GB2134392A

GB2134392A - Improvements in four bar linkages for knee joints of artificial legs

Info

Publication number: GB2134392A
Application number: GB08303148A
Authority: GB
Inventors: Denis Ronald William May
Original assignee: JE Hanger and Co Ltd
Current assignee: JE Hanger and Co Ltd
Priority date: 1983-02-04
Filing date: 1983-02-04
Publication date: 1984-08-15
Also published as: GB8303148D0; GB2134392B

Abstract

In a four-bar knee prosthesis of the general kind described in Patent Specification No. GB-A-1536007 the leg is biased towards re-extension at the beginning of the forward swing by providing in a shin tube 4 a piston 20 biased by resilient means 21 towards the top of the tube 4 with the lower end of a friction rod 11 bearing on the crown of the piston 20 so that the piston 20 is depressed as the joint is flexed in walking to compress the resilient means 21 during the rearward swing of the leg and the energy stored in the resilient means 21 biases the joint towards extension at the beginning of the forward swing. <IMAGE>

Description

SPECIFICATION Improvements in four bar linkages for knee joints of artificial legs The present invention relates to an improved knee joint prosthesis incorporating a four bar linkage.

U.K. Patent Specification No. 1287354 describes an artificial leg comprising a shin portion having a downwardly and rearwardly sloping plate that is connected by two pairs of pivoted links to a generally horizontal plate mounted on a thigh portion. The forward pair of links is shorter than the rearward pair and the articulation is such that the instantaneous centre of rotation of the thigh portion about the shin portion rom the fully extended position ascends for a predetermined angle of flexion before descending.

Both of the links are cranked to permit flexing of the leg to a sitting posture without interference.

In U.K. Patent Specification No. 1536007 there is described brake means that operates during the swing phase of walking to limit flexion of the knee. It comprises a friction rod mounted on an upper spindle member of the two rear connecting elements and slideably movable through a plastics bush that is rotatably mounted on a pair of bearing bush that is rotatably mounted on a pair of bearing pins spaced apart in the shin part at a location between the lower spindle members of the front and rear connecting elements.It has been found that the friction breaking effect of this brake means varies in a useful nonlinear manner with flexion angle, rising with increasing flexion up to flexion angles of about 50 such as are encountered in the swing phase of walking and falling off steeply at flexion angles beyond 500 so that there is little braking effect at angles of about 1200 corresponds to a sitting posture.

Although the brake device shown in U.K. Patent Specification No. 1536007 provides excellent control of flexion in the swing phase of walking it has been found to be advantageous to bias the leg towards re-extension at the beginning of the forward swing, and it is an object of this invention to provide means by which this can be done.

The invention provides in a knee joint prosthesis comprising a thigh part and a shin part interconnected by a four member linkage which has two front and two rear connecting elements rotatably mounted by means of spindle members on the thigh part and the shin part respectively, a friction rod rotatably mounted on the upper spindle member of the two rear connecting elements and slidably movable through a plastics brake bush which is rotatably mounted on a pair of bearing pins spaced apart in the shin part at a location between the lower spindle members of the front and rear connecting elements, the improvement which comprises providing in a pylon tube that depends from the shin part a piston biased by resilient means towards the top of the pylon tube with the lower end of the friction rod passing through the shin part and bearing on the crown of the piston so that the piston is depressed as the joint is flexed to compress the resilient means, whereby the energy stored in the resilient means during the rearward swing of the leg in waking biases the joint towards extension at the beginning of the forward swing.

It will be appreciated that the forward bias is provided in a way that is of simple construction, is effective and is compatible with existing parts so that it may be retro-fitted to patient's existing knee joints.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a side view of a knee joint prosthesis with braking arrangement and an extension bias arrangement; Figure 2 is a view in section taken along the line A-A of Figure 1; and Figure 3 is a view in section taken along the line C-C of Figure 1.

Referring to Figure 1, a knee joint prosthesis comprises a thigh part 1 adapted for connection to a member 2 forming the thigh of an artificial leg and a shin part 3 adapted for connection to a pylon tube 4 forming the shin of the leg. The thigh part 1 and the shin part 3 are pivotally connected to opposite ends of a pair of front links 5 by spindle members 6 and 7 respectively and to opposite ends of a pair of rear links 8 by spindle members 9, 10 respectively. The thigh part 1, front links 5, shin part 3 and rear links 8 form a four bar chain that may be designed so that there is an initial resistance to relative movement of the thigh and shin portion over small angles followed by substantially free movement until the prosthesis is fully flexed.Thus, the linkage consists of a pair of short cranked front links 5 with the pivot 6 to the thigh part posterior to the pivot 7 to the shin part and a pair of longer gently curved rear links 8 with the pivot 9 to the thigh part anterior to the pivot 10to the shin part.

