METATARSALS

The five metatarsals are a group of long cylindrical bones in the distal half of the foot between tarsals and phalanges. The metatarsal bones lack individual names hence they are numbered from 1 to 5 from medial to lateral side of the foot. The metatarsals are analogous to metacarpals in the hand. The lengths of metatarsals are in descending order 2^nd, 3^rd, 4^th, 5^th and 1^st.

Metatarsals are dorsally convex long bones having a shaft or body, a head and a base, except for 1^st and 5^th metatarsal. The shafts are long and slender, longitudinally convex & from the plantar surface they are concave. The body is prismatic in form which tapers gradually from proximal to distal. The proximal end is set obliquely in such a way which projects backwards and laterally. The base is wedge shaped articulating proximally with the tarsals. The space between two metatarsal bones is known as interosseous metatarsal space. The dorsal or the plantar surface of the is rough for the attachments of ligaments. The head of each metatarsals represent a convex articular surface which articulates the base of proximal phalanx. The medial and lateral surface of the head is flat which has a depression crossed by dorsal tubercle for a collateral ligament of metatarsophalangeal joint.

FIRST METATARSAL

The first metatarsal is the shortest, thickest and stoutest of all the metatarsals. It has a strong shaft & of marked prismoid form. The base of the bone has an oval lateral facet that is an ill-defined smooth area to articulate the second metatarsal. The proximal surface of the base is large, kidney shaped and indented on medial & lateral margins to articulate medial cuneiform. The circumference of it is grooved to attach the tarsometatarsal ligaments. The head is large, has a plantar elevation, a crista that separates 2 grooved facets where the small sesamoid bones glide.

SECOND METATARSAL

The second metatarsal is the longest and is broad & rough below the base. The base has four articulating facets. The proximal facet is concave and triangular to articulate intermediate cuneiform. The dorsomedial facet is variable in size and articulates medially and some part of intermediate cuneiform. There are two lateral facets; dorsal (upper) & plantar (lower) which are separated by a nonarticular bone. Each of these facets are divided into 2 vertical ridge, 2 anterior facets to articulate with the third metatarsal and two posterior facets that articulate with the lateral cuneiform.

THIRD METATARSAL

The third metatarsal has a smooth, flat triangular base that articulates proximally with the lateral cuneiform. The lateral side of the base has one facet which is placed dorsally to articulate with the 4^th metatarsal bone. The medial side of the base has 2 facets for second metatarsal bone. The medial plantar facet is mostly absent. The third tarsometarsal joint is relatively immobile.

FOURTH METATARSAL

The fourth metatarsal is smaller than the third. The base of it is quadrilateral to articulate cuboid. The lateral side of the base has a single facet dorsally to articulate with the fifth metatarsal bone. The medial side of the base is smooth to articulate third metatarsal bone.

FIFTH METATARSAL

The fifth metatarsal has a rough eminence, tuberosity on the lateral side of the base. The base articulates with cuboid proximally in a triangular and oblique surface; medially with the fourth metatarsal. The lateral side of the base has a tuberosity or the styloid process which projects backwards and laterally. The plantar surface of the base is grooved by the tendon of abductor digiti minimi and origin of flexor digiti minimi brevis.

MUSCLE ATTACHMENTS

The 1^st metatarsal attaches tendon of tibialis anterior medially and tendon of fibularis longus on the plantar aspect. It gives origin to medial head of 1^st dorsal interosseous on proximal aspect of lateral surface.

The 2^nd metatarsal attaches lateral head of first dorsal interosseous & medial head of second dorsal interosseous respectively to the medial and lateral surface of the shaft of the bone.

The 3^rd metatarsal attaches lateral heads of second dorsal interosseous and first plantar interosseous to the medial surface of the shaft. The medial head of the third dorsal interosseous is attached to the lateral surface.

The 4^th metatarsal attaches the lateral head of the third dorsal and second plantar interosseous are attached to the medial surface. The medial head of the fourth dorsal interosseous is attached to the lateral surface of the bone.

The 5^th metatarsal has attachment of fibularis tertius to the medial part of the surface and medial border of the shaft. The fibularis brevis attaches to the dorsal surface of the tuberosity. A strong band of the plantar aponeurosis, sometimes containing muscle, connects the apex of the tuberosity to the lateral process of the calcaneal tuberosity. The lateral heads of fourth dorsal and third plantar interosseous are attached to the medial side of the shaft.

VASCULAR SUPPLY

All the metatarsals are supplied by first dorsal and plantar metatarsal arteries. A nutrient artery enters the lateral surface of mid diaphysis in all metatarsals.

NERVOUS SUPPLY

The first & second metatarsal has nervous supply from the branches of deep fibular and medial plantar nerves. The third & fourth metatarsal is innervated by branches of the deep fibular and lateral plantar nerves. The fifth metatarsal is innervated from the branches of sural, superficial fibular and lateral plantar nerves.

OSSIFICATION

Each metatarsal ossifies from 1 primary and 1 secondary center. The primary center appears in shaft at 10^th week of gestational life in first metatarsal and at 9^th week it appears in the rest of the metatarsals. The secondary center appears in the base of first metatarsal in the 3^rd year and in rest of the bones it appears around 3^rd-4^th year. Both the centers unite by 18^th year.