These names are applied to distortions of the feet, or more rarely of the hands; the bones assume certain abnormal positions in which they are retained by the contraction of muscle.
A certain proportion are Congenital, the child being born with one, or more commonly both feet, turned rigidly in, so as to form a Talipes varus. The muscles keep the foot in this position. According to Eschricht and Berg, the foot in early foetal life is inverted, and at birth normally retains a degree of inversion, the soles being turned in. An exaggeration of this, or a retention of the early foetal condition, constitutes a congenital club-foot.
The Non-congenital forms are, in most cases, due to infantile paralysis, a disease in which some muscles are paralyzed, while others are not. In some cases the deformity is due to the rigid contraction of the unparalyzed muscles, a condition to which the name Paralytic contracture is given. In many cases, however, the faulty position is largely due to the fact that the paralyzed muscles are not able to keep the foot in its proper position, so that it tends to fall into the attitude it would assume if there were no muscles. These positions are also variously modified by the use made of the foot in walking, the parts being brought against the ground in the position most suitable to stability in the maimed condition of the limb. In a similar way clubfoot may occur in pseudo-hypertrophic paralysis.
Besides paralysis, it seems that spasm may lead to talipes, although the explanation of the local spasm is often very obscure. It is undoubted that children sometimes acquire a talipes after a convulsive attack.
These do not call for detailed description here. There are four principal forms, some of which may be combined. In Talipes varus the toes are inverted, and the inner margin of the foot is raised upwards; the tibiales anticus and posticus are the muscles which are chiefly contracted. In Talipes valgus, which is one of the rarer forms, the foot is turned outwards, the outer border is raised, and there is usually also some elevation of the heel the peronei, extensor longus digitorum, and gastrocnemius are the muscles chiefly engaged. In Talipes equinus the heel is raised and the foot extended, so that the person walks on the distal extremities of the metatarsal bones; the gastrocnemius is the muscle contracted. In Talipes calcaneus the heel is depressed, and the foot flexed at the ankle, this deformity being the reverse of the preceding one; the contracted muscles are chiefly the tibialis posticus, the peronei, and the extensors.
By long retention of the fixed position the Bones become variously modified in shape, undergoing atrophy where exposed to prolonged pressure. Where the cartilage is no longer used in the movements of the joints, it also atrophies. The bones frequently acquire adhesions in their new positions, and the ligaments, by elongating or shortening, accommodate themselves to the new position. New ligamentous attachments are sometimes formed, and the bones may become joined together by anchylosis.