WO1994006374A1

WO1994006374A1 - Artificial leg

Info

Publication number: WO1994006374A1
Application number: PCT/GB1993/001946
Authority: WO
Inventors: Graham James Harris
Original assignee: Chas A Blatchford & Sons Limited
Priority date: 1992-09-14
Filing date: 1993-09-14
Publication date: 1994-03-31
Also published as: GB9318989D0; EP0660691A1; GB2270473B; GB2270473A

Abstract

An artificial leg has knee stabilisation in the stance phase provided by a hydraulic piston and cylinder assembly (22) for resisting flexion at the knee. The resistance to flexion is controlled according to the axial load applied to the leg by means of a mechanism which allows movement of a knee axis (16) of rotation relative to a main shin component (20), the knee axis (16) being defined by a tubular shaft (14) mounted on a resilient arm (18). Movement of the knee axis (16) is detected by a rocking connector member (40) mounted on a knee chassis, one end of the connector member engaging a trigger element (36T) which remains stationary with the main shin component (20) and the other end engaging a control member (44R) on the piston and cylinder assembly (22) at a position adjacent its connection to the knee chassis. Application of an axial load results in the connector member (40) rocking about a rocking axis to move the control member (44R) which thereby increases resistance to flexion. In an alternative embodiment the resilient arm (18) is replaced by a pivoting link with an integral leaf spring.

Description

ARTIFICIAL LEG

This invention relates to an artificial leg including a knee mechanism having means for restricting knee flexion during the stance phase of the walking cycle.

It has been well known for a long period of time that one of the important attributes of an artificial leg for achieving a natural-looking walking gait is a so called stabilised knee, i.e. a knee which resists flexion when under load, that is when it is bearing at least some of the weight of the amputee. Purely mechanical devices have been produced such as one including a drum supported on radius arms and encircled by a friction brake band as disclosed in British Patent No. 779087, and one including a drum with an internal brake shoe coupled to a radius arm and a toggle link as shown in British Patent No. 1534181. In both of these devices an axial load on the limb produces a small rotation of the radius arm or arms causing the brake band or brake shoe to grip the drum and to resist knee flexion. Indeed, the resistance may be such that the knee is automatically locked if sufficient load is applied. Often such devices are combined with a pneumatic piston and cylinder assembly which applied lower degrees of resistance to flexion and/or extension of the knee to control the motion of the shin during the swing phase.

It is also known to provide resistance to flexion during the stance phase as well as the swing phase by means of a piston and cylinder assembly. One example of such an arrangement is the hydraulic "S-N-S" knee control system manufactured by auch Laboratories, Inc. In some situations, however, this system reguires the amputee to make a conscious knee- extending movement before flexion can be initiated.

According to one aspect of this invention there is provided an artificial leg comprising a thigh component, a shin

SUBSTITUTESHEET component, knee pivoting means pivotally coupling the shin component to the thigh component to permit knee flexion and extension movements, an hydraulic piston and cylinder assembly having a piston part and a cylinder part each connected to a respective one of the leg components for resisting flexion movement during the stance phase, and automatic control means to alter the degree to which the piston and cylinder assembly resists the flexion movement, wherein the shin component includes at least two portions, one of which is coupled to the thigh component by the knee pivoting means and is movable relative to the other of the two shin component portions in response to the application of an axial load, and wherein the automatic control means comprise connecting means arranged to convert relative movement of the two portions of the shin component to movement of a movable control member associated with that part of the piston and cylinder assembly which is pivotally connected to the thigh component. "Axial load" is understood to refer to a load which is axial with respect to the longitudinal axis of the shin component.

