JP4980664B2 - Bone fixation device - Google Patents

Description

  The present invention relates to a bone anchoring device, the bone anchoring device having a shank fixed to the bone, a head portion having an outer surface with a spherical segment-shaped portion, a receiving portion for receiving the head portion, The shank and the head part are separate parts.

  This type of bone anchoring device is known from US Pat. No. 6,835,196B2. The shank of the fixing element has a cylindrical end, which is received by a corresponding bore in the head, which has a spring-like edge, and when pressure is applied to the head, said end of the shank Tighten the part. In another embodiment, the end of the shank has an external thread that cooperates with an internal thread in the bore of the head that receives the end. In this bone anchoring device, the shank can be screwed first, the length of the shank can be adjusted if necessary, and then the shank can be connected to the receiving part including the head part.

  U.S. Patent No. 6,074,391 discloses a bone fixation device including a bone screw having a threaded shank with a spherical portion that forms the free end of the shank. The bone anchoring device further includes a receptacle having a conical annular surface on the inside that converges downward. A slotted cage provided to the receiver has a conical outer surface surrounding the spherical portion and cooperating with the conical surface of the receiver. The cage slot allows the bulbous portion of the shank to be clamped when pressure is applied to the cage.

  WO 94/00066 discloses an osteosynthesis device, which has a conical head portion and an adjacent fixation component designed to be fixed to the bone, and a conical shape. A slotted spherical segment clamping component with a conical bore that receives the head portion includes a clamping component that clamps within a connection component having a spherical segment shaped bore. The clamping component has an outer surface with a spherical segment shaped portion. Locking of the fixed component inside the connecting component is accomplished by retracting the conical head portion into the clamping component so that the clamping component expands and is pressed against the spherical segment shaped bore of the connecting component. The

US Pat. No. 6,063,090 discloses a device for connecting rods using pedicle screws, according to which a screw element with a spherical head is first screwed into the bone and then held in connection with the rod The head portion can be fitted into the spherical head portion. In order to fix the angular position of the screw element relative to the holding head, the spherical head is clamped by a conical spring chuck.
US Pat. No. 6,835,196B2 US Pat. No. 6,074,391 US Pat. No. 6,063,090

  It is an object of the present invention to provide a bone fixation device of the type having a head portion and a shank as separate parts, which facilitates pre-assembly of the device, and further allows the screw to eventually become a rod. Strengthen the fixing when tightening.

  This object is solved by a bone anchoring device according to claim 1. Further developments are given in the dependent claims.

  The bone anchoring element according to the invention has the advantage that different sized shanks can be combined with separate heads and receivers according to the needs in specific situations during or before surgery.

  With the bone anchoring element according to the invention, the shank can first be secured to the bone and then a receiving part comprising a spherical segment head can be attached to the shank. Because the concavity of the end of the shank and the cooperating recess of the head is conical, pre-fixing of the head to the shank is achieved even when the head is not yet locked in its final multi-axial position.

  In order to ensure that the head part cannot be detached or unintentionally separated from the shank when the cone angle of the shank end and the recess of the head part is in a certain range of 2 ° to 10 °, It is possible to achieve an automatic locking connection between the shaped head and the shank.

  The bone anchoring device further has the advantage of being compact because no external ring or nut is required.

  Further features and advantages of the invention will become apparent from the description of the embodiments with reference to the attached figures.

  As shown in FIGS. 1 to 3, the bone anchoring device has a substantially cylindrical receiving part 1 having a first end 2 and a second end 3 opposite to the first end. including. The two ends are orthogonal to the longitudinal axis 4. A coaxial bore 5 is provided coaxially with the longitudinal axis 4, and the coaxial bore 5 extends from the first end 2 to a predetermined distance from the second end 3. An opening 6 is provided at the second end 3, the diameter of which is smaller than the diameter of the bore 5. The coaxial bore 5 is tapered toward the opening 6. In the embodiment shown, the bore 5 is tapered in the shape of the spherical portion 7.

  The receiving part 1 further has a U-shaped recess 8 starting from the first end 2 and extending in the direction of the second end 3 from the second end 3 to a predetermined distance. Two free legs 9, 10 ending towards the first end 2 are formed by the U-shaped recess. Adjacent to the first end 2, the receiving part 1 includes female threads 11 at the legs 9, 10.

