WO2009117837A1

WO2009117837A1 - Surgical device for osteosynthesis

Info

Publication number: WO2009117837A1
Application number: PCT/CH2008/000139
Authority: WO
Inventors: Meinrad Fiechter; Samuel Maurer
Original assignee: Meinrad Fiechter; Samuel Maurer
Priority date: 2008-03-28
Filing date: 2008-03-28
Publication date: 2009-10-01

Abstract

A surgical device for osteosynthesis comprises a fixation element (1 ), in particular a bone plate, and a load-bearing pin-like fastener (3.1...3.4). The pin-like fastener (3.1...3.4) has a head (31.1...31.4) and a shank (30.1...30.4). The fixation element (1) has a through hole ( 10.1...10.4) for at least partly receiving the head (31.1...31.4) of the fastener (3.1...3.4). The inner surface of the through hole ( 10.1...10.4) and/or an outer surface of the head (31.1...31.4) of the fastener (3.1...3.4) is provided with a structuring for enabling a positive fit between the fastener (3.1...3.4) and the fixation element (1 ) by application of a first bonding agent (32.1...32.4) liquefiable by heat in a region between the inner surface of the through hole (10.1...10.4) and the outer surface of the head (31.1...31.4) of the fastener (3.1...3.4). The load is borne by the fastener whereas the first bonding agent serves for securely locking the pin-like fastener to the fixation element.

Description

Surgical device for osteosynthesis

Technical Field

The invention relates to a surgical device for osteosynthesis comprising a fixation element, in particular a bone plate, and a load-bearing pin-like fastener. The invention further relates to a fastener for such a surgical device, to a heating device to be used in connection with such a surgical device and to a method for affixing a fixation element, in particular a bone plate, to a bone. Background Art

The healing of broken bones 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). This is often done by employing plate-like fixation elements such as bone plates, fixation plates or stabilization plates that are affixed to the bone segments or fragments. Affixation of the plate-like fixation elements is often provided by means of pin-like fasteners such as bone screws or bonding screws.

JAs an example, US 6,080, 161 (F. E. Eaves, P. J. Capizzi) relates to the securing of osteosynthesis plates to a plurality of bone portions. For that purpose, a fastener blank is inserted through an opening in the osteosynthesis plate and into an opening drilled into the bone. The proximal end of the blank is provided by a head for affixing the blank to the plate. The blank is made from a material that when heated above the transition temperature of the material will deform to form a tight fit within the hole drilled in the bone. Preferably, the blank is made from a resorbable material, most preferably a non- reinforced lactide and glycolide copolymer composition. The blank may be provided by a hole therein to accomodate a heated wire or filament. Compared to usual bone screws, the blank shows reduced load-bearing capacity. The range of application is therefore limited.

US 5,593,425 (P. M. Bonutti) relates to surgical implants having two components, at least one of which having a bonding agent that may be activated by heat. The bonding agent may be a thermoplastic polymer, which may be biodegradable. One of the disclosed embodiments comprises a plate which may be secured to a bone by means of a screw. Both the screw and the plate are provided with the bonding agent such that the screw, in the region of the threaded screw shank, and the plate may be affixed to each other.

WO 02/069817 A1 (Woodwelding AG) relates to implants that are positively connected with human or animal tissue parts. For that purpose, the implants consist at least partially of a material that may be liquefied by means of mechanical energy (such as ultrasound), e. g. of a thermoplastic material. The liquefied material is pressed into openings or surface asperities of the tissue part so that, once solidified, it is positively joined thereto. The implants may be pin-like or dowel-like and may replace usual screws for the attachment of fixation or stabilization plates. In addition to regions made from the liquefiable material, the pin-like implants may have a core or a sleeve may form a material that is not liquefiable, such as metal, ceramics, glass or a composite material. A corresponding sleeve may be provided by openings through which the liquefiable material may escape.

|However, the distribution of mechanical vibrations such as ultrasound is difficult to control. Further, the solidity of the known systems is not up to the highest demands. Furthermore, with prior art systems that offer a good solidity of the connections it is often difficult to remove the implants when desired.

Summary of the invention

|lt is the object of the invention to create a surgical device pertaining to the technical field initially mentioned, that offers good solidity and allows for easy and secure fastening of a fixation element to a bone.

[The solution of the invention is specified by the features of claim 1. According to the invention, the pin-like fastener has a head and a shank and the fixation element has a through hole for at least partly receiving the head of the fastener. The inner surface of the through hole and/or an outer surface of the head of the fastener are provided with a structuring for enabling a positive fit between the fastener and the fixation element by application of a first bonding agent liquefiable by heat in a region between the inner surface of the through hole and the outer surface of the head of the fastener.

[The inventive device can be used to do fracture reduction and immobilization in long bones, short bones, flat bones and vertebral bodies for human as well as veterinary purposes. The pin-like fastener may have the form of a screw having a screw thread or a plain outside surface. The cross section of the shank of the screw needs not to be circular but may have another shape, e. g. that of a regular polygon. In other embodiments, the pin- like fastener may be dowel-like. In any case the pin-like fastener has a load-bearing function. For that purpose it is preferable that the fastener has a minimium tensile strength of 100 N/mm² (100 MPa). In the context of the inventive solution, the load is borne by the fastener whereas the first bonding agent serves for securely locking the pin-like fastener to the fixation element.

Instead of having a plate-like fixation element such as a bone plate, a fixation plates or a stabilization plate, the fixation element may be constituted by a bone fragment that is to be affixed to another bone fragment, e. g. in the vicinity of a joint. In this case, the through hole is directly created within the first bone fragment.

