Modular articular spacer system

Abstract

A modular articulated spacer system provides for screw-based assembly of an articular spacer intended to replace an artificial joint temporarily, whereby the articulated spacer system comprises at least two modules connectable by means of a screw connection, whereby a first module of the articular spacer system comprises a surface for formation of a sliding surface of the joint of the articular spacer and a second module of the articular spacer system comprises a stem for connection to a bone. The modules are connectable by means of the screw connection comprising at last one screw-locking device for each screw connection, whereby the screw-locking device is connected to one of the modules or is provided in the form of the same part as one of the modules. A method builds-up an articular spacer using said articulated spacer system, in which the articular spacer is screwed together using at least two modules, whereby the modules are screwed together appropriately such that the screw-locking devices prevent the modules from detaching or being unscrewed.

Claims

1. A modular articular spacer system for screw-based assembly of an articular spacer for replacing an artificial joint temporarily, wherein the articular spacer system comprises at least two modules that are connectable by means of at least one screw connection, whereby a first module of the articular spacer system comprises a first core fully covered by an outer layer of the first module except at a first connecting surface of the first module, wherein the first core is exposed at the first connecting surface of the first module, whereby the first module further comprises a curved sliding surface of the joint of the articular spacer, whereby a second module of the articular spacer system comprises a second core fully covered by an outer layer of the second module except at a second connecting surface of the second module, wherein the second core is exposed at the second connecting surface of the second module, whereby the second module further comprises a stem for connection to a bone, wherein the first and second modules are directly connectable by means of the at least one screw connection that comprises at least one screw-locking device for each screw connection, wherein the at least one screw-locking device comprises a first part provided at the first connecting surface of the first module and a second part provided at the second connecting surface of the second module, wherein, if the first and second modules are directly connected, the first connecting surface of the first module is facing towards the second connecting surface of the second module, wherein a majority of the outer layer of the first module consists of the curved sliding surface that terminates at the first part of the at least one screw-locking device, wherein the curved sliding surface has a bulbous shape that (i) is formed by continuous and uninterrupted curved surfaces that extend along the majority of the outer layer of the first module and (ii) terminates at the first connecting surface of the first module comprising the first part of the at least one screw-locking device, wherein the first and second parts of the at least one screw-locking device are provided for each screw connection, wherein the first part of the at least one screw-locking device is fixedly connected to the first core at the first connecting surface of the first module and the second part of the at least one screw-locking device is fixedly connected to the second core at the second connecting surface of the second module, wherein the first and second parts engage each other when the at least two modules are screwed together such that any detachment of the screw connection is resisted or prevented.

2. The articular spacer system according to claim 1, wherein the screw connection comprises an internal thread and an external thread that matches the internal thread, and, on ends facing each other in the connected condition, the first and second modules are connectable to each other by means of the screw connection, wherein the internal thread and the external thread of the screw connection are configured such that the screw connection is a part of the first and second modules.

3. The articular spacer system according to claim 2, wherein the at least one screw-locking device is provided at an end of the external thread or at a start of the internal thread on one of the first and second modules that are connectable to each other, or the at least one screw-locking device is provided at the end of the external thread or at the start of the internal thread on both of the first and second modules that are connectable to each other.

4. The articular spacer system according to claim 3, wherein each of the first core of the first module and the second core of the second module is a metal core, wherein each metal core projects from one end of the first and second modules, which face each other, wherein one metal core forms the external thread, wherein a hole with the internal thread is provided in the other metal core such that, when the first and second modules are connectable to each other, the external thread and the internal thread form the at least one screw connection.

5. The articular spacer system according to claim 1, wherein the at least one screw-locking device is two tooth lock washers or a multiplicity of lockable wedges.

6. The articular spacer system according to claim 5 wherein the lockable wedges are provided and are inclined against a direction of rotation of elements of the at least one screw connection and a height of the lockable wedges is larger than a pitch of threads of the elements of the at least one screw connection.

7. The articular spacer system according to claim 1, wherein the at least one screw connection consists of a bio-compatible material.

