DEFORMABLE BODY AND COMBINATION OF SUCH DEFORMABLE BODY AND A SURGICAL SCREW ELEMENT

Abstract

The present invention provides a deformable body (2), wherein the deformable body comprises a force application surface (12) opposite a bone contact surface (52) to be pressed against periosteum of a bone surface (52) of a bone such that the bone contact surface adapts its shape to the shape of the bone surface, wherein the deformable body comprises one or more through-going openings (3) and/or one or more fixation locations (34) arranged to receive a fixation element such as as screw (20), and wherein the deformable body comprises an anaesthetic that is released from or through the bone contact surface. The anaesthetic can be bupivicaine, liposome bupivacaine, lidocaine or levobupivacaine. The anaestethic can be arranged in one or more compartments (6, 7) which have ifferent release rates. The screw can comprise a detent or rim to mate with the deformable body. A sleeve (80) can be arranged in the opening (3) to receive the screw. A pusher element (81) can push the deformable body from the sleeve into position on the screw.

Claims

1. A deformable body, wherein the deformable body comprises a bone contact surface to be pressed against periosteum of a bone surface of a bone such that the bone contact surface adapts its shape to the shape of the bone surface, wherein the deformable body comprises one or more through-going openings and/or one or more fixation locations arranged to receive a fixation element, and wherein the deformable body comprises an anaesthetic that is released from or through the bone contact surface.

2. The deformable body of claim 1, wherein the deformable body is a ring shaped body having an opening being one of the one or more through-going openings and through which a shank of a surgical screw element can be placed, wherein the bone contact surface is to be pressed against bone surface by screwing of the screw element in a bone while the deformable body is placed on the shank of the screw element.

3. The deformable body of claim 1 or 2, wherein the bone contact surface is pervious for the anaesthetic to be released.

4. The deformable body of any of the preceding claims, wherein the anaesthetic is arranged in a compartment delimited by the bone contact surface and a further compartment wall, wherein the further compartment wall is a substantially non-pervious wall for the anaesthetic such that the anaesthetic will mainly be released through the bone contact surface.

5. The deformable body of any of the claims 1-3, wherein the anaesthetic is arranged in a compartment delimited by the bone contact surface and a further compartment wall, wherein the bone contact surface has a first release rate for the anaesthetic to be released and wherein the further compartment wall has a second release rate for the anaesthetic to be released, wherein the first release rate is larger than the second release rate.

6. The deformable body of claim 4 or 5, wherein the further compartment wall is an outer wall of the deformable body.

7. The deformable body of any of the preceding claims, wherein the deformable body comprises a second compartment at least partially delimited by a release surface, wherein the second compartment comprises a second pharmaceutical or biological compound, and wherein the release surface is pervious for the second pharmaceutical or biological compound.

8. The deformable body of claim 7, wherein the second pharmaceutical or biological compound comprises an antibiotic, an analgesic, a bone growth stimulating agent, stem cells and/or a chemotherapeutic agent.

9. The deformable body of any of the claims 1-8, wherein the deformable body comprises one or more deformation indicators that indicate a deformation of the deformable body.

10. The deformable body of any of the claims 1-9, wherein the one or more deformation indicators comprise one or more markers that are arranged to move upon deformation of the deformable body.

11. The deformable body of any of the claims 1-10, wherein the anaesthetic is only or mainly released from or through the bone contact surface.

12. The deformable body of any of the claims 1-11, wherein the anaesthetic comprises bupivacaine, liposome bupivacaine, lidocaine and/or levobupivacaine.

13. The deformable body of any of the preceding claims, wherein the deformable body comprises one or more indicators indicating a location of the bone contact surface.

14. The deformable body of any of the preceding claims, wherein the deformable body is made of a visco-elastic material, a degradable felt material, a sponge-like material, a gelatin material, a gel, in particular a hydrogel, a polymer or any combination thereof.

15. The deformable body of any of the preceding claims, wherein the deformable body comprises a force application surface to apply a force on the deformable body, wherein the bone contact surface is arranged at a first side of the deformable body and the force application surface is arranged at a second side of the deformable body, wherein the first side and the second side are opposite sides of the deformable body.

