Knee stabilizer

A knee brace having an anterior tibial shell and a posterior femural shell which are closely configured to the shape of the leg and are joined by a closed support band which is constructed to closely track knee flexion. The brace also has anteriorly extending tabs positioned between the patella and the femural epicondyles. The combination of shell, band and tabs provides anterior-posterior, medial-lateral and rotary stability.

BACKGROUND OF THE INVENTION 
This invention relates to orthotics, to supports or stabilizers for joints 
and, in particular, to a knee brace which serves both preventive and 
remedial functions in protecting against medial-lateral, 
anterior-posterior and rotatory instabilities. 
The knee joint is perhaps the most susceptible to injury of the major 
articulated joints of the human body, despite the presence of five major 
ligaments and two menisci which serve to connect and stabilize the tibia 
and femur. These structures include the anterior and posterior cruciate 
ligaments, the medial and lateral collateral ligaments, the posterior 
capsule ligament and the medial and lateral menisci. 
Anatomically, the knee is designed so that specific muscles or muscle 
groups, not ligaments, absorb the brunt of external or internal forces. 
That is, a muscle or group of muscles substitutes for each ligament in the 
knee to absorb force and restrict motion. As examples, the hamstrings 
substitute for the anterior cruciate ligament, the quadriceps for the 
posterior cruciate ligament, and the abductor and adductor groups for the 
medial and lateral collateral ligaments. 
The articulation of the knee joint, and the ligaments, muscles and bones 
associated with the joint are described, for example, in Gray's Anatomy 
and in The Johns Hopkins Atlas of Human Functional Anatomy, 2d ed., 1980. 
These teachings are incorporated by reference. 
When a muscle is unable to completely absorb an applied force, either 
because of inherent weakness or prior injury or simply because the force 
is too strong, the unabsorbed component of force is transmitted to one or 
more ligaments. If the transmitted component is sufficiently great, the 
ligament is strained or torn. Ligamental susceptibility to injury is also 
dependent upon the degree of flexion or extension. Typically, if the femur 
and tibia are in a relatively straight orientation or if the knee is 
slightly extended, the ligaments are fairly tight. This reduces the amount 
of displacement of the tibia and femur and the chance of injury. However, 
the inherent cooperation and relationship among the ligaments is such that 
when the knee is bent or flexed, some ligaments are relatively tight and 
tend to control displacement, but others are relatively loose. Between 
20.degree.-60.degree. of flexion the knee is very susceptible to 
displacement and to injury. This is unfortunate, because the knee is 
frequently in this position, particularly during the more active sports 
activities. It is factors such as these which make the knee relatively 
weak compared to the other major articulated joints. Some, such as the 
ball and socket hip joint, are very secure. Others, such as the arm and 
shoulder joints are complicated but nonetheless relatively secure. Despite 
its inherent weaknesses, the knee joint must both support the weight of 
the body and provide for movement, while holding the tibia and femur in 
position along their substantially planar unstable interface. In 
considering external forces applied to the knee and the resulting ligament 
injuries, it is helpful to simplify the situation somewhat and consider 
the forces as having their major components applied primarily along a 
frontal plane through the knee, or along a sagittal plane through the 
knee, or as comprising a rotatory force. Frontal plane forces are 
medial-lateral forces which displace the femur and/or tibia in a 
side-to-side direction. Saggital plane forces are anterior-posterior 
forces which displace the femur and tibia in approximately a front-to-back 
motion, and includes drawering forces applied during flexion or extension. 
Rotatory forces are those which tend to induce relative rotational 
displacement of or between the femur and tibia, primarily against the 
stabilizing force provided by the anterior cruciate ligament. 
FIGS. 1 through 3 illustrate examples of the above forces. In these 
schematic drawings, the femur, tibia and knee are respectively designated 
11, 12 and 13. Referring specifically to FIG. 1, two of the more common 
knee ligament injuries result from medial and lateral forces. The medial 
collateral ligament and lateral collateral ligament are primary 
stabilizing influences against medial and lateral force, respectively. As 
a consequence, strains or tears of these ligaments tend to result, 
respectively, from medial forces, that is, inward or medially-directed 
forces 14 applied against the outside of the leg, or lateral forces 15, 
which are outward directed forces applied against the inside of the leg. 
Perhaps the most frequent injury in sports, and certainly one of the most 
damaging injuries to the joints involves strains or tears of the anterior 
cruciate ligament. Referring to the side views shown in FIG. 2, the 
responsible force may involve an anterior tibial force alone, that is, a 
forward-directed force 21 applied to the back of the tibia. See FIG. 2A. 
