++
The cervical plexus innervates muscles, joints, and skin in the
anterior neck (Table 3–1). It is formed by the ventral rami of C1
through C4 (Figures 3–9 and 3–10). The rami form a loop
called the ansa cervicalis that sends branches to the infrahyoid muscles. In
addition, the rami form nerves that pass directly to several structures in
the neck and thorax, including the scalene muscles, diaphragm, clavicular
joints, and skin covering the anterior neck.
++
++
++
++
The ventral ramus of C1 attaches to the ventral rami of C2 to C3. The
attachment forms a loop called the ansa cervicalis, which sends branches to
the infrahyoid muscles. The infrahyoid muscles consist of the omohyoid,
sternohyoid, and sternothyroid muscles. They attach to the anterior surface
of the hyoid bone or to the thyroid cartilage. Contraction of these muscles
moves the hyoid bone or thyroid cartilage downward, effectively opening the
laryngeal aditus. This promotes inspiration. The C1 component also sends
fibers to the thyrohyoid and geniohyoid muscles. Contraction of these
muscles moves the anterior hyoid bone superiorly, closing the laryngeal
aditus. Closure of the laryngeal aditus is necessary for swallowing to occur
safely. This is one of the reasons why high levels of spinal anesthesia
result in airway compromise and the risk of aspiration.
+++
Nerves to Scalene Muscles
++
The ventral rami of C2 to C4 send branches directly to the scalene
muscles, which attach between the cervical spine and ribs. When the cervical
spine is stabilized, contraction elevates the ribs. This promotes
inspiration. Interscalene block may result in block of the scalene muscles
in addition to the phrenic block. This is typically asymptomatic in healthy
patients but may result in acute respiratory insufficiency in patients with
borderline pulmonary function or in those with an exacerbation of asthma or
chronic obstructive bronchitis. It is recommended that more distal
approaches to a brachial plexus block and smaller injection volumes be used
to limit the cephalad extension of the block, as well as shorter acting
local anesthetics to avoid prolonged blockade in case of respiratory
insufficiency.
++
The phrenic nerve is formed by junction of fibers from C3 to C5, and it
innervates the diaphragm. The phrenic nerve descends through the neck on the
anterior surface of the anterior scalene muscle, passing through the
superior thoracic aperture and descending on the walls of the mediastinum to
the diaphragm. In addition to muscular fibers, the phrenic nerve transmits
sensory fibers to the superior and inferior surfaces of the diaphragm. All
approaches to the block of the brachial plexus above the clavicle result in
phrenic blockade (Figure 3–11).
++
+++
Cutaneous Nerves of the Anterior Neck
++
Cutaneous sensory nerves arise from the cervical plexus, pass around
the posterior margin of sternocleidomastoid, and terminate in the scalp and
anterior neck. The minor occipital nerve passes to the posterior auricular
region of the scalp (Figure 3–12). The major auricular nerve
passes to the auricle of the ear and to the region of the face anterior to
the tragus. The transverse cervical nerve supplies the anterior neck. A
series of supraclavicular nerves innervate the region covering the clavicle.
Furthermore, the supraclavicular nerves provide articular branches to the
sternoclavicular and acromioclavicular joints.4
++
++
The brachial plexus innervates muscles, joints, and the skin of the
upper extremity (Table 3–2). It is formed by ventral rami of C5 to
T1 (Figure 3–13). In the posterior cervical triangle between the
anterior and middle scalene muscles, the ventral rami join to form trunks.
C5 and C6 join to form the superior trunk. C7 forms the middle trunk. C8 and
T1 join to form the inferior trunk. All trunks branch into anterior and
posterior divisions. All the posterior divisions join to form the posterior
cord. The anterior divisions of the superior and middle trunks join to form
the lateral cord. The anterior division of the inferior trunk forms the
medial cord. Several terminal nerves arise within the posterior cervical
triangle. Because they arise superior to the clavicle, they are called
supraclavicular branches. The supraclavicular branches include the dorsal
scapular nerve, the long thoracic nerve, the suprascapular nerve, and the
nerve to subclavius.5–7
++
++
+++
Supraclavicular Branches
+++
Dorsal Scapular Nerve
++
The dorsal scapular nerve arises from the ventral ramus of C5. It
follows the levator scapula muscle to the scapula and descends the medial
border of the scapula on the deep surface of the rhomboid muscles. In its
route, the dorsal scapular nerve innervates the levator scapula and rhomboid
muscles.
