Case 24- Anatomy 2

Question 1

The Adductor cana;

Answer 1

The adductor canal (subsartorial canal/ Hunter canal) is a long (approximately 15 cm), narrow passageway in the middle third of the thigh. It extends from the apex of the femoral triangle to the adductor hiatus in the tendon of the adductor magnus.
It provides an intermuscular passage for the femoral artery and vein, the saphenous nerve, and has the nerve to vastus medialis.

Question 2

The Adductor canal- femoral nerves

Answer 2

Femoral vessels leave adductor canal through the adductor hiatus to enter the popliteal fossa where they become popliteal vessels. The hiatus is a gap between the aponeurotic and the tendinous hamstrings attachments of the adductor magnus.

Question 3

What the adductor canal is bounded by

Answer 3

• Anteriorly and laterally by the vastus medialis.
• Posteriorly by the adductors longus and magnus.
• Medially by the sartorius forming the roof of the canal.

Question 4

Pes anserinus

Answer 4

• The three muscles sartorius, gracilis and semitendinosus arising from the three compartments have a common tendinous insertion, the pes anserinus (L., goose’s foot), into the superior part of the medial surface of the tibia.
• Formed from converging tendons
• They are innervated by three different nerves and provide stability to the medial aspect of the extended knee.

Question 5

Passage of the Femoral nerve (1)

Answer 5

The femoral nerve (L2–L4) is the largest branch of the lumbar plexus. The nerve originates in the abdomen within the psoas major and descends posterolaterally through the pelvis to approximately the midpoint of the inguinal ligament.

Question 6

Passage of the femoral nerve (2)

Answer 6

It then passes deep to this ligament and enters the femoral triangle, lateral to the femoral vessels.
After entering the femoral triangle, the femoral nerve divides into several branches to the anterior compartment of thigh muscles.
It also sends articular branches to the hip and knee joints and provides several cutaneous branches to the anteromedial side of the thigh.

Question 7

Passage of the femoral nerve (3)

Answer 7

The terminal cutaneous branch of the femoral nerve, the saphenous nerve, descends through the femoral triangle, lateral to the femoral sheath containing the femoral vessels. The saphenous nerve accompanies the femoral artery and vein through the adductor canal and becomes superficial by passing between the sartorius and gracilis when the femoral vessels traverse the adductor hiatus at the distal end of the canal. It runs antero-inferiorly to supply the skin and fascia on the anteromedial aspects of the knee, leg, and foot.

Question 8

Sciatic nerve

Answer 8

• Sciatic nerve arises from the anterior and posterior divisions of anterior rami of L4–S3 spinal nerves.
• Enters gluteal region via greater sciatic foramen inferior to piriformis and deep to gluteus maximus. It then descends in the posterior thigh deep to biceps femoris and bifurcates into tibial and common fibular nerves at apex of popliteal fossa
• It supplies no muscles in gluteal region; supplies all muscles of posterior compartment of thigh (tibial division supplies all but short head of biceps, which is supplied by common fibular division)

Question 9

Tibial nerve

Answer 9

• Descends through the popliteal fossa and lies on the popliteus, runs inferiorly on the tibialis posterior with the posterior tibial vessels
• It terminates beneath the flexor retinaculum by dividing into the medial and lateral plantar nerve.
• It supplies the posterior compartment muscles of the leg and knee joint

Question 10

Common fibular nerve

Answer 10

Follows medial border of biceps femoris and its tendon; passes over posterior aspect of head of fibula and then winds around neck of fibula deep to fibularis longus, where it divides into deep and superficial fibular nerves. It Supplies skin on lateral part of posterior aspect of leg via the lateral sural cutaneous nerve and also supplies knee joint via its articular branch

Question 11

Superfical fibular nerve

Answer 11

Arises between fibularis longus and neck of fibula and descends in the lateral compartment of leg; pierces deep fascia at distal third of leg to become subcutaneous. It supplies fibularis longus and brevis and skin on distal third of anterior surface of leg and dorsum of foot

