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Description  |
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FIELD OF THE INVENTION
This invention relates to dynamic joint measuring techniques, and more
particularly to arrangements for measuring and analyzing dynamic motion of
the knee and other joints in three planes.
BACKGROUND OF THE INVENTION
It has previously been proposed to measure knee motion in all three planes,
and a typical article disclosing such measurement is "An
Electrogoniometric Study of Knee Motion in Normal Gait" by Donald B.
Kettelkamp, M.D., et al., the Journal of Bone and Joint Surgery, Volume
52-A, No. 4, June 1970, pages 775 to 790.
In general, what the prior analyses show is that the human knee is a
relatively complicated joint, and its motion is not limited to hinge-type
action around a single transverse axis as might initially be expected of
the knee joint. This front-to-back motion, which of course is the
principal and major motion of the knee, is known as flexion-extension.
Full extension of the knee is when the leg is stretched out and the knee
joint locked; and full flexion of the knee occurs when the leg is bent so
that the calf is firmly against the thigh. Studies of the knee show that
in the course of normal walking, for example, the knee goes through two
flexion-extension cycles during each complete walking step, with maximum
extension occurring during the swing phase, and an additional extension
occurring during the time when the foot is engaging the ground. In
addition to the flexion-extension motion, the knee also bends toward and
away from the centerline of the body. This inward or outward motion is
known variously as abduction/adduction, or varus/valgus motion, with
"abduction" and "varus" referring to outward movement of the knee, and
"adduction" and " valgus" referring to inward movement of the knee. In the
present specification, we will use the designation varus/valgus but some
of the prior articles use the comparable terms abduction/adduction. In
addition to the two types of rotation mentioned above, the knee also may
rotate about the long axis of the leg. This rotation is referred to as
internal/external rotation. In summary therefore, the three types of
motion of the knee to which reference will be made in the present
specification are (1) flexion/extension, (2) varus/valgus, referring to
the inward or outward bending of the knee, and (3) internal/external
rotation.
The apparatus which has been employed up to the present time has been
relatively cumbersome and massive, and the measurements which have been
obtained have been similarly somewhat qualitative and inconsistent.
Accordingly, objects of the present invention include the provision of a
lighter weight three-axis goniometer which is capable of measurement of
athletes performing rapid and extreme physical movements, and one which
will provide accurate and reliable information under such arduous
conditions.
Another object of the present invention in to provide for the diagnosis of
knee injuries by comparing a pattern produced by one leg before injury
with the pattern produced by that leg after injury or by comparing the
pattern produced by one (healthy) leg with that produced by the other
(injured) leg.
Still another object of the present invention is to determine the torque
which is produced under successive different controlled test conditions,
for the purpose of testing athletic equipment or environments, such as
foot gear and playing surface qualities, by way of specific examples.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention a lightweight
three-axis goniometer is provided with arrangements for mounting it on the
outside of the thigh of a user, and the goniometer is supported from the
thigh by a yoke, which has its ends on which the goniometer is pivotally
mounted extending to the rear, to preclude mechanical interference in the
course of the measurement of the movement of the knee in all three planes,
despite concurrent extreme angular movements of the knee. In addition,
arrangements may be provided for reversing the mounting of the goniometer
on the mounting support, so that the same unit may be first used on one
leg and then on the other. In this connection, it may be noted that, with
a normal healthy person, the characteristic angular movements of the knee
in all three planes are very nearly the same for the left and right knees.
Accordingly, when a person has one leg injured, by using the healthy leg
as a control, and then measuring the injured knee, considerable diagnostic
information may be obtained. Similar information may be obtained by
measuring the same knee before and after injury.
In accordance with another aspect of the invention, the goniometer may be
employed to indicate the torque applied to the leg by different athletic
equipment conditions. For example, when a football player is playing on an
artificial surface, the effect of using different types of football shoes
with different cleat configurations or materials, for example, on an
artificial turf can be measured in the course of negotiating a
standardized course in a predetermined period of time. The resultant
comparative tests indicating the extreme angular deviations for two sets
of conditions may be compared, and equipment or playing surface selections
may be made based on such comparisons. One direct application of this type
of testing is the selection of shoes for athletes that will minimize
stress to the knee while still providing adequate traction, such selection
possibly varying as playing surface conditions vary. Another direct
application of this type of testing is to fit individuals with shoes based
upon their particular anatomy such that stress to the knee will be
minimized while walking or running. Still another direct application of
this type of testing is the selection of playing surfaces which
consistently minimize stress to the knee.