  The bone anchoring element 13 includes a shank 14 with bone screws and a head portion 15 formed as a separate piece and connected to the shank in the assembled state shown in FIG. The head portion 15 has a spherical segment-shaped outer surface portion 16. The radius of this portion of the head portion 15 is such that when the receiving portion 1 receives the head portion 15, the spherical outer surface 16 of the head portion 15 is supported by the spherical portion 7 adjacent to the opening 6 of the second end 3 or the opening. The radius is such that the portion 15 a of the head portion 15 protrudes from the opening 6, supported by the edge of the portion 6. When pressure is not yet applied to the head portion 15, the head portion 15 is rotatably held in the spherical region 7 like the ball joint.

Furthermore, by providing a pressure element 17 having a cylindrical structure with an outer diameter slightly smaller than the inner diameter of the bore 5, the pressure element can be introduced into the bore 5 of the receiving part 1 and moved axially. It is. The pressure element 17 includes a spherical recess 18 on the lower side facing the second end 3, the radius of which corresponds to the radius of the spherical part 16 of the head 15. The pressure element 17 has a U-shaped recess 19 extending across the longitudinal axis 4 on the opposite side. The diameter of the side of this U-shaped recess is selected so that the rod 20 received by the receiving part can be inserted into the recess 19 and guided laterally there. The depth of the spherical recess 19 is selected such that, in the assembled state, the pressure element 17 exerts pressure on the head portion 15 when the rod is inserted into and pressed against the bottom of the U-shaped recess.

  The bone anchoring device further includes an internal screw 21 that can be screwed between the legs 9, 10 to fix the rod 20 and exert pressure on the head 15 via the pressure element 17. The cooperating screw of the female screw 11 and the inner screw 21 can have any known screw shape. However, flat screws or negative square screws have the advantage that the use of external nuts or rings is not required since the legs 9, 10 do not open in a fan shape.

  Details of the shank 14 and head portion 15 will now be described. The shank 14 includes an end 22 that is received by the head portion 15. The end 22 has a truncated cone shape and becomes wider toward the free end 23 having a diameter ds. The cone angle α of the conical end 22 of the shank is preferably selected so that an automatic locking connection can be achieved when the shank is connected to the head. As shown in particular in FIGS. 2 and 3, the head portion 15 has a flattened spherical profile and includes a bore 24 at the end facing towards the first end 2, the bore 24 being received by the bore 24. Which is coaxial with the longitudinal axis 4 of the part and whose diameter is slightly larger than the maximum diameter ds of the free end 23 of the conical end 22. The bore 24 can be guided through the outer end 23 of the conical end 22 such that the conical end 22 protrudes from the head portion 15 when fully inserted as shown in FIG. The head portion 15 includes a recess 25 formed as a hollow truncated cone on the side facing the second end 3 of the receiving portion, the dimensions of which are defined by the shank cone when the shank is inserted into the head portion 15. It matches with the dimension of the shape end 22. The angle α ′ of the conical recess 25 preferably corresponds to the angle α of the end 22 or is larger than the angle α. The diameter db of the lower opening 26 formed by the recess 25 is smaller than the maximum diameter ds of the free end 23 of the conical end 22 of the shank.

  As shown in FIGS. 2 and 3, the head portion 15 has a plurality of longitudinal slits 27, which are open at the end facing the shank end 22 and are arranged at equal distances in the outer circumferential direction. The size of the slit 27 is such that the lower opening 26 widens to allow the conical end 22 to be inserted, and the recess 25 widens to such an extent that the end can be elastically clamped after insertion. It is big enough to be able to do it.

  As shown in FIG. 4, the free end 23 of the conical end can have a chamfer 28 to facilitate insertion into the head portion 15. The chamfer 28 can be bent to pair with the curvature of the recess 18 of the pressure element 17. The conical recess 25 can also extend over the entire head portion 15.

  Preferably, the cone angle α of the recess 25 of the head portion 15 corresponds to the cone angle of the end portion 22 and achieves an automatic locking connection when the conical end portion 22 is inserted into the recess 25 of the head portion. Selected. Once the automatic lock connection is established, removing the conical end from the recess 25 requires an additional force greater than that required to insert the conical end into the recess 25. The cone angle that achieves the self-locking effect is preferably between about 2 ° and 10 °, more preferably about 4 °.

