Polycentric variable axis hinge

A polycentric variable axis pivotal hinge system especially designed and adaptable to follow the complex movement of the knee when incorporated in orthotic devices, having an upper and a lower extension overlying a central linking member and pivotally connected thereto wherein each extension moves in a relative angular motion determined by the coaction of a guide pin follower slidably and pivotally interacting with slots in the angular terminal portions of the extensions and the guide pin follower moving in a vertical slot in the central member; with provision for motion limiting stops.

FIELD OF THE INVENTION 
This invention relates to a new improved polycentric variable axis hinge. 
More particularly, this invention relates to a hinge having improved 
extension and flexion movement, which is especially useful when 
incorporated as the pivotal system in the design of orthotic devices. Of 
special utility is the use of the novel polycentric variable axis hinge in 
hinged knee-joint supports or more involved functional knee braces. 
BACKGROUND AND PRIOR ART 
Knee braces are known in the prior art. The movement of the knee joint is 
limited in certain cases, but in almost every instance the braced knee is 
permitted some movement. The knee-joint is made up of two condyloid joints 
and a third joint, partly arthrodial, but not completely, since the 
articular surfaces are not mutually adapted to each other. The resulting 
movement is not a simple gliding motion. The principle movements that take 
place at the knee joint are flexion and extension. 
The movements of flexion and extension at this joint differ from those in a 
typical hinged joint, such as the elbow or hip. The axis around which 
motion takes place in the knee joint is not fixed, but the axis shifts 
forward during extension, as the gliding movement is superimposed on the 
rolling motion and the axis shifts backward during flexion. 
Although the knee joint has been described as a hinged joint in the prior 
literature; it has a more complicated character. The knee joint must be 
regarded as consisting of three articulations, of two different kinds. The 
first is a condyloid articulation; in this form of the joint, an ovoid 
articular surface, or condyle, is received into an elliptical cavity in 
such a manner as to permit flexion, extension, abduction, adduction, and 
circumduction, but no axial rotation. The second kind of articulation 
involved is arthrodial; this is a joint which permits only gliding 
movement. It is formed by the apposition of plane surfaces, or one 
slightly concave, the other slightly convex. The amount of motion between 
these surfaces is limited by the ligaments or osseous processes 
surrounding the articulation. 
When damage or injury occurs to the knee joint some form of suitable 
bracing is required. Associated with the bracing, in order to permit 
movement, as flexion and extension of the knee joint, there is a hinged 
structure pivotal about the knee joint. 
Previous known knee braces and protective devices contain simple hinged 
structures or more recently a biaxial hinge. All of the previously 
designed hinges attempted to parallel the complex movement of the knee 
joint. Some knee braces for support and protection of the knee joint 
incorporate both an inner and an outer bracing structure. 
Anderson, U.S. Pat. No. 4,249,524, discloses a true biaxial or double 
hinged pivotal brace and knee stabilizer. McDavid, U.S. Pat. No. 
3,528,412, describes a brace with a fixed single pivot hinge. Rigdon, U.S. 
Pat. No. 4,219,892, discloses a knee brace having an accordian-folded 
section filled with fluid and held together with tension straps. 
French Patent Application No. 79-10960 discloses a "link" hinge. The 
intermediate link has a longitudinal slot, the slot allows one of the 
uprights to move only in the direction of the longitudinal axis. The other 
end of the link has a fixed pivot to which is connected the other upright 
or brace extension. Canadian Pat. No. 1,011,204 relates to a knee brace 
with a dual planer link element between the elongated upper and lower arms 
of the brace. The arm and connecting link are essentially planer and are 
limited in pivotal motion to the plane of the link element and the front 
and back stops of the link element has an upper and lower pivot points 
spaced apart by a distance range of about 3/4 of an inch to about 2 
inches. 
Frank, U.S. Pat. No. 4,340,041, relates to an articulate splint having 
upper and lower anchor bars connected to a lock plate. The lock plate 
contains a hinge means. The hinge means in the lock plate has a single 
pivotal axis. Taylor, U.S. Pat. No. 3,902,482, describes a mechanical 
joint for orthopedic braces or prosthesis. The joint has an upper and 
lower portion attached by a link. Each portion has dual bearings which 
combine to provide a pivotal movement closely simulating the flexing 
action of a knee. 
Meany, U.S. Pat. No. 2,460,895, relates to a joint protector having a 
longitudinally movable hinged joint; one fixed pivotal end, and one 
pivotal and longitudinally sliding connection. Goodwin, U.S. Pat. No. 
58,403, relates to a surgical splint with a movable hinge having a 
set-screw moving in a slot and a single fixed pivot. Barry, U.S. Pat. No. 
1,374,177, relates to an orthopedic appliance having a free pivotal 
connection and a means for fixing the connection so as to form a rigid 
structure. There is no provision for movement. 
