THE RADIAL NERVE COURSE & BRANCHES: The radial nerve is formed from the posterior cord of
the brachial plexus. It passes out of the posterior axilla between the long head of triceps & the
humerus to run in the spiral groove on the back of the humerus. In its course the deep brachial artery
accompanies the nerve. Medial muscular branches to the long & medial heads of triceps are given off
before the nerve reaches the spiral groove. In the spiral groove the nerve gives off posterior muscular
branches to the medial & lateral heads of triceps & anconeus, & the posterior cutaneous nerve of the
forearm. The nerve leaves the spiral groove & passes anteriorly through the lateral intermuscular
septum to lie between brachialis & brachioradialis. At this point the nerve gives off lateral muscular
branches to the lateral part of brachialis, the brachioradialis & the extensor carpi radialis longus. On
reaching the front of the lateral epicondyle the nerve divides into terminal superficial & deep branches.
The superficial branch is sensory & passes to the back of the hand from below the brachioradialis
tendon. In the hand the nerve innervates the lateral three & a half digits to the nail bed of the thumb &
the proximal IP joints of the other digits. The deep branch gives off innervation to the extensor carpi
radialis brevis muscle before piercing the supinator muscle to form the posterior interosseous nerve.
The posterior interosseous nerve innervates the extensors of the wrist, thumb & fingers.
RADIAL NERVE INJURY: The radial nerve may be injured in the axilla, in the spiral groove & in the
posterior compartment of the forearm. In the axilla the nerve can be compressed (by a crutch, or by a
chair-back), or stretched by dislocation of the shoulder joint. In this case the elbow extensors &
extensors of the wrist & digits are paralysed, resulting in wristdrop. There is a sensory loss to a narrow
strip of skin on the back of the forearm & on the dorsum of the hand & lateral three & one half digits.
Injury to the radial nerve in the spiral groove presents a different picture. Injury at this site is either
due to compression against the humerus or fracture of the humerus. Injury most commonly occurs
distal to the origin of the nerve supply to the elbow extensors & the ctaneous supply to the forearm.
The loss therefore results in wristdrop & a small area of sensory loss on the dorsum of the hand &
digits. The radial nerve may also be injured in fractures of the proximal radius, resulting in loss of the
extensons of the digits. Extensor carpi radialis will be undamaged & may be able to extend the wrist.
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THE MEDIAN NERVE: COURSE & RELATIONS: The median nerve is formed in the axilla by a
branch from each of the lateral & medial cords. The nerve contains fibres from C6,7,8,T1 & may also
contain C5 fibres.. The two roots of the median nerve arise on either side of the axillary artery & fuse
to form the median nerve anterior to the artery. The median nerve lies close to the brachial artery on
its lateral side then midway down the arm it crosses anteriorly to lie medial to the artery. The nerve
enters the cubital fossa lateral to the brachialis tendon & passes between the two heads of pronator
teres to enter the forearm. Just as the nerve enters the forearm it supplies pronator teres, flexor carpi
radialis, palmaris longus & flexor digitorum superficialis. As the nerve passes through pronator teres it
gives off the anterior interosseous nerve which runs along the interosseous membrane to supply the
flexor pollicis longus, pronator quadratus & the lateral half of the flexor digitorum profundus muscles.
The median nerve continues on down the forearm attached to the underside of the flexor digitorum
ssuperficialis, & lying on the flexor digitorum profundus. Just above the wrist the nerve becomes
superficial coming to lie between the flexor digitorum superficialis & flexor carpi ulnaris muscles. At this
point the nerve gives off the palmar cutaneous branch which supplies the central part of the palm &
the thenar eminence. The median nerve then continues through the carpal tunnel into the hand. In the
carpal tunnel the nerve lies anterior & lateral to the tendons of flexor digitorum superficialis. In the
hand the nerve forms a muscular branch & the palmar digital branches. The muscular branch curves
from the lateral side of the nerve to supply the muscles of the thenar eminence. The nerve may arise
in the carpal tunnel. The Palmar digital branches supply the palmar surface of the thumb, index &
middle finger & the lateral half of the ring finger, including the nail beds on the dorsal surface. The
palmar nerves also give off branches to the two lateral lumbrical muscles.
