MSK Anatomy💪🩻🦴 Flashcards
Parts of the upper limb
Pectoral girdle
Arm
Forearm
Hand
Outline the major parts of the pectoral girdle
This term describes the clavicle (collar bone), the scapula (the shoulder blade) and the muscles attached to these bones.
Outline the arm region bone and compartments
This is the region between the shoulder and the elbow joints. The bone of the arm is the humerus. The arm contains anterior and posterior muscle compartments.
Outline the forearm region, bone and compartments
This is the region between the elbow and the wrist joint. The bones of the forearm are the radius and ulna. Like the arm, it contains anterior and posterior muscular compartments. The forearm compartments contain many muscles.
Outline the hand- placement and 2 sides
The hand is located distal to the wrist. The hand is typically discussed in terms of the palm (anteriorly) and the dorsum (posteriorly).
Joints of the upper limb
Glenohumeral joint
Elbow joint
Proximal and distal radioulnar joints
Radiocarpal joint
Outline the glenohumeral joint
The shoulder joint. This is a synovial ball and socket joint formed by the articulation between the scapula and the proximal humerus. It is highly mobile, which is key for allowing us to position our hand.
Outline the elbow joint
This joint allows flexion and extension of the forearm. It is a synovial hinge joint formed by the articulation of the distal humerus with the ulna and radius. It is extremely important in allowing us to bring things towards us and is crucial for activities of daily living, such as eating and washing ourselves.
Outline the proximal and distal radioulnar joints
These synovial joints between the radius and ulna allow pronation and supination of the forearm and hand.
Outline the radiocarpal joint
Otherwise known as the wrist joint, this is a synovial joint formed by the articulation between the distal radius and two of the carpal bones (small bones of the wrist). It allows flexion, extension, abduction, and adduction
Describe the movement of the scapula on the chest wall
The scapula moves on the posterior chest wall, but there is no bony articulation between these structures, so it is not a joint in the traditional sense. However, movement of the scapula over the chest wall is crucial for normal movement of the shoulder joint.
How does the scapula move?
Protraction (moving anteriorly – such as when you reach your arm out to push open a door) and retraction (moving posteriorly such as pulling your shoulder back). The scapula can also be elevated (shrugging), depressed (pulled downwards) and rotated.
How does the shoulder joint move?
Flexion, extension, abduction, adduction, internal (medial) rotation, external (lateral) rotation, and circumduction. Movements of the shoulder are almost always accompanied by movements of the scapula on the chest wall. When we raise our upper limb, the scapula rotates.
How does the elbow joint move?
Flexion and extension
The anatomical position
stood upright
palms facing forward
arms by the side
Feet facing forward
flexion
decreasing angle of joint
Extension
increasing the angle of a joint
Basic outline of any limb
Flat/curved bone to attach to the torso
Ball and socket joint
Singular proximal bone
Hinge joint
Pair of distal bones
Group of small irregular bones
Long thin bones for each digit
2 or 3 phalanges for each digit
Key parts of the limb bones
● Heads, necks, shafts
● Tubercles, tuberosities & trochanters
○ Rounded projections
● Condyles and epicondyles
○ Rounded projection at the
articulating end
● Fossae
○ Shallow depression or dent
Key features of the pelvis
● Ramus (rami)
○ Arm / branch
● Spine
○ Sharp projection
● Foramen (foramina)
○ Hole
Difference between origin and insertion
Origin doesn’t move
Insertion does
What are the superficial veins?
○ Cephalic vein (UL)
○ Basilic vein (UL)
○ Great saphenous vein (LL)
○ Small saphenous vein (LL)
Outline the nerves of the limbs
● Nerve roots either go to muscle direct (e.g. L1-L3 to psoas), or
merge into a named nerve (e.g. phrenic)
● Some roots make a plexus (e.g. brachial/lumbar)
● Named nerves come out of a plexus (e.g. median, ulnar, femoral)
● Specific nerves supply specific muscles
● Nerves can be injured in specific locations
○ This cuts off power to specific muscles, which give a specific
pattern of weakness
How do the radioulnar joints move?
Pronation (palm down) and supination (palm up).
How do wrist joints move?
Flexion and extension, abduction and adduction.
How do finger and thumb joints work?
Flexion and extension, adduction and abduction
Outline the clavicle
The clavicle is a slender, S-shaped bone, which is easily palpable in most individuals. It is the most commonly fractured bone
Articulations of the clavicle
It articulates with the manubrium of the sternum at its proximal (medial) end (the sternoclavicular joint) and with the acromion of the scapula at its distal (lateral) end (the acromioclavicular joint) – both of these joints are synovial.