In the first operating mode, a suitable shank 14 is selected and its end 22 connects to the head 15. The chamfer 28 facilitates the introduction of the conical end 22 into the head through the lower opening 26. By inserting the end portion 22, the lower opening 26 is widened, and the conical recess 25 is widened by the slit 27, so that the entire conical end portion 22 can be introduced. If the angle α is selected so that an automatic lock connection is established when the shank is introduced into the head, once the shank is inserted into the head, the head is removed or unintentionally removed It is not possible.

  Next, a bone anchoring element 13 consisting of a shank 14 to which a head part 15 is attached is introduced into the receiving part 1 from the first end 2 and the threaded shank 14 passes through the opening 6 of the receiving part. The head portion 15 is guided until it is arranged with respect to the edge portion of the opening 6. The pressure element 17 is then introduced and the threaded shank is screwed into the bone. The angular position of the receiving part 1 with respect to the fixing element 13 is then adjusted and the rod 20 is inserted. Next, the rod is fixed by screwing the inner screw 21. The inner screw 21 applies pressure to the rod 20 and pushes down the pressure element 17. The pressure element 17 forms an abutment of the shank end 22 against the free end 23. In this manner, the head portion 15 is pressed against the spherical region 7 or the edge of the opening 6 so that the edge of the opening 6 is slit by a slit 27 for clamping the end 22 of the shank. Squeeze. Furthermore, the pressure element 17 pushes the free end 23 of the end 22 and pushes the conical end 22 into the conical recess 25 of the head part, so that a strong connection is achieved between the head part and the shank. At the same time, the head portion is locked at its rotational position.

  The part of the bone anchoring device described above is preferably made of a biocompatible material such as titanium.

  In the second mode of operation, the threaded shank 14 is first screwed into the bone or spine. For this purpose, as shown in FIG. 1, the shank 14 has known engagement possibilities for screwdrivers, such as a hexagonal recess 30 at its free end. The receiving part 1 is then pressed against the conical end 22 of the shank 14 protruding from the bone, with the head part 15 and the pressure element 17 assembled loosely beforehand. In order to achieve this, some pressure is required to fit the head part 15 into the conical end, i.e. the head part 15 is widened by the slit and clamped to the conical end 22. The pressing force required to put the head part into the shank depends on the cone angle and / or the elasticity provided by the slit. In this state, the head part is still rotatable in the receiving part, while the shank is clamped by the head part. Next, the rod 20 is inserted, and the angular position of the receiving portion 1 with respect to the head portion 15 is adjusted. Thereafter, the inner screw 21 is screwed between the leg portions 9 and 10 until it presses the rod 20, thereby exerting pressure on the head portion 15. Due to the pressure exerted on the head part 15 by the pressure element, the slotted head part 15 is firmly connected or clamped to the shank 14 to prevent movement and at the same time the head part 15 is fixed in its rotational position.

  If necessary, the receiving part 1 together with the head part 15 can be separated from the shank in situ using the tools shown in FIGS. 8a to 8d and FIG. First, as shown in FIG. 8a, the internal screw and rod are removed. In this state, the head portion 15 is unlocked in the receiving portion 1, but the end portion 22 of the shank is clamped. Next, as shown in FIG. 8 b, the tool 100 is used to push the head portion 15 into the receiving portion 1 so that the head portion 15 no longer protrudes from the lower opening 6 of the receiving portion.

  Tool 100 includes a longitudinal bar 101 from which two arms 102 and 103 extend in a perpendicular direction. One of the arms is fixed at a distance from the free end 104 of the bar 101 so that the bar portion 105 protrudes over the arm 103 and can be easily grasped. In the embodiment shown, it is the upper arm 103 when the tool is in use. The other arm 102 is slidably attached to the longitudinal bar 101 and can be varied in the direction toward the upper arm 103 between the end position of the other end 106 and the desired position to change the distance between the arms. Can be fixed. At least the lower arm 102 is fork-shaped so that it can surround the shank 14. When the lower arm 102 is located at the end 106 of the bar, the distance between the arms is greater than the height of the receiving part 1.

