GB2092451A

GB2092451A - Improvements in artificial limbs

Info

Publication number: GB2092451A
Application number: GB8204768A
Authority: GB
Original assignee: Chas A Blatchford and Sons Ltd
Current assignee: Chas A Blatchford and Sons Ltd
Priority date: 1980-03-03
Filing date: 1981-03-03
Publication date: 1982-08-18
Also published as: GB2092451B

Abstract

An artificial foot and ankle assembly has a foot (1,2), an ankle joint and a shin-connecting socket (7). The ankle joint includes a uniaxial resilient bearing (5) with a shaft (4) to which the foot is connected and an outer shell (6) clamped to the socket (7). Between the shaft (4) and shell (6) is a rubber sleeve. A forward extension (8) of the socket (7) engages a rubber buffer (9) fixed in the foot. The arrangement permits plantar and dorsi flexion of the foot about the ankle joint axis. The elastic rates of rubber sleeve and buffer are such that the resistance of the ankle joint to plantar flexion and dorsi flexion is different. There is ample space behind the ankle joint, and also below its axis, for the foot cosmesis. <IMAGE>

Description

SPECIFICATION Improvements in artificial limbs This invention relates to an artificial leg and in particular to the connection of an artificial foot to an artificial shin.

An artificial leg may include a resilient ankle joint allowing movement between the connecting member and the foot. Uniaxial ankle joints are well known, and one common construction that has been used for some considerable time includes a rotating bearing with a transverse horizontal axis, and rubber cushions or buffers between the connecting member and the foot to limit the degree of ankle flexion. The buffers are positioned in front of and to the rear of the joint axis, and have different spring rates to provide a differential flexion resistance, the resistance to dorsi flexion usually being higher than the resistance to plantar flexion. This construction had a disadvantage in that it is difficult to make a neat cosmetic foam covering for the ankle joint due to the amount of space taken up by the bearing and rubber buffers.In particular, there is very limited space available for foam cosmesis behind the joint. Therefore according to this invention, a limb prothesis comprises:- (i) a shin component; (ii) a foot assembly including (a) a foot and an upper ankle component, which component is adapted to connect the assembly to the shin component, the assembly including an ankle joint permitting plantar and dorsi flexion of the foot about an ankle joint axis, and (b) elastic coupling means between the foot and the upper ankle component to resist the said flexion, the elastic rate of the coupling means for dorsi flexion being different from its elastic rate for plantar flexion, the coupling means including one or more elastic members none of which have their major part to the rear of the ankle joint axis; and (iii) a flexible cosmetic shin covering surrounding the skin component and at least the upper ankle component of the said assembly, which covering extends below the ankle joint axis and occupies the space between the upper ankle component and the foot. The ankle joint has flexible coupling elements which are either symmetrical about the axis or are in front of the axis so that sufficient space is available to the rear of the axis for a cosmetic foam covering. By eliminating the rear buffer of the known construction, the structural components of the limb in the region of the ankle can be made relatively compact, allowing the use of a relatively thick foam cosmetic covering which abuts neatly with a flexible foot moulding and maintains an acceptable external appearance when the ankle joint in flexed.

The invention will now be described by way of example with reference to the drawings in which: Figure 1 is a partly sectioned medial side view of a first foot assembly; Figure 2 is a sectioned front view of the ankle components of the first foot assembly; Figure 3 is a front view of the ankle components of Figure 2; and Figure 4 is a partly sectioned medial side view of a second foot assembly which is interchangeable with that of Figure 1.

In the following description two foot assembly embodiments are referred to, showing two of several possible foot assemblies which can be used. The first embodiment, shown in Figures 1 to 3, is a foot assembly having a flexible ankle joint allowing flexion about a single, substantially horizontal axis.

The assembly comprises a foot keel 1 encased in a flexible foot moulding 2 having a generally horizontal upper surface 3. The keel is attached to the inner shaft 4 of a resilient bearing 5 whose outer shell 6 is clamped in a connecting member or upper ankle component 7. The ankle component 7 has a forwardly extending projection 8 arranged to engage a front buffer 9 adjustably mounted in the keel 1. The ankle component 7 serves to fasten the foot assembly to a shin tube, and for this purpose it has a cylindrical receptacle 10 (see Figure 2) with a slotted outer wall 11 so that the shin tube 12 can be clamped in the receptacle by tightening a screw across the slot 13.

The receptacle end wall 14 constitutes a mating surface which engages the end of the shin tube 12 to define the position of the assembly relative to the tube. The position of the surface 14 relative to the sole 15 of the foot is a predetermined fixed distance, which distance is common to this and any other foot assembly intended to form part of a range of interchangeable foot assemblies.

