The inventive joint device is thus of the kind that includes two bodies between which there is mounted a joint element which enables the bodies to be angled relative to one another and which is adapted to permit compression loading of the joint device.

The joint element of such joint devices is normally comprised of glide surfaces which transfer pressure forces to one another. Such glide joints are encumbered with drawbacks, even when the glide surfaces are comprised of a smooth material, for instance a Teflon@-type material, or when a lubricant is introduced between the glide surfaces and the glide surfaces are designed to slide relative to one another in the best possible way.

An object of the present invention is to provide a joint device that eliminates friction-related drawbacks in known joint devices that are intended to be subjected to compression loads to a substantial degree.

This object is achieved with a joint device of the construction defined in Claim 1.

Further embodiments of the joint device are set forth in the independent Claims.

The invention is based on a joint device of the kind that includes two joint bodies, possibly in the form of rods, which are mutually co-axial in the"neutral position"of the joint and transfer compression forces through the common axis

of the bodies and the intermediate joint member. Compression forces are transferred between the two bodies via the joint element, even when the joint device is angled, i. e. even when the axes of said bodies define a certain angle therebetween.

The mutually proximal ends of the joint bodies overlap in the longitudinal direction of the joint element and a tensioned joint element is attached between said proximal ends of the joint bodies such as to be in alignment with the body axes when the joint is in its"neutral state". By forming the joint element from a strand, a band, a rod or a wire made of a material having a high E-modulus and yield point, such as steel for instance, the joint element can be given a very small cross-sectional size so that at a length which although small is still a relatively large multiple of the cross- sectional size the joint element will be highly flexible/bendable while, whilst not being subjected to any appreciable degree of stretch or elongation.

According to one simple embodiment of the invention, the joint element may be comprised of a thin strand or wire comprised of corrosion-resistant steel, with the ends of the strand or wire fastened securely to the bodies, for instance welded thereto or formed integrally therewith. The element attachment may be adapted for minimising the strain on the ends of the joint element as it flexes or bends. The ends of the joint element may be fastened to the bodies in the top part of a generally wedge-shaped or conical recess that has a curved wall against which said element progressively comes into abutment as bending of the joint increases.

When the joint element is comprised of a rod, wire or the like, which is readily flexible/bendable in all axial planes that contain the rod, it is necessary to stabilise the joint against rotation or to limit rotation of the joint and/or its bendability to a specific plane with the aid of special

means. In this regard, two joint elements can be positioned in mutual lateral relationship and aligned to experience the same degree of bending, wherewith the two individual elements are able to capture and restrict rotary movements of the joint bodies around their common axis. Furthermore, if the compression loading forces pass between the individual elements, the joint will obtain a self-stabilising effect which tends to align the bodies relative to one another in the plane that is pitched by the two individual elements.

In one alternative embodiment, the joint element may be given the form of a readily flexed plate of relatively large width, wherewith the mutually parallel free edge regions of the plate provide essentially the same function and effect as the two individual elements just described.

The inventive joint device can be moulded in an elastic body, for instance a rubber body, which serves to keep the central parts of the joint device free from foreign material on the one hand and which also provides relative stabilisation of the device components to some extent. The elastomeric body also provides the function of a compression element that has a shock-absorbing effect between those ends of the two bodies that are fastened to opposing ends of the joint element and that transfer pressure forces to each other when the joint device is subjected to tensile forces. The bending resistance of the elastomeric material used will be so low as not to have any great effect on the joint functions of the joint device. Although the inventive joint can be used generally, it will be noted that the joint can be used to particular benefit as a joint prosthesis for human beings and animals, particularly joints that are primarily subjected to compression forces.

The inventive joint has the essential advantage of enabling powerful compressive shock loads to be captured without

interfering with the functions of the joint to any troublesome extent.

Another advantage afforded by the invention is that compressive shock loads that are not central, i. e. that are not applied through the joint in a"neutral state" (when the joint bodies are not co-axial) cause the point of attachment of one joint body to the joint element to swing or pivot around the point of attachment of said element to the other joint body, and vice versa. This swinging movement extends the time sequence for movements in the joint region and reduces the effect of the shock loads on the joint components.

Instead of (or in addition to) embodying the joint device (excluding its connection parts) in an elastomeric body, the joint may conveniently be provided with stabilising means that while minimally increasing the bending resistance of the joint enables the joint to be stabilised against tensile loads and against displacement movements between said joint bodies transversely to the longitudinal axis of the flexible/bendable element (corresponding to the direction of the compressive loads).

