Bone nail for the heel

Abstract

A bone nail (1) for the heel includes: a front portion (2) determined for insertion into one or more bones (14, 15, 16) or bone fragments of the heel and having a tip (3), and an arc-shaped main portion (4) extending from the front portion (2) and having a rear end (5), wherein the main portion (4) includes a tapered shape such that a cross sectional diameter of the main portion (4) within at least one first section (20) increases towards the rear end (5). According to embodiments, a curvature of the arc-shaped main portion (4) includes a radius of curvature r.sub.c which amounts to at least 130 mm. According to other embodiments, the tapered shape is a conical shape.

Claims

1. A system comprising: a bone nail insertable into one or more bones or bone fragments of the heel, the bone nail defining a bore that extends through at least a portion of the bone nail and a first engagement structure formed on at least a portion of an inner surface of the bore; a tool comprising a second engagement structure configured to engage the first engagement structure to facilitate implanting of the bone nail; and a bone anchor comprising a third engagement structure configured to engage the first engagement structure for locking the bone nail when the bone nail is implanted, the bone anchor comprising a shank insertable into a first opening of the bore and out of an opposite second opening of the bore for anchoring in bone.

2. The system of claim 1, wherein the bore defines a substantially straight pathway extending from a rear end face of the bone nail to a side opening in an outer surface of the bone nail.

3. The system of claim 1, wherein the first engagement structure is an internal thread, the second engagement structure is an outer thread on the tool, and the third engagement structure is an outer thread on the bone anchor.

4. The system of claim 1, wherein the tool comprises: a guiding pin comprising the second engagement structure; and an adapter connectable to the guiding pin, and comprising a head section configured to receive an external force to drive the bone nail into the one or more bones or bone fragments when the first and second engagement structures are engaged.

5. The system of claim 4, wherein the adapter comprises: a receiving portion configured to hold the guiding pin; and a locking screw configured to lock the guiding pin when the guiding pin is held in the receiving portion.

6. The system of claim 1, wherein the tool comprises a drill jig to facilitate implanting of the bone anchor, the drill jig comprising: the second engagement structure; and an inner bore to receive a drill tool for forming an anchor bore in a bone for the bone anchor.

7. The system of claim 1, wherein the bone anchor comprises the shank at a first end for anchoring in the bone, and the third engagement structure formed at or adjacent a second end opposite the first end.

8. The system of claim 7, wherein the bone anchor further comprises a middle section having a substantially smooth surface between the first and second ends.

9. The system of claim 8, wherein the middle section is configured to contact a flat surface of the bore adjacent to the side opening for impeding ingrowth of bone material in the bore when the bone anchor is fixed to the bone nail.

10. The system of claim 1, wherein the bone nail comprises a front portion insertable into the one or more bones or bone fragments of the heel, and a main portion extending from the front portion and having a rear end face opposite the front portion, the main portion defining the bore, wherein the bore has a substantially straight pathway extending from the rear end face to a side opening in an outer surface of the main portion to receive the bone anchor therethrough.

11. The system of claim 10, wherein the first engagement structure is an internal thread, and the second engagement structure is an outer thread on the tool.

12. The system of claim 10, wherein the tool comprises a guiding pin having a first end comprising the second engagement structure, and a second end opposite the first end.

13. The system of claim 12, wherein the tool further comprises an adapter comprising: a receiving portion configured to hold the second end of the guiding pin; and a head section configured to receive an external force to drive the bone nail into the heel when the first and second engagement structures are engaged.

14. The system of claim 13, wherein the head section defines a first longitudinal axis of the tool that is substantially aligned with a longitudinal axis of the bone nail, the longitudinal axis of the bone nail extending through the front portion and the rear end face, and the receiving portion defines a second longitudinal axis of the tool that is angled relative to the first longitudinal axis and extends through the first and second ends of the guiding pin when the guiding pin is held in the receiving portion.

15. The system of claim 13, wherein the adapter comprises a locking screw configured to lock the guiding pin in the receiving portion.

16. The system of claim 10, wherein the tool comprises a drill jig comprising the second engagement structure to facilitate implanting of the bone anchor.

17. A method of implanting a bone nail into one or more bones or bone fragments of the heel, the bone nail defining a bore that extends through at least a portion of the bone nail and a first engagement structure formed on at least a portion of an inner surface of the bore, the method comprising: engaging a second engagement structure of a tool to the first engagement structure; using the tool to implant the bone nail by advancing the bone nail into the one or more bones or bone fragments; removing the tool from the first engagement structure; and engaging a third engagement structure of a bone anchor to the first engagement structure to fix the bone anchor to the bone nail and to lock the bone nail in the one or more bones or bone fragments, the bone anchor comprising a shank insertable into a first opening of the bore and out of an opposite second opening of the bore for anchoring in bone.

