Motorized intramedullary nail for bone lengthening or transport

Abstract

Motorized intramedullary nail (1) for bone lengthening or transports, comprising: - a tubular portion (2) extending along a prevalent axial direction (x) of the intramedullary nail (1); - a rod-shaped portion (3) telescopically sliding inside said tubular portion (2) and along said longitudinal axis (x) comprising an abutment element (31); - motorized electro-mechanical means (4) for driving the rod-shaped portion (3); characterized in that it further comprises: a sleeve (5), inserted inside said tubular portion (2), in a spaced relationship with respect to the proximal end along said longitudinal axis (x) adapted to form an internal shoulder acting as an end-stroke for said abutment element (31).

Description

[0001] Title: Motorized intramedullary nail for bone lengthening or transport

[0002] DESCRIPTION

[0003] Field of application

[0004] The present invention relates to the technical field of orthopedics. In particular, it relates to a motorized intramedullary nail for bone lengthening or transport of long bones comprising an abutment element.

[0005] An intramedullary nail of this type for instance allows performing a lengthening of a limb without using external fixators; moreover, it may also be used for optimal transport and alignment of bone sections or even for a desired block of a joint for the purposes of a post-traumatic or therapeutic treatment.

[0006] Prior art

[0007] In this specific technical field motorized intramedullary nails are known, which allow performing, amongst other things, a lengthening of the long limbs. In particular, a system of the discussed type, called Fitbone™ and initially developed by Prof. Rainer Baumgart, a well-known world- renowned specialist in the field, is commonly known.

[0008] This system is mainly intended also for the lengthening of single limbs that require interventions caused by trauma or congenital malformations, or still to allow the lengthening of limbs that are not fully developed.

[0009] Moreover, with adequate preoperative planning, an intramedullary nail of the type previously indicated allows providing axial and torsional corrections as part of the limb lengthening.

[0010] The nails known in the art and mentioned above include two portions: a first fixed portion and a second sliding portion that is telescopically extendable inside the first fixed portion; moreover, driving electromechanical means for controlling the lengthening of the sliding portion are provided.

[0011] Document WO202 1032823 Al relates to a medullary nail for lengthening a long bone comprising a first tubular body and a second tubular body inserted in the first tubular body and sliding therein, as well as connected by means of gears to a small electric motor which allows an axial translation thereof relatively to the first tubular body.

[0012] Another nail according to the prior art is known from document US 2016 / 0183994 Al.

[0013] In the design of intramedullary nails according to the prior art, a critical issue arises from the risk of a possible extraction of the sliding portion with respect to the fixed portion when the device is implanted on a patient.

[0014] To avoid the above risk, it is necessary to provide some type of stop, for instance a physical stop that blocks the sliding portion in an end-stroke position. By the way, the creation of said stop, to avoid complex if not impractical machining of the tool, would require the coupling of a section of the tubular portion of the telescopic coupling.

[0015] However, it is well known that the coupling of the two tubular elements, for instance through welding, weakens the structural integrity of the device and increases the risk of breaking it during use.

[0016] Therefore, the technical problem underlying the present disclosure is to make the above mechanical block between the telescopic portion economically and without compromising the structural integrity of the intramedullary nail.

[0017] Summary of the invention

[0018] The idea underlying the invention is to house, in a distal part of the tubular portion, an abutment portion, possibly elastic and biocompatible, made for instance of a sleeve, adapted to adequately stop the movement of an abutment element comprised in the rod-shaped portion that is sliding thanks to the electro-mechanical means.

[0019] According to this solution idea, the present disclosure relates to a motorized intramedullary nail for the bone lengthening or transports, comprising:

[0020] - a tubular portion extending along a prevalent longitudinal axis of the intramedullary nail comprising a proximal end and a distal end;

[0021] - a rod-shaped portion telescopically sliding inside said tubular portion along said longitudinal axis comprising an abutment element;

[0022] - motorized electro-mechanical means for driving the rod-shaped portion.

[0023] In particular the invention is characterized by further comprising a sleeve inserted inside said tubular portion with a fixed connection, in a spaced relationship with respect to the proximal end along said longitudinal axis, adapted to form an internal shoulder that acts as end-stroke for said abutment element.

[0024] More particularly, said sleeve may be radially elastic so as to be friction- fit into the tubular portion.