The force may involve the combination of a rotational tibial force 22 
which rotates the tibia relative to the femur (as by catching a shoe or 
cleats in turf) and an anterior tibial force 21. See FIG. 2B. In either 
case, injury to the anterior cruciate ligament results from excessive 
force which the substitutional muscles and the anterior cruciate ligament 
are unable to absorb and a resulting anterior tibial acceleration and 
displacement relative to the femur. See FIG. 3. The reason for the 
frequent occurrence of this injury is two-fold, namely the frequency with 
which the knee and leg are subjected to large magnitude forces, and the 
susceptibility to injury in that typically the knee can withstand only 
about 380 pounds of force and 12.5 millimeters displacement or movement 
between the tibia and the femur without injury to the anterior cruciate 
ligament. 
Referring to FIG. 4 and as shown by the arrow 41 therein, a 
posterior-directed force 41 is the opposite of anterior-directed force 21. 
The knee 13 is stabilized against posterior forces primarily by the 
posterior cruciate ligament. Unlike the anterior cruciate ligament, the 
posterior cruciate ligament is backed by the posterior capsule ligament, 
which is quite effective in stabilizing the knee against displacement. As 
a result, isolated posterior cruciate tears are rare. Usually injuries to 
other ligaments are also involved. In fact, it is not infrequent that the 
bone attachment itself tears rather than, or in addition to the posterior 
capsule ligament. 
Displacement of the femur and tibia resulting from rotational forces such 
as 22, FIG. 2B, is another primary cause of injury to the anterior 
cruciate ligament. Of course, if there is existing damage or if the 
anterior cruciate ligament has inherent instability, the knee is more 
susceptible to displacement and the ligament is more susceptible to 
injury. The same is true of the other ligaments in that existing damage or 
instability increases their susceptibility to injury. 
Concentrated efforts by the orthotics' profession to develop knee 
stabilizers are thought to have been initiated in the 1960's as a result 
of publicized knee injuries suffered by professional athletes. It is 
believed basically two types of knee braces have dominated this field. 
Referring to the FIG. 5 front view, one such brace 50 uses a three-point 
suspension which is provided by two pads 51 and 52 situated above and 
below the knee (on either the medial or the lateral side of the leg) and a 
third pad 53 on the opposite side of the leg adjacent the knee. Rigid 
braces 54--54 correct the pads. Various straps can be used to enhance 
suspension and/or stabilization characteristics. Referring to the side 
view shown in FIG. 6, the second type 60 of conventional knee brace uses 
relatively rigid anterior femur and tibial shells 61 and 62 which are 
joined by hinged uprights 63--63 and supported in the back or posterior 
side by elastic straps 64 and 65. These designs are more effective at 
protecting against medial-lateral forces than anterior-posterior forces. 
The reason is simple. The rigid shells/pads and connecting braces provide 
relatively inflexible pressure points which stabilize against lateral or 
medial forces. In contrast, the relatively flexible front-to-rear 
stabilization systems provided by these braces permit relative movement of 
the tibia and femur along the sagittal plane. 
In addition, because rotary stability is a function of both medial-lateral 
and anterior-posterior stability, the implementation of conventional knee 
brace designs tends to be less effective than desired in any derotation 
function. Furthermore, stabilization in all aspects is closely related to 
the effective suspension of the orthotic device on the knee and leg in a 
manner such that the device does not alter or shift its position on the 
leg as by planing. Many prior art devices experience planing and shifting 
which detract from their ability to provide medial-lateral stability, 
anterior-posterior stability and/or rotatory stability. In addition to the 
difficulty of achieving adequate suspension stability using typical prior 
art knee braces, frequently such braces avoid the problems associated with 
flexion by restricting movement of the knee. Because of restrictions on 
movement and because of weight, the use of these braces to prevent 
injuries puts the athlete at such a competitive disadvantage that knee 
braces are not widely used for injury prevention. Rather, the primary use 
has been remedial, to compensate for and protect against existing injuries 
and weaknesses in already damaged and/or unstable knees. Perhaps the one 
exception to the use of prior art knee braces for remedial purposes rather 
than prevention is the class of braces which consist simply of a pair of 
upright bands on the sides of the leg. These are used to provide some 
means of protection against medial-lateral forces. 
SUMMARY OF THE INVENTION 
Accordingly, it is one object of the present invention to provide a new and 
improved knee brace suspension system which restricts planing and other 
movement of the knee brace relative to the leg and knee. It is another 
object of the present invention to provide a new and improved knee brace 
which protects against displacement and injuries to the anterior cruciate 
ligament. It is another object of the present invention to provide a new 
and improved knee brace which protects against displacement and 
medial-lateral, anterior-posterior and rotary instabilities. 
