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BACKGROUND OF THE INVENTION
1. One Field of the Invention
The present invention is in the field of knee ligament testing systems, and
it relates particularly to apparatus and methods for measuring anterior
and posterior drawer shift or displacement of the proximal tibia relative
to the distal femur as a result of applied forces so as to determine the
presence or absence of a torn anterior or posterior cruciate ligament,
respectively.
2. Description of the Prior Art
The clinical test which is the most similar to the method of the present
invention for determining a disrupted or torn anterior cruciate ligament
is known as the "Lachman" test. The Lachman test has been taught for many
years by John W. Lachman, Chairman and Professor of Orthopedic Surgery at
Temple University. The Lachman test is described in considerable detail by
Torg, J. S., Conrad, W., and Kalen, V. in an article entitled "Clinical
Diagnosis of Anterior Cruciate Ligament Instability in the Athlete", in
The American Journal of Sports Medicine, Vol. 4, No. 2, March/April, 1976
at pages 84-93. In performing the Lachman test, the patient lies supine on
a table with the knee held between full extension and 15.degree. of
flexion. The person performing the test holds the thigh in one hand and
the calf in the other, applying a firm anterior pressure to the calf in an
attempt to translate the proximal tibia anteriorly relative to the distal
femur. A positive test which indicates a torn or disrupted anterior
cruciate ligament is one in which there is proprioceptive and/or visual
anterior translation of the tibia in relation to the femur with a
characteristic "mushy" or "soft" end point. This is in contrast to a
definite "hard" end point elicited when the anterior cruciate ligament is
intact.
The principal failing of the Lachman test is that it is entirely subjective
and provides no measurement of knee displacement. Thus, the Lachman test
provides no objective basis for comparison either with the sound knee of
the patient or with statistical information relating the amount of
displacement to the condition of the anterior cruciate ligament. The
entirely subjective nature of the Lachman test also precludes its use in
the development of any statistical information comparing anterior drawer
shifts between uninjured and injured knees.
Another problem with the Lachman test is that the required grasping of the
thigh and calf in the hands of the tester tends to cause patient guarding
or resistance by muscular contraction, which will mask the true condition
of the anterior cruciate ligament. The Lachman test is useless in the case
of an acute knee injury (within seven days of the occurrence of the
injury) when the knee joint is usually still swollen and painful, which
greatly increases patient guarding. Further problems with the Lachman test
are that a person with small hands has difficulty performing this test;
and even with large hands the thigh and calf of an obese person cannot be
adequately grasped to perform the test.
The first system capable of measuring or documenting the anterior or
posterior displacement of the proximal tibia relative to the distal femur
was that of J. C. Kennedy and P. J. Fowler, who described their system in
an article entitled "Medial and Anterior Instability of the Knee. An
Anatomical and Clinical Study Using Stress Machines," Journal of Bone and
Joint Surgery, Vol. 53-A, 1971, at pages 1257-1270. According to the
Kennedy ahd Fowler system, the patient was strapped upright into an
immovable seat resembling a hydraulic barber's chair and the foot strapped
down with the knee bent to 90.degree. of flexion. An anterior pulling
force or a posterior pushing force was applied to the proximal tibia by
gas-pressurized actuator cylinders. X-Rays were taken of the tibia and
femur relative positions before and after the force was applied, and the
displacements were recorded by directly measuring the motions seen on the
X-Ray films. This system had the disadvantage that it had no direct
mechanical means for indicating or measuring the tibial displacements
relative to the femur as they occurred, as well as the inherent
disadvantages of X-Rays. Another, major disadvantage of this system was
that it attempted to immobilize the femur in what can be considered to be
an earth-based or chair-based system. The problem with such reliance upon
the supposed immobilization of the femur is that the femur is encased in a
large amount of muscle tissue which, when relaxed as required for such
testing, provides no firm locational support for the femur. On the other
hand, if the muscles are tight enough for a somewhat rigid supporting of
the femur, then the muscle tightness opposes the tibia/femur displacement
which is the objective of the test.