Question 12

Deep fibular nerve

Answer 12

Arises between fibularis longus and neck of fibula; passes through extensor digitorum longus and descends on interosseous membrane; crosses distal end of tibia and enters dorsum of foot. Supplies anterior compartment muscles of leg, dorsum of foot, and skin of first interdigital cleft; sends articular branches to joints it crosses

Question 13

Blood supply to the lower limb up to the common femoral artery

Answer 13

• The abdominal aorta splits into a left and right Iliac artery
• The common iliac arteries then split into an internal and external branch
• The internal iliac artery has several branches which supply the pelvic, gluteal region and thigh. The obturator and inferior gluteal artery enter the thigh
• The external iliac artery becomes the common femoral artery as it crosses under the inguinal ligament to enter the femoral triangle

Question 13

Blood supply to the lower limb up to the common femoral artery

Answer 13

• The abdominal aorta splits into a left and right Iliac artery
• The common iliac arteries then split into an internal and external branch
• The internal iliac artery has several branches which supply the pelvic, gluteal region and thigh. The obturator and inferior gluteal artery enter the thigh
• The external iliac artery becomes the common femoral artery as it crosses under the inguinal ligament to enter the femoral triangle

Question 14

Blood supply to the lower limb= Common femoral artey -> SFA

Answer 14

• The common femoral artery then gives off a deep branch called the profonda femoris (deep femoral artery). This has two main branches the lateral and medial circumflex arteries. The profunda femoris terminates as penetrating branches which perforates the abductor magnus muscle
• After giving off the profunda femoris the common femoral artery continues as the superficial femoral artery (SFA) which travels through the adductor canal which is a muscular canal in the thigh beginning at the femoral triangle and ending at the adductor hiatus it then passes into the posterior compartment of the thigh

Question 15

Blood supply to the lower limb= SFA-> posterior tibial artery

Answer 15

• In the posterior compartment the SFA is known as popliteal artery which passes between the popliteus and the gastrocnemius muscle
• The popliteal artery gives off genicular branches which supply the knee joint and divides into the anterior and posterior tibial artery
• The posterior tibial artery runs in the posterior compartment and gives off the fibular artery which supplies the lateral compartment of the leg

Question 16

Blood supply to the lower limb from the anterior tibial artery

Answer 16

• The anterior tibial artery goes into the anterior compartment of the leg through a gap in the interosseous membrane between the tibia and the fibula. Descends down the leg and at the foot it becomes the dorsalis pedis artery
• The posterior tibial artery enters the foot via the tarsal tunnel winding behind the medial maleosus and splits into the lateral and medial plantar artery which are present on the plantar aspect of the foot. The posterior tibial is palpable inferiorly and posteriorly behind the medial maleosus.
• The dorsal pedis artery gives off the deeper plantar artery between the first and second metacarpals and this anastomoses on the plantar aspect of the foot. With the lateral plantar artery to form the deep plantar arch on the sole of the foot

Question 17

Overview of the veins in the leg

Answer 17

• Superficial veins- in the subcutaneous tissue, independent of the arteries
• Deep veins- deep to the deep fascia (crural fascia) accompanies the arteries
• Valves present- to prevent reflux of the blood and prevent back pressure
• Venous return is enhanced by contraction of muscles around the veins of the lower limbs which pumps blood towards the heart against gravity. Damage to the valves can put pressure on the more superficial valves which can then get damaged. The superficial veins will then become dilated and this is known as varicose veins

Question 18

Superficial veins of the leg- two major superficial veins in the lower limb:

Answer 18

• Just deep to the subcutaneous tissue so very superficial, superficial to the crural fascia
• The dorsal venous network is on the dorsal surface of the foot. The dorsal venous network can take one of two routes, they can go medialy which is the great saphenous vein or laterally which is the small saphenous vein
- The Great saphenous veins and the small saphenus veins

Question 19

Great saphenous veins

Answer 19

Union of dorsal vein of the great toe and the dorsal venous arch of the foot. Largest vein in the body. It ascends anterior to the medial malleolus of the tibia, it ascends along the medial aspect of the leg, passes posteriorly behind the knee. Its between the medial aspect of the patella and the medial aspect of the thigh. In the thigh it returns to a more anterior location, it passes through the saphenous opening in the fascia larta and drains into the femoral vein. Has many tributaries and interacts with the small saphenous vein

