A knee brace for externally replacing the function of a torn anterior cruciate ligament. The brace has femur and tibia levers hinged proximal the knee joint. The femur lever has an upper high cuff which bears against the front of the thigh and a lower strap which applies anterior force to the back of the thigh proximal the knee, while the tibia lever has a lower calf cuff which bears against the back of the calf and an upper strap which applies posterior force to the front of the tibia proximal the knee. Thus, the two straps apply a differential force couple forwardly to the femur and rearwardly to the tibia proximal the knee joint which serves the anterior cruciate ligament function. A resilient tubular undersleeve anchors the brace against downward migration on the leg.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to orthopedic devices for injured knees, and 
it relates more particularly to a knee brace adapted to serve as an 
external replacement or substitute for a torn anterior cruciate ligament. 
2. Description of the Prior Art 
The human knee is a very complex mechanism that is highly vulnerable to 
injury in various sports, particularly such contact sports as football, 
soccer and basketball. The primary front/rear locating means within the 
knee joint is a pair of crossed ligaments called the cruciate ligaments 
which connect between the femur and the tibia. These are the anterior and 
posterior cruciate ligaments. The anterior cruciate ligament controls 
forward drawer shifting or translocation of the tibia relative to the 
femur, while the posterior cruciate ligament controls rearward drawer 
shifting or translocation of the tibia relative to the femur. By far the 
most commonly injured of the cruciate ligaments is the anterior cruciate 
ligament, torn anterior cruciate ligaments being a major crippler of 
athletes involved in contact sports. Heretofore, an athlete having a torn 
anterior cruciate ligament was generally not able to continue athletic 
performance without corrective surgery, and even then 100 percent 
rehabilitation was not likely. 
Applicants are not aware of anyone having heretofore specifically addressed 
the possibility of an external substitute or replacement for a torn 
anterior cruciate ligament in the form of an orthopedic device, and none 
of the many knee orthotics of which applicants are aware was or is capable 
of compensating for an anterior cruciate ligament tear sufficiently for 
athletic performance. 
Applicants have determined that in order for a knee brace to be effective 
as a substitute or replacement for a torn anterior cruciate ligament, it 
must include a leverage system capable of applying a strong differential 
force anteriorly to the femur and posteriorly to the tibia proximal the 
knee joint, yet none of the prior art knee braces of which applicants are 
aware are directed to the application of such differential force, or are 
in any way capable of applying the leverage necessary to achieve such 
differential force. 
One of the factors applicants have found to be desirable in achieving the 
necessary leverage for a satisfactory external substitute for a torn 
anterior cruciate ligament is the use in the substitute brace of hinges on 
both the lateral and medial sides of the knee that are both bicentric and 
geared. Examples of such bicentric, geared hinges in knee orthotics are 
found in U.S. Pat. No. 4,381,768 to Erichsen, and U.S. Pat. No. 4,372,298 
to Lerman. Other examples are seen in two prior U.S. patent applications 
in which applicants are joint inventors, Ser. No. 474,004, filed Mar. 10, 
1983 for Articulating Graphite Knee Stabilizer, and Ser. No. 657,356, 
filed Oct. 3, 1984 for Athletic Knee Protector. Applicants said 
Application Ser. No. 474,004 disclosed pinion stops associated with the 
hinge gears for limiting the extent of flexion and extension. Another form 
of polycentric hinge that was not geared but had a similar action was 
disclosed in Cummins U.S. Pat. No. 4,245,629. Despite the presence of such 
bicentric hinges with geared or gear-like connections in these prior knee 
orthotics, none of them had a structural arrangement capable of applying 
leverage which would produce a force couple on the femur and tibia 
proximal the knee joint such as would simulate the force of a healthy 
anterior cruciate ligament. 
Applicants are aware of another group of prior art knee orthotics having 
polycentric hinges that did not have geared or gear-like connections, and 
that also were incapable of applying leverage which could produce the 
necessary differential force to serve the function of an anterior cruciate 
ligament. These devices are disclosed in U.S. Pat. Nos. 2,467,907 to 
Peckham, 3,901,223 to May, Reissue 30,501 to Almeida, 4,249,524 to 
Anderson, and 4,271,831 to Deibert. 
Applicants are also aware of a number of knee brace-type devices which 
utilize only single-pivot hinges, and like the other devices referred to 
above, none of these are capable of applying leverage that would produce a 
force couple corresponding in effect to the anterior cruciate ligament. 
Such devices are shown in U.S. Pat. Nos. 2,144,641 Snyder, 3,817,244 
Taylor, 4,088,130 Applegate, 4,320,747 Daniell, Jr., and 4,353,361 Foster. 
The basic purpose of all of this large number of prior art knee brace-type 
devices is simply to increase the stability of an injured knee, and for 
the most part such devices have simply constituted supplemental hinge 
structures strapped to the thigh and calf, intended to give added 
mechanical pivot strength to the knee. 
