Patent ID: 12207846

DETAILED DESCRIPTION

A polyaxial bone anchoring device according to a first embodiment, which is generally shown inFIGS.1to3, includes a bone anchoring element1in the form of a screw member having a threaded shank2and a head3. A shank axis S is defined by a longitudinal axis or screw axis of the shank2. On its free end3a, the head3may have a recess4for engagement with a tool. The bone anchoring device further includes a receiving part5for connecting the bone anchoring element to an elongate stabilization member, such as a rod100. A pressure member6is configured to be arranged in the receiving part on top of the head3. For securing the rod100in the receiving part5and to exert pressure onto the pressure member6, a locking element7in the form of, for example, a set screw which cooperates with the receiving part5may further be provided.

The receiving part5is substantially cylindrical, and has a first or top end5a, a second or bottom end5band a passage51extending from the top end5atowards the bottom end5b, the passage51defining a longitudinal central axis C. The passage51forms an opening52at the bottom end5b, which has a width that is greater than a greatest width of the head, so that the head3of bone anchoring element1is insertable through the bottom end52. The passage51may have several sections with different widths and/or shapes, and is not limited to the exact shape shown in the figures. Adjacent to the opening52, the passage51has a narrowing section51awhich narrows, for example conically, towards the bottom end5b. The narrowing section51acooperates with a portion of the pressure member6, such that a compressive force is exerted via the pressure member6onto an inserted head3. A widened section51bfollows the narrowing section51ain a direction towards the top end5a. The widened section51bis dimensioned such that a portion of the pressure member6can expand therein to permit the head3to enter. Further, the passage51may have an intermediate section51cthat has a smaller width than the widened section51b, and permits a portion of the pressure member to slide therein in an axial direction. Finally, adjacent to the top end5aand the intermediate section51c, the passage51is formed as a threaded bore51dwith a greater inner diameter than that the intermediate section51c, to permit the insertion of and cooperation with the locking element7. Threads53and71of the receiving part5and the locking element7, respectively, may be threads that reduce or eliminate radial forces during tightening of the locking element7, such as a square thread, for example. At the bottom end of the internal thread53, a thread runout53amay be provided. Moreover, as best shown inFIGS.1and2, a substantially U-shaped recess54is formed at the top end5aand extends to a distance therefrom. The substantially U-shaped recess54divides the upper portion of the receiving part5into two free legs55, and forms a channel for receiving the rod100. A longitudinal axis of the substantially U-shaped recess54is coaxial with or parallel to a longitudinal axis of a straight rod100when the rod is inserted.

At the center of each leg55in a circumferential direction and at an axial position above a bottom54aof the substantially U-shaped recess54, through-holes56extend through each leg55. The through-holes56are configured to receive pins57, as shown inFIG.3. The pins57may serve for rotationally securing the pressure member6in the receiving part5. Also, the pins57may serve for limiting an upward movement of the pressure member6within the receiving part5. Furthermore, cut-outs58may be formed on either side of the legs55, which may contribute to a reduced size of the receiving part5. A tool engagement portion59, such as a circumferential groove and/or central recesses can be optionally provided at the legs55to allow for engagement of the receiving part5by a tool.

Referring additionally toFIGS.4and5, the bone anchoring element1will be described in more detail. The head3has an overall shape of a segment of a sphere or, in other words, a truncated sphere, which has a size such that it includes a section with a greatest diameter E of the sphere. The segment of the sphere may be arranged in a manner between a free end3aof the head and a neck portion21of the shank2, such that one end with the smaller outer diameter is closer to the neck portion21and the other end with the greater outer diameter is closer to the free end3athan to the neck portion21. However, the segment of the sphere can also extend at both sides from the section with the greatest diameter E to the same distance, or may end at or below the greatest diameter E. The neck portion21may be substantially thread-free.

More specifically, the head3includes at its outer surface a first curved portion31and a second curved portion32. The first curved portion31is defined by the spherical segment that forms the overall shape of the head3and has a first radius of curvature R1defined by the radius of the sphere. Further, the first curved portion31is located adjacent to or close to the neck portion21and includes in the embodiment shown the greatest outer diameter E. The second curved portion32may be, for example, substantially toroid segment-shaped and has a second radius of curvature R2that is smaller than the first radius of curvature R1. The second curved portion32is located between the first curved portion31and the free end3aof the head3. In a section through the center of the head3and including the shank axis S, the surface of the first curved portion31and the second curved portion32form substantially circular arcs. Moreover, the first curved portion31and the second curved portion32are connected to each other in a manner such that the outer surface of the head3is substantially continuous at a transition33. Hence, there is no substantial step at the transition33or in other words, the transition is step-free. The first curved portion31and the second curved portion32with their transition33form a first position indication structure provided on the head3. It shall be noted that only a part of the entire first curved portion31and second curved portion32in a region around the transition may form the first position indication structure.

