The American cyclopedia of practical medicine and surgery: a digest of medical literature (Volume 2).

  • Isaac Hays
Date:
1834-1836
Catalogue details

Licence: Public Domain Mark

Credit: The American cyclopedia of practical medicine and surgery: a digest of medical literature (Volume 2). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    16/602
    astragalus; the remainder is prolonged downward and somewhat backward, into a kind of hook for the protection of a ten- don ; and this prolongation may be brought into contact with the external face of the os calcis, in violent abductions of the foot. The external descends much lower than the internal malleolus, and it is also situ- ated further back. The cavity for the re- ception of the pulley is considerably en- larged in rear by the posterior transverse ligament of the ankle joint, a band of very strong arched fibres stretching from one malleolus to the other along the posterior margin of the inferior extremity of the tibia. Into this complex cavity the pulley of the astragalus is received, and all the opposing surfaces of the bones are cover- ed with articular cartilages. The joint is secured by numerous ligaments, and has one synovial membrane common to the whole of this and the preceding articula- tions. In order to comprehend all the mo- tions of the foot upon the leg, it must be remembered that the pulley of the astra- galus is considerably narrower behind than it is before; hence, when the foot is flex- ed, the articular cavity is completely filled by it, and the motion of the joint is re- duced to a simple flexion and extension; but when the foot is extended, the cavity is not so fully occupied, and some slight lateral motion of the astragalus may take place. The interlocking between the groove in the upper face of the pulley of the astragalus, and the corresponding ridge of the tibia, together with the tonic contraction of the powerful muscles of the foot, and the position of the ligaments of the articulation, deprive the joint of all voluntary motion except that of a simple hinge; and it is only under the action of accidental forces, that it assists in the la- teral or rotatory movements of the foot. The ligaments of the ankle joint are all highly important in a surgical point of view, and their connexions must be care- fully studied by those who would perfectly comprehend the accidents to which the joint is subject. The astragalus rides upon the os calcis, and fills the cavity of the os naviculare, between which bones, and those of the leg, it acts somewhat in the manner of a fric- tion wheel, as we shall see hereafter. On its lower or plantar face, we observe a very deep groove, commencing near the posterior end of its internal margin, and passing forward and a little outward, so as to divide its lower articular surface into two nearly equal parts. Directly beneath this, is a similar groove on the upper face of the os calcis, which, with the former, completes an irregularly elliptical canal, beginning below the posterior edge of the internal malleolus, and terminating a little behind, and beneath the middle of, the an- terior margin of the articular pulley. This canal is filled by a very powerful interos- seous ligament, which is never completely ruptured except under the action of tre- mendous forces. Behind and on the outside of the inter- osseous ligament, we find the posterior or externa] articulation, between the astra- galus and the os calcis. It is arthrodial in character, the head being formed by the latter bone, and presenting upwards and forwards. The excavation in the astraga- lus which receives this head is of a lu- nated shape, and is surrounded by a rather sharp edge which posteriorly is particularly well defined. Its centre corresponds with the level of the apex of the internal malle- olus. This joint enjoys an antero-posterior motion in walking, in which case the astra- galus moves upon the os calcis ; a lateral motion in the adduction and abduction of the foot, during which the former bone re- mains at rest; and a very slight degree of rotation. A proper synovial membrane is exclusively provided for this articulation, which derives its strength chiefly from the interosseous ligament noticed above. The articulation of the head of the as- tragalus with the tarsus, is an enarthrosis. The cavity of the joint is formed, behind, by the lunated cavity of the os calcis, for its anterior or internal articulation with the former bone; before, by the concavity of the posterior face of the os scaphoides; and beneath, by the two calcaneo-scaphoid ligaments. All the parts interested in this articula- tion are lined by a common synovial mem- brane. The motions of the joint, like all those of a similar structure, are limited in extent only, i\nd not in direction ; in con- junction with the posterior articulation between the astragalus and os calcis, it permits the adduction, abduction, and ro- tation of the whole foot on the leg; in conjunction with the articulation between the os calcis and the cuboid bone, it enjoys other powers, unconnected with our pre- sent subject (see Foot); but it also con- tributes slightly to the flexion and exten- sion of the foot, and this fact is of high surgical importance, as will be elsewhere noticed. Art. II. Mechanism of the Injuries of the Ankle. Most off the peculiar inju- ries of the ankle joint result from undue and violent extension of some of the na-