Joint Device

A loss of joint flexibility is experienced by individuals recovering from neuromuscular diseases, joint replacements, burns, and traumatic injuries such as bone fractures and tendon and ligament tears. In order to regain joint flexibility, it is helpful to flex or extend the joint in a repeated, controlled and quantifiable manner. It is also sometimes necessary to apply a relatively small force of a long duration or repeatedly.

Other individuals require partial immobilization to protect a traumatized joint. The partial immobilization ideally would allow the joint to move through a predetermined range of motion that is necessary for limited locomotion but not through a range of motion that is injurious to the joint, that further traumatizes the joint, or that causes pain to the individual.

Limb devices can be classified into four distinct types. One type is a "dynamic splint" in which an undirection force is applied to the joint to lengthen or shorten connective tissue. The force has typically been applied by a simple spring in the prior art. A second type of device is a brace which is used to stabilize an unstable joint. Braces may or may not include stops to limit the degree of joint flexion or extension. A third type of device is a "CPM" device or "continuous passive motion" device which applies a cyclical force to a joint for rehabilitation after procedures such as total joint replacement, joint surgery and severe burns. The cyclical force may be applied using a lead screw mechanism operated with a controller or other suitable mechanisms. A fourth type of device is an exercise device in which an undirectional force is applied to resist muscular contraction by the patient in order to increase the patient's strength in a given range of joint movement. Again, the force is typically produced by one or more springs. It is important in each of these devices that the apparatus accommodate the natural motion of the joint to ensure stability and biomechanical alignment and to prevent migration or chafing of the device on the limb. It is often the case that different devices are used on the same joint at different stages of treatment.

The major hinge joints of the limbs, namely the knee and elbow, are particularly difficult to brace and to flex effectively. This is because both the knee and elbow joints have unusual geometries. Rather than merely bending about a pivot axis, the joints are such that the lower limb pivots about a moving axis and also twists slightly. The moving axis effect can be appreciated by reference to FIG. 1, which shows in schematic form the bone structure of the knee joint. The lower femur 22 acts as a ball joint to receive the upper tibia 24. However, the ball of the lower femur is not truly spherical. Instead, it has a radius 26 that is shorter when the joint is bent as compared to a radius 28 when the joint is straightened. In addition, the ball is offset to the rear of the femur relative to the longitudinal axis of the femur. Therefore, the tibia 24 moves away from the longitudinal axis 31 of the femur 22 as the joint bends. This movement of the tibia away from the femur actually lengthens the leg as it bends. A similar process takes place at the elbow.

It can be appreciated from FIG. 1 that the tibia 24 not only moves away from the femur as the joint is bent, thereby increasing the radius of rotation, but also that the axis of rotation moves as the tibia 24 slides down the ball of the femur 22. Again, a similar process takes place at the elbow. The moving axis of rotation describes a curved line 32 which anatomists describe as an "evolute". For purposes of the present patent, an "evolute line" is defined as a curved line having a gradually decreasing radius of curvature along the line.

Another unusual aspect of the bending of a knee or elbow is that as the lower limb straightens relative to the upper limb, it simultaneously rotates along the lower limb axis. The tibia rotates so that the toes turn outward and the heels turn inward as the joint unbends. The tibia rotates in the opposite direction as the joint is bent so that the toes turn inward and the heels turn outward. Similarly, at the elbow, the radius and ulna rotate so that the palm turns downward as the elbow is unbent, and the radius and ulna rotate in the opposite directly so that the palm turns upward as the elbow is bent.

It can be appreciated that the combination of an upper limb ball that is offset from the upper limb longitudinal axis, an upper limb ball that is nonspherical, and a twisting action of the lower limb as it bends in relation to the upper limb, results in a complex movement. This complex movement has proven to be difficult to match in devices designed to brace or cyclically flex the joint.

Typical of the prior art are U.S. Pat. Nos. 4,508,111; 4,397,308; 4,485,808 and 4,538,600, all by Hepburn. These devices are designed to bias the direction in which the joint moves by stretching or increasing the available joint extension. In other words, they are dynamic splints in the terminology used herein. They generally comprise upper and lower struts which attach to the limbs of the desired joint using an appropriate attachment means. The upper and lower struts are pivotally attached to one another at the ends adjacent the joint. The pivotal attachment includes a cylindrical housing with a cam, wherein one of the struts is attached to the cam and the other bears on the cam surface through a bearing spring. Flexing or extending the joint causes a corresponding approximation or alignment of the struts relative to one another and a compression or expansion of the spring. The use of the spring allows a somewhat quantifiable and adjustable constant force to be applied to urge the flexing or extending of the joint. It can be appreciated that the devices in the Hepburn patents make no attempt to match the curved evolute line defined by the bending joint or to account for the rotation of the lower limb about its longitudinal axis as the joint bends.