A still further failing of the Kennedy and Fowler system was that their
equipment was only capable of measuring knee displacements at 90.degree.
of flexion. Applicant has found that while 90.degree. of flexion is
sometimes satisfactory for posterior drawer testing, it is quite
unsatisfactory for anterior drawer testing because of the large amount of
posterior leverage which the powerful hamstring muscles have in opposition
to the anterior drawer test, whereby only a slight amount of hamstring
guarding will mask the anterior drawer test at large angles of knee
flexion such as 90.degree.. This problem is not present in the Lachman
anterior drawer test, wherein the knee is between full extension and
15.degree. of flexion.
In any earth-based or chair-based system such as that of Kennedy and
Fowler, the imposing nature of the large and complex equipment, the
discomfort of the apparatus employed to strap the patient down, and then
the large amount of time, usually at least about 11/2 hours, required to
strap the patient down, adjust the equipment and take the tests,
inevitably caused patient guarding that interfered with the accuracy of
the tests.
Markolf, K. L., Graff-Radford, A., and Amstutz, H. C., reported the fitst
equipment that was capable of indicating or recording anterior/posterior
tibial force versus displacement. This was reported in an article entitled
"In Vivo Knee Stability", in the Journal of Bone and Joint Surgery, Vol.
60-A, No. 5, July, 1978, at pages 664-674. In this system a handle
attached to a force transducer is strapped around the patient's calf. The
examiner manually pulls or pushes through the handle which senses the
force that is being applied as a displacement transducer records the
displacement of the proximal tibia relative to the patella on the femur.
The Markolf et al system is again an earth- or chair-based system which has
the same failings as those pointed out hereinabove for the Kennedy and
Fowler system. In the Markolf et al system the reference point for all
tibial displacement measurements is the chair, so that considerable
equipment is directed toward an attempt to immobilize the patient's femur.
Thus, there is a system of inflatable thigh compression pads, a contoured
patellar compression block, and compression of the patient's sacrum by the
rigid back of the chair. Additionally, the patient's foot is strapped
down. As with the Kennedy and Fowler apparatus, the Markolf et al
apparatus, due to its large, complex and imposing nature, the discomfort
of the strapped-down patient, and the approximately 11/2 hours required to
set up and perform the testing, caused considerable patient guarding that
seriously interfered with the testing.
Applicant is aware of only one other type of apparatus which seeks to
determine the presence or absence of a knee ligament deficit condition.
This was reported by Crowninshield, R.; Pope, M. H., Johnson, R,; and
Miller, R. in an article entitled "The Impedance of the Human Knee" in the
Journal of Biomechanics, Vol. 9, 1976 at pages 529-535. This was
laboratory apparatus which applied a cyclic rotational motion about the
longitudinal axis of the tibia. By varying the frequency of the mechanical
oscillation of the tibia while at the same time attempting to keep the
femur relatively stable, the mechanical impedance characteristics of the
knee were measured. These included the resonant frequency of oscillation
of the knee, the change in the phase lag between the force input cycle and
the displacement output cycle with varying frequency, and the like. Since
the Crowninshield et al apparatus imposed only rotational or varus-valgus
(medial and lateral bending) motions on the knee, this equipment was not
capable of indicating or measuring anterior or posterior tibia/femur
drawer shift to determine whether or not the anterior and posterior
cruciate ligaments were torn.
A general failing in the art was the inability of any of the prior art
systems to test the condition of anterior or posterior cruciate ligaments
in the case of an acute knee injury, i.e., within seven days of the
occurrence. This was primarily because of guarding that resulted either
from hand manipulation that was required for the testing or from reaction
to the discomfort of equipment used to strap down the patient's leg.
