ELASTIC ELEMENT FOR THE USE IN A STABILIZATION DEVICE FOR BONES AND VERTEBRAE AND METHOD FOR THE MANUFACTURE OF SUCH ELASTIC ELEMENT
A stabilization device for bones or vertebrae comprises a substantially cylindrical elastic element. The elastic element has a first end and a second end opposite to the first end. An elastic section extends between the first end and the second end. The elastic section includes at least first and second helical coils. The first and second helical coils are arranged coaxially so that the first helical coil extends at least in a portion between the second helical coil. The elastic element may form, for example, a portion of a rod, bone anchoring element, or plate.
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The present invention claims the benefit of the filing date under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/563,241, filed Apr. 16, 2004, which is hereby incorporated by reference. The present application also claims foreign priority benefits pursuant to 35 U.S.C. §119(a-d) for German Patent Application Number 10 2004 018 621.9, filed Apr. 16, 2004 in Germany.
BACKGROUNDThe present invention relates to an elastic element for use in a bone anchoring element, a connecting element, a rod, and a stabilization device and a method for manufacturing the same.
It is known to use fixation and stabilization devices to fix fractures and stabilize spinal columns. These fixation and stabilization devices commonly comprise at least two bone anchoring elements or bone screws. Each of the bone anchoring elements is anchored in a bone or vertebra and is connected by a rigid plate or a rod. These types of fixation and stabilization devices generally do not allow any movement of the bones or vertebrae relative to each other.
In some instances, however, it is desirable to stabilize the bones or vertebrae so that the bones or vertebrae can carry out limited, controlled motion relative to each other. This is known as dynamic stabilization. Dynamic stabilization devices commonly comprise an elastic element instead of a rigid plate or rod that connects each of the bone anchoring elements.
One example of a dynamic stabilization device for vertebra is disclosed in United States Patent Application Publication No. 2003/0109880 A1. The dynamic stabilization device comprises first and second screws that are each anchored in a vertebra. Each of the screws has a receiving member for insertion of a spring which thereby connects the screws. The spring is provided in the form of a helical spring having closely neighboring coils like a tension spring. The spring is fixed in the receiving members by clamping screws. In this arrangement, however, because the spring is flexible, the spring can evade the pressure of the clamping screw and therefore become unfixed from the bone screw. Furthermore, both the elasticity and the flexural strength of the spring depend on the length of the spring. Thus, in applications requiring a spring with a short length, the elasticity and flexural strength of the spring is relatively small.
Another example of a dynamic stabilization device for a joint such as a wrist or knee joint is disclosed in U.S. Pat. No. 6,162,223. The dynamic stabilization device comprises a rod having a proximal rod section and a distal rod section connected to bone pins. The proximal rod section and the distal rod section are connected to each other by a flexible spring. The proximal rod section, the distal rod section, and the flexible spring are arranged outside of the body. The proximal rod section and the distal rod section are not fixedly connected to the flexible spring, but can move freely along a bore therein. In this arrangement, the flexible spring must be formed to have a diameter larger than a diameter of the rod. Additionally, the flexible spring must be large in order to have a high flexural strength. This dynamic stabilization device therefore has a complicated and voluminous structure, which prevents the dynamic stabilization device from being used inside the body on spinal columns.
BRIEF SUMMARYThe invention relates to an elastic element for use in a stabilization device for bones or vertebrae. The elastic element comprises a substantially cylindrical member having a first end, a second end opposite to the first end, and an elastic section between the first end and the second end. The elastic section includes at least first and second helical coils. The first and second helical coils are arranged coaxially so that the first helical coil extends at least in a portion between the second helical coil.
The invention further relates to a stabilization device for bones or vertebrae comprising a substantially cylindrical elastic element. The elastic element has a first end and a second end opposite to the first end. At least one of the first and second ends has threads. An elastic section extends between the first end and the second end. The elastic section includes at least first and second helical coils. The first and second helical coils are arranged coaxially so that the first helical coil extends at least in a portion between the second helical coil.
The invention still further relates to a method of manufacturing an elastic element for a stabilization device for bones or vertebrae. The method includes providing a substantially cylindrical body and forming first and second helical recess in the cylindrical body from an outside so that the first helical recesses are formed at least in a portion between the second helical recesses.
Various embodiments of the invention are illustrated in
First and second internal threads 5, 5′ are formed at the first and second ends 9, 9′, respectively, of the elastic element 1. The first and second internal threads 5, 5′ extend over a predetermined length in an axial direction. The lira and second internal threads 5, 5′ do not overlap or extend into the first and second helical recesses 3, 4 formed in the outer wall. The elastic element 1 has an outer diameter, which is selected according to the desired use thereof. The length L of the first and second helical recesses 3, 4 in the direction of the central axis M of the cylindrical member, the height H of the first and second recesses 3, 4, the angle a of the helices along which the first and second helical recesses 3, 4 are formed, and the diameter D1 of the coaxial bore 2 is selected to provide a desired stiffness to the elastic element 1 with respect to axial forces Fax, bending forces FB and torsional forces FT acting on the elastic element 1.