++
The long thoracic nerve arises from the ventral rami of C5 to C7. It
descends along the anterior surface of the middle scalene to the first rib
and then transfers onto the serratus anterior muscle, which it innervates.
++
The suprascapular nerve arises form the superior trunk. It follows the
inferior belly of the omohyoid muscle to the scapula, passes through the
superior notch into the supraspinatus fossa, where it innervates the
supraspinatus muscle, and continues around the scapular notch (lateral
margin of the scapular spine) to the infraspinatus fossa, where it
innervates the infraspinatus muscle. In addition to muscle, the
suprascapular nerve innervates the glenohumeral joint.
++
The nerve to subclavius arises from the superior trunk. It passes
anteriorly a short distance to innervate the subclavius muscle and the
sternoclavicular joint.
++
The cords of the brachial plexus leave the posterior cervical triangle
and enter the axilla through the axillary inlet. The remainder of the
terminal branches arise within the axilla from the cords.
+++
Posterior Cord Branches
++
The posterior cord forms the upper and lower subscapular nerves,
thoracodorsal nerve, axillary nerve, and radial nerve.
++
The subscapular nerves are formed by fibers from C5 to C6. The upper
subscapular nerve is the first nerve to arise from the posterior cord. It
passes onto the anterior surface of the subscapularis muscle, which it
innervates. The lower subscapular nerve arises more distally. It descends
across the anterior surface of the subscapularis muscle to the teres major
muscle and innervates both the subscapularis and teres major muscles.
++
The thoracodorsal nerve is formed by fibers from C5 to C7. It arises from
the posterior cord, usually between the subscapular nerves, and descends
across the subscapularis and teres major muscle to the latissimus dorsi
muscle. It innervates latissimus dorsi.
++
The axillary nerve is formed by fibers from C5 to C6 (Box 3–1).
It passes from the axilla into the shoulder between the teres major
and minor muscles. It innervates the teres minor. The nerve continues
posterior to the surgical neck of the humerus to innervate the deltoid
muscle. The superior lateral brachial cutaneous branch of the axillary nerve
passes around the posterior margin of the deltoid to innervate the skin
covering the deltoid. In addition to muscle and skin, the axillary nerve
innervates the glenohumeral and acromioclavicular joints. Throughout it
coarse, the nerve is associated with the posterior circumflex humeral artery
and its branches.
++
++
The radial nerve is formed by fibers from C5 to T1 (Box 3–2).
It passes from the axilla into the arm through the triangular space. The
triangular space is located inferior to the teres major between the long
head of triceps brachii and the humerus. The radial nerve innervates the
long head of the triceps muscle and sends a posterior brachial cutaneous
branch to the skin covering this muscle. It descends along the shaft of the
humerus (Figure 3–14) in the spiral groove in association with the
deep radial artery. In the spiral groove, the radial nerve innervates the
medial and lateral heads of the triceps brachii as well as the anconeus
muscles. In addition to innervating these muscles, it sends an inferior
lateral brachial cutaneous nerve to the skin covering the posterior arm and
a posterior antebrachial cutaneous branch to the skin covering the posterior
surface of the forearm. The radial nerve pierces the lateral intermuscular
septum and crosses the elbow anterior to the lateral epicondyle between the
brachialis and brachioradialis muscles. Here it divides into a superficial
and deep branch. The superficial branch descends the forearm on the deep
surface of brachioradialis. Proximal to the wrist, it enters the skin
providing innervation over the dorsum of the hand onto the thumb, index,
middle, and ring fingers to the level of the distal interphalangeal joint.
The deep branch pierces the supinator muscle and descends the forearm along
the interosseous membrane as the posterior interosseous nerve. En route, it
innervates the brachioradialis, extensor carpi radialis longus and brevis,
supinator, extensor digitorum communis, extensor digiti minimi, extensor
carpi ulnaris, extensor indicis, extensor pollicis longus and brevis, and
abductor pollicis muscles. In addition, it innervates the elbow, radioulnar,
and wrist joints.8
++
++
+++
Branches from the Lateral Cord
++
The lateral cord forms the lateral pectoral nerve, musculocutaneous
nerve, and part of the median nerve.
+++
Lateral Pectoral Nerve
++
The lateral pectoral nerve is formed by fibers from C5 to C7. It
crosses the axilla deep to the pectoralis minor muscle and penetrates the
deep surface of pectoralis major muscle, which it innervates. In addition,
it innervates the glenohumeral joint.