SUMMARY OF THE INVENTION
In view of these and other problems in the art, it is a general object of
the present invention to provide a system for testing the condition of the
anterior and posterior cruciate knee ligaments that provides an objective
measurement of drawer shift or displacement between the proximal tibia and
the distal femur quickly and easily, and with a minimum of discomfort to
the patient.
Another object of the invention is to provide a system for testing the
integrity of the anterior and posterior cruciate ligaments which, while
providing an objective measurement of the tibia/femur displacement not
possible with the Lachman test, nevertheless does not require that the
patient be strapped down in a complicated chair arrangement attempting to
immobilize the femur as in both the Kennedy et al and Markolf et al
systems.
A principal object of the present invention is to provide, for the first
time in this art, a tibia-referenced system for measuring anterior and
posterior knee drawer shifts, as distinguished from the earth- or
chair-based systems of Kennedy et al and Markolf et al; the
tibia-reference system of the invention avoiding any necessity for
strapping down the thigh in an attempt to immobilize the femur, and
thereby enabling the thigh to rest in comfort during the testing and
avoiding much of the prior art problem of patient guarding by contraction
of quadriceps and/or hamstring muscles of the thigh.
A further object of the invention is to provide a knee ligament testing
system which, by being a tibia-referenced system and thereby avoiding
discomfort of the thigh and consequent patient guarding, for the first
time enables testing for deficit conditions of the anterior and posterior
cruciate ligaments in the case of an acute knee injury, i.e., within seven
days of the occurrence of the injury, which can be a time of critical
importance in the correction of a knee ligament deficit condition.
A further object of the invention is to provide a system for testing the
integrity of the anterior and posterior cruciate ligaments of the knee
which references the proximal end of the tibia and the distal end of the
femur through respective accessible, generally unyielding anterior bone
structures proximate the knee, namely, the tibial tubricle and the
patella; this referencing through the tibial tubricle and the patella
providing a much more reliable and accurate representation of the knee
joint displacement than prior art earth- or chair-based systems, and
avoiding the necessity for manually squeezing the area around the knee or
putting the thumb on the joint line as were done in the Lachman test and
which may be painful in an acutely injured patient.
A still further object of the invention is to provide a tibia-referenced
knee ligament testing system with its accompanying increased accuracy and
minimized patient guarding, wherein both the displacement measurement and
the anterior and posterior forces applied during the testing are
objective, whereby comparative test results between a patient's injured
and uninjured knees or between an injured knee and statistical data
representing either injured of uninjured knees, enables a reliable
determination to be made as to whether or not there is a torn anterior or
posterior cruciate ligament in the injured knee.
Four forms of the invention are disclosed herein, the first two being
simplified forms, the third being a form of intermediate complexity but
with a more directly readable tibia/femur displacement indicator, and the
fourth being the most complex form disclosed and having both a direct
displacement indicator and a force transducer that audibly indicates
predetermined anterior- and posterior-directed force levels. Each of these
four forms of the invention disclosed herein references two anterior bone
structures closely adjacent to the knee joint, namely, the tibial tubricle
forming a part of the tibia bone and the patella which overlies the femur
bone, making use of the fact that the skin is very close to the anterior
surfaces of both of these bone structures with minimal intervening flesh,
so that the relative anterior/posterior locations of these bone structures
accurately represents the relative anterior-posterior locations of the
proximal tibia and distal femur.
In each of the four forms of the invention an elongated reference arm has a
distal end that is oriented or fulcrumed against a distal region on the
tibia, and has a proximal end that either rests on the tibial tubricle or
on the patella; while a second reference structure that is movable
relative to this reference arm rests against the other of these two
anterior bone structures proximate the knee. Displacement indicator means
operatively associated with these two reference structures indicates the
relative positons of the proximal tibia and distal femur in the
anterior-posterior direction.
