GB2181352A

GB2181352A - Improvements in knee joints

Info

Publication number: GB2181352A
Application number: GB08524996A
Authority: GB
Inventors: Alan James Laidlaw
Original assignee: Vessa Ltd
Current assignee: Vessa Ltd
Priority date: 1985-10-10
Filing date: 1985-10-10
Publication date: 1987-04-23
Also published as: GB8524996D0

Abstract

In a prosthetic knee having a brake connected between thigh and shin parts (10, 12) to provide a friction resistance during the swing phase of walking, a depending link (44) whose head (36) is pivoted at (40) to thigh part (10) extends into an oscillating brake chamber (46) pivoted to shin part (12) by means of trunnions (48). The lower end of link (44) is secured to brake block (47) that carries a pad (48) of friction material that slides over wall (50) of the chamber (46). Roller (62) of block (47) slides over captive leaf spring (58) whose position is independently adjustable by pairs of jacking screws (56) to either end of the block so that the frictional resistance exerted by the pad (48) may be adjusted at different flexional positions of the knee. The knee may be locked in its extended position by bell-crank member (65) forming part of a toggle linkage (69, 70) in the shin part (12). The brake assembly provides mechanical swing phase control with adjustable linear deceleration and can be applied to both uniaxial and polycentric knee joints. <IMAGE>

Description

SPECIFICATION Improvements in knee joints This invention relates to a prosthetic knee joint for an artifical leg provided with a friction brake by which the movement of the shin part of the leg can be controlled during the swing phase of walking so that its travel is natural and follows that of the other leg.

Friction brakes for the above duty normally comprise a moving part attached to the thigh part of the joint which travels through a brake band or collar attached to the shin point as the joint is flexed and extended. Devices of this kind are illustrated in the case of four-bar knee joints in Patent Specifications Nos GB-A-1303738 and GB-A-1 536007. A feature of the braking requirement is that it should vary non-linearly with flexion - thus a significant frictional resistance is desirable at flexion angles of up to 50 corresponding to the swing phase of walking, but a decreased resistance is required as the angle of flexion increases towards 180 corresponding to a sitting or kneeling position.In the arrangement described in GB-A-1 536007, a desirable pattern of frictional resistance with flexion flows from the geometrical relationship that exists between the four-bar linkage and the friction brake, but that pattern is fixed and a single adjustment is provided that increases or decreases the actual value of the resistance at any particular flexion angle according to the established pattern.

This invention provides a prosthetic knee joint having a brake connected between thigh and shin parts to provide a friction resistance during the swing phase of walking, wherein first and second means are independently effective to adjust the frictional resistance exerted by the brake at different flexional positions of the joint.

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 diagrammatic, partly cut-away view of the knee joint and part of the shin of a prosthetic leg; Figure 2 is a view, partly in section, of a brake forming part of the prosthetic leg of Figure 1; and Figure 3 is a back view of the thigh part of the knee joint of Figure 1.

In the drawings, a uniaxial prosthetic knee comprises a thigh part 10 and a shin part 12 pivoted together at a knee bolt 14. The thigh part 10 may be connected to a stump socket alignment device 15 (Figure 3) e.g. as described in our co-pending Patent Application No.8518459. The shin part 12 may be provided with a socket 16 by which it stands on an endoskeletal shin tube 18. The thigh part 10 may comprise a top plate 20 and depending medial and lateral walls 22 provided with bearings for the knee bolt 14which further passes through a pair of medial walls 26 also depending from plate 20. The medial walls 26 have smoothly curving back edges 30 and curvilinear front edges 28 having abutment faces 32 at their lower extremities.

The shin part 12 is generally U-shaped in horizontal section with the medial and lateral walls 22 of the thigh part fitting between cheek plates 34 thereof with the bolt 14 passing through said plates 34 to pivotally interconnectthethigh and shin parts 10,12.

A head 36 of a friction brake unit 38 is pivotally located between the medial walls 26 by means of a pivot pin 40 held in place by screws 42. The head 36 is connected to a link rod 44 that extends into an oscillating brake chamber 46 of square section that is itself pivoted to shin part 12 by means of trunnions 48. The end rod 44 within chamber 46 is secured to a block 47 that carries on one face a brake pad of friction material 48 that slides over one wall 50 of the chamber 46. The opposed wall 52 of the chamber 46 carries at its end a pair of mounting plates 54 each having engaged therewith a pair of transversely-spaced joint screws 56 that compress a captive leaf spring 58 against a roller 60 journalled at 61 to the block 47. The leaf spring 58 is permanently in compression and is held captive by ears 62 of plate 54 that partly close off the lower end of the chamber 46.Tightening the screws 56 urges block 49 against wall 50 and increases the frictional resistance of the brake, and because the pairs of screws 56 to either end of the chamber 46 are independent, the spacing or either end of spring 58 from wall 50 may be independently varied thereby varying both the resistance and the pattern of resistance to travel of the block 47 and providing a frictional resistance the pattern of which varies adjustably with knee flexion. A coil spring 35 between collars 37,39 on rod 44 is compressed between head 36 and chamber 46 and provides extension bias.

A bell crank member 65 is pivoted at 66 between cheek plates 34 and has one limb 67 that may be brought to and from register with face 32 of the walls releasablyto lock the joint in its unflexed position. A second limb 69 of member 66 forms one part of an over-centre toggle linkage, the other part of which is provided by an oscillating lever 70 pivoted at 71 to cheek plates 34 and operated by a handle (not shown).

The above friction brake provides mechanical swing phase control in a stragiht line with adjustable linear deceleration and can be applied to both uniaxial and polycentric knee joints. It will be appreciated that alterations may be made to the embodiment described above without departing from the invention, the scope of which is defined in the appended claims.

Claims

1. A prosthetic knee having a brake connected between thigh and shin parts to provide a friction resistance during the swing phase of walking, wherein first and second means are independently effective to adjust the frictional resistance exerted by the brake at different flexional positions of the joint.,

2. A joint according to Claim 1 wherein a depending link pivoted to the thigh part carries a friction block that travels through an oscillating chamber carried by the shin part, the block presenting from one face a pad of friction material and from an opposed face a roller that travels over a partition in a second chamber having an adjustable clearance from a wall of said chamber over which the pad slides.

3. A joint according to Claim 2 wherein the partition is a captive leaf spring in compression, the position of opposed ends of the leaf spring relative to the wall of said chamber over which the pad slides being adjustable by means of first and second jacking screw means.

4. A joint according to Claim 1 or 2, wherein the depending link carries a coil spring that biases the joint towards its extended position.

5. A joint according to any of Claims 2 to 4 wherein trunnions from opposed sides of the block locate in cheek plates of the shin part.

6. A joint according to any preceding claim, wherein the link has a head supported by a pin between a pair of depending walls the link of said thigh part.

7. A uniaxial joint according to any preceding claim.

8. A joint according to any preceding claim wherein the shin part carries means for locking the joint in its extended position.

9. A joint according to Claim 8, wherein the locking means comprises a beli-crank member pivoted to the shin part and movable at one end when the joint is unflexed to and from abutment with portions of the thigh part under the control of a toggle link pivoted between the shin part and the other end of said member.

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