CA1297952C

CA1297952C - Method and equipment for evaluating the flexibility of a human spine

Info

Publication number: CA1297952C
Application number: CA000548627A
Authority: CA
Inventors: Serge Gracovetsky
Original assignee: Diagnospine Research Inc
Current assignee: BUSINESS DEVELOPMENT BANK OF CANADA
Priority date: 1987-10-05
Filing date: 1987-10-05
Publication date: 1992-03-24
Anticipated expiration: 2009-03-24
Also published as: EP0310901B1; EP0310901A3; DE3887058T2; US4971069A; DE3887058D1; EP0310901A2

Abstract

ABSTRACT

A non-invasive method and equipment for the evaluation of the flexibility of the spine of a patient and, as a result of this evaluation, the detection and identification of possible mechanical injuries in the lumbar portion of this spine. Accord-ing to this method, a string of skin-markers is fixed onto the skin of the back of the patient in the midline of his spine from at least cervical vertebra C7 down to at least sacral vertebra S3. Two other skin-markers are fixed onto the skin of the back of the patient in a bilateral and symmetrical manner on the crests of his ilium. The relative positions of all the skin-markers are then monitored and recorded as he flexes forward in this sagittal plane and the so recorded positions are processed to determine (1) the angle of flexion .alpha. of the patient, this an-gle .alpha. being indicative of the combined motion of both hip and spine of the patient, (2) the angle of rotation "h" of the hip and the actual contribution of the spine to the total flexion of the patient, this contribution, expressed as angle "s", being indicative of the spine motion of the patient. The relative variations of "h" and "s" versus .alpha., which are respectively indi-cative of the ranges of hip and spine motions in the sagittal plane, can be compared with each other and with results obtained from a group "normal" patients to determine any discrepancy or singularity in the flexibility of the spine. The data that are so obtained may be correlated with other data obtainable by the same equipment, such as the lumbo-sacral angle, the percentage arc elongation and the electromyographic activities of the pa-tient's muscles.

Description

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BACKGROUD OF T~IE INVENTION

a) Field of the lnvention The presen-t invention relates to a non-invasive method for the evaluation of the flexibility of the spine of a patient and, as a result of this evaluation, the detection and identification of possible mechanical injuries in the lumbar portion of this spine.
The invention also relates to an equipment for carrying out this method.

bl Brief description of the prior art It is well known in the medical art tha-t common back disorders have a mechanical etiology. It is also well known from pathological studies that there are two common patterns of disc injury which correspond to two different types of mechanical failure of the spine.
The first type of common injury hereinafter referred to as "compression injury", usually starts by a central damage to the disk with fracture of varying magnitude of the end plates of the adjacen-t vertebrae, sometimes followed by injection of par-t of the nucleus in-to the vertebral body. In -this particular case, the injured end plate permits the invasion of the avascular nucleus and of the avascular inner portion of the annulus by granulation tissue ingrowing through the fractured end plate, such an invasion leading to gradual des-truction of the avascular nucleus and inner annulus. [n the early stayes, the facet joints of the vertebrae are not affected and the outer annulus survives while the center portion of the disc is destroyed. With progression, the disc loses its thickness while the outer layer of the annulus remains relatively well preserved. With lo-st of disk thickness, the facet joint subluxa-tes and develops a moderate degree of osteoarthritis.

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~9~9~i2 Usually, the fracture of the end plate of a vertebra is an undisplaced fracture of cancellous bone whlch heals rapidly. The symp-toms are short lived, typically lasting two weeks. The facet joint arthritis appears late.
At this stage, symptoms may also arise from the reduction in size of the spinal canal (lateral or central spinal stenosis).
The othe~ type of common injury hereinafter referred to as "torsional injury", is characterized by a damage to the annulus occuring simultaneously with a damage to the facet joints. The annulus is avulsed from the end plate and its laminae become separated while the central disk and the end plate remain intact. At the later stage, the annulus develops radial fissures while the nucleus remains relatively untouched. The changes in the -Eacet joints are severed with massive joint destruction and osteophytosis similar to hypertropic arthritis. Relatively late in the process, there may be changes in the end-plates and central disks, with consequent collapse of the articular surfaces and chronic synovitis.
In this particular case, the basis injury is to collageneous ligamentous tissue which requires six weeks to regain 60% of its strength. Because the injury involves both the disk and facet joints, it is more difficult for the joint to stabilize itselE and recurrence is frequent. The condition is progressive and may lead to spinal stenosis, instability and degenerative spondiloli.sthesis.
Tests conducted in laboratory have shown that a compression injury is easily produced by compressing a joint between 2Mpa to 6Mpa. A torsional injury can be seen with as little as 2 to 3 degrees of forced rotation requiring only 22 to 33 Newton-meters oE torque.
Statistically, in a group of patients s~lffering from back disorders, 64% exhibit torsional injuries whereas ~2~79~i~

35% exhibit axial compression injuries. Statistics have also shown ~hat torsional injury occurs mainly at the L4-LS
level (almost 76% of forth joint problems are of torsional nature). Statistics have also shown that almost 98% of the compression injuries occur at the L5-Sl level. Statistics have further shown that double injuries where the joint is injured both in compression and torsion, occur in 22% of the cases, invariably at the L5-S1 level.
The following Table I reflects the probabilities of injuries among patients complaining from backache and seiatiea, or seiatiea alone. As ean be seen from this Table, the important frequeney of torsional injury eannot be overlooked. As ean also be seen, the probability of a third type of injury giving gymptoms is very remote.
TABLE I

CLINICAL DETERMINATION OF THE VARIOUS PROBABILITIES
OF INJURIES
JOINTP (injury)P (eompression) P (torsion) L5/S1 47% 9~% 22%
L4/L5 47% 1%~ 76%
L3/L45% < 1%< 1%
L2/L3196~ 1%< 196<
Ll/L2 1%< 1%< 1%<

lO0~ lO0~ 100%

It is also well known that health professionals are trained to use symptoms in the determination of , .