In the first simplified form of the invention the reference arm has a
distal reference pad which rests against a distal region on the tibia and
a proximal reference pad which rests against the tibial tubricle, the arm
extending proximally from the latter so as to overlie the patella. The
second reference structure in this form of the invention is a displacement
indicator rod slidably mounted near the proximal end of the reference arm,
with a patella reference pad on the posterior end of the rod and a
displacement indicator scale along the length of the rod and readable
against the reference arm. The second simplified form of the invention is
similar to the first simplified form, except that the proximal reference
pad on the elongated reference arm is a patellar reference pad, and the
displacement indicator rod has the tibial tubricle reference pad on its
posterior end. With each of these two simplified forms of the invention
for a passive anterior drawer test an anterior force is manually applied
to the back of the calf under the tibial tubricle, while a posterior force
is applied to the patellar reference pad to hold the patella securely
against the femur and to prevent the femur from rising. A passive
posterior drawer test is accomplished by manually applying a posterior
force against the tibial tubrical reference pad. Thus, while the
displacement indicator provides an objective reading of the displacement,
nevertheless the force that is applied in testing with these two
simplified forms of the invention is up to the feel and experience of the
tester, and to that extent is subjective.
In the third form of the invention, which is of intermediate complexity,
the second reference structure, instead of being a displacement indicator
rod, is a second elongated reference arm that is pivotally connected to
the other reference arm; i.e., in this form of the invention the two
reference structures are a pair of distally pivotally connected reference
arms. The shorter of these two arms is a tibial tubricle reference arm and
is formed as a main case of the apparatus; while the longer of the two
arms is a patellar reference arm. In this form of the invention the
relative angular pivotal positions of the two reference arms is transduced
to a displacement indicator dial that has a zeroing adjustment capability
so that it can provide a direct readout of anterior or posterior drawer
shift without requiring a difference calculation as is required in the two
simplified forms of the invention. This third form of the invention still
requires a hand-applied anterior force to the calf for a passive anterior
drawer test, and a hand-applied posterior force to the tibial tubricle
reference arm for a passive posterior drawer test, and is therefore
subjective insofar as the amount of the applied force is concerned.
The fourth and most complex form of the invention disclosed herein, like
the third form, has a pair of distally pivotally connected reference arms
which respectively carry the tibial tubricle reference pad and the
patellar reference pad. However, the two reference arms are pivotally
connected at their common pivot axis to a case that is adapted to be
strapped against the anterior surface of the tibia. A force-applying
handle projects above or anterior to the case, and a force-indicating
transducer is operatively arranged between the handle and the case to
audibly indicate when specific predetermined force levels are applied
either anteriorly to the calf under the tibia or posteriorly to the tibia,
for making respective anterior and posterior drawer tests. As in the third
form of intermediate complexity, the relative angular pivotal positions
between the tibial and patellar reference arms is directly readable on a
displacement indicator dial, so that with the addition of the force
indicating transducer the fourth form of the invention is objective in all
respects, including both displacement indicating and force indicating.
A novel posterior thigh support platform forming a part of the present
invention is utilized with all four forms of the invention in making
anterior drawer tests. This posterior thigh support platform automatically
establishes the knee flexion angle within the preferred range of from
approximately 20.degree. to approximately 30.degree., and allows the
patient to relax both legs on a stable support surface, avoiding the
necessity for the examiner to pick up and manually support the patient's
knee, and thereby avoiding the difficulties that were encountered with the
Lachman test with obese patients or large athletes, or if the examiner had
small hands.
A novel foot positioning platform having both a horizontal footrest and
upright lateral foot supports also forms a part of the present invention.