Most of these prior art devices involve straps that completely and tightly 
encircle the leg above and below the knee in such a way that any force 
that may incidentally be applied in a direction to aid the anterior 
cruciate ligament would be generally cancelled by an opposite force. Such 
leg-encircling straps, to have any substantial effect in increasing the 
general stability of the knee, must generally be tightened to the point 
where they are likely to interfere with blood circulation. 
In addition to their general function of stabilizing the knee, the 
leg-encircling straps characteristically used in prior art knee braces 
helped to resist the tendency of all such devices to migrate downwardly 
along the leg in use, both from the effects of gravity and because of the 
general tapering of the leg. Nevertheless, even with full leg-encircling 
straps, such prior art devices all had a general tendency to migrate 
downwardly along the leg, particularly if they were used during the rigors 
of athletic performance. 
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 knee brace which serves as an external 
replacement or substitute for a torn anterior cruciate ligament. 
Another object of the invention is to provide a knee brace which embodies a 
novel four-point leverage system that applies a force couple anteriorly to 
the femur and posteriorly to the tibia proximal the knee joint so as to 
accomplish the same function as an anterior cruciate ligament which may be 
disabled. 
Another object of the invention is to provide an anterior cruciate ligament 
knee brace wherein a posterior thigh strap applies anterior force to the 
femur proximal the knee joint without opposition from any strap or other 
structure engaged around the front of the thigh, and an anterior tibial 
strap applies posterior force proximal the knee joint without opposition 
from any strap or other structure engaged around the back of the calf. 
A further object of the invention is to provide an anterior cruciate 
ligament brace having a femur lever and a tibia lever which are joined at 
both the lateral and medial sides of the knee joint by bicentric, geared 
hinges that have hinging movements simulating those of the knee joint yet 
positively resist front/rear relaxation or tilting at the hinges for 
positive application by the levers of forces to the femur and tibia 
serving the function of a replacement anterior cruciate ligament. 
A further object of the invention is to provide a four-point anterior 
cruciate ligament brace of the character described having a femur lever 
and a tibia lever, wherein the fulcrum of the femur lever is an open, 
arcuate anterior thigh cuff and the fulcrum of the tibia lever is an open, 
posterior calf cuff, and anterior cruciate ligament-simulating leverage is 
applied to the knee joint by an open, arcuate adjustable posterior thigh 
strap urging the femur anteriorly and an open, arcuate, adjustable 
anterior tibial strap urging the tibia posteriorly. 
Yet a further object of the invention is to provide an anterior cruciate 
ligament brace of the character described wherein the posterior thigh 
strap and anterior tibial strap which apply the anterior cruciate 
ligament-type force to the knee joint are enabled to each have 
approximately 180.degree. of engagement with the respective limbs by 
having femoral and tibial side bars of the brace displaced forwardly and 
rearwardly, respectively, along the sides of the leg. 
Another object of the invention is to provide a resilient tubular 
undersleeve for a knee brace that is at least substantially coextensive in 
length with the brace and to which the brace is releaseably attachable, as 
by Velcro means, to prevent downward migration of the brace along the leg, 
such tubular undersleeve having particular utility in combination with the 
four-point anterior cruciate ligament brace of the invention wherein the 
four points of force are applied by open cuffs and straps that do not 
extend all of the way around the leg. 
The knee brace of the present invention consists essentially of a pair of 
levers, a femur lever and a tibia lever, hinged together proximal the 
knee. Each of the two levers consists of a pair of side bars hinged to the 
side bars of the other lever and joined together by a fulcrum cuff at the 
ends remote from the hinge, the femur lever having an anterior thigh cuff 
which bears against the front of the thigh, and the tibia lever having a 
posterior calf cuff which bears against the rear of the calf. The femur 
lever also includes an adjustable posterior thigh strap looped from one 
side bar to the other around the back of the thigh and tightened to apply 
anterior force to the femur proximal the knee joint. The tibia lever has a 
complementary adjustable anterior pretibial strap looped from one side bar 
to the other around the front of the shin and tightened to apply posterior 
force to the tibia proximal the knee joint. 
The hinge structure between the femur and tibia levers is preferably a 
bicentric, geared hinge on each side of the brace connecting the femoral 
and tibial side bars on the respective sides, the gears on each side being 
rigidly connected to the respective femoral and tibial side bars so as to 
prevent any possible relaxation between the hinged side bar ends at the 
hinge joint, and thereby prevent any possible relaxation of the posterior 
thigh strap and anterior tibial strap which are applying a differential 
force forwardly on the femur and rearwardly on the tibia to perform the 
same function as the anterior cruciate ligament in the knee. As the knee 
bends from an extended position toward a flexed position, the hinge gears 
attached to the tibial side bars climb or roll rearwardly along the hinged 
gears attached to the femoral side bars, thereby increasing the amount of 
traction of the anterior tibial strap on the tibia, and hence the 
effectiveness of the force functioning as an anterior cruciate ligament 
force. 
The hinged ends of the femoral side bars angle posteriorly, while the 
hinged ends of the tibial side bars angle anteriorly, providing a 
substantial anterior offset of the main lengths of the femoral side bars 
from the hinges and a substantial posterior offset of the main lengths of 
the tibial side bars from the hinges, thereby enabling each of the 
posterior thigh strap and anterior tibial strap to have at least 
approximately 180.degree. of strap loop arc to assure maximum mechanical 
advantage for each of the femur and tibia levers. 