As shown in
In order to obtain optimal elastic properties in an elastic element (not shown) with a single helical spring (not shown) having a predetermined length, the angle of the helices of the single helical spring (not shown) must be formed to have at least one whole turn. In the double helical spring 6 shown in
An elastic element according to a fourth embodiment is shown in
The elastic element according to the fifth embodiment differs from the elastic element 30 according to the fourth embodiment in that the inner diameter D1 of the continuous coaxial bore 42 is not constant but varies of the length L′ of the elastic element 40. The inner diameter D1 of the bore 42 varies in such away that it decreases from the free ends towards the middle of the elastic element 40. Accordingly, the final stiffness of the elastic element 40 varies and increases with decreasing inner diameter D1. By varying the inner diameter of the coaxial bore, the stiffness of the elastic element 40 can be varied at different positions.
Similar to the fourth embodiment the elastic element 40 includes a section with an inner thread 41, 41′ having a predetermined length adjacent to each of its free end, respectively.
In
The elastic element 35 according to the sixth embodiment differs from that of the fifth embodiment in that the outer diameter D2 of the elastic element 35 is not constant but varies over the length L′ of the elastic element 35. The outer diameter D2 varies in such a way that it increases from the free ends towards the middle of the elastic element 35. Accordingly, the bending stiffness of the elastic element 35 varies and increases with increasing outer diameter. Therefore, a position with a desired bending stiffness can be obtained by adjusting the outer diameter of the elastic element.
Similar to the fourth embodiment the elastic element 35 has adjacent to its free ends a section with an inner thread 36, 36′ of a predetermined length, respectively, and a continuous coaxial bore 37 with an inner diameter D1. Recesses 38 and 39 to form the double helical coil are formed like in the other embodiments.
In the fourth to sixth embodiments of the instant invention, the bending stiffness of the elastic element increases from the free ends towards the middle of the elastic element. However, by appropriate selection of the pitch a of the recesses, the outer diameter D2 of the elastic element and the inner diameter D1 of the coaxial bore, the bending stiffness can be adjusted to have a desired stiffness at a particular position along the length L, L′ of the double helical coil of the elastic element.
As shown in
A pressure element 73 that is provided for fixation of the head 63 in the receiving member 66 has a concave recess 74 on a side facing the head 63. The concave recess 74 has a radius substantially identical to a radius of the head 63. The pressure element 73 has an outer diameter selected so that the pressure element 73 can be inserted into the receiving member 66 and can slide towards the head 63. The pressure element 73 has a coaxial pressure element bore 75 for providing access to a tool receiving recess (not shown) in the head 63.
During assembly, the cylindrical projection (not shown) of the shaft 62 is screwed into the internal threads 5 of the elastic element 1 and the cylindrical projection (not shown) of the cylindrical section 65 of the head 63 is screwed into the internal threads 5′ of the elastic element 1 to form the screw 61. The shaft 62 of the screw 61 is then inserted into the second end of the receiving member 66 and guided through the second receiving member bore 68 until the head 63 abuts the edge of the first receiving member bore 67. The pressure element 73 is inserted into the second receiving member bore 68 so that the concave recess 74 is positioned adjacent to the head 63. The screw 61 is screwed into a bone (not shown) or vertebra (not shown). The rod 72 is inserted into the receiving member 66 and is arranged between the first and second legs 70, 70′. The angular position of the screw 61 relative to the receiving member 66 is then adjusted and fixed with the securing element 71.
Because the screw 61 is formed with the elastic element 1, the screw 61 may be diverted from the angular position by a limited extent. Additionally, if the elastic element 1 protrudes at least partially above a surface of the bone (not shown), the elastic element 1 can absorb compression forces, extension forces, bending forces and torsional forces because of the elastic properties of the elastic element 1. If the elastic element 1 does not at least partially protrude above the surface of the bone (not shown), the screw 61 can still slightly yield, when the bone (not shown) or vertebra (not shown) moves such that the occurrence of unfavorable stress is avoided.
During assembly, the cylindrical projection (not shown) of the shaft 86 is screwed into the internal threads 5 of the elastic element 1 and the cylindrical projection (not shown) of the receiving member 81 is screwed into the internal threads 5′ of the elastic element 1 to form the monoaxial screw 80. The monoaxial screw 80 is screwed into a bone (not shown) or vertebra (not shown). The U-shaped recess 83 is aligned and the rod 82 is inserted into the receiving member 81 and is arranged between the first and second legs 84, 84″. The rod 82 is then fixed by the securing member 85.