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diagnoses, the large numbers of known symptoms being quite naturally associated with a large numbex injuries and diagnoses. Unfortunately, as can be understood from the above short description of the pa-thology in the case oE back disorders, both the compression and torsion injuries give rise to identical symptomology. Hence, symptoms cannot be used to diagnose a type of injury because identical symptoms may arise from different injuries.
It is also well known in -the art that low back pain is the leading cause of disability in North America today, affecting from 8 to 9 million people. It is the most common disability in persons under the age of 45 and the third only after arthritis and heart disease in those over 45. It is also estimated that two of three persons will have a low back pain at some time of their lifes, usually between the ages of 20 and 50. The fact that problems are so common in people of working age is not coincidental.
Indeed, most of the back problems are work-related. As the injury caused by a certain task cannot be identified from the patient's symptoms, it, is of course not possible to relate directly a given task to an injury mode, although such a relationship is central to the definition of tasks that will not injure a specific worker.
The economic effects of back pain and injuries are staggering. Back problems are second only to the common cold as a cause of absenteism in the industry. It is moreover responsible for 93 m:illion lost workdays every year and is a leading cause of reduced work capacity. ~lence, an incentive for prevention of back injury is very large.
In order to unequivocally relate a given task to a given injury ln the absence of any measurement of the effec-t of the task on a given jo:int, it has already been suggested to use mathema-tical and/or biomechanical models of spine, like the one suggested by J.M. Morris et al in their ~2~ S2 article "The ~ole of trunk in stabili-ty of -the spine, J.
Bone and Joint Surg., 43A, 1961. However, a major problem with the known models of spine, including the widely used model of J.M. Morris et al, is that they do not truly reflect the physiological behaviour of the spine over -the full range of capacity.
Thus, by way of example, the model of J.M. Morris et al which assumes, as fundamental hypothesis, that the moment generated by the body weight and any external load carried by the patient is balanced by the combined action of the erectores spinae and the intra-abdominal pressure, is a very poor representation of physiological behaviour which is not supported by observations. By way of example, such a model predicts a total failure of the mechanism at about one fourth of the known potential of a spinal healthy spine.
The major reason why all of -the models known to the inventor are defective is essentially because they give an incomplete representation of the actual anatomy of a human being. It is true that a moment-supporting member is required in such a model but this cannot be the abdominal pressure only, as suggested by J.M. Morris et al.
This established fact combined with different other anatomical observations reported in the literature, has led the inventor to devise a new mathematical represen-tation of the anatomy of the human spine including (1) theposterior ligamentous system which has indeed the strength to support any moment generated onto the spine by the body weight and any external load carried by the patient, and (2) the extensors of the hip which have the bulk and the lever arm necessary to supply all the moment requirements to flex the spine.
In greater details, the inventor ha~s been noted that, under normal circumstances, most of the motion of an individual flexing Eorward from zero upright down to about 7~ ;2 45 (for an unloaded spine), is due to spinal flexion. Erom about 45 to full flexion, the motion is mostly due to the rotation of the pelvis at the hips.
In the range of 0 to about 45 (for an unloaded spine), the posterior midline ligament system is inactive and, in its place, the erectores spinae and/or the abdominal muscles support most of the moment due to the body weight.
From about 45 to full flexion, this moment can be also supported by the midline ligament system without muscular activity. This relaxation phenomenon from muscular to ligamentous support was already noted in the art by W.F.
Floyd et al in their article "The Function of the Erector Spinae Muscles in certain Movements and Postures in Man", J.
Physiology, volume 129, pp. 184-203, 1955.
Using electromyographic (EMG) measurements, W.F.
Floyd et al clearly saw a relation between the momen-t to be supported and the angle of forward flexion, and realized the meticulous coordination of muscle, ligament and joint movement. They hypothetized that in the case of injury to an intervertebral joint, this delicate coordination will be upset and this would be reflected in change of the E.M.G.
pattern. Then, they embarca-ted on an E.M.G. study and tried to compare statistically the E.M.G. pat-tern of normal individuals to that of those with common back problems in the performance to a standardized simple weight lifting taslc. However, they gave up after testing 1~0 cases because the results were inconsis-tent.
l'he mathematical model devised by the inventor, takes it from granted that the pelvis acts as a "supporting base" for entire spine, and assumes as fundamental hypothesis, that any healthy person will perEorm a task in such a way as to minimize and equalize the s-tress at each invertebra] joint.
In this model, the main power for a lift is assumed to be generated by the e~tensors of the hip, such as the Gluteus Maximae.
The moment genera-ted by these muscles is transmitted to the upper extremities by the trunk musculature and the posterior ligamentous system (PLS) which, for the purpose of this discussion, is composed of the midline ligament and -the lumbodorsal fascia. Regardless of the inclination of the trunk, the moment generated by the extensors of the hip must equal the sum of the moment generated by the trunk musculature and PLS. Therefore, for any given hip extensor moment one can find an infinite number of combinations to distribute this moment between trunk muscles and the PLS.
Because of the reserve capacity in performing a small weight lift, a normal individual may select a combination of ligaments and muscles which is not optimum from a stress minimization and equalization point of view.
However, the reserve is reduced in the presence of injury.
The option of selecting a non-optimum strategy is also reduced. Therefore one can expect a certain amount of variation in EMG pattern in a normal individual and a very limited variation in those with injury~
Assuming that the distribution of moment between ligaments and muscles is controlled by the requirement that stress be minimized and equalized at all lumbar joints, stress at one intervertebral joint wi:ll be defined as the ratio of the resultant compressive force acting perpendicular to the bisector of the disk to the area of the disk. In general, when muscles are used, the stress is higher -than when either ligament systems are used, because the lever arms of the ligament systems are longer than those of any of the muscles. The midl:ine ligament system can be activated only when the spine is sufficiently flexed.
The hip/shoulder angle ~ at which this ligament takes up tension is called ~O, which is about 45 degrees for no load ~7~3i5i~

This ligament system is strong enough to support the heaviest lift and hence, when this ligament sys-tem is activated, the spinal musculature is no longer required and therefore the muscles are electrically silent. As aforesaid, this is the muscle relaxation phenomenon observed by W.F. Floyd et al.
The thoracodorsal fascia can be activated by the contractions of the abdominal muscles, in particular the internal oblique and T. abdominis, which exert a pull at its lateral margin only when the abdominal pressure is at sufficient value to maintain a rounded abdominal cavity.
This ligament system can therefore be activated for any angle of flexion. This is an essential difference when compared to the midline ligament.
Based on this new mathematical model, the present inventor has devised and patented a new method and equipment for the detection of mechanical injuries in the lumbar spine of the patient and the identification of these injuries.
According to this method which forrns the subject matter of Canadian Patent n 1,220,273 and U.S. patent n ~,655,227 both assigned to DIAGNOSPINE RESEARCH INC., the electromyographis (EMG) activities of the erectores and abdominals of the patient are measured in the bilateral and symmetrical manner with respect to the spine o~ the patient while the same is Plexing forward in the mediane plane and pulling up a small load. The angle of flexion ~ of the patient is measured during this Plexion and is supplied as variable input to the mathemat.ical model. A computer is used to run the model with its variab].e input in order to calculate the. EMG activities of the erectores and abdominals that would normally be used by a healthy person to produce the same task. The so calculated EMG activities are then compared to the EMG activities actually measured on the patient and the parameters of the models are tuned to fit - 12~37~5~