  As shown in FIG. 8b, in use, the tool is applied to the receiving portion with the lower arm 102 in the end position. The lower arm 102 is then moved and pressed against the second end 3 of the receiving part 1, so that the receiving part 1 is moved to the head until the head part 15 is completely within the receiving part as shown in FIG. 8c. Move relative to section 15. In this state, there is a space that can expand in the head portion. Therefore, as shown in FIG. 8D, when the tool is pulled away from the shank together with the receiving portion and the head portion, the end portion 22 of the shank can be pulled out.

  Variations are possible. For example, instead of the lower arm, the upper arm 103 can be slidable. The slidable arm does not have to be fixed to the bar and can be manually pressed against the receiving part.

  The dimensions of the end 22, the head 15 and the receiving part 1 are selected such that the force necessary to overcome the frictional force of the automatic locking connection between the end 22 and the head 15 is maintained during the operation. The

  FIGS. 5 a to 5 c show a deformation of the shank 14. In FIG. 5 a, the diameter d of the shank 14 is smaller than the minimum diameter of the conical portion 22. In FIG. 5 b, the diameter d of the shank 14 is larger than the minimum diameter of the conical end 22. In FIG. 5 c, the shank includes a threaded portion 140 adjacent to the tip 141 and a portion 142 without bone screws. In all variants, the conical end 22 is shaped to be received in the recess 25 of the head portion 15.

  FIG. 6 shows a schematic view of the deformation of the head part. The head portion 15 'has a recess 25 formed as a truncated cone as in the embodiment shown in FIGS. However, the diameter of the coaxial bore 24 'is smaller than the diameter of the conical end 23 of the shank. Accordingly, the upper wall of the recess 25 forms an annular contact portion 28 with respect to the end portion 22. The diameter of the bore 24 ′ is large enough to allow the screwing tool to access the end 22. The head portion has an engaging means for engaging with a tool for holding the head portion so that the head portion 15 can be separated from the shank 14 in the original position together with the receiving portion 1. When pulled away from the shank, the head portion cannot be pulled against the opening 6. FIG. 7 shows an example of the tool 30, which is composed of a handle 31 and a bar 32 extending from the handle and having a threaded end 33. In this case, the bore 24 ′ includes an internal thread for engagement with the threaded end 33. In use, after removal of the internal screw 21 and rod, and thus after release of pressure on the head portion 15, the head portion is held by the tool 30 by screwing the threaded tip 33 into the threaded bore 24 'and simultaneously received. The part is manually pulled away from the shank. Thus, the end 22 of the shank is pulled out from the head portion 15. The present invention is not limited to the embodiments described above. Further variations are possible. For example, the present invention is not limited to a fixing element having a threaded shank, but can also be applied to a fixing element composed of a hook. In this case, the free end of the hook has a conical end 22.

  Furthermore, the shape and diameter of the shank 14 can be varied, and the length of the bone screw can also be varied. For example, the variant of FIG. 5c, in which the shank has an unthreaded part, can also be applied to the shank shown in FIG. 5a or 5b.

  The conical angle of the conical end 22 and the hollow frustoconical recess 25 can be selected to have no automatic locking effect. In this case, the number and shape of the slits 26 in the head portion 15 must be selected so that the head portion 15 can be fastened to the conical end 22.

Instead of several slits in the head part 15, it is possible to have only one slit, which extends longitudinally through the entire wall of the head part. Furthermore, it is possible to have one slit that continues in this way in addition to the slits shown in FIG. Additional slits may be provided that open toward the end opposite the lower opening 26. Furthermore, a recess 25 formed as a hollow truncated cone extends through the entire head part 15, so that the bore 24 or 24 'can be omitted.

  In other variations, the head portion is formed of a material that provides elasticity, such as a suitable plastic material. In this case, the slit may be omitted.

  The receiving part can also be deformed. As long as the opening 6 is sufficiently small so that the head portion 15 cannot be removed, the radius of the spherical portion 7 may be larger than the radius of the head portion. Instead of the spherical part 7, a part with another shape, for example a conical shape, is possible.

  Furthermore, the pressure element 17 may have a different shape. The longitudinal length of the pressure element may be so great that the leg produced by the U-shaped recess 19 projects above the rod when the rod is inserted. In this case, it is possible to individually fix the head portion 15 via the pressure element in a state where the internal nut is screwed between the leg portions 9 and 10, and to fix the rod individually by the internal screw screwed into the nut. It is.

