WO2014057086A1

WO2014057086A1 - Prosthetic ankle-foot system

Info

Publication number: WO2014057086A1
Application number: PCT/EP2013/071271
Authority: WO
Inventors: Bram SEYNAEVE; Thomas VANDAELE
Original assignee: Universiteit Gent
Current assignee: Universiteit Gent
Priority date: 2012-10-12
Filing date: 2013-10-11
Publication date: 2014-04-17
Anticipated expiration: 2015-04-12

Description

Prosthetic ankle-foot system

Field of the invention

The invention relates to the field of prosthetic systems. More specifically it relates to a prosthetic ankle-foot system and related method. Background of the invention

The walking performance of a lower limb prosthesis user is significantly affected by the prosthetic ankle-foot system. Prosthetic feet known in the art are often tuned for a specific heel height. When a shoe matches with the corresponding heel height of the prosthetic foot, the prosthesis will function optimally. Studies demonstrate that with a small difference in heel height, the performance of the foot will deteriorate. Because of the regular shoe change of the users, a need exists for a prosthetic ankle- foot system in which the heel height is easy to adjust, such that the prosthetic foot can operate in an optimized manner for each shoe.

Several such adjustable ankle-foot systems are known in the art. At least 8 commercially-available systems exist, namely: Accent (College Park Industries), Elation (Ossur), Proprio Foot with EVO (Ossur), Raize (Fillauer), Runway (Freedom innovations), Flex E (Medi), Patient Adjustable (Endolite), and Brio (Endolite). However, these systems still require manual adjustment.

The Accent (College Park Industries) and Elation (Ossur) ankle-foot systems are easily adjustable without requiring the use of tools. Through a push-button the ankle mechanism, which is linked to a carbon foot, may be unblocked so that the prosthesis can be aligned.

The Proprio Foot with EVO (Ossur) and the Raize (Fillauer) prosthetic feet have an electromechanical ankle system that can adjust the heel height without the use of tools. Thanks to an electronic control, the natural ankle movement can be stimulated and parameters such as plantar flexion and dorsiflexion range and resistance can be easily adjusted. The user may thus adjust the heel height himself. However, these intelligent ankle-foot systems are battery dependent, which may be seen as an additional burden for the user. Furthermore, the cost of these electronic control prosthetic feet is above the average cost of mechanical feet. Another disadvantage may be the fact that the electromechanical ankle system implies an increased weight.

The Runway and Flex E also allows the adjustment of the heel height by unlocking the ankle system with a push-button. The Runway functions with a push button adjustment mechanism with ten height pre-settings. Furthermore, using a hex key, it is possible to adjust the prosthetic foot more accurately.

With the adjustment of the heel height of the Patient Adjustable (Endolite), the user is forced to use a hex key which may imply some disadvantages. For instance, a cosmetic finishing touch may require the adjustment point of the ankle- mechanism to be covered, such that further adjustment may be impossible or impractical. Also, the user needs to have a hex key on hand when adjustment is desired. Finally, the way of adjustment seems to be less ergonomic compared to a push-button mechanism. Consequentially, the user may be motivated to leave the adjustment of the ankle-mechanism to a professional.

Brio (Endolite) is an add-on that can be assembled on top of common prosthetic feet. This system implies a weight increase (383g) and has a limited adjustment range of 32mm. The hinge point in this system is higher than the anatomical hinge point of the ankle. Adjustment is possible in this system by way of a push-button. Summary of the invention

It is an object of embodiments of the present invention to provide ankle-foot prostheses that can be used in an efficient and simple way.

It is an advantage of embodiments of the present invention that an ankle-foot prosthesis can be provided which can adapt automatically to the heel height of the shoe without requiring manual adjustment.

It is an advantage of embodiments according to the present invention that a user-friendly system is obtained.

It is an advantage of embodiments according to the present invention that the device can be low in weight. It is an advantage of embodiments according to the present invention that the system can be a fully mechanical system, not requiring any electronic components or battery.

It is an advantage of embodiments according to the present invention that a fully waterproof system can be provided.

It is an advantage of embodiments according to the present invention that a more natural walking can be realized compared to prior art systems.

It is an advantage of the ankle-foot system according to embodiments of the present invention that the build-in height of the system can be reduced compared to prior art devices.

The above objective is accomplished by a method and device according to the present invention.

