Dislocation of the fibula, at the upper tibio-fibular articulation, has occasionally, but rarely, been met with as the result of injury. Sir A. Cooper mentions a case of compound fracture of the tibia, where this complication was observed ; but the rarity of dislocations in this situation, is accounted for by the cir cumstance, that the fibula, owing to its com parative slightness, almost invariably breaks, on the application of a force far short of what suffices to rupture its ligamentous connections with the tibia.
The mechanism of the inferior articulation is inseparably connected with that of the neighbouring articulation of the ankle. In fact, on the perfect adaptation of the bones of the leg, at their lower extremities, essentially depends the integrity of the ankle joint itself.
By the union of the tibia with the fibula the "mortice shaped" cavity, which receives the pulley of the astragalus, is formed, and any injuries which disturb the natural rela tions of these two bones interfere propor tionally with the functions of the ankle, which is a perfect angular ginglymus.
Hence it is, that in some cases of fracture of the lower end of the fibula, a widening of the mortice is produced, from which more or less of permanent deformity and inconve nience results, abnormal lateral motion being then permitted. The connecting media be
tween the tibia and the fibula inferiorly are of extreme strength ; so much so, that no ordinary violence seems capable of rupturing them ; the bones being bound together, not only by the special ligaments of the inferior tibio-fibular articulation already described, but by the annular ligaments and fascia' of the leg also. Hence, as we might infer, the separation of these hones by injury has never been observed, except when the fibula has first been broken. In the "complete dislocation of the 'foot up wards and outwards, we are furnished with an illustration of the immense strength of the interosseous ligament ; as it is found that even in this severe injury the fibres of this ligament are not usually torn ; but the rough surface of the tibia into which they are implanted is broken off, and carried upwards and outwards with the lower end of the fibula, to which the interosseous ligament still binds it." (See b. fig. 54. vol. i. page 157 ; article " ABNORMAL CONDITIONS OF THE ANKLE JOINT.") (Ben. George 114‘Dowel.)