ARTIFICIAL TOGGLE JOINT

Abstract: An artificial knee-joint provided with linkage mechanisms, where a thight part (C) and a lower-leg part (D) are mutually connected by two base linkage arms (A, B), each of which is pivotally connected at respective ends with both the lower-leg part (D) and the thigh part (C), wherein the pivotal attachment points (9, 11) of the lower-leg part (D) are disposed in moveable attachment elements (4, 5) which mutually coact in a manner such that the knee-joint will automatically either adopt a substantially locked or a moveable position, depending on the direction of the load acting on the knee-joint. The first attachment element (4) is pivotally connected to the two base linkage arms (A, B) extending from the thigh part and has three pivot points, whereas the second attachment element has two pivot points. The other base linkage arm (B) extending from the thigh part is pivotally connected to both attachment elements (4, 5). Furthermore, the second attachment element (5) is provided with a lock-stop device (13) which limits movement of the attachment element. When walking, the movement of the attachment elements contribute to automatically locking the knee-joint and to terminate a walking step in a natural fashion.

Description: ARTIFICIAL TOGGLE JOINT The present invention relates to an artificial knee- joint according to the preamble of Claim 1. The gait of a thigh amputee is considerably different to that of the gait of a normal healthy person, due to the absence of important muscle groups. Because of the loss of the knee muscles, the amputee can no longer bend and then again actively stretch the knee-joint under load. In the case of earlier knee-joint pros¬ thesis using various types of braking mechanisms, the prevention of leg collapse in the supporting phase, i.e. that period in which the foot is in contact with the ground or like surface, has only been achieved with a greater or lesser degree of security. Thus, differing degrees of supporting-phase stability have been achiev¬ ed. The prothestetic leg is fitted to the amputee with the knee straight, and the knee then remains straight during a major part of the supporting phase. If the knee-joint mechanism is very stable, it is not possible to bend the knee until the supporting phase is ter¬ minated. This impossibility of bending the knee at the beginning and the end of the supporting phase means that the amputee must consume more energy when walking. The absence of calf muscles also means that the gait of the person wearing the prosthesis is more energy de¬ manding than the gait of a normal person. The present artificial knee-joint is constructed to imitate the working mode of the human knee-joint, so that the amputee is able to walk with a natural gait. The knee-joint can be said to be a further development of the existing quadruple-joint polycentric type of joint. By polycentric joint is meant here that the rotational centre has different positions at different knee-joint angles, i.e. there are several pivot cen¬ tres. The human knee-joint is also polycentric. By polycentrical quadruple-jointed knee is meant a knee in which the thigh part and the lower-leg part are mutu¬ ally joined by two linkage mechanisms, each being pivo¬ tally connected at its respective ends to the thigh part and the lower-leg part. This results in four pivot points. Quadruple joint mechanisms are now the most common joints available. However, in order to achieve high supporting-'phase stability, it is necessary to supplement these mechanisms with some form of mechani¬ cal/hydraulic lock or brake device. The earlier known technical solutions generally cause the knee-joint to become highly complex and undesirably heavy. Described and illustrated in U.S. Patent Specification No. 2,638,605 is a knee-joint which comprises linkage mechanisms in which locking is effected by means of a catch with the knee straight, this catch being released by means of a linkage mechanism which transmits move¬ ment of the toe-part to the knee-joint. In addition to being highly complicated, a serious drawback is that the knee-joint is apparently too heavy for practical use and results in an unnatural termination of a walk¬ ing step. The object of the present invention is to provide an improved polycentric knee-joint which has high supporting-phase stability, which is light in weight and with which locking of the knee-joint is effected automatically in a simple fashion as a result of the construction and design of the knee-joint, and also to eliminate the drawbacks encountered with earlier known techniques. These objects are achieved by means of the invention, in that the artificial knee-joint mentioned in the introduction is constructed in the manner de¬ fined in the characterizing clause of Claim 1. The inventive knee-joint is a polycentric joint and in¬ cludes a linkage mechanism consisting of a plurality of linkage arms of varying lengths which are mutually arranged to achieve high supporting-phase stability and a simple, automatic locking function. This locking function is effective solely in an extended position and solely when load is exerted on the heel. When the foot rolls over onto the forward part, as the wearer of the prosthesis walks, the locking mechanism is released automatically. This means that the locking mechanism will not prevent natural termination or completion of a walking step. The invention will now be described in more detail with reference to the accompany drawings, in which Figure 1 illustrates schematically a preferred embodi¬ ment of the invention; Figure 2 illustrates different angular positions of the embodiment shown in Figure 1 in a normal course of movement; Figure 3 illustrates another working method of the embodiment illustrated in Figure 1, which allows different angular positions with bending up to 180 degrees; and Figure 4 illustrates the embodiment in a skiing, ice- skating or dancing position. The knee-joint illustrated in Figures 1-4 comprises linkage mechanisms which include two base link-arms and seven pivot points. A thigh part C has two pivoted attachment points 1, 2 mounted on the underside of a cup-shaped structure 3, which is intended to be secured to the thigh in a conventional fashion. Two base arms A, B extend respectively from the aforesaid attachment ponts 1, 2 to attachment elements 4, 5 on the lower leg. A lower-leg part D is constructed around an elongated part 6, which is constructed to carry an artificial foot 7 at its lower end and to carry a first attach¬ ment element 4 at its upper end. A second attachment element 5 is mounted on the rear side of the elongated part 6, preferably within the range of from one to three-quarters of the length of the lower leg. These attachment elements 4, 5 are intended to receive the two base arms A, B extending from the cup-shaped part 3. The attachment elements 4, 