Other prior art devices are in U.S. Pat. No. 4,489,718 by Martin; 4,372,298 by Lerman; 4,361,142 by Lewis; 4,487,200 by Feanny; 4,686,969 by Scott; 4,256,097 by Willis and 5,016,514 by Grood. These devices do not provide for the range of movement provided for in the present device. In addition, they generally do not include a mechanism to cyclically flex and extend the joint by application of a force in the manner of the dynamic splint embodiment of the present invention and as further described in U.S. application Ser. No. 07/495,044, of which the present is a continuation-in-part.

The present invention is a device capable of acting as a brace, a dynamic splint, a CPM device and an exercise device, depending upon a variety of modular attachments used with it. The device is configured to accommodate the bending of a lower limb with respect to an upper limb about a moving axis that describes an evolute line. The limb may be above and below a knee joint, elbow joint, wrist joint, ankle joint or any other joint that bends about an evolute line. It also is configured in one embodiment to allow the lower limb to twist - that is, to rotate about its longitudinal axis - as the lower limb bends relative to the upper limb.

The invention includes an upper strut for attachment to an upper limb, a lower strut for attachment to a lower limb, and a linking mechanism for attachment of the upper strut to the lower strut. The linking mechanism allows the pivoting between the upper strut and the lower strut to describe an evolute line to approximate the evolute line described by the bending of the lower limb relative to the upper limb.

The linkage producing the evolute line may be on both sides of the brace or may be on only the inside of the brace and not on the outside of the brace. In place of the linkage on the outside of the brace, there may be a ball and socket or other suitable connector that does not pivot along the evolute line. In this manner, the rotation axis of the lower strut in relation to the upper strut becomes skewed as the lower limb bends, thereby accommodating the natural twisting of the lower limb about its longitudinal axis as that bending occurs. In an alternative embodiment, the linkage may be on both the inside and outside of the brace, and the natural twisting of the lower limb is accommodated by a pin and slot arrangement connecting the lower strut to the lower limbs through an attachment mechanism.

The linkage between the upper and lower struts in a preferred embodiment includes an upper telescoping portion that telescopes into the upper strut and a lower telescoping portion that telescopes into the lower strut. The two telescoping portions are pivotally attached to one another at a pivot point. The lower strut is pivotally attached to the upper telescoping portion through a linkage arm connected at one end to the top of the lower strut and at the other end to a flange of the upper telescoping portion at a location between the joint and the pivotal attachment of the two telescoping portions. Similarly, the upper strut is pivotally attached to the lower telescoping portion through another linkage arm connected at one end to the bottom of the upper strut and at the other end to a flange of the lower telescoping portion at a location between the joint and the pivotal attachment of the two telescoping portions. The bending of the lower strut relative to the upper strut causes the two linkage arms to drive the struts out of the telescoping portions, thereby effectively lengthening the overall mechanism and describing an evolute line about which the lower strut rotates relative to the upper strut.

The invention can be used as a brace to limit the movement in the joint. As a brace, the invention serves to protect an injured or weakened joint against further injury or weakening by requiring the joint to bend only in the predetermined manner corresponding to the natural uninjured bending of the joint. Alternatively, the invention can be used in combination with a driving mechanism to cyclically flex and extend the joint in the same predetermined manner corresponding to the natural bending of the joint, in order to prevent swelling of the joint in the manner of a CPM device. As another alternative, the invention can be used in combination with a force-applying mechanism to apply a constant force urging the flexing or extension of the joint in the manner of a dynamic splint.

One embodiment of the invention includes a design for adjustably limiting the degree of limb extension in one or more ways. One way is the use of a releasable locking device to limit the limb extension to a preset amount. The limb extension is limited to the preset amount when the locking device is locked, and is not limited to the same preset amount when the locking device is released. Another way to adjustably limit the degree of limb extension is the use of varying sized stops against which the mechanism rides, as described in more detail below.

FIG. 1 shows a side elevational view of the lower femur and upper tibia bones where they meet at a knee joint, along with the evolute line described by the bending of the joint and a phantom view of the flexed tibia.

