Principles of Osteopathy
4th Edition
Dain L. Tasker, D. O.

CHAPTER V - The Segmentation of the Body

    The Lesion as a Guide in Diagnosis. - Since the spinal lesion may be either cause or effect, i.e., a trauma or an expression of the body's protective reaction, we need certain fundamental facts upon which to base judgment.  No matter whether the lesion is cause or effect the physician must recognize it as a guide for the unraveling of a series of phenomena which are quite sure to be present in any case.  It is a well recognized fact that effects become causes and thus a cycle of reflexes become established making it difficult to recognize where the series began.  Any diagnosis worthy the name must be based on structure and function.  Much of the phenomena we are called upon to interpret is difficult to understand, unless we know not only normal structure but the development processes whereby this present structural formation was achieved.

    The Spinal Segment. - The far reaching influence of a cervical lesion can readily be understood when we study the embryological development of cervical structures.  To mention a nerve to a diagnostician should instantly bring to his mind all the structural associations of that nerve, its origin and distribution.  The thought of its origin and distribution would naturally bring to mind an association of all the tissues depending on it for innervation.  We would thus have a picture of a localized community of interests.  Considering the similar distribution on the opposite side of the body we have pictured a sort of transverse division of the body.  Every pair of spinal nerves, with the tissues directly under their influence, should form in our minds an entity, a mechanism in which reactions tend to take place independent of all other segments.  Although we may think of a segment as a unit, the development of the body has coalesced its various structures in such a way as to locate the nervous control of any one structure, such as a muscle, in more than one segment of the spinal cord, hence the controlling nerve to a muscle usually contains fibers from more than one segment.

    It is readily seen that there is an element of protection in this fact.  A slight central lesions i.e., an injury to the spinal cord, its membranes; or a pressure lesion due to disease of the bone, as in Pott's disease, might not produce complete loss of function in any single muscle because the governing nerve to that muscle is made up of fibers from two or more cord segments.

    Injury of a Single Nerve.  Example: Posterior Thoracic. - Complete paralysis of a single muscle is indicative of serious injury to its governing nerve at some point exterior to the central nervous system; in fact, beyond the point of coalescence of the fibers which form it.  As an example of injury of a single nerve we may take a case of paralysis of the Serratus Magntis.  This large muscle which acts to hold the posterior border of the scapula close to the thorax, when one is pushing with the hand or when taking a deep inspiration, is innervated by the posterior thoracic nerve which is made up of fibers from the upper portion of the brachial plexus, fifth, sixth and seventh cervicals.  Evidently an injury capable of involving all the fibers of the posterior thoracic nerve and no others must be peripheral to the point of junction of its fibers from the fifth, sixth and seventh cervicals.

    A patient came to me in 1901 complaining of a peculiar loss of power of the right arm.  He was a large, powerfully built young man whose occupation, as a lumber shover, unloading lumber on the San Pedro docks, was lost as a result of his condition.  He gave a history of perfect health at all times.  Said that two days previous, on Sunday he had erected a tent for himself and as he was tightening the guy ropes he felt a sharp pain under his right shoulder blade, which was immediately followed by an inability to push with the right arm.  The pain was of short duration.  He described his position as a somewhat awkward one, i.e., he was kneeling on his right knee facing one of the tent guy rope pegs.  With his right hand grasping the wooden clamp on the guy rope, he attempted to draw the guy rope taut.  His great strength enabled him to do this, even though his right hand was considerably behind him.  Figs. 4 and 5 show the effects of the paralysis of the Serratus Magnus in this case.

    A second case presenting exactly the same symptoms was seen in the clinic of the Pacific College of Osteopathy a short time later.  A telephone lineman, while engaged in stringing wire from pole to pole, made a vigorous awkward pull with the right hand some distance back of his hip.  His legs were entwined about the crosspieces of the pole.  At the time of greatest effort he felt a severe pain under the right shoulder, followed by a profound sense of weakness in the shoulder and arm.  The scapula immediately took a wing position and the patient could not shove with the right arm.

    These cases serve to give us a picture of the influence of position and motion of the shoulder as governed by one nerve taking origin from three cervical segments.  The lesion was not a spinal one, i.e., such as we have before described, neither was it one involving the cells of origin of this nerve in the spinal cord.  The awkward position of the patients and their naturally great strength operated to injure them in much the same way as the various nerve holds practiced by the jiu-jitsu wrestler.  The pressure where the nerve crossed the ribs became too great and, hence, caused a severe trauma of the nerve.