In a first aspect, embodiments of the present invention relate to a prosthetic ankle-foot system, which comprises a forefoot element, a heel element and a shin element. The system further comprises a forefoot hinge joint rotatably connecting the forefoot element to the heel element, and a heel hinge joint rotatably connecting the heel element to the shin element. The system also comprises a damper for exerting a dampening force for resisting a rotation of the heel hinge joint, and a transducer for adjusting the dampening force of the damper as function of an angular position of the shin element with respect to the forefoot element.

In embodiments according to the present invention, the shin element may be adapted for attaching to a prosthetic connector.

In embodiments according to the present invention, the forefoot hinge joint and the heel hinge joint may be arranged for enabling rotation around a medio- lateral flexion axis.

In embodiments according to the present invention, the damper may comprise a hydraulic cylinder.

In embodiments according to the present invention, the hydraulic cylinder may be mechanically coupled between the shin element and the heel element. In embodiments according to the present invention, the hydraulic cylinder may be a double acting hydraulic cylinder.

In embodiments according to the present invention, the damper may further comprise a valve hydraulically coupled between a first port and a second port of the hydraulic cylinder for providing an adjustable fluid constriction between a first chamber and a second chamber of the hydraulic cylinder.

In embodiments according to the present invention, the transducer may comprise a feedback cylinder mechanically coupled between the shin element and the forefoot element, in which a port of the feedback cylinder may be operably connected to the valve for controlling the dampening force of the hydraulic cylinder in response to the stroke position of the feedback cylinder.

In embodiments according to the present invention, the feedback cylinder may comprise a hydraulic cylinder.

In embodiments according to the present invention, the feedback cylinder may be a double acting hydraulic cylinder.

In embodiments according to the present invention, the system further comprises an accumulator operably connected to the feedback cylinder.

In embodiments according to the present invention, the transducer may be adapted for increasing the dampening force exerted by the damper when the angle between the shin element and the forefoot element is less than a first predetermined angle. In embodiments according to the present invention, this first predetermined angle may be a 90° angle.

In embodiments according to the present invention, the dampening force is a blocking force preventing rotation of the heel hinge joint when the angle between the shin element and the forefoot element is less than a second predetermined angle. In embodiments according to the present invention, the second predetermined angle may be in the range 80°-82°.

In embodiments according to the present invention, the transducer may comprise a resilient element, e.g. a spring, for providing a returning force for returning the angle between the shin element and the forefoot element to this first predetermined angle.

In a second aspect, embodiments of the present invention relate to a method for operating a prosthetic ankle-foot system, which comprises a forefoot element, a heel element, a shin element, a forefoot hinge joint rotatably connecting the forefoot element to the heel element, and a heel hinge joint rotatably connecting the heel element to the shin element. In one step, the method comprises determining a physical quantity indicative of a relative angular orientation between the shin element and the forefoot element. In a further step, the method comprises exerting a dampening force for resisting a rotation of the heel hinge joint, in which the magnitude of the dampening force is dependent on the physical quantity.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope.

In the different drawings, the same reference signs refer to the same or analogous elements.

Brief description of the drawings

FIG. 1A and FIG. IB illustrate the automatic alignment of the prosthetic ankle- foot system for different heel heights, according to an embodiment of the present invention. FIG. 2 illustrates the action and reaction forces when a user threatens to fall down in the prosthetic ankle-foot system according to an embodiment of the present invention.

FIG. 3 illustrates a schematic view of a prosthetic ankle-foot system according to an embodiment of the present invention during different stages of a walking cycle.

FIG. 4 illustrates a prosthetic ankle-foot system according to an embodiment of the present invention.

FIG. 5 illustrates a transducer and a damper of a prosthetic ankle-foot system according to a first embodiment of the present invention.

FIG. 6 illustrates a transducer and a damper of a prosthetic ankle-foot system according to a second embodiment of the present invention.

FIG. 7 illustrates a transducer and a damper of a prosthetic ankle-foot system according to a third embodiment of the present invention.

FIG. 8 illustrates a transducer and a damper of a prosthetic ankle-foot system according to a forth embodiment of the present invention.

FIG. 9 illustrates a schematic view of a prosthetic ankle-foot system according to an embodiment of the present invention during different stages of a walking cycle.

FIG. 10 illustrates a prototype of a prosthetic ankle-foot system according to an embodiment of the present invention.

FIG. 11 illustrates a prosthetic ankle-foot system according to an embodiment of the present invention.

Detailed description of illustrative embodiments

The present invention will be described with respect to particula r embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this invention, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the invention and aiding in the understanding of one or more of the various inventive aspects. This method of invention, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth.