FIG. 2 shows a side elevational view of the present invention from inside a knee joint looking outward.

FIG. 3 shows a side elevational view of the invention from outside a knee joint looking inward.

FIG. 4 shows a side sectional view of the ball and socket connection of the invention.

FIG. 4A shows a sectional view, taken along line 4a--4a of FIG. 4 showing the ball and socket connection of the invention.

FIG. 5 shows a series of schematic drawings of the linkage of the invention in a preferred embodiment from a side elevational view.

FIG. 6 shows a plot of the path of a point on the device as the device bends through the motion shown in FIG. 5.

FIG. 7 shows a side elevational view of the present invention from inside a knee joint looking outward in combination with a cycling mechanism to cyclically flex and extend the joint.

FIG. 8 shows a side elevational view of the present invention from inside a knee joint looking outward in combination with a force-applying mechanism to apply a continuous force urging the flexing or extending of the joint.

FIG. 9 shows an end elevational view of the slot and pin arrangement for attaching a lower cuff to a lower strut in an alternate embodiment of the invention.

FIG. 10 shows a detail of the upper portion of the invention, showing an arrangement for urging the upper strut into or out of the upper telescoping portion.

FIGS. 11A through 11D show a preferred embodiment of a hinge mechanism in accordance with the invention.

FIG. 12 shows an exploded view of the hinge mechanism of FIGS. 11A through 11D assembled into a knee brace, in accordance with the invention.

A side elevational view of the invention 10 is shown in FIG. 2, viewed from the inside of the knee looking outward. The invention 10 includes a lower strut 14 which is attached to the lower leg of the patient through a lower cuff 18 which may extend partially or fully around the calf. The invention also includes an upper strut 26 which is attached to the upper leg of the patient through an upper cuff 28 extending partially or fully around the thigh. The cuffs are held in place on the leg by a suitable attachment device such as a strap with an adjustable buckle or VELCRO brand hook and loop fasteners (not shown).

The upper strut 26 and lower strut 14 are connected to one another through a connection mechanism 34. The connection mechanism 34 includes a lower telescoping portion 38 slidably attached to the lower strut 14 and an upper telescoping portion 42 slidably attached to the upper strut 26. The struts 14 and 26 may be cylindrical members and the telescoping portions 38 and 42 may be tubular members, so that the struts and telescoping portions telescope one inside the other. This allows the combined lower strut and lower telescoping portion to lengthen or shorten as they slide along a common longitudinal axis. Similarly, this allows the combined upper strut and upper telescoping portion to lengthen or shorten as they slide along a different common longitudinal axis. The ends of the upper telescoping portion 42 and lower telescoping portion 38 that are nearest to the joint are pivotally connected to one another by a telescoping portion pivot pin 48 extending through holes 46 and 50 in the telescoping portions. The struts and telescoping portions may be of a metal or plastic or other suitable material having adequate strength and capable of being fabricated to the desired dimensions.

Each telescoping portion 38 and 48 has a flange, 52 and 54, respectively, extending roughly perpendicular to the axis of the pivot pin 48 and toward the joint. The upper strut 26 is attached to the lower telescoping portion flange 52 by an upper strut linkage arm 58. One end of the upper strut linkage arm 58 is pivotally attached to the lower end of the upper strut 26 by an upper strut linkage arm upper pivot pin 62 which pivotally extends through the lower end of the upper strut 26 and through the upper end of the upper strut linkage arm 58. The other end of the upper strut linkage arm 58 is pivotally attached to the lower telescoping portion flange 52 by an upper strut linkage arm lower pivot pin 63 which pivotally extends through the lower end of the upper strut linkage arm 58 and the lower telescoping portion of flange 52. Similarly, the lower strut 14 is attached to the upper telescoping portion flange 54 by a lower strut linkage arm 66. One end of the lower strut linkage arm 66 is pivotally attached to the upper end of the lower strut 14 by a lower strut linkage arm lower pivot pin 72 which pivotally extends through the upper end of the lower strut 14 and through the lower end of the lower strut linkage arm 66. The other end of the lower strut linkage arm 66 is pivotally attached to the upper telescoping portion flange 54 by a lower strut linkage arm upper pivot pin 73 which pivotally extends through the upper end of the lower strut linkage arm 66 and the upper telescoping portion flange 54. The flanges may have stops (not shown) that prevent the struts from pivoting too far in one direction to cause hyperextension of the joint. The stops may be adjustable and may stop the rotation in a gradual manner with the use of a cushioning system such as a shock absorber, foam or a spring.

