Distraction device for non-invasively extendable implants

Abstract

A distraction device for non-invasively extendable implants, in particular nails and stems of endoprostheses for patients with incomplete development of the upper and lower limbs, comprising an outer body (1) of the implant in which an inner body (2) of the implant is arranged in an extendable manner in the direction of implant extension. In the inner body (2) of the implant is placed a melting insert (3) on which a piston (5) is seated, which is connected with a support fixation element (6), which is adjustable in the direction of the implant extension and is placed in its outer body (1). The support fixation element (6), as well as the extendable body (2) of the implant, are equipped with spring-loaded peripheral latches (7) for their mutual adjustment, which fit into bevelled anchor grooves (9) in the direction of the implant extension, formed on the inner shell of the outer body (1) of the implant.

Description

[0001] Distraction Device for Iton-lnvasiveiy Extendable Implants

[0002] Field of the Invention

[0003] The invention relates to a distraction device for non-invasively extendable implants, in particular nails and stems of endoprostheses, for patients with incomplete development of the upper or lower limbs and enabling non-contact controlled extension thereof.

[0004] Currently, several types of so-called "growing” endoprostheses exist for paediatric patients with, for example, total knee arthroplasty, enabling their length to be adjusted,, depending on the course of their overall continued growth. Length adjustment is usually done by mechanical means such as various threaded spindles, ratchet mechanisms and the like.

[0005] A significant disadvantage of all of the above and other similar endoprosthesis solutions is the necessity of repeated and often quite extensive surgical intervention to allow access to the prosthesis construction, with each change in the length adjustment of the prosthesis, which places additional demands on the patient and a high risk of infection.

[0006] This disadvantage is to some extent eliminated, for example, by the solution according to patent fils US 2004 / 0193266, the subject matter of which is a prosthesis for children and adolescents, the length adjustment of which is carried out by a magnetic field generated outside ths previously operated limb. Also known is the solution according to EP 1642550, the subject of which is an adjustable remote-controlled orthopaedic prosthesis with telescopic segments and linear electric actuators. In addition to these disclosed examples of non-invasively electrically, magnetically or electromagnetically adjustable prostheses, a solution according to US 5,626,581 is also known, the subject matter of which is an implantable bone lengthening device that uses shape memory material to drive a hydraulic pump and a ratchet mechanism and which further consist of a piston and an extension mechanism. However, in most of these embodiments, the solutions are relatively complex and expensive, which may limit their applicability.

[0007] Somewhat simpler solutions are then known from US 5,071,435 and US 5,458,261.

[0008] The subject matter of US 5,071 ,435 is a hydraulically extendable bone prosthesis consisting of a unilaterally closed cylinder equipped with an extendable piston, under which a fluid-filled sac is placed in the cylinder as required or by the required extension of the piston via a filling valve in the cylinder wall horn its outer space. The subject matter of US 5,466,261 is a non-invasively extendable prosthesis for children with incomplete body growth created on an analogous principle, in which a hydrogel is used in the cylinder instead of the sac changing its volume according to the amount of saline solution contained therein and thus determining the size of the piston extension. The disadvantage of these solutions may be the limited adjustability of such prostheses due to the size of the used sac ar the amount of hydrogel and its absorption capacity, as well as an increased risk of failure. A separate device, suitable for these length adjustable implants and enabling the two bodies to move relative to each other, is known, for example, from US 5,720,748. The summary of this device is that it contains two elements, each of which is combined with one of these two bodies, and a means for exerting the necessary force to produce this motion. One of these elements is fitted with a collar protrusion, and the other element has a cavity corresponding at least in part to that protrusion. These two elements are movably mounted to each other so that the protrusion engages with the cavity, wherein the element with the cavity is made of a material that can be changed by induction heating from a non-deformable hard solid state to a deformable soft pasty state, while the element with the protrusion is made of a substantially hard material Ths device is also equipped with means for controlling the change of at least one part of the material surrounding the cavity from the first state to the second state and vice versa. Analogous devises are further disclosed in US 2003 / 0032958 or WO 2019 / 227859.

[0009] The disadvantage of these devices, however, is that the movement of the two bodies relative to each other is very difficult to control and predict due to the indefinable contact between the collar protrusion and the magnetic core material used in these devices, wherein their use in length adjustable implants may also pose a risk of burning patients during the readjustment process given the transfer of a significant amount of heat from these devices to the metal parts of the implants.

