WO2010006453A1

WO2010006453A1 - Intramedullary nail

Info

Publication number: WO2010006453A1
Application number: PCT/CH2008/000322
Authority: WO
Inventors: Meinrad Fiechter; Thomas Sommer; Samuel Maurer
Original assignee: Meinrad Fiechter; Thomas Sommer; Samuel Maurer
Priority date: 2008-07-18
Filing date: 2008-07-18
Publication date: 2010-01-21

Abstract

An intramedullary nail (100) for stabilizing a fractured bone is provided with at least a first duct (101) for at least partially receiving a bonding agent liquefiable by the application of energy. The duct (101) extends continuously from a proximal region of the nail (100) to a distal region of the nail (100) and whereas in the distal region the nail (100) is provided by at least one opening (102) connecting the duct (101) with an outer surface of the nail (100). When using the intramedullary nail (100), it is no longer necessary for distal locking to carry out the difficult process of precisely drilling a hole into the bone in order to be able to set locking bolts or screws, which simplifies the process and avoids the need for additional incisions. A target device is no longer necessary. Using a bonding agent that may be activated by energy allows for fast activation in the right moment (i. e. when the intramedullary nail is correctly positioned within the bone).

Description

Intramedullary nail

Technical Field

The invention relates to an intramedullary nail for stabilizing a fractured bone, to a device for applying energy to a liquifiable bonding agent of an intramedullary nail, to a method for stabilizing a fractured bone using an intramedullary nail as well as to a hip screw for stabilizing a fractured neck of femur. Background Art

The healing of broken bones in human or veterinary medicine requires realignment of the separated or dislocated bone fragments or segments and subsequent fixation for promoting proper healing of the bones. Relative motion of bone fragments or segments at the site of a fracture or osteotomy may severely affect the healing process. It is therefore necessary to immobilize the bone fragments or segments as completely as possible (osteosynthesis). In the case of long bones such as the femur, radius, ulna, humerus, fibula, metar- sals, and tibia, this is often done by means of intramedullary nails (also called intramedullary rods, locking nails or bone nails). Intramedullary nails are driven into the medullary canal of the bone and affixed therein by screws or bolts. Often, the cross-section of the intramedullary nail decreases towards the distal end of the nail. After complete healing of the bone at the fracture site, the rod may stay within the bone or it may be removed through a hole drilled in the end of the bone.

Basically, there are two approaches for intramedullary nailing, namely antegrade and ret- rograde nailing. In antegrade nailing, the nail is inserted from the proximal end of the bone, whereas in retrograde nailing, the nail is inserted from the distal end of the bone.

One of the most prominent problems with usual intramedullary nails is the locking of the distal segment of the nail. Usually this is done by means of screws or bolts crossing the bone and being accommodated within openings of the intramedullary nail. Often, this re- quires the use of complicated and expensive target devices (such as target brackets). However, they still do not guarantee perfect alignment of the drill and the respecitve distal opening of the nail, which means that adjustment of the drill for drilling the distal hole is a time-consuming and demanding process. In other cases, freehand techniques are used for positioning the drill, based on X-ray verification of the position of the distal openings of the intramedullary nail as well as of the locking screws or bolts. However, this is a difficult and time-consuming process as well.

Furthermore, with today's techniques it is often difficult to treat fractures at the end of the long bone. The number and positioning of the bolt/screw openings are limited at the distal end of the intramedullary nail because of the decreased surface area of the nail and the reduced strength at the tip of the nail. Therefore, fractured bone sections at the distal end of a femur, for example, may not be properly fastened to the intramedullary nail.

US 2007/0270833 Al (P. M. Bonutti et al.) relates to a method for stabilizing a fractured bone. The method includes positioning an elongate rod in the medullary canal of the fractured bone and forming a passageway through the cortex of the bone. The method further includes positioning a fastener in the passageway of the cortex and thermal bonding of the fastener to a bonding region of the elongate rod.

US 4,369,772 (University of Florida) discloses a method for strengthening a fractured bone by drilling a hole along the axis of the medullary canal of the bone, inserting into the hole a substantially inflexible tube having an outside diameter less than the diameter of the hole, injecting into the tube and around the tube a semisolid hardenable mixture of methyl methacrylate and poly(methyl methacrylate), and allowing time for the mixture to harden.

This method aims at filling all the interstices and voids in the bone to provide a solid struc- ture.

The use of a bone cement such as PMMA, filling out all voids between the tube and the bone simplifies the locking of the tube to the bone. However, injecting the bone cement may be difficult, depending on the geometry of the tube and the surrounding bone. Furthermore, the bone cement has to be injected with a certain pressure. Hardening of the bone cement takes some time which may lead to an extension of the operating time. Furthermore, there is a danger that the bone cement may leak in the region of the fracture.