5 can also be considered as a form of moveable linkage mechanisms or rocker means. The first attachment element 4 mounted on the upper end of the lower-leg part D can be described as a linkage mechanism having a slightly curved V-shape with three pivot points 8, 9, 10, of which the pivot point 9 is mounted or located between the other pivot points and is connected to the elongated part 6 of the lower leg. The first attachment element 4 functions as an attachment means for the base arms A, B and also as a balance-holding device whose movement is contingent on the movement of the centre of gravity of the person's body. The pivot point 9 is the point around which the first attachment element moves. The base arms A, B, which extend from the thigh part, are connected to the two pivot points 8, 10. These two pivot points 8, 10, together with the two pivot points 1, 2 at the thigh part at the ends of the first attachment element 4, can be said to form the 1, polycentric part" and the distance of these pivot points from one another is configured and dimensioned in accordance with the quadruple-pivot polycentric joint type. The other attachment element 5, which is mounted ap¬ proximately centrally on the elongated part 6, can be described as a linkage mechanism, rocker means or locking joint which has two pivot points 11, 12, of which the first pivot point 11 is connected with the elongated part 6 and the second pivot point 12 is connected with the rear base-part B, which extends from the thigh part C and has a curved extension on the rear side of the lower-leg part D. Arranged in the region around the second attachment element 5 is an adjustable mechanical lock-stop device 13 which has approximately the same longitudinal extension as the attachment element 5 and which is removable from the lower-leg part. The lock ' -stop device 13 is normally attached to the front part of the elongated part 6 and limits the movement of the attachment element 5. The lock-stop device 13 is arranged in a manner to normally provide a distinct limitation of the forward movement of the attachment element 5 and is therefore manufactured from a rigid material, preferably metal. In order to provide a certain degree of resiliency or elasticity at the movement limit position, the stop 13 may be made of a metallic material which is covered with an elastic or resilient material, or the stop and/or parts coacting therewith may alternatively be made of a material which provides a corresponding function. The knee-joint functions in the following manner. When load is exerted on the heel, in which case the knee- joint is substantially straight, the first attachment element 4 will move clockwise around the pivot point 9 and force the second attachment element 5 to move towards the lock-stop device 13. As long as weight is exerted on the heel, it is impossible for the second attachment element 5 to open and move clockwise, even if considerable forces attempt to bend the joint. On the contrary, the locking effect is amplified instead. Because of the elasticity or resiliency of the lock- stop device, the gait of the person wearing the prosth¬ esis will be highly similar to the gait of a normal person in setting the heel onto the ground, with subse¬ quent locking of the knee-joint. When walking with the knee locked, the attachment element 5 may also have a given degree of resiliency against the lock-stop device 13, thereby enabling the joint to bend slightly in its locked state, which also contributes to a more natural gait. When exerting load on the forward part of the foot, the first attachment element 4 will rock over in an anti¬ clockwise direction. Thus, when the knee-joint is subjected to bending forces, the second attachment element 5 is able to open freely and the leg is able to swing quite freely. This takes place when it is natural to terminate or complete a walking step. The realization that a polycentric joint can be ad¬ vantageously constructed with moveable attachment elements 4, 5 on the lower leg 6 has made it possible to construct the aforedescribed knee-joint with its embodied locking function which will not prevent termination of a walking step but will assist in enabl¬ ing the transition between the locking positions and the moveable positions of the knee-joint to take place automatically. Figure 2 illustrates a normal movement pattern of the knee-joint and shows the knee-joint in three different positions. In the first position, the leg is shown fully extended, whereas in the second position, the knee-joint is in a half-bent position and, finally , passes to a fully-bent position corresponding to an angle of approximately 150 degrees. Figure 3 illustrates a movement pattern which includes a bend of 180 degrees. In this case, the lock-stop device is removed and the second attachment element 5 moves in an opposite direction compared with the normal movement. The drawback with this movement pattern is that when the knee-joint is in a half-bent position the lower leg will be located more forwardly than in a corresponding position with a normal movement pattern. In turn, this results in a smaller lever-arm for the thigh when walking upstairs and when cycling. This state of the knee-joint is intended, however, for use when wishing to fully bend the leg. Figure 4 illustrates a state in which the lock-stop device 13 is displaced from the position shown in the earlier Figures. In this case, the leg can be swung freely until the user places the heel on the ground and the locking function therewith becomes operative. The advantage afforded hereby is that the user is able to participate in such activities as dancing and athletic training. The aforedescribed knee-joint is primarily constructed for children and with view to their great need to be mobile, although the knee-joint is, of course, also well suited for adults. Because of its particular construction, the knee-joint is well suited for manu¬ facture from some form of composite material. It is also stable and light in weight and has a wide angular range within which the knee-joint can be bent. In a normal case, the knee-joint can be bent through about 150 degrees, and in the case of a special design can be bent through about 180 degrees. It includes a simple, automatic locking function which does not prevent natural completion of a walking step and the locking effect is fully geometrical, so that in principle, there are no parts which can become worn. Furthermore, the knee-joint is locked only in the extended position of the joint and only when the heel of the foot is subjected to load. Since the described and illustrated embodiments of the inventive knee-joint are meant solely to illustrate the inventive concept, it will be understood that the invention is not limited to these embodiments but can embrace all knee-joints which lie within the scope of the following Claims.