The connecting means may comprise a connecting member which has an actuation element for engaging the shin component in the region of the knee pivoting means. In fact, the connecting means may comprise a connecting member which is preferably a lever mounted on the thigh component and having an actuation element for engaging, on the one hand, a trigger element associated with the lower leg component in the region of the knee pivoting means and, on the other hand, a control element in the region of the pivotal coupling between the thigh component and the piston and cylinder assembly for engaging the control member of the latter. The actuation element may be arranged to engage a trigger element on a cross member located at the knee axis and forming part of the other shin component portion referred to above. In the preferred embodiment of the invention, the actuation element of the connecting member is arranged for rotational connection with the trigger element, for example, by virtue of the trigger element engaging a curved surface on the connecting member or by virtue of the connecting member and the trigger element being pivotally connected. The curved surface may have a generally circular profile centred on the knee axis.

The connecting member is preferably a rocker pivotally mounted on the thigh component with the actuation element and the control element on opposite respective sides of the pivotal mounting of the rocker on the thigh component. Indeed, with the knee pivoting means defining a knee axis, and the pivotal coupling between the thigh component and the piston and cylinder assembly defining a coupling axis, the pivotal mounting of the rocker on the thigh component preferably defines a rocking axis which is so located that, in a vertical cross-section on a posterior/anterior plane, lines joining the knee axis and the coupling axis to the rocking axis form an inverted "V" . The actuation element and the control element of the rocker preferably both have curved surfaces for engaging the trigger element on the control member, the curved surfaces being of a generally circular profile, that of the actuation element being centred at least approximately on the knee axis, and that of the control element approximately on the coupling axis.

In the preferred embodiment, the shin component portion which is coupled to the thigh component is formed by at least part of an arm carrying the knee pivoting means. The other shin component portion comprises a main shin component portion extending distally from the thigh component and the arm is joined to an anterior wall of the main shin component portion. When an axial load is applied, the arm is deflected relative to the main shin component portion, the load being transferred from the thigh component via the knee pivoting means to the arm, and thence to the main shin component portion. The arm may be formed as a leaf spring extending at least in part in an anterior-posterior direction from the anterior well of the main shin component portion, the posterior part of the arm having a medial- lateral bore housing a tubular shaft which forms the knee pivoting means. To provide resilience, the arm is preferably a one-piece member formed of a resilient plastics material, which may be a fibre-reinforced material.

The main shin component portion may include the cross member, the latter preferably passing through the tubular shaft forming the knee pivoting means in the preferred embodiment, sufficient clearance being allowed within the shaft for movement of the cross member when axial load is applied. A resilient buffer or buffers may be placed in the tubular shaft between the inner wall of the shaft and the cross member to supplement the leaf spring. The buffer or buffers may be each in the form of an O-ring adding to the resistance to medial-lateral swinging of the main shin component portion relative to the thigh component. Conveniently, the cross-member has a projection which acts as the trigger element for engaging the actuation element on the rocker. This projection may extend through an aperture in the tubular shaft and, in addition, an aperture in the end part of the leaf spring housing the tubular shaft so as to engage the actuation element above the leaf spring.

The bore in the leaf spring, which, in the preferred embodiment, results in the arm having a bush with an annular cross-section in a plane perpendicular to the knee axis, and preferably centred on the knee axis.

In an alternative embodiment, the two shin component portions pivot relative to each other about a pivot axis upon application of an axial load to the shin component. Indeed one of these portions is a pivoting link which is pivotable on the main shin component which extends distally to the foot, the pivoting occurring against resilient biasing means in response to the axial load. The pivotal connection between the two shin component portions is formed in this alternative preferred embodiment by the combination of a pivot shaft or pins together with a spring. Indeed, the spring may be integrally formed as part of the pivoting link. The spring may be a leaf spring having a proximal end rigidly connected to a main part of the link and a distal end engaging the main shin component portion. The link may have a pivotal connection with the main shin component portion, the connection defining a connection axis to the anterior of the knee pivoting means, with the leaf spring extending downwardly from the main part of the link in the region of the pivotal connection to engage the main shin component portion so that the spring is deflected when the two portions are pivoted with respect to each other by application of a load. A trigger element on the link is joined to the distal end of the leaf spring and extends from that distal end to the region of the knee pivoting means where it engages the connecting member for transferring movement to the control member of the piston and cylinder assembly. The preferred assembly is particularly simple in that the link, its leaf spring, and its trigger part are all formed as a single component in a plastics material such as Delrin™.

