GB2189149A

GB2189149A - Artificial knee with improved stable link-type knee joint

Info

Publication number: GB2189149A
Application number: GB08700780A
Authority: GB
Inventors: Richard Zbigniew Marlow
Original assignee: JE Hanger and Co Ltd
Current assignee: JE Hanger and Co Ltd
Priority date: 1986-04-16
Filing date: 1987-01-14
Publication date: 1987-10-21
Anticipated expiration: 2007-01-14
Also published as: GB2189147A; GB2189147B; GB8609339D0; JPS62295658A; GB2189149B; GB8700780D0

Abstract

In a four bar knee mechanism for an artificial leg, resilient means such as a leaf spring (70) acts on an anterior link (10) that moves rearwardly in the latter part of travel of the mechanism from a flexed to an extended state to bias the link (10) rearwardly and assist extension of the mechanism. If the linkage geometry is such that the link (10) reverses motion at high angles of flexion, the mechanism is then biased towards its flexed position. <IMAGE>

Description

GB2189149A 1 SPECIFICATION vot positions of the unflexed joint were 146'

at the thigh pivot of the anterior link, 49' at Artificial knee with improved stable link- the shin pivot of the anterior link, 820 at the type knee joint thigh pivot of the posterior link and 530 at the 70 shin pivot of the posterior link. The stated This invention concerns improvements in artifi- angles were found in practice to be absolutely cial legs, and its object is to provide an im- vital. In an experiment, moving'the pivot proved control function for a four bar knee points one at a time by a mere 1/16 inch joint for fitment between a socket for an am- (equivalent to an average change of included putee's upper leg stump and a shin portion of 75 angle of about 0.5) was found to produce such legs. quite unacceptable loss of function. Gaping

We have described in Patent Specification between the knee part and the front upper

No. US-A3823424 a knee mechanism com- edge of the shin part occurred, the maximum prising thigh link means for attachment to up- degree of flexion was reduced and there was per portions of the leg, shin link means for 80 a tendency for angular movement to become attachment to a shin of the leg, and anterior locked.

and posterior link means pivoted between the Extensions of the four bar knee idea, e.g. to thigh and shin links, with: include swing phase control devices, are de (a) the line joining the pivot between the scribed in our Patent Specification No. GB-A- anterior link means and the shin link means to 85 1536007 and extension bias is provided in the pivot between the posterior link means the structure described in Specification No.

and the shin link means sloping rearwardly GB-B-2134392.

and downwardly; This invention provides a four bar knee (b) the anterior link means being shorter mechanism for an artificial leg comprising thigh than the posterior link means; 90 link means for attachment to upper portions (c) the pivots on the shin link means spaced of the leg, shin link means for attachment to a apart by more than twice the distance separ- shin of the leg, and anterior and posterior link ating the pivots on the thigh link means; means pivoted between the thigh and shin (d) the pivots on the thigh link means dis- links, wherein the anterior link means moves posed at intermediate positions relative to the 95 rearwardly in the latter part of travel of the horizontal positions of the pivots on the shin mechanism from a flexed to an extended state link means when the leg is in a fully extended and resilient means acting between the shin position; and link means and the anterior link means biases (e) the articulation defined by said links hav- the anterior link rearwardly to assist extension ing an instantaneous centre of rotation consti- 100 of the mechanism.

tuted by the intersection point of a line drawn In a first form a coil spring on a support through the pivots of the anterior link means coaxial with a pivot between the anterior link and a line drawn through the pivots of the and the shin link has hooked limbs respec posterior link means, said centre of rotation tively engaging the anterior and shin links.

being located in substantially the region of 105 Such a coil spring may have only a limited life that of a natural knee and lying upon a curve and give rise to fretting between the hooked that is ascending through approximately 15' of limbs of the spring and the links those limbs flexion of the knee mechanism from its fully engage. In a second and preferred form, extended position. therefore, leaf spring means attached to the The resultant articulated joint provided a 110 front of the shin link and upstanding therefrom stable weight support until it had been flexed bears against the anterior link means.