A thin elastomeric undersleeve, preferably of foam Neoprene, is slipped 
over the leg prior to attachment of the brace to the leg, this undersleeve 
having a longitudinal extent somewhat greater than the brace itself to 
assure longitudinal registry of the brace over the undersleeve. The brace 
is interlocked with the undersleeve at three longitudinal locations, the 
anterior thigh cuff, the posterior calf cuff, and proximal the knee joint 
at a pair of condyle pads mounted on the hinge structures. A patellar 
relief aperture is provided in the undersleeve. The undersleeve prevents 
downward migration of the brace, and also improves patient comfort while 
wearing the brace. Longitudinal stability of the brace on the leg may be 
further improved by encircling the leg with elastic overwrap straps in the 
regions of the thigh and calf cuffs. The elastic overwrap straps also 
secure the open-cuffed ends of the brace to the thigh and calf so that 
hinge stops in the brace are enabled to function as positive blocks 
against hyperextension of the joint. 
As described in detail hereinafter in the Detailed Description, clinical 
tests by applicants have established that the present invention is 
completely effective in externally replacing or substituting for a torn 
anterior cruciate ligament, and that on the average the present invention 
is even capable of controlling tibial anterior drawer movement relative to 
the femur in the injured knee of a patient better than the real anterior 
cruciate ligament controls it in the good knee.

DETAILED DESCRIPTION 
Referring to the drawings, and at first particularly to FIGS. 1, 2, and 
7-10 thereof, a brace according to the invention which provides an 
external replacement or substitute for the anterior cruciate ligament is 
generally designated 10. The particular brace 10 illustrated in the 
drawings is adapted to serve the function of the anterior cruciate 
ligament of a right leg, and a brace according to the invention for the 
left leg will have its parts reversed or arranged as a mirror image 
relative to those of the brace 10 shown in the drawings when viewed from 
the front or rear. The braces of the invention for the right and left legs 
will appear the same when viewed from either the lateral side or the 
medial side. 
FIG. 1 shows all of the components of the brace 10 of the invention layed 
out as viewed from the front, with the various separable straps, pads, 
overwraps, and the tubular undersleeve, separated from the hinge brace 
structure per se to facilitate understanding of the construction of the 
individual separable parts and how they are assembled to form the 
operative composite four-point anterior cruciate ligament brace 10. The 
brace 10 per se will be considered in the following description to consist 
of the hinged mechanical brace structure with its directly associated 
straps, pads, and overwraps, while the tubular undersleeve separately 
shown in FIG. 1 is generally designated 12, the undersleeve 12 being 
slideably engaged over the knee and large portions of the thigh and calf 
as shown in FIGS. 7-10 prior to attachment of the brace 10 to the leg. 
The brace 10 is best considered as generally consisting of a pair of levers 
connected by means of a hinge structure. Thus, the brace 10 includes an 
upper femur lever generally designated 14 and a lower tibia lever 
generally designated 16, the levers 14 and 16 being operatively connected 
at the lateral and medial sides of the leg proximate the knee by means of 
a pair of hinges each of which is designated 18. 
The femur lever 14 includes a pair of generally parallel, elongated, flat 
side bars which extend generally longitudinally along opposite sides of 
the thigh, these being a lateral or outer femoral side bar 20 and a medial 
or inner femoral side bar 20a. Similarly, the tibia lever 16 includes a 
pair of elongated, generally parallel but slightly downwardly converging, 
flat tibial side bars adapted for location generally longitudinally along 
opposite sides of the calf, these being lateral or outer tibial side bar 
22 and medial or inner tibial side bar 22a. The femoral side bars 20 and 
20a are rigidly connected proximate their upper ends to opposite posterior 
ends of an anterior thigh cuff 24 as by means of rivets 25 shown in FIG. 
2, the anterior thigh cuff 24 extending arcuately anteriorly from the 
upper ends of the femoral side bars 20 and 20a. Anterior thigh cuff 24 
serves as the fulcrum of the femur lever 14. Tibial side bars 22 and 22a 
are similarly rigidly connected proximate their lower ends to the anterior 
ends of a posterior calf cuff 26 as by means of rivets 27 as shown in FIG. 
2, the posterior calf cuff 26 extending arcuately rearwardly from the 
lower ends of tibial side bars 22 and 22a. The posterior calf cuff 26 
serves as the fulcrum of the tibia lever 16. 
The anterior thigh cuff is preferably made substantially rigid, but 
formably adjustable to accommodate various thigh curvatures. Applicants 
have found it desirable to produce the brace 10 of the invention in four 
sizes to accommodate all sizes of patients, and generally one arcuate 
curvature of the anterior thigh cuff 24 for each size brace 10 will fit 
most thighs of the wearers because the thigh curvatures of such wearers do 
not generally vary appreciably. The anterior thigh cuff 24 may have a 
generally rigid but formably adjustable sheet metal core, preferably of 
aluminum, laminated on both sides with a padding material such as foam 
Neoprene, making the anterior thigh cuff 24 a thick, generally rigid 
structure. 