This foot positioning platform supports both feet against external
rotation, thereby keeping the starting rotational angle of the tibia the
same in both knees for a more precise and reliable comparison of both
knees with any of the four forms of the invention disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the invention will become more
apparent from the following description taken in conjunction with the
drawings, wherein:
FIG. 1 is a perspective view illustrating the first simplified form of the
invention;
FIG. 2 is a side elevational view of the form of the invention shown in
FIG. 1, operatively positioned upon a leg that is shown in sagittal
section, with the posterior region of the thigh resting upon the raised
posterior thigh support platform of the invention, and with the foot
located on the foot support platform of the invention;
FIG. 3 is a view similar to FIG. 2, but with the second simplified form of
the invention operatively positioned on the leg;
FIG. 4 is a perspective view illustrating the third form of the invention
which is of intermediate complexity,
FIG. 5 is a horizontal section taken on the line 5--5 in FIG. 4;
FIG. 6 is a vertical section taken on the line 6--6 in FIG. 5 and
illustrating the third form of the invention applied to a leg that is
shown in saggital section;
FIG. 7 is a perspective view illustrating the fourth and most complex form
of the invention disclosed herein;
FIG. 8 is a an enlarged, fragmentary top plan view of the form of the
invention shown in FIG. 7, with the top section of the case removed from
the bottom section of the case and turned over so that its underside faces
upwardly;
FIG. 9 is a vertical section taken on the line 9--9 in FIG. 8;
FIG. 10 is a fragmentary vertical section taken on the line 10--10 in FIG.
8;
FIG. 11 is a fragmentary vertical section taken on the line 11--11 in FIG.
8;
FIG. 12 is fragmentary horizontal section taken on the line 12--12 in FIG.
11;
FIG. 13 is a diagrammatic view illustrating the electrical circuitry of the
force transducer of the fourth form of the invention;
FIG. 14 is a side elevational view similar to FIGS. 2 and 3 but with the
fourth form of the invention operatively positioned on the leg;
FIG. 15 is an enlarged, fragmentary side elevational view of the encircled
region in FIG. 14 showing the joint line reference arrow;
FIG. 16 is a fragmentary saggital section of the knee joint at 90.degree.
of flexion showing the location of the posterior cruciate ligament;
FIG. 17 is a view similar to FIG. 16, but with the knee at a flexion angle
of 25.degree., illustrating the location of the anterior cruciate
ligament;
FIG. 18 is a graph illustrating the passive anterior drawer test and
compliance or end point test differences between an average normal knee
and an average knee with a torn anterior cruciate ligament;
FIG. 19 is a fragmentary saggital section with the knee at approximately
25.degree. of flexion in preparation for an active anterior drawer test,
but prior to contraction of the quadriceps muscles;
FIG. 20 is a view similar to FIG. 19, but with the quadriceps muscles
contracted;
FIG. 21 is a fragmentary saggital section with the knee joint at a neutral
flexion angle of from about 70.degree. to about 90.degree. for an active
posterior drawer test, FIG. 21 showing the tibia/femur relative
positioning either for a normal knee or with the quadriceps contracted;
FIG. 22 is a view similar to FIG. 21, but for a knee with a torn posterior
cruciate ligament and with the quadriceps relaxed;
FIG. 23 graphically illustrates statistical information for the passive
anterior drawer difference between normal knees and known anterior
cruciate deficit knees;
FIG. 24 is a view similar to FIG. 23, but illustrating the active anterior
drawer difference between normal knees and knees having a known anterior
cruciate ligament deficit; and
FIG. 25 is a view similar to FIGS. 23 and 24 but illustrating the anterior
end point laxity between 15 and 20 pounds of anterior force for normal
knees and for knees having a known anterior cruciate ligament deficit.
DETAILED DESCRIPTION
FIGS. 1 and 2 illustrate one simplified tibia-referenced knee testing
device according to the invention, and FIG. 3 shows another. Each of these
two simplified forms of the invention embodies a single reference arm, and
both of these forms are adapted for direct hand application of the
anterior or forward testing force to the calf behind the tibial tubricle.
The first simplified form of the invention shown in FIGS. 1 and 2 is
generally designated 10, and its principal structural element is an
elongated, generally flat and preferably straight reference arm 12. The
reference arm 12 has distal tibial end 14 and femoral end 15. For clarity
and convenience in the following description, the reference arm 12 will
also be designated as having an upper or anterior surface 16 and a lower
or posterior surface 17.