MEDIAN NERVE INJURY: The median nerve can be injured at the elbow or wrist. Injury at the
elbow results in the forearm being in supination, with weak or absent wrist flexion accompanied by
adduction. Flexion of the interphangeal joints of the index & ring finger is lost. The muscles of the
thenar eminence are paralysed & may be wasted. Flexion of the terminal phalanx of the thumb is lost
due to the loss of innervation to flexor pollicis longus. There is also loss of skin innervation over the
palm & three & one half digits.
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THE MUSCULOCUTANEOUS NERVE: COURSE & RELATIONS: The musculocutaneous nerve is
formed from the lateral cord & contains the C5,6,7 nerve roots. The nerve enters the coracobrachialis
muscle & passes through it to lie laterally between the biceps & brachialis muscles. The nerve supplies
all three muscles & terminates as a sensory nerve which emerges from the lateral side of the tendon of
biceps to form the lateral cutaneous nerve of the forearm.
MUSCULOCUTANEOUS NERVE INJURY: The musculocutaneous nerve is rarely injured. If the nerve
is cut by a penetrating wound then sensation will be lost from a narrow strip of skin on the lateral side
of the forearm. Supination & flexion of the forearm will be weakened but not lost since the supinator
muscle will still be intact & innervated by the radial nerve, & the forearm flexors, inervated by the
median & ulnar nerves, & the brachioradialis & extensor carpi radialis longus innervated by the radial
nerve will still produce flexion.
THE AXILLARY NERVE COURSE & RELATIONS: The axillary nerve arises from the posterior cord &
passes backwards out of the axilla through the quadrangular space accompanied by the posterior
circumflex humeral artery. The nerve divides into anterior & posterior branches. The anterior branch
winds around the surgical neck of the humerus to pierce & supply the deltoid muscle before innervating
the skin over the lower aspect of deltoid. The posterior branch supplies the teres minor & the posterior
part of deltoid before passing out to supply the skin over the lower deltoid as the upper lateral
cutaneous nerve of the arm.
AXILLARY NERVE INJURY: The axillary nerve may be injured in dislocations of the shoulder joint,
compression of the axilla with a crutch or fracture of the surgical neck of the humerus. Injury to the
nerve results in paralysis of the teres minor & deltoid muscles, & the loss of sensation over a small part
of the lateral upper arm. Abduction of the shoulder is impaired.
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THE ULNAR NERVE: COURSE & RELATIONS: The ulnar nerve is formed by fibres from the medial
cord. It leaves the axilla to lie on the anterior surface of the medial intermuscular septum until about
half way down the arm where it pierces the septum to run between the medial epicondyle & the
olecranon. It enters the forearm between the two heads of flexor carpi ulnaris. In the uper forearm the
nerve lies between the flexor carpi ulnaris muscles & the flexor digitorum profundus muscles, supplying
half of the latter muscle. About halfway down the forearm the ulnar nerve comes to lie close to the
ulnar artery, lying on its medial side. Above the wrist the nerve gives off a dorsal branch which passes
backwards to supply the dorsal skin of the medial one & one-half digits, & a small palmar cutaneous
branch which runs over the flexor retinaculum to supply the medial palm. The nerve passes into the
hand over the flexor retinaculum together with the artery. In the hand it divides into superficial & deep
branches. The superficial branch supplies palmaris brevis & the skin over the palmar surface of the
medial one & one-half digits. The deep branch pierces between abductor digiti minimi & flexor digiti
minimi to reach the deep palm where it supplies the interossei, adductor pollicis, the medial lumbricals
& opponens digiti minimi.
ULNAR NERVE INJURY: Injury to the nerve at or above the elbow results in paralysis of the medial
half of the flexor digitorum profundus with the loss of flexion of the distal phalanges of the medial two
digits. Flexion of the wrist joint will produce abduction due to the paralysis of the flexor carpi ulnaris.