the calculated EMG activities for those measured on -the patient. The amount and type oE tuning that are necessary to complete the last step, are sufficient in practice -to detect and identify the mechanical injuries that rnay be present in the lumbar spine of the patient.
Based on the same mathematical model, the present inventor has also devised and patented another method and an equipment for the detection of a mechanical abnormality or injury in the lumbar spine of a patient and for the identification of this abnormality or injury as being of the compression or torsion type.
According to this other method which forms the subject matter of Canadian patent no. 1,220,272 and U.S.
patent n ~,664,130 both assigned to DIAGNOSPINE RESEARCH
INC., any variation of the lumbar curve of the patient is measured using a combined visual and an electromyographic (EMG) technique, and any discrepancy or asymmetry is detected in said measured vaxiation of lumbar curve. In practice, the absence of any variation or the detection oE
any discrepancy or asymmetry in the case where a variation is measured, is indicative of the presence of a mechanical abnormality or injury of the lumbar spine of the patient, and of the nature of this particular abnormality or injury.
In greater details, the method forming the subject matter oE Canadian patent no. 1,220,272 and its U-S.counter-part 4,664,130, comprises the following steps.
First of all, a first pair of surface-electrodes is fixed onto the back of the patient in a bilateral and symmetrical manner with respect to his spine in the lumbar zone, in order to xecord the electxomyographic (EMG) activities of erectores oE this patient. A second pair of surface-electrodes is fixed in a bilateral manner onto the trlangles of Petit of the patient in order to record the RMG

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activi-ty of his Internal Oblique and a third pair of surface-electrodes is fixed in a bilateral manner behind the thighs of the patient in orde:r to record the EMG ac-tivity of his hip extensors.
Then, the muscle activity of -the patient is measured with all of the surface-electrodes whi~e he is flexing forward in the median plane and pulling up a small load, andthe EMG activities measured by eachof the surface electrodes are independently recorded as a function of time.
Simultaneously, the angle of flexion a of the patient is measured and recorded as a function of time. This angle a is defined as the dihedral angle between a plane passing through the hips and shoulders of the patient and a vertical plane parallel to the frontal plane of this patient.
Last of all, the recorded EMG activities that are so measured on the patient are processed to calculate the relative variations in activities of the erectores versus the hip extensors (E/H ratio) and of the Internal Oblique versus the hip extensors (A/H ratio) and plotting said E/H
and A/H ratios versus a, and to calculate the amount of asymmetry "a" between the recorded EMG activities measured on the right side of the patient and the recorded EMG
activities measured on the left side of this patien-t.
I'he observation of a high A/H ratio which corresponds to an extenslve use of the abdominals, with the simultaneous observation of a significant delay in the detection of a sharp variation of the E/H ratio at a given angle ao or oE no variation at all of said E/~l ratio when the patient is pulling up the small load, indicate that the patient cannot relax his erectores at the beginning of t-he li~t, such a reEusal indicat:i.ng i.n turn that the patient has difficulty to flex his spine and therefore has a joint injury of the compression or torsional type.
On the other hand, the observation of a ;

significant variation of "a" when ~ varies, that is during the lift of ~he small lead, indicates that the joint injury in -the lumbar spine is of the torsional type.
In addi-tion to the above mentioned methods, the present inventor has devised and patented a further method and equipment for the detection of torsional injuries the lumbar spine of the patient, which method and equipment are much simpler than any others.
This method which forms the subject matter of Canadian patent no 1,219,673 and U.S. patent~no. 4,699,15~
both assigned to DIAGNOSPINE RESEARCH INC., derives from an observation made by the inventor that a healthy spine is characterized by its ability to flex smoothly in any plane.
Hence, an injury to any joint of the spine will always result in a reduced flexing range of motion of the spine.
15According to this method, a string o~ separa~e, dotffized skin-markers that may consist of small LEDs fir3d under computer control, are fixed onto the skin of the back of the patient in the midline of his spine from at least thoracic vertebra T1o down to at least sacral vertebra S3.
A visualization equipment including two cameras spaced a-part from each other, is used to observe, monitor and record : the relative positions of the skin-markers on the back of the patient as he leans -to the left and then to the right off his sagittal plane. The recorded positions oE the skin-markers when the patient was leant to the left, are then compared wi.th their recorded positions when the patient was leant to the right :in order to determine whether there is a s.ignificant difference between both of these recorded positions, and in the case where there is such a significant difference, whether these different recorded posit.ions are symmetrical with respect to the sag.ittal plane.
In practise, the observation of a non significant difference between the recorded positions of the skin-markers indicates a refusal by the patient to flex hisspine, such a reEusal in turn indicating the presence of a double torsional injury having damaged any lumbar intervertebral joints statistically between vertebrae L4 and L5 or L5 and Sl. On the other hand, provided that the recorded positions of the skin-markers are different, the observation of a substantial asymmetry between the recorded positions indicates a refusal by the patient to flex his spine in one direction, such a refusal in turn indicating the presence of a simple torsional injury at any lumbar intervertebral joints statistically between vertebrae L~ and 5 and Sl This method and the very particular equipment used for carrying it out, have been actually reduced into practise and successfully tested. In addition to being a real and true scienti~ic diagnosis tool, this method and the equipment used for carrying it out, as well as all the other methods reported hereinabove as having been devised by the present inventor, have the major advantage of being of the 20 "non-invasive" type in that they do not require "invasive"
tools such as X-rays, needles and the like to collect the physiological data necessary for detecting the presence of a mechanical abnormality or injury.