Rossman, U.S. Pat. No. 3,581,741, relates to a partially leg encircling 
knee brace with a hinge means on the upper inside body portion which 
includes a single rivet and a single pivot pin or rivet connecting a bar 
between the upper hinge and the lower body portion of the brace. Clegg, 
U.S. Pat. No. 901,592, relates to bracing device with a single pivot in 
conjunction with slide button in the slot which together allow vertical 
movement as well as single point pivot. Peckham, U.S. Pat. No. 2,467,907, 
describes a knee brace having springs pivotally attached top and bottom to 
two centrally disposed shaped plates on the inside and outside of the knee 
joint. In effect each pivot point is a rotary pivot at a single point. 
Peckham, U.S. Pat. No. 3,194,233, relates to a corrective and protective 
knee brace which has a pair of curved pressure members on opposite sides 
of the knee joint. The curved pressure members contain hinge joints which 
are made up of conventional hinge parts. 
McClure, U.S. Pat. No. 3,350,719, relates to a knee brace having an upper 
bar and a lower bar which are pivotally joined with a hinge arrangement. 
The hinge in McClure is a link bar with an upper pivot pin and a lower 
pivot pin. The pivot pin provides a double conventional pivoting hinge 
joint connecting the upper brace bar and the lower brace bar through the 
link bar. 
Each of the prior art hinges associated with the knee braces or protective 
devices, includes a simple pivoting hinge, either alone as a single pivot 
point or a pair of single pivot points spaced apart or in close proximity. 
All of the prior braces attempt to provide a hinge device to emulate and 
move parallel to the complex movement of the knee joint. Some braces are 
in place when the leg is extended, but fail to accurately follow the knee 
motion when flexed. 
SUMMARY OF THE INVENTION 
A principle object of this invention is to provide a new variable axis 
pivotal joint system for use in knee braces, protective devices and other 
similar orthotic devices so constructed to accurately follow the complex 
movement of the knee joint and similar human and animal body joints. 
Another object of the invention is to provide a polycentric variable axis 
pivotal joint system which can be adjusted to control extension and 
flexion to accommodate symptomatic or rehabilative instabilities. 
A further object is the provision of a polycentric variable axis pivotal 
joint system which is constructed to allow only pivotal movement and not 
lateral movement of the hinged body joint. 
Other important objects and purposes of the instant invention will be 
disclosed and apparent in the following detailed description and the 
specification and the drawings to which reference is made.

DESCRIPTION OF THE INVENTION 
With reference to the drawings, FIGS. 1-4, the polycentric variable axis 
pivotal hinge of the present invention comprises an upper extension 1 and 
a lower extension 2 secured together by the variable axis hinge. Each 
extension has a complementary angular offset to keep the extensions in 
parallel, offset planes and yet incorporate the hinge. 
As best illustrated in FIG. 4, it will be seen that the upper extension 1 
is angularly offset at its upper portion 11 and maintains this offset 
configuration down to a point just before the hinge as indicated at 15. A 
similar complementary configuration is indicated for the lower extension 2 
at 12 and 14. Angular interconnecting means 17 and 18 displace the hinge 
outward from the body joint and each secures a portion of the hinge at 20 
and 21. 
The polycentric variable axis hinge is made up of a central member 30, 
which is substantially a flat oval or semicircular or elliptical flat 
disk-like plate, having an inside surface and an outside surface, and an 
upper end and a lower end. Said central member is interiorly disposed in 
an overlying relationship with respect to each lower terminal ends 31 and 
32 of the upper extension 1 and the lower extension 2, respectively. The 
central member 30 is provided with three equally spaced openings: two 
outer openings along the same axis are holes 41 and 42, one on the upper 
end and one on the lower end, and a central opening 43 which is an 
elongated slot equally spaced between the outer openings 41 and 42 
perpendicular to the axis on which the outer openings lie. 
In the terminal ends 31 and 32 of the upper extension 1 and lower extension 
2 each are provided with a short horizontal slot, 22 and 23, opening 
parallel to the central axis of the angle of offset from the main 
extensions 11 and 12. The offset of the terminal ends is angular to the 
longitudinal axis of the extension. Also provided is an annular opening in 
each of the terminal ends 31 and 32 at 20 and 21 spaced from the 
horizontal slots 22 and 23 and on the same axis as the horizontal slots 22 
and 23. 
The central member 30 is interiorly interposed between the lower terminal 
ends 31 and 32, such that an upper pivot rivet-pin 44 can extend through 
the mating opening 21 in the lower terminal end 31 and through the mating 
opening 41 in the central member and is terminated on the outside surface 
of the central member by a terminating means, such rivet-pins. In a 
similar manner a pivot pin 45 extends through the mating opening 20 in the 
lower terminal end 32 and through the mating opening 42 in the central 
member and is terminated on the inside surface of the central member. 