8. The articular spacer system according to claim 1, wherein spacers are provided between the first and second modules in the form of tooth lock washers with teeth on both sides or wedge locks with lockable wedges on both sides.

9. The articular spacer system according to claim 1, wherein outer layers of the first and second modules are formed by a plastic material, wherein at least one of an anti-infective agent and an antiseptic agent is or are at least one of suspended and dissolved in the plastic material, wherein threads of the at least one screw connection are not formed by the plastic material.

10. The articular spacer system according to claim 1, wherein the articulated spacer system comprises a multitude of different modules having a same function and different external shapes such that the articulated spacer system is adapted to assemble a multitude of different articular spacers.

11. The articulate spacer system according to claim 1, wherein the articular spacer system provides an articular spacer as a temporary place-holder for an artificial joint.

12. The articular spacer system according to claim 4, wherein the at least one screw-locking device is formed by both of the first and second cores of the first and second modules.

13. The articular spacer system according to claim 8, wherein the spacers consist of a metal having a lower Vickers hardness than the at least one screw connection.

14. The articular spacer system according to claim 9, wherein the plastic material is a polymethylmethacrylate bone cement.

15. The articulate spacer system according to claim 1, wherein the bulbous-shaped curved sliding surface has a total length defined between the first part of the at least one screw-locking device and a tip region located opposite with respect to the first part of the at least one screw-locking device, wherein the diameter of the bulbous-shaped curved sliding surface continuously changes along the total length of the bulbous-shaped curved sliding surface.

16. A modular articular spacer system for screw-based assembly of an articular spacer for replacing an artificial joint temporarily, whereby the articular spacer system comprises at least two modules that are directly connectable by means of a screw connection, whereby a first module of the articular spacer system comprises an outer layer fully covering the first module except at a first connecting surface of the first module, whereby the first module further comprises a curved sliding surface of the joint of the articular spacer, whereby a second module of the articular spacer system comprises an outer layer fully covering the second module except at a second connecting surface of the second module, whereby the second module further comprises a stem for connection to a bone, wherein the first and second modules are directly connectable by means of the screw connection comprising at least one screw-locking device for each screw connection, wherein the at least one screw-locking device comprises wedges that are concentric and arranged about at least one of a rod and a hole with a twelve-fold rotational symmetry axis with respect to the symmetry axis of the rod and hole, wherein a majority of the outer layer of the first module consists of the curved sliding surface that terminates at a first part of the at least one screw-locking device at the first connecting surface of the first module, wherein the curved sliding surface has a bulbous shape that (i) is formed by a continuous and uninterrupted curved surfaces that extend along the majority of the outer layer of the first module and (ii) terminates at the wedges of the at least one screw-locking device, wherein the first and second parts of the at least one screw-locking device are provided for each screw connection, whereby the first part of the at least one screw-locking device is fixedly connected to a first core exposed at the connecting surface of the first module and the second part of the at least one screw-locking device is fixedly connected to a second core exposed at the connecting surface of the second module, wherein the first and second parts engage each other when the at least two modules are screwed together such that any detachment of the screw connection is resisted or prevented.

17. A modular articular spacer system for screw-based assembly of an articular spacer for replacing an artificial joint temporarily, wherein the articular spacer system comprises a first module, a second module and at least one third module that are connectable together by means of more than one screw connection, whereby the first module comprises a first core fully covered by an outer layer of the first module except at a first connecting surface of the first module, whereby the first module further comprises a curved sliding surface of the joint of the articular spacer, whereby the second module comprises a second core fully covered by an outer layer except at a second connecting surface of the second module, whereby the second module further comprises a stem extending to a distal end of the second module, wherein the second core extends from a proximal end of the second module, located opposite the distal end of the second module, through the stem of the second module to the distal end of the second module, wherein the first, second and third modules are connectable by means of the more than one screw connection that comprises at least one screw-locking device for each screw connection, wherein the at least one screw-locking device comprises a first part provided at the first connecting surface of the first module and a second part provided at the second connecting surface of the second module or an exposed third connecting surface of the third module, wherein, if the first and second modules are connected or the first and third modules are connected, the first connecting surface of the first module is facing towards the second connecting surface of the second module or the exposed third connecting surface of the third module, wherein a majority of the outer layer of the first module consists of the curved sliding surface that terminates at the first part of the at least one screw-locking device at the first connecting surface of the first module, wherein the curved sliding surface has a bulbous shape that (i) is formed by continuous and uninterrupted curved surfaces that extend along the majority of the outer layer of the first module and (ii) terminates at the first connecting surface of the first module comprising the first part of the at least one screw-locking device, wherein the first part of the at least one screw-locking device is fixedly connected to the first core at the first connecting surface of the first module and the second part of the at least one screw-locking device is fixedly connected to the second core at the second connecting surface of the second module or a third core at the exposed third connecting surface of the third module.