OBJECTS AND SUMM~RY OF T~IE INVENTION
. . ~ _ .
An objec-t of the present invention is to provide a non-invasive method for the evaluation of the ~lexibility o~
the spine of a patient and, as a result oE this evaluation, the detection and identification oE possible mechanical injuries in the lumbar portion of this spine, which method is as simple as the one disclosed and claimed in Canadian patent no 1,2L9,673 and its ~.S. counterpart ~,699,156 and derives from the same observation that a healthy spine is able to flex smoothLy in any plane. The method according to the invention however is much broader in scope and application as the one disclosed and claimed in the above patents, in that it is not restricted to the detection of torsional injuries exclusively. In fact, the method according to the present invention is of very broad application and can be used for evaluating the flexibility of the spine of a patient in any plane (not exclusively off the sagittal plane), and thus detecting any discrepancy from a `'normal" response that would help a medical doctor to establish and/or confirm a back pain diagnosis.
Another object of the invention is also to provide a non evasive equipment for carrying out this new method.
In accordance with the invention, a string of separate, dot-sized skin-markers which preferably consist of small LEDs fired under computer control, is fixed onto the skin of the back of the patient in the midline of his spine from at least cervical vertebra C7 down to at least sacral vertebra S3. Two other skin-markers are detachably fixed onto the skin of the back of the patient in a bilateral and symmetrical manner on the crests of his ilium.
A visualization equipment which preferably comprises a pair of cameras spaced a part from each other, is used to track monitor and record the relative positions of all of the skin-markers on the back of the patient as he flexes forward in this sagittal plane.
The so recorded positions of the skin-markers fixed in the midline of the patient's back are then processed to determine the angle of flexion u of the patient as a function of time,this angle being indicative of the combined motion oE both hip and spine of the patient.
The recorded positions of the skin-markers symmetrically fixed on the ilium are simultaneously processed with the recorded posltion of the skin-marker fixed on the sacral vertebra S3 to determine the angle of rotation "h" of the ~2~

hip as a function of time, this angle "h" being indicative of the hip motion of the patient.
Then angle "h" is substracted from angle a to determine the actual contribution of the spine to the total flexion of the patient as a function of time, the contribution, expressed as angle "s", being indicative of the spine motion of the patient, and the values of angles ~ , "h" and "s" are altogether processed to calculate the relative variations of "h" and "s" versus ~, which variations are respectively indicative of the ranges of hip and spine motions in the sagittal plane~ After plotting, these variations are compare with each other and with results obtained from a group "normal" patients to determine any discrepancy or singularity~
From these comparison and determination, anyone skilled in the medical art may easily derive the requested information as to the flexibility of the spine and the presence of a potential mechanical injury therein.

BRIEF DESCRIPTION OF THE DRAWINGS:
In the accompanying drawings:
Fig. 1 is a schematic representation of an equipment for use in carrying out the method according to the inven-tion;
Fig. 2 is a representation of the true sagit-tal motion of the spine oE a patient at di~ferent flexing position, obtained from a three-dimensional reconstruction oE the positions o~ -the skin-markers fixed on the spine of the patient with the e~uiprnent shown in Fig. 1;
Fig. 3 is a sagittal representation of the skin-markers fixed on the spine of ~he patient, giving one possible definition for the angle of flexion of the patient;
Fig. 4 are curves showing geometric da-ta on the i7~

trunk, spine and hip motion derived from the positlon of the skin-markers;
Fig. 5 are in-tegrated electromyographic (EMG) measurements of the activity of several muscles recorded with the equipment of Fig. 1 on a patient flexing forward a first time to lift up a barbell and then a second time to put it down;
Fig. 6 are plots showing the geometric data plotted versus time in Fig. 4, now plotted versus angle ~ ;
Fig. 7 is a sagittal view oE the lumbar position of a spine in extension, showing the portion of the external markers vis-à-vis the actual position of the vertebrae drawn from a X-ray film;
Fig. 8 is a plot showing the relation existing between the lumbo-sacral angle ~ as measured by the markers and the true lumbo-socral angle ~* as obtained by X-rays for five different values corresponding to five different postures;
Fig. 9 are plots showing the yeometric data obtained on a patient before and after rhizolysis;
Fig. 10 are plots showing the geometric data obtained on a patient before and after fusion;
F'ig. 11 are plots showing the geometric data obtained on another patient before and aEter fusion;
F'ig. 12 are plots showing the geometric data obtained on a healthy pa-tient possibly malingering;
Fig. 13 are plots showing the geometric data obtained on a patient having a torsional injury; and Fig. 1~ is a typical example of Report that may be obtained with the equipment according to the inven-tion.

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DETAILED DESCRIPTION OF THE INVENTION

a) ~eneral description of t_e equipment The non-invasive equipment 1 according to the invention as shown in Fig. 1, is primarily designed to observe and record the spatial positioning of the spine of a patient "P" during a very specific excercise, namely executing lifts in the sagittal plane. The geometry of the spine of the patient during the exercise is deduced by measuring the position of 24 dot-shaped, skin markers fixed on the patient as shown with round dots in Fig. 1. Of the 24 markers, 12 are distributed along the back above the spine.
The markers are, in fact, small light-emit-ting diodes ~ LEDs) fired under computer control (see box 3) and tracked by two spaced-apart cameras 5.
The uppermost LED in the patient's midline is preferably fixed on the spinous process of cervical vertebra C7 or Tl while the lowermost LED is fixed on a sacral vertebra, preferably S2. Two other LEDs are also preferably positioned on the spinous process of thoracic vertebra Tll and lumbar vertebra L~, the other LEDs being merely put in between at regular interval. As a matter of fact, oncesome spaced-apart LEDs are set, the positions of the other LEDs with respect to the anatomical landmark, may be easily calculated from normalized anatomical tables.
Two of the remaining 12 markers are and must be positioned onto the skin of the back of the patient in a bilateral and symmetrical manner on the crests of the patient's ilium, at height substantially halfway between lumbar vertebrae L4 and L5 (which usually correspond to the height the nin-th and tenth LEDs in the patient's midline).
The last 10 markers are merely used to track with the cameras 5 the general position of the patient while he is flexing forward. These last 10 markers are respec-tively fixed bilaterally and symmetrically onto the patien-t's shoulder at height substantially halfway between cervical S vertebra L7 and thoracic vertebra T3, on the patient's back at height substantially halfway between thoracic ver-tebra Tl1 and lumbar vertebra Ll, and on the patient's appendages (i.e. his legs and arms) , above his elbows, below his knees and at his Achilles tendons.
During the exercice, the patient is free to move in an area 4 x 6 meters, thanks to an "umbilical cord" 7 connecting the LEDs to their computer control 3. The LED
markers are tracked by the cameras 5 within an accuracy of 1/500.
The three-dimensional co-ordinates of each marker are reconstructed by a computer 9 from the data generated by the two cameras 5. As the data is collected by the cameras at a speed of 180.sets of 24 markers per second, these can be combined to improve accuracy and still maintain an acceptable dynamic range at approximately 12 images per second.
The reconstructed sagittal view of the position of the 12 markers placed above the spine in the patient's midline is shown in Fig. 2. These 12 markers define a curve which is an approximation of the true lumbar curve.

