Anterior and
Lateral Compartments of the Leg and Dorsum of the Foot Anatomy
The anterior compartment of the leg
contains muscles that extend the ankle joint and toes and evert and invert the
foot. Its neurovascular bundle comprises the anterior tibial artery and its
venae comitantes and the deep fibular nerve (Fig. 6.57). The cutaneous branches of the superficial
fibular nerve are also present.
On the dorsum of the foot are the
long extensor tendons, the dorsalis pedis artery, the dorsal venous arch and,
more laterally, the bellies of extensor digitorum brevis and extensor hallucis
brevis. The medial and lateral malleoli lie on each side of the ankle.
The dorsal venous arch (Fig. 6.58)
drains blood from the toes and sole of the foot. From its medial end the great
(long) saphenous vein passes in front of the medial malleolus where it is
palpable and accessible, and then ascends to the posteromedial aspect of the
knee. From the lateral side of the arch, the small saphenous vein passes behind
the lateral malleolus and ascends to the popliteal fossa (p. 274). The
saphenous nerve accompanies the great saphenous vein (Fig. 6.59), supplying
skin on the medial side of the leg and medial border of the foot as far as the
ball (metatarsophalangeal joint) of the great toe. The sural nerve accompanies
the small saphenous vein (Fig. 6.58) and supplies skin along the lateral border
of the foot and little toe.
The superficial fibular
(superficial peroneal) nerve enters the anterior compartment of the leg from
the lateral (fibular or peroneal) compartment at the anterior border of
fibularis longus (Fig. 6.60). Shortly after piercing the deep fascia it divides
into medial and lateral branches, which supply the skin of the leg and dorsum
of the foot (Fig. 6.58). On reaching the toes, the medial branch supplies the
medial side of the great toe and the contiguous aspects of the second and third toes, while the lateral branch innervates the adjacent sides of the third, fourth and fifth toes.
Thus, all of the digital skin is innervated by the superficial fibular nerve,
except for the cleft between the great and second toes (supplied by the deep
fibular [peroneal] nerve; Fig. 6.58) and the lateral aspect of the little toe
(supplied by the sural nerve).
The skin and subcutaneous tissues
over the anteromedial surface of the tibia are comparatively thin and have a
sparse blood supply. As a consequence,
lacerations in this region may heal relatively slowly. The subcutaneous tissues
of the ankle are a common site for accumulation of tissue fluid (oedema).
Deep fascia
In the region of the ankle and foot
there are thickenings of the investing deep fascia forming retinacula (Fig.
6.60), which prevent bowstringing of the long extensor tendons during muscular
contraction. As the tendons pass beneath the retinacula to reach the foot they
are enveloped in synovial membrane. By convention, superior and inferior
extensor retinacula are described (Fig. 6.64). The superior retinaculum forms a
broad band passing between the anterior borders of the tibia and fibula. The
inferior retinaculum is Yshaped, with its stem attached to the upper surface
of the calcaneus.
The muscles in the anterior
compartment are tibialis anterior, extensor hallucis longus, extensor digitorum
longus and fibularis (peroneus) tertius. All are sup plied by the deep fibular
nerve. Tibialis anterior is the most medial (Figs 6.57 & 6.60), attaching
to the lateral condyle and anterolateral surface of the shaft of the tibia, the
adjacent interosseous membrane and the deep fascia overlying the muscle.
Distally, its tendon crosses the
anterior border of the lower end of the tibia and attaches to the base of the
first metatarsal and adjacent part of the first cuneiform bone (Fig. 6.61). The
muscle inverts the foot and dorsiflexes the ankle joint.
The other three muscles all attach
to the narrow anterior surface of the fibula and adjacent interosseous
membrane. Extensor digitorum longus (Fig. 6.57) is attached to the proximal
threequarters of the bone, fibularis tertius (when present) to the distal
quarter, and extensor hallucis longus is overlapped by them medially at
midshaft level. In addition, extensor digitorum longus attaches to the anterior
intermuscular septum and overlying deep fascia.
The proximal part of extensor
hallucis longus is overlapped by adjacent muscles, but in the lower part of the
leg, its tendon emerges lateral to that of tibialis anterior. As it descends
towards the ankle, the tendon crosses from the lateral to the medial side of
the neurovascular bundle.
In the foot, the tendon of extensor
hallucis longus runs forwards to the great toe (Fig. 6.62), where it attaches
to the base of the distal phalanx. It is a powerful extensor of the toe,
dorsiflexor (extensor) of the foot and assists inversion. Lateral to extensor
hallucis longus, the muscle belly of extensor digitorum longus gives way
distally to four tendons, which pass to the dorsal aspects of the lateral four
toes. Each tendon forms an extensor expansion that divides into three slips.