Outline the scapula
It is mostly flat but has some important bony projections and, whilst located on the posterior thorax, some parts of the scapula can easily be palpated through the skin. Movements of the scapula can also be seen on examination.
Spine of the scapula
Ridge of bone on post. surface
Easily palpable
What is the Acromion?
Expansion of the lateral end of the spine of the scapula which articulates with the lateral end of the clavicle
The acromion can also be palpated easily.
Coracoid process
Projection of bone
Just inferior to the acromion on the anterior surface of the scapula
This is a site of attachment for several muscles
What is the pectoral girdle?
Combination of the clavicle, scapula and the attached muscles
Glenoid fossa
Shallow fossa on the lateral aspect of the scapula
Articulates with the proximal humerus to form the shoulder (glenohumeral) joint.
The glenoid fossa is shallow, making it a poor fit for the humerus
This increases the range of movement possible at the shoulder but compromises the stability of the joint
Supraglenoid tubercle and infraglenoid tubercle,
Two small projections of bone
Just superior and inferior to the glenoid fossa
Important sites for muscle attachments
What is the humerus?
The humerus is the long bone of the arm. It has a shaft and an expanded proximal and distal end.
Head of the humerus
The head of the humerus articulates with the glenoid fossa of the scapula
Anatomical neck of the humerus
Immediately distal to the smooth head of the humerus is a groove which is the position of the anatomical neck of the humerus.
Greater tubercle of the humerus
Laterally, the proximal humerus bears a projection of bone called the greater tubercle – an important site for muscle attachments
Lesser tubercle of the humerus
A smaller anterior projection – the lesser tubercle – is also a site for muscle attachment.
Surgical neck of the humerus outline and clinical relevance
Just distal to the tubercles, the bone narrows and becomes continuous with the shaft. This region is called the surgical neck and is clinically important because it is commonly fractured, especially in the elderly as a result of a fall. The axillary nerve runs close to this region and can be injured by fractures of the surgical neck or dislocation of the humeral head.
Deltoid tuberosity
The upper lateral aspect of the humeral shaft has a slight protuberance called the deltoid tuberosity which is the site of attachment for the deltoid muscle
Radial groove outline and clinical relevance
Another key landmark is the radial (or spiral) groove – this marks the path of the radial nerve over the posterior aspect of the humeral shaft. The radial nerve runs along a spiral route very close to the humerus here and can be injured in mid-shaft humeral fractures.
Can the clavicle and the scapula move
Whilst the clavicle can also move, we will concentrate on the movements of the scapula – these are vital for normal movement of the shoulder joint. The scapula is surrounded by muscles and so there is no bony articulation between the scapula and the posterior thoracic wall.
Movements of the scapula
Protraction
Retraction
Elevation
Depression
Rotation
Protraction of the scapula
This extends the upper limb, for example, when we stretch out the arm to push open a door.
Retraction of the scapula
‘squaring’ the shoulders or pulling them backwards
Elevation of the scapula
shrugging the shoulders.
Depression of the scapula
lowering the shoulders.
Rotation of the scapula
This tilts the glenoid fossa cranially to aid elevation of the upper limb. Rotation of the scapula is very important. When raising the arm above the head, for every 2˚ of abduction of the shoulder, the scapula rotates 1˚. If you observe someone from behind as they raise their arm, you will see the movement of the scapula.
Outline the musculature of the scapula
Several muscles attach the scapula to the vertebral column. When these muscles contract, the scapula moves. The attachment points of the muscles and the orientation of the muscle fibres determine the direction in which the scapula moves when the muscles contract.
Key muscle in protraction of the scapula
Serratus anterior
What are the 2 large and superficial muscles of the posterior pectoral girdle?
Trapezius and latissimus dorsi
Attachments of the latissimus dorsi and trapezius muscles
These are large, flat muscles with extensive attachments to the vertebral column (and in the case of trapezius, to the skull). Latissimus dorsi attaches to the anterior aspect of the proximal humerus, not the scapula (so it moves the shoulder joint, rather than the scapula), but it is often considered with the posterior pectoral girdle muscles.
Smaller deeper muscles of the scapula and where they attach?
There are three smaller, deeper muscles:
* Levator scapulae
* Rhomboid major
* Rhomboid minor.