b) ~n~l By suitably processing the respective positions of the 12 markers Eixed in the midline of the patient's back, one may easily determine the angle of forward Elexion ~ of the trunk of the patient as a function of time.
This angle~ which is indicative of the combined motion of both the hip and spine of the patient, can be defined as the angle between an imaginary line passing through one of the uppermost LEDS in the midline of the patient's back and one the lowermost LEDS fixed on a sacral vertebra, and a vertical axis, as shown in Fig. 3. In such a case,processing can be carried out in the computer 9 by digitizing with an X-Y digitizer the relative positions of the selected markers, then calculating the slope of the line passing through these positions and deriving from this slope the value of ~ (the slope of the imaginary line being indeed equal to tangent ~ ).
Alternatively, angle a can be defined as the angle between a mean-square fit line mathematically calculated as is known, from the relative positions of all the skin markers fixed on the patient's midline, and a vertical axis.
Once again, the slope of this calculated line is equal to tangent ~.
Angle ~ may of course be plotted or displayed as shown in Fig. ~ (see curve B).

c) Hip motion Simultaneously to the above processing, the recorded positions of the two skin-markers symmetrically fixed on the crests of the patient's ilium are processed in the computer 9 with the recorded position of the skin-marker fixed on one of the sacral vertebrae such as S2 or S3, to determine the angle o~ rotation "h" of the hip as a function of time. This angle "h" which is indicative of the hip motion of the patient, can be derived from the mot:ion of the plane (see the dotted triangle on the patient in Fig. 1) defined by the abovementioned t~ree markers.
The intersection of this plane with the sagittal plane yields a straight line. 1'he angle between this line and the vertical characterizes the motion of the hip and can ~2~ 52 be plotted as shown in Fig. 4 (see curve C).

d) Spine motion Since the total motion characterized by the angle ~ is due to the combined motion of both spine and hip, the spine motion can be deduced by measuring the motion of the hip and substracting it from the motion of the trunk. In other words, the substraction of angle "h"from angle ~
permits to determine the actual con-tribution of the spine to the total flexion of the patient as a function of time.
This contribution, which is hereinafter expressed as angle "s", is indicative of the spine motion of the patient and can be plotted as a function of time as shown in Fig. 4 (see curve D).
A very interesting peculiarity of the hip angle variation can be noticed in Fig. 4. During the first phase of the exercice, as the subject bends forward to pick up a barbell, the hip rotates forward to 30 degrees~then rotates backward to restrain the hips at an angle of about 15 degrees. This backward motion is due to the flexion of the knee as the subject squats to reach for the barbell.
Nonetheless, the total trunk motion still increases, i.e.
the hip motion has a predominant effect.
These laters are of course correlated with the spine motion (curve D), which is defined by the difference between the total trunk motion (curve B) and hip motion (curve C).As can be noticed, this spinal motion continues to increase even as the pelvis is restrained by the bending oE
the knees. This increase in spinal flexion is responsible for setting the posterior ligamentous system under tension, thus requiring no muscular contributLon. This fact is by the way confirmed by measurements that may be simultaneously taken of the electromyographic activities of multifidus, iliocostalis, longissimus lumborum and rectus abdominis of the pa-tient, as depicted in Fig. 5.
In accordance with the invention, the values of angles a , "h" and "s" are further processed to calculate the relative variations of "h" and "s" versus ~ . The variations which are respectively indicative of the ranges of hip and spine motions in the sagittal plane, are plotted or displayed (see Fig. 6) and may be used as accurate diagnosis tools by anyone skilled in the medical art to evaluate the flexibility of the spine and detec-t the presence of a potential mechanical injury in said spine. This diagnosis can very easily be made by comparing with each other the plots obtained for a given patient and, if necessary, compaxing these plots with "standard"plots obtained from a group "normal" patients to determine any discrepancy or singularity.
As will be seen hereinafter (see the reported "cases"), the determination of the ranges of hip and spine motion in the sagittal plane, is sufficient as such to establish or confirm a diagnosis. However,further informations such as the range of variation of the lumbo-sacral angle ~ , the percentage arc elongation and/or the EMG activities of the patient's muscles, may also be obtained with the same equipment to confirm, complete and cross-check the basic data already obtained.
. . .
e) Lumbo-sacral angle ~

The measurement of the lumbo-sacral angle l~ as a func-tion of time while the patient is flexing, can be carried out by using the respec-tive, recorded positions of the LEDs in the midline oE the patient's back to mathemati-cally reconstruct the true lumbar curve of the spine in the sagittal plane, then locating the inflexion point on the ~i7~52 reconstructed curve, then tracing tangents to said inflexion points, and finally measuring the angle between these tangents, the so measured angle being defined as angle l~.
The measured values of ~ may then be processed by -the com-puter 9 to calculate the relative variation of saidangle ~ versus ~ . This variation of ~ versus ~ which is indicative of the lumbar lordosis of the patient's spine and thus directly correlated with the range of spine motion, can be plotted and the plot used as further information to detect the presence of a potential mechanical injury in the lumbar spine of the patient. Indeed, a decrease in ~ indi-cates a significan-t reduction in lumbar lordosis, as the spine straightens out (see Fig. 4, curve E).

lS One may of course wonder how the displacemen-t of the markers correlates with the true lumbar curve derived from measurements that could be obtained from radiography.
In practise, this correlation was checked by the inventor by taping 3mm diameter steel balls over the spinous processes and the iliac crest. To control for image magnification of the X-ray machine, an one-inch diameter steel ring was taped above multifidus as close to the L3 spinous process as possible. As this ring appeared as an ellipse on the film, vertebrae size might be scaled up or down un-til the shadow of the largest diameter oE the ellipse is exactly one inch.
By taking several lateral radiographs of the subject so instrumented (in the erect stance and for 15,30,45,60 and 90 degrees of forward flexion), a fair idea of the relationship between the position of the markers and the vertebrae was obtained (see Fig. 7). In practise, the skin motion (i.e. the displacement of the marker vis-à-vis a given spinous process as the subject bends forward) has proved to be small (a few millimeters) and unimportant because the skin motion is in the sagittal plane. In other ~2~ 352 words, displacing a marker in that direction had little measurable effect on the calculated value of the angle ~ .
Since the true lordosis and the curve defined by the markers are uniquely related, there is no need to measure the true lordosis to interpret the data. ThereEore, it is justified to use ~ instead of the true lumbo-sacral angle l~ (defined as the angle between the bisectors of T12/L1 and L5/S1) as clearly evidenced by Fig. 8 which shows a linear correlation between these two angles, the error in measurement of the position of the markers vis-à-vis the bony structure being about - 1.5 mm.
Thus, the above reported data demonstrates that external measurements using markers placed on the skin can give a reasonable approximation of the true lordosis or lumbo-sacral angle.