16. A combination of the deformable body of any of the preceding claims and a surgical screw element having a shank, wherein the deformable body is arranged on the shank of the surgical screw element.

17. The combination of claim 16, wherein the shank comprises a circumferential rim or circumferential detention that mates with the deformable body to hold deformable body on the shank.

18. The combination of claim 16 or 17, wherein the screw element is a pedicle screw for spinal treatment.

19. A kit comprising: the deformable body of any of the claims 1-15 having an opening a sleeve, wherein the sleeve can be arranged in the opening and wherein the sleeve comprises a channel to receive a shank of a surgical screw element, and wherein the wherein the sleeve is arranged to be slid over the shank of a screw element to position the deformable body on a desired position on the shank.

20. The kit of claim 19, wherein the kit further comprises a pusher element to push the deformable body from the sleeve.

21. Bupivicaine, liposome bupivacaine, lidocaine or levobupivacaine for use in a method of treating pain, in particular pain caused by placing a surgical screw element through periosteum of a bone of a patient, wherein the bupivacaine, liposome bupivacaine, lidocaine or levobupivacaine is administered by the deformable body of any of the preceding claims.

Description

[0080] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0081] FIG. 1 shows a top view of a ring-shaped element according to an embodiment of the invention;

[0082] FIG. 2 shows a cross-section A-A of the ring-shaped element of FIG. 1;

[0083] FIG. 3 shows a combination of a screw element and the ring-shaped element of FIG. 1 arranged on the shank of the screw element;

[0084] FIG. 4 shows the combination of FIG. 3 screwed into a bone of a patient;

[0085] FIG. 5 shows an example of a release profile of the ring-shaped element of FIG. 1;

[0086] FIG. 6 shows a first alternative embodiment of a ring-shaped element according to the invention;

[0087] FIGS. 7 and 8 show a second alternative embodiment of a ring-shaped element according to the invention; and

[0088] FIG. 9 shows a third alternative embodiment of a ring-shaped element according to the invention in combination with a specifically designed screw element;

[0089] FIG. 10 shows an alternative embodiment of a deformable body according to the invention;

[0090] FIG. 11 shows a cross-section B-B of the deformable body of FIG. 10;

[0091] FIG. 12 shows a cross-section of a plate in combination with ring shaped elements according to an embodiment of the invention;

[0092] FIG. 13 shows a cross-section of a fourth alternative embodiment of a ring-shaped element according to the invention;

[0093] FIG. 14 shows a cross-section of a fifth alternative embodiment of a ring-shaped element according to the invention;

[0094] FIGS. 15a, 15b and 15c show a method to arrange a ring-shaped element on a shank of a screw element as shown in FIG. 3; and

[0095] FIG. 16 shows a further combination of a screw element and a ring-shaped element according to an embodiment of the invention.

[0096] FIG. 1 shows a top view of a deformable body according to an embodiment of the invention in the form of a ring-shaped element, generally denoted by reference numeral 1. The ring-shaped element 1 comprises a deformable ring body 2 having a central opening 3. The ring-shaped element 1 is designed to be placed on a shank of a surgical screw element, for example a pedicle screw of a spinal fixation system.

[0097] The ring body 2 is made of a deformable biocompatible material, for example gelatin material. The ring-shaped element 1 is preferably bio-absorbable.

[0098] FIG. 2 shows a cross-section A-A of the ring-shaped element 1. The outer surface wall of the ring-shaped element 1 is formed by a bone contact surface 4 and a compartment wall 5. The bone contact surface 4 and the compartment wall 5 delimit a compartment 6. The compartment 6, basically formed by the ring body 2 contains bupivacaine. The bone contact surface 4 is provided to be pressed on the periosteum of a bone to be treated. The bone contact surface 4 has, after implantation, a first release rate for the anaesthetic to be released and the compartment wall 5 has a second release rate for the anaesthetic to be released. The first release rate is substantially larger than the second release rate, for example at least 2, preferably at least 10 times the second release rate. As a result, the bupivacaine will be released from the compartment 6 mainly through the bone contact surface 4 according to a desired release profile over time.