Such a stabilising member can be comprised of one or more elastomeric blocks. When the flexible element has the form of a band or ribbon, two blocks may be disposed in mirror symmetry to the flexible element and fastened thereto in a manner such that the blocks and the band or ribbon will have a generally hourglass cross-sectional shape. As a result of this hourglass cross-sectional shape, the joint will be stabilised with respect to tensile forces and with respect to parallel displacement of the bodies of said device transversely to the direction of the load. The stabilising member will also have low resistance with respect to contemplated bending or flexing function of the joint.

In a further development of the invention, the joint (excluding the outer connection parts of the bodies) may include an enclosure (for instance instead of the earlier mentioned elastomeric material) that contains a flowable material that thickens when subjected to shear forces. Such a dilatant material may, e. g., consist of a flowable mixture of water and starch, for instance cornstarch. Because the dilatant material thickens in shear, and usually thickens more significantly in the case of rapid shear processes, it will provide a particularly favourable damping characteristic for rapid joint movements, while providing very low damping with respect to slow joint movements that generate low shear forces.

The inventive joint device also has other technical effects, as will be realised by the person of normal skill in this art.

In the case of a further development, the joint device may include a guide curve on/from which the bendable element or elements is/are reeled-up/unreeled as the joint bends. The guide curve is suitably designed to reel-up the bendable element from one end thereof (preferably its bottom end when the joint device is used as a knee joint).

The guide curve thus causes the centre of rotation of the joint to be displaced in response to bending movement. This displacement will preferably be continuous. Displacement of the rotational centre of the joint minimises the risk of the joint being put set to its natural frequency.

There may be provided on one side of the guide curve a rubber covering that co-acts with the bendable element. The bendable element may be provided with an elastomeric covering on that side thereof which lies proximal to the guide curve and/or on

the opposite side thereof. As before mentioned, the rubber covering on the bendable element may be adapted to obtain a wedge or hourglass cross-sectional shape for the purposes indicated.

The inventive joint device can withstand effectively loading situations that involve high compression forces, and is also able to withstand tensile forces to a certain extent.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.

Fig. 1 is a side view of an inventive joint device.

Fig. 2 is a view taken on the line II-II in Fig. 1.

Fig. 3 is a sectional view taken on the line III-III in Fig.

1.

Fig. 4 is a cross-sectional view corresponding to Fig. 3 of another embodiment.

Fig. 5 is a view corresponding to Fig. 2 which illustrates another embodiment.

Fig. 6 is a view corresponding to Fig. 3 illustrating the embodiment of Fig. 5.

Fig. 7 illustrates a further development of the joint, in a view corresponding to the view of Fig. 1.

Fig. 8 illustrates an inventive joint with which stabilising means are provided between the joint bodies.

Fig. 9 shows the joint enclosed in a casing which contains a flowable material that thickens in shear.

Fig. 10 is a cross-sectional view of a further embodiment of the joint and shows the joint in one end position.

Fig. 11 shows the joint of Fig. 10 in a position in which it is bent from said end position.

Fig. 1 shows two joint bodies 1 which each include a respective stem 2 having an axis 3, said stems being straight in the illustrated case. The stems have a curved end-part 4 whose respective end-portions are intersected by the axes 3 of stems 2 and extend generally perpendicular to said stem.

The bodies 1 are shown aligned co-axially with their respective axis 3 and orientated so that the end-part 5 of one body engages in the concave side of the curved end-part 4 of the other body 1. Two bendable or flexible thin steel bands 8 extend between the end-parts of the bodies 1 and together pitch a plane P that extends perpendicular to the plane of Fig. 1 and contains the respective axes 3 of said bodies 1.

The joint illustrated in Fig. 1 is intended primarily for compressive forces, wherewith compressive forces F pass through the axes 3. These compressive forces are transmitted through the medium of the steel bands 8, which, because of the configuration of the joint, are subjected essentially only to tensile forces.

The joint can be bent or flexed easily in the plane of Fig.

1, since the bands 8 have no appreciable bending resistance in this plane. However, the bands have a very high resistance to tensile forces and only a slight degree of stretch.

Because the bands 8 are separated laterally, chey provide significant resistance to relative rotation of the bodies 1 about the axes 3. It will also be seen that the individual bands 8 counteract obliqueness of the axes 3 in the plane P.

It will be understood that the two bands 8 can be replaced with a single broad band 81 whose two edge-portions 82 have essentially the same function as the two individual bands 8.

According to a more preferred embodiment (Figs. 5 and 6), the two bands 8 may be replaced with a single rod or wire 84 which is in alignment with the axes 3 when the joint is "straight".