The hypothenar eminence muscles will be paralysed & the eminence may be wasted. Since the
interossei are paralysed the patient will not be able to hold a sheet of paper between the fingers - loss
of abduction & adduction. Adduction of the thumb is lost due to paralysis of the adductor pollicis
muscle. The patient gets around this loss by strongly contracting the flexor pollicis longus to bring the
terminal phalanx of the thumb against the index finger. The fourth & fifth MCP joints are
hyperextended due to the loss of the lumbricals & interossei, while the interphalangeal joints of the
same digits are flexed. The picture is that of a 'claw hand'. The sensory loss is to the palm & both
palmar & dorsal aspects of the medial one & one-half digits. Injury to the nerve at the wirst spares the
flexor carpi ulnaris & the flexor digitorum profundus so that wrist flexion is normal & the fourth & fifth
interphalangeal nerves are even more flexed into a claw hand.
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LEGEND: 1. Subcostal nerve. 2. Iliohypogastric nerve. 3. Ilioinguinal nerve. 4. Lateral cutaneous
nerve of the thigh. 5. Femoral nerve. 6. Genitofemoral nerve. 7. Obturator nerve
The Lumbar Nerves: The lumbar anterior primary rami contribute to the formation of both lumbar &
sacral nerves. This is done through the formation of a plexus, as for the upper limb nerves. Again the
nerves fall into either anterior or posterior groups. The lumbar plexus forms within the psoas muscle, &
the nerves emerge either at the medial or lateral borders of the psoas, or through the muscle to
emerge on its anterior surface. The nerves emerging from the lateral border of psoas are the
iliohypogastric, ilioinguinal, lateral cutaneous nerve of the thigh & femoral. Emerging from the medial
border of the psoas muscle is the obturator nerve & the lumbosacral trunk.
THE ILIOHYPOGASTRIC NERVE: The iliohypogastric nerve is formed by fibres from L1, with some
contribution from T12. The nerve runs obliquely across the quadratus lumborum muscle behind the
kidney. Close to the iliac crest the nerve pierces the transversus abdomins muscle. Its lateral branch
pierces the muscle of the lateral abdominal wall to supply the skin over the lateral gluteal region. The
anterior branch runs forwards & down wards between transversus abdominis & internal oblique to
supply the skin above the pubis.
THE ILIOINGUINAL NERVE: The ilioinguinal nerve is formed in common with the iliohypogastric
nerve. The nerve lies on the quadratus lumborum muscle & the iliacus until it perforates the body wall
near the anterior iliac crest. It lies between the internal & external oblique to pass through the
superficial inguinal ring. It distributes sensory fibres to superomedial thigh, root of the penis & upper
part of the scrotum in the male, or mons pubis & labium majus in the female.
THE GENITOFEMORAL NERVE: The genitofemoral nerve is formed from L1,2 & passes through the
psoas to emerge on its anterior surface. It runs down wards on the psoas & divides into genital &
femoral branches. The genital branch enters the inguinal canal through the deep inguinal ring to supply
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the cremaster muscle & a small area of overlying skin. The femoral branch passes behind the inguinal
ligament to enter the femoral sheath & supply the skin over the femoral triangle.
LATERAL CUTANEOUS NERVE OF THE THIGH: The lateral cutaneous nerve of the thigh emerges
at the lateral body of the psoas muscle. It forms from the posterior branches of the L2,3 anterior
primary rami. It crosses the iliacus muscle to emerge close to the anterior superior iliac spine. Its
anterior & posterior branches supply the lateral thigh.
THE FEMORAL NERVE: The femoral nerve arises from posterior branches of the L2,3,4 anterior
primary rami. The nerve lies between psoas & iliacus & enters the thigh behind the inguinal ligament,
lateral to the femoral artery. The nerve will be considered further in the section on lower limb nerves.
THE OBTURATOR NERVE: The nerve arises from anterior branches of the L2,3,4 anterior primary
rami. It emerges medial to the psoas muscle & curves around the lateral wall of the pelvis on the
obturator internus muscle. The nerve leaves the pelvis through the obturator foramen as anterior &
posterior branches. An accessory obturator nerve is sometimes present arising from L3,4. The nerve
passes over the superior ramus of the pubis to enter the pectineus.
THE LUMBOSACRAL TRUNK: Part of the anterior branch of the L4 primary ramus & the L5 primary
ramus form the lumbosacral trunk. The trunk lies anterior to the ala of the sacrum to join the S1
anterior primary ramus.