Question 20

Small saphenous veins

Answer 20

Arises from the union of the dorsal vein of the little toe with the dorsal venous arch. It arises posterior to the lateral Malleolus. A continuation of the lateral marginal vein of the foot, it ascends up the leg on the midline and sits between the medial and lateral head of the Gastrocnemius muscle. It then drains into the Popliteal vein. The Small Saphenous vein penetrates the Crural fascia as it passes up the midline of the leg

Question 21

Deep veins

Answer 21

• Accompany the major arteries
• Come in pairs (accompanying veins), sandwiched between the two veins is the artery. The veins and arteries are contained within a vascular sheath
• Pulsations of the artery helps move the blood in the veins
• Main deep veins: Anterior tibial vein, Posterior tibial vein, Fibular vein
The anterior tibial, the posterior tibial and the fibular vein unite to form the Popliteal vein. The Popliteal vein lies superficial to the Popliteal artery

Question 22

Anterior tibial vein

Answer 22

On the anterior aspect of the tibia. Arises from the dorsal venous arch of the plexus, perforating veins penetrate the deep fascia and form the anterior tibial vein. It lies on either side of the anterior tibial artery. They ascend up the leg till it meets the interosseous membrane between the tibia and the fibula, the artery and vein pierce the membrane

Question 23

Posterior tibial vein and the Fibular vein

Answer 23

• Posterior tibial vein- formed from the medial and lateral plantar veins. Enters the leg posterior to the medial malleosus. On the posterior aspect of the tibia
• Fibular vein- formed from the medial and lateral plantar veins, located laterally at the fibula

Question 24

Perforating veins

Answer 24

• Penetrate the deep fascia
• Contain valves which stop blood from flowing back to the superficial veins from the deep veins
• When the muscle contract pressure increases in the deep fascia which compresses the veins, stopping blood from going to the superficial veins from the deep veins
• Allow blood to flow between the superficial and deep veins
• Assists in the musculovenous pump- returning blood to the heart from the leg against the forces of gravity
• Goes through the crural fascia

Question 25

‘Calf venous pump’

Answer 25

• The calf venous pump enhances return of venous blood from the lower extremity to the heart.
• Much of the venous blood passes from the superficial veins to the deep veins through the perforating veins that contain valves that allow blood to flow only from the superficial veins to deep veins.
• Blood is pumped upwards in the deep veins by the contractions of soleus and other calf muscles, thus aiding venous return to the heart (calf venous pump).
• Stagnation of blood in these veins predisposes to deep venous thrombosis.

Question 26

Local anaesthesia

Answer 26

• Regional loss of sensation
• Targeting pain transmission- blocks the transmission of the sensory nerve to the spinal cord
• Can be- Topical anaesthesia, Infiltration anaesthesia, Nerve block anaesthesia, Epidural, Spinal anaesthesia
• Desirable features are rapid onset of nerve block, sufficient block duration and lack of local reaction
• First agent was cocaine

Question 27

Generation of action potential

Answer 27

The action potential is driven by the conduction of Na+ and K+ through the membrane. The membrane is depolarised to -50mv and then the voltage gated channels open. Through the channels positive ions into the neurone causing an increase in the action potential, the voltage gated sodium channels then close and inactivate. The opening of voltage gates K+ channels causes positive ions to leave the neurone causing hyperpolarisation of the neurone

Question 28

Local anaesthetics target the Na+ channels

Answer 28

• The large alpha subunit of the Na+ channel contains four homologous domains (I-IV). Each domain is thought to consist of six transmembrane segments in alpha helical conformation and an additional, membrane re-entrant pore (P) loop
• There are additional, non-pore forming beta subunits
• The resting/closed conformation of the channel in which the positive charges of the S4 segments are pulled towards the cell inferior by the resting membrane potential, has a relatively affinity for LA
• On depolarisation, a confirmational change moves the positive charge outward and away from the pore interior and so intermediate/closed, open and inactivated states have a much higher affinity for LA