+++
Musculocutaneous Nerve
++
The musculocutaneous nerve is formed by fibers from C5 to C7
(Box 3–3). It pierces the coracobrachialis muscle and descends
between the brachialis and biceps brachii muscles (see Figure 3–14). En
route, it innervates all of these muscles. At the elbow, the
musculocutaneous nerve becomes the lateral antebrachial cutaneous nerve and
descends along the superficial surface of the brachioradialis muscle,
innervating the skin covering that muscle. In addition to muscle and skin,
the musculocutaneous nerve innervates the elbow and proximal radioulnar
joints.
++
++
The median nerve is formed by junction of branches from the lateral and
medial cords (Box 3–4). It descends the arm in association with
the brachial artery and crosses the cubital fossa medial to the artery (see
Figure 3–14). At the elbow, it innervates the pronator teres, flexor carpi
radialis, and palmaris longus muscles. It passes into the forearm between
the humeral and radial heads of the pronator teres muscle and descends in
the space between the flexor digitorum superficialis and profundus muscles.
En route, it innervates the flexor digitorum superficialis, the lateral part
of flexor digitorum profundus (fibers to the index and middle fingers), the
flexor pollicis longus, and the pronator quadratus muscles. In addition, the
median nerve sends a palmar cutaneous branch to the skin covering the thenar
eminence. At the wrist, the median nerve passes through the carpal tunnel
deep to the flexor retinaculum. In the hand, the median nerve sends branches
to the thenar muscles, which are the abductor pollicis brevis, flexor
pollicis brevis, and opponens pollicis. The median nerve divides into three
common palmar digital branches, which innerve the lateral two lumbrical
muscles. The common palmar branches divide into proper palmar branches that
innervate the skin of the thumb, index, middle, and ring (lateral half)
fingers. The innervation covers the palmar surface and the nailbeds. In
addition to muscle and skin, the median nerve innervates the elbow and all
joints distal to it.9,10
++
++
The medial cord forms the medial pectoral nerve, medial brachial cutaneous
nerve, medial antebrachial cutaneous nerve, and ulnar nerve and sends fibers
to the median nerve.
+++
Medial Pectoral Nerve
++
The medial pectoral is formed by fibers from C8 to T1. It pierces the
pectoralis minor and ends by branching on the deep surface of the pectoralis
major, both of which muscles it innervates. Contraction of the pectoralis
minor in conjunction with the serratus anterior and rhomboid muscles pulls
the pectoral girdle (clavicle and scapula) against the chest wall when load
is applied to the upper extremity. Without this stabilization of the
proximal joints, movement of the distal joint in the upper extremity would
collapse.
+++
Medial Brachial and Antebrachial Cutaneous Nerves
++
Both nerves descend in the arm associated with the brachial artery. The
medial brachial cutaneous nerve distributes fibers to the skin covering the
medial surface of the arm. Occasionally, the medial brachial nerve joins the
lateral cutaneous branch of the second intercostal nerve to form the
intercostobrachial nerve. The medial antebrachial cutaneous nerve crosses
the cubital fossa and enters the skin to innerve the medial aspect of the
forearm.4
++
The ulnar nerve is formed by fibers from C8 to T1 (Box 3–5).
It descends the arm in association with the brachial artery (see Figure
3–14), pierces the medial intermuscular septum, and crosses the elbow
posterior to the medial epicondyle. After crossing the elbow, the ulnar
nerve descends the forearm between the flexor carpi ulnaris and flexor
digitorum profundus, both of which muscles it innerves. The ulnar
innervation of the flexor digitorum is limited to fibers affecting the ring
and little fingers. Proximal to the wrist, the ulnar nerve sends a palmar
branch to the skin covering the hypothenar eminence and a dorsal branch to
the skin covering the dorsal and medial surface of the hand and the skin
covering the dorsal surface of the ring and little fingers. The ulnar nerve
passes through Guyon's canal (deep to the transverse carpal ligament) to
enter the hand. It divides into a superficial and deep branch. The
superficial branch sends branches to all muscles of the hypothenar eminence,
including the abductor digiti minimi, flexor digiti minimi, and opponens
digiti minimi. Then, it divides into common palmar digital branches, which
in turn divide into proper palmar digital branches. These branches innervate
the skin covering the palmar surface of ring and little fingers. The
innervation continues onto the nailbeds of these fingers. The deep branch of
the ulnar nerve passes beneath the adductor pollicis muscle, which it
innervates. The ulnar nerve sends fibers to the all interosseous muscles in
the hand and to the lumbrical muscles affecting the ring and little fingers.