  The receptacle can be part of a bone plate. In this case, the receiving part does not have a U-shaped recess, and the pressure to the head part 15 can be generated by, for example, an internal screw alone.

1 shows a cross section of a bone anchoring device according to one embodiment of the invention. FIG. FIG. 2 shows an exploded view of the bone anchoring device according to FIG. 1. FIG. 2 shows a perspective view of the head part of a bone anchoring element which is part of the bone anchoring device according to FIG. 1. FIG. 4 shows a schematic cross section of the head part at the end of the shank of the bone anchoring element of FIGS. 1 to 3. It is a figure which shows the deformation | transformation of the shank of a fixing element. It is a figure which shows the deformation | transformation of the shank of a fixing element. It is a figure which shows the deformation | transformation of the shank of a fixing element. It is a figure which shows the schematic cross section of a deformation | transformation of the head part connected to the shank. It is a figure which shows the schematic side surface of the tool used with the head part of FIG. It is a figure which shows schematically the step which removes the head part and receiving part by FIGS. 1-4 from a tool in the original position using a tool. It is a figure which shows schematically the step which removes the head part and receiving part by FIGS. 1-4 from a tool in the original position using a tool. It is a figure which shows schematically the step which removes the head part and receiving part by FIGS. 1-4 from a tool in the original position using a tool. It is a figure which shows schematically the step which removes the head part and receiving part by FIGS. 1-4 from a tool in the original position using a tool. FIG. 9 shows a bottom view of the tool used in the steps according to FIGS. 8a to 8d.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reception part, 1st edge part, 2nd edge part, 4 Longitudinal axis, 5 Coaxial bore, 7 Spherical part, 8 U-shaped recessed part, 14 Shank, 15 Head part, 16 Segment-shaped part, 17 Pressure Element, 22 end, 23 free end.

Claims (9)

A bone anchoring device,
A bone anchoring element comprising a shank (14) and a head portion (15) secured to a bone or spine, the head portion having an outer surface with a spherical segment shaped portion (16), said shank (14) and said head Part (15) is an individual part;
A first end (2), a second end (3) opposite the first end, a longitudinal axis (4) passing through the two ends, a bore (5) coaxial with the longitudinal axis, and A receiving portion (1) including a first region (7) adjacent to a second end (3) for receiving a spherical segment-shaped portion (16) of the head portion;
An inner screw (21) that can be screwed between the legs (9, 10) to secure the rod (20);
Pressure elements (17, 20, 21) are provided to exert pressure on the head part (15) in order to lock the head part to the receiving part, the pressure element being connected to the receiving part. A cylindrical structure having an outer diameter smaller than the inner diameter of the bore (5) so that it can be introduced into the bore and moved axially, the cylindrical axis of the pressure element being connected to the longitudinal axis (4) of the receiving part Coaxial ,
The head portion has a hollow inner portion (25) for receiving the free end portion (22) of the shank, the end portion of the head portion and the end portion being positioned while the head portion is not locked. The end (22) is conically shaped and its diameter increases towards the free end (23) of the end, the hollow interior part (25) is a bone anchoring device having a paired shape . The bone anchoring device according to claim 1 , wherein the conical shape is a truncated cone. The bone anchoring device according to claim 1 or 2 , wherein the cone angle is selected such that an automatic lock occurs between the head portion and the end portion. 4. The bone fixation device of claim 3 , wherein the angle is about 2 ° to 10 °. Head portion (15) comprises a spring-like pliable edges facing towards the end of the shank (22), the bone fixation apparatus according to any one of claims 1 to 4. The head portion (15) includes one or more slits (27) that are oriented substantially parallel to the axis of rotation of the head portion and open on the side facing the end (22) of the shank (14). The bone anchoring device according to any one of claims 1 to 5 . Hollow interior portion of the head portion for receiving an end portion of the shank forms an abutment (28) to the free end of the end portion (22) (23), the bone according to any one of claims 1 to 6 Fixing device. The bone fixation device according to any one of claims 1 to 6 , wherein the hollow inner portion is formed as a hollow truncated cone extending from one end of the head portion to the opposite end. The receiving part (1) has a U-shaped recess (8) extending in the direction from the first end (2) to the second end (3) forming a channel for receiving the rod. The bone anchoring device according to any one of claims 1 to 8 .

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