DE29912832U1 - Spring joint for the artificial foot of a prosthetic leg - Google Patents

Description

RDE

RICHTER, WERDERMANN & GERBAULET

EUROPEAN PATENT ATTORNEYS · PATENT ATTORNEYS

EUROPEAN TRADEMARKATTORNEYS

HAMBURG · BERLIN

DIPL.-ING. JOACHIM RICHTER · BERLIN DIPL.-ING. HANNES GERBAULET ■ HAMBURG DIPL.-ING. FRANZ WERDERMANN · - I98S

NEW WALL IO
2&Ogr;354 HAMBURG

KURFÜRSTENDAMM &Igr;&Ogr;71&THgr; BERLIN

<m (O4O) 34 OO 45/34 00 5β @ (030) 8 82 74

FAX (O40) 35 24 I5

FAX (03O) 8 82 32 IN COOPERATION WITH MAINITZ & MAINITZ LAWYERS · NOTARIES

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OUR SIGN OUR FILE

I 99334 III 2611

HAMBURG

20.07.1999

Applicant:

ipos

Society for integrated prosthesis development and orthopaedic technical service mbH & Co. KG Zeppelinstraße 30

D-21337 Lüneburg (DE)

Title:

Spring joint for the artificial foot of a leg prosthesis

The invention relates to a spring joint for the artificial foot of a leg prosthesis with a shaft designed for connection to the lower leg of the leg prosthesis and a spring element connected to the shaft and extending in the longitudinal direction of the artificial foot.

A spring joint of the type mentioned above is known, for example, from EP 600 A2. The spring joint, which is located in the longitudinal direction of the foot,

The stretching spring element is connected at its rear end, located in the heel area, to the lower end of a C-shaped spring, the upper end of which in turn has an adapter for connection to the leg prosthesis. Similar spring joints are also known from EP 0 884 033 A2 and EP 0 884 034 A2, in which a structure of at least two layers of the leaf springs used and a pressure pad for adjusting the spring elasticity are proposed. The spring joints mentioned therefore have a relatively complicated structure.

The invention is based on the object of improving an ankle joint of the type mentioned at the beginning in such a way that it has a simple structure and exhibits good rolling behavior with good energy utilization and stabilization of the leg.

This object is achieved by the features specified in claim 1.

Accordingly, the spring joint for the artificial foot of a leg prosthesis has, in a known manner, a shaft designed for connection to the lower leg of the leg prosthesis and a spring element connected to the shaft and extending in the longitudinal direction of the artificial foot. The spring joint is characterized in that the spring element contains at least three sections, namely a front section arranged in the forefoot, a middle section arranged in the midfoot and a heel section arranged in the heel. The sections mentioned have different elastic properties.

The three-part structure of the spring element provides improved overall support and is optimally adapted to the respective rolling phase of the foot.

Properties of the ankle joint. The force absorption of the leg when putting the foot down, the energy storage in the spring element when rolling and the lifting of the foot can each be optimized by selecting the transition point between the sections of the spring element and by their elastic properties.

According to claim 2, the middle section is preferably made of a unidirectional carbon fiber reinforced epoxy casting resin. This material, which is preferably in the form of a laminate, allows voltage absorption with almost no hysteresis, i.e. with only about 0.5% energy loss.

According to claim 3, the elasticity ratios between the three sections of the spring element are preferably such that the front section and/or the heel section have a lower bending stiffness than the middle section. The foot can thus dampen the introduction of force when putting the foot down, and it is possible for the forefoot to bend when the leg is lifted.

According to claim 4, the front section and/or the heel section of the spring element are preferably made of Vulkollan or a similar material. Homogeneous Vulkollan is an example of an elastomer with a highly distorted hysteresis. By using a material with these properties, the tip of the forefoot is delayed when the swing leg swings through, so that ground clearance is created during the swing phase. The Vulkollan parts also have the task of creating an intensive, firm connection between the artificial foot and the foot mechanics through a special chemo-mechanical treatment.

