Download Unit 36: Plantar Foot

Unit 36: Plantar Foot
Disscection Instructions:
Remove any skin left on the foot. Look for the medial calcaneal nerve in the superficialfascia of
the medial and inferior surfaces of the calcaneus (Plates 514, 523; 5.63, 5.75). Clean the deep fascia of
the foot. This is the plantar fascia, which consists of thin medial and lateral portions and a thick central
portion (Plates 514; 5.66). The term plantar aponeurosis is often applied to only the central thickened
portion, but some books use the terms plantar fascia and plantar aponeurosis interchangeably. Stout slips
extend into the toes leaving intervals at the base of the toes where the neurovascular bundles are
unprotected. The slips are connected in the webs between toes by the superficial transverse metatarsal
ligament. Half-way between heel and toes, make a small incision along the medial side of the thickened
fascia and separate the aponeurosis from the underlying muscle. Continue between the muscle and
aponeurosis towards the heel until they will no longer separate. At this point, cut the plantar
aponeurosis and reflect it to the toes. The slips send septa down to the metatarsal bones which must be
cut to continue the reflection.
The three muscles now seen on the plantar surface of the foot are the abductor hallucis, flexor
digitorum brevis and abductor digiti minimi (Plates 515; Table 5.12 and figure-p. 428 ). All three
take origin from the calcaneus and insert on the toes. The abductor hallucis muscle inserts on the
medial side of the base of the first phalanx of the great toe and the abductor digiti minimi inserts on the
lateral side of the base of the first phalanx of the little toe. The flexor digitorum brevis inserts in a
similar manner to the flexor digitorum superficialis in the hand. Each of its four tendons split into two
slips which encircle the tendon of the flexor digitorum longus and unite as they insert on the second
phalanx of the lesser digits. Each of the three muscles are in different compartments of the foot. The
medial compartment contains the abductor hallucis and the flexor hallucis brevis. The latter muscle
takes origin from deep in the central part of the foot and inserts by two tendons, one on each side of the
base of the first phalanx (Plates 515-517; Table 5.12 and figure-p. 428, Figure-p. 429B). Each tendon
usually contains a sesamoid bone. In this compartment is also the tendon of the flexor hallucis longus.
The lateral compartment contains the abductor digiti minimi and the flexor digiti minimi (Plates
515, 516, 518; Table 5.14 and figure-p. 431, p. 428). The flexor arises from the base of the fifth
metatarsal and inserts on the lateral side of the base of the first phalanx of the fifth toe. The flexor
digitorum brevis lies in the central compartment with the tendon of the flexor digitorum longus (Plates
501; 5.105). After studying the flexor digitorum brevis, including its insertion on the toes, reflect it from
its origin. The tendon of the flexor digitorum longus enters the foot as a single tendon, but within the
foot, divides into four tendons (Plates 516; 5.64). The main tendon serves as insertion for the quadratus
plantae (accessory flexor) muscle. This muscle arises from the sides of the calcaneus (Plates 516, 517;
5.64, Table 5.13-p. 429). The four tendons give origin to lumbrical muscles in the same way the flexor
digitorum profundus did in the hand (Plates 5.02; 5.107, 5.108). The tendons of the flexor digitorum
longus pass through the tendons of the flexor digitorum brevis and insert on the base of the distal
phalanx. The tendons of the lumbrical muscles pass on the great toe side of the lesser toes to insert on
the extensor tendon expansion. The lumbrical muscles help flex the metatarsophalangeal joints and
extend the interphalangeal joints.
Cut the tendon of the flexor digitorum longus as it enters the foot and detach the quadratus
plantar from its origin. Deep to the central compartment is the adductor-interosseous compartment
(Plates 517-519; Table 5.14-p. 430, Table 5.15-p. 431). It contains the adductor hallucis, three plantar
interossei and four dorsal interossei. A fourth plantar interosseous muscle is rarely identifiable. The
muscles in this compartment of the foot are similar to those in the homologous compartment of the hand.
Unit 36 - 1
The adductor hallucis has oblique and transverse heads of origin (Plates 517; Table 5.14-p. 430). The
oblique head arises from the bases of the middle three metatarsal bones and the transverse head arises
from the regions of the metatarsophalangeal joints of the four lesser toes. The two heads unite to insert on
the lateral side of the base of the first phalanx. The actions of adduction and abduction of the toes is
determined by using the second toe as the axis of the foot. The three plantar interossei adduct the three
lateral toes. They arise from the corresponding metatarsal bones and insert on the base of the first
phalanx of their digit. The dorsal interossei arise from adjacent metatarsal bones, filling the interosseous
space. They insert on the medial and lateral sides of the base of the first phalanx of the second toe and on
the lateral side of the bases of the first phalanx of the third and fourth toes.
Because the muscles of the foot are so similar to the muscles of the hand, it is convenient to
compare innervations also. The medial plantar nerve should be compared to the median nerve in the
hand and the lateral plantar nerve to the ulnar nerve in the hand. Both nerves enter the foot by passing
deep to the abductor hallucis muscle (Plates 516, 517, 523; 5.63, Table 5.14-p. 430). The medial
plantar nerve supplies the medial compartment muscles and enters the interosseous membrane between
the medial and central compartments. It supplies the flexor digitorum brevis (the median nerve supplied
its homologue, the flexor digitorum superficialis) and the first lumbrical muscle. The lateral plantar
nerve passes between the flexor digitorum brevis and the quadratus plantae, innervating the latter muscle,
then continues in the intermuscular septum between the central and lateral compartments. The lateral
plantar nerve innervates all the muscles in the lateral and adductor-interosseous compartments. The
lateral plantar nerve supplies sensory innervation to the lateral one and one-half toes, the rest being
supplied by the medial plantar nerve. The distal dorsal surfaces of the toes are supplied by the plantar
nerves.
The tibial artery divides under the flexor retinaculum into medial and lateral plantar arteries
which follow the nerves into the foot (Plates 500, 516-518; 5.63, 5.67, Table 5.11-p. 423). The lateral
plantar nerve crosses to the lateral side of the foot, then swings back to the medial side, passing deep to
the oblique head of the adductor hallucis to join the deep plantar branch of the dorsalis pedis artery
(Plates 518; 5.67). This deep plantar arterial arch gives off plantar metatarsal arteries which supply
the toes. The medial plantar artery attempts to form a superficial arch, but usually only supplies arteries
to the medial three and one-half toes.
Be sure to identify all of the following in this unit:
medial calcaneal nerve
plantar fascia/plantar aponeurosis
abductor hallucis muscle
flexor digitorum brevis muscle
abductor digiti minimi muscle
medial compartment
tendon of flexor hallucis longus muscle
lateral compartment
flexor digiti minimi muscle
central compartment
quadratus plantae muscle
tendons of flexor digitorum longus muscle
lumbrical muscles
adductor-interosseous compartment
adductor hallucis muscle
oblique head
transverse head
plantar interossei muscles
dorsal interossei muscles
medial plantar nerve
lateral plantar nerve
tibial artery
medial plantar artery
lateral plantar artery
flexor retinaculum
dorsalis pedis artery
deep plantar arch
plantar metatarsal arteries
superficial arterial arch
Unit 36 - 2