In one embodiment, the knee stabilizer of the present invention contains a 
relatively rigid anterior tibial shell which substantially conforms to the 
outline of the leg proximate the knee; a relatively rigid posterior 
femural shell which substantially conforms to the outline of the thigh 
proximate the knee; and a pair of uprights extending one on the lateral 
side of the knee and one on the medial side of the knee for rigidly 
interconnecting the tibial and femural shells, and substantially tracking 
flexion of the knee. In a preferred working embodiment, the tibial shell 
wraps around the posterior side of the leg, and the femural shell wraps 
around the anterior side of the thigh and has a pair of suspension pads 
located on opposite sides of the patella between the patella and the 
femural epicondyles. The combination of the configured anterior and 
posterior shells and the uprights provides excellent anterior-posterior, 
medial-lateral and rotary stability. In another preferred working 
embodiment, the uprights are part of a closed, rigid band support system 
including a femural section which is attached to the uprights on opposite 
sides of the femural shell and spans the posterior side of that shell, and 
a tibial section which is attached to the uprights on opposite sides of 
the tibial shell and spans the anterior side of that shell. In an 
exemplary light weight configuration, the tibial shell and femural shell 
have respective posterior and anterior openings and elastic straps which 
span these openings.

DETAILED DESCRIPTION 
A preferred embodiment 70 of the knee stabilizer of the present invention 
is shown in FIGS. 7, 8 and 9. The knee stabilizer 70 comprises a tibial 
shell 71, a femural shell 72 and a closed band structure 80 which joins 
the two shells and includes a joint 86 on either side of the knee for 
substantially tracking flexion of the knee. The shells and band are 
carefully tailored and configured to conform to the shape and size of the 
individual leg and knee. The tibial shell 71 is closed on the anterior 
(front) side thereof and, particularly in applications requiring light 
weight, may be open at the posterior (rear) side. The phrase "anterior 
tibial shell" as used herein refers to tibial shell 71 having a section 73 
which spans the anterior side of the lower leg. Similarly, the femural 
shell 72 is closely configured to the size and shape of the thigh, and has 
a support section 74 which spans the posterior side of the thigh. Thus, as 
used here, the phrase "posterior femural shell" refers to a femural shell 
72 which has a section 74 spanning the posterior side of the thigh. In 
addition, the tibial shell 71 has sections 75--75 which partially wrap 
around the posterior of the leg and the femural shell 72 has sections 
76--76 which wrap partially around the anterior section of the femur. The 
purpose of these partial sections is to enhance the suspension 
characteristics of the leg; at the same time, the openings defined between 
sections 75--75 and between sections 76--76 contribute to the light weight 
and ease of application of the stabilizer 70. 
The anterior sections 76--76 of the femural shell each include a 
stabilization or suspension tab 77 which is configured to and positioned 
between the patella or knee cap and the femural epicondyle located on that 
side of the knee. The tibial and femural shells have straps 78 and 79 
respectively attached thereto for spanning their respective posterior and 
anterior openings to aid the suspension of the shells on the leg and 
thigh. Typically the straps 78 and 79 are rigidly attached along one side, 
as by metal rivets, and are releasably attached on the opposite side, as 
by Velcro, to permit releasing the straps to fit the knee stabilizer onto 
the leg and to provide an adjustably snug fit of the knee stabilizer 70 
onto the leg. 
Referring in particular to FIG. 7, the tibial and femural shells 71 and 72 
are rigidly suspended relative to one another and the knee by the band 
suspension system 80. This system comprises metal bands which are 
configured to the outline of the shells and leg. The system includes a 
pair of substantially vertical uprights 82--82 attached to the medial and 
lateral sides of the femural shell 72 and, similarly, a pair of 
substantially vertical uprights 83--83 attached to the medial and lateral 
sides of the tibial shell 71. A tibial band 84 is attached to the uprights 
83--83 on opposite sides of the tibial shell 71 and spans the closed 
anterior section of the shell. Similarly, a femural band 85 is attached to 
the uprights 82--82 on opposite sides of the femural shell and spans the 
posterior side of the femural shell. The uprights 82 and 83 are joined 
proximate the knee by a conventional polycentric knee joint 86 which is 
designed to pivot in a curve which tracks the knee, i.e., is similar to 
the anatomical movement of the knee. 
The knee stabilizer 70 includes several advantageous suspension features. 