According to claim 5, the transition between the front section and the middle section of the spring element is arranged at 25 to 35%, preferably at 28%, of the total length of the artificial foot. In science,

the stride length from heel strike to toe lift is divided into 100% of the stride length of a leg. Within this stride length, large ground reaction forces are introduced into the foot structure when the heel strikes. After a local minimum, i.e. a drop in the vertical reaction force in the middle stance phase, the rolling load increases to a second maximum at the end of the stride length, i.e. shortly before the toe lifts. In the front part of the foot, the 28% area, the connection between the front section and the middle section of the spring element creates a rolling thickening that represents the load point for the introduced force. The forefoot, which is 28% of the length, prevents a thrust force from the foot onto the pelvis due to its high rolling elasticity.

The heel length from the end of the artificial foot to the axis of the shaft is approximately 5.5 to 7 cm, preferably 6.4 cm, according to claim 6. The resulting relatively short metatarsal lever brings sufficient rolling energy into the biomechanical system of the leg prosthesis.

In a further development of the invention according to claim 7, a rolling runner is arranged at the lower end of the shaft in connection with the middle section. The rolling runner is a convex (upward) curved surface which, under stress, creates a moving contact point or a moving contact line with the spring element. This advantageously changes the lever arm effective during the rolling movement. An intermediate coating can be arranged between the rolling runner and the spring element to reduce rolling friction.

According to claim 8, the rolling runner is preferably designed in such a way that it enables a dorsal flexion of the ankle joint by approximately 20 to 25°. This shifts the knee pivot point forward in a favorable manner.

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According to claim 9, the shaft is attached monocentrically to the middle section of the spring element. In this way, the elastic behavior of the spring element is influenced as little as possible and a defined point for the introduction of force is established.

According to claim 10, the middle section can be attached to the shaft via a screw connection, with a wedge element being arranged between the screw connection and the middle section on the side of the middle section opposite the shaft, which wedge element preferably extends over the entire width of the middle section. The wedge element guarantees that the bending forces introduced are transferred to the entire width of the spring. In addition, it ensures the necessary inclination compensation between the shaft and the spring element.

Furthermore, the shaft according to claim 11 can have a cavity with fastening means for fastening the artificial foot to the leg prosthesis. The fastening means can in particular be an internal thread. This makes it possible to fasten the spring joint according to the invention to various other construction elements and thus achieve a wide range of applications.

The flexibility of the use of the spring joint is increased according to claim 12 in that the end of the shaft is formed by an adjustment pyramid for adjustable fastening of the artificial foot to the lower leg. The rolling moment required individually for the patient can be adjusted via the adjustment pyramid by reducing the angle between the prosthetic tube and the forefoot lever.

The shape of the artificial foot can be achieved according to claim 12 from polyurethane (PU) foam with inner areas made of lightweight foam.

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While the PU foam guarantees sufficient stability, the lightweight foam can be used to save weight in statically non-critical areas.

The invention is explained below using the figure as an example. The figure shows a cross section through an artificial foot with an inventive spring joint 100.

The molding compound of the artificial foot consists essentially of PU foam 1. In areas where no stable material is required, the PU foam 1 can contain recesses that are filled with a lightweight foam 9.

The mechanics of the ankle joint consist of two main elements. Firstly, the shaft 11, which is connected to the patient's natural or artificial lower leg. Secondly, there is the spring element, which runs parallel to the sole of the foot in the longitudinal direction of the foot and consists of three sections.

The section of the spring element located in the forefoot V is the front section 3. It is made of homogeneous Vulkollan, an elastomer with a highly distorted hysteresis. This delays the return of the forefoot tip when the swing leg swings through, so that ground clearance is created during the swing phase. The front section 3 extends over a length V of approximately 28% of the total foot length L.

The front section 3 is followed by the middle section 2, which is formed by a carbon fiber spring made of unidirectional carbon fiber reinforced epoxy cast resin. This section preferably has a lamellar structure.

