Musculoskeletal Block: The Skull and Vertebral Column

L.O. Describe the major features of the bones of the skull, mandible and the temporomandibular joint (TMJ)

L.O. Describe the major groups that the major muscles of the head and neck fall int - muscles of facial expression, muscles of mastication etc.

‘Adduction is the movement of a limb or body part towards the midline of the body, while abduction is the movement away from the midline’

The Skull

Bones of the Skull (10 all together)

Sutures of the Skull: (6 all together)

  • between the parietal bone and the occipital bone, we have our lambdoid suture

  • where the sagittal suture joins the coronal suture - we call this the bregma

  • where the sagittal suture joins the lambdoid suture - we call this the lambda

  • the bregma (anterior fontanelle) and lambda (posterior fontanelle) are soft spots in neonate heads - this allows the brain to continue growing after birth

Bones of the Skull (inside the skull)

There are 2 new bones here which can be seen in this sagittal cross section of the skull

  1. Vomer

  2. Palatine bone - makes the posterior part of the hard palate

  • the ethmoid bone makes up the superior part of the nasal cavity whilst the vomer bone makes up the inferior part of the nasal cavity

Cranial Fossae and the Foramen

  • the cranial cavity divides itself naturally into three parts:

  1. Anterior cranial fossa

  2. Middle cranial fossa

  3. Posterior cranial fossa

  • the foramen are crucial for allowing vascularisation of the brain

  • a lot of things need access to the brain

Major Foramen:

  1. Foramen Ovale : Mandibular nerve passes through here.

  2. Foramen Magnum: the spinal cord goes through here and becomes the brain stem. The vertebral arteries also go through here

  3. Jugular Foramen: internal jugular vein and cranial nerves IX, X, XI pass through here.

  4. Carotid Canal: internal carotid artery passes through here.

Muscles of Facial Expression

  • unique muscles within the body - they are subcutaneous and insert directly into the skin

  • they are responsible for moving the skin to provide facial expression, but also act as sphincters around the eyes and mouth

  • supplied by cranial VII - the facial nerve

  • the thickness, position etc of the muscles vary greatly between people

The Major muscles you should know are:

  1. Orbicularis Oculi - this surrounds the eye and is one of the sphincter muscles which helps close the eye.

  2. Orbicularis Oris - this surrounds your mouth and helps to pucker your lips.

  3. Platsyma - goes all the way to your neck and helps to depress the angles of your mouth

  4. Occipitofrontalis - this is the muscle on your scalp and it is divided into the frontal belly and occipital belly - connected by an aponeurosis ( a large flat tendon)

The Facial Nerve

  • the facial nerve travels through the internal acoustic meatus and then through the mastoid process

  • the facial nerve comes out of the mastoid process, travels through the Parotid gland and moves superficially because our muscles are superficial

  • the facial nerve divides into 5 distinct different branches:

  1. Temporal branch

  2. Zygomatic branch

  3. Buccal branch

  4. Marginal mandibular branch

  5. Cervical branch

Bell’s Palsy

  • paralysis of facial nerve

  • causes drooping of face

  • can’t close eyelid or eyelid droops

  • difficulty closing mouth

Muscles of Mastication

  • normal skeletal muscle

  • responsible for moving the mandibular at the Temporomandibular joint

  • supplied by cranial nerve V - the trigeminal nerve

  • these muscles attach bone to bone (normal skeletal muscle)

1. Masseter - elevates mandible and protrudes your mandible. Powerful muscle.

  1. Temporalis - sits on the side of your head, over your temporal bone. Inserts into the pterygoid process - elevates and retracts mandible.

  2. Medial pterygoid - elevates and protrudes mandible.

  3. Lateral pterygoid - protrudes mandible

The Mandibular Nerve and Trigeminal Nerve

  • the Mandibular Nerve is a branch of the Trigeminal Nerve

  • the Trigeminal Nerve is sensory to the face and scalp as far back the vertex (supplies the skin of these areas and orifices such as nasal and oral cavities)

  • it also has a motor function to the muscles of mastication

The Trigeminal Nerve has 3 major branches

  1. Ophthalmic Nerve

  2. Maxillary Nerve

  3. Mandibular Neve - supplies the muscles of mastication - mixed as it has sensory neurones going to the skin and motor neurones going to the muscles of mastication.

Pharyngeal Arches

  • why are there different nerves supplying the muscles of mastication and muscles of facial expression?

Each Pharyngeal Arch has its own:

  • cartilage skeleton

  • muscular component

  • sensory nerve supply

  • motor nerve supply

When a muscle migrates it brings its nerve supply with it.

Muscles of mastication are derived from the 1st pharyngeal arch and are therefore innervated by the trigeminal nerve (V)

Muscles of facial expression are derived from the 2nd pharyngeal arch and are therefore innervated by the facial nerve (VII)

This explains why you get a different nerve supply in the head and neck.

What is the sensory nerve supply to the face?

  • trigeminal nerve

What is the motor nerve supply to the muscles of facial expression? 

  • facial nerve

The Temporomandibular Joint

  • it is a synovial joint

  • responsible for allowing movement of the mandible

  • articular cartilage decreases friction

  • synovial membrane secretes fluid to decrease friction

Movements of the Mandible

  1. depression of the mandible - causes mouth to open

  2. elevation of the mandible - causes the mouth to close

  3. protrusion of the mandible - the lower teeth come to lie in front of the upper teeth

  4. retraction of the mandible - the mandibular head is pulled back into the mandibular fossa

  5. rotation of the mandible - causes lateral chewing movements

  • articulation between the temporal bone and zygomatic bone is called the zygomatic process of the temporal bone.

  • head of the mandible sits in a groove called the mandibular fossa

  • coronoid process - where the temporalis muscle attaches to.

The Capsule and Ligaments of the Temporomandibular Bone

  • the Lateral temporomandibular ligament prevents retraction of the mandible

  • the sphenomandibular ligaments and the stylomandibular ligaments secure the joint and makes sure the head of the mandible stays in the mandibular fossa and can rotate without dislocating

The Temporomandibular Joint: articular disc

  • the reason this joint can have so many movements is due to the articular disc 

  • articular cartilage on the head of the mandible

  • articular cartilage on the mandibular fossa

  • synovial membrane and capsule can be seen

  • the articular disc separates the joint cavity into an upper joint cavity and a lower joint cavity and this allows different movements to occur

  • Upper Joint Cavity: the head of the mandible can move out from the mandibular fossa onto the articular tubercule and back again (protrusion and retraction)

  • Lower Joint Cavity: hinge rotation

The Skull and Vertebral Column Part II

L.O. Differentiate between the atlanto-occipital joint and the atlanto- axial joint and describe the movements that occur at each one.

L.O. Differentiate between different types and shapes of the vertebrae and relate their structure to function.

L.O. Describe the major components of the intervertebral (IV) and how its components reinforce as a cushioning structure between vertebrae.