These muscles attach to the medial border of the scapula and to the vertebral column.
How does the Trapezius muscle move the scapula?
Rotation, and individually: the upper part elevates, middle part retracts, and the lower part depresses the scapula.
How does the Levator scapulae muscle move the scapula?
Elevates
How does the rhomboid major muscle move the scapula?
Retracts
How does the rhomboid minor muscle move the scapula?
Retracts
How does the latissimus dorsi muscle move the humerus?
Extends, adducts, and medially rotates the humerus
What is the difference between origin and insertion?
The origin is the more ‘fixed’ or stable bone, and the insertion point is located on the bone that moves when the muscle contracts.
Attachments of the trapezius muscle
Origin: Skull, cervical and thoracic vertebrae
Insertion: Clavicle and scapula (spine and acromion)
Attachments of the latissimus dorsi muscle
Origin: Lower thoracic vertebrae
Insertion: Humerus – proximal and anterior
Attachments of the levator scapulae muscle
Origin: Upper cervical vertebrae
Insertion: Scapula - medial border
Attachments of the Rhomboid minor muscle
Origin: C7 and T1 vertebrae
Insertion: Scapula - medial border
Attachments of the rhomboid major muscle
Origin: Thoracic vertebrae
Insertion: Scapula - medial border
What innervates most muscles of the post. pectoral girdle?
Brachial plexus
What innervates the trapezius muscle?
Trapezius is not supplied by the brachial plexus but instead it is innervated by the 11th cranial nerve, the accessory nerve. Therefore, testing the function of trapezius is part of the cranial nerve examination.
What innervates the latissimus dorsi muscle?
A branch of the brachial plexus called the thoracodorsal nerve
Outline the shoulder (glenohumeral) joint
The shoulder joint (glenohumeral joint) has an extensive range of movement. This allows us to position our hand where we want to. It is a synovial ball and socket joint formed by the articulation between the glenoid fossa of the scapula and the head of the humerus.
Possible movements of the shoulder joint
The movements possible at the shoulder joint are flexion, extension, abduction, adduction, internal (medial) and external (lateral) rotation and circumduction.
Why is the fit of the glenoid fossa and head of humerus a pro and a con?
When we look at the scapula and humerus, we can see that the fit between the joint surfaces – the glenoid fossa of the scapula and the head of the humerus – is poor. This is key for extensive mobility at the joint. The downside of the shallow socket and poor fit is that the joint is less stable – the shoulder joint is the most commonly dislocated joint in the body.
Muscles that attach the scapula to the humerus
Six muscles attach the scapula to the humerus. They move and stabilise the shoulder joint. Except for deltoid, all of these muscles lie deep to the posterior pectoral girdle muscles (discussed above). The six muscles are:
* Deltoid
* Supraspinatus*
* Infraspinatus*
* Subscapularis*
* Teres minor*
* Teres major
*Alongside their individual actions moving the shoulder joint, these four muscles work together to provide vital stability to the shoulder joint – they are referred to as the ‘rotator cuff’.
Outline the deltoid muscle
Deltoid is the large muscle over the lateral aspect of the shoulder. It attaches the humerus to the lateral part of the clavicle and to the spine of the scapula. It gives the shoulder its rounded contour. It inserts onto the humerus at a landmark called the deltoid tuberosity.
What movement of the shoulder joint does the deltoid do?
It is a powerful abductor of the shoulder joint. However, deltoid cannot initiate abduction – another muscle initiates the first 15˚ of abduction before deltoid takes over. Additionally, the anterior and posterior fibres of deltoid contribute to flexion and extension of the shoulder, respectively.
Innervation of the deltoid
It is innervated by a major branch of the brachial plexus called the axillary nerve.
Clinical relevance of the deltoid
Injury to the axillary nerve can lead to atrophy and weakness (or even paralysis) of deltoid, which greatly impacts a patient’s activities of daily living.
Outline the teres major
Teres major is an interesting muscle as although it arises from the posterior aspect of the scapula, its tendon slots underneath the humerus and inserts onto the anterior aspect of the humerus. This arrangement explains its action as an internal rotator and adductor of the shoulder joint.
Outline the rotator cuff
Made up of Supraspinatus, infraspinatus, teres minor and subscapularis all move the shoulder joint. They are short muscles which attach the scapula to the tubercles of the humerus.