It can be appreciated from the drawings that the two linkage arm pivot pins 63 and 73 that extend through the two telescoping portion flanges 52 and 54, are located in different relative positions on the two telescoping flanges. Both pivot pins are located inside the angle defined by the pivoted upper and lower telescoping portions. However, the upper strut linkage arm lower pivot pin 63 extends through the lower telescoping portion flange 52 at a point that is roughly perpendicular (such as 80.degree. to 100.degree. ) to the axis of the upper strut 26 when the joint is unbent, so that the pin moves through an angle of about 0.degree. to 90.degree. as the tibia moves from being bent 90.degree. in relation to the femur to being in-line with the femur, the angle being measured from the telescoping portion pivot 48 and in relation to the axis of the upper strut 26. In contrast, the lower strut linkage arm upper pivot pin 73 extends through the upper telescoping portion flange 54 at a point that is roughly 45.degree. (such as 35.degree. to 55.degree.) from the axis of the upper strut 26 when the joint is unbent. At this position for the pivot pin, the pivot pin undergoes relatively little change in angular position in relation to the upper strut 26 as the joint flexes and extends. It has been found that this positioning of the pivot pins best approximates the evolute line of the bending joint. Of course, other positions may be desirable depending on changes in the structure of the device or use of the device in other applications.

The fact that this connecting mechanism between the upper strut 26 and lower strut 14 enables the struts to move relative to one another in a manner that closely approximates the evolute line described by the tibia as it moves relative to the femur, can be appreciated by the diagrammatic view of FIG. 5. The top drawing of FIG. 5 shows the device in a fully extended position to correspond to a fully extended leg. The lower strut 14 and upper strut 26 are approximately co-axial and the struts 14 and 26 are fully retracted into their respective telescoping portions 38 and 42. The lower drawings of FIG. 5 show the device progressively flexing to correspond to the progressively flexing of a leg. The vertical line 89 to the right of the series of drawings shows a given point on the upper strut 26. Also indicated in the drawings is the lower strut linkage arm pivot pin 72.

This series of drawings demonstrates the movement of the lower strut 14 in relation to the upper strut 26 as the knee gradually bends. One of the components of this movement is the gradual telescoping of the upper and lower struts 26 and 14 out of the upper and lower telescoping portions 42 and 38. This telescoping increases the overall length of the device as measured from the upper cuff 28 to the telescoping portion pivot pin 48 and from the telescoping portion pivot pin 48 to the lower cuff 18. The lengthening of the distance from the upper cuff to the telescoping portion pivot pin 48 is readily apparent by reference to the increasing distance between upper telescoping portion and the vertical line 89 connecting the same point on the upper strut 26 through the series of drawings.

Another component of this movement between the upper strut 26 and lower strut 14, which is really an aspect of the lengthening aspect described in the preceding paragraph, is the change in position of the lower strut linkage arm pivot pin 72. That pin is shown in the series of drawings of FIG. 5 and the movement of it is plotted in FIG. 6. It is apparent from these drawings that the pin describes an evolute line closely approximating the evolute line described by the movement of a tibia in relation to a femur or the movement of a radius and ulna in relation to a humerus.

It will be apparent to those skilled in the art that the mechanism described herein for approximating the evolute line described by the movement of a joint is not the only mechanism that will accomplish that purpose. For example, one could perhaps construct other devices that use cams, wedges, pulleys, gears or some other combination of mechanical, electrical or electromechanical elements. The important point is that, whatever the construction, the end product allows the movement between the upper and lower struts to approximate the evolute line describing the movement of the limb joints. It will be apparent to those skilled in the art that, although the invention is described primarily with reference to a knee joint, the same type of arrangement could be used on an elbow where the ulna and radius pivot and turn in relation to the humerus, or at the wrist where the radius and ulna form the concave receptive surface for the proximal row of convex carpal bones.

