Arrangement In Feet For Leg Prostheses

Abstract

An artificial leg for above-knee amputees comprising a thigh section, a shank section and a knee joint connecting the thigh and shank sections. The shank section is formed with an ankle to which a foot section is pivotally mounted by means of a horizontal shaft in said ankle. A mechanism is provided to bring about control over the shank section motions during swing and stance phases, said mechanism being housed in a shell-shaped calf section constituting a part of the shank. The improved alignment provided by the artificial leg in accordance with the invention is obtained by positioning the horizontal ankle shaft ahead of the weight supporting line passing through the thigh section, the knee joint shaft, and the ankle and by articulating the lower end of the ankle which is shaped as a plate, to a plate arranged on the foot section by means of the horizontal shaft, in addition to which a resilient means is provided behind said horizontal shaft between the foot and ankle plates for forcing the plates apart.

Description

BACKGROUND OF THE INVENTION

The use of single-axis knee joints in above-knee prostheses predominates within the prosthesis technique. Despite its deficiencies this single axis construction of the knee joint is favored both on account of its simplicity and its reliability over for instance so-called anatomic and polycentric knee joints. The present invention relates to a leg prosthesis having a single-axis knee joint.

The knee joint of the natural leg seemingly operates like a hinge connection but as a matter of fact it is much more complicated and complex in function. The motions of the natural knee joint during flexion and extension are determined as to their geometry by the femoral and tibial configuration of the condyles and by the manner in which these cooperate and are kept together by means of the meniscus and ligaments. Upon bending motion of the natural knee joint the tibia is moved backwards, resulting in a knee motion which is a combination of rolling and sliding. The tibial condyles then describe a curvature closely resembling the contour configuration of the femoral condyles.

A step may be separated into two phases, a stance phase and a swing phase. The stance phase is that part of the step when the foot has contact with the floor (ground) and the swing phase that part thereof when the foot is in the air without floor contact and is either moving backwards as upon flexion of the knee joint or is moving forwards as upon extension of the knee joint.

On account of its anatomy and geometry briefly described above the natural knee joint brings about a shortening of the leg between the two extreme positions thereof during the stance phase, i.e. the heel contact at the beginning of the stance phase and the push-off at the end of the stance phase and at the transition into the swing phase.

It is obvious that a leg prosthesis of the single-axis type cannot bring about a corresponding shortening of the leg during the intermediate position of the leg during the stance phase. A leg prosthesis having a single-axis knee joint has a fixed length, which causes difficulties, well known to doctors and prosthetists, in that the artificial foot does not clear the ground when it moves past the sound foot during the forward swing of the artificial foot. Amputees try to compensate therefor by elevating their hips on the prosthesis side or by swinging the prosthesis outwards, so called circumduction. Common measures taken by the prosthetist to remove difficulties of this nature involve making the leg prosthesis somewhat shorter than the sound leg or fixing the prosthesis foot in a slightly upwardly directed position, i.e. at an acute angle relative to the shank. The risk that the foot will touch the ground when being swung forward is thereby eliminated.

The measures enumerated above do not, however, involve desirable solutions. In fact, they may even be harmful to the patient because of the artificial leg being shorter than the natural leg. Above all, they impede obtainment of a walking pattern resembling the natural walk.

Certain prosthetic knee systems make use of a complicated pattern of links to bring about a shortening of the prosthesis during the swing phase, and in doing so they simulate the function of the natural knee joint in this respect. Unfortunately, this desired function is rendered possible only with the aid of a complicated construction and at the expense of the so-called cosmesis, i.e. a good design and an aesthetical appearance of the leg. Most important, the cosmesis, possible in the use of knees of the above type, becomes so poor and unsatisfactory that knee joints of this construction have never been put to such an extensive use as is warranted by the performance of the construction.

The purpose of the present invention is to eliminate the fundamental drawbacks of using a single-axis knee joint as the connecting and articulating means between the knee portion and shank section of the prosthesis. The construction does, however, demand that the methods of the so-called alignment of an above-knee prosthesis are briefly described, together with the problem of obtaining knee stability during the stance phase. By the denomination "alignment" in this connection is understood the relationship between the so-called weight supporting line through the femoral socket of the prosthesis and the posterior-anterior position of the knee center. This weight supporting line is often, although not completely adequately, denominated the TKA-line, i.e. the trochanter-knee-ankle line.