An axial length in the direction of the shank axis S of the second curved portion32may be considerably smaller than an axial length of the first curved portion31. For example, the second curved portion32may only have the typical axial length of a bevelled region. The second curved portion may be manufactured, for example, using a turning tool configured to form a radius at an edge of a work piece. It shall be noted that such a first position indication structure including or made up of a transition between a first curvature and a second curvature is relatively easy to manufacture, which contributes to efforts to reduce costs.

The free end portion3amay be substantially flat. The recess4for the tool may have any shape, for example, a polygon shape, a torque-shape, or any other shape to provide a form-fit connection to a tool.

Referring now in addition toFIGS.6to9b, the pressure member6will be explained more in detail. The pressure member6of this embodiment is a monolithic piece. It has a first or top end6aand a second or bottom end6b. Adjacent to the top end6a, there is an upper portion61that may be substantially cylindrical and that has an outer diameter which allows it to move in the axial direction in the passage51of the receiving part5. At the top end6a, a rod receiving recess62is formed that provides a rod support surface. A lower section of the recess61may have a substantially V-shaped cross-section with a longitudinal axis extending substantially perpendicular to the cylinder axis of the pressure member6which is configured to substantially align with the central axis C of the receiving part5when the pressure member is in the receiving part5. A depth of the recess62may be smaller than a diameter of the rod100. Hence, when the rod100rests on the support surface, the rod projects over the top end6aof the pressure member6as shown, for example inFIG.3. The V-shape of the rod support surface more effectively permits the use of rods with different diameters.

A lower portion63of the pressure member6has a tapered, preferably conical, outer surface, which is configured to cooperate at its lower region63aadjacent to the bottom end6bwith the narrowing section51aof the receiving part. A head receiving recess64is formed in the lower portion63that extends from the bottom end6bto a distance from a bottom62aof the rod receiving recess62. The head receiving recess64has a lower section64aclose to the bottom end6bthat has a substantially hollow spherical shape with a radius of the sphere matching that of the first curved portion31of the head3. Furthermore, an uppermost portion64bof the head receiving recess64is also hollow spherically-shaped, for example, with the same radius as the lower portion64a. By means of this, the lower spherical section64aand the upper spherical section64bprovide a spherical support for the first curved portion31of the head3, and thus form a seat in which the head3can pivot. Between these two spherically-shaped sections64a,64b, an intermediate section64cis provided that forms a cut-out and has a greater inner diameter than the lower end of the upper spherical section64b. In greater detail, the intermediate widened section64cwidens from the lower end of the upper spherical section64b, for example, with a substantially flat step, and continues with increasing inner diameter, for example with a conical shape, until it matches the inner diameter of the lower spherical section (FIGS.9a,9b). By means of the step, an edge65is formed. The edge65is preferably rounded. As the edge65is defined at a border of the spherical portion, the inner surface of the head receiving recess64can be formed substantially free of a separate protrusion that protrudes from the head contacting surface of the spherical portion64aand64binto an interior of the recess64.

In addition, the lower portion63of the pressure member includes flexible wall sections66that are separated by axial slots67open towards the bottom end6b. To obtain a certain degree of flexibility, the slots67may widen towards their closed end67a. The slots67may extend in the axial direction, preferably up to the transition between the intermediate section64cand the uppermost spherical segment-shaped section64b.

A size of the head receiving recess64and the sections formed therein is such that when the head3is inserted, the free end3aof the head3can extend into the upper spherical section64b. A gap68is then formed between the outer surface of the head3and the inner surface of the intermediate section64cof the head receiving recess64.

Moreover, the size of the head3and the lower portion63of the pressure member including the head receiving recess64is such that the head can be inserted through the bottom end6bby spreading apart the flexible wall section66until the upper portion of the head3abuts against or otherwise contacts the edge65. The connection is similar to a snap-fit connection. When the head3is received in the head receiving recess64, the head is held therein by friction via the flexible wall sections66before final locking is effected, for example, with the locking element7.

The pressure member further includes elongate recesses69that are formed in the sidewalls of the rod receiving recess62. The elongate recesses69are oriented with their long side substantially parallel to the central axis C. As shown inFIG.3, the elongate recesses69extend through the entire sidewall and are configured to receive the pins57. By means of this, when the pressure member6is mounted to the receiving part5, a rotational position of the pressure member6can be maintained by the pins57that extend into the elongate recesses69. Furthermore, an upward movement of the pressure member6relative to the receiving part towards the first end5ais limited by an abutment of the pins57against the lower end69aof the recesses69.