However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

In adjustable ankle-foot systems known in the art a hinged ankle, e.g. which can be fixed, may be used, in which the ankle may be connected to a rigid keel, e.g. a carbon keel. When the heel height of the shoe in which the system is inserted increases, the shape of the shoe sole will deviate more and more from the shape of the keel. With a sole, the forefoot will mostly be positioned horizontally and the shape of the sole only starts to slope behind the forefoot. To obtain a better approximation of the able-bodied ankle-foot behavior, a forefoot hinge joint may be added, as disclosed by embodiments in accordance with the present invention, so that the forefoot element can rotate with respect to the heel element as well. This results in a minimizing shape deviation and an improved roll-over quality independent of heel heights of the shoe in which the prosthetic ankle-foot system is inserted.

FIG. 4 shows a prosthetic ankle-foot system according to an embodiment of the present invention, the prosthetic ankle-foot system comprising a forefoot element 1, a heel element 2 and a shin element 3. The system shown in FIG. 4 further comprises a forefoot hinge joint 5 rotatably connecting the forefoot element 1 to the heel element 2 and a heel hinge joint 4 rotatably connecting the heel element 2 to the shin element 3.

The forefoot hinge joint 5 and the heel hinge joint 4 may be arranged for enabling rotation around a medio-lateral flexion axis as is for instance shown in FIG. 2 as a rotation (a) about an axis perpendicular to the paper surface.

The forefoot element 1 may be distinct from the heel element, i.e. the forefoot element 1 may be an element different from the heel element 2, the two elements being connected through a forefoot hinge joint.

The shin element 3 may be adapted for attaching to a prosthetic connector, for example the shin element 3 may have a proximal end portion as is for instance shown in FIG. 4, the proximal end portion adapted for attaching to a prosthetic connector (not shown), for example a lower leg prosthesis adapter or a leg prosthesis.

The shin element 3 may have a distal end portion opposite the proximal end portion, which may be connected by the heel hinge joint 4 to the heel element 2 as is also shown in FIG. 4.

Furthermore, the system comprises a damper 6, 16, 26 for exerting a dampening force for resisting a rotation of the heel hinge joint 4. In FIG. 4-FIG. 8 the damper comprises a hydraulic cylinder 16, 26, for example, a hydraulic cylinder for dampening a rotation of the heel hinge joint 4 around a medio-lateral ankle flexion axis, e.g. such as to provide a dampening force resisting rotation of the heel hinge joint 4 away from a neutral angular position. Alternatively, the damper may comprise a non-hydraulic damper 6, for example an eddy current damper. The dampening force of the damper may be sufficiently high as to act as a blocking element thereby blocking rotation of the heel hinge joint 4. The damper 6, 16, 26, e.g. a hydraulic cylinder 16, 26, may be mechanically coupled between the shin element 3 and the heel element 2 as is for instance shown in in FIG. 4.

The hydraulic damping cylinder, i.e. the hydraulic cylinder acting as a damper, may be a single acting hydraulic cylinder 16 as is for instance shown in FIG. 4 and FIG. 5. A cylinder head of the hydraulic cylinder may be connected to the shin element 3 at a position sufficiently removed from the axis of rotation of the heel hinge joint 4, while a cylinder base of the hydraulic cylinder may be connected to the heel element 2 at a position sufficiently removed from the axis of rotation of the forefoot hinge joint 5, as is for instance shown in FIG. 4. As such, a monotonous functional relationship may exist between the stroke position of the hydraulic cylinder and an angle between the shin element 3 and the heel element 2, e.g. between the stroke position and an angular position of the heel hinge joint 4.

The hydraulic damping cylinder, i.e. the hydraulic cylinder acting as a damper, may be a double acting hydraulic cylinder 26 as is for instance shown in FIG. 6-FIG. 8. A first cylinder head of the hydraulic cylinder may then be connected to the shin element 3 at a position sufficiently removed from the axis of rotation of the heel hinge joint 4, while a second cylinder head of the hydraulic cylinder may be connected to the heel element 2 at a position sufficiently removed from the axis of rotation of the forefoot hinge joint 5. The double acting hydraulic cylinder 26 preferably comprises two chambers having an equal volume in equilibrium as is for instance shown in FIG. 6. Such an embodiment has the advantage that less forces need to be exerted by the user during a walking cycle.