through the predetermined angle from the ex- According to a new and preferred aspect of tended position, which was about 15'. The the invention, it has been found possible to practical joint was capable of flexure to about increase the degree of flexion of the mecha- 120', to permit a natural sitting posture. To 115 nism to about 140' and even up to 143' by this end both the forward and rearward links modifying the geometry described in US-A were cranked rearwardly from about their mid 3823424 so as to increase the length of the points to avoid mutual interference. Alteration rear pivot and position the posterior shin pivot of the lengths of the links and of their pivot appropriately. The modified linkage geometry points could be made to adapt the character- 120 enables both a natural sitting posture and a istics of the joint to suit the individual stump posture in which the user squats back on his condition of a patient, but it was found that heels. The anterior link oscillates during knee the angulation between lines intersecting the flexion so that the extension assist means as pivot axes of the links was critical. The parti- sists flexion when the knee mechanism is in cular combination of dimensions found to be 125 the latter part of its travel towards a fully important was that the line joining the thigh flexed position.

and shin pivots of the anterior link sloped for- The use in association with a prosthetic wardly and downwardly at an angle of 41o knee joint of an extension buffer formed with from the vertical and that the included angles a first portion of relatively soft material that in an irregular quadrilateral defined by the pi- 130 serves to absorb kinetic energy as the joint is 2 GB2189149A 2 unflexed and a second portion of relatively Figure 1, a line joining pivot 21 to pivot 17 hard material for reacting loads is preferred. slopes forwardly and downwardly at a angle Embodiments of the invention will now be of about W. The line between pivots- 12 and described, by way of example only, with refer- 23 slopes rearwardly and downwardly at an ence to the accompanying drawings, in which: 70 angle of about 45'. The links 3, 10, 16 and Figure 1 is an elevation drawn approximately 20 form a four-bar kinematic chain with the to scale of a knee mechanism for an artificial following characteristics:

leg in the extended position the mechanism (a) the line joining the pivots 12, 23 of the having a first form of an extension bias device shin link 3 slopes rearwardly and downwardly; fitted thereto; 75 (b) the anterior link 10 is substantialy shor Figure 2 is a front view of the knee mecha- ter than the posterior link 20; nism in a partly flexed position; (c) the pivots 12, 23 on the shin link 3 are Figure 3 is a front elevation of a knee spaced apart by more than twice the distance mechanism according to the invention in the separating the pivots 17, 21 on the thigh link unflexed position and having a second form of 80 16; an extension bias device fitted thereto; and (d) the pivots 17, 21 on the thigh link 16 Figures 4 and 5 are side elevations of the are disposed at intermediate positions relative knee mechanism of Figure 3 in the extended to the horizontal positions of the pivots 12, position and in a partly flexed position respec- 23 on the shin link means 3 when the leg is tively. 85 fully extended; The shin portion 1 of an artificial leg embo- (e) the instantaneous centre of rotation of dies a tubular load-bearing member 2 attached the joint defined by the intersection of a line to a shin link 3 which is conveniently cast or drawn through anterior pivots 17, 12 with a machined from solid as one piece. The tube 2 line drawn through posterior pivots 21, 23 is is retained in a socket 7 at the base of the 90 located substantially in the region of that of a link 3 by means of a pinch-bolt connector 4. natural knee when fitted to a leg and lies The link 3 has an anterior limb 5 that extends upon a curve that is ascending through about upwardly for an appreciable distance and a 15' of knee flexion from the fully extended posterior limb 6 that extends rearwardly at the position; and same level as the socket so that when link 3 95 (f) the posterior link 23 is of length and has is viewed in side profile it slopes sharply a shin pivot 23 located so that the angulation downward towards the rear of the leg. The exhibits flexion exceeding 140' to enable both central region of the anterior limb 3 may be a natural sitting posture and a posture in apertured to reduce weight as at 9. which the user squats back on his heels. It A relatively short anterior link 10 is bifur- 100 will be noted that in the unflexed position cated at its lower end 11 to fit either side of shown in Figure 1, the pivots 12, 17, 21 23 the anterior limb 5 to which it is attached by form an irregular qudrilateral with respective pivot pin 12 and is cranked rearwardly included angles of 86', 157', 80' and 37' and through almost a right-angle to define a body that a line joining pivots 17 and 12 slopes portion 13. The upper end of the link 10 is 105 downwardly at an angle of 490 from the verti fitted between depending bifurcations 15 of a cal. A further difference between the motion thigh link 16 to which it is secured by pivot of the knee mechanism of this invention and pin 17. The thigh link 16 may be connected that of US-A-3823424 is that at high degrees to a stump socket via an alignment device 14, of flexion the pivot 21 joining the posterior e.g. as described in our Patent Application No. 110 link 20 to the thigh link 16 passes to the 8528992. The anterior edge of the link 16 anterior side of a line joining the pivots 12, carries a pad 18 of hard rubber against which 17 of the anterior link, resulting in a distinct the body portion 13 of link 10 abuts to define over-centre- action.