An adjustment device may be included for altering the stiffness of the leaf spring, typically by providing an abutment in the main shin component portion for the spring, the position of the abutment being adjustable.

The invention also includes a knee and shin assembly for use in an artificial leg having features set out above.

The invention will now be described by way of example with reference to the drawings in which:- Figure 1 is a side view of an artificial leg in accordance with the invention with a lower part cut away;

Figures 2 and 3 are, respectively, vertical and horizontal cross-sections through the knee mechanism of the leg of Figure 1 , the cross-sections being taken along the lines II- II and at III-III in the two Figures;

Figures 4 is a perspective view of a resilient arm forming part of the shin component;

Figures 5A and 5B are, respectively, a side elevation and a plan view of a rocker forming part of the knee mechanism of the leg of Figure 1 ;

Figure 6 is a cross-section of the knee mechanism similar to the cross-section of Figure 2 showing the relative positions of the various parts of the mechanism at partial flexion;

Figure 7 is a cross-section similar to that of Figure 2 showing the knee mechanism under load;

Figure 8 is a vertical cross-section through an alternative mechanism; and

Figure 9 is a perspective view of a link portion of the shin component shown in Figure 8.

Referring to Figures 1 to 3, an artificial leg in accordance with the invention has a knee mechanism with a knee chassis 10 for coupling to a stump socket 12. Carried by the chassis 10 is a tubular knee pivot shaft 14 defining a knee axis 16, the shaft being housed in a transverse bore of a resilient arm 18 forming part of a shin component, a main portion 20 of which comprises a carbon fibre reinforced plastics shin cradle and shin tube for connection to an artificial foot (not shown). The knee pivot shaft 14 is rotatable in the knee chassis 10 to allow knee flexion and extension movements.

Such flexion and extension movements at the knee are controlled by a piston and cylinder assembly 22 (Figure 1 ) which has a cylinder part 22C pivotally coupled at its lower end to the shin cradle of the main shin component portion 20 and a piston having a piston rod 22R pivotally coupled at its upper end by a rear pivot pin 24 to a posterior portion of the knee chassis 10 formed by two lugs 1 OL which extend rearwardly to either side of the piston rod 22R. In this embodiment, the knee chassis 10 is pivotally and resiliently connected to the socket 12 by a stance cushioning device comprising a top plate 26 which is hinged at its anterior edge to the chassis 10 by a pivot pin 28, and a buffer 30 or spring placed between the posterior part of the plate 26 and the chassis 10. Such a combination allows some flexion at the knee when the piston and cylinder assembly 22 is locked.

The resilient arm 18 of the shin component forms a link between the main portion 20 of the shin component and the tubular knee pivot shaft 14. This arm 18 is preferably formed as a single piece resilient component secured to a front wall of the main shin component 20 by, in this example, bolts 32 and extends upwardly and rearwardly towards the knee pivot 16. The arm 18 is wider (i.e. in the medial-lateral direction) than it is thick and, being made from a resilient thermoplastics or fibre-reinforced thermoset plastics material, acts as a leaf spring which is deflectable downwards in the main shin component 20 in response to an axial load applied downwardly on the knee pivot shaft 14 by the knee chassis 10, the arm being relatively stiff in the medial lateral-direction thereby resisting to a greater degree medial-lateral swinging of the main shin component 20 with respect to the knee chassis 10. A grub screw 34 threaded in a bore in the resilient arm 18 acts so as to prevent movement of the knee pivot shaf 14 with respect to the arm 18.

