Sole of the Foot Anatomy
The sole of the foot contains the
plantar aponeurosis, intrinsic muscles, tendons originating from muscles in the
leg, and plantar vessels and nerves. The tendons, accompanied by the vessels
and nerves, enter the sole deep to the flexor retinaculum (Fig.
6.48) in the tarsal
tunnel, between the medial aspect of the calcaneus and the medial malleolus.
The skin of the sole is thick and heavily keratinized and is firmly attached to
the deep fascia by fibrous septa which traverse and loculate the subcutaneous
fat. In the heel, it forms a weight bearing fat pad.
The plantar aponeurosis, the deep
fascia of the sole covering the superficial layer of muscles, is especially
thick in its central portion. Posteriorly, the aponeurosis is attached to the
medial and lateral calcaneal tubercles. Anteriorly, it widens and diverges into
five digital slips (Fig. 6.47), which attach to the fibrous flexor sheaths
and plantar metatarsal plates (Fig. 6.96). These plates give the aponeurosis
indirect attachment to the bases of all the proximal phalanges, providing an
important support for the longitudinal arches of the foot (Figs 6.98–6.102).
Inflammation of the aponeurosis (plantar fasciitis) is a cause of pain in the foot.
The muscles and tendons in the sole
of the foot are arranged in four layers.
This layer comprises three muscles,
which span the length of most of the foot and attach to the deep surface of the
plantar aponeurosis. Abductor hallucis (Fig. 6.49) lies on the medial side of the foot and
arises from the medial calcaneal tubercle and the adjacent flexor retinaculum.
Its tendon passes to the great toe with the medial tendon of flexor hallucis
brevis and attaches to the medial side of the base of the proximal phalanx. It
is supplied by the medial plantar nerve.
Flexor digitorum brevis lies
centrally (Fig. 6.49) and attaches to the medial calcaneal tubercle
(Fig. 6.50). It
has four tendons, which pass forwards to enter the fibrous flexor sheaths of
the lateral four toes. Each tendon splits to allow the passage of the long
flexor tendon (Figs 6.49 & 6.51), then reunites to attach to the flexor
surface of the middle phalanx. Flexor digitorum brevis aids flexion of the
proximal parts of the toes and is supplied by the medial plantar nerve.
Abductor digiti minimi traverses the lateral border of the sole (Fig.
6.49) and is attached
posteriorly to the medial and lateral calcaneal tubercles. Entering the little
toe, its tendon attaches to the lateral side of the proximal phalanx. The muscle
is supplied by the lateral plantar nerve.
This layer includes the tendons of
two long flexor muscles, which arise in the leg, namely flexor hallucis longus
and flexor digitorum longus. Attached to the tendon of flexor digitorum longus
(Fig. 6.52) are quadratus plantae (flexor accessorius) and the four lumbricals.
The tendon of flexor hallucis
longus grooves the posterior surface of the talus and curves forwards inferior
to the sustentaculum tali and the spring (plantar calcaneonavicular) ligament.
It passes deep to the tendon of flexor digitorum longus, to which it is usually
attached. The tendon of flexor hallucis longus continues forwards inferior to
the head of the first metatarsal, where it passes between the sesamoid bones in
the two tendons of the flexor hallucis brevis (see below) and enters the
fibrous flexor sheath of the great toe to
reach its attachment to the base of the distal phalanx (Fig. 6.52). The actions
and innervation of flexor hallucis longus are described on p. 279.
The tendon of flexor digitorum
longus passes forwards medial to the sustentaculum tali and divides into four
tendons, one for each of the lateral four toes (Figs 6.51
& 6.52). Each
tendon enters its fibrous flexor sheath and passes through the flexor digitorum
brevis tendon before attaching to the base of the terminal phalanx. The actions
and innervations of flexor digitorum longus are considered on p. 279.
Quadratus plantae (flexor
accessorius) (Figs 6.51 & 6.52) is quadrangular and is anchored posteriorly
to the medial and lateral tubercles of the calcaneus. Anteriorly, the muscle
attaches to the tendons of flexor digitorum longus. By pulling on these
tendons, it can flex the toes irrespective of the position of the ankle. Its
nerve supply is from the lateral plantar nerve.
The lumbricals are four small
muscles attached proximally to the tendons of flexor digitorum longus (Fig.
6.52). Distally, each slender tendon winds around the medial side of the
appropriate digit to attach to the extensor expansion and base of the proximal
phalanx. The lumbricals extend the lateral four toes but flex the
metatarsophalangeal joints. The first lumbrical is supplied by the medial plantar
nerve and the remainder by the lateral plantar nerve.
Deep intrinsic muscles
The three muscles in this layer are
located in the anterior part of the foot (Fig. 6.53), adjacent to the
metatarsals. Flexor hallucis brevis and adductor hallucis lie medially and are
attached to the great toe, while flexor digiti minimi brevis lies laterally and
acts on the little toe.