The posterior calf cuff 26 is a thick structure made with a flexible but 
nonstretchable core of a plastic material such as polyethylene, also 
laminated on both sides with a padding material such as foam Neoprene. 
Calf cuff 26 is made flexible so as to accommodate the wide variety of 
calf girths found in patients for each of four sizes of braces 10, and to 
allow adjustment of the tibial side bars 22 and 22a against twisting 
relative to hinges 18 which might otherwise be caused by undersized or 
oversized calves. 
The element of femur lever 14 adapted to apply anterior force to the femur 
proximal the knee joint is an adjustable posterior thigh strap 28 looped 
around the back of the thigh between a pair of elongated eyelets 30 
connected to side bars 20 and 20a by respective eyelet holders 30 and 
pivot pin rivets 32. Conversely, the force-producing element of tibia 
lever 16 add to apply posterior force to the tibia proximal the knee joint 
is anterior pretibial strap 34, which is looped over the front of the shin 
between a pair of elongated eyelets 36 attached to the respective tibial 
side bars 22 and 22a by means of respective eyelet holders 37 and pivot 
pin rivets 38. The posterior thigh strap 28 and anterior pretibial strap 
34 are both nonstretchable so that they are enabled to apply a positive 
differential force couple to the femur and tibia proximal the knee joint. 
Each of the posterior thigh strap 28 and anterior pretibial strap 34 has a 
short length of Velcro hook material 40 on both sides proximate one end, 
the remainder of both sides being covered with Velcro pad material 42. 
With this construction, the posterior thigh strap 28 is engaged to the 
brace 10 from its location shown in FIG. 1 by first lacing the end having 
the Velcro hook material 40 through the eyelet 30 of lateral femoral side 
bar 20, then pulling this laced end of strap 28 posteriorly around the 
back of the thigh, then lacing this same end through the eyelet 30 of 
medial side bar 20a and doubling the laced end back over the laced strap 
28 and anchoring the inner Velcro hook strip 40 to the outer Velcro pad 
42, and finally folding the remainder of the strap 28 over such 
doubled-back end portion and engaging the inner Velcro pad 42 with the 
exposed outer Velcro hook strip 40 to secure the strap 28. In like manner, 
the anterior pretibial strap 34 is connected to brace 10 from the location 
illustrated in FIG. 1 by first lacing its end with Velcro hook material 40 
throuqh eyelet 36 of medial side bar 22a, pulling that end portion of 
strap 42 anteriorly over the tibia, then lacing it through the eyelet 36 
on lateral tibial side bar 22 and doubling the hook strip end portion 40 
back anteriorly over the exposed side of strap 34, and then doubling the 
remainder of the strap 34 from the eyelet 36 on medial side bar 22a over 
the exposed front of the already laced portion of strap 34 and engaging 
the Velcro pad material 42 with the Velcro hook strip 40 to secure the 
strap. 
The brace 10 is applied to the leg, which already has tubular undersleeve 
12 pulled onto it, by stepping through the open center of brace 10 from 
behind the anterior thigh cuff 24 and then pulling the brace 10 upwardly 
on the leg until the biaxial hinges 18 are located adjacent the knee 
joint. The posterior thigh strap 28 and anterior pretibial strap 34 may be 
connected to the brace 10 after the brace 10 has thus been located on the 
leg, or alternatively may be prelaced onto the brace 10 in loosened 
condition, and then cinched up to the desired operative tightness. In 
practice, it has been found is preferable to tighten each of the straps 28 
and 34 as tightly as possible without substantial discomfort so as to bias 
the tibia rearwardly relative to the femur proximate the knee joint with a 
positive counterforce on the tibia such as will not only resist anterior 
translocation of the tibia relative to the femur but will actually 
counteract such anterior translocation and put a positive posterior 
traction on the tibia relative to the femur. Such positive traction 
preloads and compresses the tissues in the knee joint to a maximum extent 
such that any tendency for the tibia to translocate forwardly relative to 
the femur is far less than for any knee brace which is adapted to simply 
block such movement. 
Before the posterior thigh strap 28 is tightened against the back of the 
thigh, it is preferred to place a posterior thigh pad 44 between the strap 
28 and the thigh, the pad 44 being made of a foam elastomer such as 
Neoprene and being secured in position by engagement of a Velcro hook 
patch 46 thereon with the Velcro pad material 42 on strap 28. Similarly, 
it is preferred to place an anterior tibial pad 48 between the anterior 
pretibial strap 34 and the shin for improved comfort of the wearer, the 
pad 48 being secured in position by engagement of a Velcro hook patch 50 
thereon with Velcro pad material 42 on strap 34. 
Lateral and medial condyle pads 52 and 54 are mounted directly on hinge 
plates of the respective lateral and medial hinges 18 as described in 
detail below, and engage against opposite sides of the knee to control 
lateral knee instability. 