The central slip attaches to the base of the middle phalanx, while the two
lateral slips combine to insert into the base of the distal phalanx (Fig.
6.62). Extensor digitorum longus extends the lateral four toes and dorsiflexes
the foot. Fibularis tertius is a continuation of the belly of extensor digitorum
longus. It attaches to the lateral border of the fifth metatarsal (Fig. 6.62)
and everts the foot and dorsiflexes the ankle.
The muscles of the anterior
compartment of the leg are active during walking in both the supporting and
swing phases. In the weightbearing limb they help to incline the leg forwards,
while the foot remains stationary on the ground. In the swinging limb, the
muscles maintain the ankle in dorsiflexion, thereby preventing the foot from
dropping.
On the dorsum of the foot, extensor
digitorum brevis and extensor hallucis brevis (Fig. 6.62) are attached to the upper surface of the
calcaneus and overlying stem of the inferior extensor retinaculum. Extensor
digitorum brevis gives rise to three short tendons, which pass deep to the long
extensor tendons of the lateral three toes (Fig. 6.62) and attach to the dorsal extensor expansions
of the second, third and fourth toes. The tendon of extensor hallucis brevis
attaches to the base of the proximal phalanx of the great toe. The muscles
assist extension of the toes, particularly when the long extensors are flexing
the leg forwards on the foot just before it is lifted from the ground during
walking. The nerve supply is the deep fibular nerve.
This comprises the deep fibular
nerve and the anterior tibial artery, with its venae comitantes (Fig. 6.57).
The artery, a terminal branch of the popliteal artery (p. 278), reaches the
anterior compartment after passing through the interosseous membrane (Figs 6.76
& 6.83). It then descends on the anterior surface of the membrane (Fig.
6.63) and at the ankle
lies midway between the two malleoli. It continues distally as the dorsalis
pedis artery on the lateral side of the extensor hallucis longus tendon (Fig.
6.62), where its pulsations are palpable in the living foot.
At the proximal end of the first
inter metatarsal space, the dorsalis pedis artery gives a deep branch that
passes between the two heads of the first dorsal interosseous muscle to join
the plantar arch (p. 285). This arrangement provides an anastomosis between the
anterior and posterior tibial arteries. The dorsalis pedis artery terminates as
the first dorsal meta tarsal artery, supplying the great toe and adjacent
border of the second toe and the arcuate artery. It turns laterally beneath the
extensor tendons across the bases of the metatarsals and gives metatarsal
arteries, which divide to supply adjacent borders of the remaining three digits.
The deep fibular (peroneal) nerve,
a terminal branch of the common fibular nerve, winds around the neck of the
fibula deep to fibularis (peroneus) longus (Fig. 6.63). The nerve accompanies the anterior tibial
vessels into the foot and supplies all muscles in the anterior compartment. In
the foot, the nerve is close to the dorsalis pedis artery, usually lying
lateral to the artery but sometimes medial to it (Fig. 6.62). It gives a branch
to extensors digitorum and hallucis brevis and the tarsal joints and terminates
by supplying the skin between the great and second toes (Fig. 6.62).
Lateral compartment of leg
The lateral (fibular or peroneal)
compartment of the leg extends from the head of the fibula above to the lateral
malleolus below. Its principal contents are the fibularis longus and brevis
muscles (Fig. 6.64). Fibularis (peroneus) longus is attached to the upper
twothirds of the lateral surface of the fibula and fibularis (peroneus) brevis
to the lower twothirds, with brevis being the more anterior. Both muscles are
attached to the two crural intermuscular septa and the overlying deep fascia
(Fig. 6.57). On reaching the ankle the tendons pass behind and then below the
lateral malleolus, restrained by the superior and inferior fibular retinacula
and surrounded by synovial membrane (Fig. 6.64). The tendon of fibularis
brevis passes for wards above the fibular trochlea of the calcaneus to attach
to the base of the fifth metatarsal. The fibularis longus tendon passes forwards
below the fibular trochlea and turns medially into the sole of the foot where
it lies in a groove on the cuboid bone (Fig. 6.65). It attaches to the lateral
side of the base of the first metatarsal and the adjacent first cuneiform.
Fibularis longus and brevis are
evertors of the foot and weak plantar flexors of the ankle joint. Their nerve
supply is the superficial fibular nerve, a terminal branch of the common
fibular nerve, which enters the lateral compartment by winding around the neck
of the fibula. Here it is palpable and may sometimes be compressed.
Branches of the fibular artery, which arises
from the posterior tibial artery (p. 278), pierce the posterior intermuscular
septum to supply fibularis longus and brevis