[0099] The bone contact surface 4 to be pressed on the periosteum of a bone is arranged at a first side of the ring-shaped element. At a second side of the ring-shaped element 1, opposite to the first side, a force application surface 12 is provided. The force application surface 12 is arranged to apply a force on the ring-shaped element 12 to press the ring-shaped element 12 on the periosteum.

[0100] FIG. 3 shows a combination of a surgical screw element 20 and the ring-shaped element 1 of FIG. 1 mounted on a shank 21 of the screw element 20. The shank 21 comprises a screw thread 22 to screw the screw element 20 into bore provided in a bone of a patient. The screw element 20 further comprises a proximal part 23 having a screw head 24 integral with the shank 21 and a separate connector part 25. It is remarked that the screw element 20 is a standard screw element, i.e. not specifically adapted for use in combination with the ring-shaped element 1. The screw element 20 is for example a screw element of the spinal fixation system disclosed in US 2010/031228.

[0101] The diameter of the central opening 3 of the ring-shaped element 1 substantially corresponds to the diameter of the shank 21, such that the shank 21 can be moved through the ring-shaped element 1 to the position shown in FIG. 3. In this position of the ring-shaped element 1, the ring-shaped element 1 cannot be moved further in the proximal direction of the shank 21 as the proximal part 23 of the screw element 20 prevents such movement, since the diameter of the proximal part 23 is substantially larger than the diameter of the central opening 3.

[0102] The outer diameter of the ring-shaped element 1 may, for example, be in the range of 1 mm to 40 mm, preferably in the range of 5 mm to 25 mm. The diameter of the central opening 3 may for example be in the range 0.25 mm to 20 mm, preferably in the range of 2 mm to 15 mm.

[0103] FIG. 4 shows the combination of the surgical screw element 20 and the ring-shaped element 1 after it has been screwed into a bore 50 provided in a bone 51 of a patient to be treated. The bone 51 is for example a pedicle of a spine of a patient.

[0104] It can be seen that the ring-shaped element 1 is squeezed between the proximal part 23 of the screw element 20 and bone surface 52 of the bone 51. As a result of this squeezing, the ring body 2 is deformed resulting in an intimate contact between the bone contact surface 4 and the bone surface 52. Due to this intimate contact, the bupivacaine that is released from the compartment 6 through the bone contact surface 4 (as indicated by arrows) will be directly administered to the periosteum which is damaged due to the introduction of the screw element 20. Thus, the ring-shaped element 1 allows to directly administer locally a pharmaceutical compound, in particular bupivacaine to relief the pain that the patient experiences due to the damage of the periosteum. Since the compartment wall 5 of the ring-shaped element 1 has a relatively low permeability for the bupivacaine, the bupivacaine will mainly be released through the bone contact surface which is in direct contact with the bone to be treated. This allows for a very specific local delivery of the bupivacaine, which is generally desirable. Also, since the bupivacaine is released directly at this specific location, no or little bupivacaine will be spilled in tissue in the surrounding area, i.e. in areas where no pain relief is desired. This allows for administration of a more precise amount of bupivacaine during a predetermined timeperiod and at the desired location and also prevents side effects of the release of bupivacaine.

[0105] The deformability of the ring body 2 is designed such that the shape of the bone contact surface 4 adapts to the bone surface 52 on which it is pressed. This means that the bone contact surface 4 will follow irregularities of the bone surface. In practice, the consistency and deformability of the ring body 2 may be similar to a wine gum.

[0106] The bone contact surface 4 of the ring-shaped element 1 shown in FIGS. 1-4 is relatively flat and therefore in particular suitable for bone surfaces that are mainly flat. Generally, it is possible to adapt the shape of the deformable body and its bone contact surface 4 to other typical shapes of skeletal bones and implants at the location where screw elements are introduced into the bone in accordance with typical surgical procedures including, but not limited to, (plate—) fixation of: long bones, the pelvis, ribs, the shoulder girdle, large joints of the hip and knee and ankle, elbow, wrist, hand and foot, dental implants and cranial/maxillar/mandibular osteosynthesis instrumentations.

[0107] The bupivacaine is released according to a desired release profile over time.

[0108] FIG. 5 shows an example of such release profile. In FIG. 5, the horizontal axis indicates time T in hours and the vertical axis indicates the amount of bupivacaine R that is released from the ring-shaped element 1 through the bone contact surface 4.

