brachii
Posterior humerus proximal to radial groove
Origin of medial head of triceps brachii
Posterior humerus distal to radial groove
Function of triceps brachii
Extension of elbow
What is the most medial part of the triceps
Long head
Function of long head of triceps brachii
Contributes to extension of shoulder joint as attaches to scapula
Which nerve innervates the triceps brachii
Radial nerve
Origin of radial nerve
Major terminal branch of the brachial plexus
Winds around the posterior aspect of the humerus in the radial groove
Which nerve runs in the radial (spiral) groove of the humerus
Radial nerve
Which spinal nerves form the brachial plexus
C5/6/7/8
T1
What type of fibres are contained in the brachial plexus
Sensory and motor
5 segments of the brachial plexus
Roots
Trunks
Divisions
Cords
Branches
Roots of the brachial plexus
5 spinal nerves C5-T1
Found in the neck
Trunks of the brachial plexus
Found in neck
Superior = C5/C6
Middle = C7
C8/T1 = inferior
Divisions of the brachial plexus
Each trunk divides into an anterior and posterior division under the clavicle
Where do the trunks of the brachial plexus divide
Under clavicle
Which roots form the superior trunk of the brachial plexus
C5/C6
Which roots form the middle trunk of the brachial plexus
C7
Which roots form the inferior trunk of the brachial plexus
C8/T1
Cords of the brachial plexus
Named relative to their position around the second part of the axillary artery- formed from various divisions of the anterior and posterior divisions
3 cords of the brachial plexus
Lateral cord
Posterior cord
Medial cord
What forms the lateral cord of the brachial plexus
Anterior divisions of the superior and middle trunk
What forms the posterior cord of the brachial plexus
Posterior divisions of all the trunks
What forms the medial cord of the brachial plexus
Anterior division of the inferior trunk
Branches of the brachial plexus
Located in the axilla
Travel distally to reach the structures that innervate the shoulder, arm, forearm and hand
5 branches of the brachial plexus
Axillary
Radial
Musculocutaneous
Ulnar
Median
What forms the axillary nerve of the brachial plexus
Branch from the posterior cord
What forms the radial nerve of the brachial plexus
Continuation of the posterior cord
What forms the Musculocutaneous nerve of the brachial plexus
Branch of the lateral nerve
What forms the ulnar nerve of the brachial plexus
Branch from medial cord
What forms the median nerve of the brachial plexus
Branches of the lateral and medial cords
What does the axillary nerve innervate
Deltoid
Teres minor
Small region of skin over the upper lateral arm
What is the axillary nerve a branch of
Posterior cord
Which spinal nerves does the axillary nerve contain fibres from
C5/C6
Pathway of axillary nerve
runs close to the surgical neck of the humerus and is vulnerable to injury in fractures of the surgical neck of the humerus or dislocations of the humeral head.
What does the radial nerve innervate
Triceps in posterior arm
All muscles in the posterior compartment of the forearm (extensors of the wrist and digits)
Regions of skin over the arm, forearm and hand
What does the radial nerve arise from
Continuation of posterior cord
Which spinal nerves does the radial nerve contain
C5-T1
When is the axillary nerve vulnerable
vulnerable to injury in fractures of the surgical neck of the humerus or dislocations of the humeral head
Pathway of the radial nerve
runs along the radial (spiral) groove on the posterior surface of the humerus
When is the radial nerve vulnerable
Mid-shaft fractures of the humerus
What does the Musculocutaneous nerve innervate
3 muscles in the anterior compartment of the arm: biceps brachii, Brachialis, Coracobrachialis
Region of skin over the lateral forearm
What does the Musculocutaneous nerve arise from
Lateral cord
Which spinal nerves contribute to the Musculocutaneous nerve
C5-C7
When is the Musculocutaneous nerve vulnerable
Rarely injured in isolation
What forms the median nerve
Contributions of lateral and medial cords
What does the median nerve innervate
Most of the muscles of the anterior forearm
Small muscles of the thumb
Skin over the lateral aspect of the palm of the hand and over the lateral digits
Which spinal nerves contribute to the median nerve
C6-T1
When is the median nerve vulnerable
most vulnerable in the arm as it crosses the anterior aspect of the elbow, in a region called the cubital fossa.
What forms the ulnar nerve
Continuation of the medial cord
Which spinal nerves contribute to the ulnar nerve
C8-T1
What does the ulnar nerve innervate
Most of the small muscles in the hand - vital for fine movement of the digits
Skin over the medial aspect of the hand and medial digits
When is the ulnar nerve vulnerable
injury behind the medial epicondyle as it lies in a superficial position here (it is easily palpable in this location).