MUSCLE NERVES: The T12 & lumbar primary rami send short nerves into neighboring muscles, the
quadratus lumborum, psoas & iliacus.
THE SACRAL NERVES & THE PELVIS: The sacral anterior primary rami are joined by the
lumbosacral trunk to form the sacral plexus. The plexus lies on the piriformis muscle & projects
towards the inferior border of the piriformis muscle, behind the internal iliac vessels. The superior
gluteal artery passes backwards between the lumbosacral trunk & the S1 nerve, & the inferior gluteal
vessels run between the second & third sacral nerves. The sacral plexus supplies innervation to the
pelvic muscles, gluteal muscles, & perineal muscles. It also forms the sciatic nerve.
SUPERIOR GLUTEAL NERVE: The fibres from the posterior branches of the L4,5S1 anterior primary
rami form the superior gluteal nerve, which leaves the pelvis through the greater sciatic foramen,
above the piriformis muscle. It supplies the gluteus medius & minimus muscles, & the tensor fasciae
latae muscle.
INFERIOR GLUTEAL NERVE: The inferior gluteal nerve arises one root down from the superior, from
L5,S1,2. It leaves the pelvis through the greater sciatic notch below the piriformis. The nerve supplies
the gluteus maximus muscle.
POSTERIOR CUTANEOUS NERVE OF THE THIGH: The nerve is formed one root done from the
inferior gluteal, from S1,2,3. It leaves the pelvis below piriformis to reach the posterior thigh below the
lower border of the gluteus maximus muscle. Branches of this nerve innervate some skin over gluteus
maximus, a small part of the medial thigh, & the posterior thigh including the popliteal fossa.
MUSCULAR BRANCHES: The small muscles of the pelvis, piriformis, obturator internus, the gemelli,
quadratus femoris, levator ani, coccygeus all receive short branches from the plexus.
THE PUDENDAL NERVE: The pudendal nerve is formed from the S2,3,4 roots & leaves the pelvis
through the greater sciatic notch around the sacrospinous ligament. It then runs along the inside of the
ischium in the pudendal canal. The inferior rectal nerve supplies the external anal sphincter & the skin
around the anus. The two terminal branches are the posterior scrotal (labial) nerve, supplying the
scrotum or labia & the perineal muscles, & the dorsal nerve of the penis or clitoris.
THE SCIATIC NERVE: The sciatic nerve is formed by the L4,5,S1,2,3 roots. This large nerve leaves
the pelvis through the greater sciatic foramen, below piriformis. The nerve may split within the pelvis,
or travel either above or through the piriformis muscle.
PARASYMPATHETIC FIBRES: Parasympathetic fibres arise from roots S2,3,4 & are distributed as
the pelvic splanchnic nerves to the pelvic viscera.
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THE FEMORAL NERVE COURSE & RELATIONS: The femoral nerve enters the thigh below the
inguinal ligament, lying on the iliacus. Before entering the thigh the nerve supplies iliacus & pectineus.
The femoral nerve in the thigh divides into anterior & posterior branches. The anterior branch supplies
the sartorius muscles & gives off medial & intermediate cutaneous nerves of the thigh. The posterior
division gives off the saphenous nerve & muscular branches to rectus femoris & the vastus muscles.
The saphenous nerve & the nerve to vastus medialis lie in the subsartorial or adductor canal. At the
knee the saphenous nerve emerges from behind sartorius & accompanies the greater saphenous vein
along the medial side of the leg & foot.
FEMORAL NERVE INJURY The femoral nerve is rarely injured. Injury results in loss of knee
extension & loss of cutaneous sensation on the medial side of the leg & foot. Pain may be felt over the
femoral nerve distribution due to compression of the L2,3,4 nerve roots by an intervertebral disc.