Summary of the invention

It is the object of the invention to create an intramedullary nail pertaining to the technical field initially mentioned, that allows for fast and secure fixation of long bone fractures and which especially simplifies distal locking of the nail to the bone.

The solution of the invention is specified by the features of claim 1. According to the invention, the nail is provided with at least a first duct for at least partially receiving a bonding agent liquefiable by the application of energy. The duct extends continuously from a proximal region of the nail to a distal region of the nail. In the distal region the nail is provided by at least one opening connecting the duct with an outer surface of the nail.

Using the inventive intramedullary nail, inter alia the following steps are carried out for stabilizing a fractured bone: a) The intramedullary nail is introduced into the medullary canal of the bone. b) A device for applying energy to the liquefiable bonding agent is inserted into the duct of the intramedullary nail. c) Energy is applied to the bonding agent and the liquefied bonding agent is pressed out through the at least one opening in the distal section of the nail by further advancing the device for applying energy. Thereby, the bonding agent is applied in a region between an outer surface of the intramedullary nail and the bone to be stabilized.

When using the inventive intramedullary nail, it is no longer necessary for distal locking to carry out the difficult process of precisely drilling a hole into the bone in order to be able to set locking bolts or screws, which simplifies the process and avoids the need for additional incisions. As well, a target device is no longer necessary. Using a bonding agent that may be activated by energy allows for fast activation in the right moment (i. e. immediately after the intramedullary nail has been correctly positioned within the bone). Compared to the use of bone cement the process is sped up, as there is no need for waiting until the material is hardened. Furthermore, the inventive method does not aim at filling all voids be- tween the intramedullary nail and the surrounding bone, but the local application of the bonding agent aims only at producing a form fit between the distal segment of the intramedullary nail and the bone, in particular the trabecular (cancellous bone), where a strong fixation is possible due to the porous structure of the bone. Leaking of the bonding agent in the region of the fracture is avoided because this region is usually not contacted by the bonding agent. Correspondingly, according to the invention, the shank portion of the intramedullary nail is usually not to be provided with openings connecting the duct with an outer surface of the nail. Finally, the inventive method is particularly well suited in cases where the fracture is at the end of the long bone. The number and placement of openings for distributing the bonding agent within the bone may be chosen in such a way that tight fixation on both sides of the fracture or with all parts of the fractured bone, respectively, is ensured.

The inventive nail as well as the corresponding method can be used for human as well as veterinary purposes. The opening (ore in a preferred case, a plurality of openings) may be substantially radial, however, in special cases it may as well be oriented in an inclined fashion. The bonding agent may be provided within the intramedullary nail and/or externally applied during the fixation process.

Generally, the invention is applicable in antegrade as well as retrograde operation methods.

The device for applying energy to the liquefiable bonding agent of the intramedullary nail comprises a neck as well as a tip section to be inserted into the duct of the intramedullary nail. The tip section allows for energy transfer to the bonding agent. The length of the neck as well as its further geometrical properties are chosen in such a way that the tip section of the inserted device may reach the distal region of the nail.

Useable kinds of energy are heat, ultrasonic vibrations, other vibrations (such as oscillating rotation), electromagnetic radiation, etc.

Preferably, the tip section comprises a heating element. Most preferably, the heating element is an electrical (resistance) heating element which is supplied by electricity by means of a feed accommodated within the neck.

Having the heating element within the tip section, i. e. where the heat is required during use, supersedes complex heat shieldings for heat supplies. The heating is effected in a very localized way and the danger of heating up adjacent regions is minimized. An electrical feed is safe and requires little space.

In contrast to ultrasound or other mechanical activation of the bonding agent the dissipa- tion of heat is more easily controllable. However, in order to avoid damage to the bone it is to be avoided that the bone is heated above a certain temperature: at 42 ⁰C proteins start to coagulate, at 55 ⁰C the bone starts to decompose. Therefore, the heat has to be applied in such a way that the contact surfaces of the bone are not heated above these temperatures whereas at the same time the bonding agent is sufficiently liquefied that it may be pressed out through the opening and that it is able to fill out the structuring of the bone (in particular of the trabecular) in order to achieve a positive fit between the nail and the bone. Preferably, the bonding agent is liquefied by directly contacting the agent with the heating element.

A system for stabilizing a fractured bone comprises an intramedullary nail and a device for applying energy as described above. The nail as well as the device may be adapted to each other, especially concerning their mutual geometry.

Advantageously, the intramedullary nail, at least its distal portion, is made from a material having a thermal conductivity of 22 W/mK or less, in particular from titanium, a titanium alloy, steel or fiber-reinforced plastics. Using materials with low thermal conductivity avoids that the heat used for liquefying the bonding agent is transferred to the bone in such a way that the bone may be damaged. For example, a titanium alloy may have a thermal conductivity of about 6.7 W/mK, pure titanium is at about 22 W/mK, chirurgical steel at 15 W/mK. Fiber-reinforced plastics allow for a particularly low thermal conductivity.

