GB2151481A

GB2151481A - Lockable knee joint

Info

Publication number: GB2151481A
Application number: GB08333562A
Authority: GB
Inventors: Denis Ronald William May
Original assignee: JE Hanger and Co Ltd
Current assignee: JE Hanger and Co Ltd
Priority date: 1983-12-16
Filing date: 1983-12-16
Publication date: 1985-07-24
Also published as: GB8333562D0; GB2151481B

Abstract

A knee joint comprising thigh and shin parts (1 3) interconnected by anterior and posterior links (5, 8) to define a four bar linkage is provided with a catch member (20) and latch bar (28, 29) operable by a cable or other suitable means to releasably lock the joint in an unflexed position. <IMAGE>

Description

SPECIFICATION Lockable knee joint The present invention relates to a lockable knee joint.

Knee joints based on simple pivots commonly have locking devices operated by cable releases for holding the joint in the unflexed position. But such locking devices are not fitted to knees of the four bar linkage type, possibly because there has been no simple mechanism that latches the knee at the unflexed position but is compatable with the more complex movement of the four bar linkage, and possibly because of difficulties in managing a locking cable in a linkage of this type.

Broadly stated the invention provides a knee joint comprising anterior and posterior links pivotally connected to thigh and shin members to define therewith a four bar linkage, wherein means is provided for releaseably locking the joint in the unflexed position. It is believed that the invention provides the first mechanism of this kind wherein the locking means can latch automatically as the knee is fully unflexed, and the release cable is arranged to be paid out automatically against the action of the spring or other resilient means at the other end of the release cable as the knee is moved from a partly flexed to a fully flexed position, thereby preventing over extension of and damage to the cable.

The releaseable locking means preferably comprises a catch member attached to the thigh member at an anterior location which presents a lower posterior cam face that is concave when viewed in profile and leads to a lock face in a posterior portion of its top surface, a generally t-shaped latched bar pivoted at its base adjacent the lower pivot of the posterior link and having on its head a convex top edge that engages the cam face as the knee is unflexed to retract against the action of resilient means and in the unflexed position leaves the cam face so that an anterior angulation at its underside is snapped into engagement with the lock face by the resilient means, release means connected to the latch bar being operable to turn the latch bar in a posterior direction and unlatch it from the lock face.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view showing a knee joint according to the invention in its unflexed state, Figure 2 shows the knee joint in its fully flexed state, and Figure 3 shows the knee joint as it is straightened from flexion.

The knee joint 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 member 4 forming the shin of the leg. The thigh part 1 and the shin part 3 are pivitaily connected to opposite ends of an anterior link member by pivits 6, 7 respectively and to opposite ends of a rear link 8 by pivots 9,10 repectively.

The front link 5 and the rear link 8 are in fact provided in pairs to the medial and lateral sides of the joint. The thigh part 1 front link 5, shin part 3 and rear link 8 form a four bar chain designed so that there is an initial resistance to relative movement of the thigh and shin over a small angle followed by substantially free movement until the leg is fully flexed. Control of flexion of the knee during the swing phase of walking is provided by a shaft 11 that is pivoted in the axis of the pivot 9 and passes through a plastics bush 15 pivotally mounted on the shin part 3 midway between the front and rear lower pivots 7, 10.

The function of this friction shaft is described and claimed in our Letters Patent GB-A1536007.

A catch member 20 is attached at an anterior position on one side of the thigh part 1 by means of a locating pin 21 that engages in one of a series of apertures 22 in the catch member and thereby enables a limited range of angular adjustment to be provided between the catch member 20 and the thigh part 1.