The ulnar nerve ends by innervating the deep head of the flexor pollicis
brevis muscle.9,10
++
+++
Thoracic Spinal Nerves
++
Thoracic spinal nerves innervate the muscles, joints, skin, and
pleuroperitoneal lining of the thoracic and abdominal walls. Because the
nerves travel within the intercostal spaces, they are called intercostal
nerves. The intercostal nerves comprise the anterior rami of the upper 11
thoracic spinal nerves. Each intercostal nerve enters the neurovascular
plane posteriorly and gives a collateral branch that supplies the
intercostal muscles of the space. Except for the first, each intercostal
nerve gives off a lateral cutaneous branch that pierces the overlying muscle
near the midaxillary line. This cutaneous nerve divides into anterior and
posterior branches, which supply the adjacent skin (Figure 3–15).
The intercostal nerves of the second to the sixth spaces enter the
superficial fascia near the lateral border of the sternum and divide into
medial and lateral cutaneous branches. Most of the fibers of the anterior
ramus of the first thoracic spinal nerve join the brachial plexus for
distribution to the upper limb. The small first intercostal nerve is the
collateral branch and supplies only the muscles of the intercostal space,
not the overlying skin.
++
++
The intercostal nerves can be divided into two groups. One group is
formed by nerves arising from T1 through T5. These nerves remain in the
intercostal spaces throughout their coarse. The second group is formed by
nerves arising from T6 to T12. These nerves initially travel in the
intercostal spaces, but then cross the costal margin and terminate in the
abdominal wall. This subgroup of intercostals nerves is called the
thoracoabdominal nerves. The ventral ramus of T12 forms the subcostal nerve.
This nerve travels entirely in the abdominal wall.
++
The intercostal nerves arise form the ventral rami of T1 through T11.
They travel along the inferior margin of the rib of corresponding number
(eg, T1 nerve travels along the inferior margin of rib 1). En route, the
nerve is located between the deepest (transverse thoracis muscle) and
intermediate layer (internal intercostals muscle) of muscle. It is
associated with the intercostal arteries and veins. From the top to the
bottom, the neurovascular bundle is arranged as vein, artery, and nerve
(mnemonic VAN) (Figure 3–16). The intercostal nerves send branches
to the transverse thoracis, internal intercostals, and external intercostal
muscles. They innervate the costal joints. Through lateral and anterior
cutaneous branches, they innervate the skin covering the respective
intercostal spaces as well as the parietal pleura lining the intercostal
spaces.
++
+++
Thoracoabdominal (Intercostals T6 to T11) Nerves
++
The T6 through T11 intercostal (thoracoabdominal) nerves begin as
typical intercostal nerves, but then send branches across the costal margin
into the muscles of the anterior abdominal wall (Figure 3–17).
These branches innervate the transverse abdominis, internal abdominal
oblique, external abdominal oblique, and rectus abdominis muscles. In
addition, they innervate the skin of the anterior wall in a metameric manner
from the xiphoid process to the umbilicus.
++
++
The T12, or subcostal, nerve never enters an intercostal space. It
travels through the abdominal wall, terminating between the umbilicus and
the pubic symphysis. It innervates muscle and skin along its coarse.
++
The lumbosacral plexus innervates the muscles, joints, skin, and
peritoneal lining of the abdominopelvic wall11,12
(Tables 3–3 and 3–4).
++
++
++
It also innervates the inferior extremities. It is formed by the ventral
rami of L1 to S5 (Figure 3–18). The ventral rami join to form the
terminal nerves. Between the L2 and S3 levels, the plexus is more complex.
The ventral rami divide into anterior and posterior divisions that join to
form the terminal nerves. The plexus is located in the posterior abdominal
wall between the psoas major and quadratus lumborum muscles (Figure
3–19).
++
++
+++
Iliohypogastric Nerve
++
The iliohypogastric nerve arises from the ventral ramus of L1 and
travels in the abdominal wall to the level of the pubic symphysis
(Figures 3–18 and 3–20). It innervates the muscle, skin,
and parietal peritoneum along its coarse.