Projecting downwardly from the reference arm 12 proximate its distal tibial
end 14 is a distal tibial reference pad 18, the lower surface of which
constitutes the distal tibial reference surface 20 of the device 10.
Referencing of the device 10 to the tibia is completed by means of a
proximal tibial reference pad 22 that projects downwardly from reference
arm 12 at a location spaced proximally from the distal tibial reference
pad 18 and located closer to the femoral end 15 than the distal tibial end
14 of reference arm 12. The bottom surface of proximal tibial reference
pad 22 constitutes the proximal tibial reference surface 24 of the device
10. The two tibial reference pads 18 and 22 preferably project downwardly
at right angles from the main body of the reference arm 12.
Relative positioning and displacement between the tibia and the femur in
the anterior-posterior direction is indicated on a displacement indicator
rod 26 that is slideably mounted in a bore 28 extending in the
anterior-posterior direction through reference arm 12 preferably at right
angles to the arm 12. Mounted on the lower end of indicator rod 26 is a
patellar reference pad 30, the bottom surface 32 of which constitutes the
patellar reference surface of the knee testing device 10. Actually, the
reference pad 30 and its bottom reference surface 32 are for the purpose
of referencing the anterior-posterior location of the distal end of the
femur; however, the reference pad 30 and its reference surface 32 perform
such femoral referencing through the patella which is the only stable,
generally unyielding structure proximate the knee that is accessible for
referencing the location of the distal end of the femur. Displacement
indicator rod 26 and proximal tibial reference pad 22 are spaced apart
longitudinally along the reference arm 12 a distance approximating the
average spacing between patella 52 and tibial tubricle 50.
The displacement indicator rod 26 has an indicator scale 34 longitudinally
arranged thereon which is adapted to be read at the upper surface 16 of
reference arm 12. A knob 36 is mounted on the upper end of displacement
indicator rod 26 for receiving a posteriorly directed stabilization
counterforce during a passive anterior drawer test.
FIG. 2 shows the knee testing device 10 operatively positioned on a leg for
performing the passive anterior drawer test. The leg is diagramatically
illustrated, with the knee joint 38 shown generally in sagittal section.
The leg is supported for this passive anterior drawer test with the knee
joint 38 bent or flexed to a preferred flexion angle in the range of from
about 20.degree. to about 30.degree. of flexion, and preferably at
approximately 25.degree. of flexion, to minimize interference by ligaments
and other knee components not involved in the test, and by hamstring
guarding, as described more in detail hereinafter. This knee joint flexion
angle represents angular displacement between the general longitudinal
axes of the tibia 40 and femur 42 from the fully extended condition of the
leg, the tibia 40 being the anterior and larger of the two long bones of
the calf 44, and the femur 42 being the single long bone extending through
the thigh 46.
The knee testing device 10 is placed against the anterior surface of the
leg with the reference arm 12 arranged generally parallel to the tibia 40,
the distal tibial reference surface 20 engaged at a distal region 48 of
the tibia, the proximal tibial reference surface 24 engaged at the tibial
tubricle 50, and the patellar reference surface 32 engaged at the patella
52. The patella 52 serves as a bearing for force applied by the quadraceps
muscles 54 against the distal end of the femur 42, the quadraceps 54 all
coming in and attaching to the patella 52 and thence through the patella
52 and the patellar tendon 56 (which is really a ligament) to the tibial
tubricle 50. An anatomical factor in knee functioning which enables the
present invention in all of its forms to be basically tibia referenced
while also referencing to the patella is the fact that the patella slides
distally and posteriorly on the curved lower end of the femur so that the
patella is fully exposed on the femur in the general anterior direction of
the tibia at any knee flexion angle up to and even beyond 90.degree. of
flexion. Thus, the patella 52 is exposed as a reference point for anterior
drawer tests with flexion angles ranging from about 20.degree. to about
30.degree. and also for posterior drawer tests with flexion angles ranging
from about 70.degree. to about 90.degree..
