(4) The cuboid bone is a cube-shaped bone. It is situated on the lateral side
of the foot in front of the calcaneus and behind the fourth and fifth metatarsal bones.
(5) The cuneiform bones are placed at the anterior portion of the tarsus
lying side by side between the navicular bone and the bases of the first three
metatarsals. The first cuneiform bone is the largest. The smaller second cuneiform
bone is placed with its base (broad end) directed superiorly and its apex (thin end)
directed downwards. The third cuneiform bone is the second largest. Like the second
cuneiform, its base is directed superiorly and its apex inferiorly.
b. The Metatarsus. The foot proper is formed by the metatarsus. The
metatarsal bones are numbered one through five, from the medial to the lateral side.
Each metatarsal bone consists of a shaft, or body, and two extremities. The base or
proximal extremity is wedge-shaped and the head, or distal extremity, is rounded. The
first metatarsal, which provides attachment for the great toe, is the strongest and
shortest of the metatarsal bones. It serves as the main support of the body when in the
walking position. The large rounded head that forms the "ball of the foot" presents two
grooves on its inferior, or plantar surface, on which glide two sesamoid bones in the
tendon of the flexor hallucis brevis muscle. The heads of the second and third
metatarsals generally extend beyond the first.
c. The Digits. The digits, or toes, are composed of 14 phalanges. There are
two phalanges in the great toe and three in each of the other toes (the proximal, the
middle, and the distal). Each phalanx consists of a shaft and two extremities. The
proximal extremity of each proximal phalanx presents a concave facet for articulation
with the head of the corresponding metatarsal. The distal end presents a trochlear
articular surface for articulation with the middle phalanx. The distal end of each distal
phalanx is flattened and presents the ungual tuberosity for the support of the toenail.
d. The Foot As a Whole. The bones of the foot are so arranged and adapted to
each other that they form two distinct arches, the longitudinal arch and the transverse
arch. These arches form a firm basis of support for the human body in the standing
position, give elasticity to the step, and accommodate the plantar blood vessels, nerves,
tendons, and muscles. Abnormally high arches are called pes cavus. The longitudinal
arch is the principal one and can be seen when the foot is viewed from the medial, or
inner side. It consists of an anterior pillar formed by the heads of the metatarsals, a
posterior pillar formed by the calcaneus, and a keystone formed by the talus. The three
cuneiform bones and the cuboid (with the proximal ends of the metatarsal bones) form
the transverse arch. The "top" of the foot is referred to as the dorsal aspect, the
"bottom" as the plantar aspect. The term "march fracture" is defined as a fracture of the
distal portion of the second and third metatarsals without a history of trauma.