WO2011117033A1

WO2011117033A1 - Ankle-foot prosthesis with articulated ankle

Info

Publication number: WO2011117033A1
Application number: PCT/EP2011/052448
Authority: WO
Inventors: Dinello Mobbili
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-22
Filing date: 2011-02-18
Publication date: 2011-09-29
Anticipated expiration: 2012-09-22
Also published as: ITAN20100035A1; IT1398912B1

Abstract

The present invention relates to an ankle-foot prosthesis, which comprises a bar (100) designed to be fixed to a leg (A), an artificial foot (P) pivoted at the base of said bar (100) and suitable means to prohibit the mutual rotation of the artificial foot (P) with respect to the bar (100) beyond a predefined range of degrees, in order to reproduce a tibiotarsal articulation.

Description

Ankle-foot prosthesis with articulated ankle-

Description

The present patent application for industrial invention relates to an ankle-foot prosthesis that has been devised to allow the user to walk more comfortably.

There are currently several models of foot or ankle-foot prostheses, but none of them allows for natural walking, due to the structural configuration of the prosthesis itself.

The description continues with reference to two models of prostheses, respectively shown in fig. 1 and fig. 2, which are impaired by similar drawbacks.

Fig. 1 shows an ankle-foot prosthesis comprising a mechanical ankle (C) of rigid type and two rigid parts (1 and 2) pivoted under said ankle (C).

The first (1 ) of said parts (1 and 2) is the front part of the artificial foot, whereas the second one (2) is the back part, that is to say the heel of the foot.

Each of said parts (1 and 2) is connected to the ankle (C) with interposition of a rubber piece (G1 and G2) that allows the corresponding part to oscillate upwards; therefore, a front rubber piece (G1 ) and a back rubber piece (G2) are identified.

More precisely, each part (1 and 2) can move between two positions, the first lower position being an idle position, and the second upper position being a position in which the same is moved when the weight of the user's body is discharged onto the ground with consequent compression of the rubber pieces (G1 and G2).

The compression of said rubber pieces (G1 and G2) changes according to the user's weight, and for this reason, with the same length of the foot, the rubber pieces (G1 and G2) must be suitably chosen because their elasticity determines the balance and comfort of the user who is walking with said prosthesis.

In other words, if we consider the rolling movement of the foot during walking, the first part of the foot to touch the ground is the heel, then the weight is distributed on the entire foot and completely transferred on the toe when the heel is raised, just a few seconds before the entire foot is raised to take a step forward.

Synthetically, four steps can be identified:

- the first step in which the heel rests on the ground (as shown in fig. 3);

- the second step in which the foot starts rolling and the load is moved on the entire foot when the tibia is practically perpendicular to the ground (as shown in fig. 4);

- the third step in which the heel is raised and rolling of the foot continues, thus discharging the entire weight on the toe (as shown in fig. 5);

- the fourth step in which the toe pushes upwards and is detached from the ground (as shown in fig. 6).

During the first step, the back rubber piece (G2) suffers maximum compression, making foot support on the ground soft and comfortable according to its stretchiness.

Said back rubber piece (G2) returns the energy accumulated during the first step during rolling of the foot, favoring the raising of the heel that is pushed upwards by the rubber piece (G2) when the same has suffered the maximum initial compression.

During the third step, the heel is raised and the front rubber piece (G1 ) suffers maximum compression since the entire weight of the body is discharged on the point of the prosthesis.

Finally, during the fourth step, the foot is raised under the upward thrust exerted by the front part (1 ) when the weight of the user discharged on it is reduced. Fig. 2 shows a second type of ankle-foot prosthesis comprising two parts (10 and 20), a front part (10) and a back part (20), which are made of flexible material, such as carbon.

The thickness of said parts (10 and 20) determines their flexibility; therefore in such a type of prosthesis thickness must be calculated according to the length of the foot, and especially according to the weight of the user for the aforementioned reasons.

The main problem of similar prostheses consists in their structural limitations and in the rigidity of the ankle that, in some cases, makes the prosthesis uncomfortable and functionally limited.

The worst situation in which said prostheses are used occurs when walking downhill since, in both types of prostheses, the ankle (C) is basically rigid and unable to adjust the mechanical foot to the road surface.

More precisely, the higher the inclination of the downward hill, the higher the walking instability of the user, who can never rely on perfect support of the entire prosthesis.

In fact, the configuration of the back part and front part of said prostheses is studied to allow a disabled user to walk comfortably on the flat and therefore, when the user is walking downhill, he is forced to walk resting only the heel on the ground.

Such a way of walking is extremely unsafe, dangerous, uncomfortable and embarrassing for the user, who, when using these types of prosthesis, walks practically normally on the flat, whereas is forced to walk slowly and in a clumsy way when walking downhill or uphill.