Anatomical deviations and the special functions of various knee mechanisms call for variations from the above-mentioned basic alignment. By shifting the socket with respect to the knee center, the prosthetist is able to achieve that the body weight is transmitted through the prosthesis along a line falling in the desired position to the knee center, posterior to, on, or anterior to it.

The stability of a thigh or hip prosthesis is, in the case of conventional prostheses and provided no special mechanisms for the stance phase control are used, a question of alignment. If the knee joint shaft or pin is placed behind the weight supporting line through the socket, which line is most easily imagined as one passing between the trochanter and the ankle, hyperextension of the knee joint is obtained upon loading of the prosthesis during walking or in a standing position, whereby buckling or flexion of the knee joint is prohibited. This is referred to as alignment stability and the further behind the weight supporting line the knee joint or shaft is placed the greater the stability obtained. An increase of the stability, however, renders the initiation of the flexion of the knee joint a more difficult and energy-consuming task at the transition from the stance phase to the swing phase, which in turn counteracts the possibility of obtaining a natural gait and a pleasing and aesthetic walking pattern.

Flexion of the knee joint is most easily obtained and a pleasing style of walking ensured if the knee joint or shaft is placed on or adjacent the weight supporting line through the socket. This unstable position, known as trigger alignment, does, however, increase the risk of a sudden and unintentional flexion, for which reason this alignment may only be used in the case of good and functional femoral stumps which through a pressure backwards inside the socket are capable of retaining the prosthesis in a stable position and prevent buckling. This phenomenon usually is referred to as voluntary knee control.

The trigger alignment arrangement may, in the case of weak and less functional stumps and in the case of patients having other physical or psychological deficiencies, only be used in connection with an adequate mechanism for stance phase control, i.e. the position of the gait cycle in which the foot is in contact with the ground.

The demand for knee stability is most important during the first half of the stance phase, i.e. during the period from heel contact to mid stance when the body is in upright position. To prevent flexion of the knee joint during this period it is necessary to rely on alignment stability of varying degree -- still providing that no particular stance control mechanism is being used. The knee shaft position behind the weight line varies from about 1 centimeter to about 5 centimeters or, in exceptional cases, even more. During the latter half of the stance phase -- from a vertical position to the rearwardly inclined position of the leg before push-off and transition to the swing phase -- the same degree of alignment -- or built-in stability is not as necessary as during the first half of the stance phase. However, hitherto an unchangeable degree of built-in stability during the entire stance phase has been unavoidable.

In contrast the natural knee permits flexion without resistance when the body weight is shifted onto the other leg, the artificial knee, having a high degree of alignment stability, offers a strong resistance against knee flexion, which is energy-consuming, creates a time lag relative to the correct moment of flexion and retards the transition of the prosthesis from the stance phase to the swing phase, all of which has a considerable negative influence on both walking comfort and the style of walking, in addition to which it is highly energy-consuming and as a consequence thereof tires the patient.

In single-axis knee joints adequate alignment stability during the first half of the stance phase, when the body weight is applied primarily on the posterior of the foot, would be ideal, whereas a lower degree of alignment stability -- or ideally the above-mentioned "trigger" alignment should prevail, when the body weight is shifted onto the foot of the other leg. This ideal condition may be denominated "self-adjusting alignment" and is particularly favorable during those moments of stance phase when the major portion of the artificial foot still has ground contact but the bulk of the body weight has been shifted onto the other leg.

This is achieved by means of the present invention in that the horizontal shaft in the prosthesis ankle about which shaft the artificial foot is journalled, is positioned ahead of the weight line of the prosthesis, in that the lower portion of the ankle is in the shape of an ankle plate at the forward end of which a foot plate is articulated by means of said horizontal shaft, and in that a spring means in inserted between the foot plate and the ankle plate.

