The present application relates to a flexible stabilization device for connecting at least two bone anchoring devices which are attached to vertebrae of the spinal column.
Such flexible stabilization devices may generally include a rod which is provided with a considerable degree of stiffness in order to stabilize the spinal column. The bone anchoring devices may include receiving parts, which are provided with recesses to receive the rod, and fixation screws to accomplish a tight connection between the receiving parts and the rod. The receiving parts are further connected with, or integrally formed with bone screws, which may be screwed in to the adjacent vertebrae, e.g., pedicles. Thereby, multiple anchoring devices may be connected using the rod as described above.
In recent years there have been many efforts to provide a connection rod with flexible behaviour. The flexibility allows the spinal column to be moved in a controlled manner.
As an example, WO 1996/016608 A1 shows a vertebral instrumentation rod which is made of a basically rigid material, i.e., a metal or metal alloy. Hence, the rod is rigid in a first part where a cross section is generally cylindrical. However, in a second part, the rod is substantially flat to allow for flexion in a sagittal plane while impeding flexion in the frontal plane. In a transition zone, the degree flatness smoothly increases from the first towards the second part.
US 2005/085815 A1, by Applicant, shows a rod-shaped element wherein a flexible section is integrally formed with two adjacent rigid sections. The rod-shaped element may include a metal material, and the flexible section may be provided by a coil spring allowing for flexion. In one specific embodiment, a cross section of the flexible section, i.e., of the coil spring, is flattened in one direction in achieve desired flexion properties.
US 2007/049937 A1, by Applicant, shows in one embodiment a rod-shaped implant element wherein an flexible section is connected between stiff portions. The flexible section is made from, e.g., polyurethane or polysiloxane, whereas the stiff portions are made from, e.g., titanium. The connection is provided by threads. Further, the flexible section may have a reduced or increased thickness depending on a desired amount of compression or extension capabilities.
US 2007/270821 A1 shows a vertebral stabilizer, which includes a connector formed as a single piece construction. The connector has an annular section of a reduced diameter, as compared with interposed sections, in order to enable stretching of the same. The connector may be formed from flexible fiber material.
US 2003/191470 A1 shows a dynamic fixation system wherein a rod may be shaped and thinned to function as a spring or pivot. The rod may be connected with pedicle screws via connectors while elastomer materials may be used for the rod, although not being preferred. A stepped flattened cross sectional profile may be obtained depending on the desired flexion or torsion characteristics.
Based on the foregoing, there is a need to improve known techniques of stabilizing human vertebrae and to provide a flexible stabilization device that covers desired flexion and torsion characteristics while reducing the efforts and costs of manufacturing the same.
According to one aspect of the invention, a flexible stabilization device includes a flexible rod made of an elastomer material, and a surface of the rod having at least a first recess that is formed by separating material from the rod.
The recess may influence the local bending and/or torsional properties of the rod. In one aspect, the separation may yield a directed removal of material from the rod along a first direction. Hence, the recess formed accordingly may affect the flexural rigidity of the rod in one particular (second) direction, while the original flexural rigidity of the rod may be maintained in another direction, e.g., perpendicular to the first direction.
Therefore, the recess applied to the rod may serve to achieve a reduced flexural rigidity of the rod along an orientation direction according to the specific needs of the concerned spinal column. For example, the overall flexural rigidity of the rod may be reduced at a specific position along the spinal column in order to allow for an improved flexion in, e.g., the frontal or the sagittal plane.
In one specific embodiment, the separation process refers to punching out material from the rod using a punching or cutting tool. This further allows implementing multiple punched recesses to be formed along the rod surface considering local flexural strength and the orientation of the local flexural strength with respect to the rod, or spinal column to obtain a desired property of the rod. According to specific embodiments of this aspect, the depth, length, mutual orientation or the number density of the multiple recesses can be varied along the rod to treat different parts of the spinal column in the most appropriate manner regarding flexion and/or torsion.