Claims: CLAIMS 1. An artificial knee-joint comprising linkage mecha¬ nisms in which a thigh part (C) and a lower-leg part (D) are connected to a front and a back base linkage- arm (A, B), each of which is pivotally connected at its respective ends with both said lower-leg part and said thigh part, c h a r a c t e r i z e d in that the pivotal attachment points (9, 11) of the lower-leg part (D) are arranged in moveable attachment elements (4, 5) which when the knee-joint is substantially straight coacts in a manner such that the knee-joint will auto¬ matically either take a substantially locked or a move¬ able position, depending on the direction of the load on the knee-joint, wherein the first attachment element (4) has three pivot points and the second attachment element (5) has two pivot points. 2. A knee-joint according to Claim 1, c h a r a c - t e r i z e d in that the first attachment element (4) is pivotally connected to the two base linkage arms (A, B) extending from the thigh part. 3. A knee-joint according to Claim 1, c h a r a c - t e r i z e d in that the second base linkage arm (B) extending from the thigh part is pivotally connected to both attachment elements (4, 5). 4. A knee-joint according to any one of the preceding Claims, c h a r a c t e r i z e d in that movement of the second attachment element (5) is restricted by a lock-stop device (13). 5. A knee-joint according to Claim 4, c h a r a c ¬ t e r i z e d in that the lock-stop device (13) is intended to limit forward movement of the second at¬ tachment . element (5) and of the lower part of the second base linkage arm (B) when the knee-joint is substantially straight. 6. A knee-joint according to Claim 4 or 5, c h a r ¬ a c t e r i z e d in that the lock-stop device (13) is positionally adjustable. 7. A knee-joint according to any one of Claims 4 to 6, c h a r a c t e r i z e d in that the lock-stop device (13) is constructed in a manner to resiliently limit said movement. 8. An artificial knee-joint c h a r a c t e r i z e d by a thigh part (C) which includes a front pivot (1) and a back pivot (2) and which is intended to be con- neσted to a thigh, a lower, elongated part (6) which includes an upper pivot (9) at the upper end of the elongated part (6) and a lower pivot (11) spaced be¬ neath the upper pivot, said elongated part (6) forming the main part- of a lower leg; a forward base linkage arm (A) having pivot points at the ends thereof, wherein one end is pivotally con¬ nected to the front pivot (1) ; a rear base linkage arm (B) having pivot points at the ends thereof and a further pivot point therebetween, wherein one end is pivotally connected to the rear pivot (2); a first attachment element (4) which includes a linkage arm having three pivot points, two at the ends thereof and one located therebetween, wherein the centre pivot point is joined to the upper pivot point (9) and the two remaining pivot points are moveably connected to the lower pivot point (8) of the front base linkage arm (A) and to the intermediate pivot point (10) of the rear base linkage arm (B) respectively; a second attachment element (5) which includes a link¬ age arm having pivot points at the ends thereof, where¬ in one end is pivotally connected to the lower point (11) of the elongated part (6) and the other end is pivotally connected to the lower pivot point (12) of the rear base linkage arm (B); a mechanical stop means (13) for limiting forward movement of the lower pivot point (12) of the rear base linkage arm (B) in relation to the elongated part (6) above the lower pivot point (11), wherein the various parts are so dimensioned and arranged that the joint is locked by virtue of the fact that the lower pivot point (12) is pressed harder against the stop means (13) with increasing pressure when the weight rests on the heel, whereas the lower pivot point (12) leaves its abutment with the stop means (13), so as to enable the knee- joint to bend when the weight is transferred over to the toe.

Inventors: GRAMNAES FINN, GRAMNAES, FINN
Applicants: GRAMNAES FINN, GRAMNAES, FINN
Application year: 1991
Main classification: A61F2
IPC codes: A61F2