[0109] Directly after implantation of the screw element 20 a high level of pain is experienced by a patient in which the screw element is placed 20. To counteract this pain a peak of bupivacaine release is realized as quickly as possible in the first twelve hours after implantation. Thereafter, the bupivacaine release is maintained at a desired level until approximately 48-72 hours after implantation. Thereafter, the bupivacaine release may slowly decrease to zero.

[0110] Any other desirable release profile may also be designed using bupivacaine or another anaesthetic or combination of anaesthetics.

[0111] FIG. 6 shows a first alternative embodiment of a ring-shaped element 1 according to the invention. In the ring-shaped element 1 of FIG. 6 a first compartment 6 containing bupivacaine and a second compartment 7 containing a second pharmaceutical compound, for example antibiotics, are provided. The first compartment 6 and the second compartment 7 are separated from each other by a separation wall 8.

[0112] The first compartment 6 is partly delimited by the bone contact surface 4 that will be pressed during use against a bone surface 52 to be treated. The bone contact surface has a relatively high permeability for bupivacaine. The other walls delimiting the first compartment 6 have a relatively low permeability for bupivacaine, i.e. do not allow bupivacaine to pass the respective walls, or only allow a relatively low quantity of bupivacaine to pass the respective walls.

[0113] The second compartment is partly delimited by a release surface 9 having a relatively high permeability for the second pharmaceutical compound. The other walls delimiting the second compartment 6 have a relatively low permeability for the second pharmaceutical compound, i.e. do not allow the second pharmaceutical compound contained in the second compartment 7 to pass through these other walls, or only allow a relatively low quantity of the second pharmaceutical compound to pass through these other walls.

[0114] The release surface 9 will typically not be pressed against the bone surface 52, when the ring-shaped element 1 is squeezed between the bone surface 52 and the proximal part 23 of the screw element 20. As a result, the second pharmaceutical compound will be released at a location spaced from the bone surface 52, and the second pharmaceutical compound will be more distributed over the area in which the screw element is placed. The second compartment 7 of the ring-shaped element 1 may therefore typically be used to create such locally more distributed release of a pharmaceutical compound, for example antibiotics.

[0115] FIG. 7 shows a second alternative embodiment of a ring-shaped element 1. The ring-shaped element 1 of FIG. 7 comprises four deformation indicators, in the form of four markers 10 that indicate a degree of deformation of the ring-shaped element 1. The four markers 10 are arranged on a top surface of the ring-shaped element 1 distributed over the circumference of the ring-shaped element 1. When seen in longitudinal direction of a screw element 20 arranged through the ring-shaped element 1 the four markers are concealed behind the proximal part 23 (shown in dashed line) of the screw element 20.

[0116] To obtain an intimate contact between the bone contact surface 4 and the bone surface 52, the ring body 2 is deformed to adapt the shape of the bone contact surface 4 to the bone surface 52 on which it is placed.

[0117] The markers 10 are each arranged at a respective location that moves radially outwards when the ring body 2 is deformed due to squeezing between the bone surface 52 and the proximal part 23 of the screw element 20. As a result of this radially outwards movement of the markers 10 when the ring body is deformed, the markers 10 are no longer concealed by the proximal part 23 of the screw element 20 as shown in FIG. 7.

[0118] Since the four markers 10 are visible in the deformed state of the ring-shaped element 1 shown in FIG. 7, it can be concluded that, in this deformed state, the ring body 2 has been sufficiently deformed to create an intimate contact between the bone contact surface 4 of the ring-shaped element 1 and the bone surface 52. As such the markers 10 are suitable deformation indicators that advantageously can be used to confirm sufficient deformation of the ring body during placement of a screw element 20 in a bone of a patient.

[0119] FIG. 9 shows a third alternative embodiment of a combination of a ring-shaped element 1 and a surgical screw element 20. The surgical screw element 20 comprises a shank 21 and a proximal part 23 formed by screw head 24. The ring-shaped element 1 is arranged on the shank 21 of the surgical screw element 20.

