Joint for an orthopaedic device
The joint design addresses the challenge of providing a compact and efficient hydraulic system for orthotic devices by pivotably mounting cylinders and using sealing mechanisms, achieving effective movement and locking with reduced complexity and cost.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- OTTOBOCK SE & CO KGAA
- Filing Date
- 2025-12-08
- Publication Date
- 2026-06-18
AI Technical Summary
Existing technologies have not effectively addressed the challenges of providing a compact and efficient hydraulic system for orthoses, particularly in the design of prosthetic joints, such as those used in orthotic devices, which require a hydraulic system that can mimic the movement of an anatomical joint while allowing for a limited range of motion and efficient locking mechanisms.
A joint design where the first cylinder is pivotably mounted on the second joint part, allowing both cylinders to perform a pivoting movement, with pistons arranged to maintain a constant volume in the hydraulic chambers, and a sealing mechanism to prevent fluid leakage, enabling a compact and efficient hydraulic system.
The solution provides a compact and efficient hydraulic system that mimics the movement of an anatomical joint with a limited range of motion and effective locking, reducing complexity and cost while maintaining fluid sealing.
Smart Images
Figure EP2025085936_18062026_PF_FP_ABST
Abstract
Description
[0001]
[0002] Ottobock SE & Co. KGaA Lawyer's File:
[0003] Max-Näder-Straße 15 0108-2042 PCT-1
[0004] 37115 Duderstadt Germany Date:
[0005] December 8, 2025
[0006] Joint for an orthotic device
[0007] The invention relates to a joint for an orthopaedic device, wherein the joint comprises a first joint part, a second joint part which is pivotably arranged on the first joint part in a pivoting range about a pivot axis, and a hydraulic system comprising at least one first cylinder which is arranged on the second joint part, and a first piston which has a first longitudinal axis and is positioned in the first cylinder.
[0008] Such joints have long been known in the art and are used for a wide variety of applications. For example, such a joint can be used as an ankle joint in a leg prosthesis. One of the two joint components is connected to, or is formed by, a prosthetic foot. The other joint component is typically equipped with a connecting element, such as a pyramid adapter, to connect another prosthetic component, such as a lower leg, to this joint component. The joint enables movement between the two joint components—for example, the prosthetic foot and a lower leg—that mimics the ankle movement of the human foot. A hydraulic system provides damping and resists the movement of the two joint components relative to each other through the flow resistance of the hydraulic fluid.
[0009] Typically, such a hydraulic system has two hydraulic chambers that are fluidically connected. When the joint is moved, i.e., when the first joint part pivots relative to the second joint part around the pivot axis, the hydraulic fluid is directed from one of the two hydraulic chambers to the other. Hydraulic lines and / or valves, such as a throttle valve used for this purpose, exert flow resistance, which is perceived as damping the movement of the joint. For some applications, it is advantageous if the joint can also be completely locked, so that no movement of the two joint parts relative to each other is possible. This can be easily achieved, for example, by closing a valve in the connecting line between the two hydraulic chambers.Then it is no longer possible to direct fluid from one hydraulic chamber to the other hydraulic chamber, so the joint is blocked.
[0010] The two joint components can only pivot within a predetermined range of angles around the pivot axis. This pivot range is limited on both sides by a stop.
[0011] Conventionally, the hydraulic chambers are located in a common cylinder and separated by a piston. Alternatively, it is also possible to provide a separate cylinder for each hydraulic chamber, in which a piston is movably arranged. Regardless of the configuration used, the fluid is transferred from one hydraulic chamber to the other by moving the existing pistons. In the prior art, it is important that the movement of the pistons follows the shape of the cylinder. Typically, the cylinder has a longitudinal axis along which its cross-section is constant. The movement of the piston within the cylinder then follows this longitudinal direction and consists solely of a displacement along this direction.Since it is essential to prevent hydraulic fluid from passing between the piston and the inner cylinder wall h, the piston is typically provided with a seal on its outer surface facing the inner cylinder wall. To ensure that this seal provides a sufficient seal in every position of the piston within the cylinder, prior art ensures that the piston's orientation within the cylinder does not change. An orthotic device within the meaning of the present invention is, in particular, a prosthesis or an orthosis. These are preferably designed for the lower extremity, and the joint is used as a knee joint, a hip joint, or an ankle joint.