Origin and insertion of muscles of the rotator cuff
Supraspinatus, infraspinatus, and teres minor originate from the posterior surface of the scapula and insert onto the greater tubercle. Their tendons fuse with the fibrous capsule that surrounds the shoulder joint
Clinical relevance of the rotator cuff
Supraspinatus is particularly clinically important because as it travels from the supraspinous fossa to the greater tubercle it travels under the acromion. The tendon can become inflamed and pinched between the acromion and humerus during movements of the shoulder. This is called impingement and is a common cause of shoulder pain, particularly during large movements of the shoulder joint, such as serving in tennis.
What is the quadrilateral space and what travels through it?
The quadrilateral space is a square-shaped space bounded by: teres minor above, teres major below, the long head of triceps medially and the surgical neck of the humerus laterally. The axillary nerve travels through this space to enter the posterior scapula region and innervate deltoid and teres minor
Origin and insertion of the subscapularis
originates from the anterior surface of the scapula and inserts onto the lesser tubercle of the humerus.
Outline the deltoid muscle
Action at shoulder joint: Abduction beyond 15 degrees
Origin at scapula: Spine and acromion of the scapula and the clavicle
Insertion on the humerus: Deltoid tuberosity
Outline the Teres major muscle
Action at shoulder joint: Internal rotation + adduction
Origin at scapula: Post. surface, inf. part of lateral border
Insertion on the humerus: Ant. humerus
Outline the Supraspinatus
Action at shoulder joint: First 15 degrees of abduction
Origin at scapula: Supraspinous fossa
Insertion on the humerus: Greater tubercle- sup. facet
Outline the Infraspinatus
Action at shoulder joint: Ext. rotation
Origin at scapula: Infraspinous fossa
Insertion on the humerus: Greater tubercle- middle facet
Outline the Teres minor
Action at shoulder joint: Ext. rotation
Origin at scapula: Lateral border
Insertion on the humerus: Greater tubercle- inf. facet
Outline subscapularis muscle
Action at shoulder joint: Int. rotation
Origin at scapula: Subscapular fossa
Insertion on the humerus: Lesser tubercle
Outline the instability of the shoulder joint
The poor fit of the articular surfaces allows for the extensive range of movement at the shoulder joint (facilitated by a loose joint capsule), but this compromises stability. However, although shoulder dislocation is common, most of us haven’t dislocated a shoulder. This tells us that there are factors working to stabilise the joint and compensate for the poor fit of the articular surfaces.
What provides extra stability to the shoulder joint?
As a group, the four rotator cuff muscles provide vital stability. Contraction of the rotator cuff muscles holds the head of the humerus in the glenoid fossa and the rotator cuff tendons fuse with the capsule of the shoulder joint.
* A rim of fibrocartilage around the margin of the glenoid fossa – the glenoid labrum – which deepens the shallow fossa and aids stability. Labrum is derived from Latin meaning ‘lip’.
* The capsule is reinforced by ligaments.
* The tendon of biceps brachii, which lies in the anterior arm, also reinforces the joint.
Clinical relevance of rotator cuff
The rotator cuff muscles and / or tendons can be injured, become inflamed or degenerate. When this happens, patients usually experience pain and impaired movement, and the stability of the joint is compromised.
What is the axilla?
The axilla is the anatomical term for the armpit – the space between the torso and the upper arm. It is pyramid-shaped and has 6 boundaries
6 boundaries of the axilla
- Anterior wall – pectoralis major and minor
- Posterior wall – subscapularis, teres major and latissimus dorsi
- Lateral wall – proximal humerus
- Medial wall – serratus anterior and the thoracic wall
- Apex – first rib, clavicle, and scapula. It is the passage between the neck and the axilla.
- Base – skin and fascia between the thoracic wall and arm (the skin of armpit).
Key structures of the axilla
- Lymph nodes – which drain the upper limb, thorax, breast, and the abdominal wall as far as the umbilicus.
- Axillary artery – the major artery of the upper limb.
- Axillary vein – the major vein draining the upper limb.
- Brachial plexus (specifically the cords and branches) – a plexus of nerves that innervate the upper limb.
- Fat
Axillary lymph nodes
There are five groups of lymph nodes in the axilla. They drain the upper limb, breast, chest wall, scapular region and the abdominal wall as far as the umbilicus. The lymph nodes located in the apex of the axilla – the apical nodes – receive lymph from all other lymph nodes in the axilla.