In the data processing circuitry employed in the processing of signals from
the goniometer, switches may be provided for the reversing of the
varus/valgus and the internal/external rotation signals, as the goniometer
is switched from the left leg to the right leg, or vice versa, so that the
plots for the two legs will have the same configuration, and may be more
readily compared. In addition, the electronic circuitry may include a
trace identification pattern associated with one or more of the three
output signals from the goniometer, and if desired, these signals may be
interrupted as the associated signal shifts from positive to negative or
vice versa.
Other mechanical features of the goniometer assembly include (1) the use of
high strength, lightweight plastic such as Delrin for the unit, (2)
locating the potentiometers very close together, so that the potentiometer
subassembly is less in extent than two inches, for example, (3) the use of
mounting assemblies for securing the goniometer unit to the upper leg
mount which lock positively in either of two orientations which are 180
degrees displaced from one another for reversing purposes, and (4) the use
of a sliding rod which extends through an element such as a nylon sphere,
mounted in a two axis gimbal on the lower leg, all for the purpose of
measuring internal/external rotation.
Other objects, features, and advantages of the present invention will
become apparent from a consideration of the following detailed description
and from the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a three plane goniometer and mounting assembly
mounted on the leg of a person being tested;
FIG. 2 is a front view of the arrangement of FIG. 1;
FIGS. 3 and 4 are mutually orthogonal views of the goniometer and the lower
mounting assembly secured to the upper leg, and relating to the unit shown
in FIGS. 1 and 2.
FIG. 5 shows the unit partially disassembled to permit reversing for use on
the other leg;
FIG. 6 shows an alternative lighter weight embodiment in which only a
single mounting tube is employed instead of the three tubes shown in the
unit of FIGS. 1 through 5;
FIG. 6A is an enlarged view of one portion of the unit of FIG. 6;
FIG. 7 is a showing of a unit, including a gimbal subassembly, for securing
to the lower leg;
FIG. 7A is an enlarged view of one portion of the unit of FIG. 7;
FIG. 8 is a plot comparing normal knee motion with knee motion in which one
of the ligaments, the anterior cruciate ligament, is weak, or has been
damaged;
FIG. 9 is a plot of torque versus internal/external knee rotation;
FIGS. 10A and 10B are two parts of the circuit diagram of the circuit for
amplifying and recording the signals received from the goniometer units
described hereinabove; and
FIGS. 11A and 11B show the classic differences between a normal knee and a
knee in which a lateral miniscus or other lateral compartment injury is
present.
DETAILED DESCRIPTION
Referring more particularly to the drawings, FIG. 1 is a side view of the
leg of a man with a three axis goniometer assembly 12 mounted near the
knee. The goniometer assembly 12 is mounted from three tubes 14, 16 and 18
which slide into the three additional mounting tubes 20, 22 and 24. The
tubes 20, 22 and 24 are mounted in two brackets 26 and 28, which are
secured to a mounting pad 30, which is in turn mounted on the outer side
of the man's thigh by adjustable straps 32 and 34 provided with Velcro or
other suitable arrangements for securing the straps around the wearer's
upper leg.
As indicated in FIGS. 3 and 4, the lower mounting unit 28 is adjustable to
permit the goniometer assembly 12 to be moved closer or farther away from
the knee, all depending on the musculature and the general configuration
of the thigh relative to the knee, with the goal being to locate the
goniometer assembly 12 as close as possible to the knee. The tubes 14, 16
and 18 are slidable within the tubes 20, 22 and 24, and are held in their
desired position so that the goniometer assembly 12 is properly located
relative to the knee by the knurled adjustment screws 36.
The central tube 16 is longer than the two outer tubes 14 and 18, so that,
as shown in FIG. 5, when it is desired to reverse the position of the
goniometer assembly 12 to mount it on the left leg, the knurled screws
only have to be loosened, and tube 14 is first slid out of tube 20 and
then, following rotation, it is slid back into tube 24 and tube 18 slid
back into tube 20. Incidentally, the leads from the potentiometers 42, 44
and 46 which are included in the goniometer assembly 12 extend up through
the central tubes 16 and 22.