[0012] WO 2023 / 104919 A1 discloses a generic ankle joint that has a hydraulic system with two hydraulic chambers, each delimited by a piston moving within a designated cylinder. The pistons not only move linearly but also pivot about an axis when the joint is moved, i.e., when the first joint part pivots relative to the second joint part about the axis. The two pistons are located on the upper joint part, which is, for example, a lower leg element or is connected to, or can be connected to, one. Due to the limited installation space available in this area for the prosthetic feet described therein, this embodiment is complex and therefore time-consuming and expensive.
[0013] The invention is therefore based on the objective of further developing a generic joint in such a way that the disadvantages of the prior art are mitigated or completely eliminated.
[0014] The invention solves the stated problem by a joint according to the preamble of claim 1, characterized in that the first cylinder is arranged at a first mounting point of the second joint part such that, when the first joint part is pivoted relative to the second joint part, the first cylinder performs a pivoting movement relative to the second joint part. When a joint according to the invention is moved by pivoting the first joint part relative to the second joint part about the pivot axis, the first cylinder performs a pivoting movement relative to the second joint part on which it is arranged. To achieve this particularly simply, the first cylinder is pivotably arranged on the second joint part about a first cylinder axis. The cylinder axis therefore does not denote a longitudinal axis or an axis of symmetry of the first cylinder, but rather a pivot axis about which the first cylinder is pivotable relative to the second joint part.In this case, the first cylinder axis preferably runs through the first mounting point.
[0015] The hydraulic system has a first hydraulic chamber located in the first cylinder, which is limited on at least one side by the first piston.
[0016] In a preferred embodiment of the invention, the first cylinder is a cup-shaped component that is pivotably attached to the second joint component at the first mounting point relative to the second joint component. A cup-shaped component has a closed bottom and an opening opposite the bottom. It is preferably rotationally symmetrical about an axis of symmetry, so that it has a circular cross-section. However, cup-shaped components that are not rotationally symmetrical, but have, for example, an oval, polygonal, or free-form cross-section, are also possible. The rotationally symmetrical design is, however, the preferred configuration. The cup-shaped component has a side wall that preferably extends at a right angle to the closed bottom. In a particularly preferred embodiment, the axis of symmetry is perpendicular to the closed bottom.However, designs are also possible in which the base is not a flat surface, but, for example, a cone. The cup-shaped component then has a depth that increases towards the center, with the depth corresponding to the distance from the base at that particular point on the base to an imaginary plane that closes the opening. This imaginary plane is preferably defined by the edge of the opening of the cup-shaped component.
[0017] In a particularly preferred embodiment, the first cylinder is a cup-shaped component without a bottom. In this embodiment, the first cylinder is essentially a hollow cylinder. The bottom of the cup-shaped component, which is of course necessary to prevent hydraulic fluid from escaping, is preferably formed by an element that is part of the second joint component. This element is preferably fixed to the second joint component or formed integrally with it. It has a seal or other circumferential sealing element to seal the contact between the element and the hollow cylinder. This makes it easy to create lines and connections leading into or out of the cylinder, as they can be arranged within the element.
[0018] The first piston is arranged within the first cylinder. It is preferably located on the first joint part. In a preferred embodiment, its position and orientation relative to the first joint part do not change when the joint is moved. The first piston is preferably fixed to the first joint part. In a particularly preferred embodiment, the first piston is formed integrally with the first joint part. This embodiment is particularly preferred when the pivot range of the joint between the first and second joint parts is only a few degrees. The first piston is preferably pivotably mounted on the second joint part for a reasonable pivot range of the joint. Particularly if the first cylinder is pivotably mounted, the required pivoting movement of the first piston within the joint part can be somewhat smaller.The required swivel range can be clearly seen on the opposite piston. When one piston retracts, the other extends and tilts accordingly in the second joint part.
[0019] Preferably, the hydraulic system comprises a second cylinder arranged on the second joint part and a second piston positioned within the second cylinder. The second cylinder is arranged at a second mounting point of the second joint part such that, when the first joint part pivots relative to the second joint part, the second cylinder performs a pivoting movement relative to the second joint part. When the first joint part pivots relative to the second joint part, the first cylinder is displaced into the first cylinder in a first pivoting direction. In this case, the volume of the first hydraulic chamber decreases. During this first pivoting direction, the second piston is preferably displaced out of the second cylinder. The hydraulic system preferably comprises a second hydraulic chamber located within the second cylinder, which is bounded on at least one side by the second piston.In this case, the volume of the second hydraulic chamber is increased. Preferably, the total volume of the first and second hydraulic chambers remains constant. Preferably, the second piston has a second longitudinal axis.