[0010] One of the most recent solutions for such purposes is the distraction device, according to the file CZ 309950, comprising an outer body comprising an inner piastic protective container with an inner piastic insert, in which an inner body is inserted from one end thereof, on which a collar is formed from the head pari inside the outer body, protruding into its anchoring notch in the inner plastic insert. At the same time, a cavity is formed inside the inner body in which a pre-stressed compression spring is arranged at. one end to induce the gradual extension of the inner body from the outer body alter a temporary, at least partial melting of the material of ths inner piastic insert in the area of the anchor notch. To generate the necessary heat, the inner body is fitted with at least one ferromagnetic ring at the collar of its head section to generate eddy currents in its material from the outer space by an inductor produced by a concentrated electromagnetic field and the outer body connected at its other end directly to the metal pari of the implant is fitted with an anti -rotation plug against rotation of the inner body and an insulating seal before the inner body exits Its inner space, wherein the inner space of the outer body is closed around the exit of the inner body by the swivel-nut. In order to eliminate Induced currents, at least one outer groove and / or at least one inner groove is formed in the metallic part of the implant, and a side cut is formed in the swivel-nut.

[0011] The purpose of the present invention Is to extend the range of these length adjustable replacements further, i.e., their distraction devices, and, in particular, to eliminate their possible disadvantages that still exist. Summary of the invention

[0012] According to the present invention, this issue is seized mainly by a distraction device for non-invasively extendable implants, in particular, nails and stems of endoprostheses, for example, for patients with incomplete development of the upper and lower limbs or patients after extensive trauma where the limb has been shortened, comprising an outer body of the implant in which the inner body of the implant is arranged in an extendable manner in the direction of the implant extension. The summary'- of the invention is that a melting insert is arranged In the inner body of the implant on the front of which a piston is seated inside the inner body of the implant, which is connected to a support fixation element, adjustable in the direction of extension placed in its outer body. This support fixation element, as well as the inner body of the implant, are equipped with spring-loaded peripheral latches for their mutual adjustment in the outer body of the implant, which fit into the bevelled anchor grooves formed on the inner shell of the outer body of the implant in the direction of the implant extension.

[0013] In contrast to analogous known solutions, the length adjustment or lengthening of the implant occurs due to the change in the volume of the melting insert material during alternating phase transformations from its solid state to liquid and back.

[0014] Widen the melting insert is melted, and its material is transformed from solid to liquid due to its expansion and volume increase, pressure is exerted on the piston and thus on the support fixation element, which is, however, firmly anchored in the direction of the applied pressure in the anchor grooves in the inner shell of the outer body of the implant. This pressure, therefore, results in the necessary extension of the inner body of the implant from its outer body, which is enabled in the direction of implant extension by bevelling its anchor grooves. After the transition to the solid state and the shrinkage of the melting insert material, a negative pressure is created between the piston and the melting insert, in the inner body, which subsequently causes the displacement of the support fixation element connected to the piston and its re-anchoring in the anchor grooves of the outer body in the same direction and by the same amount. This entire procedure can then be repeated at any time as required. The summary of the invention further consists in the fact that the melting insert is made of materials with a low melting temperature, optimally in the range of 45 to 65*Ctand with a necessary expansion during the change of state from solid to liquid in the range of 5 to 14% by volume, preferably of higher saturated aliphatic hydrocarbons or polymers, or other materials such as Wood metal, etc. The lower limit of the melting temperature of the melting insert is thus safely above the patient’s body temperature to prevent spontaneous implant extension, and the lower limit of the expansion of the material of the melting insert is selected so that the change in its volume during melting induces sufficient pressure on the piston for the necessary length adjustment of the implant. According to the invention, the upper limits of the melting temperature of the melting insert and the necessary changes in its volume size can be higher, but increasing them above the above-mentioned maximum values seems unnecessary in terms of the correct functioning of the distraction device.

[0015] The summary of the invention further consists in that in order to support the readjustment process of the supped fixation ring with the piston and the inner body of the implant in the outer body of the implant the support fixation element inside the outer body of the implant is preferably spring-loaded with a support compression spring.

[0016] The summary of the invention further consists in the fact that the melting insert in the inner body is preferably equipped with a melting core made of ferromagnetic material for fusing the melting insert with a concentrated electromagnetic field using an external inductor.. However, instead of a ferromagnetic melting core for such fusion of the melting insert for example, iron filings or steel balls dispersed in the melting insert material may be used, or the fusion of the melting insert may be induced otherwise, e.g. by ultrasound.

[0017] According to the invention, the solution also allows the choice of fully biooompafibte materials that eliminate an undesirable negative reaction of the organism in the event of any damage to the implant and has the advantage of avoiding undesirable length adjustment of the implant, even in the event of an error of the device operator. Bjrfef descrtglgon_of fee Drawings

[0018] The invention is further clarified by drawings of an exemplary embodiment of a distraction device for non-invasively extendable implants according to the invention, illustrating: Fig. 1 distraction device in neutral made in the cross-section;

[0019] Fig. 2 distraction device in the cross-section in the stage of length adjustment of the implant;

[0020] Fig. 3 - implant piston with implant support fixation element;

[0021] Fig. 4 ~ outer body of the implant; Fig. 5 - inner body of the implant.