The first bonding agent may be provided with the pin-like fastener and/or with the fixation element and/or externally applied during the fixation process. Usually, there is no chemical reaction between the first bonding agent and the fastener or the first bonding agent and the opening in the fixation element, respectively. The fixation is achieved by a form fit due to the plastic deformation of the first bonding agent, supported by the structuring of the inner surface of the through hole and/or the outer surface of the head of the fastener.

In contrast to ultrasound or other mechanical activation of the bonding agent the dissipation 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 first bonding agent is sufficiently liquefied to fill out the structuring of the through hole or the head of the fastener in order to achieve a positive fit between the head of the pin and the fixation element. Preferably, the first bonding agent is liquefied by directly contacting the agent with a heatable element, in particular by means of a dedicated heating device which allows localized heating.

An inventive method for affixing the fixation element, in particular a bone plate, to the bone comprises the steps of a) guiding a pin-like fastener through a through hole being provided in the fixation element; and b) inserting the fastener into the bone, whereas c) a first bonding agent being liquifiable by heat is heated at least during the insertion of the fastener into the bone in such a way that the first bonding agent is applied in a region between an inner surface of the through hole and an outer surface of a head of the fastener.

Thereby, the liquefied first bonding agent may reliably fill out the structuring in the head and/or the through hole of the fixation element and therefore guarantee a strong fixation of the fastener to the fixation element, irrespective of where the first bonding agent is initially provided.

The fastener may be inserted into a hole that has been pre-drilled into the bone. In certain cases, where the fastener has the form of a self-tapping screw, pre-drilling may be unnecessary.

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 fastener to the fixation element. Preferably, the structuring assures two-dimensional fixation, i. e. fixation against axial as well as against rotational movement of the fastener with respect to the fixation element. In the case of an opening-fastener interface that allows multiple orientations of the fastener in respect to the fixation element it is preferred that the structuring assures three-dimensional fixation, i. e. it secures the fastener additionally against re-orientation.

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

Advantageously, the fastener 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. Besides the fastener, the fixation element may be as well manufactured from a material having a thermal conductivity of 22 W/mK or less, thereby avoiding excessive heat transfer from the fixation element to the bone. However, instead of having such a fixation element heat transfer to this element may be avoided by employing heating devices allowing for locally contacting the fastener and/or the first bonding agent.

Instead of being entirely made of a low thermal conductivity material the fastener 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 the outer region of the shank which contacts the surrounding bone is inhibited.

Preferably, the first bonding agent is a bio-compatible thermoplastic material, most preferably an amorphous polymer. As the first bonding agent is used to attach the head of the fastener to the fixation element it is preferred that the first bonding agent is not biodegradable, respectively has a long degradation time such as 24 months or more. 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 first bonding agent is l-lactide (LPLA), an amorphous thermoplastic material having a glass transition temperature of 60 -65 ⁰C and having a degradation time of more than 24 months. The material may be deformed after being heated over the glass transition temperature.

Preferentially, the first bonding agent is provided as a coating on the outer surface of the head of the fastener. Therefore, the bonding agent is already provided where it will be used to effect the bonding between the fastener and the fixation element. This allows for an easy application of the pin-like fastener to the fixation element, e. g. by heating the head of the fastener using a heating tool contacting the head of the fastener on its front side.

Alternatively, the bonding agent may be provided as a coating on the inner surface of the through hole provided in the fixation element, it may be externally provided during the fixation process or it may be provided in another region of the fastener and be transferred to the bonding region during fixation.

Advantageously, the shank of the fastener is provided by an axial duct for at least partially receiving a second bonding agent liquefiable by heat. Preferably, a main orifice of the duct will be provided in a proximal head of the fastener. Furthermore, the shank has at least one opening connecting the duct with an outer surface of the shank. This allows for heating and for squeezing out the second bonding agent through the opening, after which it will directly reach the place of bonding between the shank of the fastener and the bone. Preferably, there will be a plurality of openings in order to ensure appropriate distribution of the bonding agent with respect to the outer surface of the shank.

Usually, there is no chemical reaction between the second bonding agent and the pin-like fastener or the second bonding agent and the surrounding bone, respectively, but the fixation is achieved by the plastic deformation of the first bonding agent. Due to the presence of the trabecular structure of the bone an additional structuring of the surrounding bone is usually not required, whereas a structuring in the outer surface of the pin-like fastener improves the fixation between the fastener and the bone.

Alternatively, the second bonding agent is provided as a coating on the outer surface of the shank or externally provided during the fixation process.

The material of the second bonding agent may be identical to the material of the first bonding agent or it may be a different material. Preferably, the second bonding agent is a biodegradable thermoplastic material. Most preferably, the second bonding agent is an amorphous or semi-crystailine material. A suitable material is Poly(dl-lactide) (DLPLA). This material is biodegradable (degradation time 12 to 16 months) and has a low glass transition temperature of 55-60 ⁰C. The bonding agent may comprise a therapeutic agent supporting a healing process.

In the context of the inventive method, the second bonding agent is heated at least during the insertion of the fastener into the bone in such a way that the second bonding agenf is applied in a region between an outer surface of a shank of the fastener and the bone.

Generally, the second bonding agent may be initially provided within the shank (see below) and/or at the outside of the shank. Alternatively, the second bonding agent may be introduced into the shank or applied to the shank after fixation of the fastener to the fixation element. Furthermore, the second bonding agent may be introduced into the shank while introducing a heating device (see below). Finally, the second bonding agent may be introduced into the shank by means of a hot glue gun type device.

In certain preferred embodiments of the invention, a cross-section of the through hole is at least partly spherical. In combination with screws that have a head with an at least partly spherical cross-section such as polyaxial screws this allows for setting the screw in different orientations with respect to the fixation element, thereby enhancing the flexibility of the surgical device.