[0025] Moreover, it should be noted that the above sleeve may comprise at least one longitudinal cut so as to allow a better adaptation, therefore a better friction, to the internal surface of said tubular portion. Preferably said longitudinal cut extends along the entire extension of the sleeve; however, it is not excluded that the elasticity of the element is obtained by means of one or more cuts of lower extension.

[0026] The concerned sleeve is preferably made of biocompatible and / or elastic materials, for instance PEEK. Preferably the electro-mechanical means of the motorized intramedullary nail for the bone lengthening or transports comprise a screw drive comprising, in turn, a worm screw and a nut screw, said nut screw being operable in translation with respect to said worm screw, said rod-shaped portion being integral in translation with said nut screw and said tubular portion being integral in translation with said worm screw, or vice versa.

[0027] In the first of the two above-identified cases, said tubular portion comprises a guide segment of the nut screw having a non-circular internal section, which is proximal with respect to the housing segment of the sleeve. In particular, said non-circular internal section may be a polygonal section, with beveled or non-beveled corners, for instance a quadrangular portion. Said non-circular internal section may be obtained by creating one or more flattenings on an internal cylindrical surface.

[0028] Preferably the internal radius of said sleeve, when inserted into said tubular portion, is contiguous to said guide segment of said tubular portion. Therefore it follows that at least one larger diameter of the circle circumscribed to the non-circular section is greater than the internal diameter of the sleeve when fitted in position. Preferably, the smaller diameter of the circle inscribed in the non-circular section is instead smaller than the internal diameter of the sleeve, so that the shoulder is only created in certain points of the perimeter of the non- circular section.

[0029] The abutment element may advantageously be defined by a distal face of said nut screw.

[0030] Moreover, the concerned sleeve may preferably have a structure having at least two layers, preferably three layers. This configuration allows selecting material with high elastic coefficient as core of the sleeve, instead providing materials with a high friction coefficient for the layer. The features and advantages of the motorized intramedullary nail according to the present disclosure will become apparent from the following description of an embodiment thereof given by way of nonlimiting example with reference to the appended drawings.

[0031] Brief description of the drawings

[0032] Figure 1 shows a perspective and schematic view of an intramedullary nail according to the present invention;

[0033] Figure 2 shows a perspective and schematic view of a tubular portion and of a sleeve of the intramedullary nail according to the present invention in a separated configuration;

[0034] Figure 3 shows a sectional perspective view of the tubular portion of the intramedullary nail according to the present invention;

[0035] Figure 4 shows a side view of the sleeve of the intramedullary nail according to the present invention;

[0036] Figure 5 shows a schematic side view of a completely retracted end-stroke configuration of a rod-shaped portion inside the tubular portion of the intramedullary nail according to the present invention;

[0037] Figure 6 shows a schematic side view of a completely extended end-stroke configuration of the rod-shaped portion inside the tubular portion of the intramedullary nail according to the present invention;

[0038] Figure 7 shows an enlarged view of the detail A of Figure 6;

[0039] Figure 8 shows a perspective view of the tubular portion of the intramedullary nail according to the present invention;

[0040] Figure 9 shows a sectional front view of the sleeve of the intramedullary nail according to the present invention.

[0041] Detailed description With reference to these figures, and in particular to the example of Figure 1, an intramedullary nail 1 is globally and schematically illustrated. The nail 1 is substantially a nail that can be elongated by activating electro-mechanical drive means inserted in the nail itself.

[0042] The intramedullary nail 1 of the trochanteric type, particularly suitable for a femoral use, extends from a proximal portion 6, preferably tilted with respect to a prevailing longitudinal x direction of the nail itself, a distal portion 7, preferably extended along the same longitudinal x direction.

[0043] The intramedullary nail 1 comprises electro-mechanical means 4, which, as hereinafter better specified, allow varying the longitudinal length of the nail itself. Said electro-mechanical means 4 comprise a motor unit 42, housed in said proximal portion 6, powered via a bipolar power cable 8 and covered by a casing adapted to protect it. As reported in Figure 1, reference number 42 will indicate both the motor unit and the casing adapted to protect it.

[0044] The intramedullary nail 1, at the proximal portion 6, further comprises an outer control electronics, a transmitter and a connector adapted to comfortably connect the bipolar power cable 8 to said electromechanical means 4. Said elements, which are per se known, are no further described.

[0045] The distal portion 7 of the intramedullary nail 1 comprises a tubular portion 2 that extends along the longitudinal x direction and a sliding rod-shaped portion 3, still in the longitudinal x direction, inside said tubular portion 2.