f) Percentage arc elongation , . ..
The measurement of the percentage of elongation of the arc sustained by the skin markers while the patient is flexing, can be carried out by using the respective, recorded positions oE the markers in the midline of the patient's back to mathematically reconstruct the true lumbar curve of the spine in the sagittal plane (see Fig. 2) and then measuring the distance along the curve between the markers. Then, the measured values o~ percentage arc elongation may be processed by the computer 9 -to calculate the relative variation of elongation versus ~ . This variation which is indicative of the lumbar lordosis of the patient's spine and thus directly correlated with the range of spine motion, can of course be plotted (see Fig. ~, curve F) and used as further information to detect the presence of a potential mechanical injury inthe lumbar spine of the patient.

~97~2 The effect of the reduction in lumbar lordosis on -the rotation of the intervertebral joint is illus-tra-ted in Fig. 4 (curve F). In this example, the distance between markers #12 (point zero) and #6 (point A) was 113mm when the subject adopted an erect, relaxed stance (see Fig. 2). This distance increased to 153mm (point B) and eventually extended to 170 mm (point C) when the subject was fully bent and touching the barbell.
From the percentage increase plotted in this Fig.

2 (curve F), it is evident that this increase mirrors the variation in the lumbo-sacral angle ~ (see curve E). It should be noted -that the 50 per cent increase in the distance OA is quite significant, as it allows the posterior ligame~-tous system (PLS) to be stretched. That this subject is able to rotate all his intervertebral joints during forward flexion is also evidence that they ought to be in good condition and therefore permit the PLS to play its important role. The subject was also tested at a weight of 60 kg with similar results, thus indicating that his lifting capacity exceeds 60 kg.

g) EMG activity The measurement of the electromyographic (EMG) activities of the patient's muscles can be carried out by detachably fixing a set of surEace electrodes (shown with stars on the patient P in Fig. l) bila-terally on the latissimus dorsi beLow scapula, the longissimus lumboruni at vertebra L3, the multifidus at L5 and the harmstring semitendinosus. Alternatively, the EMG data may be co:Llected bilaterally on the multifidus (2 cm off the midline at L5 level), on the i:Liocostalis and longissimus lumborum (at 5 crn off the midl:Lne at L3), on the external obliques above the triangle of Petit, on the latissimus dorsi at T5 and on the rectus abdominis at the L3 level.
The raw EMG signals that are recorded are band filtered (5Hz to 300 Hz), digitized at 1 KHz and rectified(at ll)and integrated in the computer 9 to determine -the magnitude of activity of every muscle,and the integrated signals plotted as a function of time.
The plots obtained on the left and right sides of the patient may be compared to detect any discrepancy, and this information as well as the general muscle activity as reflected by all of these EMG plots may be used as a fur-ther information to detect the presence of a potential mechanical ingury in the lumbar spine of the patient.
Fig. 5 shows the integrated EMG (IEMG) of several muscles recorded during a very specific exercice comprising four distinct phases:

l. from a relaxed upright stance the patient bended forward to pick up a weight (a 20 kg barbell). The knees might or might not be locked, depending upon the person's choise;

2. the barbell was then lifted. The patient returned to the upright posture, keeping the barbell a-t arm's length in such a way that the arms always hang down from the shoulders;

3. the patient bended forward again to put the weight down; and ~. he returned empt~-handed to the upright stance.

Fig. 6 clearly shows how the plotting of the IEMG
may be complementary helpful to make a diagnosis. Curve A of this Fig. 6 was derived by scaling and superimposing the - 2~ -~2~5~

IEMG of the multifidus with the calculated mornent at L. The muscle relaxation phenomenon is obvious. Indead, one may note the sharp drop in muscle contribution at the very instant it is needed most according to the school of through proposing that back muscles do the lifting). This of course supports the inventor's mathematical representation of the spine anatomy and mechanics as shortly reported hereinabove in the preamble of the specification.

h) Clinical evaluation Of course, all of the objective data obtained with the method and equipment according to the invention may (and must) be correlated with the results of a clinical evaluation carried out by asking the patient to answer a set o~ psychological questions describing his pain in such specific situations as walking, sitting and lying down.
The answers may be used to determine, in broad terms, whether or not the pain is mechanical in nature (e.g.
radicular, somatic, etc.) or of another origin (e.g.
neoplastic, viscerogenic, etc.). Other test that may also be performed are: the Oswestry low back pain disability guestionnaire, the Waddell inappropriate symptom test, the Mooney-Wiltse pain drawing, the Dallas pain drawing and assessment, the pain intensity and linear pain scale, and the Million visual analog scale.

E X ~ M P L E S

The egu:ipment 1 according to the invention as disclosed hereinabove was used to coJlect da-ta on a plurality oE individuals known to have spinal injuries. The various cases r~ported hereinaEter will clearly show how the collected data may be used as diagnosis tools to evaluate 7~i2 the flexibility of the spine and detec-t any mechanical injury therein.

CASE #1:
A patient with a facet syndrome resolved by rhizolysis . _ .

This patient was tested by the equipment 1 accord-ing to the invention in October 1986. He was asked -to flex forward as far as possible without lifting a load. The collected data are shown in Fig. 9 and may be compared with those shown in Fig. 6, which may be considered as representative of a "normal" response.
This subject was reluctant to bend fully forward using spinal flexion. Here, the hip motion is equally important. In November 1986, the subject underwent a procedure called rhizolysis, in which the nerves feeding both right and left facets at L4 were burned. This is equivalent to disconnecting the local "alarm system" (and therefore the pain) without changing anything in the mechanical structure.
The same patient returned to our laboratory in January 1987 for another evaluation. As his pain was reduced by 50~ (according to the subjec-tive evalua-tion), and he was very happy. Nevertheless, thë collected data shows almost no difference in spinal motion. This confirms the nature oE the rhizolysis procedure. The level of functionality of his spine did not change.