In other preferred embodiments of the invention, a cross-section of the through hole is at least partly conical. A conical cross-section ensures an axial fixation of the fixation element against the bone.

Alternatively, the cross-section of the through hole may be cylindrical. It is possible to have a cross-section that is a combination of cylindrical, conical and/or spherical sections. The latter allows for creating connections that have a predetermined angular orientation as well as connections that offer arbitrary orientations depending on the choice of screws. A heating device that is suited to be used together with the surgical device according to the invention has a fastener provided with a duct comprises a heatable tip section, a diameter of the tip section being less than an inside diameter of the duct of the shank of the fastener.

This allows for heating the second bonding agent being held in the axial duct by at least partially introducing the heatable tip section of the heating tool into the duct. Introducing a tip section allows for a very localized heating of the second bonding agent without heating up the adjacent regions of the fastener. Thereby, heat transfer to the bone is substantially reduced.

In a preferred embodiment of a heating device, the heatable tip is provided with a heat- conductive insert, whereas an axial length of the insert is small compared to an axial length of the duct. Most preferably, the axial length of the insert amounts to a third of the axial length of the duct or less. This ensures localized heating of the second bonding agent during introduction of the heatable tip section of the heating device. At the same time, the tip section may used to eject the liquefied bonding agent through the opening(s) connecting the duct with the outer surface of the shank.

In another preferred embodiment of a heating device, the heatable tip section is at least partially convered by a thermally insulating sleeve, an outer diameter of the insulating sleeve approximating an inner diameter of the duct. The insulating sleeve inhibits heat transfer from the heatable tip section and/or a heat supply for the heatable tip section to the fastener.

The insulating sleeve may be movable in respect of the heatable tip section. In this case, the cross-section of the heatable tip section is considerably smaller than the cross-section of the axial duct. This allows for introducing the heatable tip section into the duct (especially if the second bonding agent is received within the duct in a pipe-like manner, leaving a central passageway). After or during introduction, the heatable tip section is heated, thereby heating the adjacent portions of the second bonding agent. Subsequently, the movable sleeve may be slid over the heatable tip section, thereby ejecting the second bonding agent through the opening(s) connecting the duct with the outer surface of the shank and ensuring thermal insulation between the heatable tip section and the wall of the fastener.

The heatable tip may have a shape that expands towards the free end of the tip. This is a preferred embodiment in cases where the second bonding agent is introduced into the duct of the fastener together with the heating device, i. e. where the second bonding agent is e. g. provided in the form of a sleeve enclosing the tip section of the heating device that may be inserted into the duct. After insertion, the (proximal) opening of the duct is sealed by means of a ring-shaped sealing element. As soon as the second bonding agent is liquefied at least in a distal region adjacent of the expanding section of the tip, the heating device may be retracted, thereby ejecting the second bonding agent through the opening(s) in the shank. Leakage of the second bonding agent through the axial opening of the duct is prevented by the sealing element. If the heatable section of the tip is restricted to the front end of the heating device, leakage through the axial opening is further prevented by the solid (un-liquefied) proximal part of the sleeve made of the second bonding agent.

Together, the surgical device comprising a fixation element and a pin-like fastener (or a plurality of pin-like fasteners) and the appropriate heating device constitute a system for ostheosynthesis.

For easy removal of the fixation element the first and/or second bonding agents may be heated again. For this purpose, the first bonding agent is heated by directly contacting the fixation element and/or the first bonding agent by a heatable element of a heating tool.

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 first embodiment of an inventive surgical device; Fig. 2 a second embodiment of an inventive surgical device;

Fig. 3 a third embodiment of an inventive surgical device for fixation of a thighbone;

Fig. 4 a fourth embodiment of an inventive surgical device for fixing vertebrae;

Fig. 5 a fifth embodiment of an inventive surgical device for fixing two parts of a broken calcaneus to one another;

Fig. 6, 7 further versions of screws that are applicable in the context of the invention;

Fig. 8-14 embodiments of a heating tool appropriate to be used in the context of the invention;

Fig. 15 another embodiment of a heating tool appropriate for liquefying a bonding agent that is applied to the head of the screw;

Fig. 16 a cross-sectional view of a screw head and a corresponding opening in a bone plate; and

Fig. 17-19 preferred embodiments of structurings in the screw head and/or the opening of the bone plate.

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

Preferred embodiments

Figure 1 shows a first embodiment of an inventive surgical device. The device comprises a bone plate 1 that is attached to a bone segment 2 by means of screws. Figure 1 shows a segment of the bone plate 1 that comprises four openings 10.1, 10.2, 10.3, 10.4 receiving four screws 3.1 , 3.2, 3.3, 3.4, their distal ends extending into the bone segment 2. Two of the screws 3.1, 3.3 have a threaded shank 30.1, 30.3, the two other screws 3.2, 3.4 have a cylindrical unthreaded shank 30.2, 30.4. Two of the screw heads 31.1, 31.2 have a conical cross section, a further screw head 31.3 is of the flat mushroom-type whereas the fourth screw head 31.4 has a spherical cross section. The conical heads 31.1, 31.2 can be bonded to the bone plate 1 in a single angle, defined by the orientation of the opening 10.1, 10.2. The flat mushroom-type screw head 31.3 of the third screw 3.3 and the spherical head 31.4 of the fourth screw 3.4 allow to bond the screws 3.3, 3.4 to the bone plate 1 in variable angles. For that purpose, the corresponding openings 10.3, 10.4 have an upper, substantially spherical surface and a conical cross-section that extends towards the lower surface of the bone plate 1.