L.O. Describe the embryology of normal spine development.

L.O. Illustrate and define the ligaments of the vertebral column.

L.O. Describe the surface anatomy of the vertebral column.

The Vertebral Column

The way to remember the vertebral column:

  • Breakfast at 7am

  • Lunch at 12

  • Dinner at 5pm

  • and then the Sabral and Coccygeal 

The ‘Body’ is the weight bearing part of the vertebral column. With each segment, the body gets larger because it has to bear more weight. So that’s a way to tell from what region of the body the vertebra is from by the size of the body.

The Vertebral foramen is where the spinal cord is housed.

What is a process?

Outgrowth of tissue from a larger structure, most commonly a bone. These projections serve to provide attachment points for muscles and ligaments or to form joints with other bones.

  • intervertebral disc - secondary cartilaginous joint which allows some movement

  • zygapophysial joint - synovial joint - get quite a lot of movement

Regional Variations of Vertebrae

Musculoskeletal Block: Upper Limb I - Shoulder to Elbow

L.O. Description of the major landmarks of the bones of the shoulder.

L.O. Description of the relationship between joint structure and range of motion.

L.O. Description of the muscles of the shoulder (in particular the rotator cuff), their associated ligaments and their movements.

Pectoral Girdle and Humerus - ANTERIOR view

Clavicle -

  • the clavicle attaches to the sternum on the medial end and the acromion of the scapula at the lateral end 

Scapula -

  • a fossa is just a ‘natural hollow’ in a bone 

  • Glenoid fossa articulates with the head of the humerus

  • Acromion articulates with clavicle 

  • coracoid process

Humerus -

  • the head articulates with the glenoid fossa

  • two bumps = greater tubercule

  • and lesser tubercle

  • intertubercular sulcus is the groove between the tubercles

  • surgical neck = most likely to break arm here

  • trochlea articulates with the ulna

  • capitulum articulates with the head of the radius

  • coronoid fossa fits the coronoid process of the ulna 

  • two bumps - medial epicondyle and lateral epicondyle

Pectoral Girdle and Humerus - POSTERIOR view

  • clavicle pushes the humerus away from the rib cage giving it a larger range of motion and stabilising the bone

  • Spine of the scapula - splits the posterior scapula into two;

  1. Supraspinous fossa

  2. Infraspinous fossa

Pectoral Girdle - Superior View

  • the clavicle becomes quite posterior and is not flat across the body

  • the scapula is also not flat in the body but positioned at an angle

Synovial Joints - 

  • trade off between stability vs mobility 

The Glenohumeral Joint

  • extremely mobile allowing flexion, extension, abduction, adduction, medial and lateral rotation and circumduction

  • the disadvantage is the extreme mobility as this joint is the most dislocated joint in the body

Abduction of the arm

  • mix of humerus rotating within the glenoid fossa as well as the rotation of the scapula

The Glenohumeral Joint Capsule

4 Intrinsic Ligaments

  1. Coracohumeral ligament

  2. Superior glenohumeral ligament

  3. Middle glenohumeral ligament

  4. Inferior glenohumeral ligament

  • redundant capsule hangs at the bottom when the arm is adducted as a bit of slack is needed when that person abducts the humerus as if it was taught the capsule would rip

  • tendon of long head of biceps of brachii pierces the joint capsule and goes to attach to the very top of the glenoid fossa, actually inside the joint itself. - can rip put

The Rotator Cuff

  • the rotator cuff is a group of muscles whose tendons surround the glenohumeral joint

  • as well as providing movement to the upper limb these muscles strengthen the joint

  • these muscles are;

  1. subscapularis

  2. supraspinatus

  3. infraspinatus

  4. teres minor

Rotator Cuff Muscles

  • supraspinatus initiates abduction of the arm

  • infraspinatus allows lateral rotation of the humerus 

  • teres minor allows lateral rotation of the humerus 

  • subscapularis allows medial rotation of the humerus

Rotator Cuff injuries -

  • common in people who continuously use the arms above the horizontal - throwing, racquet sports, swimming, weightlifting

  • can lead to inflammation and a result tear in the cuff especially the supraspinatus tendon

  • can test for injuries by asking a patient to adduct their arm slowly - if the arm suddenly drops to their side at 90 degrees it is likely they have injured their rotator

L.O. Description of the major muscles of each of the compartments and their associated movements.

L.O. Description of the surface anatomy of the arm and shoulder.

Muscles of the Upper Limb

  • deltoid muscle - allows abduction of arm 

  • pectoralis major - adducts arm, allows medial rotation of the humerus, extends flexed arm.

  • deltopectoral groove - major vein here

  • trapezius - allows elevation of the scapular and rotation of scapula allowing full abduction of upper arm.

  • pectoralis minor muscle - allows depression of scapula 

  • serratus anterior - allows rotation of scapula and protraction (moving in) of scapula. This muscle goes around and hugs the rips, goes around between the scapula and the ribs and inserts onto the medial border of the scapula.

Proximal Muscles of the Arm

  • teres major - allows medial rotation and extension of arm

  • latissimus dorsi - allows medial rotation and extension of arm

  • subscapularis - allows medial rotation of the humerus 

  • biceps brachii - two headed muscle in the arm - allows flexion and supination of the foramen - weak flexor of the the humerus 

  1. long head - goes into the glenohumeral joint capsule

  2. short head - inserts into the coracoid process

  • coracobrachialis - flexor and adductor of humerus 

  • brachialis - flexor of forearm 

  • triceps brachii - long head, lateral head and medial head

  • all of these muscles go to attach to the Olecranon Process of the ulna 

  • all of the muscles help extend the forearm

  • the long head goes to the lateral part of the scapula - so you do get a little bit of help with the extension of the humerus there.

Anterior Surface Anatomy -

Posterior Surface Anatomy - 

L.O. Description of the compartments of the arm.

L.O. Description of the brachial plexus, its origins and how this relates to the ulnar, median and radial nerves. 

Fascia -

(connective tissue you can see with the naked eye).

Intermuscular Septa - 

  • anterior compartment of the arm

  • posterior compartment of the arm 

Compartments of the Arm

The Spinal Cord

  • the spinal cord sits inside the vertebral foramen

  • the spinal nerve is mixed (both sensory and motor) 

  • the spinal nerve splits into two - the dorsal and ventral ramus

The Brachial Plexus (nerves which supply the arm)

  • the Roots - C5, C6, C7, C8 and T1

  • C5 and C6 join to become the Superior Trunk

  • C7 becomes the Middle Trunk

  • C8 and T1 join to become the Inferior Trunk

  • Then each trunk gives off a posterior and anterior division

  • The posterior divisions all join together to form a posterior cord

  • The middle trunk gives off an anterior division which joins from the superior trunk to form a lateral cord. And the inferior trunk just keeps going to the anterior division to form the medial cord.