[0120] The screw element 20 and the ring-shaped element 1 are specifically designed to be used in combination. The shank 21 comprises a circumferential rim 26 that is configured to hold the ring-shaped element 1 on the shank 21. The diameter of the central opening 3 of the ring-shaped element 1 is adapted to the diameter of the shank 21 and the height of the inner wall of the ring-shaped element 1 is adapted to the distance between the proximal part 23 and the circumferential rim 23.

[0121] The ring-shaped element 1 comprises a relatively small top area and a large bottom area. The top area is configured to substantially correspond with the distal surface area of the proximal part 23 so that, when the ring-shaped element 1 is squeezed between the proximal part 23 and the bone surface 52, the complete top area of the ring-shaped element 1 is pressed downwards by the proximal part 23.

[0122] The relatively large bottom area comprises the bone contact surface 4 which may therefore also be relatively large. This has the advantage that there is a relatively large surface that can be brought into contact with the bone surface 52 and through which an anaesthetic can be released to the bone surface 52.

[0123] FIG. 10 shows an alternative embodiment of a deformable body 30 according to the invention. FIG. 11 shows a cross-section B-B of the deformable body 30 of FIG. 10. The deformable body 30 comprises a bone contact surface 31 to be pressed against a bone surface of a bone, a circumferential side wall 32 and a top wall 33 opposite to the bone contact surface 31. The deformable body 30 contains an anaesthetic. The bone contact surface 31 is pervious for the anaesthetic such that, after implantation, the anaesthetic may be released through the bone contact surface 31. The circumferential side wall 32 and the top wall 33 of the deformable body 30 are not pervious for the anaesthetic such that the anaesthetic will be mainly, preferably only released through the bone contact surface 31.

[0124] The anaesthetic is arranged in the deformable body in a form that it will be released according to a predetermined controlled release profile.

[0125] The deformable body 30 is provided with four fixation locations 34 each comprising two aligned recesses 35 at opposite sides of the deformable body such that a thin part 36 is formed between each set of two recesses 35. The thin parts 36 may be pierced, for example by screw elements or separate piercing element to create through-going openings through the recesses 35. Each of these through-going openings may be used to accommodate the shank of a respective screw element to press the deformable body 30 against a bone surface. The screw elements may for example also be used to press a plate on the deformable body 30 in order to press the deformable body 30 against a bone surface. The plate may advantageously be provided with a pattern of through-going openings corresponding to the pattern of fixation locations of the deformable body 30. The plate may be provided with a lip, rim, or clip to hold the deformable body on the plate to facilitate placement of plate and deformable body 30.

[0126] It is remarked that the through-going openings created by piercing the thin parts 36 may also be used to arrange alternative fixation elements therethrough, such as wires or bands with which the bone contact surface 31 can be pressed against the bone surface in order to adapt the shape of the bone contact surface 31 to the shape of the bone surface on which the deformable body 30 is pressed. It will be clear for the man skilled in the art that many modifications may be made to adapt the deformable body, the ring-shaped element and/or the screw element to specific circumstances of the location where the deformable body and/or the combination of screw element and ring-shaped element is applied.

[0127] FIG. 12 shows a cross section of a plate element 60 with two ring-shaped elements 1 used in combination with the plate element 60. When the ring-shaped elements 1 are used in combination with the plate element 60, the ring-shaped elements 1 cannot be pre-arranged on the shank of the respective screw elements with which the plate element 60 will be mounted on a bone, since the ring-shaped elements 1 cannot be moved through the plate openings 61 provided in the plate element 60. Furthermore, it may be difficult to align a ring-shaped element 1 between the plate element 60 and an outer bone surface of a bone on which the plate element 60 is mounted once the plate element 60 is arranged in its intended location, for example when one screw element is screwed into a bone.

[0128] Therefore clips 62 are provided that hold the ring-shaped elements 1 aligned with the plate openings 61 and connected with the plate element 60, such that the ring-shaped elements 1 in combination with the plate element 60 may be arranged on a bone surface on which the plate element 60 may be mounted. The clips 62 will ensure that the ring-shaped elements 1 will remain aligned with the plate openings 61.

[0129] When a screw element 20 is arranged in the openings, the clips 62 are no longer required since the screw element 20 will keep the respective ring-shaped element 1 at the desired location, and the clips 62 may, when desired, be removed.