Inward and outward adjustment of the goniometer assembly 12, toward and
away from the knee, is accomplished by adjustments involving the pairs of
knurled knobs 48 and 50 (see FIG. 4). A screw secured to one of the two
knobs 48, is threaded into the other of the knobs 48, whereby the slanted
and movable internal beam 52 may be shifted in its angle relative to the
pad 30 as the shanks of the screws associated with knurled knobs 48 and 50
move in the slots 54 and 56. The lower tube supporting element 58 is
pivotally secured to the plastic member 52 by pin 60, and is otherwise
held in its proper alignment by the orientation of the tubes 20, 22 and 24
which are also pivotally mounted at their upper ends on the plastic
element 26 (see FIGS. 1 and 2).
Extending downwardly from the potentiometer 46 is a metal rod 64 which has
a lower end 66 which is of square or other non-circular configuration. The
square rod 66 passes through and is slidable within a nylon sphere 68,
which has a central rectangular opening and which is mounted in a two-axis
gimbal arrangement 70 shown in FIGS. 7 and 7A, and which in turn is
mounted on a cuff 72 secured to the lower leg by suitable straps 74 which
are somewhat elastic and which are adjustable in the same manner as the
straps 32 and 34 employed to secure the cuff 30 to the thigh.
The cuffs include a sheet aluminum alloy, which is approximately 0.032 inch
thick. The sheet aluminum is covered with vinyl material on its exterior
surface, and the cuffs are provided with a one-quarter inch thick foam
rubber layer on their interior surfaces.
As best shown in FIGS. 3 and 4, the goniometer assembly 12 includes two
potentiometer housings 40 and 41 which house the three precision
potentiometers 42, 44 and 46 (potentiometers 42 and 44 in housing 40 and
potentiometer 46 in housing 41). The potentiometer 42 is operated by a pin
76 which extends outwardly from the potentiometer 42 and is secured to the
end of the yoke having the two rearwardly extending arms 78 and 80. The
potentiometer 42 measures flexion/extension, the normal major pivotal
motion of the knee, and is capable of measuring up to 145 degrees. The
cutaway configuration of the support member 82 with its substantial
opening 84 provides for the varus/valgus motion as measured by
potentiometer 44 as well as for internal/external rotation as measured by
potentiometer 46, without mechanical interference, despite a full range of
movement of the three potentiometers about the pin 76.
As discussed earlier, FIG. 5 shows the method of rotation of the goniometer
assembly 12 relative to the mounting pad 30 and the associated bracket 28.
Specifically, the knurled knobs 36 are loosened, the three tubes 14, 16
and 18 are slid downward until only the central tube 16 which carries the
electrical conductors is in engagement, and the unit is rotated by 180
degrees so that tube 14 engages tube 24, and tube 18 engages tube 20 and
the unit is then reassembled for the use on the left leg. Again, with the
new orientation of the unit, and with the cuff 30 mounted on the left leg,
the ends of the yoke members 78 and 80 will again be directed to the rear,
and the unit will accommodate the full range of flexion/extension motion
of the left leg. It may be noted in passing, that in the absence of
arrangements for reversing the unit as it is shifted from the left leg to
the right leg or vice versa, the potentiometer 42 for measuring
flexion-extension would have different angular ranges for the right and
left leg, and the curved yoke including legs 78,80 would not provide
clearances for the extreme rotation about several axes simultaneously for
both the right and the left leg. Accordingly, without reversibility, some
decrease in sensitivity, and/or mechanical interference with extreme
motion, is to be expected. Alternatively, a much more bulky and heavy unit
would have to be employed.
FIGS. 6 and 6A show an alternative and somewhat lighter embodiment of the
invention in which only one tube 86 slidable within the mounting bracket
94 and the lower pivoted plastic member 98 is used. The three axis
goniometer 90 is similar in configuration to the unit 12 as employed in
the arrangements of FIGS. 1 through 5, but is slightly smaller and lighter
in weight. Again, it includes a yoke with rearwardly directed arms for
increased mechanical clearance, and three potentiometers. The unit of FIG.
