17 - The Arm and Cubital Fossa Flashcards
What do I need to know?
- Organisation and contents of the compartments
- Movements of the arm/elbow and muscles
- Disposition of arteries and nerves of the arm and their origins in the axilla
- Cubital fossa boundaries and contents
How are the anterior/flexor and posterior/extensor compartments formed?
By the medial and lateral intermuscular septa which attach to the medial and lateral supracondylar ridges of the humerus. They become continuous with the deep fascia pf the arm
Anterior compartment of the arm?
> Biceps Brachii, Coracobrachialis, Brachialis
> Musculocutaneous Nerve (pierces coracobrachialis and lies on top of brachialis under biceps
Coracobrachialis?
O: Coracoid
I: Medial humerus opposite the deltoid tuberosity
> partially attaches to biceps brachii short head
Biceps Brachii?
O:
Short head: Coracoid
Long Head: Supraglenoid Tubercle
I: Radial Tuberosity and Bicipital Aponeurosis to deep fascia of antero-medial forearm
Brachialis?
O: Front of inferior humerus
I: anterior elbow joint to coronoid process and ULNAR tuberosity
Where does the axillary artery become the brachial artery?
At the INFERIOR border of teres major
What nerves accompany the brachial artery?
- The median nerve on the antero-lateral side and ulnar nerve posterior
Path of the ulnar Nerve?
- travels into the arm behind the brachial artery
- passes BEHIND the MEDIAL intermuscular septa and the lower arm and passes behind the medial epicondyle
- enters the forearm between the 2 heads of Flexor Carpi Ulnaris
Path of the Median Nerve?
- passes straight down to forearm on brachialis with brachial artery
O and I and nerve supply of deltoid?
O= anatomical horseshoe (lateral clavicle, acromion, spine of scapula) I= deltoid tuberosity on lateral humerus
> axillary nerve
Anterior Fibres of Deltoid
> unipennate (strong)
> flex shoulder and internally rotate arm
What does uni/multipennate mean?
Describes the architecture of the fasicle arrangement which affects how strong a muscle is
Middle Fibres of Deltoud
> multipennate (very strong)
> ABDUCT
Posterior Fibres of Deltoid?
> unipennate
> extend shoulder and externally rotate arm
Describe the mechanism of the middle fibres of the deltoid
- draw a line of axis linking the centre of the head of the humerus to the origin (acromion)
- in the anatomical position the fibres would have to lengthen to get to the line of axis
- the fibres try to lift the humerus up which they can’t do so they aren’t effective in the anatomical position
- need to move the humerus/point of insertion out TO the line of axis before the middle fibres are effective and can abduct
- supraspinatus abducts this 15 degrees before deltoid works
What is the pivot point of the shoulder joint?
Middle of the head of the humerus
How can the posterior and anterior fibres of the deltoid BOTH abduct and adduct?
- in anatomical position the insertion is so far away from the line of axis that the fibres both adduct (below the axis)
- once the arm is abducted then the fibres ABDUCT
(depends on the position of the arm/on the insertions relative position to the line of axis)
Teres Major?
O: Inferior angle and lateral border of scapula
I: Medial Lip of intertubercular groove of anterior humerus (lady between 2 mjrs)
> Lower Subscapular nerve
Internally rotates arm and adducts
> lat dorsi twists around teres major to insert
What muscles internally rotate arm?
Lat dorsi, Teres Major, Pec Major
What forms the compartments in the upper arm?
Deep Brachial Fascia, Lateral Intermuscular Septa, Medial Intermuscular Septa
Describe the arrangement of the compartments at the lower arm/elbow
- the LIS and MIS have become vertical to form 4 compartments
- flexor comp (anterior)
- extensor comp (post)
- flex/pronator of forearm (median/ulnar nerve)
- extens/supinator of forearm (radial nerve)
> as you move down the forearm and the arm muscles become tendons the sup/pro compartments become post/anterior
Why is the elbow such a busy area with muscles?
Fingers are dextrous and need to manipulate environment but also need strength to grab things. Can’t have the big muscles needed for this in a dextrous structure so move them off site to the forearm. Hands also have a lot of movement and muscles only shorten 1/3 of there length so the muscles also have to be long to generate a lot of movement - they therefore originate on the humerus
What muscles of the forearm do not originate from the common extensor/flexor tendons?
- pronator teres (medial supracondylar ridge and septa)
- brachioradialis and ECRL (lateral supracondylar ridge and septa)
- brachialis (LIS MIS and ant inferior humerus)
What does the MIS and LIS do?
Increases SA for muscle attachment and anchorage
Biceps Brachii?
O Long head: Supraglenoid Tubercle
O Short head: Coracoid
I: Radial tuberosity and bicipital aponeurosis
- Supination
- Elbow flexor (and shoulder)
(when you flex with pronated arms biceps does little to nothing)
What structures are intracapsular at the glenohumeral joint?
The tendon of the long head of biceps - runs from the supraglenoid tubercle down the intertubercular groove
What does the bicipital aponeurosis do?
Blends with the deep fascia of the arm and protects the structures of the cubital fossa
What movements do the ulna and radius permit?
Ulna only flexion and extension
Radius flex/extends and pronation/supination
Describe pronation and how this relates to biceps
The radius rotates its distal end over the ulna and takes the hand with it. The radial tuberosity on the medial radius also rotates and rolls under the bone to the lateral side to become pronated.
