February 04, 2012
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Metatarsals

The metatarsal bones, five in number, are situated in the anterior part of the foot in front of the tarsals and behind the phalanges. They are enumerated from the medial to the lateral side.

THE COMMON CHARACTERISTICS OF THE METATARSAL BONES

Like the metacarpals the metatarsals are miniature long bones, and each possesses a shaft, a base or proximal end, and a head or distal end.

With the exception of the first and, to a lesser degree, the fifth, the shafts are long and slender, and are slightly convex longitudinally on their dorsal aspects and concave on their plantar aspects. They are prismoid in form and taper from the base to the head.

The bases articulate with the distal row of the tarsals and with one another. The line of each tarsometatarsal joint, excluding the first, passes backwards and laterally, and the bases of the metatarsals are therefore set somewhat obliquely relative to their shafts, a fact which assists in the recognition of the side of the body to which the bones belong.

The heads articulate with the proximal phalanges of their own digits, each by means of a convex articular surface, which extends further on the plantar than on the dorsal surface ; the plantar extension ends on each side on the summit of a slight articular eminence. The sides of the heads are flattened and each shows a depression surmounted dorsally by a tubercle, which gives attachment to one of the collateral ligaments of the metatarsophalangeal joint.

THE CHARACTERISTICS OF THE INDIVIDUAL METATARSAL BONES

The first metatarsal bone (fig. 495) is the shortest and thickest of the metatarsal bones. The body is strong, and of well-marked prismoid form. The base has no articular facets on its sides, but there is occasionally a pressure facet on the lateral side caused by contact with the second metatarsal bone. Its proximal articular surface, of large size and kidney-shaped, articulates with the first cuneiform bone; the lateral border of the facet shows a slight indentation, which represents the hilum of the kidney. Its circumference is grooved for the tarsometatarsal ligaments, and medially gives insertion to a part of the tendon of the tibialis anterior; its plantar angle presents a rough, oval prominence for the insertion of the tendon of the peroneus longus. The lateral surface of the shaft is flat and gives origin to the medial head of the first dorsal interosseous muscle. The head is large; on its plantar surface there is a median elevation separating two grooved facets, on which sesamoid bones glide.

Figure 495
First metatarsal bone medial and lateral views - Figure 495

The second metatarsal bone (fig. 496) is the longest of the metatarsal bones. Its wedge-shaped base bears four articular facets - one on its proximal surface, of a triangular form, for articulation with the intermediate cuneiform bone; one at the upper part of its medial surface, for articulation with the medial cuneiform bone; and two on its lateral surface, an upper and lower, separated by a rough non-articular interval. Each of these lateral articular surfaces is divided by a vertical ridge ; the two anterior facets articulate with the third metatarsal bone; the two posterior (sometimes continuous) with the lateral cuneiform bone. A pressure facet is occasionally present caused by contact with the first metatarsal bone; it is oval in shape, and is situated on the medial side of the base, distal to the facet for the medial cuneiform bone. The medial and lateral surfaces of the shaft give origin respectively to the lateral head of the first and the medial head of the second dorsal interosseous muscle.

Figure 496
Second metatarsal bone medial and lateral views - Figure 496

The third metatarsal bone (fig. 497) has a triangular base, which articulates proximally with the lateral cuneiform bone ; medially it articulates by two facets with the second metatarsal bone, ; and laterally, by a, single facet situated at the dorsal angle, with the fourth metatarsal bone. The medial surface of the shaft gives origin to the lateral head of the second dorsal and to the first plantar interosseous muscle ; the lateral surface gives origin to the medial head of the third dorsal interosseous muscle.

Figure 497
Third metatarsal bone medial and lateral views - Figure 497

Figure 498
Fourth metatarsal bone medial and lateral views - Figure 498

The fourth metatarsal bone (fig. 498) is smaller than the third. The proximal surface of its base bears an oblique quadrilateral facet for articulation with the cuboid bone; on its lateral side a, single facet, for the fifth metatarsal bone; on its medial side a facet divided by a ridge into an anterior portion for the third metatarsal bone, and a posterior portion for the lateral cuneiform bone. The medial surface of the shaft gives origin to the lateral head of the third dorsal and to the second plantar interosseous muscle ; the lateral surface gives origin to the medial Bead of the fourth dorsal interosseous muscle.

The fifth metatarsal bone (fig. 499) is recognized by a rough eminence, termed the tubercle. on the lateral side of its base. The base articulates proximally by a triangular, oblique surface with the cuboid bone, and medially, with the. fourth metatarsal bone.

Figure 499
Fifth metatarsal bone medial and lateral views - Figure 499

The tendon of the peroneus tertius is inserted on the medial part of its dorsal surface, and that of the peroneus brevis on the dorsal surface of the tubercle. A strong band of the plantar aponeurosis connects the projecting part of the tubercle with the lateral tubercle oďż˝ the calcaneus. The plantar surface of the base is grooved for the tendon of the abductor digiti minimi, and gives origin to the flexor digiti minimi brevis. The medial side of the shaft gives origin to the lateral bead of the fourth dorsal and to the third plantar interosseous muscle.