The damper 6, 16, 26 may have an adjustable, e.g. a controllable, dampening force, e.g. a controllable dampening coefficient or mechanical resistance. For example, a valve 10 may be hydraulically coupled between a first port and a second port of the hydraulic cylinder for providing an adjustable fluid constriction between a first chamber and a second chamber of the hydraulic cylinder as is for instance shown in FIG. 5-FIG. 8. Such adjustable fluid constriction may thus control the dampening force exerted by the hydraulic damping cylinder 16, 26. For example, such valve and hydraulic cylinder may jointly form an adjustable hydraulic dashpot.

The system also comprises a transducer 17 for adjusting the dampening force of the damper 6 as function of an angular position of the shin element 3 with respect to the forefoot element as is shown in FIG. 4.

The transducer 7, 17, 27 may be adapted for increasing the dampening force exerted by the damper 6 on the heel hinge joint 4 when the angle between the shin element 3 and the forefoot element 1 differs from, e.g. is less than, a predetermined first angle. In preferred embodiments of the present invention, this predetermined angle may be in the range of 70° to 110°, even more preferred in the range of 80° to 100°, even more preferred in the range of 80° to 90°, for example a 90° angle. In preferred embodiments of the present invention, the dampening force exerted by the damper on the heel hinge joint 4 may be increased when the angle between the shin element 3 and the forefoot element 1 becomes smaller than 90°. Increasing the dampening force may be such that the heel hinge joint 4 is blocked when a certain predetermined second angle between the shin element 3 and the forefoot element 1 is reached, the angle may depend on the predetermined angle chosen in the previous step. In case the dampening force exerted by the damper on the heel hinge joint 4 is for instance increased as soon as the angle between the shin element 3 and the forefoot element 1 becomes smaller than 90°, the transducer may for instance be adapted for blocking the heel hinge joint 4 as soon as the angle between the shin element 3 and the forefoot is in the range of 75°-85°, preferably in the range of 80°- 82° as is for instance shown in FIG. 9D.

In some embodiments of a system according to the present invention, a horizontal positioning of the forefoot element 1 may be assumed, when inserted in a shoe which is supported by a level ground. The preferred angle between shin element 3 and forefoot element 1 may be 90°, in order to provide stable support to a prosthesis user. While most shoes may position the forefoot element 1 in a sufficiently horizontal position, such that the predetermined angle may be chosen close or equal to 90°, it will be clear to the person skilled in the art that an additional adjustment means may be provided to adjust this predetermined angle in order to allow the use of shoes which deviate significantly from this assumption.

In a prosthetic ankle-foot system according to embodiments of the present invention the first predetermined angle between the shin element 3 and the forefoot element 1 is equal to 90°. The first predetermined angle may be independent of the heel height as is for instance shown in FIG. la and FIG. lb.

The transducer 7 may furthermore comprise a resilient element for providing a returning force for returning the angle between the shin element 3 and the forefoot element 1 to this first predetermined angle as is for instance shown in FIG. 3. For example, the transducer 7 may be spring-loaded. For example, the transducer 17, 27 may be an automatically returning hydraulic control cylinder as is for instance shown in FIG. 4.

The transducer 17, 27 may comprise a feedback cylinder mechanically coupled between the shin element 3 and the forefoot element 1 as is for instance shown in FIG. 4-FIG. 8. The feedback cylinder may be a hydraulic cylinder as shown in FIG. 5- FIG. 8. A port of the feedback cylinder may be hydraulically connected to the control valve for controlling the dampening force of the dampening hydraulic cylinder in response to the stroke position of the feedback cylinder as is for instance shown in FIG. 5-FIG. 8.

The transducer 17 may comprise a single acting hydraulic feedback cylinder as is for instance shown in FIG. 5 and FIG. 6. Alternatively the transducer 27 may comprise a double acting hydraulic feedback cylinder as is for instance shown in FIG. 7 and FIG. 8. The latter has the advantage that less forces need to be exerted by the user during a walking cycle.

The single or double acting hydraulic feedback cylinder may be connected to an accumulator 11 as is for instance shown in FIG. 6-FIG. 8. Such an accumulator may allow to compensate for temperature variations and as such provide a calibration of the hydraulic feedback cylinder or the hydraulic transducer cylinder. Alternatively or in addition thereto, the accumulator may act as a buffer and be provided for receiving at least part of the hydraulic fluid from the hydraulic feedback cylinder after the control valve, connecting the hydraulic feedback cylinder with the hydraulic damping cylinder, has been closed.

Alternatively, or in addition thereto, the prosthetic ankle-foot system may comprise an accumulator operably connected to the damping hydraulic cylinder. Such an accumulator may allow to compensate for temperature variations and as such provide a calibration of the hydraulic damping cylinder.