All the screw heads 31.1...31.4 have a thin thermoplastic coating 32.1 ...32.4 of LPLA (I- lactide) on the outer surface. Both the outer surfaces of the screw heads 31.1...31.4 as well as the inner surfaces of the openings 10.1...10.4 are provided with a structuring (see below). Therefore, the screws 3.1...3.4 can be bonded together with the bone plate 1 as soon as they are placed in their final position. The bonding reaction happens due to a heating tool 4 which will be pushed against the screw head 31.1...31.4. By means of the heating tool 4 the thermoplastic coating 32.1...32.4 may be heated above the glass transition temperature (i. e. above 60-65 ^CC for LPLA) and therefore liquefied. Due to the liquefying process the material adheres on the bone plate 1 and the screw head 31.1 ...31.4 and guarantees a rigid fixation between the bone plate 1 and the screw 3.1 ...3.4.

Figure 2 shows a second embodiment of an inventive surgical device. The device comprises a bone plate 101 that is attached to a bone segment 102 by means of screws.

Figure 2 shows a segment of the bone plate 101 that comprises four openings 1 10.1,

1 10.2, 1 10.3, 1 10.4 receiving four screws 103.1, 103.2, 103.3, 103.4, their distal ends extending into the bone segment 102. The screws 103.1 ...103.4 have threaded shanks

130.1 ...130.4. Two of the screw heads 131.1, 131.2 have a conical cross section, the other two screw heads 131.3, 131.4 have a spherical cross section. The conical heads

131.1 , 131.2 can be bonded to the bone plate 101 in a single angle, defined by the orientation of the opening 1 10.1, 1 10.2. The spherical heads 131.3, 131.4 of the further screws 103.3, 103.4 allow to bond the screws 103.3, 103.4 to the bone plate 101 in a variable angle. For that purpose, the corresponding openings 1 10.3, 1 10.4 have an upper, substantially spherical surface and a conical cross-section that extends towards the lower surface of the bone plate 101. In this embodiment, the screws 103.1...103.4 are partially cannulated, their shanks 130.1 ...130.4 having a central axial duct 133.1 ...133.4. Each of the ducts 133.1...133.4 is provided with a plurality of generally radial openings 134 connecting the duct with the outside of the screw shank 130.1 ...130.4. The placement of the radial openings 134 is adapted to the structure of the bone segment 102. In the given example, the bone segment 102 is a middle portion of a long bone, the screws 103.1 ...103.4 diametrically traverse the bone and the openings 134 are placed in the regions of the compact bone tissue. The ducts 133.1 ...133.4 are partially filled with an amorphous thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). Furthermore, the screw heads 131.1 ...131.4 have a thin thermoplastic coating 132.1 ...132.4 of LPLA on the outer surface.

The screws 103.1 ...103.4 can be bonded together with the bone plate 101 as soon as they are placed in their final position. The bonding reaction happens due to a heating tool 104 having a heatable tip 140 which fits into the duct 133.1 ...133.4 of the screw 103.1 ...103.4. The heatable tip 140 of the heating tool 104 is heated and pushed into the duct 133.1...133.4 during application. Thereby, the thermoplastic, biodegradable material is heated above its glass transition temperature of 55 - 60 ⁰C and therefore liquefied. Furthermore, the material is squeezed through the openings 134 into the clearance between the screw shank 130.1...130.4 and the bone segment 102. The bonding of the thermoplastic material with the bone guarantees a rigid fixation of the screw 103.1 ...103.4 in the bone. At the same time, by means of the heating tool 104 the thermoplastic coating 132.1 ...132.4 of the screw head 131.1 ...131.4 is heated above the glass transition temperature (i. e. above 60-65 ⁰C for LPLA) and therefore liquefied. Due to the liquefying process the material adheres on the bone plate 101 and the screw head 131.1 ...131.4 and guarantees a rigid fixation between the bone plate 101 and the screw 103.1 ...103.4.

Figure 3 shows a third embodiment of an inventive surgical device for fixation of a thighbone. The device comprises a hip screw 203.1 having a threaded shank 230.1. The screw 203.1 is pushed or turned in trough the bone plate 201 into the femoral head 202. The screw 203.1 is partially cannulated, its shank 230.1 having a central axial duct 233.1. The duct 233.1 is provided with a plurality of generally radial openings 234 connecting the duct 233.1 with the outside of the screw shank 230.1. The duct 233.1 is partially filled with a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA).

The screw 203.1 can be bonded together with the femoral head 202 by employing a heating tool 204 having a heatable tip 240 which fits into the duct 233.1 of the screw 203.1. The heatable tip 240 of the heating tool 204 is heated and pushed into the duct

233.1 during application, thereby liquefying and pushing away the thermoplastic, biodegradable material. This results in a liquid material flow through the openings 234 into the clearance between the screw shank 230.1 and the femoral head 202. The bonding of the thermoplastic material with the bone guarantees a rigid fixation of the screw 203.1 in the bone.

The bone plate 201 is secured to the thighbone 221 by means of further three screws 203.2, 203.3, 203.4. As described above, in connection with Figure 1 , the heads 231.2...231.4 of these screws 203.2...203.4 are received by corresponding openings 210.2...210.4 in the bone plate 201. One of the screws 203.2 has a threaded shank 230.2, whereas the two other screws 203.3, 203.4 have cylindrical shanks 230.3, 230.4. Two of the screw heads 231.3, 231.4 have a conical cross section, a further screw head

231.2 has a spherical cross section. The conical heads 231.3, 231.4 can be bonded to the bone plate 201 in a single angle, defined by the orientation of the opening 210.3, 210.4. The spherical head 231.2 of the further screw 203.2 allows to bond the screw 203.2 to the bone plate 201 in a variable angle.