CASE #2 _ _ A patient with a clinically diagnosed disc injury at L /S , resolved by intervertebral body fusion (anterior approach) 5- a successful case.

This patient was evaluated by the equipment according to -the invention February 1987 (see Fig. 10). His data show restricted spinal motion, with almost no measur-able variaton in his lumbo-sacral angle (notice the almost fla-t response of the lumbo-sacral angle ~ before surgery).
The pain was so intense that the entire spine was rotating as a unit around the acetabulum. Following surgery and the fusion of L5/S1, the entire lumbar section recovered a significant amount of mobility. The patient's psychological scores also show improvement. This is believed to be a successful case.
This is a paradoxical result -that may be due to the relief in pain at L5/Sl which allowed the upper section of -the spine to move more freely. This surgical intervention was, therefore, successful in the sense that it improved the range of motion of the spine and, it is believed, its functionali-ty.
I-t was noted, however, -that other fused patients who were tested exhibited considerable reduction in spinal functionality. The benefits oE spinal Eusion are debated rather vigorously in the literature. There seems to be as many successes as failures, with no coherent explanation as to why this is so. The equipment according to the invention sees successes and failures in terms of functionality and, :in that sense, represents an object:ive method of evaluating the beneEits of surgery.

CASE ~3:

A patient with a classically diagnosed multiple injury at L failed chemopapain (resolved by fusion) - a less-than--successful case.
, . .

This patient was fused from L4 to S1. The significant loss of range of motion that resulted from the fusion, proved that the casè was less than successful. The EMG of multifidus shows erratic data, demonstrating extensive damage to the muscle Isee Fig. 11).

CASE ~4:

Symptom exaggeration - possible malingering.

A patient examined with the equipment according to the invention in March 1987 scored randomly on the various psychological tests. Objective data on his spine motion demonstrated a very good, almost normal response. Lateral bending demonstrated a small residual problem at L4/5, possibly from a Eresh torsional injury (see Fig. 12).
The conclusion in -this case was that the patien-t demonstrated objective signs, most likely due to a small torsion injury at L4/5, which was demonstrated by examination of the lateral bendin~ response. This injury does not interfere significantly with spinal functionality.
The randomness o~ his scores on the psychological tests may point out an attempt to exaggerate the symptoms in order to obtain better compensation Eor his real :injury.

CASE #5 Torsional ini~y at L -EMG response in flexion-extension.
_ 4/5 - 2~ -This patient had occasional back pain -two years before this recording was made (Fig. 13). The clinical diagnosis was torsional injury at L~/5.
The data demonstrate a complete lack of confidence in the ability of the spine to flex. The maximum percentage of elongation was 10%. The EMG responses of multifidus and iliocostalis and longissimus lumborum confirm the patient's reluctance to trust his PLS and flex his spine. The erectores immediately fire as a group as soon as the forward flexion begins. This is a characteristic response which should be compared with Fig. 5.
The lateral bending test demonstrates a reluctance to bend the spine to the right. This refusal can be explained by the need to prevent lateral bending of L4/5 so that no axial torque in the direction of the initial injury is induced.
Although the masculine pronoun has been used exclusively hereinabove and in the following claims, it has to be interpreted as including the feminine.

Claims

1. A non-invasive method for the evaluation of the flexibility of the spine of a patient and, as a result of this evaluation, the detection and identification of possible mecha-nical injuries in the lumbar portion of this spine, said method comprising the steps of:
a) detachably fixing a string of separate, dot-sized skin-markers onto the skin of the back of the patient in the midline of his spine from at least cervical vertebra C7 down to at least sacral vertebra S3;
b) detachably fixing two other dot-sized skin-markers onto the skin of the back of the patient in a bilateral and symmetrical manner on the crests of the ilium of the patient;
c) monitoring and recording the relative positions of all of said skin-markers on the back of the patient as he flexes forward in this sagittal plane;
d) processing the recorded positions of the skin-markers fixed in the midline of the patient's back to determine the angle of flexion .alpha. of the patient as a function of time, said angle .alpha. being indicative of the combined motion of both hip and spine of the patient;
e) processing the recorded positions of the skin-markers symmetrically fixed on the ilium with the recorded po-sition of the skin-marker fixed on a sacral vertebra to determine the angle of rotation "h" of the hip as a function of time, said angle "h" being indicative of the hip motion of the patient;
f) subtracting angle "h" from angle .alpha. to determine the actual contribution of the spine to the total flexion of the patient as a function of time, said contribution, expressed as angle "s",being indicative of the spine motion of the pa-tient; and g) processing the values of angles .alpha., "h" and "s"
to calculate the relative variations of "h" and "s" versus .alpha. , and plotting said variations which are respectively indica-tive of the ranges of hip and spine motions in the sagittal plane; and h) comparing said plots with each other and with plots obtained from a group "normal" patients to determine any discre-pancy or singularity and derive from these comparison and de-termination the requested information as to the flexibility of the spine and the presence of a potential mechanical injury therein.

2. The method of claim 1 wherein, in steps (a) and (b), use is made of LEDs fired under computer control, as skin-markers,and wherein step (c) is carried out with a pair of ca-meras spaced apart from each other in order to track, monitor and record the relative positions of the LEDs in the space which said LEDs are fired.

3. The method of claim 2, wherein, in step (d) the determination of angle c is carried out by mathematically drawing an imaginary line passing through one of the uppermost LEDs in the midline of the patient's back and one the lowermost LEDs fixed on a sacral vertebra, and measuring -the angle between said imaginary line and a vertical axis, said measured angle being used as angle .alpha. .

4. The method of claim 2, wherein, in step (d), the determination of angle .alpha. is carried out by using the respective, recorded position of every LED in the midline of the patient's back to mathematically draw a mean-square fit line indicative of the general angle of flexion of the patient and measuring the angle between said line and a vertical axis, said measured angle being used as angle .alpha..

5. The method of claim 1, 3 or 4, comprising the addi-tional steps of:
i) measuring the lumbo-sacral angle ? as a function of time while the patient is flexing, said measurement being carried out by using the respective, recorded positions of the LEDs in the midline of the patient's back to mathematically reconstruct the true lumbar curve of the spine in the sagittal plane, then locating the inflexion point on the reconstructed curve and tracing tangents to said inflexion points, and finally measuring the angle between said tangents, said measured angle being used as angle ?, j) processing the measured values of ? to calculate the relative variation of said angle ? versus .alpha., and plotting said variation which is indicative of the lumbar lordosis of the patient's spine and thus directly correlated with the range of spine motion; and k) using this plot as further information to detect the presence of a potential mechanical injury in the lumbar spine of the patient.