Alternatively, or in addition thereto, the double acting hydraulic feedback cylinder 27, or the transducer in general, may be connected to a first and/or a second one-way valve as can be seen for instance in FIG. 7 and FIG. 8. A first one-way valve 12 may act as an overpressure valve that allows flow from the second chamber of the double acting hydraulic feedback cylinder, connected to the control valve 10, to the first chamber of the double acting hydraulic feedback cylinder, when a predetermined pressure is reached in the second chamber. This predetermined pressure may be chosen to be higher than the predetermined pressure upon which the control valve connecting the feedback cylinder with the damping cylinder is closed. Once the overpressure valve is opened, pressure in the feedback hydraulic cylinder will not increase. This eases rotating the forefoot element 1 about the forefoot hinge joint 5 when the control valve is closed. A second one-way valve 13 may be provided to allow flow from the first chamber and/or from the accumulator, to the second chamber allowing the feedback hydraulic cylinder to automatically return to his original position when the foot is lifted from the ground.

Alternatively, the first one-way valve may be a controllable overpressure valve 14 as is for instance shown in FIG. 8, which may be chosen as a function of the weight of the user wearing the prosthetic ankle-foot system. Controlling the overpressure valve may comprise controlling the predetermined pressure upon which the overpressure valve is opened.

Alternatively, the transducer may comprise a non-hydraulic transducer, e.g. an electronic sensor element for detecting a relative orientation of the shin element 3 and the forefoot element 1. Such detecting may be effected directly, e.g. by an angular position sensor, or indirectly, e.g. by a linear position sensor. One or more parts of the prosthetic ankle-foot system may be made as removable cartridges, that can be plugged in and out. The cartridges are for instance designed to work in a certain range and can be tuned to optimally function for a specific user, having a specific weight or wearing shoes with a specific heel height. As an example, without being limited thereto, the control valve connecting the transducing cylinder and the damping cylinder, can be made as a cartridge. The predetermined pressure upon which the control valve is opened can be adjusted in a certain range, depending on for instance the weight of the user of the prosthetic ankle-foot system.

In a second aspect, the present invention relates to a method for operating a prosthetic ankle-foot system, for example a prosthetic ankle-foot system as described hereinabove in relation to the first aspect. Such method comprises the step of obtaining a prosthetic ankle-foot system which comprises a forefoot element 1, a heel element 2, a shin element 3, a forefoot hinge joint 5 rotatably connecting the forefoot element 1 to the heel element 2 and a heel hinge joint 4 rotatably connecting the heel element 2 to the shin element 3. Alternatively, the prosthetic ankle-foot may already be in place. The method further comprises the step of determining a physical quantity indicative of a relative angular orientation between the shin element 3 and said forefoot element 1. For example, a hydraulic pressure exerted by a transducer 7, 17, 27 as described hereinabove may encode such relative angular orientation. The method also comprises the step of exerting a dampening force for resisting a rotation of the heel hinge joint 4 of the prosthetic ankle-foot system, in which the magnitude of this dampening force is dependent on the determined physical quantity. For example, the dampening coefficient of a damper 6, 16, 26, mechanically coupled to the heel hinge joint 4, may be an increasing function of the physical quantity, e.g. the hydraulic pressure.

The method may furthermore comprise steps expressing the functionality of components of the ankle-foot system as described in the first aspect. A number of examples of embodiments of the present invention will be provided further herein as well as a comparison with existing systems, the present invention not intended to be limited by specific details of such examples.

The current adjustable ankle-foot systems use a hinged ankle (that can be fixed) connected to a rigid (carbon) keel. When the heel height increases, the shape of the shoe sole will deviate more and more of the shape of the keel. With a sole, the fore foot will mostly be positioned horizontally and the shape of the sole only starts to slope behind the forefoot. Thus, the shape deviation leads to the deformation of the keel of the prosthesis which leads to different characteristics of the foot system for instance a greater unroll resistance. To obtain a better mimic of the able-bodied ankle-foot behavior, the prosthetic ankle-foot system according to the present invention comprises a forefoot element 1 and a forefoot hinge joint 5 rotatably connecting the forefoot element 1 to the heel element 2. This results in a minimal shape deviation. FIG. 1 shows a schematic view of a prosthetic ankle-foot system according to an embodiment of the present invention. Figure 1 shows the heel element 2, the forefoot element 1, the heel hinge joint 4 and the forefoot hinge joint 5 being part of a parallel four-bar linkage. FIG. 1 shows the angle between the shin element 3 and the forefoot element 1 being 90° when standing, independent of the heel height of the shoe. The upper bar of the parallel four-bar linkage preferably comprises a resilient member, allowing the 90° angle to decrease and to an energy depository with dorsiflexion.