18. The method of claim 17, wherein the engaging of the second engagement structure to the first engagement structure comprises: engaging the second engagement structure formed on a first end of a guiding pin of the tool to the first engagement structure; and locking a second end of the guiding pin opposite the first end to a receiving portion of an adapter of the tool, wherein a force is applied to the adapter to drive the bone nail into the one or more bones or bone fragments.

19. The method of claim 17, wherein the engaging of the third engagement structure to the first engagement structure comprises: engaging a fourth engagement structure of a drill jig to the first engagement structure; inserting a drill tool into an inner bore of the drill jig; forming an anchor bore in the bone using the drill tool; disengaging the drill jig from the first engagement structure; inserting a first end of the bone anchor comprising a shank into the anchor bore; and engaging the third engagement structure formed at or adjacent a second end of the bone anchor opposite the first end to the first engagement structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and aspects will become apparent from the detailed description of embodiments taken in conjunction with the drawings. Therein:

(2) FIG. 1 shows a perspective view of the bone nail and a locking bone nacho according to an embodiment in an assembled state.

(3) FIG. 2 shows the same as FIG. 1, but in an explosion view;

(4) FIG. 3 shows the same as FIG. 1, but in a cross-sectional view;

(5) FIG. 4 shows the same as FIG. 1, but in an implanted state in the hindfoot;

(6) FIG. 5 shows the bone nail of FIG. 1 with a partial cross-sectional view of its rear end;

(7) FIG. 6 shows a side view of the bone nail as seen from the right side of FIG. 5;

(8) FIG. 7 shows a perspective view of the locking bone anchor shown in FIG. 1;

(9) FIG. 8 shows the same as FIG. 7, but with a partial cross-sectional view of a head portion of the bone anchor;

(10) FIG. 9A shows a perspective view of a closing cap;

(11) FIG. 9B shows a side view of the closing cap;

(12) FIG. 10 shows an enlarged cross-sectional view of the rear end of the bone nail with locking bone anchor and the closing cap attached;

(13) FIG. 11 shows a first step of mounting the bone nail to an adapter in a perspective view;

(14) FIG. 12 shows a second step of mounting the bone nail to an adapter in a perspective view;

(15) FIG. 13 shows a cross sectional view of the assembly shown in FIG. 12;

(16) FIG. 14 shows the assembly of FIG. 12 in a step prior to inserting the bone nail into a bore already formed in the hindfoot;

(17) FIG. 15 shows the assembly of FIG. 12 in a step after the bone nail has been driven into the bore via a hammer;

(18) FIG. 16 shows a step of applying a drill jig pin to form a bore for receiving the locking bone anchor;

(19) FIG. 17 shows a step of inserting the locking bone anchor;

(20) FIG. 18 shows a step of attaching a closing cap to cover a recess of an engagement portion positioned at the rear end of the bone nail, when the locking bone anchor is attached to the bone nail.

DETAILED DESCRIPTION

(21) An embodiment of a bone nail 1 for the heel used in conjunction with a locking bone anchor 7 is described with reference to FIGS. 1 to 10 and a method of using the same illustrated with reference to FIGS. 11 to 18. With respect to FIGS. 1 and 2, the bone nail 1 is shown which is configured to be used to perform arthrodesis of bones or bone fragments of the hindfoot, in particular mutual immobilization of the calcaneus, talus and tibia. A medical and technical background regarding this field of application is also provided in above referenced document WO 2009/067831 A1, which description is incorporated herein by reference and shall not be repeated herein.

(22) The bone nail 1 includes a front portion 2 and a main portion 4. The main portion 4 represents the largest part of the bone nail 1 and extends from the front portion 2 up to the rear end 5 of the bone nail 1. As can be seen from the drawings, the main portion 4 is arc-shaped, and—as is depicted in FIG. 3—has a central axis A whose radius of curvature r.sub.c in this specific embodiment is constant along each infinitesimal section of the central axis.

(23) The front portion 2 of this embodiment occupies a small portion of the bone nail 1 as compared with the main portion 4. The main portion has a first section 20, which in this embodiment is conically shaped and extends over the entire length of the main portion 4. The front portion 2 includes a rounded tip 3 and a second section 21, which in this embodiment is also conically shaped, see FIG. 2. The second conically shaped section 21 deviates from the first conically shaped section 20 of the main portion 4 in that its conicity, i.e., the variation of cross-sectional diameter per unit length, is larger than that a conicity of the second conically shaped section 21, respectively. This feature particularly allows an improved self-adjustment characteristic of the bone nail position within the bore during insertion, in particular during passage of the front portion at the transition between the talus and the tibia.