Cord position compared to Artery:

  • The lateral cord is lateral to the artery

  • the posterior cord is posterior to the artery

  • the medial cord is medial to the artery

  • The posterior cord just keeps going and becomes the Radial Nerve

  • The medial and lateral cord will split and join together to form the median nerve

  • The lateral cord continues as the muscular cutaneous nerve

  • The medial nerve continues as the ulnar nerve 

Motor Innervation of the Upper Arm

  • Musculocutaneous Nerve - supplies the anterior compartment;

  1. biceps brachii

  2. coracobrachialis

  3. brachialis

  • Radial nerve supplies the posterior compartment

  • 1. triceps brachii 

Upper Limb 2: Elbow to Hand

L.O. Recall the major landmarks of the humerus, radius and ulna including the ligaments (e.g. annular ligament).

L.O. Demonstrate the structure and movements of the elbow joint.

Bones of the Upper Limb

  1. Arm Proper

  • contains the humerus

  1. Forearm 

  • contains the radius and ulna

  1. Hand

  • contains 8 carpal bones in the hand, 5 metacarpals in the palm and 14 phalanges in the digits

Proximal Humerus

  • greater tubercle

  • lesser tubercle

  • head of humerus

Distal Humerus - Anterior View

  • lateral epicondyle

  • medial epicondyle

  • capitulum

  • trochlea

  • coronoid fossa

  • radial fossa 

  • at the superior end the radius is much smaller than the ulna

  • at the inferior end the radius is much bigger than the ulna

  • the radius articulates with the capitalism

  • the ulna articulates with the trochlea

  • head and neck of the radial as well as the radial tuberosity

Proximal Ulna

  • trochlear notch (where ulna articulates with the trochlear of the humerus)

  • coronoid process - ‘beak like’ projection

  • radial notch - where the head of the radius sits on the ulna

  • olecranon fossa - see it posteriorly on the humerus - big indentation where the olecranon sits when elbow is fully extended

  • the olecranon is the bony point of the elbow at the top of the ulna bone

Elbow Joint

3 separate Articulations make up the elbow joint!

  1. The capitulum and head of radius - allows flexion and extension

  2. Trochlea of humerus and trochlea notch of ulna - allows flexion and extension

  3. Head of radius and radial notch of the ulna - involved in pronation and supination of the forearm.

Stability of the Elbow Joint

  • fibrous membrane of the joint contributes to the stability 

  • thickened medially and laterally to form the collateral ligaments

  • support flexion and extension movement

Taking the ligaments away you can see…

  • external surface of the joint capsule reinforced laterally

  • cuffs the head of the radius

  • annular ligament of radius

  • allows the head of the radius to slide against the radial notch of the ulna and pivot on the capitulum during pronation and supination

At the Distal End…

  • distally the ulnar notch of the radius slides anteriorly over the convex surface of the head of the ulna

  • bones held together during this movement by

  1. the articular disc at the distal radio-ulnar joint

  2. the interosseus membrane

Muscles of Pronation and Supination

Pronation = inward rotation of the forearm

Supination = outward rotation of the forearm

  1. Two muscles supinate the hand

  • biceps brachii

  • supinator

  1. Two muscles pronate the hand

  • pronator teres

  • pronator quadratus

Pronation

Pronator teres

  • Origin: medial epicondyle of the humerus

  • Insertion: lateral surface of the radius midway along shaft

Pronator quadratus

  • Origin: anterior surface of the distal end of the ulna

  • Insertion: anterior surface of the distal end of the radius

Action of movement

  • as muscles contract the distal end of the radius is pulled over the ulna

  • this causes tendon of biceps brachii muscle and the supinator muscle to become wrapped around the proximal end of the radius

  • when these muscles contract they unwrap from the bone, producing supination.

L.O. Describe the bones of the wrist/hands with particular attention to carpal bones and the carpal tunnel.

L.O. Classify the muscles of the forearm and their associated movements on the wrist and the hand.

Bones of the Upper Limb - The Hand

Carpal Bones -

Straight Line To Pinky

Here Comes The Thumb

  • Scaphoid

  • Lunate

  • Triquetrum

  • Pisiform

  • Hamate

  • Trapezoid

  • Capitate

  • Trapezium

The Anatomical Snuffbox

  • this region is highly palpated in order to see if the scaphoid bone is broken

  • the scaphoid bone has a good blood supply so if this is interrupted complications can occur 

X - RAY

Wrist Joint

Articulation between;

  • the distal end of the radius and the articular disc overlying the distal end of the ulna

  • ellipsoid concave

  • scaphoid and lunate

  • ellipsoid convex

Radius

  • the scaphoid and the lunate articulate with the radius

  • sometimes a small part of the triquetrum may articulate with the articular disc of the distal radio-ulnar joint, but not directly with the radius itself 

Ulna

  • the ulna does not directly articulate with any carpal bone.

  • instead, the triangular fibrocartilage complex (TFCC) sits between the ulna and the proximal carpal row (mainly the triquetrum and lunate)

Meta Carpals

  • I, II, III, IV, V (from thumb to pinky finger)

Muscles of the Forearm

  • muscles in the anterior compartment help flex the wrist joint and fingers

  • muscles in the posterior compartment help extend the fingers and wrist joint

Anterior (flexor) Compartment

Muscles in this compartment;

  • move the wrist joint

  • flex the fingers and thumb

  • pronate the hand

Arranged in three layers

  • superficial

  • intermediate

  • deep

Deep Layer

Made of three muscles

  1. Flexor digitorum profundus

Action;

  • flex the metacarpophalangeal joints (knuckles)

  • flexes the proximal and distal interphalangeal joints of four finger

  • flexes the wrist

  1. Flexor pollicis longus

Action; flexes the thumb

  1. Pronator quadratus

Action; pronating the forearm

Intermediate Layer

Flexor digitorum superficialis muscle

Action;

  • flexes metacarpophalangeal joint

  • flexes the proximal interphalangeal joint of four fingers

  • flexes the wrist

The Carpal Tunnel

  • tendons of flexor digitorum profundus, flexor digitorum superficialis and flexor pollicis longus pass through carpal tunnel

  • formed by the carpal bones and flexor retinaculum (prevents bowing of tendons)

  • median nerve innervates this area

  • compression of this nerve causes rheumatoid arthritis or carpal tunnel syndrome

Carpal Tunnel Syndrome

  • increased pressure in the carpal tunnel

  • pins and needles and pain in distribution of median nerve

  • weakness and loss of muscle bulk of thenar muscles

Treatment;

  • reducing inflammation (rest/splint/steroids)

  • surgical decompression of the flexor retinaculum

Superficial Layer

Four muscles all with a common origin on the medial epicondyle of the humerus

  1. Flexor carpi ulnaris

  • Action - flexes and adducts the wrist 

  1. Palmaris Longus

Absent in ~15% of the population

Action; flexes the wrist

  1. Flexor carpi radialis

  • tendon is easily palpated in the wrist and is usually used to find the pule in the radial artery

  • action; flexes and abducts the wrist

  1. Pronator Teres

  • rotates radius on its axis

L.O. Classify the muscles of the forearm and their associated movements on the wrist and hand.