    A Unilateral Cervical Spinal Lesion. - The foregoing cases present the classical first symptoms of a severed motor nerve.  In order to present the symptoms accompanying a cervical lesion of the spinal lesion type we will describe a case which has been under observation for a long time. A woman, 41 years of age, has been under my professional care for three years.  At the time of my first examination she appeared to be constitutionally ill, but careful examination failed to discover any organic disease.  Functional rhythm seemed discordant everywhere, hence our first efforts were to see that environment was fairly normal.  Rest, nutritious diet and an optimistic atmosphere served to eliminate many of the irritating symptoms.

    The first examination of the spinal area discovered a lesion between the sixth and seventh cervical vertebrae.  There was muscular ankylosis controlling this articulation and any attempted movement of the whole cervical area, sufficient to make demand on this joint, caused pain of a sharp neuralgic character to radiate into the left shoulder and arm.  This pain could be produced most easily by either voluntary or passive rotation of the head to the left.  A persistent effort to rotate the head in this direction caused the hand and arm to become numb.  The hand would become bloodless, cold and moist; power to pick up a book or cup was greatly lessened.  These symptoms would wear off in twenty-four to thirty-six hours, but the pain would leave her in almost a state of collapse.  Massage of the arm and hand would bring no reaction; heat also failed to stimulate circulation.

    These attacks had been brought on by any sort of housework, at first only sweeping or such work as required arm leverage.  Later it seemed as though the attacks came without any mechanical reason.  They were accompanied by severe headache, tachycardia, meteorism, cold extremities and subnormal temperature.  As might be expected in such a case the spinal lesion picture was a mixed one and it seemed, in view of so many symptoms of autointoxication, as though the mid dorsal lesions were more nearly primary than the others.  The sensitiveness of this spinal column was so great and so many compensations were in evidence that it was deemed best to attempt at first merely to simplify the symptom complex as much as possible by giving the spinal column physiological rest.  The patient was kept in bed, thus reducing the demand on the weight carrying function of the spine.  This, and the psychological influence of trying a new plan under optimistic circumstances, served to reduce the number and complexity of symptoms, but in no wise changed the character, or viciousness, of the reactions arising from any disturbance of the articulation between the sixth and seventh cervical vertebrae.

    Treatment. - Direct extension, slowly and gentle, was attempted with marked success.  Great care had to be exercised when releasing the extension, else the closure of the cervical articulations acted as though a nerve had been caught by direct pressure.  Gradually the muscular tension around this joint was decreased and a slight degree of rotation toward the lesion, i.e., in this case the left side, could be accomplished without arousing severe pain.  Digital pressure made against the left side of the sixth cervical spine would always cause a severe reaction.  It was not possible to use any quick leverage or thrusting movements in this case for correction of the lesion until about eighteen months after we gave our initial treatment.  A fairly wide range of movement is now possible.  The patient can voluntarily rotate the head to the left, but the sensitiveness on the left side of the cervical spine has never entirely disappeared.  She lives a normal existence as a busy housewife.  She has gained thirty pounds in weight.

    In this case the lesion is nearer center, i.e., closer to the spinal cord.  The symptoms it presents are nearer in character to those of true central origin, except that they are unilateral.  The local symptoms, pain, muscular tension, anaesthesia and vaso-constriction, are manifested in the area of distribution of the brachial plexus.  Although the spinal muscles, whose tension constituted an ankylosis of the articulation between the sixth and seventh cervical vertebrae, are innervated by branches of the posterior division of the lower cervical nerves, the reflexes, through the cells of origin of the lower cervical nerve trunks in the spinal cord, were manifested in all divisions of the brachial plexus, not only in the plexus but overflowed into the sympathetics, as shown by the vaso-motor disturbance and rapid heart action.