The spring means between the ankle plate and the foot plate is held under a certain bias, whereby said plates, upon loading of the posterior portion of the foot, assume a position wherein they are practically parallel to each other but, in the absence of such a load, they automatically assume positions in which they are angularly displaced relative to each other. When the body weight is shifted from the prosthesis onto the sound leg but the artificial foot is still in contact with the ground over the entire sole surface (complete ground contact), the relative angular position of the plates causes the knee joint or shaft to be moved forward relative to the weight line, i.e. a change or self-adjustment of the prosthesis alignment occurs. When the artificial foot is lifted clear of the ground, i.e. when ground contact ceases completely, the spring means urges the plates further apart and the angle between them increases even more. In addition, the plates no longer exert an influence on the knee joint or shaft position, as any back pressure from the ground has ceased. Owing to the arrangement of the spring means, the anterior of the foot is thus lifted at this stage. This toe "pick-up" results in elimination of the risk of the foot touching the ground during the swing forward.

When the prosthesis carries the entire body weight, the knee joint or shaft is thus in its extreme rear position providing maximum safety against buckling, whereas when the body weight is being shifted onto the other leg, the knee joint or shaft is moved forwards and that prosthesis alignment which is most favorable for flexion of the knee joint -- and as a consequence thereof for the taking of one step -- is automatically established.

DESCRIPTION OF THE DRAWINGS

Further characteristics of the invention and the advantages obtained thereby will become apparent upon reading of the following detailed description of a preferred non-limiting embodiment of the invention. In the drawings:

FIG. 1 is a vertical longitudinal section through a leg prosthesis in accordance with the invention,

FIG. 2 is a similar longitudinal section at an angle of 90.degree. relative to the view in FIG. 1,

FIGS. 3 and 4 illustrate on an enlarged scale a vertical longitudinal section through the joint connecting the ankle and the foot in various angular positions thereof,

FIGS. 5, 6, and 7 illustrate schematically the alignment of prostheses adapted for various lengths of the legs,

FIG. 8 illustrates on an enlarged scale various angle positions of the joint between ankle and foot,

FIG. 9 illustrates on the same scale as in FIGS. 3 and 4 a vertical section through the prosthesis ankle plate,

FIG. 10 shows the plate of FIG. 9 from beneath,

FIG. 11 is a vertical section through the prosthesis foot plate,

FIG. 12 illustrates the plate of FIG. 11 from underneath, and

FIG. 13 is a similar vertical section as in FIG. 3 but in accordance with another embodiment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The upper (thigh) section or socket-and-knee part 1 is, as illustrated in FIG. 1, by means of a knee joint or shaft 2 connected to a lower (shank) section 3 at the lower end of which is attached an ankle 4 which is articulated to an artificial foot 5. From the knee part of the thigh socket 1 there extends forwardly an arm 6 which by means of a pivot 7 is journalled to the upper end of a hydraulic knee control mechanism 8 enabling a swinging motion of the shank section 3 relatively the thigh socket 1 over an angular section of approximately 130.degree.. In accordance with the embodiment illustrated on the drawings the hydraulic mechanism 8 comprises two cylinders 9, 10 which are located in co-axial positions relative to each other in the longitudinal direction and which contain liquid, one piston (not shown) being arranged for displacement in each cylinder. The pistons are securely attached on a common piston rod 11. Reference number 12 designates the attachment loop of the lower cylinder 10. The piston rod projects through a bushing in a valve housing 13 positioned intermediate the two cylinders 9, 10. The valve housing encloses a valve 14 serving to close off a channel intercommunicating the interior of cylinder 9 with that of cylinder 10, thus providing blocking of the knee joint in a particular position. A traction spring 15 is provided to turn the valve to closing position.

The knee control mechanism 8 is articulated at its lower end to a fork-like member 17 by means of a bolt 16, said fork-like member 17 being detachably secured to a base portion 19 by means of a bayonet catch 18 at the lower end of the shank section 3. Preferably, the base portion 19 is made integral with the lower portion of the shank section 3, which lower portion is designed as a shell-shaped calf portion. In the fork-like member 17 about a pin 20 (or bolt) is pivotally mounted the one end of a lever 21, the opposite end 22 of which is connected to the lower portion 24 of the valve arm 14 by means of a thread-like wire 23. The upper end 25 of a coupling wire 26 which freely passes through a vertical channel 27 made in the fork-like member 17 is secured to the lever 21. The lower end of the wire 26 is by means of a chuck 28 attached to an operating device 29, which device is actuated by the verticalmovements of the artificial foot and is vertically displaceable in the ankle 4.