L.O. Illustrate the vascular supply of the upper limb.

L.O. Discuss the innervation of the hand.

L.O. Describe the contents and the boundaries of the cubital fossa (brachial artery, cubital vein and median nerve and their relationship to each other). 

Extensor Compartment (Posterior view of the forearm)

Muscles in this compartment;

  • move the wrist joint

  • extend the fingers and thumb

  • supinate the hand

Arranged into two layers

  • superficial

  • deep

The Deep Layer

  • there are 5 muscles in the deep layer of the posterior forearm

  1. Abductor pollicis longus; abduct the thumb at joint between metacarpal and trapezium.

  1. Extensor pollicis brevis

  • tendon forms the lateral border of the anatomical snuff box 

  • action; extends the metacarpopharangeal and carpometacarpal joints of the thumb

  1. Extensor pollicis longus

  • tendon forms the medial border of the anatomical snuffbox

  • action: extends joints of the thumb

  1. Extensor Indicis

  • action: accessory extensor of the index finger

  1. Supinator

  • it is wrapped around the radius, once it contracts it will try to unravel itself and cause supination

The Superficial Layer of the Posterior Forearm

  • seven muscles

  • all originate from the supraepicondylar ridge and lateral epicondyle of the humerus

  1. Brachioradialis

  • Action; accessory flexor of the elbow joint as it is anterior to that joint even though it is in the posterior compartment

  1. Extensor carpi radialis longus

  • Action: extends and abducts the wrist

  1. Extensor carpi radialis brevis

  • Action: extends and abducts the wrist

  1. Extensor digitorum

Action: major extensor of the four fingers

  1. Extensor digiti minimi

Action: accessory extensor of the little finger

  1. Extensor carpi ulnaris

Action: extends and adducts the wrist

  1. Anconeus

Action: accessory extensor of the elbow and abducts the ulna during pronation.

Arteries of the Upper Limb

  • right subclaviar artery

  • axillary artery

  • brachial artery

  • radial artery

  • ulnar artery

  • subclavian veins

  • axillary veins

  • brachial veins

  • radial veins

  • ulnar veins 

Innervation of the Hand

  • radial nerve innervates thumb and side of the thumb, first finger, middle finger and half of the ring finger on the dorsal view

  • median nerve innervates the thumb, index finger, middle finger and half of the ring finger in the palmar view

  • the ulnar nerve innervates the pinky finger and half the ring finger on both sides of the hand

Cubital Fossa

  • important transition area between the arm and forearm

  • formed by: 

  • line between the epicondyles forms a ridge 

  • when taking blood pressure readings, the clinician places the stethoscope over the brachial artery in the cubital fossa

A way to remember is:

Really need (radial nerve)

Beer to (biceps tendon)

Be at (brachial artery)

My nicest (median nerve)

Cubital Fossa - Roof

MSK: Cartilage of the Joint

L.O. Describe the different types of cartilage.

L.O. Describe fibrocartilage, its function and location.

L.O. Describe hyaline cartilage, its function and location.

L.O. Describe the components of cartilage and their functions.

L.O. Describe the process of wear, lubrication and lambda ratio.

Cartilage composition and function

The Skeletal System and Cartilage

Skeletal tissues are examples of specialised connective tissues (one of the four basic tissue types).

  • the skeletal system is mainly comprised of bone which forms a framework for the rest of the body tissues.

  • adult skeleton also includes cartilage

Cartilage

  • is more elastic than bone

  • forms a semi-rigid part of the skeleton (a firm yet resilient gel)

  • forms a protective layer at many joints surfaces

What is cartilage?

  • cartilage is a specialised form of connective tissue that consists of cells embedded in extracellular matrix (ECM)

  • one cell type = chondrocyte (means cartilage cell_

  • few cells and a large amount of ECM

  • the ECM gives cartilage its unique characteristics

Other important points, Cartilage is….

  • avascular: cartilage does not contain blood supply

  • aneural: cartilage does not have a nerve supply

  • cartilage has no lymphatic supply - so in order to get nutrients and get rid of waste, it relies on diffusion.

  • chondrocytes maintain their phenotype to retain their function in permanent cartilage.

  • limited capacity for regeneration and repair in response to injury or disease

Cartilage Function

Functions:

  • structural support for soft tissues

  • connects bones together

  • sliding area for joints

  • growth in long bone length

  • embryonic skeleton

Chondrocytes

  • they are mature cartilage cells

  • they are located in spaces called lacunae

  • the matrix surrounds the lacunae

  • they are derived from chondroblasts (immature chondrocytes) that become trapped in extracellular matrix that they secreted

  • chondrocytes rely on diffusion for oxygen, nutrients and waste removal

Composition of Cartilage Matrix

Cartilage is hydrated: 70-75% of its wet weight is water.

Rest of the matrix is composed of structural macromolecules.

Collagen typically makes up 15-20% of cartilage.

  • typically type II collagen

  • forms a fibrillar network

  • provides tensile strength

Proteoglycans make up about 2-10% of cartilage.

  • also has non-collagenous proteins as well

Some Cartilage has a Perichondrium - fibrous outer lining of cartilage which also has an inner cellular layer

What are Proteoglycans?

  • a protein

Structure

  • core protein

  • GAG chains (covalently bound)

‘GAG chains - glycosaminoglycan (long unbranched polysaccharide chains of repeating disaccharide units)’

Characteristics of Proteoglycans

  • negatively charged

  • attract Na+ ions

  • osmotic effect, attracts water

Major Proteoglycan of cartilage = aggrecan

Aggrecan in cartilage

Aggrecan is the major proteoglycan of cartilage

  • it contains GAGs that are sulfated, mainly chondroitin sulfate and keratan sulfate

Cartilage also contains hyaluronic acid (HA)

  • this is a non-sulfated GAG

  • HA can bind to the aggrecan core protein via a link protein 

  • forms large aggrecan aggregates

Summary

  • interactions of aggrecans, water and collagen fibrils gives cartilage its resistance to compression (stiffness) and resilience.

Cartilage Types

Three types of cartilage, defined by their histological appearance and ECM:

  • hyaline

  • fibrocartilage

  • elastic

Hyaline

  • most common cartilage in the body

  • you can find it in synovial joints, respiratory passages, costal cartilages and foetal skeleton

Fibrocartilage

  • find it in very specific places

  • pubic symphysis, intervertebral discs, menisci, articular discs (TMJ and sternoclavicular), entheses (ligament and tendon attachments to bone)

Elastic cartilage

You find it in….