The other side of the invention 10, shown from the outside of the knee looking inward, is depicted in FIG. 3. The outside portion of the invention includes an outside lower strut 82 attached to the lower cuff 18 and an outside upper strut 84 attached to the upper cuff 28. In the preferred embodiment, the attachment of the outside lower strut 82 to the outside upper strut 84 is much simpler than the attachment of the lower strut 14 and upper strut 26 on the inside of the invention. Rather than including the telescoping portions included on the inside of the invention which allow the device to flex and extend along the evolute line of the bending knee, the attachment of the outside lower strut 82 and outside upper strut 84 is by a ball and socket. The upper end of the outside lower strut 82 is attached to a ball 86 and the lower end of the outside upper strut 84 is attached to a mating socket 88. The ball 86 and socket 88 mate with one another to thereby attach the outside lower strut 82 to the outside upper strut 84 in a manner that allows universal pivoting of the two struts about the ball and socket. In other words, each strut can move in any manner in relation to the other strut, provided that they remain pivotally connected at the point of the ball and socket.

A side sectional view of the ball and socket arrangement is shown in FIG. 4. The ball 86 is a spherical-shaped enlargement attached to the upper end of the outside lower strut 82. The socket 88 is attached to the lower end of the outside upper strut 84, and includes a void 101 defined by a ball seat 104, a wall 106 and a cap 108. The cap 108 preferably has an opening 109 to receive the upper end of the outside lower strut 82, as better shown in FIG. 4a. The opening 109 is oval shaped, with the long dimension of the oval in the vertical direction, so that there is a relatively large amount of play of the outside lower strut in the vertical direction and a relatively small amount of play in the horizontal direction. The cap 108 may be attached to the ball seat 104 through threads or an adhesive or other suitable arrangement. To assemble the device, the outside lower strut lower end is inserted through the opening 109 from the upper side of the opening and pushed all the way through the opening until the ball 86 rests against the top of the cap 108. The cap is then attached to the ball seat 104, thereby enclosing the ball 86 in the void 101 of the socket 88 while leaving the outside lower strut 82 free to move up and down considerably and side to side slightly through the opening 109.

Of course, it will be apparent to those skilled in the art that the ball and socket could be reversed so that the ball 86 is attached to the outside upper strut 84 and the socket 88 is attached to the outside lower strut 84. Also, universal movement between the outside upper and outside lower struts could be accomplished in ways other than through a ball and socket.

In operation, it can be appreciated that the device approximately matches the alignment of an extended joint. In that condition, the upper and lower struts 26 and 14 are retracted into the upper and lower telescoping portions 42 and 38 and the upper strut 26 is parallel to the lower strut 14. As the joint is flexed so that the tibia bends relative to the femur, the tibia slides over the eccentric ball of the femur to describe an evolute line. The corresponding movement of the lower strut 14 relative to the upper strut 26 on the inside of the device approximates this evolute line, as the upper and lower struts are driven out of the upper and lower telescoping portions 42 and 38 by the upper strut linkage arm 58 and the lower strut linkage arm 66.

At the same time, the outside of the device is restrained by the ball and socket so that there is no evolute movement of the outside lower strut 82 relative to the outside upper strut 84. The tracing of an evolute line by the lower strut 14 in relation to the upper strut 28 while no evolute line is traced by the movement of the outside lower strut 82 relative to the outside upper strut 84, causes a skewing of the axis of rotation. This accommodates the natural tendency of the tibia to twist as the joint bends to cause the toe to turn inward. The play in the ball 86 and socket 88 on the outer side of the device accommodates this twisting of the tibia and skewing of the axis of rotation by allowing a corresponding twisting of the outside lower strut 82.

The discussion above describes the use of the invention 10 as a brace, that is, a device to limit the movement of a joint to a predetermined range. Braces are useful in partially immobilizing an injured joint to prevent further injury so that the joint can heal while the patient makes limited use of it. Next described is the use of the invention 10 in combination with devices to apply a continuous force urging the continuous flexing or extension of the joint, or a device to cyclically flex and extend joint.

FIG. 7 shows a side elevational view of the invention in combination with a cycling mechanism 120, looking from the inside of the brace outward. FIG. 7 does not show the ball and socket connection on the outside of the knee, but it should be appreciated that such connection may be utilized. The cycling mechanism may be substantially the same as the cycling member described in application no. 07/495,044 of which this is a continuation-in-part and which is hereby incorporated by reference. Briefly, the cycling mechanism includes an extendable cable 212 having a fixed cable sleeve 216 enclosing an inner cable 222 which is rotatably but not slidably mounted in the cable sleeve 216. The inner cable 222 has threads 234 on the lower end which engage mating threads on a lower mounting bracket 238 which is attached to the lower cuff 18. The upper end of the inner cable 222 is attached to a drive means such as a motor 228 which is mounted on the upper cuff 28 and the upper end of the cable sleeve 216 is mounted to the upper cuff 28 through an upper mounting bracket 218.