THE OBTURATOR NERVE COURSE & RELATIONS: The obturator nerve from anterior branches of
L2,3,4 anterior primary rami leaves the pelvis through the superior part of the obturator foramen as
anterior & posterior divisions. The anterior branch, lying anterior to adductor brevis supplies the
adductor brevis, pectineus, adductor longus & gracilis. It supplies cutaneous branches to the medial
thigh. The posterior branch supplies obturator externus, adductor brevis & adductor magnus. The
nerve supplies innervation to the knee joint. Pain from the hip joint might be referred to the medial
An accessory
obturator nerve may be present, arising frm L3,4 & passing into the thigh over the superior pubic
ramus. The nerve may supply pectineus, the hip joint & may communicate with the anterior branch of
the obturator.
side of the thigh or to the knee joint since the obturator nerve supplies all three.
OBTURATOR NERVE INJURY: The nerve might be injured in pelvic surgery since it lies on the lateral
wall of the pelvis. In that case the adductors would be paralysed, & there would some sensory loss on
the medial side of the thigh.
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THE SCIATIC NERVE COURSE & RELATIONS: The sciatic nerve is formed in the pelvis by fibres
from the lumbosacral trunk (L4,5) & by fibres from S1,2,3. This thick nerve immediately leaves the
pelvis through the greater sciatic notch, below the piriformis muscle (P on diagram). The nerve may
divide immediately, or may pass either above the piriformis or through the piriformis. In the gluteal
region the nerve lies deep to gluteus maximus, between the greater trochanter (GT) & the ischial
tuberosity(IT). The nerve then passes down the back of the thigh to the apex of the popliteal fossa. In
the thigh the nerve divides into lateral common peroneal & medial tibial divisions. In the upper part of
its course the sciatic nerve supplies the semimembranosus, semitendinosus, the ischial head of
adductor magnus & long head of biceps femoris from its tibial division. The common peroneal division
supplies fibres to the short head of biceps femoris.
SCIATIC NERVE INJURY: The sciatic nerve is commonly injured during intramuscular injections into
the buttocks. The nerve may also be injured by posterior dislocations or fracture dislocations of the hip
joint. Injury to the nerve might result in loss of the hamstrings & calf muscles resulting in loss of knee
flexion, & loss of the muscles of the anterior & lateral compartments of the leg resulting in foot drop.
Cutaneous sensation would be lost over the calf & dorsum, sole & lateral side of the foot.
THE TIBIAL NERVE COURSE & RELATIONS: The tibial nerve passes through the popliteal fossa to
pass below the arch of soleus. In the popliteal fossa the nerve gives off branches to gastrocnemius,
popliteus, soleus & plantaris, & the sural nerve. The sural nerve is joined by fibres from the common
peroneal nerve & runs down the calf to supply the lateral side of the foot. Below the soleus muscle the
nerve lies close to the tibia & supplies the tibialis posterior, the flexor digitorum longus & the flexor
hallucis longus. The nerve passes into the foot below the medial malleolus. Here it is bound down by
the flexor retinaculum in company with the posterior tibial artery. The nerve & artery divide into medial
& lateral plantar branches. The medial plantar nerve supplies the abductor hallucis, the flexor digitorum
brevis, the flexor hallucis brevis & the first lumbrical. Cutaneous distribution of the medial planter nerve
is to the medial sole & medial three & one half toes, including the nail beds on the dorsum (like the
median nerve in the hand). The lateral plantar nerve supplies quadratus plantae, flexor digiti minimi,
adductor hallucis, the interossei, three lumbricals. & abductor digiti minimi. Cutaneous innervation is to
the lateral sole & lateral one & one half toes (like the ulnar nerve).
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THE COMMON PERONEAL NERVE COURSE & RELATIONS: The common peroneal nerve leaves
the popliteal fossa between the tendon of biceps femoris & the lateral head of gastrocnemius. It
crosses behind the head of the fibula & passes laterally around the neck of the fibula (where it may be
palpated). The nerve gives of the sural communicating branch to the sural nerve, & the lateral
cutaneous nerve of the calf. The nerve pierces the peroneus longus muscle to divide into deep &
superficial branches.
THE DEEP PERONEAL NERVE supplies the muscles of the anterior compartment - the tibialis
anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius & extensor digitorum
brevis. The deep peroneal nerve supplies cutaneous branches to the cleft between the big toe & the
second toe.
THE SUPERFICIAL PERONEAL NERVE supplies the muscles in the lateral compartment (peroneus
longus & brevis) & the skin over the anterior lower leg & dorsum of the foot.