It should be noted that the word "suspension" refers to retaining a knee 
brace on the knee and leg without movement, such as planing, of the brace 
relative to the knee. Suspension, of course, contributes to the ability of 
the brace to stabilize the knee and leg and many of the factors which are 
necessary for adequate suspension also contribute to stabilization. That 
is, improving suspension improves stabilization. One advantageous feature 
of stabilizer 70 is the custom-tailored contour of the shells 71 and 72 
and band system 80. In being precisely configured to the shape of the leg 
and thigh, both at the anterior and posterior sides as well as the medial 
and lateral sides, a secure fit is provided and movement of the stabilizer 
relative to the leg is inhibited. A second, related aspect is that the 
closely configured shells of the stabilizer 70 also encompass or cover 
more of the perimeter of the leg and thigh than conventional braces. 
Third, the rigid band support system 80 comprises a unitary configuration 
which tracks the primary stress points (the back of the thigh, the front 
of the tibia, and the sides of the legs), and thereby keeps the configured 
shells firmly in place on the leg and contributes to excellent stability. 
Also, as mentioned above, the polycentric knee joints 86--86 track in a 
curve much the same as does the knee, which facilitates maintaining the 
shells in position during flexion and extension of the knee. Fifth, the 
knee joint 86 can be misaligned slightly. That is, (1) the joints can be 
rotated slightly relative to the anatomical track to create a stabilizing 
force at the anterior superior edges of the tibia to stabilize rotatory 
instabilities or (2) the knee joint 86 can be misaligned or offset 
relative to the anatomical knee so that the plastic material of the shell 
bends faster than the knee and thus maintains pressure on the knee to 
counter anterior cruciate instability of the knee. For example, the joint 
86 can be positioned posteriorly and/or superiorly relative to the 
anatomical knee center to counter the inherent instability of the knee 
during 20.degree.-60.degree. of flexion, or the joint can be positioned 
rotationaly to the knee center to counter the anterior rotatory 
displacements of the tibia. An example of such positioning is illustrated 
in FIG. 7 wherein the orthosis knee center provided at knee joint 86 is 
positioned above the anatomical knee center 87 so that, e.g., in flexing 
as shown in phantom by line 88-0 the orthosis flexes faster than does the 
knee at 88-A and creates posterior pressure on the knee and leg. 
Sixth, the brace incorporates a circumferential perimeter differential. 
That is, the distal border (lower portion) of the femural shell 72 has a 
smaller circumference than the adjacent underlying femural condyles. This 
is done to apply pressure to the anterior edges of the abductor and 
adductor epicondyles on the medial and lateral sides of the femural 
condyles. A seventh, related feature is the suspension tabs 77--77 which 
are discussed below. Finally, but not to exhaust the advantages, an 
auxiliary strap can be used to connect the superior border of the tibial 
shell to provide additional stabilization against inertia in unusually 
high stress situations. 
In considering the stabilization characteristics of the knee stabilizer 70, 
refer initially to the front and rear depictions of FIGS. 8 and 9, as well 
as the side view of FIG. 7. In contrast to prior art braces, the 
stabilizer 70 stabilizes against medial-lateral forces very well, in part 
because the shells 71 and 72 circumferentially encompass more of the leg 
than prior art braces. The shells fully cover both the lateral and medial 
sides of the thigh and leg proximate the knee. Displacement side-to-side 
is further constrained by the closed anterior section 73 of the tibial 
shell 71, the partial wraparound of the posterior section 75 of the tibial 
shell, the closed posterior section 74 of the femural shell 72 and the 
partial wraparound of the anterior section 76 of the femural shell, in 
conjunction with the additional constraint against side-to-side 
displacement provided by the closed configuration of band 80, that is the 
posterior femural band 85, the anterior tibial band 84 and the 
interconnecting uprights 82 and 83. In contrast to the three-point 
medial-lateral suspension of many prior art braces, the described 
construction of the knee stabilizer 70 provides essentially continuous 
support and stabilization against displacement from the lower or distal 
edge of the tibial shell 71 to the upper or superior edge of the femural 
shell 72. 
Those skilled in the art will appreciate that the abovedescribed structural 
features which provide medial-lateral stability also contribute to 
anterior-posterior stability. The structure of the knee stabilizer 70 
incorporates key pressure points which are designed to protect against 
anterior-posterior instability as well as medial-lateral and rotary 
instability. Referring to FIG. 7, five of these points are indicated 
generally by the arrows designated 91-95. These include three pressure 
points or regions which securely lock the tibia: the distal (lower) 91 and 
proximal (upper) 92 borders of the closed anterior tibial shell section 
73, and the posterior point 93 defined by the posterior section and 
elastic strap 78 of the tibial shell; and two femural pressure points: the 
anterior proximal (superior) femural border 94 and the posterior distal 
border 95 of the closed posterior section 74 of the femural shell. Also, 
due to the large amount of tendon motion in the distal posterior border of 
the femural section, the inverted popiteal-shaped relief 74 is preferably 
set in a slight lateral tilt. Those skilled in the art will quickly 
appreciate that the other structural features such as tabs 77--77 also 
serve important stabilization functions. 