    There is a history of accident in this case which classes this lesion as traumatic.  We have its effects shown in the reaction of the cerebro-spinal and sympathetic systems.  In other words, the somatic and splanchnic structures, innervated by nerves from the lower cervical group, act and react upon each other in an effort to adapt themselves to this lesion.  As time went on the whole body was engaged in a losing effort at adaptation, simply because the lesion area was never given physiological rest, i.e., eliminating all demand on the weight carrying and balancing functions of the joint.  The manipulation of this spinal joint was also in the nature of physiological rest because it reduced the hypertension and gradually reestablished normal functional movements.

    Involvement of the Central Nerve Cells. - The next step in severity in lesions is the involvement of the contents of the spinal canal, either through direct invasion of the tissues of the cord, or by pressure due to destruction of sections of the spinal column.  The point we wish to illustrate is that the diagnostician must, in order to do scientific work, make a diagnosis based on the facts of anatomy as interpreted by embryology.  If symptoms were noted and interpreted with the same precision with which the trouble man on a telephone system works out his problems we would not find so many fantastic medical theories.  It is, in large measure, the failure to teach the fundamentals of anatomy, physiology and pathology in a thorough manner that is responsible for the vagaries in medical practice. We are not forgetting the fact that the public is not educated to this view and, therefore, the one who attempts to act irrespective of the public's state of education has a hard row to hoe.

    Cervical Muscles. - In the first case described, wherein the Serratus Magnus was paralyzed, we noted that it receives its innervation from the cervical region.  This makes it a cervical muscle.  In this same sense the trapezium and latissimus dorsi are cervical muscles and will necessarily enter into any reactions involving the segments of the spinal cord which give origin to their nerves.  In order to bring to your attention some of these peculiar changes which have taken place in the development of the body, we will review a few of the most notable which will aid its in the interpretation of the effects of lesions.

    Embryology. - Embryology is the "histology of very young beings."  We may question here what contribution the study of embryology has made wwhich has practical significance in the diagnostic and therapeutic work of our practitioners.  Since we have a "division of labor," as evidenced by a variety of tissues having special functions, and since self-preservation for purposes of perpetuating organisms of a similar character is a prime requisite of life, groups of tissues are associated into mechanisms.  Comparative embryology has helped us to recognize, in part, these mechanisms.  The recognition of the segmental arrangement of the body is one of the great contributions of embryologists.

    Segmentation. - Early in the development of the embryo the mesodermic cells on either side of the longitudinal groove show transverse divisions which form a series of segments called protovertebrae or mesodermic somites.  With out our going into a lengthy description of the arrangement of the mesodermic cells to form the spinal column and its muscles, we want this early series of divisions kept in mind.

    "The appearance of the mesodermic somites is an important phenomenon in the development of the embryo, since it influences fundamentally the future structure of the organism.  If each pair of mesodermic somites be regarded as an element and termed a metamere or segment, then it may be said that the body is composed of a series of metameres, each more or less resembling its fellows, and succeeding one another at regular intervals.  Each somite differentiates, as has been stated, into a scleratome and a myotome, and, accordingly, there will primarily be as many vertebrae and muscle segments as there are mesodermic somites, or, in other words, the axial skeleton and the voluntary muscles of the trunk are primarily metameric.  Nor is this all.  Since each metamere is a distinct unit, it must possess its own supply of nutrition, and hence the primary arrangement of the blood vessels is also metameric, a branch passing off on either side from the main longitudinal arteries and veins to each metamere.  And further, each pair of muscle segments receives its own nerves, so that the arrangement of the nerves, again, is distinctly metameric.

    "This metamerism is most distinct in the neck and trunk regions, and at first only in the dorsal of these regions, the central portions showing metamerism only after the extension into them of the myotomes.  But there is clear evidence that the arrangement extends also into the head and that this, like the rest of the body is to be regarded as composed of metameres.  There is reason, therefore, for believing that the fundamental arrangement of all parts of the body is metameric, but though this arrangement is clearly defined in early embryos, it loses distinctness in latter periods of development.  But even in the adult the primary metamerism is clearly indicated in the arrangement of the nerves and of parts of the axial skeleton, and careful study frequently reveals indications of it in highly modified muscles and blood vessels.