[0046] The tubular portion 2, singularly visible in Figures 2, 3 and 9, comprises a cylindrical shell that is internally hollow, where the rodshaped portion 3, also preferably tubular, is telescopically mounted.

[0047] In the proximal portion 6 and / or in the distal portion 7, in order to constrain the axial sliding, for instance via a transversal bone screw, proximal transversal holes 9 and distal transversal holes 32 are arranged, respectively. As for the distal transversal holes 32, these are preferably arranged in the most distal part, in the longitudinal x direction, of the rod-shaped portion 3, as visible in Figures 1, 5 and 6, but they can also be inserted in an intermediate position of the rodshaped portion 3 itself.

[0048] The motorized electro-mechanical means 4 are configured to axially displace, with millimeter precision, the rod-shaped portion 3 inside the tubular portion 2.

[0049] Preferably, the electro-mechanical means 4, in addition to the above motor unit 42, comprise a screw drive 41. Said screw drive 41, as visible in Figures 5 and 6, is formed by a worm screw 411 and a nut screw 412 coupled thereto. The worm screw 411 is rotatably mounted inside the tubular portion 2, integral in translation and coaxial with respect thereto. Instead, the nut screw 412 is integral to an end of the rodshaped portion 3 and is sliding within a guide segment 21 of the tubular portion 2 which prevents the relative rotation thereof. The motor unit 42, coupled to the worm screw 411, is arranged to set it in rotation, thus favouring the displacement in the longitudinal x direction of the nut screw 412 and of the rod-shaped portion 3 integral thereto.

[0050] For illustrative purposes, in Figures 5 and 6 the start-stroke position, which is more compact, and the end-stroke position, which is therefore more extended, of the rod-shaped portion 3 are shown, respectively, due to the implementation of the electro-mechanical means 4, as previously stated.

[0051] More in detail, the tubular portion 2, starting from a proximal end 23 thereof up to a distal end 24 thereof, comprises four distinct segments: a proximal connecting segment 25; the above guide segment 21; a housing segment 22 and a distal connecting segment 26.

[0052] The proximal connecting segment 25 has a relatively short extension and an outer diameter that is larger than the rest of the tubular portion 2. Therein the bearings that support the worm screw 411 and the joint that allows its mechanical coupling with the motor unit 42, proximal thereto, are housed.

[0053] The subsequent guide segment 21 has lower diameters than the proximal connecting segment 25, both internally and externally. It has a longitudinal extension that is substantially greater than that of the proximal connecting segment 25. The internal section of the guide segment 21, countershaped with respect to the outer profile of the piece which forms the nut screw 412, only allows the translational movement thereof, constraining the degree of freedom thereof relating to the rotation. Said internal section is thus not circular; in the embodiment represented in the appended figures, as well visible in Figure 8, it has a quadrangular profile with rounded corners.

[0054] The subsequent housing segment 22 has a circular section having a diameter that is greater than the diameter of the circumference that encloses the internal section of the guide segment 21. It has a longitudinal extension that is comparable to that of the guide segment 21.

[0055] The last distal coupling segment 26 has an internal section that is slightly greater than that of the housing segment 22, whereas the longitudinal extension is comparable to that of the proximal connecting segment 25. At said housing segment 22 a tip 27, which has the mouth for the telescopic exit of the rod-shaped portion 3, is integrally coupled.

[0056] A sleeve 5, adapted to narrow the internal diameter of this segment to provide a shoulder 52, which acts as end-stroke for an abutment element 31 defined on said rod-shaped portion 3, is housed within the above housing segment 22. In particular, said abutment element 31 is defined by the distal face of the nut screw element 412. As previously said, said nut screw element 412 slides with shape-coupling within the non-circular section of said guide segment 21. The sleeve 5 narrows the diameter of the housing segment 22 below the value of the maximum circumference circumscribed to the non-circular section. By the way, said narrow diameter is preferably greater than that of the minimum circumference inscribed in the non-circular section. Therefore, the result is a shoulder 52 that only emerges at certain portions of the perimeter of the non-circular section: in the example illustrated, the abutment surfaces of the shoulder 52 are located at the connections of the quadrangular profile.

[0057] The sleeve 5, visible in Figures 2, 5 and 6, preferably has an elasticity in the radial direction such as to be friction-fit into said tubular portion 2.