In operation, the motor 228 is cycled back and forth to repeatedly rotate the inner cable 222 in one direction and then the other. The rotation of the inner cable 228 causes the inner cable threads 234 to thread in and out of the lower mounting bracket 238, thereby shortening and lengthening the distance between the upper mounting bracket 218 and the lower mounting bracket 238. The lengthening of the distance between the brackets causes a bending of the joint along the evolute line described by the connecting mechanism between the upper and lower struts 26 and 14, while a shortening of that distance causes an extension of the joint along that same evolute line. If the apparatus includes the ball and socket connection on the outside of the knee, then the bending of the joint will also accommodate the natural twisting of the tibia.

Other actuation devices are possible and potentially preferable. For example, an actuatable pneumatic cylinder or hydraulic cylinder may be used to repeatedly flex and extend the joint. Such an actuation arrangement is probably more compact and is mechanically simpler.

Shown in FIG. 8 is the use of the invention in combination with a continuous force-applying mechanism 340 which may be substantially the same as shown in application no. 07/550,256 of which this is a continuation-in-part and which is hereby incorporated by reference. Briefly, the force-applying mechanism 340 includes an expandable cylinder portion 350 with a lower shaft 338 and an upper shaft 339 that extends from the cylinder portion. The lower end of the lower shaft has a lower shaft ball 336 that mates with a socket 360 in a lower bracket 362 attached to the lower cuff 318. The top of the upper shaft 339 has an upper shaft ball 337 that mates with a socket 370 in an upper bracket 335 attached to the upper cuff 338. The upper shaft 339 can be slid in and out of the cylinder portion 350 to obtain a desired distance between the upper bracket and lower bracket corresponding to a desired degree of bending of the joint. Once appropriate length adjustment are made, a spring (not shown) inside the cylinder portion 50 applies a predetermined adjustable force urging the upper shaft 339 out of or into the cylinder portion 350, thereby urging the flexing or extension of the joint.

An alternate mechanism for applying a continuous force to the joint is shown in FIG. 9, which shows a detail of the upper portion of the invention where the upper strut 26 meets the upper telescoping portion 42. As shown in FIG. 9, a spring 510 is positioned on the upper strut 26. One end of the spring 510 is attached to or abuts against the upper end of the upper telescoping portion 42 and the other end is attached to or abuts against a stop 514 which is attached to the upper strut 26. In operation, the spring 510 is a compression spring which applies a force urging the upper strut 26 out of the upper telescoping portion 42, thereby lengthening the device to cause the joint to bend. Alternatively, the spring 510 may be a tension spring which applies a force urging the upper strut 26 into the upper telescoping portion 42, thereby shortening the device to cause the joint to unbend. Such springs may also be used in combination with hydraulic or pneumatic actuation cylinders. It will be apparent to those skilled in the art that a wide variety of other force-applying mechanisms are possible, both for applying continuous force and for applying cyclical force, such as pneumatic devices and hydraulic devices.

An alternate mechanism for accommodating the natural tendency of the lower limb to twist as it bends in relation to the upper limb is shown in FIG. 10. This mechanism may be used with an embodiment of the invention wherein there are linkage mechanisms on both the inside and outside of the limb, rather than a linkage mechanism on one side of the limb and a ball and socket mechanism on the other side of the limb. An advantage to having linkage mechanisms on both sides of the limb rather than having a linkage mechanism on one side and a ball and socket on the other, is that the device is then more rigid and better able to brace the limb against externally induced trauma.

The mechanism as shown in the view of FIG. 10 from the lower limb looking toward the joint, includes the lower strut 14 and the outside lower strut 82 attached to the lower cuff 18. The lower cuff 18 is slidably attached to an inner lower cuff 418 which, in turn, extends partially around and is attached to the lower limb through straps or other suitable means (not shown). As explained previously, the tibia tends to twist so that the toes turn inward as the knee joint bends. Therefore, the end view of FIG. 10 depicts the device on a partially bent left limb such as the left leg. The slidable attachment is accomplished through a slot 420 through the lower cuff 18 which receives a pin 426 attached to the inner lower cuff 418. This slidable attachment allows the inner lower cuff 418 to slide back and forth in relation to the lower cuff 18 in a plane roughly perpendicular to the longitudinal axis of the lower limb. In addition, the curvature of the lower cuff 420 accommodates the twisting of the lower limb by causing the inner lower cuff 418 to rotate slightly in relation to the lower cuff 18 as this sliding takes place. Ideally, this rotation is about the axis of rotation 430 of the lower limb, so that the inner lower cuff 418 moves through an angle B from the unrotated position to the rotated position.