Instead of being made of a low thermal conductivity material the nail may comprise a heat barrier made from such a material, e. g. in the form of a sleeve, whereas the heat barrier is designed in such a way that the dissipation of heat into further regions contacting the surrounding bone is inhibited.

Preferably, the bonding agent is a bio-degradable thermoplastic material, most preferably an amorphous polymer. Amorphous polymers are preferred, because it is not necessary to heat these materials above the melting point in order to deform them, but only their glass transition temperature has to be reached which usually is considerably lower. A suitable material for the bonding agent is PLLA (poly-L-lactide), an amorphous thermoplastic material having a glass transition temperature of 50 - 80 ⁰C. Alternatively, other bio-degradable materials that are liquefiable by the application of energy may be employed. In yet further embodiments, materials may be used that are not bio-degradable but biocompatible. The bonding agent may be provided by a therapeutic agent, e. g. with an agent that promotes wound healing.

Preferably, the bonding agent is initially provided within the duct of the intramedullary nail, i. e. the nail is shipped with the bonding agent in place. This ensures that the material and quantity of the bonding agent match the intramedullary nail and the additional step of inserting the bonding agent is spared during the operation.

Alternatively, the bonding agent is introduced into the duct prior to inserting the device for applying energy or simultaneously with inserting the device for applying energy.

The form fit between the intramedullary nail and the bone may be improved by providing the outer surface of the distal region of the nail with a structuring. Preferably, the structuring comprises at least one of the following:

a) grooves or notches; b) a sand blasted or micro blasted surface; c) a porous surface; d) a nano-structured surface; e) etched microstructures.

In principle, all these structurings are appropriate for providing a strong fixation of the intramedullary nail to the bone. Preferably, the structuring assures two-dimensional fixation, i. e. fixation against axial as well as against rotational movement of the intramedullary nail with respect to the bone.

The structurings may be produced by techniques that are known as such, as sand blasting, etching, cutting, milling etc.

The intramedullary nail may comprise one or several bends. This allows for optimally adapting the geometry of the nail to the geometry of the bone.

Correspondingly, it is preferred that the neck of the device for applying energy is flexible. This allows for fully inserting the neck as well as the tip even in cases where the inside geometry of the bone is complicated. For providing a flexible neck, a heating device having in its tip an electrical heating element which is supplied by electricity by means of a feed accommodated within the neck, is particularly preferred.

In a preferred embodiment of the inventive intramedullary nail, an internal cross-section of the duct is reduced in the distal region of the nail compared to a shank region of the nail. This allows for utilizing a device for applying energy that has a thin tip (and neck) and which is therefore easily insertable within the duct of the nail. At the same time, the energy may be easily transferred to the distal region of the nail by direct contact between the tip and the inside surface of the nail.

Alternatively, the internal cross-section of the duct is substantially constant along the length of the nail, and the thickness of the tip of the device for applying energy is correspondingly larger, adapted to the internal cross-section of the duct. Finally, in other embodiments, the tip of the device may be expandable once positioned in place, e. g. by an umbrella-like mechanism.

The intramedullary nail may comprise a second duct for receiving a guide wire. In the context of operation techniques it is known to use a guide wire into the medullary canal before opening the canal and inserting the intramedullary nail. The wire serves as a guide for the (cannulated) drill, for a cannulated awl or a reaming device. In a further step, the nail is inserted over the guide wire.

Preferably, especially in cases, where the internal cross section of the duct is substantially constant, the tip section of the device for applying energy has a shape that converges towards a free end of the tip section, whereas the free end section of the tip section is preferably spherical or conical. Such forms greatly facilitate the insertion of the device into the duct of the intramedullary nail.

The tip section of the device for applying energy may further comprise a sealing element, in particular on O-ring sealing element. This element will inhibit the passage of liquefied bonding agent to the back of the tip. Its outside diameter is adapted to the inside diameter of the duct in the distal region of the nail. The device for applying energy may comprise a further section allowing for energy transfer to a bonding agent provided in the proximal region of the intramedullary nail, the further section being distant from the tip section. This allows for simultaneously locking (or unlocking) the intramedullary nail in its distal as well as in its proximal region.

In order to be able to use the device with nails having different lengths, a distance between the tip section and the further section is preferably variable.

In a preferred embodiment, the tip section comprises a flexible helical element (having approximately the form of a usual cork-screw) allowing for energy transfer to the bonding agent. Such an element allows for high flexibility despite a large outside surface.

In another preferred element, the tip section comprises a plurality of elements, each of which allows for energy transfer to the bonding agent, whereas the elements are mounted in such a way that they are movable in respect to each other. Again this provides for high flexibility without having to reduce the active (i. e. energy-transferring) surface of the tip.