Housed in upper side ears 20E (Figures 1 and 3) of the shin cradle part of the main shin component portion 20 is a crossbar 36 which lies within the knee pivot shaft 14 and, in the absence of an axial load on the limb, is concentric with the shaft 14. The diameter of the crossbar 36 and the internal diameter of the tubular pivot shaft 14 are such that a clearance between the two components exists to allow relative movement between them. Such relative movement is, however, restricted by a pair of 0-rings 38 located in grooves on the crossbar 36 positioned so that the 0-rings are spaced apart and a short distance in each case from a respective end of the pivot shaft 14, as shown in Figure 3. Alternative resilient spacing means may be used. The functions of the O-rings 38 are to supplement the resistance provided by resilient arm 18 to medial-lateral movement of the shin component 20 with respect to the knee chassis 10, to limit the movement of the crossbar 36 within the shaft 14 at the limits of extension and flexion, and to avoid generation of an audible click in limiting situations such as heavy load, hyper-extension, or hyper-flexion.

In the preferred embodiment of the invention, the resilient arm 18 is a one-piece resin-transfer moulded carbon fibre reinforced plastics component with a carbon fibre lay-up that is predominantly +/- 45° to the longitudinal axis of the spring to provide flexibility in the anterior-posterior direction and comparative stiffness against a medial-lateral moment (i.e. about a anterior-posterior axis of rotation).

In the centre of the crossbar 36 there is a trigger element 36T which projects generally axially from the crossbar 36 in an upward direction through appropriately located bores in the tubular knee pivot shaft 14 and the resilient arm 18. In this embodiment, the trigger element 36T is a threaded stud housed in diametrically located threaded hole in the cross bar 36, the upward axial extent of the stud being such that, under no-load conditions, the upper end of the stud 36T is approximately flush with the upper outer surface of the reslient arm 18 where it houses the shaft 14. The other end of the stud is accessible through oppositely located lower bores in the shaft 14 and the resilient arm 18 to allow adjustment of the distance by which the stud projects from the crossbar 36. It will be understood that, under application of an axial load to the leg, the annular part 18A of the resilient arm will, together with the shaft 14, move downwardly with respect to the crossbar 36 and its trigger element 36T so that the upper end of the trigger element projects beyond the resilient arm 18 by a distance which is dependent on the magnitude of the load.

The above-described relative movement of the trigger element 36T with respect to the knee pivot shaft 14 is used to activate a control member on the piston and cylinder assembly 22. Specifically, housed in the knee chassis 10 is a rocker 40 capable of rocking about a transverse pin 42 defining a rocking axis. To the anterior of the pin 42 the rocker has an actuation element 40A which, at least in the extended configuration of the knee, is in registry with the trigger element 36T, a concave curved surface having a circular profile centred on the knee axis being presented to the upper surface of the resilient arm 18 in the region of the knee axis. In fact the concave surface of the actuation element 40A engages the outer surface of the arm 18 in the no-load condition. To the posterior of the transverse pin 42 the rocker has a control element portion 40C formed as two circular annuli encircling the rear pivot pin 24 which, it will be recalled, attaches the piston rod 22R to the knee chassis 10. Comparison of Figures 1 and 2 shows that the posterior annuli 30C of the rocker 40, which are, in the normal position of the rocker 40, substantially concentric with the rear pivot pin 24, are in registry with a control member associated with the upper end of the piston and cylinder assembly 22, specifically a transverse pin 44 housed in a longitudinal slot 46 in the piston rod 22R.

It will be appreciated that during flexion of the knee, the upper end of the trigger element 36T will engage the downwardly facing concave surface of the actuation element 40A of the rocker 40 at different positions, until, beyond about 30° flexion it will pass beyond the anterior end of the rocker 40.

The shapes of the resilient arm 18 and the rocker 40 are both seen in Figures 4, 5A and 5B.

The piston rod 22R is coupled to a main piston 48 which is arranged for reciprocation in the lower part of the cylinder 22C. Pivot axles 50 projecting from the lower end of the cylinder 22C secure the assembly in the shin component 20.

