ANTHROPOLOGICAL PAPERS MUSEUM OF ANTHROPOLOGY, UNIVERSITY OF MICHIGAN No.4 Lumbar Breakdown Caused By Erect Posture In Man With emphasis on Spondylolisthesis and Herniated Intervertebral Discs by FREDERICK P. THIEME ANN ARBOR UNIVERSITY OF MICHIGAN PRESS, 1950 © 1950 by the Regents of the University of Michigan The Museum of Anthropology All rights reserved ISBN (print): 978-1-949098-39-6 ISBN (ebook): 978-1-951519-63-6 Browse all of our books at sites.lsa.umich.edu/archaeology-books. Order our books from the University of Michigan Press at www.press.umich.edu. For permissions, questions, or manuscript queries, contact Museum publications by email at umma- [email protected] or visit the Museum website at lsa.umich.edu/ummaa. CONTENTS Page Introduction .... Acknowledgments 4 Material ...•.. •, 4 Separate Neural Arches 5 Herniated Vertebral Discs 14 General Anatomy ..... . 18 Detailed Lumbar Anatomy. 20 Fractures of the Spine • 25 Anthropometric Data 27 Discussion. 35 Summary. 38 Literature Cited 40 LUMBAR BREAKDOWN CAUSED BY ERECT POSTURE IN MAW INTRODUCTION It has long been assumed that man suffers many disorders as a result of his erect posture and that b~pedal locomotion imposed on an anatomy of quadrupedal heritage has caused breakdowns. The purpose in this paper is to investigate this assumption and to place in an evolutionary setting certain clinical and anatomical findings related specifically to lumbar breakdown. Becoming erect on the ground was a critical stage in human evolution and a prerequisite to the final stages in human cerebral evolution (Weidenreich, 1941). Gross as well as minute anatomi cal changes were required to meet the new postural adaptation. Changes in the anatomy have resulted as new functions were im posed on old parts. Although the semierect posture of the brachi ating apes would seem to have been the postural preadaptation which prepared the way for human locomotion, the addition of the lumbar curve was necessary to complete the change. This change in the anatomy of the lumbar region makes erect locomotion pos sible, and man alone possesses this. Skeletally, the morphology of the lumbar region has its herit age rooted in a mammalian development adjusted to quadrupedal function. With erect posture the skeletal form remains much the same, but with considerable change in functional mechanical re quirements. In no mammal except man is there paleontological (Moodie, 1923) or modern evidence of lumbar breakdown. Nor have I seen in a search of the literature any substantial frequency of lumbar area disorders in any other mammal. It would seem, therefore, that man is unique in frequently having low back disorders. The structural adjustment to erect posture is typically human and not limited to any one anatomical area. One such example of human locomotion adaptation is in the greater length of the lower extremities (Schultz, 1937). Many characteristics of the foot (Wood-Jones, 1916), changes in the pelvis (Darwin, 1871; Schultz, 1930), and many changes in the muscles (particularly the gluteus maxim us and quadriceps extensor femoris [Hooton, 1946]) are features which clearly distinguish man from the great apes. All are concerned with upright posture. 'Submitted as partial fulfillment of the requirements for the degree of Doctor of Philosophy for the Faculty of Political Science, Columbia University. 2 LUMBAR BREAKDOWN The structural adjustment to erect posture is very old in man. Terrestial locomotion was probably the adaptation which began the separation of man from the other primates and seems to have been rapidly accomplished. In the earliest known human fossils the limb bones are essentially human although differing from mo dern man in details (Weidenreich, 1946, 1947). The femur of Pithecanthropus erectus was so similar to that of modern man that its correct association with the skull finds was long doubted and this morphological asymmetry gave rise to considerable dis cussion (Hooton, 1925). In discussing recent australopithecine finds from South Africa, LeGros Clark (1947) has this to say about these forms: "Lastly, the limb bone fragments, particularly the lower end of the humerus of Paranthropus, and the lower end of the femur of Plesianthropus, seem to indicate a limb structure which evidently approximates very closely indeed to that of Homo sapiens. This evidence of the limb bones is sufficiently startling in character to raise a doubt as to whether they actually belonged to the same creatures as the skulls of Plesianthropus and Paran thropus. That the association is entirely correct, however, seems quite well assured." The recently announced discovery of the pelvic bones of Austra pithecus prometheus (Dart, 1949) confirms the indications of upright posture seen in earlier finds. Whether these finds are considered to be in the line of evolution leading Homo sapiens is of no moment here, but they do demonstrate that the locomotive adaptation was early and not necessarily associated with other typically human morphology. This early and rapid change in pos ture contrasts with that in the skull, of which an almost complete series of intermediate forms is in existence, bridging the gap from earliest to recent man. The skull series is apparently sc orthogenetic that some anthropologists judge the antiquity of skulls more by their situation on this morphological time scale, less with regard to their geological location. Cranial capacity, dental pattern, and many facial features exemplify the apparent gradual change. Regions of the body as they relate to function, thus have different evolutionary patterns. The locomotor system changed from quadrupedal to bipedal very early in man 1 s evolutionary development and has changed little since. The skull, in modifica tions relating to increased brain size and decrease in mastication equipment, has changed gradually and without reversals. In contrast to the limb bones and the skull the vertebral column has changed very little in response to the demands of upright loco- INTRODUCTION 3 motion. "Man is very significantly more stable in regard to nu merical variations in vertebrae than are the other forms of higher primates" (Schultz and Straus, 1945). Schultz (1930) stated that man in comparison to the anthropoids is more generalized in this region. The specialization in posture has been accomplished with little change in the vertebral column, except for the development of curves. The total effect of these evidently different rates of evolutionary reponse to the single postural change is an unbalanced adaptation. The frequency and type of ·structural breakdown in the spine, particularly in the lumbosacral region, seem to bear this out. In this region the anatomical adaptation to upright posture is apparently unsatisfactory and probably incomplete. In fact the lumbar curve is probably developed anew in each individual during the growth period, and many of the typically hu man characteristics of the spine are similarly developed in re sponse to function rather than inherited. The situation is similar to other skeletal features in the body which reflect upright locomotion. For example, Weidenreich (1940) has shown it to be true for the external tubercle of the tuber calcanei. Although the lower back is particularly subject to structural disorders due to the development of the lumbar curve, other regions concerned with locomotion are also affected. Keith (1923) was the first to give a general account of the inadequacies of hu man adjustment to erect postural adaptations, and the matter has been gloomily reviewed by Hooton (1939). Morton (1935) traced many foot disorders back to inadequate pedal mechanics. The semilunar cartilages of the knee are frequently torn (Callander, 1939). The neck of the femur is a region of frequent fractures {Watson-Jones, 1943). In the pelvis the shortening of the lower ilium (Straus, 1927) and the development of the true bony birth canal have given rise to obstetrical difficulties (Cauldwell, Moloy, and D'Esopo, 1934). Hernia, visceral optoses, and prolapses in human beings have frequently been traced to erect posture (Keith, 1923; Gregory, 1928). Although the idea is very old that structural weakness of the lumbosacral area followed the assumption of erect posture, the exact nature of these pathological breakdowns and their mechanics has only recently been understood. The development of orthopedic surgical techniques together with improved roentgenographic methods has made possible the diagnosis, treatment, and under standing of the mechanical breakdowns causing backache. Since 1930 voluminous clinical literature resulting from this has focused attention on conditions previously considered rare but now known to be rather common.