The study of the limitations to motion in the joints of the body is important for several reasons; first among them this, that beyond that limitation is the danger of lesion; second, that since, for correction, tension must be gotten on the bones in lesions, and since to get tension on them they must be carried to the limit of their normal motion, therefore this knowledge is essential to a scientific technic.

    There is no proper motion at all in the sacrum.  If it moves at all it is in excess of the limitations of its motion, and with danger of lesion.  Normally there is a mere elastic yielding of the ligaments of the sacrum, with possibly a slight grinding of the articular surfaces.  In view of the fact that many statements on this subject have been made of an opposite character, this statement requires some supporting.

    In the first place I challenge anyone to show where Dr. Still has said that the sacrum normally moves on or between the innominates in mature persons.  That the sacrum is found in lesion, having been moved abnormally, he has said; and the fact is proven daily in Osteopathic experience.  But this is not to attribute normal motion to the sacrum.

    Tests made in the classes above referred to at the A. S. O. seemed at first  to give positive results in many cases.  First the diameter between dorsum of sacrum and symphysis pubis seemed to be increased in flexion of the body, decreased in extension.  A moment’s thought will reveal the interesting fact that this is motion in the wrong direction, if it is motion at all.  Second, the interval between the posterior iliac crests seemed to decrease with flexion and to increase with extension.  This again is the wrong motion, if the sacrum moves as above indicated.  A moment’s thought will reveal the interesting fact that to accomplish this motion either the bones at the symphysis pubis must be absolutely separated from each other and by several times as ;much as they are approximated at the posterior superior spines—being much the longer arm of the lever; or else the sacrum must slide forward far enough to allow this approximation—a very great distance, because the sacro-iliac surfaces are not beveled in and back at all points of the surface, but are uneven and actually slope out and back at some points, which points, small though they be, would absolutely determine a separation instead of an approximation of these spines if the sacrum glided downward and forward in flexion of the trunk within the area oaf the articular surface.

    This seeming motion was then found to be due to the tensing of the fibrous mass at the root of the erector spine muscle, both over the dorsum of the sacrum and between the iliac spines.  It was found impossible to make satisfactory measurements of body movement in active emotions of the body on account of this fact; and in passive movements t here was to some extent the same difficulty, and also little or no force leading to movement of the sacrum in any case.

    We then have resource to anatomical examination of the parts for evidence of movement or the lack of it.  All evidence points to lack of it.  We find that the sacro-iliac joint is not smooth, as it would have to be to permit of actual normal motion; that fibrous adhesions are the rule between the opposing surfaces.  Why then the articular membranes, or the remains of them?  Examining the surfaces with the eyes closed, the fingers are able to outline in practically all sacra an uneven groove about the width of the ends of the fingers describing a fairly accurate curve, concentric about a point which proves to be the point of attachment of the sacro-iliac ligament—the great ligament by which the sacrum is suspended.  It may be supposed then that the sacrum did move about this center in early life or in foetal life; perhaps chiefly at the time when the child is learning to walk upright, before the bone is fully developed.  This groove should define whatever motion might be normal to the sacrum; which would be a turning about this center with a freer movement of the caudal end; but at the caudal end this motion is checked by the great sacro-sciatic ligament, and is probably no greater than is allowed by the stretching of this ligament.  (In the immature, before the sacral vertebrae became ossified, motion might have occurred with bending of the sacral vertebrae on each other.)

    Why would not motion occur in the opposite direction, that is with depression of the caudal end and relaxation of the sacro-sciatic ligament?  Because every normal force that applied to the sacrum forces it in the opposite direction.  On the front end the full weight of the body together with the force of its muscular action pressed down; on the caudal end the great tension of the erector spinae muscle pulls up.  Of the other muscles, the gluteus maximum and pyriformis pull out, and the muscles of the pelvic floor, small and delicate, are the only ones that pull down.

    The sacro-iliac joint is a spring joint, a safety joint, without normal functional movement.

    The limitations to motion in this joint are those of the uneven (as though dove-tailed) joint, the great sacro-iliac ligament, largest in the body (sometimes an inch in diameter); the sacro-sciatic ligament, scarcely less strong, and the suspensory ligament on the ventral aspect.  Sometimes there is a further limitation formed by actual contact of the posterior superior spine of the ilium with the dorsum of the second sacral vertebra, making another pseudo joint in the horizontal plane.  Except for the elasticity of these ligaments and the cartilage of the joint, these limitations are absolute.