18. A method for building-up an articular spacer using the articular spacer system according to claim 1, the method comprising: screwing the articular spacer, according to claim 1, together using at least the first and second modules, which are selected from a multitude of different modules to suit at least one of an anatomy and a treatment situation, wherein the first and second modules are screwed together appropriately such that the at least one screw-locking device prevents the first and second modules from detaching or being unscrewed.

Description

(1) Exemplary embodiments of the invention shall be illustrated in the following on the basis of six schematic figures, though without limiting the scope of the invention. In the figures:

(2) FIG. 1 shows a schematic cross-sectional view of the modules of a two-part hip spacer system according to the invention;

(3) FIG. 2 shows a schematic top view in viewing direction A onto the connection side of the articular head module according to FIG. 1;

(4) FIG. 3 shows a schematic top view in viewing direction B onto the corresponding connection side of the stem module according to FIG. 1;

(5) FIG. 4 shows a schematic cross-sectional view of the modules of a three-part hip spacer system according to the invention;

(6) FIG. 5 shows a schematic side view of a detail of the connection site of two connected modules of an articulated spacer system according to the invention; and

(7) FIG. 6 shows a schematic side view of a detail of the connection site of two connected modules of another articulated spacer system according to the invention.

(8) To some extent, identical or similar components are identified in the figures through the same reference numbers.

(9) FIG. 1 shows a schematic cross-sectional view of the modules of a two-part hip spacer system according to the invention. The hip spacer system consists of an articular head module 1 and a stem module 2 that can be connected to each other by screws. The articular head module 1 consists, on its inside, of a metal core 4 that extends further as threaded rod 5 on the underside (facing downwards and to the left in FIG. 1) that is to be connected to the stem module 2. The threaded rod 5 has an external thread 6. The metal core 4 consists of a medical steel such as, for example, a chromium-cobalt steel.

(10) A part of a wedge lock device 8, in which multiple wedges 8 are arranged on the metal core 4 circumferentially about the connection of the threaded rod 5 to the metal core 4, is situated on the underside of the articular head module 1 and forms the end of the threaded rod 5. Preferably, the wedges 8 are provided as single-parts or in the form of the same part as the metal core 4. Alternatively, the wedge lock device 8 can also be attached by gluing or soldering in said place. The wedges 8 of the wedge lock device 8 comprise one flat side and one vertical wedge surface.

(11) The outside of the articular head module 1, which is to serve as sliding surface of the hip spacer, is fully covered by a plastic layer 10 made of a polymethylmethacrylate bone cement (PMMA bone cement). The PMMA bone cement contains a mixture of two antibiotics as anti-infective agent that can be dissolved from the PMMA bone cement and serves for treatment of an infection. Moreover, using the plastic layer 10 prevents metal parts from abrading and causing problems during the treatment.

(12) The sliding surface, in inserted condition, touches against an acetabulum, which might also be artificial, and assumes the function of the hip joint in this place.

(13) The stem module 2 is intended to be connected to a thigh bone of the patient. The stem module 2 comprises a bore hole matching the threaded rod 5 of the articular had module 1 or a matching cylindrical hole, in which an internal thread 12 matching the external thread 6 is provided. The hole provided with the internal thread 12 is contained in a metal core 14 of the stem module 2. The internal thread 12 and the external thread 6 as well as the hole and the threaded rod 5 form a screw connection by means of which the articular head module 1 can be connected to the stem module 2. In connected condition, the two modules 1, 2 of the hip spacer system form a hip spacer for temporary replacement of an artificial hip.