The ankle 4 comprises an ankle plate 31 articulated to the artificial foot 5 by means of a horizontal shaft 30, and a tubular upright 33 with a flange 32 thereon is attached to said ankle plate 31. The upper end 34 of the upright 33 is adapted to be received in a clamping sleeve 35 extending downwardly from the shank section base portion 19. The clamping sleeve 35 is provided with a vertically extending slit 36 and the clamping sleeve sections on either side of said slit 36 may be tightened about the upper upright end 34 by means of a clamping screw 37.

The shaft 30 passes through two lugs 38 on the lower face of the ankle plate 31 and also through a lug 39 at at the forward end of a foot plate 40 incorporated in the artificial foot 5. A universal joint 41 connects the foot plate with the artificial foot 5. The sole thereof is designated 42. In the artificial foot 5 is inserted a cushion or pad 43 or the like of a compressible material, such as plastics or rubber, shaped so as to allow the artificial foot to perform angular movement about the joint 41 in various planes relative to the plate 40.

Into the rear end of the ankle plate 31 is screwed from behind a nipple 44 having a downwardly projecting pin 45 freely passing through a bore 46 in the foot plate 40. Between a flange 47 on the nipple 44 and the foot plate 40 is inserted an insert or washer 48 of rubber or some other suitable resilient material. Also on the lower face of the foot plate 40 between said face and a head 49 on the lower end of the pin 45 is mounted an insert on washer 50 of rubber or similar resilient material. These two washers 48 and 50 serve to dampen noise. The head 49 of the pin 45 and a washer 49' arranged inside said head limit the relative angular movements of plates 31 and 40. Said plates are urged apart when the washer 50 is being compressed under the influence of a helical spring 51 held between a flange 52 on the chuck 28 and the top 53 of the bore 54 in which the chuck 28 is vertically displaceable. The movement of the chuck 28 in a downwards direction is limited by a bayonet catch 55 retaining the chuck in the ankle 4. The lower end of the chuck 28 presents a head 56, preferably made from steel or a wear-resisting material of plastics by means of which the chuck 28 is held pressed against the foot plate 40 by means of the spring 51.

When the prosthesis supports the entire body weight, the knee shaft 2 occupies its extreme posterior position providing maximum safety against buckling. This position is illustrated schematically in FIG. 5. The knee shaft 2 is then positioned behind the broken line representing the weight line 57 between the hip joint 58 and the ankle 4. In this position the washer 48 (FIG. 3) is in a compressed state. The longitudinal line 60 of the shank section 3 forming a right angle 61 with a line 62 passing through the shaft 30 and extending in parallel with the foot plate 40 when the prosthesis is loaded, then extends obliquely rearwardly and upwards such that the knee shaft 2 will occupy a position behind the weight-supporting line 57 and good stability is obtained. When the body weight is shifted to the sound leg with the sole 42 still in contact with the ground 59 the spring 51, being heavily compressed during loading, may expand, whereby the chuck 28 together with the head 56 press against the upper surface of the foot plate 40. Because the foot plate 40 cannot be urged downwards to any considerable extent (as the foot sole 42 still rests against the ground 59) the ankle plate 31 is urged to assume an angularly displaced position relative to the foot plate 40 and the upright 33 that is attached to the ankle plate 31, and the entire shank section will be swung forward as a result of the thrust to the position illustrated in FIG. 5 by line 63, while the washer 50 (FIG. 4) is being slightly compressed, whereby the knee shaft 2 will be positioned ahead of, or alternatively on, or in any case closer to the weight-supporting line 57. Upon this swinging upwardly and forwardly of the ankle 4 there is a relative displacement between the chuck 28 and the ankle, resulting not only in a swinging motion of the ankle 4 to bring the toe portion of the foot 5 into a position wherein it is at a more acute angle relative to the shank but also having the result that the valve in the valve housing 13 between the cylinders 9 and 10 is opened through the intermediary of the coupling wire 26 and the wire 23, and the valve 14 whereby the mechanism 8 controlling the knee joint functions is released and the swing phase of the leg may be initiated.