Another circumstance in which said prostheses are not functionally satisfactory occurs when the user is sitting and wants to extend the prosthetic leg forward.

In such a position, the current ankle-foot prostheses are impaired by the fact that, being the ankle articulation completely rigid, the foot is always tilted by 90° with respect to the ankle. The above makes it impossible to put the foot on the ground spontaneously and normally, unless the tibia is perfectly at 90° with respect to the ground.

Likewise, when the user is sitting, in order for him to stand up, the tibia must be perfectly at right angle with the ground, otherwise the user will stand up while balancing on the heel, rather than using the entire surface of the artificial foot.

Another type of drawback of said ankle-foot prostheses consists in the fact that the design of the front rubber piece, in the first type of prosthesis, or the thickness of the carbon of the front part, in the second type of prosthesis, must be suitably made in order to find a correct compromise between two apparently opposite needs.

In fact, while it is necessary to give flexibility to the front of the foot in order to favor rolling of the artificial foot, at the same time it is necessary to allow the prosthesis to suffer a sort of preload in the front part in order to return the upward thrust in favor of the foot during the last walking step, as described above.

The purpose of the present invention is to remedy the aforesaid drawbacks by devising a new type of ankle-foot prosthesis.

Additional advantageous characteristics are the object of the enclosed claims, which are an integral part of this text.

The ankle-foot prosthesis of the invention comprises a bar designed to be fixed to a leg, thus replacing the lower section of tibia and fibula of the leg and a frame designed to act as artificial foot.

Said frame is pivoted with respect to a horizontal axis and by means of suitable pivoting means in the lower end of the bar.

The prosthesis of the invention also comprises stop means to prohibit mutual rotation of the frame with respect to the bar beyond a predefined range of degrees, at least one elastic return member to maintain the front part of the frame normally raised and finally shock- absorbing means to slow down the lowering of the front part of the frame with respect to said pivoting means. For more clarity the description of the ankle-foot prosthesis of the invention continues with reference to the enclosed drawings, which only have an illustrative, not limiting purposes, wherein:

- figure 7 is an axonometric view of the ankle-foot prosthesis of the invention;

- figures 8 and 9 are diagrammatic side views of the prosthesis of the invention in three different positions.

Referring to fig. 7, the ankle-foot prosthesis of the invention is composed of:

- a bar (100) designed to be fixed to a leg (A) to replace the lower section of the tibia and fibula of said leg (A);

- a box-shaped frame (102) designed to act as artificial foot (P), which is pivoted, by means of suitable pivoting means (103 and 104), under said bar (100), in the lower end (101 ) of the latter.

Said pivoting means (103 and 104) consist in a pin (103) with horizontal axis, the direction of which is transversal with respect to the longitudinal axis of the box-shaped frame (102), which comprises a front part (105) designed to act as toe of the artificial foot (P), and a back part (106) designed to act as heel of the artificial foot (P).

More precisely, said box-shaped frame (102) is provided with a pair of longitudinal vertical borders (107) in adjacent parallel position, which are provided on top with ear (108) exactly where the malleolus of the foot is supposed to be situated.

Said two ears (108) are provided with holes (104) where the pin (103) is inserted, being also inserted inside a transversal through hole obtained on the lower end (101 ) of the bar (100).

Thus, the box-shaped frame (102) can rotate with respect to the bar (100) in such a way that the ankle-foot prosthesis of the invention has a very natural movement.

The prosthesis of the invention also comprises stop means to prohibit the mutual rotation of the frame (102) with respect to the bar (100) beyond a predefined range of degrees exceeding the ones of a tibiotarsal articulation.

More precisely, the angle (a) on the front of the prosthesis, formed between bar (100) and frame (102), ranges from a maximum angle (higher than 90°) and a minimum angle (lower than 90°).

Moreover, the prosthesis also comprises two return springs (109) designed to raise the toe of the foot when, for instance, the artificial foot (P) is detached from the ground and shock-absorbing means (1 10) to slow down the extension of the artificial foot (P), which are actuated when the back part (106) is rested on the ground.

More precisely, each of said springs (109) has a back end (109a) attached on the front of the bar (100) in the lower end (101 ) of the latter, whereas the front end (109b) of the spring (109) is attached to the box- shaped frame (102) in the proximity of the front part (105) by means of a U-shaped bracket, as shown in fig. 7.

Said shock-absorbing means consist in a piston (1 10) disposed between the pair of plates (107), which is provided with a front end (1 10a) hinged in proximity of the front part (105) of the frame (102), whereas the back end (1 10b) is hinged to the lower end (101 ) of the bar (100) under the pin (103), as shown in fig. 8 to 10.

Referring to fig. 8, during the first walking step, as soon as the back part (106) touches the ground, the artificial foot (P) extends, the spring extends, and the piston shortens gradually, thus ensuring gradual and controlled support and extension.