(14) With the exception of the connecting surface of the stem module 2 to the articular had module 1 (pointing upwards to the right in FIG. 1), the surface of the stem module 2 is fully covered by a plastic layer 16 made of PMMA bone cement. The metal core 14 is exposed at the connecting surface of the stem module 2, from which the hole extends into the metal core 14 as well. The wedges 18 of the second part of the wedge lock device 18 are provided on the surface of the metal core 14 of the connecting surface and form a joint wedge lock device 18 together with the wedges 8 of the articular head module 1. For this purpose, the wedges 18 are arranged about the opening to the hole. The two parts of the wedge lock device 8, 18 engage each other when the articular head module 1 is screwed fully into the stem module 2 and prevent the connection from detaching by means of the vertical wedge surfaces of the wedges 8, 18.

(15) Preferably, the wedges 18 are provided as single-parts or in the form of the same part as the metal core 14. Alternatively, the wedge lock device 18 can also be attached in said location by gluing or soldering. The wedges 18 of the wedge lock device 18 comprise one flat side and one vertical wedge surface, whereby the slopes and the heights of the flat wedge surfaces and vertical wedge surfaces are the same as those of the wedges 8 of the articular head module 1.

(16) As a matter of principle, the wedges 8, 18 form a matching pair of wedge lock washers, whereby the wedge lock washers are firmly connected to the metal cores 4, 14 of the two modules 1, 2 at the base of their threads 6, 12 of the screw connection or preferably are even provided in the form of the same part as the metal cores 4, 14 of the two modules 1, 2 on the basis of their threads 6, 12 of the screw connection.

(17) The stem module 2 is angled at a CCD angle of 142 and thus replicates the shape of a specific thigh bone that is not typical in Europe. Alternatively, a different stem module (not shown) having a different CCD angle can be selected just as well, for example one having the standard angle in Europe of 135. Just as well, instead of the articular head module 1, a different articular head module (not shown) having a different shape and/or size can be selected. For treatment, a multitude of different stem modules and articular head modules are available as sets, but always have the same thread bore holes and threaded rods 5 and thus are always compatible with each other, i.e. can be screwed together. By means of this measure, different shapes of hip spacers can be generated using the hip spacer system. In this context, the screw-locking device 8, 18 formed by the wedge lock device 8, 18 ensures that the two modules 1, 2 can no longer be detached from each other without any need to cement the two parts.

(18) FIG. 2 shows a schematic top view in viewing direction A onto the connection side of the articular head module 1 according to FIG. 1 and FIG. 3 shows a schematic top view in viewing direction B onto the corresponding connection side of the stem module 2 according to FIG. 1. Viewing directions A and B are indicated in FIG. 1 by a schematically depicted eye in order to illustrate the viewing direction.

(19) In FIG. 2, the threaded rod 5 points towards the observer (out of the image plane). The external thread 6 can be seen to be situated on the outside around the threaded rod 5. Analogously, the hole 19 and/or the tapped hole 19 extends vertically from the image plane into the image plane, i.e. away from the observer. The internal thread 12 can be seen on the edge of the hole 19.

(20) The wedges 8, 18 are concentric and are arranged about the threaded rod 5 and/or the tapped hole 19 with a twelve-fold rotational symmetry axis with respect to the symmetry axis of the threaded rod 5 and tapped hole 19. The vertical lines between the wedges 8, 18 of the wedge lock parts 8, 18 correspond to the vertical wedge surfaces of the wedges 8, 18. The surfaces correspond to a view onto the flat wedge surfaces.

(21) The extension on the stem module 2 that extends towards the right in FIG. 3 is the angled stem of the stem module 2. By means of a set of modules 1, 2 that includes stem module 2 and articular head module 1 of different external shapes and dimensions, hip spacers that are adapted to the needs of the treatment situation on hand can be produced easily. Using screw-locking devices 8, 18 according to the invention allows hip spacers screwed together as described to be inserted directly into the patient without any need for additional fixation of the two modules 1, 2.