The piston rod 22R houses a slidable coaxial control rod 44R attached to the transverse pin 44 and acting as a valve control member for a valve having a valve member 52 housed in the main piston 48. A spring 54 inside the piston rod 22R biases the control rod 44R upwardly to bring the transverse pin 44 into contact with the outer surfaces of the posterior annuli 40C of the rocker 40. The valve member 52 is secured to the lower end of the control rod 44R and is arranged to close off progressively passages 48P connecting one side of the piston 48 to the other as the control rod 44R moves downwardly in the piston rod 22R, thereby restricting fluid flow through the piston 48 to the extent that, when the valve member 52 covers fully the passages 48P, an hydraulic lock results, thereby locking the knee.

The piston and cylinder assembly 22 has a secondary piston 56 mounted inside an internal secondary cylinder 58. This secondary piston 56 is fixed to the same piston rod 22R as the main piston 48 and they therefore move together. Passages 60 connect the fluid spaces on either side of the secondary piston 56. In fact, the walls of the secondary cylinder 58 are perforated at various longitudinal positions, the apertures 62 so formed connecting with the passages 60 leading to one end or other of the secondary cylinder 58 via non-return valves 64 . The arrangement is such that on a downward stroke of the secondary piston 56, resistance to movement of the piston at any given position in its stroke is governed by the total orifice area defined by those of the apertures 62 which remain uncovered below the piston and which connect via passages 60 to the top of the secondary cylinder 58. Similarly, on the upward stroke, at any point in the stroke the resistance is governed by the orifice area represented by the uncovered apertures 62 above the secondary piston 56 and connected via passages 60 to the bottom end of the secondary cylinder 58. It will be appreciated that by selecting the sizes and positions of the perforations, the resistance to movement can be varied so as to be different at different parts of the upward stoke and the downward stoke respectively.

Since the operation of the secondary piston 56 and secondary cylinder 58 is independent of the position of the valve member 52, they resist flexion and extension regardless of whether the leg is weight-bearing or not. In effect they operate as a swing phase control device.

In the upper part of the secondary cylinder 58, a passage 66 opens out into the wall of the cylinder to provide a large orifice area at the beginning of the downward stroke of the secondary piston 56. The passage 66 links the cylinder space below the piston 56 to the space above the piston either directly, as shown in Figure 1 , or via a non-return valve (not shown) if cushioning towards the end of the extension stroke is to be retained. As a result, the resistance to flexion provided by the piston 56 during the initiation of flexion, preferably during the first 35° of flexion, is very low, and resistance is provided mainly by the main piston 48 subject to the position of the control rod 44R.

The piston and cylinder assembly 22 is constructed to provide resistance to both flexion and extension movements at the knee. From toe-off to heel contact, i.e. during the swing phase of the walking cycle, the assembly 22 damps movement of the shin component with respect to the thigh component. At heel contact, the knee is at or near full extension, this being the condition of the knee mechanism as shown in Figures 1 and 2, and as soon as the amputee begins to apply load to the foot, the axial component of the applied load in the shin component causes the knee axis 16 to move downwardly with respect to the shin component 20, the resilient arm 18 deflecting downwardly by a small amount as shown in Figure 6. This deflection of the arm 18 causes the trigger element 36T, being connected to the cross bar 36 to bear against the downwardly facing curved surface of the actuation element 40A of the rocker 40 to pivot about its pivot pin 42 in an anti- clockwise direction with respect to the chassis 10, as shown in Figure 6. This, in turn, causes the posterior annuli 40C of the rocker 40 to move downwardly by a distance of up to approximately 1mm with respect to the rear pivot pin 24 mounting the piston rod 22R of the piston and cylinder assembly 22 so as to engage the control member or pin 44 in the piston rod. As described above, this causes restriction of hydraulic fluid flow in the piston and cylinder assembly 22 to increase the resistance to inward movement of the main piston 48 in the cylinder 22C. In other words, the relative movements of the portion of the shin component constituted by the free or upper end part of the resilient arm 18 with respect to the main shin component portion actuates a partial or full hydraulic lock in the piston and cylinder assembly 22 which thus acts as a knee stabilising device. As the amputee's body moves forward over the foot, the resultant reaction force from the foot is directed along a load line which moves progressively further forward with respect to the knee axis so that the deflection of the resilient arm 18 decreases during the latter part of the stance phase of the walking cycle and on weight is transferred to the sound limb, to a point at which the applied load is insufficient to overcome the resilience of the arm 18 and the rocker 40 rotates back to its normal position as shown in Figure 2, thereby removing the knee stabilising resistance of the piston and cylinder assembly 22. The instant in the walking cycle at which the stabilising resistance is removed can be altered by adjusting the position of the trigger element 36T. It will be seen from Figure 6, that at about 30 degrees flexion and over, the trigger element 36T is no longer in registry with the actuation element 40A of the rocker 40, passing beyond its anterior end when an axial load is applied, so that no stabilising action is actuated above 30 degrees of flexion. Limits other than 30 degrees can be used by shortening or lengthening the rocker arm as required. To magnify the effect of the relative movement of the shin component portions the distance between the trigger element upper end and the rocking pivot defined by pin 42 is smaller than that between the pivot and the control member 44, at least at full knee extension.

