This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The foot may be dislocated from the leg in nine different manners.
1. The foot as a whole may be carried outward. This is almost always associated with fracture of the fibula, and sometimes of the internal malleolus, constituting Pott's fracture (see page 557).
2. The foot may be carried directly inward. This likewise is associated with fracture of the internal malleolus.
3. The foot may be rotated out on its own anteroposterior horizontal axis (parallel with the sole).
4. It may be rotated in on its anteroposterior horizontal axis. Both these may be accompanied by fractures.
5. The foot may be rotated inward on a vertical axis longitudinally through the leg.
6. It may be rotated outward on a vertical axis.
7. The foot may be luxated backward, the tibia coming forward on the astragalus (Fig. 572).
8. It may be luxated forward.
9. The astragalus may be pushed up between the bones of the leg.
In Numbers 1 and 2 inward and outward displacement the foot is not immediately beneath the leg, but is to one side of the leg. The outward luxation when accompanied with laceration of the inferior tibiofibular ligaments or tearing off of a small portion of the tibia and fracture of the internal malleolus and fibula constitutes Dupuy-tren's or Pott's fracture. In Numbers 3 and 4 the foot remains beneath the leg bones and is not displaced much laterally. Numbers 1 and 3 are usually grouped together as outward luxations, and 2 and 4 as inward luxations. Numbers 5 and 6 are very rare. The foot is rotated so that one side looks forward and the other backward.
Number 7 backward luxation is the most common, with the exception of Number 1. When associated with Pott's fracture, backward luxation is produced by hyperextension followed by a thrust and is often compound. The leg is bent backward until the anterior and lateral ligaments rupture, and then the thrust sends the tibia forward on the instep. The articular surface of the astragalus being wider in front opposes the luxation, and fracture of one or both malleoli may result.
Numbers 8 and 9 forward and upward luxations are extremely rare, the former on account of the difficulty in the application of the dislocating force, - the flexion and thrust, - and the latter on account of the extreme strength of the inferior tibiofibular ligaments.
In attempting reduction of these luxations the principal thing is to relax the tendo calcaneus (Achillis) by flexing the knee. If this is not sufficient, tenotomy should be practiced. Simple extension with slight rotation and manipulation will then accomplish reposition.
Fig. 572. - Backward luxation of the foot at the ankle-joint.