a fully extended attitude of the knee, from The above knee mechanism lends itself to which pad 18 depend primary buffers 18a of 115 fitting of a remarkably simple and effective ex somewhat softer rubber. As the knee is tension bias. In a first form, the pivot 12 con unflexed during the swing phase of walking necting the lower part of anterior link 10 to the primary buffers 18a absorb the kinetic en- the shin link 3 has an extension 60 on which ergy of the shin and prevent sharp impact is supported a coil spring 61. The ends of the between the body portion 13 and the pad 18 120 coil spring 61 are bent to define limbs 62, 63 but during the stance phase of walking or directed parallel to the axis of the pivot 12 when the patient is standing, load is reacted and having hooked ends that engage the an through the pad 18. terior portion 5 of link 3 and link 10. The A pair of posterior links 20 are pinned at action of the coil spring 61 depends upon upper pivot 21 to posterior lateral faces 22 of 125 angle of flexion because the movement of link the thigh link 16 and are pivoted at pin 23 to 10 during knee flexion is an oscillation rather the posterior limb 6 of the shin link 3. It will than a simple rotation. At low angles of flex be noted that the pivots 17, 21 of the thigh ion the link 10 moves in an anterior direction link 16 are relatively close together and that in against the bias of spring 61 which tends to the unflexed position of the knee shown in 130 return the knee to its unflexed position. At 3 GB2189149A 3 intermediate angles of flexion the link 10 wherein the tip of the leaf spring means is moves little but at higher degrees of flexion it cranked in a posterior direction.

Claims

moves in a posterior direction so that the ac- 6. A mechanism according to

Claim 4 or 5, tion of spring 61 is then to assist flexion. The wherein the leaf spring meTber comprises a knee mechanism is used in a cosmesis that 70 relatively long leaf attached directly to the shin resists flexion so that when the user is sitting link and a relatively short leaf attached to the down his cosmesis tries to straighten the shin link so as to overlie a lower portion of knee again. The opposition by spring 61 to the outer face of the relatively long leaf.

straightening of the knee by the cosmesis 7. A mechanism according to any preceding means that the finished limb exhibits neutral 75 claim, wherein, in an unflexed state of the behaviour when flexed to sitting or squatting knee:

angles, which is of obvious benefit to the (a) the line joining the pivot between the user. anterior link means and the shin link means to Figures 3 and 4 show a second and pre- the pivot between the posterior link means ferred form of the extension bias mechanism 80 and the shin link means slopes rearwardly and where upstanding primary and secondary leaf downwardly; springs 70, 71 are attached to the front face (b) the anterior link means is shorter than of the shin link 3 at approximately the same the posterior link means; vertical position as the pivot 23. The primary (c) the pivots on the shin link means are leaf spring 70 has a posteriorly cranked tip 72 85 spaced apart by more than twice the distance that bears against a front nose portion 74 separating the pivots on the thigh link means; (Figure 2) of the anterior link 10. The move- (d) the pivots on the thigh link means are ment of the link 10 is towards the posterior disposed at intermediate positions relative to as the knee is unflexed and the spring 70 the horizontal positions of the pivots on the which is in compression biases the link 10 90 shin link means; rearwardly, with the nose 74 sliding over the (e) the articulation defined by said links has posterior face of spring 70. The secondary an instantaneous centre of rotation constituted spring 71 is shorter than the primary spring by the intersection point of a line drawn and is secured to lie over the lower part through the pivots of the anterior link means of the anterior face of spring 70 in the man- 95 and a line drawn through the pivots of the ner of a carriage spring. The springs 70, 71 -posterior link means, said centre of rotation are held to the link 3 by means of a block 75 being located in substantially the region of and clamping screw 76. that of a natural knee and lying upon a curve that is ascending through approximately 15' of CLAIMS 100 flexion of the knee mechanism from its fully 1. A four bar knee mechanism for an artifi- extended position; and cial leg comprising thigh link means for attach- (f) the posterior link means is of length and ment to upper portions of the leg, shin link has a shin pivot position such that the articu means for attachment to a shin of the leg, lation exhibits flexure exceeding 140' to ena and anterior and posterior link means pivoted 105 ble both a natural sitting posture and a pos between the thigh and shin links, wherein the ture in which the user squats back on his anterior link means moves rearwardly in the heels.

latter part of travel of the mechanism from a 8. A knee meechanism according to any flexed to an extended state and resilient preceding claim, in which the link means are means acting between the shin link means 110 curved so that end portions thereof are dis and the anterior link means biases the anterior posed rearwardly of central portions thereof.

link rearwardly to assist extension of the 9. A knee mechanism according to Claim 7 mechanism. or 8, wherein the pivots are so disposed that 2. A mechanism according to Claim 1, when the mechanism is unflexed they define wherein the anterior link oscillates during 115 an irregular quadrilateral whose included angles movement from a fully flexed to an extended are 157' at the thigh pivot of the anterior link position,the resilient means at low angles of means, 86' at the shin pivot of the anterior flexion biases the joint towards its extended link means, 80' at the thigh pivot of the post position and at high angles of flexion biases erior link means and 37' at the shin pivot of the joint towards its flexed position. 120 the posterior link means.

3. A mechanism as claimed in Claim 1 or 2, 10. A knee mechanism according to Claim wherein a coil spring on a support coaxial 9, wherein when the knee is unflexed, the line with a pivot between the anterior link and the joining the thigh and shin pivots of the anter shin link has hooked limbs respectively engag- ior link is directed downwardly at an angle of ing the anterior and shin links. 125 49' to the vertical.

4. A mechanism according to Claim 1 or 2, 11. A knee mechanism according to any wherein leaf spring means attached to the preceding claim, wherein the anterior link car front of the shin link and upstanding therefrom ries at its extremity upstanding catch means, bears against the anterior link means. and the anterior link means fits and is pivoted 5. A mechanism according to Claim 4, 130 between bifurcated brackets depending from 4 GB2189149A 4 the thigh link, which brackets pivotally support posterior facing catch blade means resiliently biased to rotate downwardly, the arrangement being such that the blade travels over andIs 5 reverse rotated by the catch means until the unflexed position is reached, when it snap engages an anterior face of the catch means.

12. A knee mechanism as claimed in any preceding claim, further comprising an exten- sion buffer formed with a first portion of relatively soft material that serves to absorb kinetic energy as the joint is unflexed and a second portion of relatively hard material for reacting loads.

-15 13. A knee mechanism for an artificial leg substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 or Figures 4 and 5 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Lid, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.