Axillary artery
The axillary artery is the continuation of the subclavian artery as it progresses laterally. The subclavian artery travels over the first rib and under the clavicle and into the axilla. It becomes the axillary artery after it passes over the lateral border of the first rib. The axillary artery gives rise to several branches. It continues into the arm as the brachial artery (it becomes the brachial artery as it crosses the inferior border of teres major).
Axillary vein
The axillary vein is a large vein which drains the upper limb and is continuous with the subclavian vein. The axillary vein travels alongside the axillary artery. The axillary vein is formed by the union of the brachial veins with the basilic vein. The cephalic vein also joins the axillary vein in the axilla. At the lateral border of the first rib, the axillary vein becomes the subclavian vein.
Dislocation of the shoulder
In a dislocation of the shoulder, the humeral head moves out of the glenoid fossa. Anterior dislocation, where the humeral head ends up resting anterior to the glenoid fossa, is much more common. It is often caused by blunt force trauma, such as a fall. X-ray imaging confirms the direction of displacement of the humeral head and whether there is an associated fracture. Dislocation can injure the axillary nerve.
Rotator cuff injury
The rotator cuff can be injured by acute trauma or by repetitive use. The tendons can also degenerate with age. Tears of the rotator cuff are usually painful at rest and on movement, and cause weakness. If the supraspinatus tendon becomes injured and inflamed it may become impinged between the acromion and the humeral head, as the space here is small. The first part of abduction is not painful, but between 60˚– 120˚ of abduction, the inflamed tendon is compressed against the acromion, and this is when patients experience pain. An inflamed tendon may ultimately rupture.
Axillary lymph nodes clinical relevance
Because lymph from the breast drains to the axillary lymph nodes, breast malignancy typically metastasises first to these nodes. A malignant axillary node may be felt as a lump in the armpit and may be noticed before a mass in the breast itself. Axillary lymph nodes can be biopsied to assess whether or not breast malignancy has metastasised and can be removed as part of the patient’s treatment. Because they drain lymph from the upper limb, removal of the nodes can lead to fluid accumulation and swelling in the affected upper limb.
Clinical relevance of long thoracic nerve
- The long thoracic nerve innervates serratus anterior and lies superficially on the surface of the muscles in the medial wall of the axilla. Injury to this nerve causes weakness or paralysis of serratus anterior. One of the functions of this muscle is to hold the anterior border of the scapula flat against the posterior thoracic wall. If the muscle is paralysed, the anterior border lifts off the thoracic wall and the scapula appears to ‘stick out’. This is called a ‘winged scapula’.
Clinical relevance of the thoracodorsal nerve
The thoracodorsal nerve to latissimus dorsi is also vulnerable to injury as it runs along the subscapularis muscle, which forms part of the posterior wall of the axilla.
Shaft of the humerus and what it forms when it expands
The shaft of the humerus expands distally to form bony prominences called the medial and lateral epicondyles – these are palpable on examination
Trochlea and capitellum of the humerus
Prominences of the distal humerus
which articulate with the trochlear notch of the ulna and the head of the radius, respectively, at the elbow joint.
Arm and its compartments
The arm lies between the shoulder and elbow. Intermuscular septa, which extend from the deep brachial fascia which surrounds the arm, separate the arm into anterior and posterior compartments.
Muscles of the anterior compartment of the arm
The anterior compartment of the arm contains three muscles: biceps brachii, brachialis and coracobrachialis. All three act as flexors and all three are innervated by the musculocutaneous nerve.
Biceps brachii
) lies most superficially in the anterior arm. It has two heads – the long head and the short head
Attachments and tendons of the biceps brachii
Proximally, both heads are attached to the scapula; the long head to the supraglenoid tubercle and the short head to the coracoid process. The tendon of the long head of biceps pierces the capsule of the shoulder joint and helps to stabilise the joint. The two muscle bellies converge to their insertion via a common tendon onto the radial tuberosity of the radius.
What does biceps brachii flex?
Biceps is a flexor of the elbow joint – you can feel biceps contracting if you place a hand over it whilst flexing your elbow. However, because it crosses the shoulder joint, it is also capable of contributing to flexion of the shoulder joint.
How does biceps brachii supinate the arm?
Biceps is also a powerful supinator of the forearm when the elbow is flexed. Using a screwdriver helps understand this. When a right-handed person tightens a screw (turning to the right) they supinate the forearm – however, the power to turn the screw very tightly depends upon the elbow being flexed at the same time; supination is much weaker if the elbow is extended.