In FIGS. 6 and 7 is indicated the alignment of leg prostheses of different lengths in the position assumed by the leg immediately before the beginning of the swing phase.

The self-adjusting alignment described above in a leg prosthesis in accordance with the present invention during the stance phase together with the change of foot angle and toe pick-up during the swing phase make it possible to impart extremely desirable functions to a single-axis knee joint prosthesis as well as a highly satisfactory performance.

FIG. 13 illustrates a similar longitudinal section through the artificial foot as FIG. 3 but the connection between the ankle plate 31 and the foot plate 40 is slightly different. In accordance with FIG. 13 the nipple 44 and the bolt 45 have been replaced by a bracket 65, preferably made from sheet metal, which is attached by means of one or several bolts 66 to the ankle plate 31 at the rear part thereof in such a position as to engage with required play 67 with the lower face of the foot plate 40 by means of its lower portion 68. The upper surface of this lower portion 68 of the bracket 65 is provided with an elastic covering 69, preferably consisting of rubber.

This constructional arrangement considerably facilitates the disassembling of the artificial foot as well as the mounting thereof, while at the same time ensuring movability between the ankle plate and the foot plate and also the movability of the foot relative to the foot plate.

The embodiments as illustrated and described are to be regarded as examples only and the device enabling the self-adjusting alignment described above may be constructively altered in many ways within the scope of the appended claims. The resilient means 51 need not necessarily act on a chuck 28 to securely clamp a coupling wire or coupling rod for operating the valve of a hydraulic mechanism controlling the knee joint functions. Furthermore, the invention is not either limited to a particular construction of such a mechanism. The device in accordance with the invention may be used in connection with other types of artificial feet, for instance the so called SACH foot. In this case the universal joint 41 is replaced by an attachment plate secured to the lower face of foot plate 40. Alternatively, the foot plate 40 may simply be altered for attachment directly on the foot. The mechanism for controlling the knee joint functions need not necessarily consist of a more or less complicated hydraulic device, but the invention is also applicable to a simple friction-operated device to achieve the swing and stance phase control.

Claims

What I claim is:

1. In an improved artificial leg, particularly intended for above-knee amputees, comprising a thigh section, a shank section, a knee joint shaft articulating said thigh section to said shank section, an ankle section on said shank section, said ankle section comprising an upper ankle plate forming the upper portion of said ankle section, a horizontal shaft, a lower foot plate articulated at the forward end of said ankle plate by means of said horizontal shaft, and a spring being mounted between said foot plate and said ankle plate behind said horizontal shaft for forcing them apart, an artificial foot, means pivotally connecting said artificial foot to said foot plate, and a mechanism for controlling the knee joint functions, said horizontal shaft being located ahead of the prosthesis weight supporting line passing through said thigh section, said knee joint shaft and said ankle section, a vertical bore in said upper ankle plate, a clamping element displaceable in said bore, an elongate member clamped by said element and being provided to actuate said knee-joint function controlling mechanism as a result of the vertical displacement of the clamping element in said bore, and a shoulder at the upper end of said bore for holding said spring in a compressed state between said shoulder and said clamping element.

2. An improved artificial leg as claimed in claim 1, further including an inset of a resilient material arranged between said ankle plate and said foot plate.

3. An improved artificial leg as claimed in claim 2, wherein said resilient material is rubber.

4. An improved artificial leg as claimed in claim 1, wherein said clamping means is provided with a flange and presents a head on its lower part, said spring being arranged to press against said flange to urge said head against said foot plate.

5. An artificial leg as claimed in claim 1, wherein a bolt is arranged on said ankle plate, said bolt freely passing through said foot plate behind said weight line, an inset of a resilient material being arranged between said foot plate and a head of said bolt projecting beneath said foot plate.

6. An artificial leg as claimed in claim 5, wherein the inset is made from rubber.

7. An artificial leg as claimed in claim 4, wherein a bracket is attached to the rear portion of said ankle plate, a lower portion of said bracket adapted to engage the lower face of said foot plate.

8. An artificial leg as claimed in claim 7, wherein an elastic cover is provided on the upper face of said lower portion of said bracket.