6 is very similar to that of FIGS. 1 through 5 and employs a cuff 92 with
associated straps, and a similar upper mounting bracket 94 and a lower
mounting bracket 96. The lower mounting bracket 96 is provided with
similar arrangements for adjusting the height of the lower pivoted plastic
member 98 which corresponds generally to the pivoted member 58 as shown in
FIG. 4. The front bracket member 98 is provided with a knurled clamping
nut 100 to hold the tube 86 in one of two orientations, which are 180
degrees displaced from one another. These two orientations are
accomplished through the use of a rectangular plastic block 102 which is
secured to the tube 86 and which is held in its proper orientation by the
upper and lower protruding lips 104 extending downwardly from the block
98. With this arrangement, and with the block 102 being slightly wider
than it is high, there are only two possible orientations with block 102
in engagement with member 98, one being for use on the right leg and the
other for use on the left leg.
FIGS. 7 and 7A show the arrangements whereby internal/external rotation of
the knee as measured at the lower leg rotates the shaft 64 and in turn
rotates the potentiometer 46 or the corresponding potentiometer of the
single tube arrangement of FIG. 6. As mentioned above, the lower end 66 of
the shaft 64 has a non-circular or square configuration, and is journalled
in the nylon ball 68 in order to permit the rod 64 to freely slide up and
down relative to the element 68. Further, in order to permit changes in
angle of the rod 64 relative to the cuff 72, a two-axis gimbal is provided
which includes the U-shaped frame 112 which is secured to the cuff 72.
Mounted in the U-shaped frame 112 is the gimbal ring 114, and it in turn
mounts the ball 68 about an axis which is perpendicular to the base 112.
With this arrangement, changes in alignment of the shaft 64 relative to
the cuff 72 are readily permitted, but actual rotation of the lower
portion of the leg is fully transmitted to the shaft 64 and result in
changes in the output from potentiometer 46.
The plots of FIG. 8 represent the culmination of the use of the units as
described hereinabove, together with the processing and recording
circuitry to be discussed below. In FIG. 8, an injured knee is compared
with a normal knee by switching the unit as described hereinabove from one
leg to the other. Plots from the "control" or normal knee are shown in
solid lines, while output plots from the injured knee are shown by dashed
lines. In FIG. 8 the top graph represents flexion/extension, the middle
graph represents varus/valgus movement, and the lowermost graph refers to
internal/external rotation. The first portion, proceeding from left to
right represents a normal walking pattern, the second portion between
lines 122 and 124 represents a cross-over turn, the next section between
lines 124 and 126 is again normal walking while the space between lines
126 and 128 represents a sidestep, and this is followed again by normal
walking.
In reviewing the normal knee plots as shown in the solid lines, it is noted
that there are two maxima in leg flexion or bending which occur during
each cycle of walking from one heel strike to the next heel strike, for
example. One of these maxima occurs while the leg is swinging and the
other smaller maxima or peak occurs while the foot is in engagement with
the ground. A similar pattern, but with less angular extent is present
with the varus/valgus characteristic and also with the internal/external
rotation characteristic. Further, while the overall magnitude of the
characteristics vary from person to person, the patterns are normally
quite similar. In addition, and as mentioned above, for any particular
individual, the left leg and the right leg normally produce patterns which
have maxima and minima which are very nearly the same, and with the entire
patterns being substantially the same, when there is no injury present.
If there were no injury present in the person being examined in FIG. 8, the
solid line plot would be very nearly identical with the dashed line plot,
or vice versa. However, in FIG. 8, there are in fact a number of
significant departures of the injured knee characteristic as shown in
dashed lines, as compared with the normal knee. These are emphasized by
the circles 132, 134, 136 and 138. As indicated on the chart, the circle
132 indicates guarded internal rotation while walking; and all of the next
three anomalies are involved in the cross-over turn which is accomplished
between lines 122 and 124. Specifically, the encircled area 134 in the
internal/external rotation characteristic shows external rotation
anticipating a cross-over; the encircled area 136 shows a variation in the
valgus thrust, and the encircled area 138 indicates inhibited extension
during cross-over.
As may be appreciated from the foregoing discussion, the knee is by no
means a simple hinge-type joint, but is relatively complex. More
specifically, the lower end of the femur, or heavy upper leg bone, is
provided with two rounded protuberances, and these seat in the upper end
of the tibia, which is the larger, lower leg bone. Two ligaments extend at
angles across the knee joint, with these two crossing ligaments being
referred to as the anterior cruciate and posterior cruciate ligaments, the
anterior cruciate extending across from the upper outer side of the knee
to the lower inner side of the knee in front of the posterior cruciate
which extends from the upper inner side of the knee across behind the
anterior cruciate toward the lower outside of the knee.