[0022] Exemplary Embodiments of the Inyantion

[0023] The distraction device for non-invasively extendable implants comprises, as can be seen from Fig. 1 io 5, of an outer body 1_pf the implant, in this embodiment in the form of a nail in which an inner body 2 of the implant is arranged, extendable from the outer body 1. of the implant by the application of a concentrated electromagnetic field induced by an external inductor not shown here.

[0024] In the extendable inner body 2 of the implant, a melting insert 3 is arranged together with its melting core 4, which is made of ferromagnetic material on which a piston 5 is seated,, which is connected to a support fixation element 6, adjustable in the direction of implant extension arranged in its outer body 1. The support fixation element 6, as well as the inner body 2 of the implant, are equipped with spring-loaded peripheral latches 7 for their mutual adjustment, which fit into the bevelled anchor grooves 9 formed on the inner shell of the outer body 1 of the implant in the direction of the implant extension. The support fixation element 6 is spring-loaded inside the outer body .1 by the support compression spring 10.

[0025] As shown in more detail in Fig. 3, separation grooves 8 are formed between the peripheral latches 7 of the support 11x01100 element 6, and the inner body 2 to spring them and to facilitate their movement, over the inclined anchor grooves 9 of the outer body 1 of the implant.

[0026] The melting insert 3 in the extendable inner body 2 cf the implant, which is fusible by its melting core 4 using an external inductor and its induced concentrated electromagnetic field, is made of paraffin wax, which comprises an amorphous mixture of higher saturated hydrocarbons having a melting temperature of 56.8*C and specific heat of solid of 2.0 kJ / kg.K, specific heat of liquid of 2.15 kd / kg.K, latent heat ef fusion of 190 kJ / kg, thermal conductivity of solid of 0.24 W / m.K, thermal conductivity of liquid of 0.22 Wfm.K, density of solid at 16*0 of 910 kg / msand density of liquid at 70*0 of 790 kg / m3. Its solid-liquid expansion rate is 13.2% by volume.

[0027] Fig. 2 then shows in more detail the area 11 of the increase in the volume of the melting insert 3 material during its melting, which causes the inner body 2. to be extended from ths outer body 1 of the implant by the required step. After the melting insert 3 has cooled down again, a negative pressure is created in this area 11, as a result of which, with the contribution of the support compression spring 10, the support fixation element 6 is displaced by the same step, and its piston 5 sits back on the front of the cooled melting insert 3. These steps can be repeated at any time if necessary using an external inductor.

[0028] According to the invention, the distraction device, i.e. the non-invasively extendable implants with the present device are widely applicable both for length adjustable replacements of, for example, hip, knee or shoulder joints, and, if necessary, for other length adjustable implants such as intra-articular nails, especially for paediatric patients with oncological diseases or for patients after extensive trauma. Reference Signs List

[0029] 1 ~ outer body

[0030] 2 - inner body 3 -- melting insert

[0031] 4 melting core

[0032] 5 - piston

[0033] 6 •- support fixation element

[0034] 7 - spring-loaded peripheral latches 8 - separation grooves

[0035] 9 - anchor grooves

[0036] 10 - support compression spring

[0037] 11 - emerging negative pressure area

Claims

PATENT C L A I M S 1. Distraction device for non-invasiveiy extendable implants, in particular nails and stems of endoprostheses for patients with incomplete development of the upper and lower limbs, comprising an outer body (1) of the implant wherein an inner body (2) of the implant is arranged in an adjustable manner in the direction of implant extension, characterised in that a melting insert (3) is placed in the inner body (2) of the implant and a piston (5) is seated on the front of the inner body (2) of the implant which is connected to a support fixation element (6) adjustable in the direction of implant extension arranged in its outer body (1), wherein the support fixation element (6) as well as the inner body (2) of the implant is equipped with spring-loaded peripheral latches (7) for their adjustment in the outer body (1 ) of the implant which fit into the bevelled anchor grooves (9) formed on the inner shell of the outer body (1) of the implant.

2. Distraction device, according to claim 1 , characterised in that the melting insert (3) is made of a material having a melting temperature of 45 to 65°C with a solid-to-iiquid expansion in the range of 5 to 14% by volume.

3. Distraction device, according to claim 2, characterised in that the melting insert (3) is made of higher saturated aliphatic hydrocarbons.

4. Distraction device, according to claim 2, characterised in that the melting insert (3) is made of polymer.

5. Distraction device according to at least one of the preceding claims, characterised in that the support fixation element (6) is spring-loaded inside the outer body (1) by a support compression spring (10).

6. Distraction device according to at least one of the preceding claims, characterised in that the melting insert (3) in the inner body (2) is provided with a melting cere (4) thereof made of ferromagnetic material for melting the melting insert (3) by a concentrated electromagnetic field using an external inductor.

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