At the other end of the middle section 2, this is connected to the heel section 8 of the spring element. This is in turn made of VuI-kollan and extends over the heel of the artificial foot 100, the length F of which is preferably 6.4 cm. When the heel strikes, the vertical force introduced should be absorbed non-destructively between the foam and the extending spring.

The middle section 2 is connected monocentrically to the shaft 11 in its heel-side end area by means of a screw connection 6. The screw connection 6 passes on the lower side of the middle section 2 through a wedge-shaped compensation piece 7 that covers the entire spring in the transverse direction. As a result, the introduced bending forces are transferred to the entire width of the spring.

The underside of the shaft 11, which faces the middle section 2, is formed by a rolling runner 4. This is made of aluminum and is held in the rolling curve in such a way that, at maximum rolling load, a forefoot spring travel of between 30 and 40 mm is created at point F _1. Between the rolling runner 4 and the middle section 2 there is a sliding disk 5, which is preferably made of polyethylene. This sliding disk has the task of reducing the rolling forces between the aluminum and the synthetic resin spring without friction.

The shaft 11 has an axially arranged cavity 10 that is open at the top and can accommodate different construction variants in the foot part. For this purpose, it has a fine thread on the inside at its upper end, into which suitable construction elements can be screwed. The figure shows an adjustment element for connection to other prosthetic elements, consisting of an adjustment cap 13 and an adjustment pyramid 14. The adjustment

A screw depth stop 12 made of slightly elastic material is arranged on the cap 13, with which it is possible to bring the adjustment pyramid into a certain position and then to mechanically secure it in this position.

In the last 35 years of prosthetic research and development, the knowledge about foot construction and foot functions has changed fundamentally. In the second half of the 1960s, J. Prahl published a paper on construction criteria taking into account the biomechanics of the leg (Orthopädie-Technik 1971, 209). In this, the importance of plantar flexion in existing foot constructions was questioned for the first time. In 1994, a similar paper was published, in which plantar flexion was also considered a mechanically and biomechanically dispensable design feature (Blumentritt et al., Med.Orth.Tech. 114 (1994), 287-292).

Scientific publications divide the stride length from heel strike to toe lift as 100% of the stride length of a leg. Within this stride length, large ground reaction forces are introduced into the foot structure when the heel strikes. After a local minimum, i.e. a decrease in the vertical reaction force in the middle stance phase, the rolling load increases to a second maximum at the end of the stride length, i.e. shortly before the toe lifts (see e.g. Blumentritt, op. cit., Fig. 3, Figure a).

The ankle joint 100 according to the invention takes into account a forefoot of approximately 28% of the total length L, a midfoot up to the lower leg tube attachment, and a rear foot from the lower leg tube attachment to the heel attachment of approximately 6.4 cm. The forefoot of 28% of the foot length L prevents a thrust force from the foot onto the pelvis due to its high rolling elasticity, the short midfoot lever A brings sufficient rolling energy into the biomechanical system of the leg prosthesis.

The fact that foot movements must be carried out over a certain resistance without unintentionally consuming kinetic energy in buffer elements has become increasingly important. For example, a buffer in dorsal flexion was compressed by the rolling force, the buffer itself was deformed and part of the deformation energy was returned to the prosthesis movements as recoil. Rolling force or deformation energy is residual energy that is available as recoil to save kinetic energy. The energy lost from the buffer deformation is the so-called hysteresis, which ultimately led to the destruction of the buffer elements.

In the spring joint according to the invention, carbon fiber springs are primarily integrated into the rolling process of the prosthetic foot in order to use the rolling energy to control the prosthesis in an energy-saving or energy-balancing manner. The new foot development only uses the rolling side of the carbon fiber spring as a foot movement element.

The adjustment pyramid with the adjustment cap is an integral part of the foot according to the invention. The rolling moment required individually for the patient is adjusted via the foot connection pyramid by reducing the angle between the prosthetic tube and the forefoot lever. The rolling load during the stance phase, which is mathematically introduced into the forefoot lever A at 28% of the forefoot length, enables a reduction in the angle between the lower leg and the surface where the foot is treading on the ground. Dorsiflexion is created by the defined elasticity of the carbon fiber-reinforced epoxy spring.