A tool according to a related aspect includes a socket die with a first bore for receiving the rod connector, and at least one second bore for receiving a first punching press, and further includes the punching press, which fits within the at least one second bore being moveable with respect thereto. Thereby, the first and the at least one second bore intersect each other to enable punching out material from the flexible rod to form the recess due to the movable punching press.
By using a rod having punched recesses and employing a corresponding punching tool as described above, the shaping of the rod can be accomplished by the surgeon or another person prior to the actual surgery, since no complex injection molding method is required. The tool can also be used easily in the operating room environment.
a and 13b show a perspective and top view, respectively, of a rod according to embodiments of the disclosure.
a and 14b show two embodiments of a cross-section of a rod taken at section AB of
In a dynamic stabilization device, a flexible rod 22 may be employed to provide a fusion to vertebrae of the spinal column when the rod is clamped by respective bone anchoring devices 20. Thereby, the bone anchoring devices 20 are screwed into specific vertebrae at appropriate height positions selected by the surgeon. The bone anchoring devices may be one of the monoaxial type bone anchoring devices (i.e., the bone thread part and receiving part are rigidly fixed to each other) or the polyaxial type bone anchoring devices (i.e., the bone thread part being pivotable with respect to an axis of receiving part prior to locking), but the present embodiments shall not be limited to the specific functions of the bone anchoring device.
The rod 22 which is schematically indicated in the center portion of
However, in various instances, it may be desirable to increase the flexibility of the rod. In one instance, the load which acts on vertebrae in a direct neighbourhood of fused parts of the spine may be too high. In order to relieve the load, the end part of the fusion can be provided with an enhanced degree of flexibility to enable a slight bending movement of the respective vertebrae.
Hence, in the present embodiment, a rod 10 made of an elastomer material is manufactured from the rod 22, wherein the rod 10 now includes recesses 12 formed on opposite sides of the rod. The recesses are formed by removal of material from the rod 22. Due to this removal, the rod is thinned, as a result of which the bending flexibility increases locally. The outermost vertebrae are thus allowed to perform a slight movement depending on the load.
The opposing recesses 12 are formed between two respective clamping sections 14 of the rod 10, which are defined such as to be received by the receiving parts of respective bone anchoring devices 20 and thus include an appropriate length section of the rod 10.
In order to allow further portions of the spine to undergo a slight bending movement, an additional pair of recesses 12′ is formed in the rod surface. The opposing recesses 12′ may leave a same thickness of the rod as the recesses 12, while the length may be slightly extended, as an example.
In
The rod according to the embodiments includes a preferably bio-compatible elastomer material. Examples of such materials which may be embodied herein are polyurethane, polysiloxane, Poly(styrene-block-isobutylene-block-styrene) (SIBS), or polycarbonate urethane (PCU).
It may be noted that the term “rod” as used herein basically denotes a rod-shaped element, which may be provided as a single piece rod as well as a multi-part composite element, that is put together to yield a fusion. In the latter case, those parts may for example be provided with corresponding threads to connect the corresponding pieces. Further, one of the parts may include the elastomer material while another part of the rod may include, e.g., a metal.
A case in which for example a single piece rod is formed from injection molding of two or more different elastomer material components shall also be encompassed by the invention, wherein the recesses are applied afterwards.
The recesses 12, 12′ have a well-defined shape of limited length. As becomes evident from
It may be noted that a rod 10 as described herein may also be formed with multiple recesses 12 or 12′, all of which have the same shape—possibly with orientations with respect to the longitudinal axis of the rod, which differ from each other.
It may be noted that if a recess is formed by later removal of material, this later removal of material may in some instances be recognizable from the product. For example, when the recess is formed by punching, due to a slight deformation or flow of stressed elastomer material during punching and/or heating, plane surfaces or straight lines which are formed thereby also may become slightly concave or convex, respectively. Further, score marks or miniature rims may form across the cut surface along the punching direction.