The brace 10 attaches with the undersleeve 12 so as to prevent the brace 10 
from migrating downwardly on the leg, and the undersleeve 12 also serves 
to increase patient comfort while wearing the brace 10. Undersleeve 12 is 
made of thin (preferably approximately 1/16 inch) foam elastomer sheet 
material, such as foam Neoprene, preferably with a knit or loop-type 
fabric bonded to the outer surface thereof. Undersleeve 12 is preferably 
somewhat longer from its upper end to its lower end 58 than the length of 
brace 10 to assure that the undersleeve 12 will always remain at least 
coextensive with the brace 10 during athletic operation of the brace 10. 
Undersleeve 12 has a patellar aperture 60 therein for knee-cap comfort and 
as an indicator of correct longitudinal location of the undersleeve 12 on 
the leg. 
Applicants have found in practice that the tubular undersleeve 12 has 
substantially no tendency to migrate downwardly on the leg because of its 
continuous conformation with the varying curvatures of the leg from middle 
thigh to lower calf, and particularly because of the downwardly increasing 
girth of the calf below the knee. Advantage is taken of such longitudinal 
stability of the tubular undersleeve 12 against downward migration by 
positively securing the knee brace 10 to the tubular undersleeve 12 by 
Velcro means at three discrete longitudinally spaced locations along the 
length of brace 10. Thus, a pair of anteriorly facing, circumferentially 
spaced Velcro pad patches 62 on sleeve 12 connect to a corresponding pair 
of Velcro hook patches 64 within the anterior thigh cuff 24; a pair of 
lateral and medial Velcro pad patches on sleeve 12 proximate the knee 
attach to the Velcro hook surfacing of the registering pair of condyle 
pads 52 and 54; and a pair of posteriorly facing Velcro hook patches 66 on 
sleeve 12 connect to a registering pair of anterior facing Velcro pad 
patches 68 in posterior calf cuff 26. 
An additional measure is preferably employed to further assure against 
downward migration of the brace 10, in the form of a pair of thin 
elastomer overwrap straps, preferably of gum rubber, which wrap around the 
thigh and calf and attach to the anterior thigh cuff 24 and posterior calf 
cuff 26, respectively, by Velcro means. Thigh cuff overwrap 72 has a 
Velcro pad strip 74 on the underside at one end which attaches to a Velcro 
hook patch 76 on the outside of thigh cuff 24. From the connection of 
these Velcro units 74 and 76 the thigh overwrap is wrapped all of the way 
around the thigh until a Velcro hook strip 78 on the underside of its 
other end is attached to a Velcro pad 80 on the outside of overwrap 72. 
Similarly, calf cuff overwrap 82 has a Velcro pad strip 84 at one end that 
is attached to a Velcro hook patch 86 on the outside of cuff 26, the 
overwrap 82 being wrapped around the calf, with a Velcro hook strip 88 on 
its underside at the other end attaching to a Velcro pad 90 on the outside 
of overwrap 82. These cooperative engagements of the thigh and calf 
overwraps 72 and 82 over the respective thigh and calf cuffs 24 and 26 are 
illustrated in FIGS. 7-9. The thigh and calf overwraps 72 and 82 secure 
the open-cuffed ends of the brace 10 to the thigh and calf, respectively, 
so that extension stop gears in the hinges, described hereinafter in 
connection with FIGS. 3, 4 and 6 of the drawings, are enabled to prevent 
hyperextension of the knee, blocking extension at a preferred preset 
71/2.degree.. 
Preferably, all of the four side bars 20, 20a, 22, and 22a are covered with 
foam elastomer padding sleeves 92, which may be of foam Neoprene and are 
preferably covered in the same manner as undersleeve 12 with a knit or 
loop-type fabric. 
As best seen in FIGS. 2, 3 and 10, the femoral side bars 20 and 20a have 
short posteriorly angled lower end portions designated 100 and 100a, 
respectively. Conversely, the tibial side bars 22 and 22a have short 
anteriorly angled upper end portions 102 and 102a, respectively. 
Otherwise, the principal portions of the lengths of both of the femoral 
side bars 20 and 20a above the posterior angled lower portions 100 and 
100a are preferably straight; and the principal portions of the lengths of 
both of the tibial side bars 22 and 22a below the anterior angled short 
upper end portions 102 and 102a are preferably straight. The preferred 
angle of inclination of each of the lower end portions 100 and 100a 
relative to the principal straight portion of its respective femoral side 
bar 20 and 20a is approximately 45.degree. . Similarly, the preferred 
angle of inclination of the upper end portions 102 and 102a relative to 
the principal straight portions of tibial side bars 22 and 22ais 
approximately 45.degree. . 
The short angled end portions 100, 100a, 102, and 102a of the side bars 
located proximal the hinge structures 18 are for the purpose of placing 
the principal, straight lengths of the femoral side bars 20 and 20a 
anteriorly along the sides of the thigh, while at the same time placing 
the principal, straight lengths of the tibial side bars 22 and 22a 
posteriorly along the sides of the calf. This then enables the posterior 
thigh strap 28 to have at least approximately 180.degree. of strap loop 
arc around the back of the thigh for maximum mechanical advantage of the 
femur lever 14; while at the same time enabling the anterior pretibial 
strap 34 to also have at least approximately 180.degree. of strap loop arc 
around the front of the shin proximal the tibial tubrical to assure 
maximum mechanical advantage of the tibia lever 16. 