  • pinna of ear

  • external auditory meatus

  • auditory tube

  • epiglottis

Histology of Cartilage

Function of hyaline cartilage

  • resists compression

  • provides cushioning, smooth, and low-friction surface for joints

  • provides structural support in respiratory system 

  • forms foundation for development of fetal skeleton and further endochondral bone formation and growth

  • the perichondrium is present on nearly all types of hyaline cartilage except at the articular surface and in a growth plate (epiphyseal plates)

Perichondrium - fibrous outer lining of cartilage which also has an inner cellular layer

Function of elastic cartilage

  • provides flexible support for soft tissues

  • has a perichondrium

Function of Fibrocartilage

  • resists deformation under stress

  • does not have a perichondrium

All three of these tissues have chondrocytes and chondroblasts

Characteristics of Extra cellular matrix

  1. Hyaline cartilage ECM

  • contains only Type II collagen fibrils

  • aggrecan monomers 

  1. Elastic cartilage ECM

  • contains only Type II collagen fibrils

  • elastic fibres

  • aggrecan monomers

  1. Fibrocartilage ECM

  • Type I and II collagen fibres

  • proteoglycan monomers: aggrecan (secreted by chondrocytes) and versican (secreted by fibroblasts)

Growth and repair of cartilage is very limited.

  • cartilage can try to repair, but it commonly forms scar tissue composed of fibrocartilage which does not have the right mechanical properties

The appearance of Hyaline cartilage

  • hyaline means glossy

  • hyaline cartilage has a translucent, glassy appearance

  • it is the most common type of cartilage

The appearance of Elastic cartilage

  • lots of elastic fibres, that are rich in the protein elastin

  • elastic cartilage is more flexible

  • when bent, it will bounce back to its original form

The appearance of Fibrocartilage

  • durable and tough due to presence of more type I collagen fibres

  • a mixture of hyaline cartilage (collagen type II) and dense fibrous connective tissue (collagen type I)

  • resists compression, absorbs shock, and prevents damage

  • found in sites subjected to high tensile and compressive forces.

What is articular cartilage?

  • it is hyaline cartilage that covers the ends of bones involved in a joint (i.e. articular surface of synovial joints)

  • articular cartilage is remnant of the original hyaline cartilage template of developing bones, that persists through life.

  • articular cartilage is divided into four zones

  • articular cartilage is in contact with subchondral bone

The Four Zones of Cartilage

Zone 1: Superficial or tangential) zone

  • elongated and flattened chondrocytes

  • collagen is parallel to the articular surface

Zone 2: Transitional/middle zone

  • rounder chondrocytes distributed randomly in the matrix

  • collagen fibrils are less organised and oblique to the surface

Zone 3: deep (radial ) zone

  • small, round chondrocytes arranged in columns

  • collagen fibrils are perpendicular to cartilage surface

Zone 4: Calcified Zone

  • large, hypertrophic chondrocytes

  • collagen is perpendicular to the cartilage surface

Articular cartilage resists mechanical load

  • the negatively charged GAG sidechains of aggrecan repel each other and attract water

  • this increases matrix volume

  • expansion of the matrix is limited by the collagen network (tensile strength)

Cartilage Loading

  • compression pushes GAG side chains closer together and releases water, decreasing the matrix volume

  • decompression (unloading) allows re-expansion of the molecules and matrix volume

Synovial membrane and fluid

  • articular surfaces are in contact with each other at a synovial joint (or have an intervening disc)

  • must be lubricated to lower friction and allow wide range of movement

All synovial joints have a joint capsule and synovial cavity:

  • outer fibrous membrane

  • inner synovial membrane

  • encloses the synovial cavity which is filled with synovial fluid

Synovial membrane function

Specialised connective tissue

  • not epithelial! Lacks a basement membrane

2 main layers:

  • Intimal lining cells = synoviocytes (Type A = immune cells such as macrophages, type B = fibroblasts)

  • Subintimal matrix = loose connective tissue that is highly vascularised

Functions:

  • to produce synovial fluid

  • to remove cellular and connective tissue debris

  • nutrition

Synovial Fluid

Synovial fluid is an ultrafiltrate of blood plasma.

  • less protein, but similar electrolyte concentrations

Hyaluronic Acid

  • non-sulfated GAG secreted by synoviocytes

  • gives the synovial fluid its high viscosity

  • also helps to maintain the thickness of the lubricating fluid film

Lubricin

  • proteoglycan secreted by both superficial cartilage cells and synovium

  • lubricates the surface of the cartilage

  • stick to the articular cartilage, projecting a highly negatively charged domain that repel each other, preventing the surfaces from touching

Phospholipids are also bound to the articular surface, providing hydrophobicity (repel each other).

When two articular surfaces come into contact they try and repel each other. 

Wear, lubrication and lambda ratio

Wear = the gradual breakdown or erosion of the smooth cartilage

Synovial joints are subjected to an enormous range of loading conditions

Yet under normal circumstances, the cartilage sustains little wear.

How?

A number of lubrication mechanisms to aid articulation.

Fluid film lubrication

  • a thin fluid film separates the articular surfaces

  • load is supported by the increased hydrostatic pressure that develops in the fluid when it is compressed

The three types of fluid film lubrication

a) Hydrodynamic fluid film lubrication; where fluid gets trapped and pressurised within the space, due to perhaps the cartilage becoming deformed as it is depressed, changes shape, trapping some fluid and increasing the pressure in the fluid. This forms a lifting pressure again.

b) Squeeze film; surfaces move towards each other, squeezing fluid and generating pressure

c) boosted;  when the joint is loaded, water is forced into the cartilage rather than the synovial fluid —> this increases the concentration of the hyaluronic acid in the synovial fluid, increasing the viscosity and this helps bear load.

Summary:

Joints use all three of these lubrication mechanisms depending on the load/movement.

—> Fluid film lubrication is the most ideal type of lubrication that we would like to see when we’re loading our joints, however it is not always possible when you are…

  • bearing heavy and prolonged loads

  • geometry incongruence

  • or have low synovial of fluid viscosity

Then boundary lubrication occurs

What is Boundary Lubrication?

  • involves lubricant molecules attached to the articular surface (i.e. lubricin, phospholipids).

  • prevents the cartilages surfaces coming into direct contact

  • reduces friction and prevents cartilage wear

Mixed Lubrication can occur - where we get boundary and fluid film lubrication occur together.

Lambda Ratio

Lambda ratio is the minimum film thickness (h) needed in relation to the roughness of the surfaces.

A higher lambda ratio indicates greater separation between surfaces and suggests a move towards full fluid film lubrication, which is the ideal scenario with minimal wear due to low friction.

  •  Model Stribeck curve - where the friction coefficient and the fluid film thickness are plotted as a function of velocity, fluid viscosity and load for the boundary, lubrication and hydrodynamic lubrication regimes.

Lubrication in disease

In healthy joints, the lambda ratio is about 1-3, meaning the joint operates in mixed fluid-film modes of lubrication, maintaining a low friction.