Brachialis- incl. attachments and what is flexes
Brachialis lies deep to biceps. Proximally, it is attached to the anterior aspect of the distal half of the shaft of the humerus, and it crosses the elbow joint to insert distally upon the ulna tuberosity. It is a powerful flexor of the elbow joint, but it does not cross the shoulder joint, so cannot act upon it.
Coracobrachialis- incl. attachments and where it flexes
Coracobrachialis is a deep and much smaller muscle that attaches proximally to the coracoid process of the scapula and distally to the medial aspect of the middle part of the humerus. It crosses the shoulder joint and acts upon it as a weak flexor.
Muscles of posterior arm
A single large muscle – triceps brachii – is located in the posterior compartment of the arm
Outline the heads of the triceps brachii and what they do
It has three muscle bellies, or heads, which all converge via a common tendon onto a single insertion point – the olecranon of the ulna. The muscle crosses the posterior aspect of the elbow joint, therefore, when it contracts, it extends the elbow.
Where does the long head of the triceps originate?
Infraglenoid tubercle of the scapula. It is the most medial part of triceps.
Where does the lateral head of the triceps brachii originate?
Posterior humerus, proximal to the radial groove.
Where does the medial head of the triceps brachii originate?
Posterior humerus, distal to the radial groove.
Can triceps brachii contribute to the movement of the shoulder as well as the elbow?
Yes bc of its attachment to the scapula
Innervation of the triceps brachii
All three parts of triceps are innervated by the radial nerve. The radial nerve is a major terminal branch of the brachial plexus. It winds around the posterior aspect of the humerus in the radial (spiral) groove between the medial and lateral heads of triceps. The nerve runs along the surface of the bone in this region, so a fracture of the shaft of the humerus may also cause injury to the radial nerve.
What is a plexus?
In anatomy, the term ‘plexus’ is used to describe complex networks of nerves or blood vessels.
Brachial plexus
The brachial plexus is the network of nerves that provides motor and sensory innervation to the upper limb. It is formed by the spinal nerves that leave the lower cervical spinal cord segments and the first thoracic spinal cord segment: these are spinal nerves C5, C6, C7, C8 and T1. The spinal nerves are mixed nerves, which carry motor and sensory fibres.
Segments of the brachial plexus
Roots, trunks, divisions, cords, and branches.
Trunks of the brachial plexus
Also located in the neck, they are formed from the roots.
* C5 and C6 combine to form the superior trunk.
* C7 continues as the middle trunk.
* C8 and T1 combine to form the inferior trunk.
Divisions of the brachial plexus
Each trunk divides into an anterior and a posterior division under the clavicle.
Cords of the brachial plexus
Named relative to their position around the second part of the axillary artery, they are formed by various combinations of the anterior and posterior divisions.
* Anterior divisions of the superior and middle trunks combine to become the lateral cord.
* Posterior divisions of all the trunks combine to becomes the posterior cord.
* Anterior division of the inferior trunk continues as the medial cord.
Branches of the brachial plexus
Located in the axilla, they are formed from the cords. They then travel distally to reach the structures that they innervate in the shoulder, arm, forearm or hand.
* Axillary – a branch from the posterior cord.
* Radial – the continuation of the posterior cord.
* Musculocutaneous – a branch from the lateral cord.
* Ulnar – a branch from the medial cord.
* Median – formed by branches from the lateral and medial cords.
What else does the brachial plexus do?
In addition to giving rise to the five large terminal branches in the axilla, the different segments of the brachial plexus give rise to other nerves that innervate the shoulder and pectoral muscles
Terminal branches of the brachial plexus
Axillary nerve
Radial nerve
Musculocutaneous nerve
Median and ulnar nerves
Axillary nerve
It innervates deltoid and teres minor and a small region of skin over the upper lateral arm.
* It is a branch of the posterior cord and contains fibres from spinal nerves C5 and C6.
* It 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.
Radial nerve
The radial nerve innervates triceps in the posterior arm. The radial nerve also innervates all the muscles in the posterior compartment of the forearm which are extensors of the wrist and digits. The radial nerve also innervates regions of skin over the arm, forearm, and hand.
* It is the continuation of the posterior cord and contains fibres from C5 - T1.
* It runs along the radial (spiral) groove on the posterior surface of the humerus and is vulnerable in mid-shaft fractures of the humerus.
Musculocutaneous nerve
The musculocutaneous nerve innervates the three muscles in the anterior compartment of the arm: biceps brachii, brachialis and coracobrachialis.