Referring to Figure 2, the resilient bearing has two sections, one to each side of the shin tube axis 16, and each section comprises an inner sleeve 17 bonded to a rubber sleeve 18 which is bonded in turn to the outer shell 6. The shaft 4 is fixed in the inner sleeve 17 and both bearing sections are clamped in the ankle component 7 by means of screws (not shown) which tighten the wall 19 of the component 7 around the outer shells 6. All flexion of the ankle is therefore taken up by the rubber sleeve 18, to produce shear deformation. This type of coupling enables a relatively large ankle flexion range to be obtained compared with conventional rubber buffers which are deformed by compression rather than shear, and in addition the compliance of the bearing is relatively predictable.These characteristics of the bearing make the foot assembly particularly suitable for patients of limited activity since the resistance to plantar flexion (i.e. anti-clockwise movement of the foot relative to the shin as seen in Figure 1) can be relatively low, so that stable contact of the whole foot with the ground occurs relatively easily and rapidly after heel contact. This joint is predominantly uniaxial, in that it allows only relatively little flexion of the ankle about the longitudinal axis of the foot, a factor which constributes to the stablity of the assembly and hence its suitability for limited activity patients.

The dorsi flexion of the ankle, the forward projection 8 engages the rubber buffer 9 for increased flexion resistance. Normally, the position of the buffer 9 in the keel 1 is adjusted so that engagement with the projection 8 occurs only after flexion of the joint has passed through the neutral position of the bearing 5 from plantar flexion to dorsi flexion.

Heel height, i.e. the height of the heel sole 15 above the ground when the limb is substantially vertical, is adjusted by releasing the clamping of the bearing 5 in the ankle component 7 and rotating the foot to the required heel height, ensuring that the buffer 9 is not in contact with the projection 8 when the clamping screws are re-tightened. This adjustment can be performd either before or after fitment of the foot assembly to the limb, and since the clamping of the bearing 5 is quite separate from the clamping of the shin tube in the ankle component 7, the foot assembly can be attached and removed without disturbing the heel height setting.The construction of the ankle component 7 which incorporates both the shin tube fastening means and a clamp for the resilient bearing is such that the shin is connected to the foot by a single intermediate component, in contrast to some prior art ankle designs. The assembly of the foot, ankle and shin is thus a relatively quick and simple operation.

It will be seen that the ankle joint is relatively compact and in particular is characterised by the absence of any structural components to the rear of the bearing 5. A relatively large space is therefore available between the bearing 5 and the rear end 20 of the foot for a foam cosmetic covering which is an extension of the shin cosmesis. It will be seen from Figure 1 that the upper surface of the foot moulding 3 is below the ankle joint axis 21. As a result, the interface between the shin cosmesis and the foot moulding is at a level where the join does not seriously affect the external appearance of the limb in the ankle region. The relatively large permitted thickness of cosmesis behind the ankle joint also improves the external appearance.

Referring now to Figure 4, a second embodiment of foot assembly is shown which is intended mainly for active patients. The reference numerals in Figure 4 correspond where appropriate to those in the preceding Figures. As with the first embodiment, the foot assembly comprises a keel 1 and a foot moulding 2 with an upper surface 3 below the axis 21. The upper ankle component 7 has a receptacle 10 which is virtually identical to the receptacle in the first embodiment, and the mating surface 14 is positioned relative to the ankle joint and the sole of the foot such that the first and second embodiments are interchangeable on a limb without necessarily requiring any adjustments to the limb above the ankle.In this embodiment the resilient bearing is in the form of a rubber-filled ball and socket joint 22 having a central ball member 23 fixed to the keel 1, a socket formed by a recess in the ankle component 7 and a clamping cup 24, and a rubber sleeve 25 sandwiched between the socket and the ball member 23. To assemble the joint, the clamping cup 24 and the sleeve 25 are fitted over the ball member 23.

The ankle component 7 is then brought down over the sleeve and its lower flange 26 is tightened with four screws 27 onto the flange 28 of the clamping cup to clamp the sleeve and the ball member in the socket. Any flexion of the ankle from the neutral position results in shear deformation of the rubber sleeve 25. Unlike the resilient bearing 5 of the first embodiment the ball and socket joint allows flexion of the ankle about any axis passing through the centre of the joint, and therefore gives the active patient greater freedom of movement. The rubber buffer 9 provides differential flexion resistance in the same manner as in the first embodiment. Heel height adjustment is carried out in a similar manner as described above in relation to the first embodiment.

Claims

CLAIM

A limb prosthesis comprising: (i) a shin component; (ii) a foot assembly including (a) a foot and an upper ankle component, which component is adapted to connect the assembly to the shin component, the assembly including an ankle joint permitting plantar and dorsi flexion of the foot about an ankle joint axis, and (b) elastic coupling means between the foot and the upper ankle component to resist the~said flexion, the elastic rate of the coupling means for dorsi flexion being different from its elastic rate for plantar flexion, the coupling means including one or more elastic members none of which have their major part to the rear of the ankle joint axis; and (iii) a flexible cosmetic shin covering surrounding the shin component and at least the upper ankle component of the said assembly, which covering extends below the ankle joint axis and occupies the space between the upper ankle component and the foot.