Referring to Figures 8 and 9, in an alternative embodiment of the invention, the resilient arm 18 is replaced by a shin component upper portion 70 which forms a link between the main portion 20 of the shin and a solid knee pivot shaft 14. This link 70 is pivotable about an anterior pivot shaft 72 housed at each of its ends in the upper side ears 20E of the shin cradle part of the main shin component portion 20. In this embodiment, the link 70 is formed as a block of thermoplastics material which is sufficiently rigid that medial and lateral movement of the main shin component portion 20 with respect to the chassis 10 is negligible. Integrally formed with this block and extending downwardly from its anterior edge is a two-part leaf spring 70S, which is best seen in Figure 9. This spring 70S is enclosed within the upper part of the shin cradle and at its distal end has a transverse bore 70SB for a retaining pin 20P extending between the two sides of the shin cradle, as shown in Figure 2.

Referring to Figure 8 , a horizontal adjuster bar 20B is mounted for upward and downward adjustment in a vertical slot 20S in the main shin component portion 20. This bar 20B acts as an abutment for the leaf spring 70S. On either side of the slot 20S, the adjuster bar 20B has a cross- section in the form of the segment of a circle with anterior clamping faces, and a screw 20BS mounted in a bore in a central boss of the adjuster bar 20B clamps the bar at a selected position in the slot 20S according to the required stiffness of link 70 when an axial load is applied to the shin component.

Referring to Figure 9 in conjunction with Figure 8, the link 70 has a vertical slot formed between the two parts of the leaf spring 70S which contains a trigger arm 70T having a proximal end joined to the distal end of the spring 70S and a free end formed as the posterior end of a free end portion 70TF of the trigger arm 70T which extends in the posterior direction from the region of the leaf spring 70S beneath the block part of the link 70 to the region of the knee pivot shaft 14, as shown in Figure 8.

The free end portion 70TF of the trigger arm 70T forms an actuating element which engages an actuation cam surface 74C of a rocker 74 mounted in the knee chassis 10. For reasons which will become clear below, the cam surface 74C has a generally circular profile which in the normal position of the rocker 74, as shown in Figure 8, is centred on the knee axis 16. To achieve this largely concentric relationship, the anterior portion of the rocker 74 bearing the cam surface 74C is formed as an annulus 74AA which encircles the knee pivot shaft 14 and lies in a posterior recess 70R of the link 70 (see Figure 8). The rocker 74 is pivotally mounted, as in the previously described embodiment, on the underside of the chassis 10 by the transversely directed pin 42 located above and to the posterior of the knee axis 16. On the opposite side of the pin 42 from the anterior annulus 74AA, the posterior part of the rocker 74 is formed, as before, as two circular annuli 74PA encircling the rear pivot pin 24 which, attaches the piston rod 22R to the knee chassis 10.