    Although the sacrum does not move, it yields in elastic fashion to foraces of movement.  The direction of the fibres of ligaments is the key to the direction of lines of tension.  Some of the fibres of the sacro-iliac ligament incline inward, from iliac crest to sacral spines, indicating that there is often tension in this direction; which tension would incline the articular surface to gap open on the dorsal side, with leverage at the ventral side of the articular surface; as in walking when the opposite leg is lifted.  Advantage is taken of this in the correction of lesions.  The greater proportion of the fibres of this ligament extend directly down, in the line of the weight of the body.
 

MECHANICS OF SACRAL LESIONS

    More than ninety per cent of the lesions of the sacrum present a slipping of that bone ventrally on its articulation with the ilium (the so-called posterior innominate). This may be unilateral, the axis of rotation being of course the opposite side; or as in probably fifty per cent of the cases, bilateral.

    This lesion would seem to involve a direct stretching of the great sacro-iliac ligament.  The size of this ligament is tremendous, such that production of lesions would seem to require overwhelming force.  This, however, is not the case.  Lesion does not involve direct stretching of this great ligament, but on the contrary stretches only a few of its outer fibres.  Examining the mechanics of the part we find that as the sacrum slips forward it first turns so as to lie at a more acute angle with the iliium, and that then the tension on the fibres of this ligament draw down the crest and the posterior superior spine closer to the dorsum of the sacrum; draw it down by as much as the fibres are tensed, so that only those fibres closest to the ilium itself are unduly stretched, while those farthest from it (those passing to the sacral spines) may be actually relaxed; the intervening ones being neutral, or slightly stretched or slightly relaxed, according to position.  The articulation itself is then gapped at the bottom and under heavy pressure at its top edge, where an indentation is made in the soft tissue of the periosteum and the articular membranes by the upper corner of the sacral articular surface; the whole bone on that side being found slightly forward of its normal position.

    This change is, of course, reflected to the opposite articulation.  If on the depressed side there is a gap below, then on the sound side there must be a corresponding gap above, with tensing of the ligaments along the upper edge.  Wherefore we often find that there is more tenderness along the inside of the iliac crest of the sound side than there is on the side in lesion; except that at the point where the sacrum emerges from between the ilia (the sacro-iliac “X”) there is always more pain on the lesion side.

    Nature always distributes equally the tension on ligaments so far as possible; indeed that is a ;mechanical result  in any structure not absolutely rigid.  That brings about secondary changes in position of these bones.  The ligaments involved here are the two sacro-iliac ligaments, the one tensed, the other partly tensed and partly relaxed, and the suspensory ligaments, the one tensed (on affected side) the other relaxed.  We have also the joint gapped below on the affected side and gapped above on the sound side.  The natural effect therefore is to so swing the whole pelvis that these tensions are balanced.  Being hinged only at the symphysis, this shift of position is easy.  The first  shift swings both articulations to the side opposite the lesion.  But this leaves the gaps still greater.  To more or less close those the second shift occurs, which is a rotation, forward on the sound side, backward on the lesion side.  Experimenting with the actual bones in the position of sitting one quickly realizes to what this leads—a tilting of the two innominata so that the posterior superior spine of the affected side is lower or nearer the table than its fellow.  It is this secondary result that gave rise to the diagnosis of “rotated ilium.”  But the sound side being shifted forward there is a natural tendency to force this ilium backward—to cause lesion also on this side.

    There is usually a perceptible difference in the tension of the sacro-sciatic ligaments, it being less on the sound side.

    The relative height of the posterior superior spines from the table in sitting is altered by difference in thickness of the cartilaginous pads, in tension of muscles, in habits of sitting, etc., which make that an unreliable basis for diagnosis.  In general all measurements that involve other joints or other factors than the actual bones in lesion and at the very points where lesions occurs, are unreliable.  Diagnosis should be made at the very point where lesion actually exists, or as near to it as possible.

    Diagnosis of sacro-iliac lesion should be made at the only points where the bones are in actual contact that is reachable by the examining finger—at the points where the sacrum emerges from between the two ilia, the sacro-iliac “X,” just below and in contact with the posterior superior spines of the ilia.