Viewing the brace 10 from the front as in FIGS. 1 and 7, it will be seen 
that the medial tibial side bar 22a has a lateral offset, designated 103, 
between the hinge structure 18 and strap mounting eyelet 36. This is to 
accommodate the natural lateral offset of the shin below the knee joint. 
It is desirable that the hinge joints 18 between the anteriorly offset 
femoral side bars 20 and 20a and the respective posteriorly offset tibial 
side bars 22 and 22a be bicentric or biaxial, and if so, it is essential 
that they be geared. Because of the complex bending action of the knee 
joint, a single pivot is generally incompatible with the movement of the 
knee joint and would unduly stress the knee under the loading necessarily 
imposed by the brace 10 of the invention. A biaxial or bicentric hinge of 
correct dimensions is, on the other hand, substantially completely 
compatible in its action with the action of the knee joint, and therefore 
does not undesirably stress the knee under the loading of the brace 10 of 
the invention. 
A reason for the essentiality of the geared connections in the hinges 18 if 
they are bicentric is that for operability of the present invention in 
applying rearward traction to the tibia relative to the femur proximal the 
knee joint, there can be no relaxing of the tension of either the 
posterior thigh strap 28 or the anterior pretibial strap 34 that might 
originate at the hinge structures 18. Thus, with bicentric hinges that 
were not geared, the hinges could rock or tilt, which would be in a 
counter-clockwise direction as viewed in FIGS. 2 and 8-10, which would 
then cause relaxation of both the posterior thigh strap 28 and the 
anterior pretibial strap 34, thereby defeating the operability of both the 
femur lever 14 and the tibia lever 16. However, the geared connection 
between the hinged ends of femoral side bars 20 and 20a and respective 
tibial side bars 22 and 22a positively interlocks the hinged ends of the 
tibial side bars 22 and 22a against anterior shifting relative to the 
respective hinged ends of the femoral side bars 20 and 20a, thereby 
providing positive assurance against such relaxation at the hinges 18. 
Not only do the geared connections in the hinges 18 positively prevent such 
relaxation, but as a further aspect of this bicentric, geared connection, 
during flexion from the straight, extended position of the knee joint 
shown in FIG. 10 to a flexed position such as shown in FIG. 8, the gears 
affixed to the upper ends of the tibial side bars 22 and 22a in effect 
climb or roll rearwardly along the peripheries of the mating gears affixed 
to the lower ends of the femoral side bars 20 and 20a, respectively, 
serving to add further traction of the anterior pretibial strap 34 
relative to the posterior thigh strap 28, thereby pulling the tibia 
anteriorly relative to the femur even further during flexion. 
In addition to these reasons for the geared bicentric or biaxial hinges 18, 
the geared connection in hinges 18 maintains the anterior offset of 
femoral side bars 20 and 20a and the posterior offset of tibial side bars 
22 and 22a, and thereby maintains the full approximately 180.degree. of 
strap loop arcs to assure maximum mechanical advantage for each of the 
femur and tibia levers 14 and 16, and hence for the entire four-point 
leverage system of the brace 10. The preferred amount of 
anterior/posterior offset of the principal straight portions of femoral 
side bars 20 and 20a relative to the principal straight portions of tibial 
side bars 22 and 22a in the extended, parallel relationship as illustrated 
in FIGS. 2 and 10 is approximately two inches, and the preferred minimum 
offset is approximately one and one-half inches. It is also preferred that 
the femoral and tibial side bar offsets from the centers of hinges 18 be 
substantially equal and opposite in the anterior and posterior directions, 
respectively. 
The hinges 18 are the same on the lateral and medial sides of the brace 10, 
so only one of these hinges, the lateral hinge 18, has been shown in 
detail in the drawings, in FIGS. 3-6. For stability in supporting the 
hinge gears on the angled ends of the side bars, the angled ends 104 of 
femoral side bars 20 and 20a and the angled ends 106 of tibial side bars 
22 and 22aare enlarged in area. An arcuate gear 108 is rigidly affixed to 
the lateral side of each enlarged end 104, and an arcuate gear 110 is 
rigidly affixed to the lateral side of each of the enlarged ends 106. Each 
of the femoral bar gears 108 is in meshing engagement with the respective 
one of the tibial bar gears 110. 
Each hinge 18 has a pair of elongated, flat, parallel hinge plates 
generally longitudinally arranged relative to the brace 10, including an 
inner hinge plate 112 which lies medially of the side bar ends 104 and 
106, and an outer hinge plate 114 which lies laterally of the gears 108 
and 110. A pair of hinge pins 116 and 118, preferably rivets as 
illustrated, extend through both hinge plates 112 and 114 near their 
longitudinal ends and extend through the arcuate centers of respective 
gears 108 and 110 and respective enlarged side bar ends 104 and 106. 