The pivot pins 44 and 45 provide a means for pivotally connecting the upper 
extension 1 and the lower extension 2 to the central member. A guide pin 
follower 50 extends pivotally and glidably through the slot 23 in the 
lower terminal end 31 of upper extension 1, through vertical slot 43 in 
the central member 30 and through slot 22 in the lower terminal end 32 of 
lower extension 2. The terminal ends 31 and 32 in which the slots 22 and 
23 are located are angled toward the full extension configuration. As 
shown in FIG. 1. At this extended position the guide pin follower is at 
the top of the slot 43 in the central member. The upper extension 1 and 
lower extension 2 are longitudinally aligned with each other and with the 
central member. The top of the vertical slot 43 in the extended position 
acts as a stop when the guide pin follower 50 engages the top of the slot, 
in this way further rotation which results in hyperextension is prevented. 
The pivotal movements of the upper and lower extensions are limited, so 
that when they have rotated in a longitudinally aligned position 
simulating the thigh and calf of the leg when they are aligned in standing 
position. However, pivotal movement of the upper and lower extension 1 and 
2 in the opposite direction is limited only by the flexural limits of the 
knee joint. 
By having a common guide pin follower 50 coacting with the central member 
30 and interactive pivots at 20 and 21, which also coact with the central 
member, there is provided in essence a triaxial hinge. Such a triaxial 
hinge more naturally follows the complex movement of the human knee. The 
variable axis hinge action provided when the instant hinge is incorporated 
into a knee brace in which the upper and lower extensions are 
approximately laterally aligned with the pivotal portions of end of the 
femur and the end of the tibia, respectively, affords a very accurate 
approximation of the true knee action. Thus, in this hinge, the upper 
extension 1 simulates the action of the femur and the lower extension 2 
simulates the action of the tibia. The central member 30 spans the joint 
space and is connected to each extension 1 and 2 by one individual pivot 
pin each 44 and 45, and one common guide pin follower 50 in order to 
simulate the complex pivotal hinge action of the knee. 
In its operation and movement from extension to flexion the hinge displays 
a variable axis with continuously changing central pivot point as the 
guide pin follower 50 moves within the slot 43 in the center member 30. 
The slot 43 acts as a guide means for receiving and cooperating with the 
guide pin follower 50. The movement of the hinge defines the extension and 
flexion of the extensions 1 and 2. Said guide pin follower causes the 
motion to be transmitted to angular rotation and pivot about each of the 
extensions 1 and 2. The pivotal action for each extension is centered on 
the axis of the pivot points 20 and 21. The slot in each angular terminal 
portion of the extensions permits the angular motion to follow the 
horizontal movement of the guide pin follower. Each extension moves in a 
relative angular movement determined by the coaction of the guide pin 
follower interacting with the slots in the angular terminal portions of 
the extensions and the guide pin follower moving in the horizontal slot in 
the central member. In the central member the spatial placement of the 
pivot points are spaced apart and equidistant from the central vertical 
slot, which is perpendicular to the longitudinal axis of the pivot points 
41 and 42. 
Bushing members formed separately from the pivot or pin are used in the 
hinge to cooperate with the pivot or pin and further assist in the ease of 
movement of the various members of the instant hinge. Since the movement 
and relative ease of movement is important for the successful acceptance 
of the device by potential users. Alternative, to the use of bushings for 
the pivot pins is the use of washers or gaskets placed between the pivot 
pin head or terminal portion and the surface immediately registerable with 
said pivot pin or rivet head or terminal portion. Also bushings or washers 
maybe placed between registerable surfaces, as between the extension 
terminal portion and the central member. 
A series of spaced holes 61-68 are provided in the central member 30 for 
insertion or adaption of bumpers or stops or limit the extent of pivot 
movement. Hence the bumpers or stops are adapted to engage the lower 
terminal ends 31 and 32 of the upper and lower extensions and prevent the 
further movement of the extensions. Hyperextension and excessive flexion 
by the knee is prevented by use of said bumpers or stops placed in holes 
61 through 68. The bumpers or stops may be set screws or the like placed 
in threaded holes. Thus, the hinge imposes no vertical axial restraint 
unless said bumper or stop is in place. The only other restraint is the 
guide pin follower 50 within the slot 43 as described above, when the 
guide pin 50 engages the top extreme of the slot 43. The hinge imposes 
restraint in compression, and no stress when the knee is flexed. 
The present polycentric variable axis hinge is very compact and light in 
weight. It may be made of a light metal or alloy, or it may be made of a 
rigid plastic material. 
Preferably, the material of construction is stainless steel. The upper and 
lower extensions may be covered or placed in a soft resilient 
covering--woven, knitted or one or two way stretch fabric, sponge rubber 
or similar resilient material sleeves and secured therein by stitching or 
adhesive or both. These features adapt the hinge to comfort of the user. 
For certain other uses the extensions may be embedded in plastic or 
plaster of Paris for fitting to the users leg or the like. 
It will be apparent to those skilled in this art that various changes may 
be made in the invention without departing from the spirit and scope 
thereof, and therefore the invention is not limited by that which is shown 
in the drawings and described in the specification, but only as indicated 
and defined in the appended claims.