Referring to fig. 9, during the second walking step, the artificial foot (P) completely rests on the ground and the bar (100) rotates with respect to the pin (103) until the piston (1 10) extends reaching the maximum permitted extension, which corresponds to the minimum value of the angle (a).

It is therefore possible to adjust the minimum and maximum value of the angle (a) by adjusting the maximum length of the piston, or providing a stop element. Figures 7, 8 and 9 show a stop insert (1 1 1 ) disposed between the pair of longitudinal vertical borders in adjacent parallel position (107), which acts as stop for the extension travel of the piston (1 10).

By changing the position of said stop insert (1 1 1 ), either forward or backward, the adjustment of the minimum value of the angle (a) is much faster.

It appears evident that the prosthesis of the invention is not impaired by the aforesaid drawbacks, since its structure comprises an articulation, between foot and tibia, similar to a real tibiotarsal articulation.

Referring to figs. 7, 8 and 9, according to a preferred embodiment, the artificial foot (P) is provided, under said front part (105), with a thin plate (1 12) made of flexible material, preferably carbon.

Said plate (1 12) extends from the arch of the artificial foot (P), where is it anchored, to the point (B) of the artificial foot (P) where its free end (1 12a), in idle position, is situated at a height lower than the point of the frame (102) that is the artificial foot (P).

It appears evident that as soon as the artificial foot (P) rests on the ground, said plate (1 12) is pressed upwards under the body weight of the user.

Referring to fig. 9, said plate (1 12) is designed to be engaged under the frame (102), and precisely under the pair of longitudinal vertical borders in adjacent parallel position (107) that practically act as stop element at the end of the upper travel for the bending of said plate (1 12).

Referring to figs. 5, 6 and 8, as soon as the artificial foot (P), during walking, has completed rolling and the heel has raised from the ground, said plate (1 12) tends to go back to its idle position, detached from the adjacent parallel borders (107).

In view of the above, immediately before the point of the artificial foot (P) is raised from the ground, the entire foot is pushed upwards, because of the elastic return of said plate (1 12) in such a way that the user can benefit from the same effect that toes of a human foot would generate in a similar situation. In other words, the prosthesis of the invention allows for comfortable rolling of the foot thanks to an especially flexible plate (1 12), whereas, thanks to the stop means against which the plate (1 12) is engaged, the prosthesis ensures stable rigid support during the third walking step when the entire weight is transferred on the toe of the foot.

Claims

1 ) Ankle-foot prosthesis comprising:

- a bar (100) with lower end (101 ) designed to be fixed to a leg (A) to replace the lower section of tibia and fibula of said leg (A);

- a box-shaped frame (102) designed to act as artificial foot (P) and pivoted, with respect to a horizontal axis, by means of suitable pivoting means (103 and 104), in the lower end (101 ) of the bar (100); said frame (102) being provided with front part (105) and back part (106);

- stop means to prohibit mutual rotation of frame (102) with respect to bar (100) beyond a predefined range of degrees;

- at least one elastic return member (109) to maintain normally raised the front part (105) of the frame (102);

- shock-absorbing means (1 10) to slow down the lowering of the front part (105) of the frame (102) with respect to said pivoting means (103 and 104).

2) Ankle-foot prosthesis as claimed in the above claim, characterized in that said box-shaped frame (102) is formed of a pair of longitudinal vertical borders in adjacent parallel position (107).

3) Ankle-foot prosthesis as claimed in the above claim, characterized in that said longitudinal vertical borders in adjacent parallel position (107) are provided on top with ear (108) with holes (104) where the pin (103) is inserted, being also inserted inside a through transversal hole obtained on the lower end (101 ) of the bar (100).

4) Ankle-foot prosthesis as claimed in one of the above claims, characterized in that said at least one elastic return member (109) consists in at least one spring with back end (109a) attached on the front of the bar (100) in the lower end (101 ) of the bar (100) and a front end (109b) attached to the box-shaped frame (102) in the proximity of the front part (105).

5) Ankle-foot prosthesis as claimed in one of claims 2 to 4, characterized in that said shock absorbing means consist in a piston (1 10) disposed between the pair of plates (107), which is provided with front end (1 10a) hinged in the proximity of the front part (105) of the frame (102), whereas the back end (1 10b) is hinged to the lower end (101 ) of the bar (100) under the pin (103).

6) Ankle-foot prosthesis as claimed in the above claim, characterized in that it comprises a stop insert (1 1 1 ) disposed between the pair of longitudinal vertical borders in adjacent parallel position (107), which acts as stop for the extension travel of the piston (1 10).

7) Ankle-foot prosthesis as claimed in one of the above claims, characterized in that it comprises a thin plate (1 12) made of flexible material under the front part (105), which extends from the arch (F) of the artificial foot (P), where it is anchored, to the point of the artificial foot (P), where its free end (1 12a) is at a height lower than the point of the frame (102) in idle position.