Suitable antifriction washers such as the washers 120 may be carried on 
the hinge pins 116 and 118 to maximize freedom of movement in the hinge 
structure 18. A support 122 for condyle pad 52 is attached to the center 
of inner hinge plate 112 by means of a screw 124. 
An extension stop gear 126, in the form of a small spur gear, is carried on 
an arm 128 located between hinge gear 108 and plate 114, the arm 128 being 
hinged on pin 116. Stop gear 126 is mounted on arm 128 by means of a screw 
130. The extension stop gear 126 meshes with the arcuate gear rack of 
hinge gear 108. Screw 130 holds stop gear 126 in frictional engagement 
with the arm 128, screw 130 being staked to gear 126 so that stop gear 126 
can be rotated by screw 130 for adjustable positioning along the periphery 
of hinge gear 108. A pointer 132 on arm 128 indicates the limit of 
extension of the brace 10, and hence correspondingly of the knee joint, 
that will be permitted by any particular positioning of stop gear 126 on 
hinge gear 108. FIG. 6 illustrates the brace 10 in a position of 
approximately 90.degree. of flexion, and it will be seen that in such 
position the extension stop gear 126 is moved with its hinge gear 108 
counterclockwise approximately 90.degree. from engagement with the other 
hinge gear 110. Then, as flexion decreases, stop gear 126 as carried by 
hinge gear 108 moves clockwise toward the other hinge gear 110 until it 
finally engages against the gear 110 as a wedge between the two gears 108 
and 110 as seen in FIG. 3 to positively stop further extension of the 
brace. 
Similarly, a flexion stop gear 136 is adjustably carried on the tibial 
hinge gear 110, being rotatably adjustably mounted by a screw 140 on an 
arm 138 that is pivoted on pin 118. As seen in FIG. 5, the screw 140 holds 
flexion stop gear 136 in frictional engagement against the arm 138 and is 
staked to flexion stop gear 136 so that stop gear 136 can be adjustably 
positioned along the arcuate rack of hinge gear 110 by adjustment of screw 
140 to the desired limit of flexion to be permitted. Such flexion limit is 
indicated by means of a pointer 142 on arm 138 which points to flexion 
index 144 on gear 110. 
Each of the hinges 118 is covered by a hinge cover shell 146 attached to 
outer hinge plate 114 by means of a screw 148. The hinge cover shells 146 
are removed for access to the extension and flexion stop gear mechanisms 
for adjustment of the latter. The pair of extension stop gears 126 and 
flexion stop gears 136 on opposite sides of brace 10 will be set to the 
same amount of extension on the one hand and flexion on the other hand. 
Referring now to FIG. 10, the forces involved in the four-point lever 
system of the present invention are illustrated by phantom arrows on the 
four members which are applying forces to the leg. Thus, in the femur 
lever 14, a posterior force 150 is applied by the fulcrum cuff 24 against 
the front of the thigh distally of the knee joint; while the posterior 
thigh strap 28 applies an anterior force 152 against the rear of the thigh 
proximally of the knee joint. Conversely, in the tibia lever 16, the 
fulcrum cuff 26 applies an anterior force 154 against the rear of the calf 
distally of the knee joint; while the anterior pretibial strap 34 applies 
a posterior force 156 against the front of the shin proximally of the knee 
joint. Because of the geared interlock between the angled ends of the 
femoral side bars 20 and 20a and the angled ends of the respective tibial 
side bars 22 and 22a, a force couple is developed between the two forces 
152 and 156 proximal the knee joint to serve the very same function as the 
anterior cruciate ligament within the knee, namely, to resist anterior 
drawer shift of the tibia relative to the femur proximal the knee joint. 
FIG. 10 provides a good illustration of the structural compatibility 
between the brace 10 of the present invention and the bone structure 
within the knee. Thus, most of the lengths of the femoral side bars 20 and 
20a laterally and medially overlap the femur 158; most of the lengths of 
the tibial side bars 22 and 22a overlap the lateral and medial sides of 
the tibia 162 and fibula 164; and the angled end portions 100 and 100a of 
the femoral side bars and 102 and 102a of the tibial side bars overlap the 
lateral and medial sides of the enlarged ends of the femur 158, tibia 162 
and fibula 164 proximal the knee joint. FIG. 10 also illustrates the 
freedom allowed the knee in the region of patella 160 by the patellar 
aperture 60 in undersleeve 12. 
One of the surprising things which distinguishes the present invention from 
all prior art knee orthotics of which applicants are aware is the fact 
that none of the four principal elements of the brace which cooperate to 
externally reproduce the function of the anterior cruciate ligament 
extends all of the way around the leg. This is important for a number of 
reasons. First, and of primary importance, the two straps 28 and 34 which 
apply the torquing force couple to the femur and tibia proximal the knee 
are not either one reduced in force-applying capacity by an opposing loop 
at the same longitudinal location extending around the other side of the 
leg. Thus, the posterior thigh strap 28 has its full force effectively 
applied anteriorly to the femur proximal the knee joint, without 
opposition from any strap or other loop extending anteriorly around the 
thigh at the same longitudinal location, which would otherwise pull 
against the leverage gained by the posterior thigh strap 28. Similarly, 
the anterior pretibial strap 34 is unopposed by any strap or other 
structure extending posteriorly around the calf at the same longitudinal 
location that would otherwise pull against the leverage gained by the 
anterior pretibial strap 34. 