    Patient seated on table; operator seat ed on stool behind; places two thumbs on posterior superior spines and notes corresponding points of the two; passes thumbs downward until they com into contact with the dorsum of the sacrum.  The thumbs should then lie with the balls pressing on the dorsum, the upper edges pressing against the inferior margins of the posterior superior spines.  Difference may be noted on the two sides.  On the side in lesion there will be greater depth between posterior superior spine and sacrum, possibly a definite gap; possibly the edge of the ilium below the spine may be flelt as it turns forward and grows more sharp.  More or less sensitiveness should be noted on the affected side.  There is rarely so much fat here as to make diagnosis impossible.
 

CORRECTION OF ANTERIOR SACRUM

    The lesion above described is usually defined as a “rotated ilium” or “posterior innominate,” but in reality is much more accurately defined as a sacrum anterior on one or both sides.

    Patient lying on side on table, lesion side uppermost.  Assume that lesion is on right side.  Patient lies on left side.  Extend left leg; draw right knee in front and place in contact with table.  Operator stands facing patient.  With left hand outlines the crest of ilium, places forearm along crest so as to bring pressure on whole anterior and upper edge thereof, especially over the anterior superior spine.

    (Caution:  Operator must not allow elbow to come into contact with patient at any point, as it causes exquisite pain; operator must not allow forearm to slip down from upper edge of crest so as to bring pressure on the fibres of the glutei muscles which are here raised from the bone in tented fashion; as this both defeats the purpose of the technic and causes much pain to patient.)

    With forearm thus placed operator is in position to produce pressure downward and forward over iliac crest and particularly over anterior superior spine, the effect of which is to bend the ilium down in front and up in the back around an axis passing through the symphysis and the points in contact in the lesion, so as to reverse the gapping in the lesion; to cause, that is, gapping behind and to prize up the engaged corner of the lesions from its indentation.

    Operator then places right forearm in the hollow of the patient’s right shoulder (grasping for convenience the fat of the patient’s forearm, being careful that the sharp olecranon process does not hurt patient’s pectoral muscles).  He rotates the shoulder back and slightly down, and rotates the ilium forward and slightly down, both at the same time, until all of the intervening joints are at the limit of their normal tension, making sure that the patient’s muscles are all relaxed.  This position alone with practically no tension is sufficient to correct many lighter lesions, proving the correctness of the technic.  Pressure is then exerted backward and downward on the shoulder, forward and downward on the ilium, until the articulation yields and is restored.  Force must be adjusted to the stubbornness of the lesion.  A quick and shallow thrust is better than a gradual one which requires to be much heavier, as will be explained later.

    Mechanics:  The student should follow the effect of the force that he applies from the point where he applies it, through all intervening joints, ligaments or muscles, to its actual effect in correcting the lesion.  The force applied to the shoulders tenses pectoral and serratus muscles, passes to ribs, thence to transverse processes and the spine as a whole, which it carries back over the fulcrum of the right shoulder and also rotates, as far as the sacrum, which is being held.  At the sacrum it is effective in drawing back the base, through traction, and drawing back the upper articular surface through rotation over the lower articular surface as fulcrum.

    The effect of the force applied to the anterior superior spine is as noted.

    Criticisms.  This technic as practiced especially by beginners shows usually certain typical faults.  The operator forgets and leans his weight on the pelvis without making sure that it is applied at the anterior superior spine.  Or he makes jerky motions without first getting the patient relaxed and his spinal joints all at the limit of their motion—in which case the whole effect of the energy is used up in them, and not in correction of the lesion.  Or, before making the quick and shallow thrust, he releases, draws back as it were, however slightly, when of course the patient’s muscles follow him and the effect is lost because the joints are not at the limit of motion before the corrective pressure is applied.

    Some straining of the pectoral muscles is usually felt, but is not so severe as to make the treatment painful, with care and practice.  Poppings at various points along the spine may be noted, which may or may not have significance.  Usually it is very easy to correct lesions and very hard to produce them, so that unless specially indicated these poppings may be ignored, as they are probably corrective in themselves.  In some patients, especially in females with large pelvis and short waists, this technic puts such a strain upon the tissues about the twelfth rib that it cannot be used.
 