Of course, the pin and slot arrangement described above would be reversed. In other words, the slot could be in the inner lower cuff 418 and the pin could be in the lower cuff 18. Other arrangements for sliding between the lower cuff 18 and inner lower cuff 418 will be apparent to those skilled in the art such as guide tracks or other suitable arrangements.

Exploded views of a preferred embodiment mechanism for producing the evolute movements described herein. FIG. 11A shows an upper strut 511 which mates with an upper telescoping portion 514 in the manner shown. The upper telescoping portion includes a barrel 518 to receive the upper strut 511 and a central flange 520 having a central opening 522 therethrough. Integral with the barrel 518 and extending over the flange 520 is the linkage arm bearing element 524. The flange 520 has a linkage arm pin 526 extending parallel to the axis of the hole 522.

The upper strut 511 has an upper strut linkage arm pin 530. Slot 532 extends through the upper strut 511 perpendicular to the longitudinal axis of the strut. The strut receives a locking key 534 which is sufficiently long to extend out of either one side or the other side of the slot 532. A hole 536 extends from the end of the upper strut opposite the end having the linkage arm pin 530 along the longitudinal axis to the slot 532. The hole receives a spring plunger 538 having a plunger tip 540 to bear against the locking key 534. The spring plunger 538 is threaded in place so that the plunger tip 540 bears against the slot key 534. A slot 519 is in the inner surface of the barrel 518 of the upper telescoping portion 514 to receive the locking key 534.

FIG. 11B shows the lower strut 550 positioned within the barrel 552 of lower telescoping portion 554. The assembly of FIG. 11B is shown upside down for clarity. The lower telescoping barrel 552 is connected to a lower telescoping portion flange 556, which includes a central hole 558 and a linkage arm pin 560. The lower strut 550 includes a pair of attachment holes 564 for attachment to a limb cuff in the manner described below. A pin 569 is on the barrel 554 of the lower telescoping portion 552.

A wedge-shaped stop 568 attaches to the face 570 of the lower telescoping portion barrel 554 where it meets the flange 556, by means of a screw 572 which extends through a hole 574 in the stop 568 and threads into a threaded hole 574 of the face 570 of the lower telescoping portion barrel 554.

An exploded view of the assembly of FIG. 11A and the assembly of FIG. 11B being attached to one another is shown in FIG. 11C. A post 580 extends into the central hole 522 (see FIG. 11A) of the flange 520 of the upper telescoping portion 514. A hub 582 prevents the post 580 from slipping out the hole 522. Similarly, the post 580 includes another hub 584 on the opposite end to prevent the post 580 from slipping out the hole 558 of the flange 556 of the lower telescoping portion 552.

A pair of linkage ms 602 and 604 positioned within the assembly as follows. The two linkage arms 602 and 604 each include a pair of holes 606 and 608, and 610 and 612, respectively. A hole 606 in the first linkage arm 602 receives the pin 560 on the flange 556 of the lower telescoping portion 552. The opposite hole 608 in the same linkage arm 602 receives the pin 530 on the upper telescoping portion strut 511. One hole 610 of the other linkage arm 604 receives the pin 569 on the lower strut 550, and the other hole 612 on the same linkage arm 604 receives the pin 526 on the flange 520 of the upper telescoping portion 514.

The elements of FIG. 11A and FIG. 11B, shown assembled, are depicted in FIG. 11D. In addition, each side of the assembly is covered and retained by retaining plates 620 and 622, by screws 624 extending through the cover plates 620 and 622 and into the barrel 518 and 554 of the telescoping portions 514 and 552. Screws 630 and 632 may be used to further stabilize the assembly by extending through holes 634 and 636, respectively, the cover plates 620 and 622 and into the post 580.

An assembly drawing of an entire device is shown in FIG. 12. The embodiment of FIG. 12 utilizes two hinge assemblies 710 of the type shown in FIGS. 11A through 11B. One assembly 710 is attached to an upper cuff 714 by a set of attachment fasteners 716 extending through the upper cuff 714 and through the holes 542 in the upper strut 511. The assembly 710 similarly attaches to a lower cuff 720 via a set of attachment fasteners 722 extending through the lower cuff 720 into the holes 564 of the lower strut 550. Similarly, the other assembly 710 attaches to the other side of the lower cuff 720 via a pair of attachment fasteners 728 extending through the lower cuff 720 and into the holes 564 of the lower strut 550. Positioned between the lower strut 550 of this particular assembly 710 and the lower cuff 720 is a spacer 730 having a flange 732 with a hole 734 therethrough.