Axillary nerve injury
Because of its close proximity to the surgical neck of the humerus, the axillary nerve can be injured by fractures in this region (which are common in the elderly) or dislocation of the shoulder joint. The motor fibres of the axillary nerve innervate deltoid and teres minor. Its sensory fibres innervate a patch of skin over the upper lateral arm. Injury to the axillary nerve can therefore result in weakness or paralysis of deltoid – this presents functionally as difficulty abducting the shoulder - and altered sensation or numbness over the upper lateral arm.
Radial nerve injury
As it travels along the radial groove of the posterior humerus, the radial nerve lies very close to the bone, thus fractures of the humeral shaft can injure the nerve. This can lead to weakness or paralysis of the muscles that are innervated by the radial nerve ‘downstream’ of the point at which the nerve is injured. As most of the radial nerve fibres that supply the triceps have already branched and entered the triceps at the point of the mid-humerus, the triceps itself is not likely to be significantly affected by damage to the radial nerve at this level. However, it will likely affect movements at the wrist because the radial nerve innervates all the muscles of the posterior forearm, which extend the wrist and digits.
Ulnar nerve injury
The ulnar nerve is vulnerable in the lower arm as it travels behind the medial epicondyle – it is superficial here. Fractures of the medial epicondyle may injure the nerve. Injury to the nerve at this level leads to motor impairments of the hand (as it innervates most of the small muscles of the hand) and causes sensory impairment in the hand (the medial side and the medial 1½ fingers). It is extremely common to knock the elbow in this region - referred to as the ‘funny bone’. A blow to the nerve here causes pain and tingling in the same regions of the hand.
Upper brachial plexus injury- Erb’s palsy
In this type of injury - which is uncommon - the upper parts of the brachial plexus are affected. It may involve C5 - C6, or C5 - 7. The typical picture is one of paralysis of the lateral rotators of the shoulder and the extensors of the wrist. The affected limb typically appears medially rotated with the wrist flexed.
It is typically caused by trauma – specifically mechanisms that stretch the head away from the shoulder. This may be seen when someone is thrown from a motorbike or a horse. It may also be seen in new-borns if the baby’s shoulder becomes stuck during delivery and its neck is excessively stretched to one side.
Lower brachial plexus injury- Klumpke’s palsy
This type of injury is also uncommon. The lower parts of the brachial plexus are affected, classically C8 and T1. The typical picture is one of paralysis of the small muscles of the hand. Again, it is most often caused by trauma – specifically mechanisms that forcefully and suddenly pull the arm upwards – this stretches the lower nerves of plexus. It may be sustained in babies during delivery if their arm is forcefully pulled superiorly to aid delivery.
Horner’s syndrome
Horner’s syndrome is the triad of drooping of the eyelid (ptosis), a constricted pupil (miosis) and lack of sweating (anhidrosis) on one side of the face. It results when the sympathetic nerve supply to the face is interrupted. The T1 spinal nerve carries sympathetic fibres which are destined to supply the face. Therefore, a brachial plexus injury affecting the T1 nerve root may result in Horner’s syndrome as well.
Brachial plexus block
This is a form of regional anaesthesia and can be used as an alternative to general anaesthesia for surgery on the upper limb. Under ultrasound guidance, local anaesthetic is infiltrated around the nerves of the plexus, which anaesthetises the upper limb.
- In a patient with a mid-shaft humeral fracture, which movements could you test to try and ascertain whether the radial nerve had been injured?
The radial nerve innervates triceps (extends the elbow) and the posterior compartment of the forearm (extends the wrist). Therefore, assessment should involve asking the patient to extend the elbow and then extend the wrist. The patient is asked to do this against gravity and against resistance. In the latter, the examiner applies a little force against the movement the patient is asked to perform – this tests the strength of the movement and again should be compared to the other side.
o Weakness of elbow extension and / or wrist extension would indicate a radial nerve injury. ‘Wrist-drop’ is the term given to the appearance of the wrist and hand when the forearm extensors are weak / paralysed.
- Describe how the cords of the brachial plexus are situated relative to the second part of the axillary artery.
o The lateral cord lies laterally, the medial cord medially and the posterior cord lies posterior to the artery.
- Which muscle of the upper limb is the most powerful supinator of the forearm? How does the position of the elbow joint affect the action of this muscle?
Biceps brachii is the most powerful supinator of the forearm and is much more powerful when the elbow is flexed.
- Which muscles are innervated by the musculocutaneous nerve? Which area of skin does it carry sensory fibres from?
o Biceps brachii, brachialis and coracobrachialis. It supplies sensation to the skin over the lateral forearm. The musculocutaneous nerve becomes the ‘lateral cutaneous nerve of the forearm’ after it has supplied motor fibres to the three muscles above.
Which nerve branches form the long thoracic nerve
C5/6/7
MAMRU
Musculocutaneous nerve
Axillary nerve
Median nerve
Radial nerve
Ulnar nerve