The effectiveness of this suspension and pressure system design can be 
illustrated by considering application of the anterior tibial force 21 
shown in FIG. 2A and the external rotation anterior tibial force 21-22 
shown in FIG. 2B. As indicated previously, these are frequently 
responsible for injury to the anterior cruciate ligament, perhaps the most 
frequency injury in sports. In response to an anterior tibial force 21 of 
sufficient magnitude, the tendency is for the lower leg 12 to move and 
potentially injure the anterior curciate ligament. However, this movement 
transmits pressure against the anterior section 73 of the tibial shell 71 
and tends to move the tibial shell. This tendency is in turn transmitted 
via the band support system 80 and femur band 85 thereof to the femural 
shell 72. The closed posterior section 74 and, in particular, the distal 
border pressure 95 transmit any displacement of the lower leg into like 
displacement of the thigh and thereby prevent displacement of the tibia 12 
relative to the femur 11. In short, the anterior-directed tibial force 21 
is transmitted as an anterior-directed femural force to stabilize the 
femur and tibia and prevent relative displacement. 
Considering now the rotational component 22 of the exterior force, one will 
recall that the tendency of prior art braces is to rotate on the leg. In 
the knee stabilizer 70, an additional stabilizing influence to those 
previously described is provided by the stabilizing pads 77--77 which 
provide pressure at the distal border of the anterior femural shell 
section 76. In response to such rotational forces (either or both 
anterior-lateral or anterior-medial), one of the pads 77 is constrained 
from movement by the opposite epicondyle, while the other pad is 
constrained by the patella. As a result, the anterior cruciate ligament is 
stabilized, along with the other knee ligaments and the entire knee. In 
addition, those skilled in the art will appreciate that rotational forces 
and rotary instability are functions of the force vectors in the frontal 
plane (medial-lateral forces) and the sagittal plane (anterior-posterior 
forces). Thus, derotation and rotary stability are aided by the features 
described previously which contribute to enhanced anterior-posterior 
stability and medial-lateral stability. 
In working embodiments of the knee stabilizer 70 designed for a six foot, 
180 pound male, the overall length of the stabilizer was 19.5 inches. The 
femural shell was polypropylene plastic three-sixteenths of an inch thick 
while the tibial shell was one-eighth inch thick polypropylene. The shells 
were lined with one-quarter inch thick medium density aliplast. The bands 
and uprights were both made of 2024 aluminum alloy to provide light weight 
and strength. The bands ranged from one-eighth by three-quarters inch to 
one-eighth by one and one-half inch, depending upon the patient's size and 
activities, while the uprights were one-eighth by three-quarters of an 
inch. The joints were Becker 1009B aluminum polycentric knee joints, 
formed by machining to provide enhanced smoothness and tracking. Silver 
solder can be inserted into the joint gear to limit flexion to a 
prescribed range. The straps 78 and 79 were gum rubber reinforced by 
leather at the Velcro and Dacron at the copper rivet attachment points. 
The resulting stabilizer weighed 24-40 ounces and provided excellent 
movement and mobility. 
The combination of light weight, freedom of movement and stabilization 
provided by the above-described stabilizer 70 make it suitable for both 
preventive and remedial use. For light weight and preventive use, the 
thickness of the materials can be reduced, the shells can be drilled or 
extensive use made of apertures or other openings and the size of the 
solid anterior and posterior sections reduced. To give only one 
illustration of the value of such preventive use, in the National Football 
League, approximately 50 percent of injuries involve the knee. This means 
during the 1983 season perhaps five to seven of the fourteen lineman on 
each team will have suffered disabling knee injuries. This figure could be 
substantially reduced by the preventive use of an effective knee 
stabilizer. 
For remedial use to protect against further aggravation of existing 
injuries and instabilities, the thickness and other dimensions can be 
tailored as required by the orthotics specialists to fit individual needs. 
In addition, in applications requiring very great strength and stability, 
albeit at the sacrifice of slightly greater weight, a material such as 
stainless steel can be used for the band system. One potential use which 
might require this substitution is mountain climbing, where safety 
considerations are paramount and repair or replacement may not be 
available. Having thus described the knee stabilizer which embodies the 
principles of my invention, and specific examples of its use,