To perform the passive anterior drawer test as illustrated in FIG. 2, the
patient is preferably fully supported from head to foot on a firm
horizontal surface 57. The knee joint 38 is stabilized for the test by
placement of a raised posterior thigh support platform 58 under the thighs
proximal to the patient's patella 52. Further stabilization of the knee
joint 38 is accomplished by means of a foot support platform 60 which has
a horizontal foot rest 62 preferably covered with foam rubber or neoprene
and a pair of upright lateral foot supports 64 at opposite sides of the
platform 60. The raised posterior thigh support platform 58 automatically
establishes the desired knee flexion angle within the preferred range of
about 20.degree. to 30.degree., and keeps this knee flexion angle constant
throughout the test for accuracy of measurement. The foot support platform
60 supports the foot against external rotation which might otherwise
interfere with the reliability and repeatability of the tests. Since most
tests utilizing the present invention involve a comparison of the
tibia-femur displacement of the injured knee with that of the uninjured
knee, both of the thighs are supported on the raised thigh support
platform 58 and both of the feet are supported by the foot support
platform 60.
The tibia 40 provides an almost ideal base or referencing structure for the
tibia-referenced system of the invention because the skin 66 is very close
to the anterior surface of tibia 40, both in the distal region 48 thereof
and at the tibial tubricle 50, with minimal intervening flesh.
To perform a passive anterior drawer test, the knee testing device 10 is
operatively positioned as shown in FIG. 2 and the reading on displacement
indicator scale 34 is noted and preferably recorded. An anterior-directed
testing force is then applied, preferably with the right (or dominant)
hand, to the back of the calf 44 behind tibial tubricle 50 as indicated by
the arrow 70. As discussed in detail hereinafter, this anterior-directed
force 70 is preferably about 20 pounds of force; however, since the
simplified form 10 of the invention does not embody any force indicating
means, the amount of this force will be up to the feel and experience of
the tester, and therefore will be somewhat subjective. During this
application of the anterior force 70, a posterior-directed stabilization
counterforce is applied to the top of the force knob 36 as indicated by
the arrow 72 to keep the entire knee and thigh firmly against the
posterior thigh support platform 58, thereby blocking the tendency of the
leg to lift off of the thigh support platform 58 during the test, which
would cause the knee joint to flex and introduce an error in the
measurement. The displacement indicator scale 34 is again read and
preferably recorded while the force 70 and counterforce 72 are applied,
and the difference between these two indicator scale readings will
constitute a measurement of the anterior drawer shift or displacement of
the tibial tubricle 50 relative to the patella 52, and hence relative to
the distal end of femur 42. Preferably, the readout on displacement
indicator scale 34 is directly in millimeters of anterior drawer shift or
displacement at the knee joint line. Because the length from the fulcrum
of distal tibial reference pad 18 to displacement indicator rod 26 is
approximately 10 percent greater than the length from pad 18 to the knee
joint line, the actual scale of displacement indicator scale 34 is
expanded by approximately 10 percent from a true metric scale to give this
direct readout in millimeters of drawer shift.
Accuracy of this anterior drawer test made with the knee testing device 10
may be slightly improved by applying the posterior stabilization force 72
and taking the first reading on the displacement indicator scale 34 prior
to application of the anterior force 70. This causes the patellar
reference pad 30 to seat firmly upon the skin 66 overlying the patella 52
and assures that the patella 52 is firmly seated in the femoral notch;
otherwise, such seatings might occur between the two displacement
indicator scale readings and introduce an error in the reading.