6. The method of claim 1, 3 or 4, comprising the ad-ditional steps of:
1) measuring the percentage of elongation of the arc sustained by the skin markers while the patient is flexing, by using the respective, recorded positions of said markers in the midline of the patient's back to mathematicaly recons-truct the true lumbar curve of the spine in the sagittal plane and then measuring the distance along the curve between the markers;
m) processing the measured values of percentage arc elongation to calculate the relative variation of said elonga-tion versus .alpha., and plotting said variation which is indicative of the lumbar lordosis of the patient's spine and thus directly correlated with the range of spine motion, and n) using this plot as further information to detect the presence of a potential mechanical injury in the lumbar spine of the patient.

7. The method of claim 1, 3 or 4, comprising the addi-tional steps of:
o) measuring with a set of surface electrodes the electromyographic (EMG) activities of the patient bilaterally on the latissimus dorsi below scapula, the longissimus lumbo-runi at vertebra L3 the multifidus at L5 and the harmstring semitendinosus;
p) integrating said EMG signals to determine the ma-gnitude of activity of every muscle;
q) plotting said integrated signals as a function of time; and r) comparing the plots obtained on the left and right sides of the patient to note any discrepancy, and using this information as well as the general muscle activity as reflected by all of these EMG plots as a further information to detect the presence of a potential mechanical injury in the lumbar spine of the patient.

8. The method of claim 1, 3 or 4, comprising the addi-tional steps of:
s) detachably fixing further dot-sized skin-markers bilaterally and symmetrically onto the shoulders, the arms above the elbows and the legs below the knees and at the Achilles tendons; and t) using said further skin-markers to tract the general position of the patient while he is flexing forward.

9. An equipment for the non-invasive evaluation of the flexibility of the spine of a patient and, as a result of this evaluation, the detection and identification of possible mechanical injuries in the lumbar portion of said spine, said equipment comprising:

a) a plurality of separate, dot-sized skin-markers attachable to the skin of the back of the patient in the mid-line of his spine from a-t least cervical vertebra C7 down to at least sacral vertebra S3;
b) two other dot-sized, skin-markers attachable to the skin of the back of the patient bilaterally and symmetri-cally on the crests of the ilium of said patient;
c) a visualization equipment for observing and moni-toring the relative positions of all of said skin-markers on the back of the patient as he flexes forward in his sagittal plane;
d) means connected to the visualization equipment for recording the monitored positions of the skin-markers as the patient is flexing forward;
e) means connected to the recording means for pro-cessing the recorded positions of the skin-markers fixed in the midline of the patient's back to determine the angle of flexion .alpha. of the patient as a function of time, said angle .alpha. being indicative of the combined motion or both hip and spine of the patient;
f) means connected to the recording means for pro-cessing the recorded positions of the skin-markers symmetrically fixed on the ilium with the recorded position of the skin-marker fixed on the sacral vertebra S3 to determine the angle of rota-tion "h" of the hip as a function of time, said angle "h" being indicative of the hip motion of the patient;
g) means connected to processing means (e) and (f) for substracting angle "h" from angle .alpha. to determine the actual contribution of the spine to the total flexion of the patient as a function of time, said contribution, expressed as angle "s", being indicative of the spine motion of the patient;
h) means connected to processing means (e) and (f) for calculating the relative variations of angles "h" and "s"
versus angle .alpha.,; and i) means connected to said calculating means (h) for plotting the processed variations of "h" and "s" versus .alpha., said variations being respectively indicative of the ranges of hip and spine motion in the sagittal plane.

10. An equipment as claimed in claim 9, wherein:
- the skin-markers (a) and (b) consist of LEDs fired as given interval by a computer;
- the visualization equipment (c) consists of a pair of cameras spaced apart from each other in order to tract and monitor the relative positions of the LEDs in the space while said LEDs are fired; and - all of said recording, processing and calculating means (d) to (h) are included into another computer.

11. An equipment as claimed in claim 10, wherein said other computer further includes:
j) means for measuring the lumbosaccral angle ? as a function of time when the patient is flexing, said measuring means comprising:
- means for mathermatically reconstructing the true lumbar curve of the spine of the sagittal plane from the respective, recorded positions of the LEDs in the midline of the patient's back;
- means for locating the inflexion point on the reconstructed curve.; and - means for tracing tangents to said inflexion point, and - means for measuring the angle between said ten-sions, - said measured angle being used as angle ?;
and k) means for processing the measured values of ? to calculate the relative variation of said angle ? versus .alpha., said variation being indicative of the lumbar lordosis of the patient's spine and thus directly correlated with the range of spine motion, said relative variation of said angle ? versus .alpha. being plotted by said plotting means (i).

12. An equipment as claimed in claim 10 or 11, wherein said other computer further includes:
l) means for measuring the percentage of elongation of the arc sustained by the skin-markers in the midline of the patient's back while said patient is flexing, said measuring means including:
- means for mathematically reconstructing the true lumbar curve of the spine of the pa-tient in a saggital plane from the respective, recorded positions of the markers in the midline of the patient's back; and - means for measuring the distance along the curve between the markers; and m) means for processing the measured values of percentage arc elongation to calculate the relative variation of said elongation versus .alpha., said variation being indicati-ve of the lumbar lordosis of the patient's spine and thus directly correlated into the range of spine motion, said relative variation of said elongation versus being plotted by said plotting means (i).

13. An equipment as claimed in claim 10 or 11, further comprising:
o) a set of surface, electrodes for mesuring the electromyographic (EMG) activities of the patient bilaterally on the, latissimus dorsi below scapula, the longissimus lum-boruni at vertebra L3, the multifidus at L5 and the harms-tring semitendinosus; and p) means for integrating said EMG signals to deter-mine the magnitude of activity of every muscle, said integrated signals being plotted by said plotting means (i) as a function of time.

14. An equipment as claimed in claim 10 or 11, further comprising:
q) further dot-sized skin-markers attachable bi-laterally and symmetrically onto the back, shoulders, arms above the elbows and legs below the knees and at the Achilles tendons to track with the cameras the general position of the patient while he is flexing forward.