Roots:The plexus is formed by the anterior primary rami of C5 to C8 nerves along with the bulk of T1 nerve. Occasionally there may be a contribution from C4 or T2 nerves leading to the formation of pre-fixed or post-fixed plexus. The roots emerge from the respective intervertebral foramina to enter the perivascular shealth.
Trunk:Sandwiched between the scalenus anterior and medius muscle, the roots combine to form the trunks. The C5 and C6 roots combine to form the upper trunk, C7 continues
as the middle trunk and C8 and T1 combines to form the lower trunk
Divisions: Behind the clavicle the trunks divide into a anterior and posterior divisions and stream into the axilla.
Cords: In the upper part of the axilla the six divisions combine to form lateral, medial and posterior cords.
The lateral cord is formed by the union of anterior division of the upper and
middle trunks.
The medial cord is the continuation of the anterior division of the lower trunk.
The posterior cord is due to union of the posterior divisions of all the three trunks
Terminal branches: Lower down in the axilla the cords give rise to terminal branches namely the ulnar, median and radial nerves.
Relationship of the brachial plexus:
Roots: These lie between the scalenus anterior and medius muscles. It lies above the second part of the subclavian artery. The classical interscalene approach to the brachial plexus blocks is at the root level.
Trunks: These lie in close relationship to the subclavian artery above the clavicle. Here also they are sandwiched between the scalene muscles. The trunks extend upto the lateral border of the first rib. The subclavian perivascular approach blocks the plexus at this level.
Divisions: they start at thelateral border of the first rib and lie behind the clavicle. The rib hitching technique causes blockade at this level.
Cords: The divisions unite to form cords at the upper part of the axilla. They remain grouped around the axillary artery. The infraclavicular approach causes blockade at the junction of cords and divisions.
Terminal Branches: They are formed lower down in the axilla. The reorganization of the cords to form the terminal branches occurs at the lateral border of the pectoralis minor muscle. The axillary approach causes blockade at this level
ANATOMICAL CONSIDERATIONS:
The anatomic factors which determine the success and complications of the brachial plexus blockade are
The perivascular sheath
The vertical arrangement of the cervical roots
The interconnections – This is due to combining, dividing, recombining and
redividing of the original five cervical roots.
The relationship of the site of needle entry to vital structures.
Perivascular Sheath – Its Importance
The perivascular sheath is a fibrous sheath covering the brachial
Plexus in its entirety. It extends from the origin of the scalene muscles down to middle of upper arm. The potential space formed by this sheath can hold upto 80-100 ml of local anaesthetic.
This sheath gives a classical ‘Pop Off ‘ feeling when pierced by the needle.
This sheath is the single most important factor in determining the success of bracial plexus blockade. The plexus can be blocked by introducing a needle at any point along the sheath. But the site of needle entry determines which components arepreferentially blocked and which compenents are spared. However this can be overcome to a certain extent by increasing the volume of the local anaesthetic and by applying proximal or distal digital pressure.
The suggestion that the covering is discontinuous with septa subdividing the space into separate compartments that clinically prevent the spread of local anaesthetic
However these septal divisions are more prominent in the axilla than above. This probably is the reason for frequent sparing of the radial and musculocutaneous nerves during axillary blockade.As the septa are more prominent in the lower part, there may be more sparing in the infraclavicular approach than in the supraclavicular approach. The perivascular sheath may also be discontinuous leading to spillage of drug out side thesheath.
Vertical arrangement of roots:
This arrangement of the brachial plexus assumes significance in the classical interscalene approach. Here the needle is applied close to the C5 and C6 nerve roots. As the roots are vertically arranged the local anaesthetic will have to travel caudally to reach C8 and T1 level. If the caudal travel of the local anaesthetic is deficient then these roots may be spared leading to poor analgesia in the ulnar nerve distribution. In the infraclavicular approach sparing of the ulnar nerve is rarely seen.
The interconnections:
The interconnections between the original five cervical roots means that the cutaneous distribution of the individual nerve terrioratories differs from the myotomal and detematomal pattern and that the muscular and other deep structures do not underlie the sensory distribution of that nerve. For example blockade of the ulnar nerve at the elbow, produces sensory loss on the ulnar side of the hand but motor loss of the flexor muscles on the anterior aspect.
Site of needle entry and complications:
If site of needle entry is at the C6 level, r=the chances of epidural and
subarachnoid injections are more. The chances of vertebral artery puncture,
phrenic and recurrent laryngeal nerve paralysis are also higher.
If the site of needle entry is close to the clavicle the chances of pneumothorax
and subclavian artery puncture are more.
If the site of needle entry is below the clavicle as in the infraclavicular approach,
complication rate is much less than in the above routes but the chances of
incomplete blockade are more.
In the axillary site apart from accidental artery puncture other complications are
less but chances of incomplete blockade increases
ANATOMY OF FEMORAL NERVE AT GROIN
Candaveric Anatomy of Femoral Nerve at groin
Root Value: L:2, L3, & L4
Course: It enters the femoral triangle by passing behind the inguinal ligament to course posterolateral to the femoral artery. The nerve lies outside the femoral sheath. After coursing for about 3-4 cms it divides into anterior and posterior divisions. Anterior division mainly supplies the sartorius muscle while the posterior division innervates the three vasti muscles and rectus femoris.
ANATOMY OF SCIATIC NERVE
Candaveric Anatomy of Sciatic Nerve
Root Value: L4, L5, S1, S2, S3.
Course: The roots join to form the sciatic nerve on the anterior surface of the piriformis muscle. It is formed due to the union of the following major trunks.