If we assume that approximately 20 - 25° of dorsal flexion occurs during rolling, the knee pivot point is shifted forward. Knee flexion can be considered complete in terms of energy expenditure.

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when the pivot point itself crosses the load line forwards. Dorsiflexion reduces the rolling load for the patient. As this spring travel returns when the rolling load decreases, the dorsalflexion energy is converted into a plantar movement and stabilizes the safety in the knee joint. This means that the energy input is reduced until the knee movement (flexion) is initiated. After the prosthesis is relieved and the knee movement is initiated, the safety in the knee joint is stabilized by a backward movement of the pivot point of the knee. This function delays the critical point, the crossing of the vertical load line.

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Reference number: Spring joint 100 Pu foam 1 Middle section 2 Front section 3 Roller skid 4 Sliding disc 5 Screw connection 6 Compensating piece 7 Heel section 8th Lightweight foam 9 cavity 10 shaft 11 Screw depth stop 12 Adjusting cap 13 Adjustment pyramid 14

Claims (13)

1. A spring joint ( 100 ) for the artificial foot of a leg prosthesis with a shaft ( 11 ) designed for connection to the lower leg of the leg prosthesis and a spring element connected to the shaft and extending in the longitudinal direction of the artificial foot, characterized in that the spring element contains a front section ( 3 ) arranged in the forefoot (V), a middle section ( 2 ) arranged in the metatarsal (A) and a heel section ( 8 ) arranged in the heel (F), wherein the said sections ( 3 , 2 , 8 ) have different elastic properties. 2. A spring joint according to claim 1, characterized in that the central section ( 2 ) contains unidirectional carbon fiber reinforced epoxy casting resin. 3. Spring joint according to one of claims 1 or 2, characterized in that the front section ( 3 ) and/or the heel section ( 8 ) have a lower flexural rigidity than the middle section ( 2 ). 4. A spring joint according to claim 3, characterized in that the front section ( 3 ) and/or the heel section ( 8 ) consists of Vulkollan or a similar material. 5. Spring joint according to one of claims 1 to 4, characterized in that the transition between the front section ( 3 ) and the middle section ( 2 ) is arranged at 25 to 35%, preferably at 28%, of the total length (L) of the artificial foot. 6. Spring joint according to one of claims 1 to 5, characterized in that the heel length (F) from the end of the artificial foot to the axis of the shaft ( 11 ) is approximately 5.5 to 7 cm, preferably 6.4 cm. 7. A spring joint according to one of claims 1 to 6, characterized in that a rolling skid ( 4 ) is arranged at the lower end of the shaft ( 11 ) in contact with the central section ( 2 ). 8. A spring joint according to claim 7, characterized in that the rolling runner ( 4 ) is designed in such a way that it enables a dorsal flexion (α) of the spring joint by approximately 20 to 25°. 9. A spring joint according to one of claims 1 to 8, characterized in that the shaft ( 11 ) is fixed monocentrically to the central portion ( 2 ). 10. A spring joint according to claim 9, characterized in that the fastening of the central section ( 2 ) to the shaft ( 11 ) is carried out via a screw connection ( 6 ), wherein on the side of the central section ( 2 ) opposite the shaft ( 11 ) a wedge element ( 7 ) is arranged between the screw connection ( 6 ) and the central section ( 2 ), which preferably extends over the entire width of the central section ( 2 ). 11. A spring joint according to one of claims 1 to 10, characterized in that the shaft ( 11 ) has a cavity ( 10 ) with fastening means, preferably with an internal thread, for fastening the artificial foot to the leg prosthesis. 12. A spring joint according to one of claims 1 to 11, characterized in that an adjusting pyramid ( 13 , 14 ) for the adjustable fastening of the artificial foot to the lower leg is arranged at the end of the shaft ( 11 ). 13. Spring joint according to one of claims 1 to 12, characterized in that the artificial foot is made of polyurethane foam ( 1 ) with inner regions made of lightweight foam ( 9 ).