    "Although the dermal mesenchyme is unsegmental in character, yet the nerves which send branches to it are segmental, and it might be expected that indications of this condition would be retained by the cutaneous nerves, even in the adult.  A study of the cutaneous nerve-supply in the adult realizes to a very considerable extent this expectation, the areas supplied by the various nerves forming more or less distinct zones and being, therefore, segmental.  But a considerable commingling of adjacent areas has also occurred.  Thus, while the distribution of the cutaneous branches of the fourth thoracic nerve, as determined experimentally in the monkey (Macacus), is distinctly zonal or segmental, the nipple lying practically in the middle line of the zone; the upper half of its area is also supplied or overlapped by fibers of the third nerve and the lower half by fibers of the fifth, Fig. 14, so that any area of skin in the zone is innervated by fibers coming from at least two segmental nerves (Sherrington).  And furthermore, the distribution of each nerve crosses the mid-ventral line of the body, forming a more or less extensive crossed overlap.

    "And not only is there a confusion of adjacent areas, but an area may shift its position relatively to the deeper structures supplied by the same nerve, so that the skin over a certain muscle is not necessarily supplied by fibers from the nerve which supplies the muscle.  Thus, in the lower half of the abdomen, the skin at any point will be supplied by fibers from higher nerves than those supplying the underlying muscles (Sherrington), and the skin of the limbs may receive twigs from nerves which are not represented at all in the muscle supply (second and third thoracic and third sacral)."

    Widespread Influence of a Spinal Lesion. - No skin area (or individual muscle) is supplied wholly by fibers from one segment of the spinal cord, but, in fact, is innervated by a nerve made up of fibers from two or more segments.  A spinal lesion of traumatic origin, granting that only one articulation is involved, will influence, in some cases, widely separated structures.  For example: A lesion between the fourth and fifth cervical vertebrae might influence the diaphragm, latissimus dorsi and trapezius, and through the spinal accessory the muscles of the larynx.  Such apparently widely separated structures must be kept in mind when considering a lesion at the location under discussion.  Nor is this enough, because skin areas must be reckoned with.

    To learn these tissue associations, through the study of anatomy, is quite possible, but embryology furnishes an interpretation which tends to keep them in one's mind.  When we know that the diaphragm, trapezius and latissimus dorsi are essentially cervical muscles which have migrated but remain under the control of cervical nerves, we cease to think of one as the dividing wall betweem thorax and abdomen, a great muscle of respiration; the others as constituting the first layer of dorsal muscles.

    Association of Muscles Innervated by the Same Segment. - Such structures, as we have just mentioned, have migrated far from their original segments and have taken on functions and are concerned in reactions which are no longer segmental but have for their aim the preservation of the whole body, hence any injury to one, or all, of them would tend to produce a reflex localized in the segment from which they received their innervation.  Compare with these migrated structures a segmental muscle of primitive character like the intertransversalis or interspinalis.  The influence of these primitive muscles is wholly on the one articulation, but they are part of the mechanism supplied from the same segment as the migrated muscles.  These small muscles, which are the intrinsic muscles of the spinal arthrodial joints, are important prime movers in the effort to maintain the erect position, i.e., they enter into the weight carrying and balancing functions of the spinal column.  In case of their injury, a spinal lesion, the lost motion in the joint causes widespread influences, as heretofore mentioned.  The fifth layer of dorsal muscles, according to Gray, consists of a network of small muscles, the deepest of which extend between portions of two adjoining vertebrae; more superficially placed layers extend greater distances so as to influence the movements between more than two vertebrae.  The next layer of muscles, consisting of the erector spinae and its continuations, influence a greater number of vertebrae and bring rib positions under the influence of cervical nerves.  The splenius capitis et colli, of the third layer, and the rhomboids, of the second layer, are likewise supplied by cervical nerves.  Thus we find the nerve which takes its exit between the fifth and sixth cervical vertebrae supphes a series of over-lapping muscles, the first one supplied, intertransversalis, being wholly intrinsic to the spine and the one on the surface of the body, the latissimus dorsi, having a very widespread influence.

    Effect of Sectioning Single Spinal Nerve. - To cut the fifth cervical nerve at its exit from the intervertebral foramen would not paralyze any but the intrinsic spinal muscles between the fifth and sixth cervical vertebrae.  All muscles beyond that point would be weakened in proportion to the number of fibers their governing nerves received from that cut trunk.  In other words, it appears probable that the severing of the pair of nerves, the fifth cervical, could weaken the gross movements made by muscles innervated by them, but since only the intrinsic spinal muscles of one intervertebral articulation are wholly supplied by them there would be no complete muscular paralysis apparent.  The sixth cervical nerves innervate about twenty-eight pairs of muscles in the neck, chest, shoulders and upper extremities and back, and the diaphragm.