[0020] If the first joint part is pivoted relative to the second joint part in the second pivoting direction opposite to the first pivoting direction, the first piston is moved out of the first cylinder and the second piston is moved into the second cylinder.
[0021] Preferably, the second cylinder is a cup-shaped component that is pivotably attached to the second joint part at the second mounting point relative to the second joint part. To make this particularly easy to achieve, the second cylinder is pivotably arranged on the second joint part about a second cylinder axis. In this case, the second cylinder axis preferably runs through the first mounting point. The second cylinder axis is preferably parallel to the first cylinder axis.
[0022] Preferably, the second piston is fixed to the first joint part in a manner that prevents movement. It is preferably formed integrally with the first joint part. This configuration is particularly preferred when the pivot range of the joint between the first and second joint parts is only a few degrees. The second piston is preferably pivotably mounted on the second joint part for a reasonable pivot range of the joint. In particular, if the second cylinder is pivotally mounted, the required pivoting movement of the second piston within the joint part can be somewhat smaller. The required pivot range can be readily observed by looking at the opposite piston. When one piston retracts, the other extends and tilts accordingly within the second joint part. Preferably, the joint is designed for use as an artificial ankle joint.An orthotic device is, for example, a prosthetic foot comprising a foot section and a lower leg section connected to it by means of a joint, or a connecting piece for a prosthetic lower leg. In this case, the joint should preferably replicate the movement and range of motion of an anatomical ankle joint. Therefore, it is not necessary for the joint to allow a particularly large range of motion between the two connected components. The range of motion extends, for example, from a neutral position by 20° in the direction of dorsiflexion and by 40° in the opposite direction of plantarflexion. Deviations from this are possible depending on the neutral position. Preferably, the joint allows a total rotation of between 50° and 70° of the two components connected by the joint, and particularly preferably by 60°.
[0023] Particularly in cases where the element connected to the foot section is a connecting part, for example equipped with a pyramid adapter for connection to a prosthetic lower leg, the modular system consisting of the pyramid adapter on the one hand and the pyramid mount on the other allows an angle of approximately 14° to be set. In this case, it is sufficient for the joint to allow a pivoting angle of 46°, preferably 23° in both directions from the neutral position.
[0024] Preferably, the longitudinal axis of the two pistons arranged in the cylinders extends at a right angle, i.e., orthogonally, to the respective lever arm over which the pivoting occurs, in the neutral position of the joint. This lever arm represents the distance between the connection between the respective piston and the first joint part on the one hand, and the pivot axis of the joint on the other. If the two joint parts are then pivoted by these 23°, the two pistons do not move in a straight line, but rather along a chord of the circle whose radius corresponds to the length of the lever arm. In this case, the pistons could be moved within a stationary piston, resulting in a slight tilting between the longitudinal axis of the pistons and the longitudinal axis of the respective cylinders.However, the pivoting of the first joint part relative to the second joint part also moves the base of both cylinders, specifically the respective mounting point where the cylinder is attached to the second joint part, resulting in a pivoting of the cylinder. The respective piston then extends along a chord of the pivot circle, but due to the relatively small pivot angle, this results in only a slight change in the piston's direction compared to the joint's neutral position.
[0025] If the pistons are designed to be immobile relative to the first joint part, a pivoting movement of the cylinders occurs because the second joint part is pivoted and because the tilting of the piston described above cannot take place and the cylinder compensates for this movement.
[0026] Preferably, the pistons are arranged on the first joint part so that they can be tilted about a tilting axis, with the tilting axes running parallel to the pivot axis of the joint.
[0027] Preferably, the path of the first mounting point intersects the first longitudinal axis twice when the first joint part pivots relative to the second joint part. Particularly preferably, the path of the second mounting point also intersects the second longitudinal axis twice when the first joint part pivots relative to the second joint part.
