66 while others have sought to avoid misunderstanding, by using such a phrase as dislocation of the fifth upon the sixth." The latter form can be advantageously employed in the report of cases, or whenever any doubt might arise as to the meaning, but it will be convenient here to follow the more general practice, and speak of the upper vertebra as the 1. Anterior tubercle of transverse process. 2. Foramen for vertebral artery. 3. Posterior tubercle of transverse process. 4. Transverse process. 5. Superior articular process. 6. Inferior articular process. one that is dislocated, and of the direction and character of its displacement, as those of the dislocation. 1. Superior articular process. 2. Facet for tubercle of rib. 3. Demi-facet for head of rib. Classification and Pathology.-The relations of the vertebræ to each other are so complex, and the combinations of different directions which the displacements may present are so variable and numerous, that a classification of the varieties based upon these directions is not only very complicated, but it also fails to offer comparative advantages sufficient to compensate for its complexity. The classification made by Hueter, according to the character of the movement or the direction of the force which produces the dislocation, is simple, and at the same time indicates the main features of the displacement and suggests the proper method of reduction. It fails, however, to distinguish between the varieties; and, therefore, while adopting it, it has appeared desirable also to use in connection with it other terms indicative of special features. FIG. 25. The provisions for normal motion between adjoining vertebræ consist in the elasticity and compressibility of the intervertebral disks between the bodies, and in the articulations placed just behind those upon the arches. The normal range of motion, though varying in the different portions of the column, is at best slight, and can be referred in the main to two axes for each pair, one of which lies in the median plane and passes through the centre of the disk from behind forward, with an inclination downward of its anterior end which is slight in the lumbar and lower dorsal regions, more marked in the upper dorsal, and greatest in the cervical regions (Fig. 25). The other axis is a horizontal transverse one, passing through the posterior part of the disk. Motion about the first axis produces a lateral bending of the column, and, in the cases in which the axis is inclined downward and forward, with this motion must be associated a rotation of the upper vertebra, by which the anterior surface of its body is turned to the side toward which the column is inclined; and the greater the inclination of the axis, the more marked is this associated rotation. The movement is arrested by the contact of the margins of the adjoining articular surfaces with their bases on the concave side, and if it persists beyond this point dislocation is produced, the opposite inferior articular surface of the upper vertebra being raised above the one with which it articulates by the lateral bending, and being carried forward by the rotation. To these dislocations Hueter gives the name dislocations by abduction or rotation. Direction of the median axis in the different sections of the spinal column. (HENKE) Motion about the other, transverse, axis produces a bending forward (or, to a less degree, backward) of the column, during which the ante 1 This normal rotation toward the concave side should not be confounded with the pathological rotation toward the convex side observed in scoliosis; the latter is, in part at least, produced by a progressive asymmetry of the vertebra itself, the shortening of the pedicle upon the convex side. rior portion of the disk is compressed, the posterior portion stretched, and both inferior articular surfaces of the upper vertebra moved upward and forward along the superior articular surfaces of the underlying vertebra. The movement is checked, when its normal limit is reached, by the ligaments of the joints and arches, and, if these yield, a dislocation is produced, in which the inferior articular processes of the upper vertebra pass forward and in front of those with which they articulate-dislocation by flexion. Under the first head, dislocations by abduction, are to be included the complete or incomplete unilateral dislocations forward or backward, and the bilateral dislocations in opposite directions, described as distinct forms under these names by Blasius, all of which, with one exception. (the unilateral dislocation backward), represent only different degrees of the same displacement. Instead of being entirely separated from each other, the articular surfaces may remain in contact at their edges (incomplete dislocation). If the displacement is somewhat greater, the inferior process of the upper vertebra passes further forward, and sinks into the notch between the body and the superior articular process of the lower vertebra (complete unilateral dislocation) (Fig. 26), and at the same time Complete unilateral dislocation by rotation or abduction; cervical vertebra. (KÖNIG.) the inferior process on the opposite side may be carried backward by the movement of rotation (bilateral dislocation in opposite directions). Blasius quotes four cases in which the latter variety was observed and verified by post-mortem examination; the dislocated vertebræ were the second, fourth, and fifth cervical, and the eleventh dorsal, and the dislocation was forward on the left side in the first three, and forward on the right side in the last one. The unilateral dislocation backward, of which Blasius refers to a few examples exclusive of those of the occiput upon the atlas, may, I think, be attributed to the same mechanism, the displacement being effected in consequence of the yielding of the ligaments of the joint on the side toward which the body is bent, instead of on the opposite side as in the other cases. In a case observed by Cloquet, and briefly mentioned by Blasius, the second lumbar vertebra was dislocated in this manner, the dislocation being complicated, but unessentially, by fracture of the body and arch of the vertebra; all the processes were uninjured. The patient survived several years, and the condition of the parts was