    Developmental Changes in Muscles. - This gives us some idea of the great changes that have been consummated in the development of the body.  The many changes in position and direction of fibers are recognized through the fact that they remain under the nerve control of the one segment.  The various changes in the development of muscles are thus described by McMurrich: "It may be seen that the changes which occur in the myotomes may be referred to one or more of the following processes:

"1. A longitudinal splitting into two or more portions, a process well illustrated by the trapezium and sternomastoid, which have differentiated by the longitudinal splitting of a single sheet and contain, therefore, portions of the same myotomes.  The sterno-hyoid has also differentiated by the same process, and indeed, it is of frequent occurrence.

"2.  A tangential splitting into two or more layers.  Examples of this are also abundant and are afforded by the muscles of the fourth, fifth and sixth layers of the back, as recognized in English textbooks of anatomy, by the two oblique and transverse layers of the abdominal walls, and by the intercostal muscles and the transversus of the thorax.

"3.  A fusion of portions of successive myotomes to form a single muscle, again a process of frequent occurrence, and well illustrated by the rectus abdominis (which is formed by the fusion of the ventral portions of the last six or seven thoracic myotomes) and by the superficial portions of the erector spinae.

"4. A migration of parts of one or more myotomes over others.  An example of this process is to be found in the latissimis dorsi whose history has already been referred to, and it is also beautifully shown by the serratus anterior and the trapezium, both of which have extended far beyond the limits of the segments from which they are derived.

"5. A degeneration of portions or the whole of a myotome.  This process has played a very considerable part in the evolution of the muscular system in the vertebrates.  When a muscle normally degenerates, it becomes converted into connective tissue, and many of the strong aponeurotic sheets which occur in the body have their origin to this process.  Thus, for example, the aponeurosis connecting the occipital and frontal portions of the occipito-frontalis is due to this process and is muscular in such forms as the lower monkeys, and a good example is also to be found in the aponeurosis which occupies the interval between the superior and interior serrati postici, these two muscles being continuos in lower forms.  The strong lumbar aponeurosis of the oblique and transverse muscles of the abdomen are also good examples.

    "Indeed, in comparing one of the mammals with a member of one of the lower classes of vertebrates, the greater amount of connective tissue compared with the amount of muscular tissue in the former is very striking, the inference being that these connective-tissue structures (fasciae, aponeurosis, ligaments) represent portions of the muscular tissue of the lower form (Bardelben).  Many of the accessory ligaments occurring in connection with diarthrodial joints, apparently owe their origin to a degeneration of muscle tissue, the fibular lateral ligament of the knee joint, for instance, being probably a degenerated portion of the peroneous longus, while the sacro-tuburous ligament appears to stand in a similar relation to the long head of the biceps femoris (Sutton).

    "Finally, there may be associated with any of the first four processes a change in the direction of the muscle-fibers.  The original antero-posterior direction of the fibers is retained in comparatively few of the adult muscles and excellent examples of the process here referred to are to be found in the intercostal muscles, and the muscles of the abdominal walls.  In the musculature associated with the branchial arches the alteration in the direction of the fibers occurs even in the fishes, in which the original direction of the muscle-fibers is very perfectly retained in other myotomes, the bronchial muscles, however, being arranged parallel with the bronchial cartilages or even passing dorso-ventrally between the upper and lower portions of an arch, and so forming what may be regarded as a constrictor of the arch.  This alteration of direction dates back so far that the constrictor arrangement may well be taken as the primary conditions in studying the changes which the branchial musculature has undergone in the mammalia."

    Please note that, "since the relation between a nerve and the myotome belonging to the same is established at a very early period of development and persists throughout life, no matter what changes of fusion, splitting or migration the myotome may undergo, it is possible to trace out more or less completely the history of the various myotomes by determining their segmental innervation."  In view of this the clinician ought to be well versed in the knowledge of anatomy, i.e., the gross structures innervated from the same segment of the cord.  Much of the physical diagnostic work of the osteopath is based on the fundamental facts of embryology and anatomy, i.e., metamerism.