++
++
The ilioinguinal nerve (see Figures 3–18 and 3–20) arises from the
ventral rami of L1, travels in the abdominal wall, pierces in the posterior
wall of the inguinal canal, passes through the superficial inguinal ring,
and terminates on the anterior scrotum or labia majora. It innervates the
muscle, skin, and parietal peritoneum along its coarse.
++
The genitofemoral nerve arises from the ventral rami from L1 and L2. It
travels in the abdominal wall and passes through the deep inguinal ring into
the inguinal canal. A femoral branch pierces the anterior wall of the canal
and innervates the skin covering the femoral hiatus in the crural fascia.
The genital branch passes through the superficial inguinal ring to innervate
the skin on the scrotum or labia majora. En route, it innervates the
cremaster muscle. Contraction of the cremaster elevates the scrotum.
+++
Nerve to the Coccygeus and Levator Ani
++
The nerve to the coccygeus and levator ani muscles arises from the
posterior division of the ventral rami at S3 to S4. It travels anteriorly
onto the superior surface of the coccygeus and levator ani.
++
The pudendal nerve arises from the anterior division of the ventral
rami from S2 to S4. It passes from the pelvis through the greater sciatic
foramen into the gluteal region. It enters the gluteal region inferior to
the piriformis muscle, passes posterior to the ischial spine, then enters
the perineum by passing through the lesser sciatic foramen. It innervates
the muscle and skin of the perineum.
+++
Superior Gluteal Nerve
++
The superior gluteal nerve arises from the posterior division of the
ventral rami at L4 to S1. It passes from the pelvis through the greater
sciatic foramen to the gluteal region. It enters the gluteal region superior
to the piriformis muscle, passes in the plane between gluteal medius and
minimus muscles, and terminates in the tensor fascia lata muscle. En route,
it innervates the gluteus medius and minimus muscles as well as the tensor
fascia lata.
+++
Inferior Gluteal Nerve
++
The inferior gluteal nerve arises from the posterior division of the
ventral rami at L5 to S2. It passes from the pelvis through the greater
sciatic foramen into the gluteal region. It enters the gluteal region
inferior to the piriformis muscle and terminates on the deep surface of the
gluteal maximus muscle, which it innervates.
++
The nerve to piriformis arises from the posterior division of the
ventral rami at S1 to S2 and passes onto the deep surface of the piriformis
muscle, which it innervates.
+++
Nerve to Obturator Internus and Superior Gemellus
++
The nerve to the obturator internus and superior gemellus muscles
arises form the anterior division of the ventral rami at L5 and S1. It passes from the pelvis through the greater sciatic
foramen into the gluteal region. In enters the gluteal region inferior to
the piriformis muscle and passes along the deep surface of the superior
gemellus to the obturator internus, innervating these last two muscles.
+++
Nerve to the Quadratus Femoris and Inferior Gemellus
++
The nerve to the quadratus femoris and inferior gemellus muscles arises
from the anterior division of the ventral rami at L4 to L5. It passes from
the pelvis through the greater sciatic foramen to the gluteal region and
enters the gluteal region inferior to piriformis, passing deep to obturator
internus to terminate in the inferior gemellus and quadratus femoris
muscles. As indicated by its name, the nerve innervates the inferior
gemellus and quadratus femoris muscles.
+++
Lateral Femoral Cutaneous Nerve
++
The lateral femoral cutaneous nerve arises form the posterior divisions
of the ventral rami at L2 to L3. It descends the posterior abdominal wall,
crosses the iliac crest into the pelvis where it descends on the iliacus
muscle, passes deep to the inguinal ligament at the anterior iliac spine,
and distributes cutaneous innervation on the lateral aspect of the thigh to
the level of the knee (see Figure 3–20).
+++
Posterior Femoral Cutaneous Nerve
++
The posterior femoral cutaneous nerve arises from the anterior and
posterior divisions of the ventral rami at S1 to S3. It passes from the
pelvis through the greater sciatic foramen into the gluteal region. It
enters the gluteal region inferior to the piriformis muscle, descends in the
muscle plane between gluteus maximus posteriorly and oburator internus
anteriorly, and passes into the posterior thigh where it supplies cutaneous
innervation from the hip to the midcalf.4
++
The obturator nerve (see Box 3–6) arises from the anterior division of
the ventral rami at L2 to L4 (see Figure 3–18). It descends through the
pelvis medial to the psoas major muscle, crosses the superior pubic ramus inferiorly,
passes through the obturator foramen into the medial compartment
of the thigh where it divides into posterior and anterior branches
(Figure 3–21). The posterior branch descends superficial to the adductor
magnus muscle, which it innervates. The anterior branch passes superficial to
the obturator externus muscle, descends the thigh in the muscle plane
between the adductor brevis and adductor longus, and
terminates in the gracilis muscle. En route, it innervates all of these
muscles. Furthermore, it provides articular branches to the hip and
cutaneous branches to the skin covering the medial thigh.