For stabilizing a fractured neck of femur, the inventive method may further comprise the following steps:

d) guiding a hip screw through a through-hole in a proximal region of the intramedullary nail, the hip screw having an axial duct provided by a bonding agent liquefiable by applying energy, the duct extending continuously from a proximal region of the hip screw to a distal region of the hip screw and whereas in its distal region the hip screw is provided by at least one opening connecting the duct with an outer surface of the screw;

e) liquefying the bonding agent provided in the duct of the hip screw;

f) pressing out the liquefied bonding agent through the at least one opening in order to fix the hip screw to the surrounding bone. Therefore, the hip screw and correspondingly the intramedullary nail are distally locked by means of the bonding agent, radial bores and the corresponding additional incisions are not required.

It is to be understood that the described hip screw for stabilizing a fractured neck of femur, whereas the hip screw is provided with a duct for at least partially receiving a bonding agent liquefiable by applying energy, the duct extending continuously from a proximal region of the nail to a distal region of the screw and whereas in the distal region the screw is provided by at least one opening connecting the duct with an outer surface of the screw, may be used in hip screw applications known from the prior art, i. e. in principle its use is independent from the use of the inventive intramedullary nail.

In certain cases it is desirable to remove an intramedullary nail, sometimes already before the bonding agent is degraded. In the context of the present invention, an intramedullary nail being fixed to a bone by a liquefiable bonding agent comprises the step of liquefying the bonding agent by applying energy (e. g. heat) to the bonding agent by a device as de- scribed before. This will lead to liquefaction of the bonding agent and therefore to unlocking of the intramedullary nail. Subsequently, the nail may be pulled out of the medullar canal. Preferably, the device for applying energy may be mechanically fastened to the intramedullary nail, such that the nail may be removed by retracting the device.

This method for removing an intramedullary nail, as well as devices for carrying out the method may be used as well in the case of removing hip screws or bolts and screws used to affix a bone plate to a bone, respectively, all being provided with a duct for at least partially receiving a bonding agent liquefiable by the application of energy.

Other advantageous embodiments and combinations of features come out from the detailed description below and the totality of the claims.

Brief description of the drawings

The drawings used to explain the embodiments show: Fig. 1 a cross-sectional view of a first embodiment of an inventive femoral nail;

Fig. 2 a cross-sectional view of a second embodiment of an inventive femoral nail;

Fig. 3A, 3B cross-sectional views of a first embodiment of an inventive tibial nail;

Fig. 4 a cross-sectional view of a second embodiment of an inventive tibial nail;

Fig. 5 a cross-sectional view of a first embodiment of an inventive heating device;

Fig. 6 a cross-sectional view of a second embodiment of an inventive heating device;

Fig. 7A-C schematic views of tips of an inventive heating device;

Fig. 8 a side view of a tip of an inventive heating device;

Fig. 9 a cross-sectional view of a flexible tip of an inventive heating device; and

Fig. 10 a cross-sectional view of a tip of an inventive heating device, the tip having a reduced diameter.

In the figures, the same components are given the same reference symbols.

Preferred embodiments

The Figure 1 shows a cross-sectional view of a first embodiment of an inventive femoral nail. The nail 100 made of titanium has been fully inserted into the intramedullary canal of the femur 1, which is fractured in the region of the femoral head 2 (fracture 3). The nail 100 comprises two sections 100a, 100b being offset to each other by an angle of about 1 r and being connected to each other by a bend 100c. In the given example, the length of both sections 100a, 100b is about equal. However, generally the exact geometry of the femoral nail will be chosen according to the geometry of the femur 1. The proximal section 100a is provided with a duct 101 which extends into the region of the bend 100c, where it is provided with a plurality of radial openings 102 connecting the duct 101 with the outer surface of the nail 100.

The nail 100 may be axially locked by introducing a blank of PLLA (poly-L-lactide) into the duct 101 and by subsequently heating the blank above its glass transition temperature (50 - 80 ⁰C for PLLA) using a heating device (see below) and pressing the liquefied material out of the openings 102. This leads to a stable form fit between the nail 100 and the surrounding region of the femur 1 , in particular of the trabecular of femur 1.

A hip screw 120 made of titanium is positioned through a corresponding opening 103 in the proximal section 100a of the nail 100, close to the bend 100c. The distal end of the hip screw 120 extends into the femoral head 2, where it is locked. For that purpose a blank 121 made from PLLA is introduced into a duct 122 of the hip screw 120. Again, locking is established by heating the blank using a heating device 140 and pressing out the liquefied material out of radial openings 123 connecting the duct 122 to the outer surface of the hip screw 120. This leads to a stable form fit between the hip screw 120 and the surrounding region of the femoral head 2.