Examples of the slightly concave or slightly convex portions of the recess are illustrated in
Despite the above mentioned possible presence of concave surfaces, score marks or miniature rims, it has been found that a punching operation may still fulfil the requirements with respect to surface roughness and punching accuracy quite satisfactorily, if a tool for punching a rod according to another aspect of the invention is used.
The punching presses 40, 40′ are also shaped and sized to fit into the bores 34, 34′. As the bores 34, 34′ are formed in parallel to each other, the orientation and guidance of the punching presses 40, 40′ are also parallel. The bores 34, 34′ intersect with the bore 32 such that the punching presses 40, 40′ may cut material from rod 10a inserted in the bore 32. For this purpose, both presses are provided with cutting edges 42, 42′ and cutting faces 44, 44′ whose rake angle relative to the cutting direction serves to separate the removed elastomer material from the rod. The removed material may be discharged into a container not shown in the figures.
Upon exerting a load on the flexible rod, an inevitable deformation or flexible flow of material will occur in the rod. As depicted in the cross sections of
The separating tool may be placed or installed in the vicinity of surgeon's operating site, i.e., in a hospital. Accordingly, the surgeon or an attending person may in situ decide where and to what extent recesses shall be applied to the rod. Hence, costs and efforts can be reduced which are necessary to provide a flexible stabilization device suited for the specific needs of a patient.
The bottom die plate 130 includes one half of a bore 132 designed to receive the yet un-punched rod 10a. A presser plate 133 is supported by a first spring device (e.g., a coil spring not shown) in a distance above the bottom die plate 130 and includes the other half part of the bore 132 in a bottom face thereof. When the presser plate 133 moves down until the upper face of the bottom die plate 130 is contacted, the rod 10a is held fixed inside the bore 132.
Two guide rods 135a extend upwards from the bottom die plate 130. The presser plate 133 has corresponding bores which receive the guide rods such that the presser plate 133 is held to be movable up and down along the guide rods 135a. The die plate 130 and the presser plate 133 correspond to the socket die of the previous embodiment.
A cutting plate 137 supported in a distance above the presser plate is also guided by the guide rods 135a. The distance between plates 133, 137 is maintained by a second spring device whose spring force is larger than that of the first spring device. Two further guide rods 135b extend downward from the cutting plate 137 in order to be received by corresponding bores of presser plate 133. The presser plate 133 is also movable with respect to the guide rods 135b.
Similar to the previous embodiment, the cutting plate 137 further has two cutting presses extending downward through an opening 131 of the presser plate 133 towards corresponding bores 134 formed in the bottom die plate 130. Bores 132 and 134 intersect each other as in the embodiment shown in
The tools shown in
A method of manufacturing a rod 10 as shown in
First, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
The shapes and sizes of recesses formed in the rod by removing material are not limited to those examples shown in the embodiments above. As shown in
Further, the separation of elastomer material from the rod as proposed herein is not limited to a cutting or punching operation. As shown in the upper left section of
The rod can have any cross-section in sections other than those having the recesses, e.g., cylindrical, hexagonal, square, etc.
According to the invention, recesses are applied to a rod of a flexible stabilization device by removal of material in selected areas. Hence, clamping sections can be maintained between the recesses which may serve to be clamped by bone anchoring devices. The desired bending properties of the rod are thus concentrated in these selective areas outside the clamping sections. As a result, conventional abrasion of elastomer material due to the grinding of a bending rod surface inside a rigid receiving part can be considerably reduced. Consequently, the endurance of the rod can be prolonged.
While a particular form of the disclosure has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited, except as by the appended claims.
Number | Date | Country | Kind |
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08 014 378.7 | Aug 2008 | EP | regional |
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/088,276, filed Aug. 12, 2008, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 08 014 378.7, filed Aug. 12, 2008, the contents of which are hereby incorporated by reference in their entirety.
Number | Date | Country | |
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61088276 | Aug 2008 | US |