++
++
++
The femoral nerve arises from the posterior division of the ventral
rami at L2 to L4 (Box 3–7). It descends through the pelvis lateral
to the psoas major muscle, passes deep to the inguinal ligament, and enters
the anterior compartment of the thigh where it divides into multiple
branches supplying the muscle, joints, and skin in that region. In the
femoral crease-inguinal area, the nerve is positioned lateral to the femoral
artery and vein (mnemonic: NAVEL) (Figure 3–22). Muscular branches
innervate the iliacus, psoas major, pectineus, rectus femoris, vastus
lateralis, vastus intermedius, vastus medialis, and sartorius muscles.
Articular branches innervate the hip and knee.13 Of note,
the femoral nerve bellow the inguinal ligament consists of an anterior and
a posterior part. The anterior part contains branches to the sartorius
muscle and the posterior contains the saphenous nerve (most medial part) and
branches to the individual heads of the quadriceps
muscle.14
++
++
+++
Saphenous Nerve and Other Cutaneous Branches of the Femoral Nerve
++
The superficial branches of the femoral nerve supply the skin covering
the anterior thigh. One cutaneous branch follows the deep surface of the
sartorius muscle to its attachment on the tibia. Here, it passes onto the
skin, providing innervation of the medial leg from knee to the arch of the
foot (Figure 3–23). En route, the nerve is accompanied by the
saphenous vein, so it is called the saphenous branch of the femoral nerve.
As previously mentioned, the saphenous nerve is the most medial part of the
femoral nerve at the inguinal (femoral) crease.14
++
++
The sciatic nerve is formed by the junction of the tibial and common
peroneal nerves (Box 3–8). The tibial nerve arises from the
anterior division of the ventral rami at L4 to S3 (see Figure 3–18). The
common peroneal nerve arises from the posterior division of the ventral rami
at L4 to S2. The sciatic nerve passes from the pelvis through the greater
sciatic foramen into the gluteal region. It enters the gluteal region
inferior to the piriformis muscle, descends in the muscle plane between the
gluteus maximus posteriorly and the obturator internus anteriorly, and
passes lateral to the ischial tuberosity to enter the posterior thigh
(Figure 3–24). In the posterior thigh, it passes between the
adductor magnus and the long head of the biceps femoris.
It descends in the groove between the biceps femoris medially and the
semitendinosus and semimembranosus laterally. En route, it innervates the
adductor magnus, biceps femoris, semitendinosus, and semimembranosus muscles
(Figure 3–25).15 Posterior to the knee the
sciatic nerve descends into the popliteal fossa, where it diverges into the
tibial and common peroneal nerves (Figure
3–26).16 Of note, these two branches are distinct from
the onset and travel together enveloped in the same tissue
sheath.17
++
++
++
++
++
The tibial nerves exits the popliteal fossa
passing between the heads of the gastrocnemius muscle into the superficial
posterior compartment of the leg. Here, it descends deep to the
plantaris and superficial to popliteus muscles. It passes between the tibial and
fibular heads of the soleus muscle to enter the deep posterior compartment.
The nerve passes posterior to the medial malleolus, where it enters the foot
and divides into medial and lateral plantar nerves that innervate the muscle
and skin on the plantar surface of the foot. The common peroneal nerve
follows the tendon of the biceps femoris to its attachment on the fibula.
The nerve passes inferior to the neck of the fibula and divides into
superficial and deep branches. The superficial branch enters the lateral
compartment of the leg, where it innervates the peroneus longus and brevis
muscles. The nerve terminates as cutaneous fibers on the dorsal and lateral
surface of the foot. The deep peroneal nerve enters the anterior compartment
of the leg, where is innervates the tibialis anterior, extensor digitorum
longus, and extensor hallucis longus muscles. It crosses the anterior
surface of the ankle into the foot, where it innervates the extensor
digitorum brevis and extensor hallucis brevis muscles. It terminates as
cutaneous fibers supplying skin between the hallux and second
toe.18