(22) FIG. 4 shows a schematic cross-sectional view of the modules of a three-part hip spacer system according to the invention. The hip spacer system according to FIG. 4 differs from the one according to FIGS. 1 to 3 in that a third module 20, namely an adapter module 20, is provided in addition to an articular head module 1 and a stem module 2.

(23) The articular head module 1 is designed analogous to the articular head module according to FIGS. 1 and 2. A V4A steel is used presently as the steel for the metal core 4, threaded rod 5, and wedges 8. The sliding surface and the outside, except for the connecting surface to the adapter module 20, are covered by PMMA bone cement containing at least one pharmaceutically active substance.

(24) Unlike the stem module according to FIGS. 1 and 3, the stem module 2 has no CCD angle, since same is defined presently by means of the adapter module 20. The stem module 2 according to FIG. 4 comprises a metal core 14 and wedges 18 of a wedge lock device made of a V4A steel that is covered by a PMMA bone cement on its outside, except for the connecting surface to the adapter module (on the top in FIG. 4). A tapped hole having an internal thread 12 is provided in the metal core 14.

(25) The adapter module 20 has a tapped hole having an internal thread 22 for connection to the articular head module 1. The tapped hole is provided in a metal core 24 made of a V4A steel (for example 1.4401, 1.4404 or 1.4571). The metal cores 4, 14, 24 consist of the same V4A steel.

(26) Except for the connecting surface to the articular head module 1 (towards the top right in FIG. 4) and the connecting surface to the stem module 2 (downwards in FIG. 4), the outside of the adapter module 20 is enveloped by a PMMA bone cement 26. The PMMA bone cement envelopes 10, 16, 26 contain at least one antibiotic and/or at least one antiseptic agent that can be dissolved from the PMMA bone cement envelopes 10, 16, 26 to treat the surrounding human tissue, in patient-inserted condition, for a period of several days or weeks.

(27) Wedges 28 are arranged on the connecting surface to the articular head module 1 in concentric and rotationally symmetrical manner about the tapped hole and match the wedges 8 of the articular head module 1 and form a wedge lock device together with the wedges 8. A threaded rod 15 having an external thread 36 matching the internal thread 12 of the stem module 2 is provided on the connecting surface to the stem module 2. Likewise, wedges 38 matching the wedges 18 of the stem module 2 and forming a second wedge lock device together with these are provided on the connecting surface to the stem module 2.

(28) When the modules 1, 2, 20 are screwed into each other, the wedges 8, 28 and the wedges 18, 38 engage each other and become connected to each other. Due to the form-fit of the wedges 8, 28 and wedges 18, 38, the modules 1, 2, 20 can no longer be unscrewed. The vertical sides (flanks) of the wedges 8, 28 and wedges 18, 38 resist the rotary motion upon detachment of the screw connection, whereas the flat sides of the wedges 8, 28 and wedges 18, 38 can still slide one over the other when the screw connections 8, 18, 28, 38 are being screwed together such that the interlocking is established only upon detachment of the screws.

(29) The side views of the internal threads 12, 22 are shown on the inside of the tapped holes according to FIGS. 1 and 4, i.e. the structures on the inside of the tapped holes are not cross-hatching to depict a sectioned material, but are actually the grooves of the internal threads 12, 22. In the cross-sectional views, the sectioned surfaces of the articulated spacer systems and/or of the modules 1, 2, 20 are always shown by cross-hatching.

(30) FIG. 5 shows a schematic side view of a detail of the connection site of two connected modules 51, 52 of an articulated spacer system according to the invention. The modules 51, 52 each comprise, on the surfaces facing each other, one part of a pair of wedge lock washers 54, 64 that are attached to the modules 51, 52. Each wedge lock washer 54, 64 comprises, on the surfaces facing each other, wedges 58, 68 that engage each other in assembled condition.