* It arises from the lateral cord and contains fibres from spinal nerves C5 - C7.
* After supplying motor fibres to three muscles named above, it continues as a sensory nerve that innervates a region of skin over the lateral forearm.
* Because of its location, the musculocutaneous nerve is rarely injured in isolation.
Median nerve
The median nerve is formed from contributions from both the lateral and medial cords.
* Normally, it contains fibres from C6-T1, but in some individuals, it may contain fibres from C5-T1.
* It innervates most of the muscles of the anterior forearm, which are flexors of the wrist and digits.
* It also innervates the small muscles of the thumb.
* It provides sensory innervation to skin over the lateral aspect of the palm of the hand and over the lateral digits*.
* It is most vulnerable in the arm as it crosses the anterior aspect of the elbow, in a region called the cubital fossa.
Ulnar nerve
The ulnar nerve is formed by the continuation of the medial cord, after it has given a contribution to the median nerve.
* It contains fibres from spinal nerves C8 - T1.
* It innervates most of the small muscles in the hand and therefore is vital for fine movements of the digits.
* It also innervates skin over the medial aspect of the hand and medial digits*.
* It is vulnerable to injury behind the medial epicondyle as it lies in a superficial position here (it is easily palpable in this location).
Outline injury to different parts of the brachial plexus
Injuries to different parts of the brachial plexus result in different clinical presentations. The most catastrophic type of brachial plexus injury occurs when all five roots of the brachial plexus are injured – this is uncommon but devastating, as it effectively denervates the whole of the upper limb.
Axial 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.
Causes of Upper brachial plexus injury (Erb’s Palsy)
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.
Outline the radius and ulna interactions
They are connected by an interosseous membrane. The radius and ulna also articulate with each other at the proximal and distal radioulnar joints.
Outline the trochlear notch
It articulates at its proximal end with the distal humerus to form the elbow joint: the trochlea notch of the ulna articulates with the trochlea of the humerus
Outline the radial head interaction with the humerus
the radial head articulates with the capitellum of the humerus
What does the radiocarpal joint allow you to do?
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.
What is the olecranon and where does it sit?
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.
What is the coronoid fossa and where does it sit?
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
Outline the radial tuberosity
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. Often implicated in fractures
Outline the styloid process
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.
Outline the elbow joint
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.
How is the hinge joint of the elbow reinforced?
The joint capsule is reinforced by medial (ulnar) and lateral (radial) collateral ligaments
Outline the proximal and distal radioulnar joints
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
Outline the carpus
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.
How does the distal radius articulate with the carpus
Outline the proximal row of carpal bones
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.
Outline the distal row of carpal bones
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.
Outline the radiocarpal joint
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).
Outline the intercarpal joints
The intercarpal joints between the carpal bones are synovial joints, which are also reinforced by ligaments, but they do not allow much movement.
Outline the bones of the hand
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.
Several muscles of the forearm travel into the hand and move the fingers and thumb.
What is the cubital fossa?
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’.
Borders of the cubital fossa
- 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.
Contents of cubital fossa
Tendon of biceps brachii
Bicipital aponeurosis
Brachial artery
Median nerve
Radial nerve
Outline the tendon of the biceps brachi
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
Outline the bicipital aponeurosis
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.
Outline the brachial artery
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
Outline the median nerve
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.
Outline the radial nerve
The radial nerve also passes through the lateral aspect of the cubital fossa. It is deep to brachioradialis here.
Outline the superior veins of the cubital fossa
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 and intravenous access. Highly variable
Radial head subluxation (‘pulled elbow’)
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.
Scaphoid fracture
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. 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.
Avascular necrosis
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
Fracture of the distal radius
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.
Outline the 8 muscles of the anterior forearm
- They are arranged in three layers: superficial, middle, and deep.
- Most of them act as flexors of the wrist, fingers, or thumb.
- Most of them are innervated by the median nerve.
Muscles of the superficial layer from lateral to medial
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor carpi ulnaris
Superficial muscles attachment and function
These superficial muscles are attached proximally to the medial epicondyle of the humerus. As most of these muscles are flexors, this region of the humerus is also commonly referred to as the ‘common flexor origin’.
Outline the pronator teres
As its name suggests – is a pronator (of the proximal radioulnar joint), rather than a flexor.
Outline the flexor carpi radialis (FCR)
Flexes and abducts the wrist. It inserts onto the radial side of the carpus and hand, hence its name.
