The first metatarsal articulates with the internal cuneiform by a complete joint, which undergoes an outward subluxation in the condition called hallux valgus, the suppurating bunion, which frequently forms in this condition, sometimes communicating with and causing disorganization of the joint. The second and third metatarsal bones articulate with the middle and external cuneiform bones respectively being connected by dorsal and plantar ligaments, the latter reinforced by slips from the tibialis posticus tendon. The second metatarsal, however, is connected to both internal (ligament of Lisfranc) and external cuneiforms by means of interosseous ligaments. The fourth and fifth metatarsals articulate with the cuboid, being connected by dorsal and plantar ligaments, the latter reinforced by slips from the long plantar ligament. The fourth also is connected to the external cuneiform by an interosseous ligament, and the bases of the third and fourth are also connected by an interosseous ligament. There are six separate joint cavities in the tarsus and metatarsus-namely, (i) Posterior calcaneo-astragaloid. (2) Calcaneo-astragalo-scaphoid. (3) Calcaneo-cuboid. (4) Anterior tarsal. This is a large articulation, and extends (a) between the scaphoid and three cuneiforms ; (b) between each of the cuneiforms, and between the external cuneiform and cuboid ; (c) between the bases of the second and third metatarsals, and middle and external cuneiforms respectively ; (d) between the contiguous surfaces of the second, third, and fourth metatarsals. (5) Between internal cuneiform and first metatarsal. (6) Between cuboid and fourth and fifth metatarsals.
The bones of the foot are frequently affected by tubercular disease, the os calcis being most frequently affected, then the base of the first metatarsal, astragalus, cuboid, etc. The disease generally affects the neighbouring joints, and in the case of the scaphoid the large anterior tarsal joint may be involved, and the disease thus become widely diffused. The tendon sheaths also become affected at times, especially the tibial and peroneal. In operating it is important to preserve, where possible, the os calcis, which supports the heel, and the head of the first metatarsal, which supports the ball of the toe. The os calcis is frequently affected by tubercular cario-necrosis, in which a spherical portion of bone is killed in mass (necrosis) by a spreading ulceration (caries), which surrounds and cuts it off. Such disease can frequently be removed without excision of the bone. The os calcis, while frequently fractured, is seldom dislocated, and when displaced is generally displaced outwards. It is the most frequently fractured tarsal bone, the fracture occurring from falls on the heel or from muscular action, the tendo Achillis tearing off the posterior portion. Ossification begins in the sixth month of foetation. 1 The astragalus may be dislocated forwards, backwards, or laterally, the latter being generally associated with forward movement. Forward dislocation is the most common, is generally complete, frequently compound, and is generally associated with fracture of the tibia, fibula, or astragalus itself.
In all cases the malleoli come nearer the sole, and there is also inversion in the forwards and outwards variety, and eversión in the forwards and inwards variety. Sub astragalo id dislocation of the foot occurs through the astragalo-scaphoid and astragalo-calcaneal joints, the astragalus retaining its position, and the foot being displaced generally backwards, and either in or outwards. In the former the foot is inverted and curved with the convexity on the outer side, thus resembling talipes varus ; in the latter the foot is everted, and the head of the astragalus forms a projection on the inner aspect. The condition is frequently compound, and is generally incomplete as regards the astragalo-calcaneal joint, and complete in the astragalo-scaphoid joint. The astragalo-calcaneal ligaments are torn, and the malleoli are frequently fractured. Fracture of the astragalus may result from a fall on the feet, and is frequently associated with fracture of the os calcis, but fracture of the bones of the leg is a more usual consequence. Ossification begins in the astragalus in the seventh month of foetal life. Dislocations of the scaphoid, cuneiforms, and individual metatarsals have been reported, but none of the cuboid alone. The cuboid begins to ossify at birth, and the scaphoid in the third year. Dislocations of all the metatarsals occur rarely, that upwards being the most common.
Deformities of the foot are generally classed under the heading of talipes, of which there are four principal varieties : talipes varus, talipes valgus, talipes equinus, and talipes calcaneus. The most common form of talipes is a combination of two of these-namely, talipes equino-varus-the foot being turned inwards, so that the patient walks on the outer side (talipes varus), while the heel and posterior portion of the foot are drawn up, so that the patient walks on the anterior portion of the foot only (talipes equinus). In addition the foot as a whole is somewhat curled, the sole becoming concave, and the toes being frequently so much turned inwards that in running the child requires to lift one foot over the other. This form is generally congenital, being due to a want of foetal unwinding, and consists primarily of a deformity of the bones, the astragalus being principally affected, the muscles and ligaments being sometimes affected secondarily. The neck of the astragalus is lengthened and curved, so that the head, which articulates with the scaphoid, looks inwards instead of forwards, as it normally does, and while the body of the bone is roughly cubical normally, it becomes wedge-shaped in talipes, the base of the wedge being directed to the outside of the foot, and the apex to the inside. The scaphoid and the os calcis may also become somewhat wedge-shaped, and the former may be so turned round that its tubercle touches the internal malleolus, while the latter is placed almost vertically. The weight of the body rests therefore, not on the heel, but on the cuboid and external surface in front of it, the prominence of the cuboid on the outer side of the foot being generally accentuated by the presence of a bursa. At birth and for some time afterwards the condition can generally be rectified by manipulation alone, the bones being cartilaginous and soft, and tending to unwind. Later, they become hard and unyielding, and other changes occur, the muscles attached to the tendo Achillis becoming atrophied and contracted, the tibiales possibly becoming similarly affected, while the plantar fascia also becomes contracted, and the knees tend to become slightly hyperextended and stiff. In such cases excision of the astragalus, combined if necessary with tenotomy of the tendo Achillis, yields good results.