(31) One of the wedge lock washers 54, 64 can be supported as in a bearing on one of the modules 51, 52 such that it can rotate, whereby the wedge lock washer 54, 64 either locks when exposed to sufficient pressure due to the screw-based assembly or it is pressed against the module 51, 52 due to the contact pressure after screw-based assembly. As a result, it can be ensured that the wedge lock washers 54, 64 engage each other easily. Rotatability of the one of the wedge lock washers 54, 64 is not necessary, since the elastic deformation of the wedges 58, 68 is sufficient for the wedges 58, 68 to engage each other appropriately such that they can no longer be detached in the opposite direction of rotation.

(32) The steep (perpendicular) flanks of the wedges 58, 68 are oriented against the direction of rotation of the screw connection of the two modules 51, 52 and the pitch of the thread of the screw connection is smaller than the height of the wedges 58, 68 of the wedge lock washers 54, 64. The modules are covered on the outside by a PMMA bone cement 60, 66 containing soluble antibiotics.

(33) As an alternative to the wedge lock devices shown in the embodiments according to FIGS. 1 to 5, other screw-locking devices can be used just as well to prevent modules that have been screwed into each other from detaching. For example, serrated ratchets made of a hard metal can be provided that embed themselves in a softer region at the base of the tapped hole or of the threaded rod and prevent a reverse rotation. A spring-actuated Schnorr safety washer can be connected to one side to the metal core at the base of the threaded rod (for example can be attached by welding). The teeth (and/or wedges) of the spring-actuated Schnorr safety washer can either engage a spring-actuated Schnorr safety washer on the other module to be connected and connect to it or the teeth can be sunk into a softer material of the opposite metal core. Due to the spring properties, the modules can be connected to each other more easily and with less force.

(34) FIG. 6 shows a schematic side view of a detail of the connection site of two connected modules 71, 72 of an articulated spacer system according to the invention, in which oblique elastic metal washers 74 of the type of tooth lock washers are connected to the modules 71, 72 as screw-locking devices. The metal washers 74 are equivalent to the wedges 8, 18, 28, 38, 58, 68 according to FIGS. 1 to 5 and assume the same function, whereby the vertical surfaces are missing in the present case and the oblique flanks are formed by one side of the metal washers 74.

(35) The metal washers 74 are the teeth 74 of the tooth lock washers. As a result, the metal washers 74 can undergo an elastic deformation when they are screwed together (upper module 71 is rotated towards the right, i.e. counter-clockwise, against the lower module 72), whereas the metal washers 74 of the modules 71, 72 engage each other and prevent the modules 71, 72 from detaching when they are unscrewed (upper module 71 rotates towards the left, i.e. clockwise against the lower module 72)).

(36) The metal washers 74 are arranged rotationally symmetrical with respect to a central screw connection (threaded rod and tapped hole, not shown in FIG. 6). The metal washers 74 are welded along their upper edges, at the inclination angles shown, to a metal core 76 of the lower module 71 and are welded at their lower edges to a metal core 78 of the lower module 72 or, preferably, are structured to be the same part as the respective metal cores 76, 78.

(37) Due to their elasticity, the metal washers 74 can be screwed into each other. Upon any attempt to detach the modules 71, 72 through a rotation in the opposite direction, the metal discs 74 engage each other and block the rotation. The modules 71, 72 are then connected to each other in non-detachable manner.

(38) The features of the invention disclosed in the preceding description and in the claims, figures, and exemplary embodiments, can be essential for the implementation of the various embodiments of the invention both alone and in any combination.

LIST OF REFERENCE NUMBERS

(39) 1, 51, 71 Articular head module/first module 2, 52, 72 Stem module/second module 4, 14, 24 Metal core 5, 35 Threaded rod 6, 36 External thread 8, 18, 28, 38 Wedge/wedge lock device 10, 16, 26 Plastic layer 12, 22 Internal thread 19 Hole/tapped hole 20 Adapter module/third module 54, 64 Metal core 58, 68 Interlocking 60, 66 PMMA envelope 74 Metal washer 76, 78 Metal core A Viewing direction of the top view according to FIG. 2 B Viewing direction of the top view according to FIG. 3