The medial sciatic nerve is due to fusion of the ventral branches of the ventral
rami of L4-S3. This is functionally the tibial nerve.
The lateral sciatic nerve is due to fusion of the posterior branches of the ventral
rami of L4S3. This is functionally the common peroneal nerve.
The nerve comes out of the pelvis through the greater sciatic foramen. Once the nerve crosses the piriformis muscle it lies anterior to gluteus maximus and posterior to obturator internus and quadriceps femoris. The nerve continues through the thigh along the posteromedial aspect of the femur to reach the popliteal fossa. In the fossa it divides into tibial and common peroneal nerve.
ANATOMY OF POPLETEAL FOSSA
Candaveric Anatomy of Popleteal fossa
The popliteal fossa is a quadrilateral space behind the knee joint. It is formed cephalically by Semimembranosus and Semitendinosus muscles medially and biceps femoris laterally. Caudally it is bound on both sides by the neads of the gastrocnemius.
The part of the popliteal fossa above the knee joint can be separated into a triangle by drawing a line over the skin crease. This triangle is further divided into two equal quadrants by a perpendicular line drawn from the apex of the fossa to the skin crease. The lateral quadrant is of importance as the nerve lies here. The popliteral artery is in the medial quadrant. After coursing for 3cm in the fossa, the nerve divides into a tibial and common peroneal nerves.
ANATOMY OF ANKLE BLOCK
Candaveric Anatomy of Ankle Block
Nerves:
Two deep nerves : Posterior tibial, deep peroneal
Three superficial nerves : superficial peroneal, sural, saphenous
Common peroneal nerve
The common peroneal (lateral popliteal) nerve separates from the tibial nerve (L4-5 and S1-2) and descends along the tendon of the biceps femoris muscle and around the neck of the fibula. Just below the head of the fibula, the common peroneal nerve divides into its terminal branches: the deep peroneal and superficial peroneal nerves. The peroneus longus muscle covers both nerves.
Deep peroneal nerve
The deep peroneal nerve runs downward below the layers of the peroneus longus, extensor digitorum longus, and extensor hallucis longus muscles to the front of the leg. At the ankle level, the nerve lies anterior to the tibia and the interoseeous membrane and close to the anterior tibial artery. It is usually "sandwiched" between the tendons of the anterior tibial and extensor digitorum longus muscles. At this point, the nerve divides into two terminal branches for the foot: the medial and the lateral branches. The medial branch passes over the dorsum of the foot, along the medial side of the dorsalis pedis artery, to the first interosseous space, where it divides into two dorsal digital branches for the nerve supply to the first web space between the big toe and the second toe. The lateral branch of the deep peroneal nerve is directed anterolaterally, penetrates and innervates the extensor digitorum brevis muscle, and terminates as the second, third, and fourth dorsal interosseous nerves. These branches provide the nerve supply to the tarsometatarsal, metatarsophalangeal, and interphalageal joints of the lesser toes.
Superficial peroneal nerve
The superficial peroneal nerve (also called the musculocutanous nerve of the leg) is a branch of the common peroneal nerve. The superficial peroneal nerve gives muscular branches to the peroneus longus and brevis muscles. After piercing the deep fascia covering the muscles, the nerve eventually emerges from the anterolateral compartment of the lower part of the leg and surfaces from beneath the fascia 5-10 cm above the lateral malleolus. At this point, the nerve divides into terminal cutaneous branches: the medial and lateral dorsal cutaneous nerves. These branches carry sensory innervation to the dorsum of the foot and communicate with the saphenous nerve medially, with deep peroneal nerve in the first web space and sural nerve on the lateral aspect of the foot.
Sural nerve
The sural nerve is a sensory nerve formed by the union of the medial sural nerve - a branch of the tibial nerve - and lateral sural nerve, a branch of the common peroneal nerve. The sural nerve courses between the heads of the gastrocnemius muscle and after piercing the fascia covering the muscles, emerges on the lateral aspect of the Achilles tendon, 10 to 15 cm above the lateral mallelus. After giving lateral calcaneal branches to the heel, the sural nerve descends 1-1.5 cm behind the lateral malleolus, anterolateral to the short saphenous vein and on the surface of the fascia covering the muscles and tendons. At this level, the nerve supplies the lateral malleolus, Achilles tendon, and the ankle joint. The sural nerve continues on the lateral aspect of the foot supplying innervation to the skin, subcutaneous tissue, fourth interosseous space, and sensory innervation of the fifth toe.
Tibial nerve
The tibial nerve (medial popliteal or posterior tibial nerve) separates from the common popliteal nerve at various distances from the popliteal fossa crease and joins the tibial artery behind the knee joint. The nerve runs distally in the thick neurovascular fascia and emerges at the inferior third of the leg, from beneath the soleus and gastrocnemius muscles on the medial border of the Achilles tendon. At the level of the medial malleolus, the tibial nerve is covered by the superficial and deep fasciae of the leg. It is positioned laterally and posteriorly to the posterior tibial artery, and midway between the posterior aspect of the medial malleolus and posterior aspect of the Achilles tendon. Just beneath the malleolus, the nerve divides into lateral and medial plantar nerves. The posterior tibial nerve provides cutaneous, articular, and vascular branches to the ankle joint, medial malleolus, inner aspect of the heel, and Achilles tendon. It also carries the branches to the skin, subcutanous tissue, muscles, and bones of the sole.
Saphenous nerve
The saphenous nerve is a terminal cutaneous branch (branches) of the femoral nerve. Its course is in the subcutaneous tissue of the skin on medial aspect of the ankle and foot.