[0058] In particular, in the preferred embodiment visible in Figure 4, said sleeve 5 has a longitudinal cut 51 extended along the entire extension of said sleeve 5. Therefore, said sleeve 5 has a non-deformed configuration, in which its outer diameter is greater than the internal diameter of the housing segment 22 and a deformed configuration, in which it collapses with respect to the longitudinal cut 51 and reaches an external diameter equal to the internal diameter of the housing segment 22.

[0059] Obviously, in order to obtain the desired result, it is possible to make several cutting patterns on the concerned sleeve 5 providing, for instance, at least one longitudinal cut extended by a length that is less that the length in the longitudinal x direction of said sleeve 5. The elastic deformation of the sleeve 5 defines a radial force which significantly increases the friction of the element with respect to its seat, thus creating a stable coupling between the two elements.

[0060] As previously said, the sleeve 5 allows stopping the advancement of the screw drive 41, thus avoiding the serious problems related to the rodshaped portion 3 coming out of the tubular portion 2.

[0061] As visible in Figure 9, the sleeve 5 preferably has a layered internal configuration comprising an outer layer 55, an intermediate layer 54 and an internal layer 53. The intermediate layer may thus be made of a different material, for instance a metal material, compared to the outer and internal layers made for instance of synthetic-plastic material.

[0062] The other components of said motorized intramedullary nail 1 are also made of synthetic-plastic material, such as for instance silicon, thermoplastic resin, PEEK, whereas, preferably, the tubular portion 2 is made of metal or biocompatible metal alloy.

[0063] The main advantage of the present invention is to allow creating an abutment, preventing the rod-shaped portion 3 from coming out of its seat at low costs and without introducing points of structural fragility of the device.

[0064] All components are easy to be manufactured and with particularly low costs.

Claims

CLAIMS1. Motorized intramedullary nail (1) for bone lengthening or transports, comprising:- a tubular portion (2) extending along a prevalent longitudinal axis (x) of the intramedullary nail (1) comprising a proximal end (23) and a distal end (24);- a rod-shaped portion (3) telescopically sliding inside said tubular portion (2) along said longitudinal axis (x) comprising an abutment element (31);- motorized electro-mechanical means (4) for driving the rod-shaped portion (3); characterized in that it further comprises: a sleeve (5), inserted inside said tubular portion (2) with a fixed connection, in a spaced relationship with respect to the proximal end (23) along said longitudinal axis (x), which is adapted to form an internal shoulder (52) acting as an end-stroke for said abutment element (31).

2. Motorized intramedullary nail (1) for bone lengthening or transports, according to the preceding claim, wherein said sleeve (5) is radially elastic so as to be friction-fit inside said tubular portion (2).

3. Motorized intramedullary nail (1) for bone lengthening or transports, according to the preceding claims, wherein said sleeve (5) comprises at least one longitudinal cut.

4. Motorized intramedullary nail (1) for bone lengthening or transports, according to the preceding claim, wherein said at least one longitudinal cut extends along the whole extension of said sleeve (5) .

5. Motorized intramedullary nail (1) for bone lengthening ortransports, according to one of the preceding claims, wherein said sleeve is made of a biocompatible material, for example PEEK.

6. Motorized intramedullary nail (1) for bone lengthening or transports, according to one of the preceding claims, wherein said motorised electromechanical means (4) comprise a screw drive (41) comprising a worm screw (411) and a nut screw (412), said nut screw (412) being operable in translation with respect to said worm screw (411), said rod-shaped portion (3) being integral in translation with said nut screw (412) and said tubular portion (2) being integral in translation with said worm screw (411), or vice versa.

7. Motorized intramedullary nail (1) for bone lengthening or transports, according to the preceding claim, wherein said rod-shaped portion (3) is integral in translation with said nut screw (412) and said tubular portion (2) is integral in translation with said worm screw (411), wherein said tubular portion (2) comprises a guide segment (21) of the nut screw (412) with a non-circular internal section, which is proximal to a housing segment (22) of the sleeve (5).

8. Motorized intramedullary nail (1) for bone lengthening or transports, according to claim 7, wherein the internal radius of said sleeve (5), when inserted inside said tubular portion (2), is adjacent to said guide segment (21) of said tubular portion (2).

9. Motorized intramedullary nail (1) for bone lengthening or transports, according to claim 6 or 7, wherein the abutment element (31) is defined by a distal face of said nut screw (412).

10. Motorized intramedullary nail (1) for bone lengthening or transports, according to one of the preceding claims, wherein said sleeve (5) has at least two layers (53, 54, 55) of a different material.

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