During flexion of the knee, the free end 70TD of the free end 70TF of the trigger arm 70T will engage the cam surface 74C of the rocker 74 at different positions, progressively approaching the line joining the knee axis and the pivot axis of the rocker 74 in the chassis 10, as defined by the rocker pivot pin 42. To accommodate the trigger arm free end 70TD at full flexion, the rocker 74 has an aperture 74A between the anterior annulus 74AA and pivot pin 42.

Actuation of the knee stabilising effect is performed in a similar manner to that described above with respect to the embodiment of Figures 1 to 7. When the amputee begins to apply load to the foot, the active component of the applied load in the shin component causes the knee axis 16 to move downwardly with respect to the shin component 20, the link 70 rotating by a small amount anti-clockwise about the anterior pivot shaft 72. This rotation causes flexion of the leaf spring 70S (shown in Figure 9), and the trigger finger 72F, being connected to the distal end of the spring

70S bears against the anterior annulus 74AA of the rocker 74, causing the rocker 74 to pivot about its pivot pin 42 in an anti-clockwise direction with respect to the chassis 10.

The piston and cylinder assembly 22 is activated in the manner already described with respect to the first embodiment.

Claims

1. An artificial leg comprising a thigh component, a shin component, knee pivoting means pivotally coupling the shin component to the thigh component to permit knee flexion and extension movements, an hydraulic piston and cylinder assembly having a piston part and a cylinder part each connected to a respective one of the thigh and shin components for resisting flexion movement during the stance phase, and automatic control means to alter the degree to which the piston and cylinder assembly resists the flexion movement, wherein the shin component includes at least two portions, one of which is coupled to the thigh component by the knee pivoting means and is movable relative to the other of the two shin component portions in response to the application of an axial load, and wherein the automatic control means comprise connecting means arranged to convert relative movement of the two portions of the shin component to movement of a movable control member associated with that part of the piston and cylinder assembly which is pivotally connected to the thigh component.

2. An artificial leg according to claim 1, wherein the connecting means comprise a connecting member which has an actuation element for engaging the shin component in the region of the knee pivoting means .

3. An artificial leg according to claim 1, wherein the connecting means comprise a connecting member which is a lever mounted on the thigh component and having (a) an actuation element arranged to engage a trigger element associated with the shin component in the region of the knee pivoting means, and (b) a control element in the region of the pivotal coupling between the thigh component and the piston and cylinder assembly, the control element being operable to engage the control member of the piston and cylinder assembly.

4. An artificial leg according to claim 3, wherein the actuation element is arranged to engage a trigger element on a cross-member located at a knee axis and forming part of the said other shin component portion, the knee axis being defined by the knee pivoting means.

5. An artificial leg according to claim 3, wherein the actuation element of the connecting member is arranged for rotational connection with the trigger element.

6. An artificial leg according to claim 5, wherein the trigger element engages a curved surface on the connecting member.

7. An artificial leg according to claim 5, wherein the curved surface has a generally circular profile substantially centred on a knee axis defined by the knee pivoting means.

8. An artificial leg according to claim 3, wherein the connecting member is a rocker having a rocker pivot for pivotal mounting of the rocker on the thigh component with the actuation element and the control element on opposite respective sides of the rocker pivot.

9. An artificial leg according to claim 8, wherein the knee pivoting means define a knee axis, and the pivotal coupling between the thigh component and the piston and cylinder assembly defines a coupling axis, the rocker pivot defining a rocking axis which is so located that, in a vertical cross-section on a posterior/anterior plane, lines joining the knee axis and the coupling axis to the rocking axis form an inverted "V" .

10. An artificial leg according to claim 1 wherein the said two shin component portions are movable relative to each other against resilient biasing means in response to the axial load.

11. An artificial leg according to claim 9, wherein the said one shin component portion comprises at least part of an arm carrying the knee pivoting means, and the said other shin component portion comprises a main shin component portion extending distally from the thigh component, and wherein the arm is joined to the main shin component portion and is deflectable relative to the main shin component portion on application of an axial load on the leg from the thigh component via the knee pivoting means to the arm.