Modifications of the rod 50, the polyaxial bone screw 60, the monoaxial screw 80, and the connecting element 90, shown in
A method of manufacturing the elastic element 1 by wire electrical discharge machining (EDM) is shown in
As shown in
As shown in
As shown in
Alternatively, the elastic element 1 may be milled. A first helical recess is milled along a first helix of a central axis of a solid cylinder formed of a bio-compatible material, such as titanium, having a predetermined outer diameter. The first helical recess is formed collinear with the central axis of the cylinder by a side mill. A second helical recess is milled along a second helix of the central axis such that coils of the second helical recess run between coils of the first helix. A bore is formed along the central axis of the cylinder over the whole length of the cylinder so that the first and second helical recesses communicate with the bore. The first and second helical recesses have first and second run-outs, respectively. The first and second run-outs of the first and second helical recesses at a transition between the first and second helices and end sections of the cylinder have a large influence on the stability of the elastic element 1. The first and second run-outs of the first and second helixes at both of the end sections are reworked by an end mill so that Sharp edges on an internal surface of the bore are removed. The first and second run-outs are milled by the end mill at an angle that is tangential relative to a helical line. The part is then chamfered on an inside and on an outside. Internal threads are then formed along the central axis in the end sections of the bore adjacent to first and second ends of the cylinder.
Further alternative methods for manufacturing the elastic element 1 are, for example, laser milling or hydro milling. These methods are performed similar to the wire EDM method, but instead of simultaneously forming the first and second helical recesses by a wire, a laser beam or a water beam is used. Additionally, instead of forming at least one of the internal threads, a cylindrical projection with external threads may be formed at a beginning of any one of the manufacturing methods by a lathe. In this instance, the bore has a diameter smaller than a diameter of the cylindrical projection. The spring element 1 may also be formed without the bore.
The embodiments described above and shown herein are illustrative and not restrictive. The scope of the invention is indicated by the claims, including all equivalents, rather than by the foregoing description and attached drawings. The invention may be embodied in other specific forms without departing from the spirit and scope of the invention.
Claims
1-25. (canceled)
26. A bone anchoring element for bones or vertebrae, comprising:
- a shaft with a free end;
- a receiving portion opposite to the free end along a longitudinal axis of the shaft, the receiving portion having a U-shaped recess opening in a direction away from the free end of the shaft and forming two legs for accommodation of a rod therebetween; and
- a locking element configured to secure to the receiving portion to lock the rod in the U-shaped recess;
- wherein a first section of the shaft has a first end and a second end spaced apart along the longitudinal axis, the first section being cylindrical and having an exterior surface that is entirely threadless from the first end to the second end and an interior surface defining a coaxial bore extending from the first end of the first section to a portion of the shaft between the second end of the first section and the free end of the shaft; and
- wherein the first section of the shaft further defines at least two recesses each extending through a wall of the first section and forming an opening on the exterior surface of the first section, wherein the exterior surface of the first section completely separates the respective openings of the at least two recesses from one another along an entire length of the cylindrical section from the first end to the second end.
27. The bone anchoring element of claim 26, wherein the shaft further comprises a second section having an exterior surface that is threaded.
28. The bone anchoring element of claim 26, wherein the first section of the shaft comprises first and second helical coil segments arranged coaxially around the coaxial bore and separated from one another in a circumferential direction by the at least two recesses.
29. The bone anchoring element of claim 28, wherein the first and second helical coils are substantially identical to one another.
30. The bone anchoring element of claim 28, wherein each of the first and second helical coils extends along an entire length of the cylindrical section from the first end to the second end.
31. The bone anchoring element of claim 28, wherein the first helical coil is rotated approximately 180 degrees with respect to the second helical coil.
32. The bone anchoring element of claim 28, wherein the first and second helical coils each has a pitch, and wherein the pitches of the first and second helical coils are identical.
33. The bone anchoring element of claim 26, wherein the first section of the shaft is elastic.
34. The bone anchoring element of claim 26, wherein the bone anchoring element comprises a bio-compatible material.
35. The bone anchoring element of claim 26, wherein at least one of the first end and the second end of the first section of the shaft is provided with internal threads.
36. The bone anchoring element of claim 26, wherein at least one of the first end and the second end of the first section of the shaft is provided with a cylindrical projection having an external thread.
37. The bone anchoring element of claim 26, wherein the each of the recesses extends in a radial direction relative to the longitudinal axis through the wall of the first section of the shaft.
38. The bone anchoring element of claim 26, wherein the shaft and the head are monoaxially connected.
39. The bone anchoring element of claim 26, wherein the shaft has a spherical segment-shaped head at an end of the shaft opposite the free end, and wherein the receiving portion is a separate part which is provided with a seat for pivotably holding the head.
40. The bone anchoring element of claim 39, further comprising a pressure element configured to lock the head against the seat.
41. The bone anchoring element of claim 26, wherein the coaxial bore extends partially through the shaft and ends at the portion of the shaft between the second end of the first section and the free end of the shaft.
Type: Application
Filed: Mar 2, 2015
Publication Date: Aug 27, 2015
Applicant:
Inventors: Lutz Biedermann (VS-Villingen), Jürgen Harms (Karlsruhe), Wilfried Matthis (Weisweil)
Application Number: 14/635,633