Question 29

Na+ channels- The voltage sensing S4 segment

Answer 29

The voltage sensing S4 segment has charged residues within it, when there is a voltage across the membrane. If the inside of the cell is very negative then the positively charged segment enters the cell. When the inside of the cell is positive it repels the positive segment and it leaves the cell, this changes the shape of the channels causing opening and closing of the channel. The local anaesthetic does not bind to the closed sodium channels very well but des bind to the intermediate state when it starts to open and the open state. They bind within the pore of the Na+ channel and prevent the movement of ions through the channel, blocking action potentials

Question 30

Electrophysiology of lidocaine

Answer 30

• Local anaesthetics cause both tonic (all the time) and use dependent block of voltage gated sodium channels
• Classical anticonvulsant drugs only show use dependent block and to a slower, lesser degree
• Dramatically reduces the current through the channel through administration of a local anaesthetic

Question 31

Local anaesthetic structure

Answer 31

• Most local anaesthetic consist of a hydrophobic (aromatic) moiety, a linker region and a substituted amine (hydrophilic region)
• Procaine is a prototypic ester-type local anesthetic, esters generally are rapidly hydrolyzed by plasma esterase contributing to the relatively short duration of drugs in this group
• Lidocaine is a prototypic amide-type local anaesthetic, these structures generally are more resistant to clearance and have longer durations of action

Question 32

Structure activity relationships and physiochemical properties of local anaesthetics- Hydrophobicity

Answer 32

• Hydrophobicity increases both the potency and the duration of action of the local anaesthetics, association of the drug at hydrophobic sites enhances the partitioning of the drug to its sites of action and decreases the rate of metabolism
• The receptor site for these drugs on Na+ channels is thought to be hydrophobic, so that receptor affinity is greater for the motor hydrophobic drugs
• Hydrophobicity also increases toxicity so the therapeutic index is decreased for more hydrophobic drugs

Question 33

Structure activity relationships and physiochemical properties of local anaesthetics- Molecular size

Answer 33

• Molecular size increases the rate of dissociation of local anaesthetics from their receptor sites. Smaller drug molecules can escape from their receptor site more rapidly
• Important in rapidly firing cells in which local anaesthetic bind during action potentials and dissociate during the period of membrane repolarisation. Rapid binding of local anaesthetics during action potentials causes the frequency and voltage dependence of their action
• Linkage group impacts duration of action (esters cleared more rapidly)

Question 34

Differential sensitivity of nerve fibres

Answer 34

• For most patients, treatment with local anaesthetics cause a sequence of blockade of sharp pain, cold, warmth, touch, and finally conduction in motor fibres
• The differentiate rate of block which is exhibited by the fiber mediated different sensation is of considerable practical importance in the use of local anaesthetic
• This is driven by the different types of nerve fibres
• Alpha fibres (fast, myelinated) are the least sensitive to local anaesthetic whereas C fibres (slow, unmyelinated- Dorsal root and Sympathetic) are the most sensitive to be blocked by local anaesthetic. So will block pain sensation but not motor function

Question 35

Local anaesthetics- Prolongation of action by vasoconstrictors

Answer 35

• The duration of action of a local anaesthetic is proportional to the time of contact with the nerve prolonging the period of anaesthesia
• For example, cocaine inhibits the neuronal membrane transporters for catecholamines, increasing the effect of Norepinephrine at alpha adrenergic receptors in the vasculature resulting in vasoconstriction and reduced cocaine absorption in vascular beds where alpha adrenergic effects predominate
• In clinical practise, a vasoconstrictor usually adrenaline is often added to local anaesthetics. The vasoconstrictor will localise the anaesthetic at the desired site and allow the drugs elimination to keep pace with its entry into the systemic circulation, thereby reducing the drugs systemic toxicity

Question 36

Adverse drug reactions- local anaesthesia

Answer 36

• In addition to blocking conduction in nerve axons in the peripheral nervous system, local anaesthetic interfere with the function of all organs in which conduction or transmission of impulses occurs
• These agents affect the CNS, autonomic ganglia, neuromuscular junctions and all forms of muscle (skeletal, cardiac and smooth muscle)
• Lots of adverse reactions can occur when there is systemic administrations of local anaesthetics