All the further screw heads 231.2...231.4 have a thin thermoplastic coating 232.2...232.4 of LPLA on the outer surface. The screws 203.2...203.4 can be bonded together with the bone plate 201 as soon as they are placed in their final position. The bonding reaction happens due to a heating tool (not displayed) which will be pushed against the screw head 231.2...231.4. By means of the heating tool the thermoplastic coating 232.2...232.4 may be heated above the glass transition temperature (i. e. above 60-65 °C for LPLA) and therefore liquefied. Due to the liquefying process the material adheres on the bone plate 201 and the screw head 231.2...231.4 and guarantees a rigid fixation between the bone plate 201 and the screw 203.2...203.4. Figure 4 shows a fourth embodiment of an inventive surgical device for fixing vertebrae. Two vertebral bodies 323, 324 are relatively fixed to each other by means of a bone plate 301. Similar to the embodiment displayed in Figure 1 , two screws 303.1 , 303.2 are held in corresponding openings 310.1 , 310.2 of the bone plate 301. One of the screws 303.1 has a threaded shank 330.1 whereas the other screw 303.2 has a cylindrical shank 330.2. Both screw heads 331.1 , 331.2 have a spherical cross section allowing to bond the screws 303.1, 303.2 to the bone plate 301 in a variable angle.

The two screw heads 331.1 , 331.2 have a thin thermoplastic coating 332.1 , 332.2 of LPLA on the outer surface. The screws 303.1 , 303.2 can be bonded together with the bone plate 301 as soon as they are placed in their final position. The bonding reaction happens due to a heating tool (not displayed) which will be pushed against the screw head 331.1, 331.2.

By means of the heating tool the thermoplastic coating 332.1, 332.2 may be heated above the glass transition temperature (i. e. above 60-65 ⁰C for LPLA) and therefore liquefied.

Due to the liquefying process the material adheres on the bone plate 301 and the screw head 331.1, 331.2 and guarantees a rigid fixation between the bone plate 301 and the screw 303.1 , 303.2.

Figure 5 shows a fifth embodiment of an inventive surgical device for fixing two parts of a broken calcaneus to one another. In this embodiment, a bone plate is not required. A screw 403 is received in a bore that extends from a first bone segment 425 of the calcaneus into a second bone segment 426 of the calcaneus. The screw 403 has a threaded shank 430 and a screw head 431 which is supported on the outside surface of the first bone segment 425. The screw 403 is partially cannulated, their shank 430 having a central axial duct 433 being provided with a plurality of generally radial openings 434 connecting the duct 433 with the outside of the screw shank 430. The duct 433 is partially filled with a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). The screw 403 can be bonded together with the bone segments 425, 426 by employing a heating tool 404 having a heatable tip 440 which fits into the duct 433 of the screw 403. The heatable tip 440 of the heating tool 404 is heated and pushed into the duct 433 during application, thereby liquefying and pushing away the thermoplastic, biodegradable material. This results in a liquid material flow through the openings 434 into the clearance between the screw shank 430 and the bone segments 425, 426. The bonding of the thermoplastic material with the bone guarantees a rigid fixation of the screw 403 in the bone and therefore a rigid fixation of the two bone segments to one another.

The Figures 6 and 7 show further versions of screws that are applicable in the context of the invention. The screw 503 shown in Figure 6 has an unthreaded cylindrical shank 530 and a flat head 531 having a concave, generally spherical bottom side. The opening 510 in the bone plate 501 for receiving the screw 503 is conical, its diameter increasing towards the upper side and has a recessed, correspondingly convex, generally spherical upper side. This allows for fixing the screw 503 to the bone plate 501 in a variable angle. The shank 530 of the screw 503 extends into a bone segment 502.

The screw 603 shown in Figure 7 has a threaded shank 630 and a flat cylindrical head 631 having a flat bottom side. Correspondingly, the opening 610 in the bone plate 601 for receiving the screw 603 is cylindrical, having a recess for receiving the head 631 of the screw 603.

The screw heads 531, 631 have a thin thermoplastic coating 532, 632 of LPLA on their bottom side, and additionally on the outer surface in the case of the screw 631 shown in

Figure 7. The screws 531, 631 can be bonded together with the bone plate 501 , 601 as soon as they are placed in the desired position. The bonding reaction may be actuated by employing a heating tool (not displayed) to heat the thermoplastic coating above the glass transition temperature (i. e. above 60-65 ⁰C for LPLA) such that the material is liquefied. Due to the liquefying process the material adheres on the bone plate 501, 601 and the screw head 531, 631 and guarantees a rigid fixation between the bone plate 501, 601 and the screw 503, 603.

The Figure 8 shows a first embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4a comprises a heating unit 741 which is covered by a heatable insert 742 on its front face. The shell of the heating unit 741 is covered by a thermally insulating sleeve 743. The outer cross-section of the heating unit 741 together with the sleeve 743 as well as the outer cross-section of the insert 742 are smaller than the inner cross-section of the duct 733 in the shank 730 of a screw 703 such that the insert 742 as well as the insulated heating unit 741 may be introduced into the duct 733. As described above, the duct 733 is partially filled with a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). This material is applied to the inner surface of the duct 733 and leaves a central passageway. The heatable insert 742 has a conical rear section 742a and terminates in a cylindrical section 742b, where the cross section of the cylinder roughly matches the cross section of the central passageway. The heating tool 4a may be linearly moved into the duct 733. Thereby, the thermoplastic material is locally heated and therefore liquefied in the region of the insert 742. The liquefied material is squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment 702. Local heating of the thermoplastic material and the provided insulation ensures that the heating up of the bone segment 702 is marginal. Furthermore, the insert 742 seals the duct 733 against leaking of the thermoplastic material along the axis of the duct 733, through its main orifice.