The pattern of departure from normality indicated by FIG. 8 represents an
anterior cruciate ligament insufficiency. As developed below, other
injuries to the knee produce characteristic anomalies in the pattern of
normal and injured knee movement when standardized procedures are
undertaken of the type described hereinabove in connection with FIG. 8.
These characteristic patterns can be a useful diagnostic tool to indicate
the type of injury, or the compartment in which the injury is probably
located. Incidentally, in many cases, following diagnosis by normal
techniques, the method of analysis as described herein has resulted in an
improved, changed or more complete diagnosis which was useful in directing
the corrective surgery or other medical techniques.
Consideration will now be given to torque applied to the knee. Initially,
it must be clearly understood that a three-plane or three-axis goniometer
does not measure torque. However, because of the torque versus angular
rotation characteristic of the normal knee, the magnitude of the angle of
internal/external rotation is a good indicator of changes in knee torque,
under different conditions.
FIG. 9 is a plot of the average value of torque required to produce angular
rotation of the tibia for seven normal knees. While the absolute value of
the individual points of this plot may differ with a different group of
knees, the shape and slopes will be similar for most normal knees.
In the course of studying different types of athletic shoes, an athlete
initially wearing shoe "A" performed a specific set of maneuvers which is
known to rotationally stress the knee a predetermined number of times such
as 10 times. The results of these tests showed that the average value of
maximum internal tibial rotation was 20 degrees, and reference to FIG. 9
shows that 20 degrees of internal rotation is produced by a torque of
approximately 3Nm (Newton-Meters) on the joint. Subsequently, using shoe
"B", the athlete repeated the same maneuvers on the same surface for the
same number of times. For shoe "B" the average value of maximum internal
rotation was 25 degrees, and reference to FIG. 9 reveals that
approximately 7 Nm of torque is required to produce 25 degrees of tibial
rotation. Accordingly, shoe "B" apparently transmits 21/2 times the torque
to the knee as shoe "A" for the same activity. And serious consideration
must be given as to whether shoe "B" may safely be used in view of the
greatly increased torque which is produced. Of course, torque is only one
factor to be considered, and the degree of control achieved by the athlete
with the two shoes must obviously be considered and perhaps a suitable
compromise shoe configuration selected.
It is also noted that the qualities of various playing surfaces may also be
tested by repetitive activity on the different surfaces using a single
pair of shoes on both surfaces, and a standardized series of maneuvers.
Such tests could be useful in the design or selection of suitable natural
substances or artificial "carpets" to be employed as coverings for
athletic fields. It is also noted in passing that tiring of the athlete
may be a factor; accordingly, the athlete should either rest between
successive series under different conditions, or alternate tests, first
using one set of conditions, then the other, and continuing successive
alternations.
Still another specific example of how the goniometer readings may be used
is the fitting of shoes to an individual such that stresses to the knee
will be minimized. Because of differences in the physical make-up of
individuals, some shoes create considerable stresses to the knee, while
others will dampen such stresses. The inward or outward slant of a shoe
sole has such effects depending on how an individual's foot normally
contacts the ground. By having a person negotiate standard maneuvers
wearing different shoes and comparing goniometer readings, the shoes that
are best for that person from a knee stress standpoint can be found.
Still another specific example of how the goniometer readings may be used
is the selection of shoes for athletes that will minimize knee stresses
while providing adequate traction on varying playing surfaces. Most teams,
such as football, soccer, baseball, etc., today play on a variety of
surfaces depending on location and weather. One such surface for a given
athlete with a given pair of shoes might create knee stresses of a
relatively small magnitude, while another surface with the same athlete
and shoes might create knee stresses of a dangerously high magnitude. By
having the athlete perform standard maneuvers with different shoes on any
given field and comparing goniometer readings, the shoes from that lot
that are best in minimizing knee stresses while providing adequate
traction, can be selected.