The passive anterior drawer test is for the purpose of testing the laxity
of the anterior cruciate ligament. Referring to FIG. 17 of the drawings,
the anterior cruciate ligament is generally designated 74, and its
position in the knee joint 38 is illustrated for a knee flexion angle of
25.degree., which is the preferred testing angle for the anterior drawer
test. It will be seen that the anterior cruciate ligament 74 comes from
the posterior notch of the femur 42 and runs to the anterior plateau of
the tibia 40. The anterior cruciate ligament 74 resists the tendency of
the tibia 40 to slide forwardly relative to the femur 42. Cartilage
surfaces at the ends of the tibia 40 and femur 42 are generally designated
76.
FIG. 16 shows the posterior cruciate ligament, generally designated 78,
with the knee joint 38 at 90.degree. of flexion, which is the preferred
knee flexion for performing a posterior drawer test. Such test will be
described later. It will be seen that the posterior cruciate ligament 78
comes out of the distal end of the femur 42 and runs posterior to the
tibia 40. The posterior cruciate ligament 78 mechanically functions as one
of the stabilizers resisting posterior displacement of the tibia 40
relative to the femur 42.
The other cruciate ligament is not shown in each of the illustrations in
FIGS. 16 and 7 for clarity of illustration.
Referring now to FIG. 3 of the drawings, the second simplified form of the
invention is generally designated 10a, and it has as its principal
structural element an elongated and preferably generally flat reference
arm 12a having distal tibial end 14a, femoral end 15a, upper or anterior
surface 16a, and lower or posterior surface 17a. The distal tibial
reference pad 18a is the same as the reference pad 18 of the first form 10
shown in FIGS. 1 and 2, extending downwardly or posteriorly from the
distal tibial end 14a of reference arm 12a preferably at right angles to
arm 12a. The bottom surface of distal tibial reference pad 18a constitutes
the distal tibial reference surface 20a of the device 10a.
Integral with the reference arm 12a and projecting downwardly from its
femoral end 15a preferably at right angles to arm 12a is the patellar
reference pad 30a, the bottom surface of which constitutes the patellar
reference surface 32a of the device 10a. Thus, the reference arm 12a
directly references the anterior-posterior locations of the distal region
48 of tibia 40 and the patella 52; whereas the reference arm 12 of the
device 10 of FIGS. 1 and 2 directly references the distal region 48 of
tibia 40 and the tibial tubricle 50.
In the knee testing device 10a of FIG. 3, the proximal tibial reference pad
22a, the lower surface of which is the proximal tibial reference surface
24a, is mounted or formed integrally on the lower end of the displacement
indicator rod 26a which is slideably mounted in a suitable bore (not
shown) through arm 12a for sliding movement in the anterior-posterior
direction. Preferably, the rod 26a has its longitudinal axis directed at
right angles to the arm 12a. The displacement indicator rod 26a is spaced
longitudinally along the reference arm 12a from patellar reference pad 30a
a distance approximating the average spacing between tibial tubricle 50
and patella 52.
The knee testing device 10a is operatively positioned as illustrated in
FIG. 3, with the distal tibial reference surface 20a against the skin at
the distal region 48 of the tibia, the patellar reference surface 32a
against the skin at the patella 52, and the proximal tibial reference
surface 24a against the skin at the tibial tubricle 50. With the device
10a thus located, the displacement indicator scale 34a on rod 26a is read
and preferably recorded. Then, the anterior-directed displacement force
indicated by the arrow 70a is applied to the back of calf 44, preferably
with the right (or dominant) hand of the tester, while the
posterior-directed stabilization counterforce indicated by the arrow 72a
is applied to reference arm 12a proximate the patellar reference pad 30a
with the left (or non-dominant) hand of the tester. While these forces 70a
and 72a are being applied, the displacement indicator scale 34a is again
read relative to the upper surface 16a of arm 12a, and this reading
preferably recorded, and the difference between the two readings on
indicator scale 34a will directly provide the amount of anterior drawer
shift or displacement of tibia 40 relative to patella 52 and hence the
distal end of femur 42, in millimeters of displacement. Because the length
from the fulcrum of distal tibial reference pad 18a to displacement
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