During standing, the ankle-foot system offers for each heel height the same balance as a result of the power function between ankle/lower leg and forefoot as shown in FIG. 2. Namely, the system makes sure that the freedom of motion of the heel hinge joint 4 is settled through the forefoot. When the user threatens to fall face down, the heel hinge joint will encounter a moment (a) that will be converted in a pressure force in the upper bar of the four-bar linkage system. This force tries to cause a downward rotation of the forefoot (b), this one will get blocked by the reaction force of the floor (c). Subsequently the heel hinge joint 4 is blocked (d). While walking, the ankle-foot mechanism mimics the sagittal plane motion of the anatomical ankle-foot reasonably well as is shown in an embodiment of the present invention shown in FIG. 3. The prosthetic ankle-foot element shown in FIG. 3 comprises a four-bar linkage. The upper bar of the four-bar linkage comprises a spring, functioning as transducer 7. In initial stance phase (A-B) the heel hinge joint 4 can move freely with a certain resistance that may be given to the heel hinge joint 4. In the midstance phase (C), the resistance starts to increase because the rotation of the forefoot element 1 is hindered by the surface and the spring is compressed. With a biological ankle-foot mechanism there is preferably a peak dorsiflexion of 8 to 10 degrees after the foot has become flat (D). By choosing the right parameters for the elasticity in the upper bar, in general for the transducer, the stiffness of the heel hinge joint 4 should increase in proportion as the leg rolls over the foot. Once the dorsiflexion peak is reached (D), the stiffness of the heel hinge joint 4 will be invincible and the extra energy of this movement will be saved in the spring. From there, the forefoot starts to rotate opposite the rest of the foot and the heel begins to leave the ground (E-G). In the pre-swing phase (H) the energy of the spring will be released in form of plantarflexion and the forefoot will be rejected which leads to an initial positioning of the foot, ready to take the next step. The angle between the forefoot element 1 and the shin element 3 in unloaded conditions is always 90 ° which will make sure that this operation will apply for each heel height.

To test the concepts of the prosthetic ankle-foot system according to the present invention, several prototypes were made that were tested by one or more test persons, the working principle of the prototypes being shown in FIG. 3.

Prototypes were made using laser technique, whereby a sequence of laminas were lasered from a flat plate. After the lasering, these laminas were assembled against each other, creating a 3D model. In the prototypes, the laminas were made from polyethylene plates with a thickness of 6 mm. This kind of synthetic material has been chosen because of its strength and has a relative high strain before it breaks. Other manufacturing techniques and/or materials can be chosen as will be understood by the person skilled in the art. These prototypes were tested by a below- knee and above-knee amputate user. In the tests, a treadmill ergometer was used allowing the stable gait and roll-off patterns to be analyzed. After the tests, a video interview and a survey were taken. Human subjects testing is good for evaluation of hypotheses related to ankle-foot prosthetic components because it yields results that are most relevant to the actual use of the devices. However, the external factors that can influence the results (e.g. socket type, shoe type) need to be taken into account as well.

From the results it appeared that the test users could wear shoes with different heel heights without the ankle-foot system needed to be outlined manually. In order to improve the roll-over, it has been found that the forefoot needs to overpower the moment in the ankle. This could for instance be achieved by increasing the length of the upright bar connected to the ankle hinge joint compared to the length of the upright bar connected to the forefoot hinge joint 5. By using a longer bar, a higher leverage can be obtained and a better roll-off can be realized. The upright bar connected to the heel hinge joint may for instance be made three times longer than the upright bar connected to the forefoot hinge joint 5. It has been further shown that preferably the dampening force on the heel hinge joint 4 is gradually adjusted using a valve. This valve may be managed with a part of the energy held by the spring in the upper bar. The more the spring will be pushed, the more stiffen the heel hinge joint 4 will get. The parallel four-bar linkage system allows an automatic adjustment for each heel height. As long as the angle between the forefoot element and the shin element 3 is larger than 90° the heel hinge joint 4 will undergo a little stiffness because there are no compressive forces on the upper bar. From the moment the angle decreases below 90°, the heel hinge joint 4 will stiffen more and more as the angle gets smaller. By controlling the valve, the ideal ankle rotation resistance in function of the dorsiflexion can be obtained.