FIGS. 10A and 10B together form a circuit for processing the signals from
the three axis goniometers described hereinabove. More particularly, the
leads from the three potentiometers are connected through one of the
tubes, and are brought through the tubes onto the wearer's body. In the
case of routine walking tests, such as those described in connection with
FIG. 8, long leads may be employed to connect to the connector block 142
as shown in FIG. 10A. Alternatively, in the event that more freedom of
activity to conduct wider-ranging tests is required, simple telemetry
arrangements could be employed to route the signals from the person
wearing the goniometer assembly to the processing and recording equipment
of FIGS. 10A and 10B. In all events, signals from the three axis
goniometer are routed to the connector 142 and from this connector the
flexion/extension signals are routed to channel 144, the varus/valgus
signals are routed to channel 146, and the internal/external rotation
signals are routed to channel 148.
There are two instrumentation amplifiers A and B associated with each of
the channels 144, 146, and 148. The reason for these two instrumentation
amplifiers involves the different resistor settings required to
accommodate the different impedances provided by the three axis goniometer
as shown in FIGS. 1 through 5, and that shown in FIG. 6. Accordingly, when
a switch is made from one of the goniometers to the other, the switch 150
is actuated to select signals from either the "A" or the "B" set of
instrumentation amplifiers. The sensitivity controlling potentiometers
152, 154 and 156 control the sensitivity for flexion/extension,
varus/valgus and internal/external rotation, as the maximum values for
these various parameters may vary from patient to patient. Immediately
after the sensitivity controlling potentiometers 152, 154 and 156, are
found the voltage follower circuits 158, 160 and 162, respectively.
Associated with the varus/valgus and the internal/external rotation
channels are the polarity reversing circuits 164 and 166, respectively.
The switch 168 serves to reverse the polarity and it is actuated as the
three axis goniometers are switched from one leg to the other of a
patient, thereby facilitating comparison of plots made by the left and
right legs.
The switch 170 is the galvanometer on-off switch. The circuitry associated
with chip 172 is a warning signal which energizes the warning lamp 174
when the galvanometers are turned off, to avoid an attempted test cycle
with a patient proceeding through the specified maneuvers when the
galvanometers are turned off. A recorder unit is generally indicated by
the dashed line block 176. Within the block 176 are shown a series of
three galvanometers 178, 180 and 182 associated respectively with the
three channels corresponding to the three outputs from the goniometers.
The two additional galvanometers 184 and 186 provide marker signals for
the varus/valgus and internal/external rotation channels, as shown in
FIGS. 11A and 11B to be described below. More specifically, a low
frequency signal in the order of 10 to 30 hertz is provided by any
suitable oscillator 188. The field effect transistors 190 and 192
selectively block the oscillator signal from the galvanometers 184 and 186
when the corresponding signals pass through a predetermined level. This
serves to uniquely identify the particular signals associated with that
channel and avoid their confusion of traces associated with adjacent
channels, despite some occasional overlap. This will be shown in greater
detail in connection with FIGS. 11A and 11B. The input circuits to the
field effect transistors 190 and 192 are comparison circuits which
establish the levels at which the FET's will block the signals from
oscillator 188.
Now, referring to FIGS. 11A and 11B, the upper trace in each case
represents flexion/extension; the central trace represents varus/valgus;
and the lower trace represents internal/external rotation, in accordance
with the normal practice in displaying these features. In FIG. 11A, the
signal from the oscillator 188 appears at 196 and 198, and is interrupted
between these two data plots, indicating that the varus/valgus signal
exceeded the predetermined level represented by the lowermost extreme of
the plots 196 and 198. Similarly, the marker pattern designated by the
reference numerals 200 and 202 associated with the flexion/extension
characteristic in FIG. 11A, is interrupted when the characteristic exceeds
a predetermined level.
The plots of FIG. 11A are the graphs from a healthy right leg. However, the
plots of FIG. 11B represents an injured left leg, which includes a lateral
meniscus tear. In this case, the internal/ external rotation is relatively
normal, but there are anomalies in the flexion/extension and in the
varus/valgus characteristics. More specifically, the flexion/extension
characteristic shows about 8 degrees lack of extension in late mid-stance
as indicated by the circle 204; and in the varus/valgus characteristic as
indicated at the circle 206, instead of a slight varus signal in
mid-stance, we find a 4 degree relative valgus at this point. These
indications are characteristic of a lateral meniscus tear.