Flexor hallucis brevis lies along
the medial side of the foot and is attached posteriorly to the cuboid and the
three cuneiforms. Passing forwards on either side of the flexor hallucis longus
tendon (Fig. 6.52), the muscle gives rise to two short tendons, which lie
inferior to the first metatarsophalangeal joint. Each tendon contains a
sesamoid bone (Figs 6.101 & 6.102) and enters the great toe to attach to
the appropriate side of the base of the proximal phalanx. Flexor hallucis
brevis flexes the proximal phalanx and is innervated by the medial plantar
nerve.
Adductor hallucis (Fig. 6.53)
consists of an oblique head which is attached to the bases of the second, third
and fourth metatarsals, and a transverse head which lies across the anterior
part of the sole, attached to the deep transverse metatarsal ligaments and the
lateral three metatarsophalangeal joints. The two heads converge and attach to the lateral tendon and sesamoid
of flexor hallucis brevis.
Adductor hallucis assists flexor hallucis brevis and may help to support the
transverse arch of the foot. It is supplied by the lateral plantar nerve.
Flexor digiti minimi brevis lies
along the plantar surface of the fifth metatarsal (Fig. 6.53), attaching posteriorly to the base of the
bone and anteriorly to the lateral side
of the base of the proximal phalanx
of the little toe. The muscle flexes the proximal phalanx and is innervated by the lateral plantar nerve.
Lying deeply in the sole, attached
to the metatarsals, the three plantar interosseous muscles (Fig.
6.54) attach by single
heads to the plantar borders of
the third, fourth and fifth metatarsals. The four dorsal interossei (Fig.
6.55) are bicipital and
attach to contiguous surfaces of the shafts of the metatarsals. The tendons
pass forwards dorsal to the deep transverse metatarsal ligaments and attach to
the bases of the proximal phalanges and dorsal extensor expansions. These
muscles are supplied by the lateral plantar nerve. They assist extension of the
phalanges and flexion of the metatarsophalangeal
joints. Their attachments indicate that plantar interossei should adduct and
dorsal interossei should abduct the toes, but these movements are often poorly
developed, especially in the shod foot.
The tendons of fibularis (peroneus)
longus and tibialis posterior (Fig. 6.56) pass deeply into the sole to reach their
attachments on tarsal and metatarsal bones. The fibularis longus tendon enters
the lateral side of the sole and is retained in a groove inferior to the cuboid
by the long plantar ligament. The tendon passes forwards and medially to reach
the lateral aspect of the base of the first metatarsal and adjacent medial
cuneiform (compare with tibialis anterior, p. 288). The tendon of tibialis
posterior enters the medial aspect of the foot deep to the flexor retinaculum
(Figs 6.48 & 6.56), attaches to the tuberosity of the navicular and sends
additional slips to other tarsal bones and the metatarsal bases. These two
tendons may help to support the medial longitudinal arch. The other actions of
fibularis longus and tibialis posterior and their innervation are considered on
pp 279, 290.
Blood supply
Deep to the flexor retinaculum, the
tibial artery divides into medial and lateral plantar branches (Fig. 6.51).
Passing forwards, the medial plantar artery runs deep to the superficial
intrinsic muscles, gives off
plantar cutaneous branches, which pass between abductor hallucis and flexor
digitorum brevis, and terminates by supplying digital branches to the medial
(and occasionally lateral) side of the great toe. The larger lateral plantar
artery passes for wards and laterally (Fig. 6.54) deep to the superficial
intrinsic muscles towards the base of the fifth metatarsal. Here the artery
inclines medially and deeply to form the plantar arch, lying on the interossei
and bases of the metatarsals. A perforating branch between the first and second
metatarsals usually links the arch with the dorsalis pedis artery (p. 290).
From the arch, plantar metatarsal arteries (Fig. 6.54) pass distally to the
webs of the toes where they divide into digital branches. Venae comitantes
accompany medial and lateral plantar arteries and their branches.
Nerve supply
Cutaneous branches of the tibial
nerve supply the skin over the heel. Deep to the flexor retinaculum the tibial
nerve divides into medial and lateral branches, which supply their respective
sides of the sole (Figs 6.48 & 6.51). The larger medial plantar nerve
accompanies the corresponding artery and gives cutaneous branches to the medial
three and onehalf digits, including the nail beds. The nerve also supplies
abductor hallucis, flexor hallucis brevis, flexor digitorum brevis and the
first lumbrical.
The lateral plantar nerve
accompanies the corresponding artery (Fig. 6.51), supplying quadratus plantae
and abductor digiti minimi and giving cutaneous branches to the sole. Near the
base of the fifth metatarsal it divides into superficial and deep branches,
which supply the remaining muscles of the sole. The deep branch accompanies the
plantar arch and terminates in adductor hallucis. In addition to muscular
branches, the superficial branch also gives cutaneous branches to the lateral one and onehalf toes.