[0028] The longitudinal axis of the first piston, like the first piston itself, is preferably positioned at the first joint part and is fixed relative to this first joint part. The first mounting point is part of the first joint part and is fixed relative to it. Therefore, if the two joint parts are pivoted relative to each other, the first mounting point is also pivoted relative to the first longitudinal axis of the first piston. In a preferred embodiment, the first longitudinal axis of the first piston runs perpendicular to the pivot axis of the joint, with the two axes being skew in the mathematical sense, meaning they do not intersect, even if they are conceptually extended.
[0029] Since, during pivoting, the first component performs a circular motion, or at least a partial circular motion, relative to the second component, the first mounting point also performs a circular motion relative to the first longitudinal axis of the first piston. A portion of a circular path can either not intersect a straight line, it can touch it once, or it can intersect it twice. The preferred configuration is one in which the circular path described by the mounting point during pivoting intersects the first longitudinal axis twice.
[0030] Within the scope of the present invention, this does not necessarily mean that the circular path tracing the first attachment point and the first longitudinal axis must lie in a common plane. While this is an advantageous embodiment, it is not necessary for the invention. For the effect described here, it is sufficient if the first longitudinal axis intersects the perpendicular projection of the circular path twice. The perpendicular projection of the circular path is the projection from which the circular path appears as a circular path.
[0031] Preferably, the pivoting range is limited by a first limiting angle and a second limiting angle, wherein the distance between the mounting point of a cylinder and the longitudinal axis of the respective piston is the same for both limiting angles. Since the two joint parts can only pivot relative to each other within a predetermined pivoting range, i.e., a predetermined angular range, the portion of the circular path is also limited to this angular range. In a preferred embodiment, the distance of the first mounting point from the first longitudinal axis of the first piston is the same for both limiting angles that define the respective pivoting ranges. Particularly preferably, the distance of the first mounting point from the first longitudinal axis is the same for these two limiting angles as in the intermediate position, in which the angle between the first joint part and the second joint part lies exactly at the midpoint of the two limiting angles.Advantageously, the outer surface of the first piston, which faces an inner surface of the first cylinder, is formed with at least one sealing element, for example an O-ring, preferably made of an elastic material, such as rubber. Particularly preferably, the outer surface of the first piston has a groove in which the sealing element is arranged. The sealing element projects beyond the outer surface of the first piston. In the unassembled state, it projects beyond the outer surface of the first piston by a distance greater than the distance between the outer surface of the first piston and the inner surface of the first cylinder in the assembled state.
[0032] In a preferred embodiment, the first piston and / or the second piston are pivotably arranged on the first joint part. Preferably, the sealing element is designed such that it seals the piston on which it is arranged against both a round cylindrical shape and an elliptical cylindrical shape. Such an elliptical seal is necessary when the cylinder is tilted relative to the piston. Preferably, the piston is designed as a spherical segment in the area where the sealing element is arranged. This means that the outer contour of the piston in this area has a constant curvature, i.e., a constant radius around a single center point. To increase the elasticity of the seal provided by the sealing element, it is advantageous to deepen a groove arranged in the piston in which the sealing element is positioned and to partially fill this groove with an elastic bearing material.Alternatively or additionally, the sealing element is provided with a sealing lip which, in the unloaded state, protrudes further than a ring seal from the groove receiving the sealing element in order to be able to seal a larger sealing gap.
[0033] Preferably, the pistons are each tiltable about a tilting axis attached to the first joint part, the tilting axes preferably extending parallel to the pivot axis. Advantageously, the joint is an artificial ankle joint, and the first joint part or the second joint part has a connection for a further prosthetic part, in particular a prosthetic lower leg.
[0034] With the aid of the accompanying drawings, some exemplary embodiments of the present invention are explained in more detail below. They show:
[0035] Figures 1 and 2 - schematic partial representations of a joint
[0036] Figure 1 schematically shows a part of a joint according to an embodiment of the present invention. A portion of the first joint part 2 and a portion of a second joint part 4 are visible. A first cylinder 8 is pivotably mounted on the second joint part at a first mounting point 6. A first piston 10 is shown in this first cylinder 8, which has a groove 12 in which a sealing element (not shown) is arranged. The first cylinder 8 and the first piston 10 define the volume of a first hydraulic chamber 14. The first piston 10 is pivotably mounted on the first joint part 2 about a pivot point 16.
[0037] Figure 1 shows how the distance of the chord along which the piston extends in the spent state from the circular arc is compensated by cylinder tilt. Figure 2 shows a combination of cylinder tilt and piston tilt for the same reason. The rotation of the piston in the piston bearing is comparable in both figures and differs only in the discrepancy compensation.