(24) On the contrary, a conicity, i.e., variation of cross-sectional diameter per unit length, is comparatively small in the case of the first conically shaped section 20 of main portion 4. This allows a substantial contact of the outer surface 9 of main portion 4 with the surrounding bone tissue over substantially the entire length of the main portion 4. Upon insertion of the bone nail, the smooth variation of the cross-sectional diameter allows a controlled compression of the surrounding bone tissue and creating a stable and secure interference fit between the bone nail and the bone material.

(25) In the specific embodiment shown, a diameter in a mid-portion of main portion 4 as measured along its entire length amounts to about 12 mm, while the corresponding diameter, at the transition to the front portion 2 amounts to 11.7 mm, whereas the corresponding diameter close to the rear end 5 amounts to 12.3 mm.

(26) Nevertheless, typical diameters for the bone nail, more specifically as measured in its mid portion, range from 9 to 13 mm, but smaller or larger diameters than these may still be covered by the scope of embodiments. The above given conical tolerances of ±0.3 mm (−0.3 mm near front portion, +0.3 mm near rear end 5) from the reference value (12 mm in the embodiment at the mid portion) are also applicable to those other diameters given above (9 to 13 mm). Nevertheless, conical tolerances of ±0.6 mm or even up to ±0.9 mm, respectively, may still be within the scope of other embodiments. Note that if there is no clear transition between the front portion, or the tip, and the main portion, a point on the central axis A distant from the tip by a length amounting between one or two cross sectional diameters may be taken as a measure.

(27) Regarding radii of curvature, it may be noted, that according to other embodiments, variations of the radius of curvature r.sub.c may vary along the central axis A. In this specific embodiment, the radius of curvature r.sub.c amounts to 200 mm. However, further embodiments of a bone nail allow for radii of curvature r.sub.c amounting to at least 130 mm, others to at least 140 mm, still others to at least 150 mm, and according to most specific embodiments, amount to at least 190 mm or at least 200 mm. The geometry selected depends on the specific conditions, which are individual for each patient.

(28) Likewise, upper limits of the radius of curvature r.sub.c may amount to not more than 240 mm, preferably to 210 mm or less. A length of the bone nail as measured from the tip 3 to the rear end 5 amounts to at least 110 mm. According to other embodiments, the length for a bone nail 1 may amount to 125 mm or more, preferably 130 mm or more.

(29) The circular arc, over which the bone nail 1 of specific embodiments may extend, may range from 38° to 70°, preferably from 48° to 55°. A maximum length of bone nail 1 may amount to 200 mm or less, preferably 160 mm or less. Specific embodiments reveal amounts of 150 mm or less.

(30) It may be noted, that the main portion 4 may be partially curved, or may be curved with varying curvature, or may be curved with constant radius of curvature, as in the present embodiment. Likewise, the front portion 2 may continue to show the same curvature as the main portion 4, or may also vary in curvature, or may be formed in a straight, non-curved shape.

(31) The outer surface 9 of the main portion 4 is further provided with a pattern of longitudinal grooves 24, which thereby form a groove-and-rib pattern, wherein the grooves are oriented parallel to the central axis A in order to allows and improve guiding of the bone nail 1 during insertion of the same into the bore of the hind-foot. This pattern further increases the surface area and allows an improved integration of the bone nail 1 within the growing bone tissue surrounding the nail once bone ingrowth into the grooves has started. Moreover, the groove and rib pattern oriented in this direction allows a larger amount of interference fit during insertion while the force needed is decreased.

(32) The bone nail 1 comprises in the region of the main portion 4 a transverse bore 12 and a longitudinally inclined bore 6, which extends from the rear end 5 through the main portion 4 towards an opening 8 in the outer surface 9. As shown in FIG. 3 a locking bone anchor 7 is designed to be inserted into the bore 6, wherein said bore has a longitudinal axis B, that is inclined with respect to the central axis A of the main portion 4 by an angle α, which amounts to 0-20°, more preferably 10-20°. In this embodiment, the longitudinal axis B lies within the plane of curvature of the bone nail 1.

(33) As can be seen in FIG. 4, the locking bone anchor 7 is fixed through the calcaneus and talus thereby urging the bone nail further into the bore (not shown) due to its small inclination with respect to the central axis A, thereby preventing the bone nail 1 from loosening and falling-off from the bore. As can also be seen in FIG. 4, the bone nail 1 in its inserted state is accessible through an end face 141 of calcaneus 14 and extends further through the talus 15 into the tibia 16. Longitudinal bore 12 penetrating transversely through a region adjacent the front portion 2 of the bone nail 1 is designed to receive a second locking bone anchor (not shown) for further securing the nail in the tibia, wherein such fixation via bore 12 is only optional and depends on the circumstances.

(34) FIGS. 5 and 6 show more details of the main portion 4 close to the rear end 5. The first bore 6 further has an engagement structure (e.g., an inner thread 10) close to its opening (e.g., a first opening) towards the rear end 5, and further has a flat surface towards the opening 8 (e.g., an opposite second opening) in the outer surface 9 of the main portion 4.