One set of interrelated features of the present invention deserves
recapitulation. This involves the asymmetric configuration of the
goniometer and its supporting yokes, in combination with the arrangements
for mechanically reversing the goniometer relative to the thigh mount and
also the electrical circuit reversing arrangements. More particularly, the
fact that the upper yoke from which the potentiometers are supported
curves to the rear to permit measurement during full movement of the leg
in all three planes, has previously been pointed out. Also, the
corresponding need for reversing the orientation of the goniometer
relative to the thigh mounting cuff has been mentioned, both with regard
to the three tube embodiment and also relative to the single tube
embodiment of the invention. In addition, in connection with the circuit
diagrams, the linked reversing switches for the varus/valgus signal and
for the internal/external rotation signal have been mentioned. The result
of these arrangements involves the accommodation of full and vigorous
maneuvers while the plots are being taken through the special asymmetric
yoke configuration, the use of the identical unit for both the right and
left legs through the mechanical reversing configuration, and finally, the
normalization of the plots for both the right and the left leg by the use
of the electrical reversing switches for the varus/valgus and for the
internal/external rotation signals. The overall result achieved is a very
high sensitivity lightweight unit of universal applicability.
Incidentally, it has been mentioned above that the goniometer assembly is
made of lightweight plastic and is of relatively small configuration. In
the description, the slightly larger three-tube unit of FIGS. 1 through 5
has been described, and in addition, the one tube unit of FIGS. 6 and 6A
has also been discussed. With regard to their specific configuration and
constructional features, these two units are both made of high strength,
lightweight plastic, such as Delrin. The rotational axes of the two yokes
which are included in each of the goniometer units cross at a single
point, and this point is located as close as possible in alignment with
the flexion/extension axis of rotation of the knee. To give an indication
of the dimensions of the units, the overall height of the three-tube unit
from the upper surface of the upper support member 82 (see FIG. 3) to the
lower surface of the potentiometer housing 46 is approximately 31/4
inches, with the corresponding dimension for the one tube unit of FIGS. 6
and 6a being approximately 2.9 inches. In this regard, the distance from
the axis of rotation of the upper yoke to its upper surface for the three
tube unit is approximately 2 inches, while the corresponding dimension for
the one tube unit is approximately 1.5 inches. Similarly, the distance
from the centerline of rotation of the lower yoke to its lower surface is
approximately 17/8 inches for the three-tube unit and approximately 1.4
inches for the one tube unit. Concerning the spacing of the arms 78-80
making up the yoke for the three tube unit, the outer dimension is
approximately 11/4 inches total width, and the space within the yoke is
approximately 1 inch, with the yoke arms 78 and 80 being about 1/8 inch
thick; and the outer and inner corresponding dimensions for the one tube
unit of FIG. 6 are approximately 1.115 inches and 0.835 inch,
respectively.
Concerning the dimensions of the plastic housing containing potentiometers
42 and 44, it has dimensions of approximately 1 inch by 15/8 inches long
by 5/8 inch thick for the three tube unit; and the corresponding
dimensions for the one tube unit were approximately 0.835 inch, by 1 inch
long by 0.6 inch thick. It is interesting to note that the actual size of
the goniometer unit including the three potentiometers is only about 2
3/16 inches in height in the case of the three tube unit, and only
approximately 1.8 inches in height for the single tube unit. In addition,
the thickness in the direction extending outwardly from the knee is only
about 11/4 inches across the yoke for the three tube unit and
approximately 1.115 inches for the one tube unit. From the foregoing
dimensions, the very small size of the actual goniometer unit carrying the
three potentiometers is evident, as is the reduced thickness of the unit
as aligned with the knee, so that the center of rotation may be located
very close to the knee.
Incidentally, the potentiometers employed in the three tube unit were New
England Instrument Company Part No. 55 FL1-120, each having a total
resistance value of 10,000 ohms. The potentiometers used in the single
tube unit were plastic film type potentiometers, which were made by the
inventors for this particular application.
In conclusion, it is to be understood that the present invention is not
limited to that precisely as described hereinabove. For example, the three
axis goniometer could have minor mechanical and electrical changes without
departing from the guiding principles indicated in connection with the
embodiments of FIGS. 1 through 5, and those of FIGS. 6 and 6A; the
electrical circuit and the methods described herein could be implemented
by somewhat different arrangements than those specifically shown and
described; and the principles disclosed herein are applicable to
goniometer assemblies for measuring joints other than the knee.
Accordingly, the present invention is not to be considered limited to that
precisely as described hereinabove.
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