The upper strut 511 of this assembly 710 is attached to the upper cuff 714 via attachment fasteners 736 which extend through the upper cuff 714 and the holes 542 of the upper strut 511. A spacer 740 is provided between the upper strut 511 and the upper cuff 714 to account for the space produced by the lower spacer 730 described above.

A pneumatic cylinder 760 having a housing 762 and a plunger 764 with a housing attachment hole 766 on the housing end and a plunger attachment hole 768 on the plunger end is attached to the rest of the assembly. The attachment is accomplished by attaching the plunger 764 to the upper strut 511 of one of the hinge assemblies 710 via one of the attachment fasteners 736 that extend from the upper cuff 714, through the upper spacer 740 and through the holes 542 of the upper strut 511. A pneumatic cylinder spacer 770 is provided between the pneumatic cylinder plunger 764 and the upper strut 511 of the hinge assembly 710 in order to off-set the pneumatic cylinder 760 from the hinge assembly 710. The housing 762 end of the pneumatic cylinder 760 is attached to the flange 732 of the lower spacer 730 via a fastener 774 which extends through the hole 766 in the housing 760 and through the hole 734 in the flange 732 of the spacer 730. A lower pneumatic gas cylinder spacer 776 is provided between the gas cylinder housing 762 and the lower spacer 730 to account for the spacing provided by the upper spacer 770.

In operation, it can be appreciated that force of the pneumatic cylinder 760 urges the upper cuff 714 and lower cuff 720 apart, that is toward limb extension. Such urging provides a constant and quantifiably adjustable force to assist in rehabilitation therapy. The force results in an extension about an evolute line in the manner described in detail above and in accordance with anatomical requirements.

Moreover, the extent of the extension can be adjustably limited. At one extreme, full extension is possible, by omitting any stop 568 (see FIG. 11B) and positioning the lock key 534 so that it extends into the slot 519 of the upper telescoping portion barrel 518 (see FIG. 11A). In that event, there is nothing to prevent the upper strut 511 and lower strut 550 from coming parallel to allow full extent or even overextension depending upon the dimensions and geometry chosen for the components.

Something less than full extension can be achieved by adding a stop 568 (see FIG. 11B) to the face 570 of the lower telescoping portion barrel 554. In that event, the upper strut 511 and lower strut 550 will extend only until the face 523 (see FIG. 11A) on the barrel 518 of the upper telescoping portion 514 contacts the stop 568 mounted on the face 570 of the barrel 554 of the lower telescoping portion 552. The thickness of the stops 568 can be chosen from an array of different thicknesses in order to closely control the amount of extension.

Another approach to limiting the amount of extension is by activation of the lock key 534 (see FIG. 11A). Activation is accomplished by sliding the lock key 534 out of the slot 519 of the barrel 518 of the upper telescoping portion 514. By doing so, the lock key 534 no longer slides through that slot 519, but instead is restrained by the other side of the barrel 518 which does not include an accommodating slot. Depending on the precise positioning of the slot 532 of the upper strut 511 in relation to the terminus of the barrel 518 of the upper telescoping portion 514, activating the lock key 534 in this manner limits the amount of extension to a predetermined maximum. The predetermined maximum depends upon the dimensions and geometry chosen for the elements, but it has been found that extension that results in roughly a 90.degree. angle between the upper strut 511 and lower strut 550 is convenient in rehabilitation therapy. The lock is easily releasable, by simply shifting the lock key 534 through the slot 532 so that it once again extends out the opposite side of the upper strut 511 to be received by the slot 519 of the barrel 518 in the upper telescoping portion 514.

It can be appreciated that the lock has another function as well, in preloading the pneumatic cylinder 760 (or a corresponding spring) or to act as an on-off button in usage.

The description in the paragraphs immediately above describe a device for extending the joint. The same device can be used for flexion as well, by reversing the direction of the force applied by the pneumatic cylinder so that it draws the struts together rather than urging them apart. A single device can be used for both flexion and extension by using a pneumatic or hydraulic cylinder in which the direction of force is reversible, or by the addition of a second cylinder between the spacer 770 and the assembly 710.