[0130] The clips 62 may be designed such that the clips 62 can be removed by pulling the clips 62 out of the plate openings 61 when the screw elements 20 are placed in the plate openings 61. The clips 62 may also be made of a material than can be broken or flexed by the screw element 20 such that the clips 62 do not prevent or hinder the placement of the screw element 20 through the plate openings 61 and the ring-shaped elements 1. It is also possible that the clips 62 are not removed, for example when the clips do not prevent placement of the screw element 20 and/or when the clips 62 are made of bio absorbable material.

[0131] In alternative embodiments, other means or devices may be provided to connect the ring-shaped elements 1 to the plate element 60 in an aligned position with respect to the plate openings 61. For example, the ring-shaped elements 1 may be glued to the plate element 60, or other features such as rims or bumps, matching the diameter of holes in a plate, may be provided to at least temporarily connect the ring-shaped elements 1 to the plate element 60. The ring-shaped element may also be held by clips or other elements that are not arranged in plate openings through which the fixation elements are placed but at other locations, such as other openings or an edge of the plate.

[0132] FIG. 13 shows a fourth alternative embodiment of a ring-shaped element according to the invention. The ring-shaped element 1 of FIG. 13 comprises an outer shell 70 that functions as the further compartment wall which is less pervious for the anaesthetic in the deformable body compared to the perviousness of the bone contact surface. The outer shell provides both mechanical robustness and directional release, i.e. release of the anaesthetic at the bone contact surface 4.

[0133] The shell 70 can be constructed from the same material as the anaesthetic containing interior of the deformable body, with altered mechanical and chemical properties, for example comprising more dense crosslinking or by an alternative method of crosslinking that results in a more stiff and non-pervious material. Alternatively, the shell 70 can be constructed from a different material, for example a polymer material. The polymer material is for example a synthetic polymer such as polylactic-co-glycolic acid (PLGA), polycaprolactone (PCL) or polyvinyl alcohol (PVA), or a biopolymer such as hyaluronic acid, chitosan, alginate, collagen or gelatin. These polymers can be functionalized with a variety of chemical groups to precisely modulate their characteristics.

[0134] The shell 70 provides a robust housing for the anaesthetic containing interior of the deformable body and can bear most of the mechanical strain/loads during insertion. As the permeability and porosity of the shell 70 can be adjusted, the release of the anaesthetic can be directed towards the desired location, typically the bone contact surface. This bone contact surface, with which the deformable body is placed on periosteum and bone, is not covered with the external shell 70 to provide an opportunity for diffusion of the drug and degradation of the inner part of the device.

[0135] In an alternative embodiment, the bone contact surface may be covered with the shell 70 but this part of the shell 70 has an increased porosity and permeability for the anaesthetic compared to the other parts of the external shell 70. This can be for example be achieved with macroscopic or microscopic pores. To control the ratio between anaesthetic diffusion towards the bone contact surface of the deformable body and diffusion towards the compartment wall, the porosity of the part of the shell that encapsulates the non-bone contact surfaces of the device can be adjusted via either micro- or macroscopic pores or other means of altering permeability.

[0136] The shell 70 is constructed to be flexible to adapt its shape to the bone contour on which it is implanted. The shell 70 may be biodegradable, with the degradation time ideally being similar or slightly surpassing the degradation time of the inner, drug-containing part of the device.

[0137] FIG. 14 shows an embodiment of a ring-shaped element 1 for percutaneous placement of a screw element 20 into a bone. To facilitate safe placement of deformable body and screw element 20 through the skin of a patient, the shape of the outer surface of the ring-shaped element 1 is conical wherein the diameter of the outer surface in proximal direction, i.e. away from the bone contact surface 4, increases.

[0138] Further, the maximal diameter of the ring-shaped element 1 is substantially the same as the diameter of the screw head 24. The maximum diameter of the ring-shaped element 1 may also be smaller than the diameter of the screw head 24.