12. An artificial leg according to claim 11, wherein the arm is formed as a leaf spring extending at least in part in an anterior-posterior direction, and wherein the said part of the arm has a medial-lateral bore housing a tubular shaft forming the knee pivoting means.

13. An artificial leg according to claim 12, wherein the arm is a resilient member formed of a resilient plastics material and comprising a strip joined at one end to the main shin component portion and carrying at its other end an integral bush having a central axis substantially parallel to a major face of the strip.

14. An artificial leg according to claim 13, wherein the arm is a one-piece fibre-reinforced plastics member.

15. An artificial leg according to claim 12, wherein the said other shin component portion includes a cross-member which passes through the tubular shaft with clearance for movement in the shaft.

16. An artificial leg according to claim 15, wherein the actuation element is arranged to engage a trigger element forming part of the said other shin component portion.

17. An artificial leg according to claim 16, wherein the trigger element is a projection on the cross-member, the projection extending through an aperture in the tubular shaft to engage the actuation element of the connecting member.

18. An artificial leg according to claim 11, wherein the said part of an arm is annular in a cross-section in a plane perpendicular to the knee axis, and is centred on the knee axis.

19. An artificial leg according to claim 8, wherein the actuation element and the control element of the rocker have curved surfaces for engaging respectively the trigger element and the control member, wherein the knee pivoting means define a knee axis and the pivotal coupling between the thigh component and the piston and cylinder assembly defines a coupling axis, and wherein the curved surfaces of the actuation element and the control element have circular profiles which are centred respectively on the knee axis and the coupling axis.

20. An artificial leg according to claim 10, wherein the two shin component portions are pivotally connected, the connection being formed by the combination of a pivot shaft or pins together with a spring.

21. An artificial leg according to claim 20, wherein the said one shin component portion forms a pivoting link between a main shin component portion and the thigh component and wherein the spring is a leaf spring having a proximal end rigidly connected to a main part of the link and a distal end engaging the main shin component portion.

22. An artificial leg according to claim 21, wherein the link has a pivotal connection with the main shin component portion, the connection defining a connection axis to the anterior of the knee pivoting means, and the leaf spring extends downwardly from the main part of the link in the region of the pivotal connection to engage the main shin component portion so that the spring is deflected when the two portions are pivoted with respect to each other by application of the axial load, the link having a trigger part joined to the distal end of the leaf spring and extending from that distal end to the region of the knee pivoting means where it engages the connecting member for transferring movement to the control member of the piston and cylinder assembly.

23. An artificial leg according to claim 22, wherein the link, its leaf spring, and its trigger part are all formed as a single component.

24. A knee and shin assembly for an artificial leg, the assembly comprising an upper component for connection to a stump socket, a shin component, knee pivoting means pivotally coupling the shin component to the upper component to permit knee flexion and extension movements, an hydraulic piston and cylinder assembly having a piston part and a cylinder part each connected to a respective one of the upper and shin components for resisting flexion movement during the stance phase, and automatic control means to alter the degree to which the piston and cylinder assembly resists the flexion movement, wherein the shin component includes at least two portions, one of which is coupled to the upper component by the knee pivoting means and is movable relative to the other of the two shin component portions in response to the application of an axial load, and wherein the automatic control means comprise connecting means arranged to convert relative movement of the two portions of the shin component to movement of a movable control member associated with that part of the piston and cylinder assembly which is pivotally connected to the upper component.

25. An artificial leg according to claim 24, wherein the connecting means comprise a connecting member which is a lever mounted on the upper component and having (a) an actuation element arranged to engage a trigger element associated with the shin component in the region of the knee pivoting means, and (b) a control element in the region of the pivotal coupling between the upper component and the piston and cylinder assembly, the control element being operable to engage the control member of the piston and cylinder assembly.