In osteoarthritis where cartilage matrix is altered and cartilage is degraded:

  • surface roughness can increase

  • fluid film thickness can decrease (due to loss of key proteins such as lubricin, aggrecan etc, which can affect osmotic balance)

  • can reduce the lambda towards boundary lubrication, with increased friction —> may increase mechanical wear of the cartilage, alongside non-mechanical changes!

Osteoarthritis

  • it is a heterogenous (a medical condition with diverse multifactorial causes), whole joint disease

  • affects over 500 million people worldwide

  • causes pain

  • leading cause of disability and premature work loss

  • no effective treatment

  • causes degradation of cartilage mass

  • marked by cell stress and ECM degradation

Multifactorial and complex disease

  • all joint tissues have a role

  • cartilage, synovium, discs, bone, osteophytes, fat pad, tendons, ligaments, synovial fluid etc

  • obesity and joint injury increase risk of getting OA

  • inflammation, metabolic alterations and trauma 

OA and ECM

Imbalance between catabolic and anabolic processes

Cartilage

  • increase in enzymes that breakdown matrix

  • e.g. MMPs, aggrecanases, collagenases, low tensile strength, resilience, osmotic effect

Subchondral bone

  • increased bone turnover and sclerosis of the bone adjacent to the cartilage

  • osteophytes (bony spurs)

  • microfractures

What happens in OA?

  • There is excessive activity of matrix degrading enzymes that break down collagen and proteoglycans.

  • Collagen becomes disorganised.

  • Cartilage becomes thinner and cracked, compromising its cushioning function, and causing joint pain and stiffness.

May get cartilage fibrosis as it tries to repair.

  • proteoglycan loss is an early indicator of OA

MSK: Cartilage and Bone Growth

L.O. Describe the embryology of normal limb growth.

L.O. Describe the function and structure of different types of cartilage.

L.O. Describe the functional importance of epiphyseal plates and the process of growth.

L.O. Describe the structure, function and role of chondrocytes in growth.

L.O. Describe how hormones control and modify bone growth.

L.O. Describe the differences between membranous and endochondral ossification processes.

L.O. Describe the process of bone growth, modelling and remodelling.

Three Embryonic Germ Layers

3rd week of human development

—> Gastrulation occurs:

Formation of the trilaminar embryonic disc that contains the primary germ layers.

—> will form all foetal tissues

—> establishment of major body axes

  1. Ectoderm - outer skin which forms the covering of the body as well as nervous system

  2. Endoderm - inner skin which forms the lining of the gastrointestinal and respiratory systems and urogenital systems and associated glands

  3. Mesoderm - middle skin which forms the skeletal, connective and muscle tissues of the body and some organs and glands (everything else basically) - limb bud comes from here

Limb Bud development - from Mesoderm

Week 4

  • Limb buds appear towards the end of the 4th week of development

  • Upper limb bud (26-27 days)

  • Then lower limb buds 1-2 days later

The limb bud consists of a mass of mesenchyme covered by a layer of ectoderm.

Thickening of ectoderm at the apex of each limb bud forms the apical ectodermal ridge (AER).

The AER….

  • promotes outgrowth of the bus

  • bone morphogenetic protein (BMP) is essential for this

  • retinoic acid promotes formation of the limb bud, by inhibiting fibroblast growth factor 8

  • The AER influences growth and development of the limbs along a proximodistal axis

  • FGFs from the AER cause expression of sonic hedgehog which controls anteroposterior patterning

Week 6

  • digital rays being to develop in hand plates

  • 5-8 days later for lower limb (in week 7)

  • these outline the pattern of the digits

  • digital rays are separated by loose mesenchyme

Week 7

  • limbs change considerably

  • loose mesenchyme undergoes apoptosis forming notches between the digital rays, separating future digits

Week 8

  • fingers and toes are now separate digits

  • coordinated limb movement begins

  • hands and feet rotate into position

Limb rotation and adult anatomy

During week 8, the limbs rotate in opposite directions

Upper limb rotates 90 degrees laterally.

  • extensor muscles are on lateral and posterior surfaces

  • thumbs lie laterally

Lower limb rotates 90 degrees medially

  • extensor muscles are on the anterior surface

  • big toe is medial

Limb bud tissues

  • this ectoderm is thickened at the distal end of the limb bud to form the apical ectodermal ridge (AER)

  • The AER is important for regulating limb development

Cells nearest to it remain undifferentiated.

Cells further from it start to become cartilage and muscle.

Limb development proceeds proximodistally.

Three segments to the limb

Limb develops from proximal to distal into its three components

  1. Stylopod = humerus/femur

  2. Zeugopod = radius and ulnar / tibia and fibular

  3. Autopod = carpals, metacarpals and digits / tarsals, metatarsals and digits

Limb Bone development

The Mesenchyme in a limb bud gives rise to bones, ligaments and blood vessels.

As the limb buds elongate in week 5, the mesenchymal models of the bones are formed by cellular aggregations that become chondrification centres. (cells differentiate into chondroblasts).

By the end of week 6, the entire limb skeleton is cartilaginous.

Osteogenesis of long bones begins in 7th week.

  • primary ossification centres in the diaphysis

  • all long bones have ossification centres by week 12

  • primary ossification of carpal bones begins after birth (during first year)

Muscles come from somites (also mesoderm).

Motor and sensory nerves come from spinal cord (ectoderm).

Development of bone and cartilage cells

Key genes expressed during chondrogenic and osteoblastic differentiation.

Key chondrocyte genes:

  • SOX9 (transcription factor)

  • COL2

  • IHH (for hypertrophy)

Key Osteoblast genes:

  • RUNX2 (transcription factor)

  • COL1

  • SP7 (osterix; transcription factor)

  • BGLAP (osteocalcin; marker of bone formation)

IMPORTANT!

Sox9 persists in chondrocytes until they become hypertrophic.

  • induces collagen X

  • inhibits RUNX2 (osteoblast marker)

Key Osteocyte genes:

  • DMP1 (regulates phosphate homeostasis and bone mineralisation)

  • Sclerostin (inhibits bone formation)

When chondrocyte-osteoblast transformation occurs, SOX9 is degraded, allowing expression of RUNX2 (chondrocyte —> osteoblast).

An overview of Joint Formation

  • gene expression is controlled spatially and temporally to cause joint formation. This is the simplified version:

  • cells in the cartilage model express Sox9, Col2 and Dcx. Joint site is determined.

  • Gdf5 expression is activated with other inter-zone-specific genes. Cells in the cartilage model are Sox9, Col2 and Matn1 positive.

  • Gdf5 positive cells that are Matn1 negative become articular chondrocytes

(Gdf5 is critical for articular cartilage development)

  • Joint cavitation occurs and development of other joint tissues occurs (ligaments meniscus etc)

Where does bone come from?