COMMON PERONEAL NERVE INJURY: The common peroneal nerve may be injured as it winds
around the neck of the fibula, resulting in foot drop (anterior compartment muscles), & loss of
sensation on the lower anterior leg & dorsum of the foot. The nerve is also at risk in anterior
compartment syndrome. The roots of the nerve may also be compressed by a prolapsed disc, giving
pain over part of the distribution of the nerve - sciatica.
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SELF ASSESSMENT FIND THE LESION:
Use the following information to determine the most likely site of the problem. Note: in practice it is rare that a
nerve is completely transected. In all of the following cases it is assumed that the nerve is completely cut. You
should consider how the patient might present if the nerve in question had only suffered a partial loss.
UPPER LIMB
Case 1.Paralyzed or weak muscles: supraspinatus, biceps, brachialis, deltoid, teres minor.
Loss of sensation down the lateral side of the arm
Ans: Erb-Duchenne Palsy - C5,6 roots torn.
Case 2.Paralyzed or weak muscles: small muscles of the hand. Hand has a clawed appearance.
Loss of sensation on medial side of arm, forearm & palmar surface of the hand & fingers, extending over on to
the nail beds.
Ans: Klumpke Palsy - C8,T1 roots torn.
Case 3. Following axillary lymph node biopsy the patient has a 'winged scapula'.
Ans: Long thoracic nerve to serratus anterior cut.
Case 4. A patient with a sprained ankle now complains of weakness in abducting the arm & loss of sensation over
the lower half of the deltoid muscle.
Ans: Axillary nerve compressed by crutch in axilla.
Case 5. The patient is unable to extend the elbow joint & has 'wrist-drop. There is loss of sensation in a narrow
strip of skin down the back of the arm & forearm, & a small area on the dorsum of the hand.
Ans: Radial nerve damaged in axilla.
Case 6. The muscles of the thenar eminence are paralyzed & wasted. The thumb is laterally rotated & adducted
(note: it says abducted in the handout). Loss of sensation over the palmar surface of the medial three & one half
digits.
Ans: Median nerve at wrist - carpal tunnel syndrome.
Case 7. Flexion of the wrist joint results in abduction. Patient cannot flex the distal interphalangeal joints of the
little & ring finger. Patient cannot hold a sheet of paper between the fingers. Loss of sensation from little & ring
fingers. Flattening of the medial side of the anterior forearm.
Ans: Ulnar nerve at elbow.
Case 8. A patient who has just completed an information technology course is complaining of being unable to
extend her fingers strongly in her right hand. There is no loss of sensation.
Ans: posterior interosseous nerve - posterior compartment syndrome.
LOWER LIMB
Case 1. Quadriceps femoris is paralyzed & the knee cannot be extended. There is a loss of skin sensation over
the anterior & medial sides of the thigh, the medial side of the lower part of the leg & the medial side of the foot.
Answer : Femoral nerve injury above the inguinal ligament.
Case 2. Almost total loss of flexion of knee. Ankle plantar flexed, with 'foot-drop'. Loss of sensation below the
knee except for a medial strip extending down the leg & along the medial border of the foot.
Answer: Sciatic nerve in gluteal region.
Case 3.Patient cannot dorsiflex or evert the foot. 'Foot-drop' is present. Loss of sensation on the anterior & lateral
aspects of the leg & dorsum of the foot.
Answer: Common peronel nerve at fibular neck.
Case 4. Patient cannot plantar flex the foot. Loss of sensation on the sole of the foot.
Answer: Tibial nerve above popliteal fossa.
Case 5.Adduction of the lower limb is weak. Minor sensory loss on the medial side of the thigh.
Answer: Obturator nerve in the pelvis.
Next two cases involve loss of nerve components.
Case 6.Low back pain. Pain over posterior & lateral leg & sole of foot. Weak plantar flexion of big toe & foot.
Unable to walk on toes. Ankle jerk diminished.
Answer: S1 root.
Case 7. Pain over a narrow strip beginning at the back & running laterally around the thigh & down the anterior
surface of the leg. Numbness over a patch of medial thigh just above the knee. Difficulty in rising from a squating
position. Knee jerk diminished.
Answer: L4 root.
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