[0038] In addition, a second cylinder 20 is pivotably arranged at a second attachment point 18 on the second joint part 4, in which a second piston 22 is located.
[0039] This second piston 22 also has a groove 12 for a sealing element and is pivotably arranged about a pivot point 16 on the first joint part 2. In the situation shown, the axis of symmetry of the respective cylinder 8, 20 is identical to the longitudinal axis of the respective associated piston 10, 22. This is not always the case, as shown in Figure 2. Figure 2 shows that, in particular, the first piston 10 is tilted relative to the first cylinder. This tilting and the associated change in the gap between the outside of the piston 10 and the inside of the cylinder 8 is compensated for by the sealing element, which is arranged in the groove 12.
[0040] The figures show that the two cylinders (8, 22) are designed as bottomless cylinders. A closing element, which can also be called a bottom element, is arranged at the end of the cylinders (8, 22) facing the second joint part (4). In the illustrated embodiment, it is formed integrally with the second joint part (4) and has a circumferential sealing ring.
[0041] Reference symbol list
[0042] 2 first joint part
[0043] 4 second joint part
[0044] 6 first attachment point
[0045] 8 first cylinder
[0046] 10 first piston
[0047] 12 Nut
[0048] 14 first hydraulic chamber
[0049] 16 swivel point
[0050] 18 second attachment point
[0051] 20 second cylinder
[0052] 22 second piston
Claims
* nin part il ec tua ä proper ty Ottobock SE & Co. KGaA Lawyer's File: Max-Näder-Straße 15 0108-2042 PCT-1 37115 Duderstadt Date: December 8, 2025 Patent claims 1. Joint for an orthopaedic device, wherein the joint - a first joint part (2), - a second joint part (4) which is arranged on the first joint part (2) so as to be pivotable about a pivot axis in a pivoting range, - and a hydraulic system comprising at least one first cylinder (8) arranged on the second joint part (4) and a first piston (10) having a first longitudinal axis and positioned in the first cylinder (8), characterized in that the first cylinder (8) is arranged at a first attachment point (6) of the second joint part (4) such that the first cylinder (8) performs a pivoting movement relative to the second joint part (4) when the first joint part (2) is pivoted relative to the second joint part (4).
2. Joint according to claim 1, characterized in that the first cylinder (8) is a cup-shaped component which is pivotably attached to the second joint part (4) at the first attachment point (6) relative to the second joint part (4).
3. Joint according to claim 1 or 2, characterized in that the first piston (10) is immovably attached to the first joint part (2) relative to the latter, preferably being formed integrally with the latter.
4. Joint according to one of the preceding claims, characterized in that the hydraulic system has a second cylinder (20) arranged on the second joint part (4) and a second piston (22) located in the second cylinder (20) is positioned, wherein the second cylinder (20) is arranged at a second attachment point (18) of the second joint part (4) such that the second cylinder (20) performs a pivoting movement relative to the second joint part (4) when the first joint part (2) is pivoted relative to the second joint part (4).
5. Joint according to claim 4, characterized in that the second cylinder (20) is a cup-shaped component which is pivotably attached to the second joint part (4) at the second attachment point (18) relative to the second joint part (4).
6. Joint according to claim 4 or 5, characterized in that the second piston (22) is immovably attached to the first joint part (2) relative to the first joint part (2), preferably being formed integrally with the first joint part.
7. Joint according to one of the preceding claims, characterized in that the path of the first fastening point (6) intersects the first longitudinal axis twice when pivoting the first joint part (2) relative to the second joint part (4).
8. Joint according to one of the preceding claims, characterized in that the pivoting range is limited by a first limiting angle and a second limiting angle, wherein a distance between the mounting point (6, 18) of a cylinder (8, 20) and the longitudinal axis of the respective piston (10, 22) is the same for both limiting angles.
9. Joint according to one of the preceding claims, characterized in that the pistons (10, 22) are each tiltable about a tilting axis attached to the first joint part (2), wherein the tilting axes preferably extend parallel to the pivot axis.
10. Joint according to one of the preceding claims, characterized in that the joint is an artificial ankle joint and the first joint part (2) or the second joint part (4) has a connecting means for a further prosthetic part, in particular a prosthetic lower leg.