The catch member presents on a lower posterior portion of the rear edge a concave cam surface 25 that leads to a lock face 26 on a posterior part of its top edge. A generally Tshaped latch bar has a head 28 and a stem 29 pivoted at its base adjacent the lower end pivot of posterior link 8 by means of a pivot 30. A coil spring surrounds the pivot 30 between the link 8 and the latch bar and engages them at its hooked ends to urge the head 28 of the latch bar towards locking engagement with the catch member 20. Between the head 28 and the top anterior portion of the stem 29 is defined an angulation 31 that is adapted to snap into locking engagement with the lock face 26 by the action of the spring 32. The top edge of the head 28 is convex when viewed in profile in order that it may slide along the cam surface 25 as the joint is unflexed.A release cable 33 is attached to a posterior part of the head 28 by means of a pin 34 that traps a loop at the lower end of the cable between a bifurcated rear part of the head. The cable passes through a guide ring 35 attached to the top of the thigh part 1 and thence to an operating mechanism 40 on the thigh member 1 or on a stump socket.

It is an important feature of the invention that the release cable 33 should be paid out by the operating means 40 as the joint is moved from a partly flexed to a fully flexed attitude. Failure to provide such a paying-out mechanism leads to the cable becoming over stretched and damaged.

Thus in one kind of operating device arranged for automatic operation the end of the release cable remote from the knee joint is attached to an operating device that includes resilient means urging the cable 33 upwardly to withdraw the head 28 of the latch bar from the catch member but permits the cable 33 to move downwardly against the resilient means as the knee is moved from a partly flexed to a fully flexed position. Thus the operating device has a plunger 41 sliding in a cylinder 42 and biased upwardly by means of a coil spring in compression 42a. The plunger has a pin 44 that runs in a generally J-shaped slot 48 in the cylinder 42 so that the plunger 41 may be depressed by the actuation of an operating handle 47 connected to the plunger 41, and rotated to trap the pin 44 at the base of the slot 48. Thereby the cable is held in a position where it permits locking. The above arrangement provides purely manual operation of the release mechanism. But it is also possible to dispense with the spring 42a and the pin 44 to provide a semiautomatic mechanism (not shown) in which the plunger is manually lowered to permit locking and manually raised to maintain the joint unlocked.

The feature is retained that the cable is paid out as the joint is moved from the partly to the fully flexed positions.

It will be appreciated that various modifications can 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 knee joint comprising anterior and posterior links pivotally connected to thigh and shin members to define therewith a four bar linkage, wherein means is provided for releaseably locking the joint in an unflexed position.

2. A joint according to Claim 1, wherein the releaseable locking means comprises a catch member attached to the thigh member at an anterior location which presents a lower posterior cam face that is concave when viewed in profile and leads to a lock face in a posterior portion of its top surface, a generally T-shaped latch bar pivoted at its base adjacent the lower pivot of the posterior link and having on its head a convex top edge that engages the cam face as the knee is unflexed to retract against the action of resilient means and in the unflexed position leaves the cam face so that an anterior angulation at its underside is snaped into engagement with the lock face by the resilient means, release means connected to the latch bar being operable to turn the latch bar in a posterior direction and unlatch it from the lock face.

3. A joint according to Claim 2, wherein the release means is an inextensible cable attached to the head of the latch bar that is passed through a guide ring attached to the thigh member at a posterior location.

4. A joint according to Claim 3, wherein the cable is connected at its end remote from the knee joint to an operating device including resilient means urging the cable upwardly to withdraw the latch bar from the catch member but permitting the cable to move downwardly against the resilient means as the knee is moved from a partly flexed to a fully flexed position.

5. A joint according to any preceding claim, wherein the operating device is a plunger sliding in a cylinder and biased upwards by means of a coil spring in compression, the plunger having a pin that runs in a generally J-shaped slot in the cylinder so that the plunger may be depressed by actuation of an operating handle connected thereto and rotated to trap the pin at the base of the slot and hold the cable in a position where it permits locking.

6. A knee joint according to Claim 4 wherein a semiautomatic locking mechanism is provided at the upper end of the cable.

7. A joint according to any preceding claim, wherein a coil spring acting between the posterior link and the locking bar urges the locking bar towards its locking position.

8. A four bar knee joint provided with a releaseable lock for holding it in the unflexed pgsition substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.