Question 37

CNS effects- local anaesthesia

Answer 37

• Following absorption with local anaesthetic toxicity, local anaesthetic may cause CNS stimulation, producing restlessness and tremor that may progress to clonic convulsions
• In general the more potent the anaesthetic, the more readily convulsions may be produced
• Central stimulation is followed by CNS depression, death usually is caused by respiratory failure
• Lidocaine and procaine may alternatively present with mild sedation prior to seizure
• The apparent stimulation and subsequent depression produced by applying local anaesthetics to the CNS presumable is due solely to depression of neuronal activity, a selective depression of the inhibitory neurones likely accounts for the excitatory phase

Question 37

CNS effects- local anaesthesia

Answer 37

• Following absorption with local anaesthetic toxicity, local anaesthetic may cause CNS stimulation, producing restlessness and tremor that may progress to clonic convulsions
• In general the more potent the anaesthetic, the more readily convulsions may be produced
• Central stimulation is followed by CNS depression, death usually is caused by respiratory failure
• Lidocaine and procaine may alternatively present with mild sedation prior to seizure
• The apparent stimulation and subsequent depression produced by applying local anaesthetics to the CNS presumable is due solely to depression of neuronal activity, a selective depression of the inhibitory neurones likely accounts for the excitatory phase

Question 38

Local anaesthesia- Cardiovascular ADR’s

Answer 38

• Local anaesthetics are related to some class 1B antiarrhythmic drugs i.e. Mexilitine
• The primary site of action is the myocardium where decrease in electrical excitability, conduction rate and force of contraction occur
• Negative CV effects usually are soon only after high systemic concentrations are attained and CNS symptoms are evident. However, on rare occasions, low doses of some local anaesthetics will cause cardiovascular collapse and death probably due to an action on the pacemaker or the sudden onset of ventricular fibrillation

Question 39

Main clinical applications of local anaesthesia- Topical/Infiltration anaesthesia and Nerve block anaesthesia

Answer 39

• Topical anaesthesia- used to numb the surface of a body. Reversible block of nerve conduction near the site of administration by targeting free nerve ending in the dermis or mucosa, producing temporary loss of sensation in a limited area
• Infiltration anaesthesia- local anaesthesia produced by injection of the anaesthetic solution directly into the area of terminal nerve endings
• Nerve block anaesthesia- form of regional anaesthesia, local anaesthetic agent is injected directly near a nerve going to a particular area to block pain in that region

Question 40

Main clinical application of local anaesthetics- Epidural and spinal anaesthesia

Answer 40

Epidural and spinal anaesthesia= the main difference is placement. With an epidural, anesthesia is injected into the epidural space. With a spinal, the anaesthesia is injected into the dural sac that contains cerebrospinal fluid. The direct access means that a spinal gives immediate relief. Everything below the spinal level you are injecting into will not feel pain, however the patient will remain conscious

Question 41

Some commonly used local anaesthetics

Answer 41

Lidocaine, Bupivacaine, Cocaine

Question 42

Lidocaine

Answer 42

• An aminoethylamide, is the prototypical amide local anaesthetic with intermediate duration of action
• Produces faster, more intense, longer lasting and more extensive anaesthesia than the equal concentration of procaine
• Lidocaine is dealkylated in the liver by CYP’s to active metabolites. If the rate of leakage in the CNS is equal to the rate of excretion then there wont be any systemic effects
• In humans about 75% of the end metabolite is excreted in the urine
• Used in most forms of clinical local anaesthesia
• Lidocaine patch is a common treatment for localised chronic pain

Question 42

Lidocaine

Answer 42

• An aminoethylamide, is the prototypical amide local anaesthetic with intermediate duration of action
• Produces faster, more intense, longer lasting and more extensive anaesthesia than the equal concentration of procaine
• Lidocaine is dealkylated in the liver by CYP’s to active metabolites. If the rate of leakage in the CNS is equal to the rate of excretion then there wont be any systemic effects
• In humans about 75% of the end metabolite is excreted in the urine
• Used in most forms of clinical local anaesthesia
• Lidocaine patch is a common treatment for localised chronic pain