> this means the tendon of biceps is wrapped around the proximal head of the radius between the 2 bones
> when biceps contracts it pulls on the radial tuberosity to return to supination
Coracobrachialis?
O= coracoid (attached to biceps short head)
I = Medial humerus opposite deltoid tuberosity
> shoulder flexor/adduction but mostly is a SHUNT muscle
> musculocutaneous n
Brachialis?
O = anterior distal humerus and intermuscular septa I = Tuberosity of ulna > main elbow flexor > below biceps > mc nerve
What is the significance of having the biceps tendon intracapsular to the shoulder joint?
Stabilises the joint and stops SUPERIOR dislocation as when it contracts it holds the head of the humerus hard in the glenoid.
> if you adduct and abduct your arm a lot then the tubercles move up and down on the tendon and can wear it out and rupture
> may fuse with the capsule
Muscles of the extensor compartment of the arm?
Triceps (anconeus ASSISTS)
Triceps Brachii?
Long head: Infraglenoid Tubercle
Lateral Head: Back of humerus
Medial head: radial/spiral groove under the lateral head (most active)
I = Olecranon of the ulna
> radial nerve
elbow extension
Where does the radial nerve run?
In the radial groove between the lateral and medial haeds of triceps
Anconeus?
O: Lateral Epicondyle
I: Posterior ulna
> assists in elbow extension
radial nerve
What is the purpose of shunt muscles and what is an example?
Coracobrachialis/deltoid/short head of biceps/long head of triceps
> shunt muscles prevent unwanted inferior movement of the humerus head at the shoulder joint during loading. They are stimulated but don’t shorten
Describe the course of the musculocutaneous nerve
- lateral cord
- runs into coracobrachialis and then runs between brachialis and biceps
- terminates as the lateral cutaneous nerve of the forearm (next to radial nerve)
Describe the course of the Median Nerve
- medial and lateral cord
- runs medially to biceps and then under the bicipital aponeurosis (the roof of the cubital fossa)
- runs w/brachial A
Describe the course of the Ulnar Nerve
- medial cord
- runs with median nerve along medial biceps until half way down it goes behind the MIS and behind the medial epicondyle into the posterior compartment and then back into the anterior compartment in the forearm
Describe the course of the Radial Nerve
- posterior cord
- stays posterior by coming through the TRIANGLE interval and runs down the spiral groove between triceps lateral and medial heads
- it then runs round the FRONT of the lateral epicondyle and LIS to enter the anterior compartment between brachialis and brachioradialis
Describe the course of the axillary nerve
- posterior cord
- more superior than radial nerve so comes posterior through the quadrangular space
- deltoid and teres minor
Describe how the spaces are formed
- there are 3 spaces formed by boundaries: Superior: Teres minor Inferior: Teres Major Medially: medial scapula and long head of triceps Laterally: front of the humerus > triangular space > quadrangular space > triangular interval (largest)
Where do the long head or biceps and triceps originate?
Biceps: Supraglenoid tubercle
Triceps: Infraglenoid tubercle
Triangular Space?
- most medial and smallest space
- borders: medially scapula, laterally long head biceps, inferior teres major
- only contains an artery; circumflex scapular artery
Quadrangular Space?
- most superior Superior: teres minor and humerus Inferior: teres major Medially: Long head triceps Laterally: humerus - Axillary Nerve and POSTERIOR circumflex humeral artery
Triangular Interval?
- Largest
- teres major superiorly, long head triceps medially, humerus laterally
- Radial nerve and profunda brachii artery
Describe the arteries of the arm
Axillary A > anterior and posterior circumflec humeral A (surgical neck of humerus)
Brachial A > profunda brachii (posterior and runs in the radial groove with the radial nerve and then meets the radial artery laterally)
Ulnar and Radial A
What structures are at risk during a midshaft fracture of the humerus?
The profunda femoris artery as is right up against the bone
What is the cubital fossa?
Diamond shaped area anterior elbow that allows structures to get from the arm to the forearm
What are the borders of the cubital fossa?
Superior: line between the medial and lateral epicondyles
Medially: Pronator Teres
Laterally: Brachioradialis
Floor: Supinator and tendon of brachialis
What vein in the arm do you often puncture?
The median cubital vein running between the basilic and cephalic veins
Which nerves does the brachial artery run with?
Median and ulnar
What are the subcutaneous structures at the cubital fossa?
- basilic v
- cephalic v
- median antebrachial v (runs off of median cubital v)
- the lateral and medial cutaneous nerves of the forearm become subcutaneous at the fossa
What vein in the arm do some people have?
Median antebrachial vein coming off of the median cubital vein
Describe the veins of the arm
IVC > Subclavian V > Axillary V > cephalic vein which goes over pec minor in the deltopectoral groove and is subcutaneous > the axillary V continues cutaneous down the arm and gives off profunda brachii veins which are deeper and run with the brachial artery and link with the basilic vein > half way down the arm the axillary vein becomes subcutaneous and becomes the basilic vein > basilic and cephalic form the median cubital vein in the cubital fossa which in some people gives off the Median Antebrachium Vein
Veins of the arm?
IVC Subclavian Axillary > Cephalic > Profunda brachii Basilic Median Cubital V Median Antebrachium V
What vein does the brachial A, median N and ulnar N run with
The basilic vein
