FOOT, ABNORMAL CONDITIONS OF TI1E.—The dislocation of any of the bones of the foot is an accident of unfrequent occur rence, particularly of the tarsus and metatarsus, where the ligaments are powerful, and the joints very limited in their motions. When a dis placement does occur here, the violence neces sary to produce it is often so great, that the foot is destroyed. Cases, however, are met with where a dislocation of one or more of these bones has been successfully treated without loss of the limb. Sir A. Cooper mentions several instances. The astragalus alone, without the other bones of the foot, is never thrown back wards, nor is it ever thrown directly inwards nor directly outwards, but it may be dislocated forwards on the instep and then may incline inwards, so as to be situated below and in front of the inner malleolus, or it may incline out wards and be placed below and in front of the outer malleolus ; the rest of the foot in the latter case is thrown inwards, and in the former outwards.
In these cases there is what Boyer calls a double luxation of the astragalus, for this bone is not only expelled by violence from the mor tise-shaped cavity formed for it by the bones of the leg, but is at the same time driven from the space formed between the os calcis and os naviculare, where it naturally rests or plays in standing or progression.
Most of the ligamentary ties which bind it to the other bones of the foot and leg are vio lently ruptured, yet in these eases the surgeon almost invariably finds great difficulty in ex tracting the bone from its new situation, and to return it back to its original space in general is quite impracticable.
One reason for the difficulty the surgeon experiences in replacing the luxated astragalus may, we imagine, be found in this, that the bones once expelled by violence, the muscles attached to the tendo Achillis, and, indeed, all those of the leg before and behind, act so on the foot as to have a powerful and effective influence in effacing the interspacc between the os calcis and articulating surfaces of the tibia and fibula, so that there is now no room for its return.
Moreover, it should be recollected that the astragalus is sometimes only partially luxated, and perhaps at the same time has revolved on its long axis in such a way that it shall be placed as it were on its side, as we have known an example, in which the pulley-shaped sur face of the astragalus looked outwards, the peroneal articular surface looked downwards towards the os calcis, and the facet for arti culation with the tibial malleolus was placed upwards in contact with that part of the tibia which was naturally shaped for articulation with the upper part of the trochlea of the astm gains : when the astragalus is thus rotated on its longitudinal axis, a broader part of the bone is wedged in between the tibia and os calcis than the vertical height of the astragalus would measure, and hence there is difficulty in re storing the bone or removing it. Fig. 16t re presents the simple dislocation. More than one example is mentioned by Sir A. Cooper in which this bone was removed entire after a compound dislocation of it, and yet a very tolerable use of the foot was regained.
A heavy weight falling upon the foot will sometimes displace the double articulation be tween the first and second row of tarsal bones. When this accident has occurred, the appear ance which the limb assumes bears a striking resemblance to the internal variety of the club foot. In fact this state of the parts really con stitutes neither more nor less than the pied-hot, with the exception of the difference of the cause, the state of ligamentous connections, and the facility of reduction.
Dislocation of the other tarsal bones is very rare, yet Sir A. Cooper has seen the inner cuneiform bone displaced in two instances, in neither of which could the bones be reduced. See also Diet. des Sciences M6dicales, art. Pied.