In order to lock the hip screw 120 against rotation, a threaded bolt 104 is screwed into the proximal section 100a of the femoral nail 100, which is provided with a corresponding inner thread. The tip of the threaded bolt 104 contacts the outer surface of the hip screw 120 and thereby inhibits further rotation of the hip screw 120. The proximal openings of both the duct 101 of the femoral nail 100 as well as of the duct 122 of the hip screw 120 are sealed by sealing caps 105 (the sealing cap for the hip screw 120 which is not shown in Figure 1 will be inserted after extraction of the heating device). The sealing caps 105 protect the soft tissue and inhibit bone or tissue growing and occluding the opening created for inserting the femoral nail 100 into the bone. Instead or additional to the sealing cap, a locking screw may be screwed into the duct 122 of the hip screw in order to compress the fractured segments of the femoral head 2.

Distally, the femoral nail 100 is locked using a screw 106 which radially traverses the femur 1 and which is accommodated within an opening 107 of the femoral nail 100 arranged close to the distal tip of the nail 100. It is to be noted that the application area of the hip screw 120 as described in connection with Figure 1 is not restricted to the example shown. Generally, it may be used in most of the known applications of hip screws, especially in connection with locking screws or intramedullary nails that are of the conventional type.

The Figure 2 shows a cross-sectional view of a second embodiment of an inventive femoral nail. The nail 200 has been fully inserted into the intramedullary canal of the femur 1, which is fractured in the region of the shaft 4 (fracture 3). The nail 200 made of titanium is provided with a duct 201 which extends along substantially the entire length of the nail 200. Close to the distal end of the nail 200, the duct 201 is provided with a plurality of radial openings 202 connecting the duct 201 with the outer surface of the nail 200.

The nail 200 is axially locked on the distal side of the fracture 3 by introducing a blank made from PLLA into the duct 201 and by subsequently heating the blank using a heating device (see below) and pressing out the liquefied material out of the openings 202. This leads to a stable form fit between the nail 200 and the surrounding region of the femur 1.

A bolt 220 is positioned through a corresponding opening 203 in the nail 200 for proxi- mally locking the nail 200. The distal end of the bolt 220 is locked by introducing a blank made from a thermoplastic material into a duct 222 of the bolt 220. Again, locking is established by heating the blank using a heating device and pressing out the liquefied material out of the radial openings 223 connecting the duct 222 to the outer surface of the bolt 220. This leads to a stable form fit between the bolt 220 and the surrounding region of the femur 1.

The proximal openings of both the duct 201 of the femoral nail 200 as well as of the duct 222 of the bolt 220 are again sealed by sealing caps 205, 224.

Figures 3A, 3B are cross-sectional views of a first embodiment of an inventive tibial nail. The nail 300 has been fully inserted into the intramedullary canal of the tibia 10, which is fractured in the region of the shaft 1 1 (fracture 12). The nail 300 made of titanium comprises two sections 300a, 300b being offset to each other by an angle of about 14°, the sections 300a, 300b being connected to each other by a bend 300c. Thereby, the geometry of the nail 300 is adapted to the geometry of the tibia 10. The tibial nail 300 is provided with a duct 301 which extends about substantially the entire length of the nail 300. The duct 301 is provided with a plurality of first radial openings 302 in the distal section 300b, close to the distal end of the nail 300, as well as with a plurality of second radial openings 303 in the proximal section 300a. The openings 302, 303 connect the duct 301 with the outer surface of the nail 300.

The nail 300 is axially locked on the distal as well as on the proximal side of the fracture 12 by introducing a blank made from PLLA into the duct 301 and by subsequently heating the blank using a heating device (see below) and pressing out the liquefied material out of the openings 302, 303. The corresponding process is described in more detail below. This leads to a stable form fit between the nail 300 and the surrounding regions of the tibia 10. The duct 301 of the tibial nail 300 may be sealed by means of a sealing cap, or a locking screw may be screwed into the tibial nail 300.

The Figure 4 shows a cross-sectional view of a second embodiment of an inventive tibial nail. The tibial nail 400 mostly corresponds to the one described above, in connection with Figure 3. Distally, it is locked in the same way as the tibial nail according to the first embodiment. However, proximal locking is effected using screws 410, 41 1, 412 traversing the tibia and accommodated in corresponding radial openings 413, 414, 415 in the tibial nail 400. The middle opening 414 is elongated whereas the other openings 413, 415 have a circular cross-section. Instead of screws, it is possible to use locking bolts having a duct and openings connecting the duct with the outer surface of the bolts, similar to the bolt described above, in connection with Figure 2. This allows for locking the bolts using a thermoplastic material such as PLLA providing for a form fit between the bolt and the surrounding bone.