Lastly, the pressure member6has a coaxial bore60for allowing access to the head3, more particularly to the recess4of the bone anchoring element1with a tool.

The parts and portions of the bone anchoring device may be made of any material, preferably however of titanium or stainless steel or any bio-compatible metal or metal alloy or plastic material. For bio-compatible alloys, a NiTi alloy, for example Nitinol, may be used. Other materials that can be used are magnesium or magnesium alloys. Bio-compatible plastic materials that can be used may be, for example, polyether ether ketone (PEEK) or poly-L-lactide acid (PLLA). The parts can be made of the same or of different materials from another.

In use, the bone anchoring element1may be inserted first into a prepared hole in bone or in a vertebra, and the receiving part5with the pre-assembled pressure member6is mounted onto the head3. Alternatively, the bone anchoring device is pre-assembled in such a manner that the receiving part5with the pressure member6is already mounted onto the head3. For mounting, the head3is inserted from the lower end5aof the receiving part while the pressure member6is at an uppermost insertion position where the pins57abut against the lower end69aof the elongated recesses69. Once the head3has been inserted, the pressure member6is moved downward until the lower outer tapered portion63aenters into the narrowing section51aof the receiving part5and exerts a compression force onto the head3. Also, in this condition, the head3cannot be removed through the lower opening52.

As long as the bone anchoring device is not yet finally locked by inserting the rod and fixing it with the locking element7, the receiving part5and the bone anchoring element1can be pivoted relative to each other so that the bone anchoring element1can assume various angular positions of the shank axis S with respect to the central axis C of the receiving part. Depending on the strength of the frictional clamping of the head3, any position can be maintained provisionally before locking. This is possible without insertion of the rod and the locking element7.

A predetermined position in this embodiment may be the position in which the shank axis S and the central axis C of the receiving part coincide, as shown inFIGS.3and11. In other words, the bone anchoring element assumes a zero angle position with respect to the receiving part5. A position different from the zero angle position is shown inFIGS.10and12. When the bone anchoring element1is moved out of the zero angle position, the edge65contacts the second curved portion32of the head3at a side opposite the side to which the shank is pivoted. When the head3is then pivoted relative to the receiving part5back towards the zero angle position shown inFIGS.3and11, the edge65moves along the outer surface of the head3from the second curved portion32with the smaller radius back to the first curved portion31with the greater radius, thereby passing the transition. During the movement, the pressure member may be slightly expanded until the first curved portion31contacts the upper spherical section64b. The transition from the smaller radius to the greater radius functions in a ramp-like manner and produces a tactile feedback to a user. A user may experience the change in slope until the zero angle position is reached, and/or is left again by pivoting towards another angular position. As the position indication structure provided by the differently curved sections is rotationally symmetrical, the feedback is generated when pivoting in any direction.

Once a suitable angular position is found, the whole construct is locked by inserting the rod and the fixation element7and tightening the fixation element7.

Referring now toFIGS.13to16, a second embodiment of the polyaxial bone anchoring device will be described. The polyaxial bone anchoring device according to the second embodiment differs from the polyaxial bone anchoring device of the first embodiment in the shape of the bone anchoring element and the pressure member. The receiving part is the same as in the first embodiment. Identical or similar parts are indicated with the same reference numerals, and the descriptions thereof will not be repeated. The bone anchoring element1′ has a head3′ which has a spherical segment-shaped portion31′ that may include a section with the greatest diameter E and that joins the neck21. The spherically-shaped outer surface is interrupted by a conical portion34that tapers towards the neck portion21. The conical portion34is located closer to the neck portion21than to the free end surface3a. More specifically, the conical portion34is located in a lower portion of the head3′, i.e., is sandwiched between the section with the greatest diameter E and the spherically-shaped portion adjoining the neck portion21. An axial extension or length of the conical portion34may be considerably smaller than the axial extension of the entire spherical segment-shaped portion31′. The axial length or height may be as large as there is still enough spherical surface for allowing pivoting. Specifically, it may be, for example, less than a third or even less than a quarter of the axial length of the spherical segment-shaped portion31′.

The pressure member6′ is identical to the pressure member of the previous embodiment except that it instead has a counterpart conical section for engaging the conical section34of the head3′. As shown inFIGS.15and16, a conical section64dis formed within the lower spherical section64aof the head receiving recess64. The conical section64dmay have the same cone angle as the conical section34of the head3′ and may have the same axial extension or length. However, the axial extension may also, for example, be smaller than that of the conical section34of the head3′. The conical section64dextends fully circumferentially around the inner wall of the head receiving recess64and is at a height such that in the zero angle position, it matches with (i.e., is at substantially the same height as) the conical portion34of the head3′.

