The joints of the toes, as they are more moveable and their ligaments more lax, are more easily dislocated than the other joints of the foot, and especially the great toe, which has more extent of motion than the rest, and is more exposed to the influence of accident.
Congenital displacement of the bones of the foot is by no means an uncommon occurrence, and though in our English systematic works on surgery this case has met with little notice, yet, as a subject of great importance to the comfort and well-being of a numerous class of sufferers, it is by no means undeserving of a place in a professed work on surgery. As, however, the scope of the present is not strictly surgical, we shall, in this article, content our selves with a pathological description of the principal varieties of these deformities, and in doing this we shall freely avail ourselves of the assistance of an able article on the " Pied-hot," by Bouvier, in the Diet. de Mt decine et de Chirurgie Pratiques.
The ankle-joint is not generally implicated in congenital deformities of the foot ; displace ment of the bones may occur to an extreme degree, and yet the natural form and functions of the ankle remain. But this rule is by no means universal. The ankle-joint may be the sole seat of the unnatural condition, or it may share it in common with the bones of the foot; but these cases are rare, they form only the ex ception to the general rule. There are three principal forms of distortion to which the foot is congenitally subject: 1. when the foot is turned inwards, which has been termed varus: 2. when it is turned outwards, called va/gus: 3. when the foot is permanently extended, and the patient can only put the toes to the ground, termed pes equinus. Almost all the varieties of club-foot may be referred to one of these species.
1. When the foot is turned inwards, (varus,) the following modifications in the form of the parts present themselves. (See figs. 162, 163.) The dorsum faces forwards, the sole is turned backwards, and very considerably curved upon itself. The inner side of the foot is uppermost, the outer side rests upon the ground, the heel is more or less turned inwards and upwards.
The integuments of the outer side are thickened by pressure, and there is a sort of provisional cushion, of a somewhat elastic nature, formed under it, while the thickness and hardness of the integuments of the sole are not found to the usual degree. The joints that suffer most in this malformation are, as might be expected from a review of their natural structure, the double articulations between the first and second row of tarsal bones. The scaphoid bone is twisted inwards in such a manner, that the dorsum of it presents forwards and its apex backwards, and the navicular cavity is brought to the inner edge of the astragalus. The cuboid bone generally preserves its relation to the scaphoid, being more or less displaced from the os calcis, and turned under the foot. The cuneiform bones, the metatarsus, and toes, are little altered in their relation to those tarsal bones to which they join, the peculiarity of their position and direction being entirely the result of the alterations in the scaphoid and cuboid, just mentioned. The os calcis is turned, so that its outer side is inclined to wards the ground, and further than natural from the outer malleolus; the inner hollow side is inclined upwards and inwards, and nearer to the inner malleolus than natural, and the heel itself is elevated. By this means the articula tions between this bone and the astragalus are altered somewhat, particularly if the ankle-joint itself remains natural, the astragalus not having partaken of the general malposition ; this bone is then thrown in some degree upon the outer side of the os calcis. The astragalus, we have said, rarely shares in the general deformity ; when it does it is tilted outwards, so that its upper surface inclines towards the external malleolus, and the articular portion itself be comes altered in form, as is also the corre sponding portion of the tibia ; in one instance re lated by Bouvier, the astragalus, by the pressure of the inner side of the tibia above and of the calcis below, was reduced to a mere thin edge on this side, the whole bone being something in form of a wedge between them.