 
OTHER LESIONS OF THE SACRUM

    In rarer cases the sacrum is found deviated not at all ventrally but caudally—the articulation having slipped in its longitudinal axis.  Diagnosis of this lesion is very difficult.  When it is suspected, have patient on side with lesion uppermost, as before, his back near to back edge of table; extend left leg; lift right leg, carry backward beyond edge of table, and allow it to hang down as far as possible.  Operator now fixes shoulder of patient with his right arm or axilla, while with right hand (if possible) he presses up and forward on affected tissues, and with left hand lifts patient’s right leg and then carries it smartly downward behind table to full limit, so as to spring the right ilium away from the sacrum, which is being held by traction through the spine.  The practical success of this technic seems to depend on keeping the pelvis in such position of balance, that the downward thrust takes effect at the articulation, and not on the muscles in front of or behind it; and on keeping the spine in such alignment that it exerts firm traction on the sacrum.

    Mechanics:  The lower articular surface becomes the fulcrum, traction through the spine over this fulcrum draws upper surface; force applied to leg finds its fulcrum at the symphysis and the sacro-iliac X and so gaps open the whole joint and draws down on lesion.

    In still rarer cases the sacrum is found displaced dorsally.  These cases give a history usually of some unusual form of violence, as wrenches in foot ball games, railroad wrecks, etc.  Diagnosis is difficult, may even be said to be presumptive and by exclusion.  The correction is, however, extremely easy, so easy in fact that there is danger of over-correction, or of producing lesion where none exists.

    Patient seated on table, operator stands behind.  Assuming that the sacrum is displaced dorsally on the right:   Operator places fingers of right hand along crest of ilium with enough pressure to secure a hold for the fingers; the thumb extending over the crest and bringing pressure ventrally on the dorsum of the sacrum by means of the hold with his fingers.  Operator then passes his left arm under patient’s left axilla and grasps patient’s right shoulder, carrying patient slightly forward and partly supporting his weight.  With the left arm he then rotates the patient’s shoulders, the right forward, the left slightly backward until the spinal joints are all at the limit of their motion and on tension, then brings extra tension to bear in the same direction, with pressure from the right thumb.  The lesion is usually felt to yield immediately.

    Merchanics:  Elastic yielding is prevented by thumb and finger pressure so that joint is gapped by the rotation and slid forward by the thumb pressure.

    Many other forms of technic are in vogue.  Many of them are open to criticism on this very simple mechanical ground—that they do not consider the necessity of having tension on both of the bones involved in the lesion.  To break a stick it is necessary to have hold of both ends.  For instance the following very simple form of technic for right anterior sacrum which looks at first sight very simple and correct, is yet found to be not effective, and for the reason that will be pointed out.  Patient lying on face on table; operator stands on side opposite to lesion (left side); draws patient’s shoulders from table until patient’s axilla rests over operator’s right thigh; grasps shoulder on side of lesion with left hand and lifts until all spinal joints are at limit of motion.  With right hand reaching across table he presses down on posterior superior spine of ilium in lesion; then with extra pressure and lifting-rotation-traction of shoulder he endeavors to correct.

    This technic is rarely successful for the reason that the pelvis is not fixed; so that the only effect of the effort is to turn the pelvis around the axis made by pressing the anterior superior spine against the table.  The effort is not focused on the lesion and is wasted.  Sometimes, however, it is successful (where pelvis is heavy enough to fix left ilium against table).

    The same criticism may be made of the technic which lifts the leg of the side in lesion while pressing down on the posterior superior spine. There is nothing to hold the sacrum.  Except in patients with very large chests and relatively stiff spines, the effort is wasted.

    Two forms of technic which depend for success on a sudden jar rather than on well directed tensions may be described.  Patient prone on table.  Operator stands at side of lesion.  Lifting heels and sliding knees from table toward side of lesion (toward himself), with turning of pelvis, he carries knees well up (while chest remains flat on table).  Operator then hooks pisiform bone of other hand under posterior superior spine of lifted ilium, prepared to follow it with pressure as it rotates toward  prone position in next phase.  Then grasping and lifting ankles until tension is complete, and keeping ankles well in air so as to lift knees above level of table, he swings legs back to prone or median position and beyond, with pressure always over posterior superior spine of affected side.

    Mechanics:  At moment of correction there is tension caudally (through legs) and ventrally (through pressure of hand) on ilium; and tension upward and dorsally on sacrum (through spine).  The value of coming suddenly to limit of motion in this way is that patient’s muscles are all relaxed and that the quick tension in the right direction more easily overcomes the elastic “set” of the parts.

    The other form of using this same principle is applied with patient prone, assistant maintaining continuous heavy pressure over posterior superior spine of affected side; operator grasps ankle and lifts leg of affected side, and without allowing it to touch table, cracks it downward as though cracking a whip—a downward and an upward jerk, with traction.