After insertion, the tibial nail 400 is distally fixed as described above, inserting a heating device into the duct 401. Next, the midle screw 41 1 is inserted into the elongated opening 414. By means of screwing a threaded bolt into the tibial nail 400 it is possible to effect pressure onto the screw 41 1 being accomodated inside the elongated opening 414, thereby compressing the fracture 12. Subsequently, the further two screws 410, 412 are set. It is to be noted that it may not be necessary to have three screws for proximal lock- ing. in some cases two screws or a single screw (preferably a screw accommodated in an elongated opening) will suffice.

The Figure 5 is a cross-sectional view of a first embodiment of an inventive heating device. The tip section 51 1 of the heating device 510 may be inserted into the duct 501 of the intramedullary nail 500. The device 510 comprises a handle 512, a power supply (not displayed), an elastic neck 513 and a tip section 51 1 connected to the distal end of the neck 513. The tip section 51 1 comprises a resistance heating element 514 and a contact element 515 being in thermal contact. The electrical power for the heating element 514 is provided by means of conductors contained within the neck 513. The shape of the contact element 515 is adapted to the geometry of the duct 501 of the intramedullary nail 500. Its axial dimension is rather small in order to facilitate the insertion of the tip section 51 1 , especially to facilitate the passing of bends of the intramedullary nail 500.

In order to lock the intramedullary nail 500 within the bone, a blank of a biodegradable thermoplastic material such as PLLA is introduced into the duct 501. Subsequently, the tip section 51 1 of the heating device 510 is introduced into the duct 501 until the contact element 515 contacts the blank. Now, the heating element 514 is heated. Subsequently, the thermoplastic material 505 accomodated within the duct 501 and being contacted by the contact element 515 is liquefied, and the device 510 may be further introduced into the duct 501 using the handle 512, thereby pressing out the liquefied material 505 through openings 502 connecting the duct 501 with the outer surface of the nail 500. Introduction of the neck 513 and tip section 51 1 is enabled due to the flexibility of the neck 513. Despite its flexibility, the neck 513 is designed in such a way, that axial forces may be transmitted. The pressed out material 505 is distributed within the trabecular of the surrounding bone and provides for a positive fit after solidification.

The proximal end of the intramedullary nail 500 may be provided with an inner thread 503, which may be used for affixing the heating device 510. Subsequently, the elastic neck 513 together with the tip section 51 1 may be further introduced using a (mechanical, electromechanical or pneumatic) pressing aid. The locking of a corresponding hip screw, locking bolt or proximal locking of the intramedullary nail may be effected using the same device or a different device. For straight intramedullary nails, simple cylindrical tip sections may be employed, and it is not required that the neck is elastically deformable.

In the case of an intramedullary nail (such as the tibial nail shown in Figure 3A, B) which is locked in two spaced apart regions, for locking the more proximal region an insert will be used which seals the portion of the duct lying distally of this region, prohibiting the permeation of thermoplastic material into this region. The insert may be screwed into a corresponding thread or it may be positioned on a dedicated seat that is provided within the duct. After locking, the insert may be removed or it may be left within the intramedullary nail.

The Figure 6 is a cross-sectional view of a second embodiment of an inventive heating device, which is specifically suited for simultaneous proximal as well as distal unlocking in cases where an intramedullary nail is to be removed. This may be required in the case of complications or due to other reasons, when the biodegradable material is not yet sufficiently degraded.

Again, the tip section 521 of the heating device 520 may be inserted into the duct 501 of the intramedullary nail 500. The device 520 comprises a handle 522, a power supply (not displayed), an elastic neck 523 and a tip section 521 connected to the distal end of the neck 523. The tip section 521 comprises a heating element 524 and a contact element 525. Furthermore, the heating device 520 comprises a further heating element 526 en- closed by a further contact element 527 attached distally to the handle 522. Introduction of the neck 523 and tip section 521 into the duct 501 is enabled due to the flexibility of the neck 523. The neck 523 is designed in such a way, that axial forces may be transmitted.

In order to remove the intramedullary nail 500 after insertion, the device 520 is attached to the nail 500 by means of a screw connection between the device 520 and the inner thread 503 of the nail 500.

The shapes of the contact elements 525, 527 are adapted to the geometry of the duct 501 of the intramedullary nail 500. The heating elements 524, 526 are heated, they are in thermal connection with the contact elements 525, 527. Subsequently, the thermoplastic material 505 accomodated within the openings 502, 504 and close to the outer surface of the intramedullary nail 500 is liquefied. Thereby, the intramedullary nail 500 is unlocked from the surrounding bone tissue and may be removed by pulling the handle 522 of the device 520.

The distance of the contact elements 525, 527 is adjustable such that the same device 520 may be used for differently shaped and sized intramedullary nails. Removal of hip screws, locking bolts etc. may be effected the same way.