FIG. 9 shows a schematic view of a prosthetic ankle-foot system according to an embodiment of the present invention during a whole walking cycle. The prosthetic ankle-foot system comprises a four-bar linkage connecting the heel hinge joint 4 and the forefoot hinge joint 5. While walking, again the ankle-foot mechanism mimics the sagittal plane motion of the anatomical ankle-foot reasonably well as shown in FIG. 9. From the midstance phase (C) a pressure in the upper bar of the parallel system starts to build up. On the one hand, these compressive forces will be caught by the spring, or the transducer in general, and on the other hand they will also control the control valve, provided between the upper and lower bar, which makes the heel hinge joint 4 more stiffen. Eventually the resistance gets invincible with a peak dorsiflexion of 8 to 10 degrees. The blocked ankle mechanism (D) doesn't obstruct the fact that the forefoot can keep on rotating as can be seen in E-G. It will only increase systematically the rotation resistance of the heel hinge joint 4. During the pre-swing phase H the energy saved in the spring, i.e. in the transducer in general, will be liberated by which the foot will push off. Through the energy release the control valve will open again which will lead to loss of stiffness of the heel hinge joint 4. Because the angle between the forefoot element 1 and the shin element 3 is 90°, independent of the heel height, the working principle of the ankle-foot mechanism is independent of the heel height.

To test the concepts of the prosthetic ankle-foot system according to the present invention, several prototypes were built. The first prototype was made to investigate a prosthetic ankle-foot system whereby the heel hinge joint 4 resistance is dependent on the angle between the shin element 3 and the forefoot element 1. The first prototype is equipped with a four-bar mechanism in which the bar above the heel hinge joint 4 is three times longer than the bar above the forefoot hinge joint 5. The consequence is that the forefoot creates enough torque to overpower the torque of the heel hinge joint 4. This causes the forefoot to control the position of the ankle. From the moment that the angle between the shin element 3 and the forefoot is less than 90 °, the heel hinge joint 4 blocks. With this first prototype, the concept can be simulated from the initial contact stage to the midstance phase. The second prototype was built to investigate a system in which the forefoot can rotate under a certain resistance. The resistance of the forefoot hinge joint 5 was created by springy bars that were connected with the forefoot element 1. By changing the number of rods, the stiffness of the forefoot hinge joint 5 can be arranged. For this prototype a prosthetic ankle-foot system was made that can be blocked at different angles. This second prototype allows to demonstrate the occurring effects of the gait cycle starting from the midstance phase until the toe off stage. By testing these two prototypes, the effects of the total concept can be demonstrated. FIG. 10 shows a third prototype of a prosthetic ankle-foot system according to an embodiment of the present invention.

The first prototype scored very well for the two subjects from the initial contact stage until the midstance phase. From there, the ankle mechanism blocked too quickly resulting in a shock with hyperextension of the knee. On the video recordings it can be clearly seen that the ankle-foot movements are much more natural making walking more anesthetic. The subjects testing the first prototype acknowledged that the roll-over quality is substantially constant for several heel heights. The best results were obtained when the rotational resistance of the foot was the smallest by using one springy bar.

The second prototype proved the hypothesis of minimizing shape deviation because the roll-over quality for several heel heights was found constantly.

The third prototype that was tested manually provided good results. The rollover went very smoothly from the initial contact stage until toe off stage. The dynamic ankle system worked like it was hypothesized. For every heel-height, the ankle blocked at 90° measured from the ground. With the first prototype it could be shown that a lower limb prosthesis user can walk easily with an ankle system which blocks at 90° during midstance phase. The only drawback that was experienced was the shock caused by blocking.

This could be eliminated providing a valve that provides a gradual stiffening of the heel hinge joint 4 as is for instance shown in FIG. 11. FIG. 11 shows another embodiment of the present invention using hydraulic cylinders. A control valve is hydraulically managed using an automatic returning hydraulic cylinder that operates as upper bar of the four bar mechanism. Using this, the heel hinge joint 4 will experience more rotation resistance as the hydraulic cylinder shortens. When the forces on the hydraulic cylinder are zero, the latter will return to its original length and the heel hinge joint 4 will lose its stiffness. The spring constant of the spring in the hydraulic cylinder will determine the roll-off resistance of the forefoot. In the virtual prototype shown in FIG. 11, both the ankle system as the forefoot hinge joint 5 are assembled on a carbon foot. This carbon construction comprises 2 plates that are assembled wedge-shaped. This construction allows to temporarily save the energy of the heel strike and therefore operates as heel damper. Between the 2 carbon plates there's a consolidation pillow that will empower the structure of the foot. An optimized heel filling would be obtained if the pillow could be produced in different lengths and be chosen according to the weight of the person. In consequence, the expensive carbon structure can be used by person having different weights just by replacing one cheap part. The fully mechanical ankle-foot system allows to wear shoes with different heel heights without the prosthesis must be aligned manually. Thanks to the dynamic ankle-foot system, the resistance of the heel hinge joint 4 will change in function of the position of the shin element 3 relative to the ground, i.e. relative to the forefoot element 1. This gives the leg a greater freedom of movement that provides physiological benefits. The dynamic ankle with the hinged forefoot result in an ankle-foot system that approaches the characteristics of a human foot reasonably well. The control valve may determine the amount of resistance of the heel ankle joint and the hydraulic transducing cylinder may determine the resistance of the forefoot.