[0139] The advantage of the conically increasing diameter of the outer surface of the ring-shaped element 1 and that the maximal diameter of the ring-shaped element 1 substantially corresponds with the diameter of the screw head 24 is that the ring-shaped element 1 may relatively easily be pushed through skin and underlying soft tissue until it is pressed against the periosteum of the bone in which the screw element 20 is placed. Thereby, there is less risk of damaging the ring-shaped element 1.

[0140] To protect the material of the ring-shaped element 1, the material of the deformable body may, at least partially, for example the outer surface, be made relatively strong.

[0141] FIGS. 15a, 15b and 15c show a method to mount a ring-shaped element 1 on a shank 21 of a screw element 20. The method provides a relatively easy and reliable manner to arrange the ring-shaped element 1 on a screw element 20. The method may also protect the relatively soft material of the ring-shaped element 1, and does not require direct manual contact with the hands of a person handling the ring shaped-element 1.

[0142] In FIG. 15a, the ring-shaped element 1 is shown before being mounted on the shank 21 of the screw element 20. The ring-shaped element 1 is arranged on one end of a sleeve 80. The sleeve 80 may be made of relatively strong material that is not easily damaged by the screw thread 22. The ring-shaped element 1 may be arranged during production on the sleeve 80 or this may be done just for mounting of the ring-shaped element 1 on the screw element 20. When the ring-shaped element 1 is arranged on the sleeve 80, the sleeve will also facilitate placement of the ring-shaped element 1 in the correct orientation on the screw element 20, i.e. with the bone contact surface 4 facing the distal end of the screw element 20.

[0143] On the sleeve 80, a pusher element 81 is arranged. The pusher element 81 is provided to push, as explained hereinafter, the ring-shaped element 1 from the sleeve 80. The pusher element 81 can slide over the outer surface of the sleeve 80.

[0144] In FIG. 15b, the screw element 20 is moved into the sleeve 80, as indicated by arrow 82. The ring-shaped element 1 is now properly aligned with the location where the ring-shaped element 1 should be arranged on the shank 21 of the screw element 20. Since the shank 21 and its screw thread 22 are moved through the interior of the sleeve 80, the ring-shaped element 1, which is arranged on the outer surface of the sleeve 80 cannot be damaged by the screw thread.

[0145] From the position in FIG. 15b, the sleeve 80 can be pulled from the shank 21 of the screw element 20, while the ring-shaped element 1 is held in its relative position with respect to the screw element 20, for example by pushing the pusher element 81 against the ring-shaped element 1. As a result, the pusher element 81 will push the ring-shaped element 1 from the sleeve into the position shown in FIG. 15c. Once the ring-shaped element 1 is arranged in its desired position with respect to the shank 21 of the screw element 20, as shown in FIG. 15c, the sleeve 80 and the pusher element 81 may be removed from the shank 21.

[0146] The sleeve 80 shown in FIGS. 15a, 15b and 15c is a stiff sleeve. In an alternative embodiment, the sleeve may be more flexible.

[0147] Before use, the ring-shaped element 1 and the sleeve 80 may be connected to each other, for example by a tear line or cut line that is torn or cut after the ring-shaped element 1 is arranged at the desired location on the shank 21 of the screw element 20. The tear line or cut line may be provided between the ring-shaped element 1 and the sleeve 80, or in the sleeve 80 itself.

[0148] In another embodiment of the ring-shaped element, the inner surface of the ring-shaped element, i.e. the surface facing towards the longitudinal axis may be provided with a layer of relatively strong material, such as for example shown in FIG. 14, to protect the ring-shaped element 1 when it is moved over the shank 21 of the screw element 20.

[0149] FIG. 16 shows an embodiment of a ring-shaped element 1 in combination with a screw element 20. The screw element 20 comprises a conical shank part 27 having a conical outer surface 28 mating with a conical inner surface 11 of the ring-shaped element 1. The angle of conical outer surface 28 and the conical inner surface with respect to the longitudinal axis of the screw element 20 and the ring-shaped element 1 are substantially the same. When the screw element 20 is screwed into a bone and the bone contact surface will be pushed against the periosteum of the bone, the ring will not only be pressed in axial direction but also in radial direction. This may have the advantage that the ring-shaped element 1 may be applied over a larger insertion range of the screw element 20 without exerting a too large, radially-directed, force on the material of the ring-shaped element 1.