The Figures 7A-7C show different possible forms of contact elements for heatable tips of heating devices for locking inventive intramedullary nails. The contact element 540 may be generally spherical (see Figure 5) or conical (see Figure 7A). The heating element 541 and the contact element 540 may be in one piece or two pieces. The contact element may be further provided with a sealing element such as an O-ring 542 (see Figure 7B), inhibiting backflow of the thermoplastic material in a region behind the tip section of the heating device.

In another embodiment, a heat conductive insert 543 (e. g. made of steel or titanium) is separate from a heating element 541, whereas the heating element 541 is designed in such a way that it may contact the insert 543 for transmitting heat. The insert 543 is introduced into the duct of the intramedullary nail prior to the locking operation, e. g. together with the blank of thermoplastic material. Alternatively, the insert 543 may be provided within the duct already during manufacture of the nail.

The Figure 8 to 9 show exemplary tip geometries which are specifically suited for the removal of intramedullary nails being locked using a thermoplastic material. In this case - contrary to the case of locking - it is necessary to simultaneously heat all regions in which the thermoplastic material has been distributed when locking the nail. Therefore, it is nec- essary to have extended contact elements. At the same time it has to be possible to introduce these contact elements into the duct of the intramedullary nail, even in cases where the nail has one or several bends.

The Figure 8 is a side view of a first variant of a suitable tip of an inventive heating device. The contact element 551 has a helical shape (similar to a corkscrew). It constitutes the heating element, being made of a flexible material or based on a flexible supporting body having a coating constituting the heating element.

The Figure 9 is a cross-sectional view of a flexible tip of another inventive heating device. It comprises a plurality of contact elements 552.1...552.4 having the shape of spherical caps which are movable to each other. This allows for passing bends of the intramedullary nail, whereas the contact elements 552.1 ...552.4 are slightly pushed apart from each other.

The Figure 10 is a cross-sectional view of a tip of an inventive heating device, the tip having a reduced diameter compared to the tips described above. This tip is to be used to- gether with intramedullary nails 506 having a distal region 506a, in which the inside diameter of the duct 507 is reduced accordingly. Reduction of the diameter of the heatable tip of the device allows for easily introducing the tip into the duct 507 of the intramedullary nail 506 even in the case of bends. At the same time, the corresponding reduction of the inside diameter of the duct 507 ensures good thermal contact for locking and/or unlocking the nail.

Further designs of heatable tips that are suitable for the removal of the inventive intramedullary nails are the following:

a balloon filled with a liquid acting as a heat conductor;

- a heating element that is integrated into the intramedullary nail itself and that may be e. g. electrically contacted from the outside;

- other kinds of flexible, specifically shaped dimensionally stable or modular heating elements.

The invention is not restricted to the embodiments described above. As an example, the bonding agent may be chosen differently from PLLA. Furthermore, it may comprise a therapeutic agent. The bonding agent may be introduced into the duct in the form of a blank prior to the locking step or it may be already provided within the duct during manufacture of the nail or hip screw. The geometry of the intramedullary nails, locking screws, hip screws may be chosen differently or combined in a different way, etc. As an example, the outside contour of the intramedullary nail may be polygonal (having rounded edges), circular, star-shaped etc. and it may be fluted. The diameter of the intramedullary nail needs not be constant along the length of the nail, e. g. it may slightly decrease from its proximal to its distal end. As mentioned above, the intramedullary nail may comprise a further canal (which may be essentially parallel to the duct) for guide wire applications. Concerning the hip screw, its diameter is preferably circular, whereas in the contact region with the intramedullary nail it may be provided with flat surface portions or it may have a polygonal cross-section in order to provide for a lock against rotation. The intramedullary nail as well as the hip screw may be made of a different material than titanium such as implant steel or reinforced plastics. The outside surface of the nails, bolts or screws may be additionally provided by a structuring as mentioned above.

In order to liquify the bonding agent ultrasonic waves, mechanical energy (such as oscillat- ing motion), electromagnetic energy etc. may be used instead of heat.

In summary, it is to be noted that the invention creates an intramedullary nail that allows the fast and secure fixation of long bone fractures and which especially simplifies distal locking of the nail to the bone.

Claims

1. An intramedullary nail (100; 200; 300; 400; 500) for stabilizing a fractured bone, the nail (100; 200; 300; 400; 500) being provided with at least a first duct (101; 201; 301; 401; 501) for at least partially receiving a bonding agent liquefiable by the application of energy, the duct ( 101 ; 201 ; 301 ; 401 ; 501 ) extending continuously from a proximal region of the nail (100; 200; 300; 400; 500) to a distal region of the nail (100; 200; 300; 400; 500) and whereas in the distal region the nail (100; 200; 300; 400; 500) is provided by at least one opening (102; 202; 302; 502) connecting the duct (101; 201; 301; 401; 501) with an outer surface of the nail (100; 200; 300; 400; 500).