In use, when the head3′ is inserted into the pressure member6′, which is in the receiving part5, and the pressure member is moved downward so that the outer conical section63aof the pressure member and the narrowing section51aof the receiving part are engaged to clamp the head, the head is captured in the head receiving recess64such that the spherical segment-shaped portion31′ contacts the spherical sections64aand64bof the head receiving recess64to allow pivoting of the bone anchoring element. When the bone anchoring element1′ is in the zero angle position as depicted inFIG.15, the conical sections34of the head3′ and64dof the pressure member6′ are engaged. By means of this, the zero angle position is automatically centered. When the bone anchoring element is pivoted to an angular position different from the zero angle position as shown inFIG.16, the conical sections34of the head3′ and64dof the pressure member are substantially out of engagement. Moving into the zero angle position or out of the zero angle position produces a feedback, preferably a tactile feedback to a user. Hence, the zero angle position can be easily identified.

It shall be noted that the bone anchoring element1′ depicted inFIGS.13to16does not include the second curved portion32close to the free end surface3awhich has a smaller radius in the previous embodiment. However, it is conceivable that the bone anchoring element1′ also has the second curved portion32with a smaller radius as in the first embodiment.

Referring toFIGS.17to20b, a third embodiment of the polyaxial bone anchoring device will be described.

The polyaxial bone anchoring device according to the third embodiment differs from the polyaxial bone anchoring device according to the first and second embodiment in the shape of the bone anchoring element, and more specifically in the shape of the head of the bone anchoring element. Parts and portions that are identical or similar to those of the previous embodiments are indicated with the same reference numerals, and the descriptions thereof will not be repeated. The bone anchoring element1″ includes a head3″, which has an overall spherical segment-shaped portion31″ similar to the prior embodiments. The spherical segment-shaped portion31″ may include the section with the greatest diameter E. At a distance from the free end3a, a groove35is formed that extends circumferentially and concentrically around the central axis. The groove35may have a rounded inner contour, such as a spherical contour. Moreover, the groove35is relatively small and shallow. Specifically, the depth of the groove35may be such that it is sufficient to generate a transition between the spherical outer contour of the spherical segment-shaped portion31″ and the groove35. An axial position of the groove is such that the groove35is closer to the free end3athan to the neck portion21. It may be, as shown in the figures, at a distance from the free end3athat is the about same or only slightly greater than a width or height of the groove in the axial direction.

In use, when the head3″ is inserted into the head receiving recess64of the pressure member6, when the pressure member6is in the receiving part, and moved downward so that the lower outer conical portion63aof the pressure member6engages the narrowing portion51aof the receiving part to clamp the head, the head3″ abuts against the upper spherical segment-shaped portion64bof the pressure member. As shown inFIGS.19aand19b, when the bone anchoring element is in the zero angle position, the edge65is slightly protruding into the groove35. hence, the bone anchoring element1″ is slightly held in the zero angle position. When the bone anchoring element1″ is pivoted as shown inFIGS.20aand20b, the edge65is moved out of the groove35. This gives a feedback, for example a tactile feedback, to a user. Similarly, when the edge65moves into the groove35, a feedback is also generated. The feedback may be a haptic resistance. Hence, when moving into the zero angle position, a feedback is given to a user who may more easily identify the zero angle position.

It shall be noted that the head may additionally have a conical surface like in the second embodiment and the pressure member also additionally a conical surface as in the second embodiment. Alternatively or in addition, the head may have an additional section with a smaller radius like in the first embodiment.

Further modifications of the embodiments described above are conceivable. The features of one embodiment can be combined with those of other embodiments to provide a variety of further embodiments. The receiving part is not limited to the receiving part of the various embodiments shown. As the interaction is only between the head and the pressure member, any of various other known receiving parts may be used and retrofitted with suitable bone anchoring elements and pressure members that have first and second position indication structures. In addition, the position indication structures are not limited to only being able to indicate the zero angle position. They can also be used to indicate a predetermined position in which the shank assumes an angle different from the zero angle with respect to the receiving part. In such a case, the position indication features may be at other locations and/or may itself be angled or otherwise tilted relative to the shank axis.

While the head is shown to be a spherical head and the pressure member is shown to have a spherical head receiving recess, bone anchoring devices according to embodiments of the invention are also not limited thereto. For example, it is conceivable that the head and the pressure member are shaped so as to permit angulation in one or more distinct planes only.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.