Claims

1. A prosthetic ankle-foot system, the prosthetic ankle-foot system comprising a forefoot element (1), a heel element (2), a shin element (3), a forefoot hinge joint (5) rotatably connecting the forefoot element (1) to the heel element (2), a heel hinge joint (4) rotatably connecting the heel element (2) to the shin element (3), a damper (6, 16, 26) for exerting a dampening force for resisting a rotation of said heel hinge joint (4), a transducer (7, 17, 27) for adjusting the dampening force of said damper (6, 16, 26) as function of an angular position of said shin element (3) with respect to said forefoot element (1).

2. The prosthetic ankle-foot system according to claim 1, in which said shin element (3) is adapted for attaching to a prosthetic connector.

3. The prosthetic ankle-foot system according to claim 1 or claim 2, in which said forefoot hinge joint (5) and said heel hinge joint (4) are arranged for enabling rotation around a medio-lateral flexion axis.

4. The prosthetic ankle-foot system according to any of the previous claims, in which said damper comprises a hydraulic cylinder (16, 26).

5. The prosthetic ankle-foot system according to claim 4, in which said hydraulic cylinder (16, 26) is mechanically coupled between said shin element 3 and said heel element (2).

6. The prosthetic ankle-foot system according to any of claims 4-5, in which said hydraulic cylinder is a double acting hydraulic cylinder (26).

7. The prosthetic ankle-foot system according to any of claims 4-6, in which said damper (16, 26) further comprises a valve (10) hydraulically coupled between a first port and a second port of said hydraulic cylinder for providing an adjustable fluid constriction between a first chamber and a second chamber of said hydraulic cylinder (16, 26).

8. The prosthetic ankle-foot system according to claim 7, in which said transducer comprises a feedback cylinder (17, 27) mechanically coupled between said shin element (3) and said forefoot element (1), a port of said feedback cylinder being operably connected to said valve (10) for controlling the dampening force of said hydraulic cylinder in response to the stroke position of said feedback cylinder.

9. The prosthetic ankle-foot system according to claim 8, in which said feedback cylinder is a double acting hydraulic feedback cylinder (27).

10. The prosthetic ankle-foot system according to any of claims 8-9, in which the system further comprises an accumulator (11) operably connected to the feedback cylinder (17, 27).

11. The prosthetic ankle-foot system according to any of the previous claims, in which said transducer is adapted for increasing the dampening force exerted by said damper (6) when the angle between said shin element 3 and said forefoot element (1) is less than a first predetermined angle.

12. The prosthetic ankle-foot system according to claim 11, in which said first predetermined angle is a 90° angle.

13. The prosthetic ankle-foot system according to any of claims 11-12, in which the dampening force is a blocking force preventing rotation of the heel hinge joint (4) when the angle between said shin element (3) and said forefoot element (1) is less than a second predetermined angle.

14. The prosthetic ankle foot system according to claim 13, wherein the second predetermined angle is in the range 80°-82°.

15. The prosthetic ankle-foot system according to any of claims 11-14, in which said transducer comprises a resilient element for providing a returning force for returning said angle between the shin element (3) and the forefoot element (1) to said first predetermined angle.

16. A method for operating a prosthetic ankle-foot system comprising a forefoot element (1), a heel element (2), a shin element (3), a forefoot hinge joint (5) rotatably connecting the forefoot element (1) to the heel element (2), and a heel hinge joint (4) rotatably connecting the heel element (2) to the shin element (3), the method comprising

- determining a physical quantity indicative of a relative angular orientation between said shin element (3) and said forefoot element (1), - exerting a dampening force for resisting a rotation of said heel hinge joint (4), wherein the magnitude of said dampening force is dependent on said physical quantity.