2. The intramedullary nail as recited in claim 1, whereas the nail is made from a material having a thermal conductivity of 22 W/mK or less, in particular from titanium, a titanium alloy, steel or fiber-reinforced plastics.

3. The intramedullary nail as recited in claim 1 or 2, whereas the bonding agent is a biodegradable thermoplastic material.

4. The intramedullary nail as recited in one of claims 1 to 3, whereas the bonding agent is provided within the duct.

5. The intramedullary nail as recited in one of claims 1 to 4, whereas in the distal region an outer surface of the nail is provided with a structuring.

6. The intramedullary nail as recited in one of claims 1 to 5, comprising at least one bend (100c; 300c).

7. The intramedullary nail as recited in one of claims 1 to 6, whereas in the distal region (50όa) of the nail an internal cross-section of the duct (507) is reduced compared to a shank region of the nail.

8. The intramedullary nail as recited in one of claims 1 to 7, comprising a second duct for receiving a guide wire.

9. The intramedullary nail as recited in one of claims 1 to 8, in a proximal region comprising a through-hole (103) for accommodating a hip screw (120).

10. A device (140; 510; 520) for applying energy to the liquefiable bonding agent of an intramedullary nail as recited in one of claims 1 to 9, comprising a neck (513; 523) as well as a tip section (51 1 ; 521 ) to be inserted into the duct (501 ) of the intramedullary nail (500), the tip section (51 1 ; 521 ) allowing for energy transfer to the bonding agent.

1 1. The device as recited in claim 10, whereas the tip section (51 1; 521) comprises a heating element (514; 524) , in particular an electrical heating element being supplied by electricity by means of a feed accommodated within the neck (513; 523).

12. The device as recited in claim 10 or 1 1 , whereas the neck (513; 523) is flexible.

13. The device as recited in one of claims 10 to 12, whereas the tip section (51 1; 521) has a shape that converges towards a free end of the tip section (51 1 ; 521), whereas the free end section of the tip section (51 1 ; 521 ) is preferably spherical or conical.

14. The device as recited in one of claims 10 to 13, whereas the tip section comprises a sealing element (542), in particular on O-ring sealing element.

15. The device as recited in one of claims 10 to 14, comprising a further section (526, 527) allowing for energy transfer to a bonding agent provided in the proximal region of the intramedullary nail, the further section being distant from the tip section (521).

16. The device as recited in claim 15, whereas a distance between the tip section (521) and the further section (526, 527) is variable.

17. The device as recited in one of claims 10 to 16, whereas the tip section comprises a flexible helical element (551) allowing for energy transfer to the bonding agent.

18. The device as recited in one of claims 10 to 16, whereas the tip section comprises a plurality of elements (552.1...552.4), each of which allows for energy transfer to the bonding agent, whereas the elements (552.1 ...552.4) are mounted in such a way that they are movable in respect to each other.

19. A system for stabilizing a fractured bone comprising an intramedullary nail as recited in one of claims 1 to 9 and a device for applying energy as recited in one of claims 10 to 18.

20. A method for stabilizing a fractured bone comprising the steps of:

d) introducing an intramedullary nail as recited in one of claims 1 to 9 into the medullary canal of the bone;

e) inserting a device for applying energy as recited in one of claims 10 to 18 to the liquefiable bonding agent into the duct of the intramedullary nail;

f) applying energy to the bonding agent and pressing out the liquefied bonding agent through the at least one opening in the distal section of the nail by further advancing the device for applying energy, in such a way that the bonding agent is applied in a region between an outer surface of the intramedullary nail and the bone to be stabilized.

21. The method as recited in claim 20, for stabilizing a fractured neck of femur, characterized by the additional steps of

g) guiding a hip screw through a through-hole in a proximal region of the intramedullary nail, the hip screw having an axial duct provided by a bonding agent lique- fiable by applying energy, the duct extending continuously from a proximal region of the hip screw to a distal region of the hip screw and whereas in its distal region the hip screw is provided by at least one opening connecting the duct with an outer surface of the screw;

h) liquefying the bonding agent provided in the duct of the hip screw;

i) pressing out the liquefied bonding agent through the at least one opening in order to fix the hip screw to the surrounding bone.

22. A method for removing an intramedullary nail being fixed to a bone by a liquefiable bonding agent, comprising the step of liquefying the bonding agent by applying energy to the bonding agent by a device as recited in one of claims 10 to 18.

23. A hip screw (120) for stabilizing a fractured neck of femur (1), whereas the hip screw (120) is provided with a duct (122) for at least partially receiving a bonding agent (121) liquefiable by applying energy, the duct (122) extending continuously from a proximal region of the screw to a distal region of the screw and whereas in the distal region the screw (120) is provided by at least one opening (123) connecting the duct (122) with an outer surface of the screw (120).