The Figure 9 shows a second embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4b comprises a heatable tip 750 of generally cylindrical cross section. The rear part of the heatable tip 750 being connected to a heating unit (not displayed) which is arranged rearwards of the heatable tip 750 is covered by a thermally insulating sleeve 753. The outer cross-section of the heatable tip 750 together with the sleeve 753 is smaller than the inner cross-section of the duct 733 in the shank 730 of a screw 703, such that the heatable tip 750 as well as the insulating sleeve 753 may be introduced into the duct 733.

Again, the duct 733 is partially filled with a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). In the embodiment shown in Figure 9, the thermoplastic material fills out the entire lower part of the duct 733, leaving no central passageway. The heating tool 4b may be linearly moved into the duct 733. Thereby, the thermoplastic material is locally heated and therefore liquefied in the region of the heatable tip 750. Simultaneously, a passageway for the heatable tip 750 is created within the thermoplastic material and in a second step, the liquefied material is squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment 702. Local heating in a region around the axis of the duct 733 ensures that the heating up of the bone segment 702 is marginal. Furthermore, the insulating sleeve 753 seals the duct 733 against leaking of the thermoplastic material along the axis of the duct 733, through its main orifice.

The Figure 10 shows a third embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4c comprises a heatable core 761 that ends in a conical heatable tip 760. The rear part of the heatable core 761 is covered by a thermally insulating sleeve 763. The outer cross-section of the heatable core 761 together with the sleeve 763 as well as the outer cross-section of the heatable tip 760 are slightly smaller than the inner cross-section of the duct 733 in the shank 730 of a screw 703 such that the heatable core 761 may be introduced into the duct 733.

Similar to Figure 8, the duct 733 is partially filled with a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). This material is applied to the inner surface of the duct 733 and leaves a central passageway. The heating tool 4c may be linearly moved into the duct 733. Thereby, the thermoplastic material is locally heated and therefore liquefied in the region of the heatable tip 760. The liquefied material is squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment 702. Local heating of the thermoplastic material and the provided insulation ensure that the heating up of the bone segment 702 is marginal. The main orifice of the duct 733 is sealed by the insulated rear part of the heatable core 761.

The Figure 1 1 shows a fourth embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4d comprises a heatable tip 770 of generally cylindrical cross section. The rear part of the heatable tip 770 is connected to a heating unit (not displayed) which is arranged rearwards of the heatable tip 770. The heatable tip

770 is enclosed by a slidable insulating sleeve 773. The outer cross-section of the heatable tip 770 together with the sleeve 773 is slightly smaller than the inner cross- section of the duct 733 in the shank 730 of a screw 703, such that the heatable tip 770 as well as the insulating sleeve 773 may both be introduced into the duct 733.

Again, the duct 733 is partially filled with a thermoplastic, biodegradable material, namely

Poly(dl-lactide) (DLPLA). This material is applied to the inner surface of the duct 733 and leaves a central passageway. For adhering the screw 703 to the surrounding bone segment 702 by means of the thermoplastic material, first the heatable tip 770 is linearly introduced into the central passageway of the thermoplastic material. At this time, only the tip section of the slidable insulating sleeve 773 is introduced into the duct 733 such that the duct 733 is sealed against the outside. Next, the heatable tip 770 is heated in order to liquefy the surrounding thermoplastic material. As soon as the material is liquefied the slidable sleeve 773 may be slid linearly with respect to the heatable tip 770, introducing the sleeve 773 into the duct 733. Thereby, the liquefied material is squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment 702. Local heating in a region around the axis of the duct 733 ensures that the heating up of the bone segment 702 is marginal. Furthermore, the insulating sleeve 773 seals the duct 733 against leaking of the thermoplastic material along the axis of the duct 733, through its main orifice.

The Figure 12 shows a fifth embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4e comprises a heatable cylindrical core 781 whose front part is enclosed by a sleeve 784 made from a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). The rear part of the heatable core 781 is enclosed by a movable insulating sleeve 783. The outer cross-section of the heatable core 781 together with the sleeves 783, 784 is slightly smaller than the inner cross-section of the duct 733 in the shank 730 of a screw 703, such that the heatable core 781 together with the thermoplastic sleeve 784 and the insulating sleeve 783, respectively, may be introduced into the duct 733.

For adhering the screw 703 to the surrounding bone segment by means of the thermoplastic material, the unheated core 781 together with the sleeve 784 are introduced into the duct 733 of the screw 703. By activating the heating tool 4e the heatable core 781 is heated up to a desired temperature and liquefies the material of the sleeve 784. As soon as the material is liquefied the slidable sleeve 783 may be slid linearly with respect to the heatable core 781 along a predetermined distance, introducing the sleeve 783 into the duct 733. Thereby, the liquefied material is squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment. By changing the moving distance and or velocity of the sleeve 783 the degree of adherence of the screw 703 in the bone segment may be adjusted. The Figure 13 shows a sixth embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4f features a heatable container 795 containing a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). By heating the thermoplastic material may be liquefied. The container 795 is provided by a movable piston 796 which allows for squeezing out the liquefied material through a front orifice. The heating tool 4f is provided by a thermally insulating front cap 797 having a form that is adapted to the form of the head 731 of a screw 703 and designed in such a way that the orifice of the heating tool 4f fitted to the screw 703 allows for directly introducing the liquefied material into the duct 733 of the shank 730 of the screw 703. The material passes through the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment.