Question 43

Bupivacaine

Answer 43

• Bupivaine has a wide range of clinical uses as a local anaesthetic, almost any application where a local anaesthetic of long duration is needed
• Its absorbed more slowly than lidocaine
• Long duration of action plus its tendency to provide more sensory than motor block has made it a popular drug for providing prolonged analgesia during labor or the postoperative period. By taking advantage of indwelling catheter and continuous infusions, bupivacaine can be used to provide swelling several days of effective analgesia
• More cardiotoxic than lidocaine due to slower off rate
• Slower onset and duration of action
• Can be administered at the specific site to cause relief

Question 44

Cocaine

Answer 44

• The clinically desired actions of cocaine are the blockage of nerve impulses as a consequence of its local anaesthetic properties and local vasoconstriction secondary to inhibition of the NET
• High toxicity and pro-euphoric actions are due to reduced catecholamine uptake in both the central and peripheral nervous system
• Currently cocaine is used primarily for topical anaesthesia of the upper respiratory tract where its combination of both vasoconstrictor and local anaesthetic properties provides anaesthesia and shrinking of the mucosa as well as in eye surgery where local vasoconstriction is also desirable.

Question 45

The foot is made up of

Answer 45

• Seven tarsal bones — the talus, calcaneus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform
• Five metatarsals
• Five digits — each of which comprises three phalanges (proximal, middle, and distal)—except for the first digit (the great toe), which lacks the middle phalanx

Question 46

Ankle joint- tibia and fibula

Answer 46

Hinge type of synovial joint
• Tibia and fibula form a deep recess for the body of talus
• The distal ends of the tibia and fibula articulate with the superior part of the talus. The Talus is one of the largest Talus bones and its rounded superior surface is the trochlear. The projection of the medial aspect of the inferior end of the tibia is called the Medial malleolus. The lower end of the fibula is the lateral malleolus
• Weight bearing occurs between inferior facet of the tibia and superior surface of talus at the ankle joint.

Question 47

Ankle joint- lateral and medial malleolus

Answer 47

• The lateral and medial malleolus and the inferior aspect of the tibia form the Malleolar mortise in which the troachlear of the talus fits
• Joint is stabilised by medial and lateral malleoli gripping sides of the body of talus as it drops in the mortise during the movement of the joint. This grip is strongest during dorsiflexion of the foot. As the wider part of the trochlear is forced inferiorly inbetween the two Malleoli spreading the tibia and fibula slightly apart

Question 48

Ankle joint- Capsule, instability

Answer 48

• The ankle joint is relatively unstable during platar flexion because the trochlear is narrow posteriorly and lies loosely within the mortus
• A capsule is attached superiorly to the joint at the articular surfaces of the tibia and the malleoli and inferiorly to the talus. The capsule is lined by the synovial membrane, the capsule is thin anteriorly and posteriorly but is supported on each side by strong lateral and medial collateral ligaments

Question 49

Lateral ligaments of the ankle joint

Answer 49

• They all attach to the lateral malleolus and extend anteriorly and posteriorly to the talus. One part of the ligament is attached to the calcaleus which is a bone in the foot
• Commonly injured by inverion- ‘sprained ankle’
• Anterior talofibular ligament- anterior, attaches to the talus and the lateral malleolus of the fibula
• Posterior talofibular ligament
• Calcaneofibular ligament- attaches to the calcular bone and the tip of the lateral malleolus

Question 50

Medial ligament of the ankle joint

Answer 50

• Dislocation rare unless malleoli fractures. An eversion ankle sprain is often associated with a fracture of the fibia
• Medial (deltoid) ligament- four parts attached to the medial malleolus. Its stronger and larger then the lateral ligament
• Superficial parts- Tibionavicular, Tibiocalcaneal, Posterior tibiotalar. The Tibionavicular ligament is from the medial malleolus of the tibia to the Navicular bone. The Tibiocalcaneal ligament is from the medial malleolus to the calcaneus bone. The Posterior tibiotalar is from the tibia to the talar
• Deep parts- Anterior tibiotalar
• Attaches anteriorly at the navicle bone
• Stabilises the ankle joint during inversion and prevents subluxation of the joint
• Difficult for the medial ligaments to be injured as the fibula prevents the ankle from moving far enough to sprain or overstretch the ligaments on the inside of the ankle