Outline the palmaris longus
Has a small muscle belly but a long, thin, easily recognisable tendon when present (approximately 15% of us do not have one). Its tendon inserts into the fascia of the palm of the hand.
Outline the flexor carpi ulnaris (FCU)
Flexes and adducts the wrist. It inserts onto the ulnar side of the carpus and hand. This muscle is another exception to the general rule, as it is innervated by the ulnar nerve, not the median.
Outline the middle layer of the muscles of the anterior forearm
There is one muscle in the middle layer: flexor digitorum superficialis (FDS). It gives rise to four tendons. Its name tells us that it is a flexor of the digits – so we can deduce that its tendons must travel beyond the wrist, into the hand and to the fingers (digits 2-5).
It is innervated by the median nerve, which travels between flexor digitorum superficialis and one of the deep muscles, flexor digitorum profundus.
Muscles of the deep layer of the muscles of the anterior forearm
There are three muscles in the deep layer:
* Flexor digitorum profundus
* Flexor pollicis longus
* Pronator quadratus
Outline the flexor digitorum profundus (FDP)
A flexor of the digits and is located deep to flexor digitorum superficialis. It too gives rise to four tendons, which travel into the hand and to the fingers (digits 2-5). The tendons of superficialis and profundus are closely related in the hand and digits.
Innervation of the lateral half of the FDP
The lateral half of the muscle, which gives rise to the tendons that travel to the index and middle fingers, is innervated by the median nerve.
Innervation of the medial half of the FDP
The medial half of the muscle, which gives rise to the tendons that travel to the ring and little fingers, is innervated by the ulnar nerve.
Flexor pollicis longus (FPL)
Flexes the thumb (pollex is the Latin word for thumb). ‘Longus’ distinguishes it from another muscle, flexor pollicis brevis, which is much smaller and located within the hand.
Pronator quadratus
Is the deepest forearm muscle (it is considered a fourth layer by some). It is square-shaped (‘quadratus’) and is located over the distal ends of the radius and ulnar. It pronates the distal radioulnar joint.
Outline the muscles of the posterior compartment
- they are arranged in two layers: superficial and deep.
- most of them are extensors of the wrist, digits, or thumb.
- they are all innervated by the radial nerve.
What are the Superficial layer of the muscles of the posterior compartment of the forearm?
There are seven superficial muscles. They are:
* Brachioradialis
* Extensor carpi radialis longus
* Extensor carpi radialis brevis
* Extensor digitorum
* Extensor digiti minimi
* Extensor carpi ulnaris
* Anconeus
General rule of the Superficial layer of the muscles of the posterior compartment of the forearm
These muscles are attached proximally to the lateral epicondyle of the humerus and, as most of them are extensors, their origin is known as the ‘common extensor origin’.
Brachioradialis
Is an exception to some of the rules of posterior compartment muscles. It is located on the boundary between the posterior and anterior compartments. It originates from the humerus, proximal to the lateral epicondyle, and inserts on the distal radius. It acts as a weak flexor of the elbow joint and hence functions as an anterior compartment muscle of the arm. However, it is innervated by the radial nerve
Extensor carpi radialis longus (ECRL) and brevis (ECRB)
Are located on the radial side of the posterior compartment. ECRL inserts onto the 2nd metacarpal and ECRB inserts onto the 3rd metacarpal, hence they extend and abduct the wrist. Brevis is the Latin word for ‘short’.
Extensor digitorum (ED)
Extends the digits via four long tendons that insert onto the dorsal aspects of the fingers (digits 2-5). The tendons of ED are connected by fibrous bands – this makes it difficult to fully extend the middle or ring fingers independently.
Extensor digiti minimi (EDM)
Extends the little finger via its insertion onto the dorsum of the little finger.
Extensor carpi ulnaris (ECU)
Is the most medial of the superficial muscles. It extends and adducts the wrist via its insertion onto the 5th metacarpal.
Extensor retinaculum
At the wrist, the tendons of these muscles travel under a band of tissue, the extensor retinaculum. It prevents the tendons from bowing when the wrist is extended.
Aconeus
Anconeus is another small muscle in the superficial posterior compartment of the forearm. It is found proximally, near the olecranon so it is sometimes considered to be part of the posterior compartment of the arm instead. Its small size and position spanning from the lateral epicondyle of the humerus to the olecranon means it acts as a very weak extensor of the elbow. It is also innervated by the radial nerve.