Another important advantage of the simple half-loop concept of the present 
invention embodied in all four of the leg-engaging lever structures, 
including the cuffs 24 and 26 and the straps 28 and 34, is that this 
arrangement substantially eliminates projecting structures like those of 
the prior art which would interfere with athletic performance and thereby 
render the apparatus virtually useless for athletic use. 
Applicants' cuff overwraps 72 and 82 serve no function in the four-point 
leverage operation of applicants' brace 10 as a substitute or replacement 
for an injured anterior cruciate ligament, and need not be applied so 
tightly as to in any way interfere with blood circulation in the leg. To 
the contrary, most prior art knee orthotics of which applicants are aware 
rely upon bands of one sort or another which completely encircle the leg 
both above and below the knee, and which depend for their utility upon 
their tightness so as to tend to interfere with blood circulation in the 
leg and to be uncomfortable in use. 
Applicants' use of only half-loop type structures in the four leverage 
units, the two cuffs 24 and 26 and the two straps 28 and 34, further 
enables applicants' brace 10 to have a minimum of weight and bulk that 
would otherwise interfere with athletic performance. 
While applicants' knee brace 10 is primarily for the purpose of limiting 
anterior drawer shift of the proximal tibia, while serving this function 
it also synergistically controls rototory instability movements which 
might occur with injury of some of the secondary restraining structures in 
the knee. This is because rototory instability movements generally require 
some forward translocation of the tibia relative to the femur which 
relieves interengagement between the intercondular eminence on the tibial 
plateau and a matching irregularity of the femur. However, with the 
control the present invention applies against forward translocation of the 
tibia relative to the femur, the intercondular eminence and matching femur 
irregularity are maintained in close interfitting relationship against 
rototory motion. 
Applicants have conducted clinical anterior drawer tests on 79 patients 
with a torn anterior cruciate ligament in one leg. Normally, in a healthy 
person without anterior drawer trauma in either knee, the anterior drawer 
will be approximately the same for both knees under the application of 
various anterior drawer forces. However, if the anterior cruciate ligament 
in one knee is torn, then under any applied translocating force the 
injured knee will translocate a considerably larger amount than the 
healthy knee. Thus, to test the effectiveness of the brace 10 of the 
invention as a replacement or substitute for an injured anterior cruciate 
ligament, on each of the 79 persons tested applicants tested the uninjured 
knee, the injured knee without the present invention, and the injured knee 
with the present invention. These three comparative tests were run for 
three separate anterior drawer applied forces, a measured 15 lbs., a 
measured 20 lbs., and an estimated 60 lbs. The results of these tests 
established not only that the present invention was effective in 
completely replacing or substituting for the injured anterior cruciate 
ligament, but on the average the present invention controlled tibial 
anterior drawer movement in the injured knee better than the real anterior 
cruciate ligament controlled it in the good knee. Thus, at 15 lbs. applied 
force, 90 percent of the injured knees tested as good or better than the 
noninvolved knee; at 20 lbs. applied force, 74 percent tested as good or 
better than the noninvolved knee; and at an estimated 60 lbs. applied 
force, 75 percent tested as good or better than the noninvolved knee. 
There was greater than 50 percent reduction in anterior drawer shift with 
the present invention applied in every knee tested, and in some cases 
there was as much as 80 percent reduction in the amount of anterior drawer 
shift. 
The averages and ranges for all knees tested were as follows. At 15 lbs. 
applied force, the good knees averaged approximately 5 mm of anterior 
excursion, and ranged from approximately 1 mm to approximately 10 mm; the 
injured knees without the present invention averaged approximately 10 mm 
and ranged from approximately 4 mm to approximately 17 mm; while with the 
present invention applied, they averaged only 3 mm and ranged from 
approximately 1 mm to approximately 7 mm. With 20 lbs. force applied, the 
good knees averaged an anterior excursion of approximately 7 mm, with a 
range of from approximately 11/2 mm to approximately 111/2 mm; the injured 
knees averaged approximately 121/4 mm, and ranged from approximately 41/2 
mm to approximately 20 mm; while with the present invention applied, the 
injured knees averaged approximately 43/4 mm, and ranged from 
approximately 21/2 mm to approximately 91/2 mm. With approximately 60 lbs. 
of applied force, the good knees averaged approximately 8 mm of anterior 
excursion, and ranged from approximately 21/2 mm to approximately 12 mm; 
the injured knees averaged approximately 15 mm, and ranged from 
approximately 51/2 mm to approximately 20 mm; while with the present 
invention applied, they averaged approximately 61/3 mm, and ranged from 
approximately 21/2 mm to approximately 11 mm. 
While the instant invention has been described with regard to a particular 
embodiment, modifications may readily be made by those skilled in the art, 
and it is intended that the claims cover any such modifications which fall 
within the spirit and scope of the invention.