  1. Mesenchyme

  • from mesenchymal membranes

  • intramembranous bone formation

  • most facial bones are formed from mesenchyme

  • skull vault and clavicles are formed from mesenchyme

  1. Cartilage

  • cartilage models that are replaced by bone

  • endochondral bone formation

  • the base of the skull, vertebral column, ribs, sternum, limb girdles and limb bones are formed this way

Both osteogenesis and chondrogenesis are programmed early in development.

Independent processes, under the influence of molecular and vascular events.

Hox genes, BMPs (5 and 7), GDF5, VEGF and other signalling molecules are important in the regulation of cartilage and skeletal development.

B-catenin levels commits skeletal precursors to become chondrocytes and osteoblasts.

Ossification

  • the process of laying down bone

Typical anatomy of a gross long bone

Diaphysis - cylindrical shaft, composed of compact bone.

Epiphysis - expanded ends of the bone.

Metaphysis - between epiphysis and diaphysis.

Medullary cavity

  • surrounded by a shell of compact bone

  • contains bone marrow

  • site of blood production (red marrow) but becomes progressively replaced by adipose tissue (yellow marrow).

Periosteum - outer lining

Endosteum - inner lining

Articular surfaces (hyaline cartilage)

Endochondral Ossification

  • endochondral ossification of a typical long bone

Mesenchymal cells condense and express Sox9.

  • prehypertrophic chondrocytes differentiate and secrete collagen type II and other matrix proteins (i.e. proteoglycans) and perichondrium develops in diaphysis region.

  • some chondrocyte become pre-hypertrophic (IHH) and then hypertrophic (enlarged, collagen X), surrounded by a calcified matrix

  • this increases the size of the cartilage model, usually elongating it.

  • A bone collar forms; hypertrophic chondrocytes gives rise to osteoblasts in the region of the perichondrium, forming cortical bone.

  • Ossification begins when the developing bone is invaded by blood vessels that branch from limb vasculature.

  • blood vessels bring pre-osteoblastic cells that differentiate into osteoblasts.

  • osteoblasts can also arise from the hypertrophic chondrocytes (degradation of Sox9)

  • these osteoblasts form the primary spongiosa, by laying down collagen type I and the mineralised bone matrix. The cartilage matrix is broken down and replaced by bone.

  • ossification then spreads from the primary ossification centre towards the epiphyses, forming a loose trabecular network of bone.

  • blood vessels also bring osteoclasts, which are important for remodelling the growing bone (and throughout adult life)

At birth, the diaphysis has a bone collar and trabecular bone core. The epiphyses are still cartilaginous.

  • at birth, secondary ossification centres develop (with blood vessels) in the epiphyses, which gradually ossify.

  • cartilage remaining at the end of the bone —> articular cartilage.

  • a layer of cartilage persists between the epiphysis and diaphysis (where it is still growing), in the region of the metaphysis.

  • epiphyseal cartilage plate

  • chondrocytes are present in distinct zones: proliferating, pre-hypertrophic and hypertrophic.

  • chondrocytes are in columns, directing growth along the axis of the bone.

  • chondrocytes proliferate, differentiate and are then replaced with bone = growth in bone length (interstitial growth).

Growing bone example (mouse)

Hand X-rays

Bone Growth

Length (interstitial growth)

  • bones grow in length via endochondral ossification at the growth plate

  • actively proliferating plate of cartilage

  • converted to trabecular bone

  • progressively increases length of the bone

  • becomes epiphyseal line (after it ossifies)

Width (appositional growth)

  • to grow in width and thicken the cortical bone

  • bone is deposited on the outer surface and resorbed in the inner surface

Intramembranous Ossification

  • the direct formation of bone within membranes (condensed mesenchyme).

  • mesenchyme contains mesenchymal stem cells —> osteoprogenitor cells —> osteoblasts

  • osteoblasts form ossification centres, deposit osteoid and mineralise it. Entrapped osteoblasts will become osteocytes.

  • initially this occurs in isolated islands, but eventually they merge to form trabecular bone. This is woven bone at this stage.

  • tissue becomes vascularised. Mesenchyme on the outer surface of the woven bone condenses to form periosteum.

  • trabecular bone adjacent to the periosteum will be replaced with compact bone.

  • lamellar bone will replace woven bone

Lamellar versus woven bone

  • there are two main patterns of bone identified according to the pattern of collagen forming the osteoid (unmineralised bone matrix).

Woven Bone

  • haphazard organisation of collagen fibres.

  • mechanically weak

  • when osteoblasts produce osteoid rapidly

  • collagen fibres are deposited in an irregular loosely intertwined pattern

  • initially woven bone is all foetal bone (then remodelling takes place and this bone is replaced by more resilient lamellar bone).

Lamellar Bone

  • regular parallel alignment of collagen into sheets called lamellae

  • mechanically strong

  • virtually all bone in the healthy adult is lamellar

Bone Physiology

Bone is constantly being remodelled throughout life by bone-remodelling units composed of osteoblasts and osteoclasts.

Bones can change their shape and density in response to mechanical load.

Physiological aspects of bone:

  • the physiology of calcium and phosphate metabolism, formation of bone and teeth, and regulation of vitamin D, parathyroid hormone (PTH), and calcitonin are all closely intertwined.

  • phosphate homeostasis and calcium homeostasis are closely associated. 

What affects bone growth?

Diet

  • need adequate intake of vitamins and minerals

  • calcium and phosphorus

  • vitamin C for collagen synthesis, and differentiation of osteoblasts into osteocytes

  • vitamin A for stimulation of osteoblasts

Slight changes in calcium can cause extreme immediate physiological effects.

Hormones

  • IGFs (insulin-like growth factors) stimulate bone growth and maintain bone mass.

  • IGFs produced by bone and liver.

  • IGF production is stimulated by hGH (human growth hormone) produced by the anterior pituitary

  • thyroid hormones and insulin are also important

Far lower or higher phosphate changes does not cause immediate effects on the body.

i.e. low calcium causes nervous system excitement and tetany

i.e. high calcium depresses the nervous system and muscle activity

Bone Matrix

80% of bone is cortical

20% of bone is trabecular

  • much more porous

  • greater surface area

  • greater turnover

Bone is composed of:

  1. Tough organic (protein) matrix (i.e. collagen for tensile strength)

  • inorganic matrix (i.e. bone mineral)

  1. Inorganic matrix (i.e. bone mineral)

  • calcium phosphate salts in the form of hydroxyapatite

  • compressive strength

The concentrations of calcium and phosphate ions in extracellular fluid are considerably greater than those required to cause precipitation of hydroxyapatite.

Why do all tissues not mineralise?

Inhibitors are present in almost all tissues, and the plasma, to prevent precipitation of hydroxyapatite.

An example of an inhibitor would be: Pyrophosphate

In bone, mineralisation of bone matrix occurs when calcium salts are deposited.

This is regulated mainly by pyrophosphate.