The Figure 14 shows a seventh embodiment of a heating tool appropriate to be used in the context of the invention. The heating tool 4g comprises a heatable tip 810 of generally cylindrical cross section. The rear part of the heatable tip 810 is connected to a heating unit (not displayed) which is arranged rearwards of the heatable tip 810. The heating tool 4g further comprises a thermally insulating sleeve 813 which may be supported on the head 731 of the screw 703. The heatable tip 810 has a shape that expands towards the free end of the tip. The outer diameter of the expanded section 818 corresponds to the inner diameter of the duct 733 of the screw 703, whereas the diameter of the heatable tip 810 is considerably smaller.

The heatable tip 810, with the exception of the expanded section 818, is enclosed by a sleeve 814 of a thermoplastic, biodegradable material, namely Poly(dl-lactide) (DLPLA). This material is held between the expanded section 818 and the thermally insulating sleeve 813 which closely surrounds the heatable tip 810.

For adhering the screw 703 to the surrounding bone segment by means of the thermoplastic material, the unheated heatable tip 810 together with the thermoplastic sleeve 814 are introduced into the duct 733 of the screw 703. Next, the heating tool 4g is activated and the heatable tip 810 is retracted relative to the insulating sleeve 813 and the screw 703. The material of the thermoplastic sleeve 814 is liquefied and squeezed out of the openings 734 into the clearance between the shank 730 of the screw 703 and the adjacent bone segment. The insulating sleeve 813 seals the duct 733 against leaking of the thermoplastic material along the axis of the duct 733, through its main orifice.

The Figure 15 shows another embodiment of a heating tool appropriate for liquefying a bonding agent that is applied to the head of the screw. The heating tool 4h has a heatable tip 820 of a generally cylindrical form and having a rounded tip section whose form is adapted to the form of the screw head 731 but which leaves a void 829 in front of the tip.

The outer surface of the screw head 731 is covered with a bio-compatible thermoplastic material, namely l-lactide (LPLA). This material may be liquefied by applying the heatable tip 820 of the heating tool 4h to the screw head 731 and heating up the heatable tip 820 to a predetermined temperature. The heat will be transferred to the liquefiable material by the screw head 731. The void 829 in front of the heatable tip 820 ensures that the head is mainly transferred to the side surfaces of the screw head and not to the screw's shank 730. Thereby, heating up of the surrounding bone segment is avoided.

Instead of the void 829 the front end of the heatable tip 820 may be constituted by a thermally insulating material, e. g. by a ceramic material. A heating tool may comprise both a heatable section that may be applied to the screw head (as shown in Figure 15) as well as a heatable tip that may be inserted into a duct of the screw (as shown in Figures 8-14).

The Figure 16 shows a cross-sectional view of a screw head and a corresponding opening in a bone plate. The opening 10a has an upper conical section as well as a lower spherical section. The opening 10a allows for establishing connections having a predetermined angle between the screw and the bone plate 1a as well as for establishing connections having an arbitrary angle. In the first case, the corresponding screw (such as a screw having a conical head) is supported on the conical section of the opening 10a. In the second case, the corresponding screw 3a (such as a screw having a head 31a with a spherical underside) is supported on the spherical section of the opening 10a as displayed in Figure 16.

The Figures 17 - 19 show preferred embodiments of structurings in the screw head and/or the opening of the bone plate. Generally, the outer surface of the screw head and or the inner surface of the opening, interacting with the outer surface of the screw head, are provided with a three dimensional structuring. The structuring may have grooves, channels or notches that may have different directions, it may have knurls, a wide thread or a toothing. The liquefied thermoplastic material will enter the cavities of the structuring(s), fill them out and establish a form fit between the screw head and the opening of the bone plate. Preferably, the structure is formed in such a way that a form fit is established in all directions. For achieving an even better form fit, the structuring may be additionally sand blasted, micro blasted or etched or it may be provided with a nano structuring.

In a preferred embodiment as shown in Figure 17, a conical screw head 31b features a circumferential notch being initally filled with the thermoplastic material. After liquefying, the material enters the cavities of the (e. g. sand-blasted) structuring of the opening 10b of the bone plate 1b and ensures axial fixation of the screw. The metallic sections of the conical screw head 31 b, adjacent the notch, ensure firm angular support of the screw.

In another preferred embodiment as shown in Figure 18, a cylindrical screw head 31c features a circumferential notch in its cylindrical section. The opening 10c in the bone plate 1c is generally cylindrical and has a first circumferential notch in its side wall as well as a second ring-shaped notch in its base wall. Initally, the screw head 31c, especially the notch provided in the screw head 31c, is coated with the thermoplastic material. After melting, the material will enter the notches in the opening 10c. The notch in the side wall of the opening 10c ensures axial form fit whereas the notch in the base wall mainly serves for collecting excess thermoplastic material.

As shown in Figure 19, notches may also be provided in cases where the angular orientation of the screw in relation to the bone plate is largely arbitrary. The screw head 31d has a spherical underside provided with a circumferential notch. Correspondingly, the spherical inner surface of the opening 1Od in the bone plate 1d has three coaxial circumferential notches. Again, the screw head 31d, especially the notch provided in the screw head 31 d, is initally coated with the thermoplastic material. After melting, the material will enter some of the notches in the opening 1 Od. Some of the notches may serve for collecting excess thermoplastic material. (The invention is not restricted to the embodiments described above. As an example, the bonding agents may be chosen differently from DLPLA or LPLA. The geometry of the fasteners or bone plates as well as the form and orientation of the structuring may be chosen differently or combined in a different way, etc.