As shown in Fig. 7, one of the bodies 1 of said joint may be provided with an abutment peg 7 so as to restrict pivotal movement of the joint to an angular range which is delimited by co-action of the peg 7 with the other body 1.

It will also be seen from Fig. 7 that the curved end-parts 4 and the element/elements 8,81,84 subjected to tensile forces may be embodied in an elastomeric body 14, conveniently a rubber body which is preferably transparent, with parts 2 of said bodies 1 extending out from the elastomeric body 14. The elastomeric body 14 prevents the ingress of foreign material into the area of mutual co-action between the bodies and the elements 8,81,84.

It will also be seen from Fig. 7 that the end-parts 5 overlap so as to act alternately with one another, possibly via the material of the body 14, so as to enable tensile forces to be transferred between the bodies 1.

Because the end-parts 5 of a body 1 can experience pivotal movement about the points at which the bands 8 are attached to the other of said bodies 1, there is obtained in the joint

a pattern of movement which is favourable in the event of rapid changes in load and angular settings between the bodies.

The invention provides a joint for universal use. However, it will be evident that the joint has particular advantages in respect of applications in which the joint is subjected primarily to compressive loads whilst, at the same time, enabling changes to be made to the angle of the joint (with low resistance) and particularly when the joint shall have a low malfunctioning tendency, even when subjected to load above the elastic limit of the material used, particularly with respect to the bands 8,81 or the rod/wire 84. The joint is particularly favourable for use in those cases when it is desired to restrict the possibility of relevant rotation of the bodies in said joint about their axes, said axes being generally aligned with respect to one another.

The bodies of the inventive joint device are designed so that an easily bent/flexed but essentially non-stretchable interconnecting element fastened between said bodies will essentially be subjected solely to tensile forces when the joint is subjected to compressive forces. In this regard, the element 8 may be made of a material that has a high E-modulus and elastic limit, so that high tensile forces can be taken- up with a small cross-sectional area, at the same time as the interconnecting element subjected to tensile loads will have a very low bending resistance and essentially no compression resistance.

Because the attachment point between the joint element 8 under tension is able to swing about the element attachment point on the other body 1, and vice versa, stabilisation of the joint is particularly effective under the influence of the external forces. The joint device can therefore be considered to be a force stabilised type of device.

Fig. 8 illustrates an embodiment which includes a stabilising element in the form of two elastomeric members 11 which have generally the same width as the bendable/flexible band 8. As shown in cross-section in Fig. 8, each rubber member 11 is firmly attached to the surface of the band 8 across the full height of the band, and is also firmly attached to the inner surface of the curved parts 4,5 of said bodies 1. Each member may conveniently taper towards its longitudinal midway point and the element members 11 in combination with the band 8 have an hourglass-like cross-sectional shape.

In practice, the elastic element/the band 8 is comprised of steel or some like material, and will preferably have a small thickness in view of its bending/flexing function. The rubber blocks 11 compensate for the low buckling stability of the bendable element 8 and its low bending resistance about said attachment points.

Fig. 9 illustrates schematically a joint device (including its connecting parts 9) which is enclosed in a casing 15, for instance an elastomeric casing. The casing 15 contains a dilatant, flowable material 16, i. e. a material which will thicken when subjected to shear forces. The flowable material will preferably be of a kind that thickens more rapidly with increasing shear, i. e. the faster the joint moves the quicker the material will thicken. The material 16 may consist of a flowable or liquid mixture of water and starch. The casing or enclosure 15 may be formed partially by the bodies 1. The casing 15 containing the dilatant material 16 may, of course, be used in the absence of elastomeric stabilising blocks 11. As shown in Figs. 10 and 11, the joint may be supplemented with a band guide surface 71 so that the effective rotational centre of the joint will be displaced as the joint is bent or flexed.

Figs. 10,11 illustrate a joint that can be used as a knee joint for instance, wherewith the rotational centre is conveniently displaced upwards as the angle between the upper and lower part of the joint decreases. That side of the guide curve which lies proximal to the band may be provided with a rubber covering. The side of the band that lies proximal to the guide curve and/or its opposite side may also be provided with a rubber covering. The rubber coverings on the band may be given the form of an hourglass-like profile, as illustrated in conjunction with other, previous embodiments.

The joint device illustrated in Figs. 10,11 also includes a limit stop 74 in one bending direction beyond the position in which the connecting stems of the bodies and the band 8 are in mutual alignment, whereby the inventive joint provides the same bending limitation as a natural knee joint. Naturally, in other embodiments a bending limit position can be established correspondingly in selected positions in one or the other, or in both, bending directions.