Pyrophosphate is then regulated by 3 other molecules secreted by osteoblasts:

  1. TNAP (tissue specific alkaline phosphate)

  • this breaks down pyrophosphate to allow mineralisation.

  1. NPP1 (nucleotide pyrophosphate phosphodiesterase 1)

  • produces pyrophosphate outside the cell

  1. ANK (ankylosis protein)

  • increases extracellular pyrophosphatase

Bone Remodelling

Bone is continuously remodelled

Osteoblasts deposit bone.

  • osteoblasts found on surfaces of bone

  • active on about 4% of all bone surfaces

Osteoclasts resorb bone.

  • found on surfaces of bone

  • normally active on <1% bone surfaces

  • PTH controls their activity

Why is it continuously remodelled?

  • adjust to load: strengthen and change shape

  • old bone can become brittle and weak: must be replaced.

  • blood calcium levels

Bone remodelling cycle

The Innervation of the Upper and lower limb

L.O. Outline the functional units of the nervous system and how it is divided.

L.O. Describe the origin and structure of spinal nerves.

L.O. Define the difference between dermatomes versus myotomes including their embryological origin.

The Central Nervous System

  • the brain and the brain stem AND the spinal cord

  • responsible for integrating, processing and coordinating sensory data and motor command.

  • also responsible for higher functions such as intelligence, memory, learning and emotion.

The Peripheral Nervous System

  • consists of all the neural tissue EXCEPT the brain and spinal cord.

  • delivers sensory information to the CNS

  • carries motor demands to the peripheral tissues and systems.

  • functionally divided into afferent (carry signals toward the CNS) and efferent (carry signals away from CNS to periphery)

A Single Spinal Nerve

Dermatomes and Myotomes

Myotome Embryology

  • a golden rule of anatomy - when a muscle migrates it brings its nerve supply with it

  • a single spinal nerve can supply a single muscle = mytome

  • a single spinal nerve can supply a group of muscles = myotome

  • myotomes can fuse together. This is why multiple spinal levels may supply a single muscle. The portion of the muscle supplied by a single spinal nerve.

L.O. Describe the structure and major nerves of the brachial and lumbar plexuses.

L.O. Revise ulnar, median and radial nerves and describe how to test each of these.

Brachial Plexus

  • the ulnar nerve is sitting on the median side of the brachial artery

  • the median nerve starts on the lateral side of the brachial artery and then crosses over to lie on the medial side of the brachial artery

  • the radial nerve is posterior to the brachial artery

The Radial Nerve

  • the radial nerve emerges into the posterior compartment through the gap called the triangular interval

  • triceps are medial to the radial nerve

  • teres major is superior to the radial nerve

Cutaneous Innervation

The Ulnar Nerve

  • the ulnar nerve sits on the medial side of the auxiliary artery of the brachial artery

  • it travels into the forearm, just posterior to the medial epicondyle

  • when you hit your funny bone you are actually hitting your ulnar nerve

  • in the forearm the ulnar nerve runs between the flexor carpi ulnaris and the flexor digitorum profundus

Cutaneous Innervation

The Median Nerve

  • the median nerve starts in the lateral part of the brachial artery before crossing over to the medial part of the artery and entering the forearm through the space known as the cubital fossa

  • the nerve travels through the forearm between the two heads of the pronator teres before lying in the same plane as the ulnar nerve (the surface of the flexor digitorum)

  • the median nerve enters the hand through the carpal tunnel

Cutaneous Innervation

  • the median nerve has a branch called the palmer branch which innervates the cutaneous surface of the hand

Testing the integrity of the nerves of the upper limb

Radial Nerve

If injury occurs in the arm when the nerve is in the radial groove (usually humeral break)

You get:

  • weakness of triceps brachii as medial head of triceps is affected

  • characteristic wrist drop - extensor carpi muscles are paralysed and therefore cannot counteract flexor carpi muscles

  • inability to extend metacarpophalangeal joints and thumb

  • if injury occurs in forearm and affects the deep branch of the radial nerve you get the inability to extend the metacarpophalangeal joint

Ulnar Nerve

Ulnar nerve injury commonly occurs when the medial epicondyle fractures

  • results in the loss of power during wrist adduction. During flexion on the wrist the hand will be drawn to the lateral side due to flexor carpi radialis

  • affects the intrinsic muscles of the hand - the person is unable to make a fist as they cannot oppose the thumb. The person will have extended MCP joints and flexion of the digits 2 and 3. Person will be unable to adduct and abduct the digits

  • the person will also have the parathesia of the medial part of the hand.

Median Nerve

When severed in the elbow region

  • difficulty in flexion of the interphalangeal joints (except the 4th and 5th digits which are supplied by the medial part of the flexor digitorum profundus (ulnar nerve)

  • cannot flex the 2nd and 3rd digits

Carpal Tunnel Syndrome

  • loss of sensation on the lateral 3 and a half digits. Palm unaffected

  • difficult to oppose thumb due to thenar muscles being affected

L.O. Describe the innervation of the sciatic and femoral nerves including how you test them.

L.O. Illustrate the importance of the correct location of intramuscular injections (gluteus maximus).

Lumbosacral Plexus

The lumbosacral plexus is formed from the ventral rami of L1-S4.

It gives rise to…

The femoral nerve

  • motor to the muscles of the anterior compartment

  • sensory innervation to the anterior thigh, anteromedial knee, medial leg and foot

The obturator nerve

  • motor to the muscles of the medial compartment

  • sensor innervation to the proximal medial thigh

The sciatic nerve

  • motor to the muscles of the posterior compartment and all the muscles in the leg and foot

  • sensory innervation to the lateral leg and lateral, dorsal and planter surface of the foot

The Obturator Nerve

  • the obturator nerve is MOTOR to the adductor muscles of the hip

  • the obturator nerve is medial to the Psoas Major

  • the obturator nerve travels down the pelvic brim and then exits via this obturator foramen

Sensory Supply

The Femoral Nerve

  • the femoral nerve is motor to the Quadriceps muscle and sartorius

  • the femoral nerve travels close to the sartorius muscle

  • femoral nerve helps extension of the knee

  • femoral nerve gives sensory supply to below the knee

The Sciatic Nerve

  • the sciatic nerve is motor to the hamstrings and all muscles of the leg and foot

  • thick nerve

  • you can use the piriformis muscle to find the sciatic nerve

  • sciatic nerve innervates the hamstrings

  • sciatic nerve divides at the knee; tibial nerve and the fibular nerve

  • the tibial nerve travels down the calf behind the tibia, supplying muscles in the posterior compartment and skin on the back/sole of the foot before splitting into the medial and lateral plantar nerves in the foot.

  • the fibular nerve divides into a deep fibular nerve (peroneal nerve) which goes to the anterior compartment, and the superficial fibular nerve which goes to the lateral compartment.

Cutaneous Innervation

Intermuscular Injections

  • when giving injections you have to avoid the sciatic nerve

  • stick to the upper lateral quadrant