156 



ABNORMAL CONDITION OF THE ANKLE-JOINT. 



reception of the astragalus, makes with the 

 latter a perfect mortise joint, which admits 

 of motions of flexion and extension, but 

 allows of no motion whatever laterally or 

 horizontally; for it must be recollected that 

 those motions of inclination of the foot, known 

 under the names of adduction and abduction, 

 are not movements in the ankle-joint, but take 

 place in the joints of the tarsus : but the un- 

 natural mobility in question is very great when 

 the fibula is broken at its lower part; this is 

 shewn, when, after the surgeon has bent the limb 

 to relax the muscles, the leg is fixed by one 

 hand placed at its lower extremity, whilst the 

 other moves the foot from within outwards; 

 the foot is then seen to move in a transverse 

 line and to quit the axis of the leg ; the mal- 

 leolus internus projects inwards, and the mal- 

 leolus externus is moved upwards and out- 

 wards, and all these appearances vanish, when 

 by a contrary movement we bring the foot to 

 its natural position. 



When we le,ave the limb for a moment to 

 itself, we notice that there is a remarkable 

 change in the point of incidence of the axis 

 of the leg upon the foot. The tibia and upper 

 fragment of the fibula, although really remain- 

 ing in their natural position, appear driven in- 

 wards, while the foot is rotated outwards. 



The changes of direction of the leg and foot 

 are such, that if the axis of the leg were pro- 

 longed inferiorly, instead of falling on the 

 astragalus, it would leave this bone, and con- 

 sequently the whole foot, more or less on its 

 outer side; hence the impossibility patients 

 experience of bearing upon the foot , which 

 only presents its inner edge to the ground. 



Fig. 51. 



Fig. 52. 



Partial luxation of the Tibia inwards, or Pott's 

 luxation. 



This change is a necessary and constant effect 

 of the displacement of the foot, when the 

 fibula ceases to support it on the outer side, 

 arid when the peronsei muscles begin to con- 

 tract. The foot and external malleolus which 

 make part of one system, move in one direc- 

 tion ; the tibia and upper fragment of the fibula 

 move, or, to speak perhaps more correctly, 

 remain, in another. The centre of this new 

 motion is no longer in the articulation, but, 

 in an oblique line, passing through the joint, 

 and extending from the malleolus internus to 

 the point of fracture of the fibula: this line is 

 well expressed in Jig. 51, representing the frac- 

 ture of the fibula, and taken from the engrav- 

 ing which accompanies the work of Pott. 



The retiring angle seen (fig.5\, 52, a) in this 

 partial luxation of the tibia inwards, on the 

 outer part of the articulation, and the pro- 

 jecting one (b) existing at the inner, consti- 

 tute the most striking features of the accident ; 

 these angles correspond exactly to the extremi- 

 ties of the line above-mentioned, in the direc- 

 tion of which the weight of the body acts, when 

 the foot being turned outwards this line may 

 be seen to traverse the leg obliquely from the 

 lower part of the upper fragment of the broken 

 fibula to the malleolus internus. 



We cannot omit to notice also, that there is 

 in all these cases a remarkable rotation of the 

 whole foot on its long axis, in such a direction 

 that the upper surface of the astragalus looks 

 obliquely upwards and inwards, f/g.52,cj the 

 inner edge of the foot is turned downwards, 

 the sole inclined outwards, the outer edge 

 raised, and the dorsum turned directly upwards. 

 The extent of this rotatory motion is besides 

 always proportioned to the displacement out- 

 wards ; both are attributable to the same causes, 

 viz. the weight of the body, and the action of 

 the peronaei muscles, when the patient has at- 

 tempted to walk after the fracture has occurred. 



It is on these combined movements when 

 not corrected by a proper mode of treatment, 

 that the deformity of the foot, and all the 

 consequent difficulties in walking, depend. 



Complete luxation of the tibia inwards from 

 the astragalus, complicated with a simple frac- 

 ture of the fibula. This is a very severe, and, 

 fortunately, a very rare accident. In alluding 

 to it, Dupuytren says,* that " the foot is not 

 only susceptible of being carried outwards, but 

 also upwards at the same time;" a double 

 displacement, which he had observed to occur 

 only once in 200 cases of fractures of the 

 fibula treated in the Hotel Dieu for fifteen 

 years, " but the case was so marked," he says, 

 " that in future it cannot be mistaken or passed 

 over in silence." It cannot occur unless the 

 fibula is fractured ; for this condition is indis- 

 pensable to any displacement of the foot in- 

 wards or outwards ; it requires besides a com- 

 plete laceration of the short thick ligaments 

 placed between the tibia and fibula, the strength 

 of which is such that, in most experiments on 



* Sur la Fract. de 1'Extremite inferieure du Pe- 

 rone, in Annuaire Med. Chir. des Hopitaux de 

 Paris, 1809, 4to. and folio. 