A friction rod 11 is pivotally mounted at one end about the axis of the spindle member 9 connecting the upper end of the rear link 8 with the thigh part 1.

A tube 12 coaxial with the spindle member 9 is mounted in the thigh part 1 and passes through a hole in the enlarged end 13 of the friction rod 11,the thigh part 1 having a recess 14 to accommodate the end 13. The other end of the friction rod 11 passes through a plastics bush 15 and is a sliding fit therein.

The bush 15 is pivotally mounted on the shin part 3 midway between spindle members 7, 10 of the front and rear links 5,8. The top of the shin part 3 is formed with a cylindrical recess 16 to receive the bush 15. Pins 17, 18 project into the recess to form a bearing for the bush 15 and their inner ends are spaced apart to allow passage between them of the shaft 11. The bush 15 is split longitudinally on one side and a screw 19 connects the portions of the bush on opposite sides of the split. The screw 19 may be threaded in or out to increase or reduce the frictional engagement between the friction rod 11 and the plastics bush.

When the knee joint prosthesis 13 is flexed the rod 11 slides through the plastis bush 15 against the frictional force acting therebetween so that movement of the knee joint prosthesis is controlled in the swing phase of walking at least so far as an angle of about 500. The frictional engagement is adjusted by tightening the plastics bush 15 around the rod 11.

It has now been found that with a friction brake of the aforesaid kind present in a four bar linkage it is desirable to provide a means for biasing the leg towards re-extension at the beginning of the forward swing to overcome the friction imposed by the brake 11 t 15. Accordingly, the lower end of the rod 11 bears on the crown of a piston 20 that slides in the interior of pylon tube 4 and is urged upwardly by a coil spring 21 in compression. The lower end of the coil spring 21 is supported on the base of an inverted cup member 22 having a split rim or skirt formed with a female frustoconical inner surface that bears on the inner surface of pylon tube 4 when expanded by the action of male frustoconical expander plug tightened by screw 24.When the screw 24 is slackened the cup member 22 may be slid to a desired vertial position inside pylon tube 4 to produce an intended degree of pre-compression in the coil spring 4 after which the screw 24 is re-tightened to clamp the cup member 22 in position. The upward travel of piston 20 is limited by formations in the shin part 3 and the length of the downward stroke during flexion of the prosthesis that friction rod 11 brings about is a constant determined by the particular geometry adopted. The load applied on rod 11 by piston 2 during joint flexion is therefore generally linearly dependent on the degree of pre-compression of spring 21 which in turn can be set simply by adjusting the vertical position of spring 21. It may be mentioned also that in the fully flexed position ofthe knee the action of the piston 20 and rod 11 alters and they now urge the leg towards the fully flexed position.

It will be understood that the invention is not restricted to the details of the preferred form described by way of example which may be modified without departure from the scope of the accompany-

Claims

ing claims. CLAIMS

1. In a knee joint prosthesis comprising a thigh part and a shin part interconected by a four member linkage which has two front and two rear connecting elements rotatably mounted on the upper spindle member of the two rear connecting elements and slidably movable through a plastics brake bush which is rotatably mounted on a pair of bearing pins spaced apart in the shin part at a location between the lower spindle members of the front and rear connecting elements, the improvement which comprises providing in a pylon tube that depends from the shin part a piston biased by resilient means towards the top of the pylon tube with the lower end of the friction rod passing through the shin part and bearing on the crown of the piston so that the piston is depressed as the joint is flexed to compress the resilient means, whereby the energy stored in the resilient means during the rearward swing of the leg in walking biases the joint towards extension at the beginning of the forward swing.

2. A knee joint according to claim 1, wherein the resilient means is a coil spring in compression.

3. A knee joint according to claim 2, wherein the lower end of the coil spring is supported pylon tube by means of an inverted cup member having a split sidewall or skirt that is expandible by means of a tapered plug into clamping engagement with the inner surface of the pylon tube as a clamping screw or bolt is tightened that passes through the plug and threadedly engages the cup member.

4. A knee joint according to any preceding claim, wherein the linkage consists of a pair of short cranked front links with the pivot to the thigh part posterior to the pivot to the shin part and a pair of longer gently curved rear links with the pivot to the thigh part anterior to the pivot to the shin part.

5. A knee joint according to any preceding claim, wherein means is provided on the brake bush for adjustment of the frictional engagement between the brake bush and the friction rod.

6. A knee joint according to any preceding claim, wherein the adjustment means comprises a screw that traverses a longitudinal slot in the brake bush and is threadable in or out to tighten or loosen the bush around the shaft.

7. A knee joint substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.