Furthermore, the field of application of the described elements is not restricted to a surgical device for osteosynthesis comprising a plate-like fixation element. Screws and heating tools as described above may also be used for other fastening purposes, e. g. a dental implant may be provided with a screw having a structured surface and being provided with a coating of a bonding agent that is liquefiable by heat. After insertion of the implant, the bonding agent may be liquefied which will establish a tight form fit between the structured surface of the screw and the surrounding bone.

In summary, it is to be noted that the invention creates a surgical device that offers good solidity and easy and secure fastening of a plate-like fixation element to a bone.

Claims

1. A surgical device for osteosynthesis comprising a fixation element (1), in particular a bone plate, and a load-bearing pin-like fastener (3.1 ...3.4), the pin-like fastener (3.1 ...3.4) having a head (31.1...31.4) and a shank (30.1 ...30.4), the fixation element (1) having a through hole (10.1 ...10.4) for at least partly receiving the head

(31.1 ...31.4) of the fastener (3.1 ...3.4), the inner surface of the through hole (10.1 ...10.4) and/or an outer surface of the head (31.1...31.4) of the fastener (3.1 ...3.4) being provided with a structuring for enabling a positive fit between the fastener (3.1...3.4) and the fixation element (1) by application of a first bonding agent (32.1 ...32.4) liquefiable by heat in a region between the inner surface of the through hole (10.1 ...10.4) and the outer surface of the head (31.1 ...31.4) of the fastener (3.1 ...3.4).

2. The surgical device as recited in claim 1 , whereas 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.

3. The surgical device as recited in claim 1, whereas the fastener (3.1 ...3.4) is made from a material having a thermal conductivity of 22 W/ml< or less, in particular from titanium, a titanium alloy, steel or fiber-reinforced plastics.

4. The surgical device as recited in claim 1, whereas the first bonding agent (32.1...32.4) is a bio-compatible thermoplastic material.

5. The surgical device as recited in claim 1, whereas the first bonding agent is provided as a coating (32.1...32.4) on the outer surface of the head (31.1...31.4) of the fastener (3.1...3.4).

6. The surgical device as recited in claim 1, whereas the shank (230.1...230.4) of the fastener (203.1 ...203.4) is provided by an axial duct (233.1 ...233.4) for at least partially receiving a second bonding agent liquefiable by heat and whereas the shank (230.1 ...230.4) has at least one opening (234) connecting the duct (233.1 ...233.4) with an outer surface of the shank (230.1 ...230.4).

7. The surgical device as recited in claim 4, whereas the second bonding agent is a biodegradable thermoplastic material, in particular Poly(dl-lactide) (DLPLA).

8. The surgical device as recited in claim 1 , whereas a cross-section of the through hole ( 10.3, 10.4) is at least partly spherical.

9. The surgical device as recited in claim 1, whereas a cross-section of the through hole (10.1, 10.2) is at least partly conical.

10. A fastener for a surgical device for osteosynthesis, in particular for a device as recited in claim 1, the fastener (3.1...3.4) being pin-like and having a head (31.1...31.4) and a shank (30.1...30.4), the head (31.1...31.4) of the fastener (3.1...3.4) being provided with a structuring for enabling a positive fit between the fastener (3.1...3.4) and a fixation element (2), in particular a bone plate, by application of a bonding agent (32.1...32.4) being liquefiable by heat.

1 1. A heating device (4) for a surgical device as recited in claim 6, comprising a heatable tip section (240; 440; 750; 760; 770; 810; 820), a diameter of the tip section (240; 440; 750; 760; 770; 810; 820) being less than an inside diameter of the duct (233.1 ; 433; 733) of the shank (230.1 ; 430; 730) of the fastener (203.1 ; 403; 703).

12. The heating device as recited in claim 1 1, whereas the heatable tip is provided with a heat-conductive insert (742) and whereas an axial length of the insert (742) is small compared to an axial length of the duct (733), in particular amounts to a third of the axial length of the duct (733) or less.

13. The heating device as recited in claim 1 1, whereas the heatable tip section (750; 760; 770) is at least partially convered by a thermally insulating sleeve (753; 763; 773), an outer diameter of the insulating sleeve (753; 763; 773) approximating an inner diameter of the duct (733).

14. The heating device as recited in claim 13, whereas the insulating sleeve (773; 783) is movable in respect of the heatable tip section (770, 781 ).

15. The heating device as recited in claim 1 1, whereas the heatable tip (810) has a shape that expands towards the free end of the tip (810).

16. A method for affixing a fixation element, in particular a bone plate, to a bone, comprising the steps of

a) guiding a pin-like fastener through a through hole being provided in the fixation element; and

b) inserting the fastener into the bone,

whereas

c) a first bonding agent being liquefiable by heat is heated at least during the insertion of the fastener into the bone in such a way that the first bonding agent is applied in a region between an inner surface of the through hole and an outer surface of a head of the fastener.

17. The method as recited in claim 16, whereas a second bonding agent being liquefiable by heat is heated at least during the insertion of the fastener into the bone in such a way that the second bonding agent is applied in a region between an outer surface of a shank of the fastener and the bone.

18. The method as recited in claim 17, whereas the second bonding agent is held in an axial duct being provided in the shank of the fastener and whereas the second bonding agent is heated by at least partially introducing a heatable tip section of a heating tool into the duct.

19. A method for removing a fixation element, in particular a bone plate, from a bone, whereas the fixation element is affixed to the bone by a a pin-like fastener which extends through a through hole being provided in the fixation element and into the bone and whereas a first bonding agent is applied in a region between an inner surface of the through hole and an outer surface of a head of the fastener, comprising the step of heating the first bonding agent by directly contacting the fixation element and/or the first bonding agent by a heatable element of a heating tool.