The following Journals have been added to the files. Archives of Otology. Archives of Ophthalmology. Archiv für Laryngologie und Rhinologie. Archives Générales de Chirurgie. Comptes Rendus Hebdomadaires, Société de Biologie, Paris. Journal of Obstetrics and Gynecology of the British Empire. Monatsschrift für Ohrenheilkunde. Medizinische Klinik. Zeitschrift für Geburtshülfe und Gynäkologie. Deaths Joseph Hibble, of Enon, O., died August 10, aged 85. Medical Journal VOL VII OCTOBER, 1908 The Mechanics of Lateral Curvature By HENRY O. FEISS, M. D., Cleveland, O. No 10 By the mechanics of lateral curvature, I mean the study of the forces which actually bring about the pathologic effects. I assume that there are remote causes inciting these forces, but with these remote causes I wish to have little to do. I simply wish to deal with the proximate causes, or, as I say, the forces which actually bring about the disfiguration. This distinction between remote and proximate causes is in the main arbitrary, but in the present investigation is especially appropriate because the proximate causes of scoliosis are already suggested in conditions of the normal. It is namely in postural asymmetry in the normal that these forces seem revealed, and tonight I propose first to demonstrate the forces implied in normal posture or what I style the tendencies of normal posture, and secondly, to offer an explanation of the important points in the pathologic as based upon these normal tendencies. The relation between normal posture and scoliosis has already been carefully studied, notably by Lovett, but in these works the column alone has been examined. It is my purpose to consider the body in its entirety, for I believe the peripheral strains are just as essential for the comprehension of the phenomena as the strains in the column. I. THE NORMAL TENDENCIES OF POSTURE Segmentation and balance: The first point to which I wish to call your attention in the normal is the law of segmentation and balance. The body is not a firm mass but consists of segments Presented at the Philadelphia County Medical Society, May 13, 1908 For a fuller and more technical account of this subject, the reader is referred to the original articles appearing in the American Journal of Orthopedic Surgery, 1906, 1907, 1908. jointed together, one segment resting upon another. In all postures in which a balance is maintained the weight of these segments must be evenly distributed about an imaginary perpendicular which passes through the center of gravity and which is called the line of support; so with every change of attitude there must be a constant equilibration by means of these shifting segments. The integrity of the thorax: The next point to which I wish to refer, is the fact that the thorax may be regarded as one of these segments so that in every movement it acts as one piece. This is due to the construction of the thorax, because the upper 10 ribs are closely connected in front by the sternum and intricately joined behind each with two vertebræ and one transverse process. There is, moreover, an intimate ligamentous union between the ribs and vertebræ; so that the dorsal column really acts as part of the thorax. Of course, there may be some inherent motion between the vertebræ of this part of the column, but practically speaking, the thorax including the dorsal column moves as one piece. The trunk muscles: Another important point in the anatomy, as it applies to posture, is the manner of regarding the trunk muscles. According to the anatomist, G. Herman Meyer, the muscles running down the torso from the neck to the pelvis may be considered as a sheath or tube containing the viscera. He divides this tube into five systems (Fig. 1.) referring to them as the posterior system, the anterior system, the two oblique systems which cross each other, and the transverse system. The posterior system includes the large spinal muscles; it begins at the occiput and ends at the pelvis. The anterior system begins at the neck with the sternocleidomastoid and is continued from the sternum to the pubis in the shape of the two recti. The transverse system is the transversalis muscle. With regard to the oblique systems, he considers the external intercostals as continuous with the external oblique, and the internal intercostals as continuous with the internal oblique, the difference in the region of the thorax being simply that the ribs form rigid interruptions. The ribs, therefore, may be considered as nothing more than stiffenings in a flexible muscle tube and act like an umbrella in keeping this tube spread. Peripheral strain: As a result of the segmental movement of the body, to which I already referred, you will readily under stand that the tube of soft parts, made up as I have shown you, and connecting adjacent segments, must be subject to a constant change in tension. Therefore, if one segment moves upon an underlying one, the fact that such motion takes place must imply that the soft parts which connect them must be under greater tension on some sides than on others; so if the thorax moves as a segment any diversion thereof must mean that its walls come under strain on account of this peripheral tension. FIG. 1. G. Herman Meyer. The scheme of the trunk musculature indicating the direction of the various muscle pulls. a-posterior longitudinal muscle pull (m. sacrospinalis). b anterior longitudinal muscle pull. c-oblique descending muscle pull. d-oblique ascending muscle pull. e-transverse muscle pull. Studies on the living: To illustrate these points, let us turn to photographs of the normal. There are two primary positions -lateral bend and twist. All asymmetric attitudes come under one of these two heads, except those in which the two are combined. Studying first lateral bend, you will note the movement of the thorax as a unity and the tension of the muscular tube on the convex side of the body. This tension bears directly upon the thoracic wall which must, therefore, be under strain so that the ribs on the convex side must tend to distortion. The concave side of the body is relaxed. The picture of twist brings out the same general principles. Again it is plain that the ribs are strained owing to the tension of the peripheral tissues. Röntgen pictures: In the examination of Röntgen pictures these points are also borne out. If we take a fetus and bend it to one side (Fig. 2), the results of peripheral stress are noticeable FIG. 2. Röntgengram of fetus bent sideways. in that the thorax becomes narrowed on the convex side; but there is more, for the ribs actually descend and separate on the same side on account of the extreme tension. In a twist (Fig. 3), we note about the same result, although it is a difficult picture to interpret on account of the distortion of shadows due to the conical radiation of rays from the anode of the tube. In two living children which were bent to one side and radiographed, |