determined by autopsical examination. Under the second head, dislocations by flexion, are included bilateral dislocations forward or backward. The force continuing to act after the normal limit of forward flexion of the column has been reached, the ligamenta subflava are ruptured, and the posterior portion of the intervertebral disk is torn or separated from the vertebra with or without avulsion of a portion of the bone, the articular processes of the upper vertebra lodge in front of those of the lower in the notches. Sometimes the processes do not pass entirely beyond each other, but remain in contact at their extremities; and sometimes, the movement being accompanied by slight rotation of the vertebræ upon each other, one articular process is displaced further forward than the other. The lumen of the vertebral canal may be seriously encroached upon in this dislocation, and its contents injured by compression against the upper edge of the body of the lower vertebra. The mechanism of the double dislocation backward, of which a few cases have been accurately observed, has not been demonstrated, but the possibility of its production by extreme dorsal flexion of the column is such that it may, provisionally at least, be placed in this class. Its comparative rarity is to be explained by the infrequency with which the trunk is exposed to this movement, and by the greater resistance to dislocation which arises from the relations of the bones. The motion is arrested by bony contact at the arches, and by the intervertebral disks, the efficiency of whose resistance is increased by their greater distance from the fulcrum about which the rupturing movement must turn. It is interesting to note that in a case reported by Stanley,' dislocation backward of the fifth cervical vertebra, the upper five vertebræ were firmly united together by bony fusion. The displacement was so great that the body of the fifth rested upon the lamina and spinous processes of the sixth. The additional leverage created by this ankylosis may be invoked as an argument in favor of the theory of production by dorsal flexion. Transverse dislocation has been diagnosticated in several cases, but the only one in which sufficient anatomical proof has been obtained is one mentioned by Charles Bell. A child was run over by a stage coach and died of croup thirteen months later. The last dorsal vertebra was found completely displaced to the left side of the first lumbar with slight chipping of the bone. The articulation between these vertebræ is of such a character that this form of dislocation would seem impossible without fracture of the articular processes, and probably it may still properly be deemed so except in a child. The same anatomical conditions exist in the lumbar vertebræ, but in the dorsal and cervical regions the articular surfaces look backward and forward or are only slightly inclined to one side, consequently this form of dislocation must then be regarded as possible. In the greater part of the dorsal region it would necessarily be associated with dislocation of the vertebral end of the corresponding rib. Bell's case and another involving the same vertebra reported by Mohrenheim are quoted by Blasius but rejected on the ground that the primary dislocation was probably bilateral backward or forward, and the transverse displacement secondary. There is nothing in the original report of Bell's case to warrant this assumption, which must therefore rest on 1 Stanley Edinburgh Med. and Surg. Journ., October, 1841, p. 404. theoretical considerations alone. In all the clinical cases quoted by Blasius, with one exception, the cervical vertebræ were concerned, and he says that the correctness of the diagnosis is very doubtful in all. The main groups and varieties, then, are as follows: Dislocations by flexion, ventral or dorsal. Bilateral forward. Unilateral backward (incomplete. The associated lesions comprise rupture of the various ligaments, muscles, blood vessels, and nerves, fracture of the bones, and injuries of the spinal cord and its membranes, and those later changes which may be induced by the primary ones. The intervertebral disk is always ruptured or torn away from one or the other vertebra, and this rupture or separation is almost invariably complete, the exceptions having been found in a few of the slighter forms or in diastasis. The line of separation may run entirely within the substance of the disk or between it and the body of the vertebra, but usually it combines the two forms and is accompanied by the avulsion of larger or smaller fragments of the bone. In one or two cases the disk appears to have been crushed. The capsular ligament, on one or both sides according to the character of the displacement, is always torn. The anterior and posterior ligaments are either torn, wholly or in part, or stripped from their attachments to the bodies of the vertebræ, sometimes bringing with them in the latter case portions of the bone. The ligaments between the lamina and the spinous processes are either torn or put upon the stretch, and those between the transverse processes were torn in the only reported case found by Blasius in which their condition was mentioned. Instead of rupture of the ligaments fracture of the processes to which they are attached may occur, and various other fractures of the adjoining processes or of more distant parts are frequently observed. The surrounding and the attached muscles may be torn by the displacement or by the direct action upon them of the dislocating violence. Bloodvessels. The veins coming from the bodies of the vertebrae and those of the meninges of the cord are so large and their relations with the bones and ligaments are so close that hemorrhage is always free and sometimes very profuse. In Robert's case of backward dislocation of the fifth dorsal vertebra the blood escaped into the mediastinum and through the torn pleura into the pleural cavities; in it also, as in many others, the adjoining muscles were extensively infiltrated with blood. In dislocations of the cervical vertebræ the vertebral arteries so commonly escape injury that the possibility of their rupture has been denied, but in a case received into St. Thomas's Hospital' the vertebral artery 1 Robert Bull. de la Soc. de Chirurgie, September 21, 1853. |