(35) The bone nail 1 of this embodiment is solid, i.e., basically non-tubular—except for the bores 6 and 12. Nevertheless, tubular shapes or channels provided within respective portions 2 or 4 may also be encompassed by other embodiments.

(36) Further details of the locking bone anchor 7 to be inserted into bore 6 of the bone nail 1 become apparent from FIGS. 7 and 8. The locking bone anchor 7 includes an engagement portion 72 for engagement with an external tool for screwing-in the locking bone anchor 7 into the bore 6 and the bone material of the calcaneus 14 and talus 15. In this example, a hexagon-shaped engagement portion 72 is used, but any other shapes of engagement portions are possible as well, e.g., star, polygon, etc.

(37) The engagement portion 72 is provided as a recess 78 formed in an end face 79 of the bone anchor 7. The protruding edges of the end face 79 form an abutment for the locking bone anchor 7 at the rear end 5 of the main portion for the anchor 7. Adjacent the end face 79, an engagement structure (e.g., a first outer thread section 73) is provided, which is configured to interact with the inner thread 10 formed in the bore 6 near the rear end 5 of the main portion 4 of bone nail 1. Adjacent the first outer thread section 73 a threadless section 77 extends preferably having a length such as to accomplish contact with the flat inner surface of the bore 6 provided in main portion 4. As a consequence of this plain contact between section 77 and bore 6 in growth of bone material into the bore 6 is advantageously impeded, which is useful, since during the lifetime of the implant, access and readjustment of the locking bone anchor 7 should be possible at any time.

(38) Adjacent to the threadless section 77, a second outer thread section 75 extends up to the tip of the locking bone anchor 7. This section 75 forms the bone thread for fixing the bone anchor 7 in the surrounding bone material.

(39) The threadless section 77 and the second outer thread section 75 together form a shank 74 of anchor 7, wherein an outer diameter of both sections 75, 77 is smaller than an outer diameter of the first outer thread section 73 such as to allow for insertion of these sections without screwing through the inner thread 10. In this manner, the shank 74 is insertable into the first opening (e.g., the opening towards the rear end 5) and out of the opposite second opening (e.g., the opening 8) of the bore 6 for anchoring in bone. Further, the thread lead of the second outer thread section 75 is larger than the thread lead of the first outer thread section 73 to provide self-locking of anchor 7. As shown in FIGS. 9A and 9B, a closing cap 76 is provided to cover and seal the recess 78, which includes the engagement portion 72.

(40) For this purpose, the closing cap 76 is formed with a thread portion 80 and with a cap portion 81, wherein the thread portion 80 interacts with an inner thread 85 provided in a recess 78. By means of this closing cap, inward growth of bone tissue or soft tissue into the recess 78 is advantageously impeded allowing easy and less disruptive access to the bone anchor 7 at any time. The closing cap 76 may easily be attached and removed by means of an engagement portion 82.

(41) An overview of the mechanism provided by a corresponding head section of the bone anchor 7 in a state wherein it is installed to the bone nail 1 and closed by closing cap 76 is shown in FIG. 10.

(42) The materials used for the bone nail 1, the locking bone anchor or the closing cap are preferable metals such as stainless steel, titanium, nickel titanium alloys, nitinol or the like. Other biocompatible materials are possible as well. All components are preferably made from rigid materials.

(43) A process of implanting the bone nail 1 with the locking bone anchor 7 according to the above embodiment is depicted in FIGS. 11 through 18.

(44) As shown in FIG. 11, the bone nail 1 without the locking bone anchor 7 is attached to an adapter 100 by means of a guiding pin 90. The guiding pin 90 has an engagement structure (e.g., an outer thread section 91) configured to interact with the inner thread 10 at the rear end 5 of the bore 6. The other end section 92 of the guiding pin 90 is inserted into a receiving portion 101 of adapter 100 and locked by screw 102, as shown in FIG. 12.

(45) FIG. 13 shows a cross-sectional view with details of the adapter 100 attached to the bone nail 1. As shown therein, the adapter 100 further comprises a head section 103 for receiving hammer strokes from a hammer 120, which is also shown in FIG. 14. Prior to inserting the connected assembly consisting of bone nail 1 and adapter 100, a circular arc-shaped bore 30 has been formed via the end face 141 of calcaneus 14 through the talus 15 into the tibia 16 by means of a targeting device not shown. The shape of the bore 30 is schematically indicated in FIG. 16 as described below.

(46) As shown in FIG. 15, the bone nail 1 has been inserted in its entirety into the bore 30 by means of hammer strokes via hammer 120 such that only the adapter 100 protrudes from the opening of bore 30 in the axial end face of calcaneus 14. Next, the adapter 100 may be removed by loosening the screw 102, where after the pin 90 may be unscrewed from the inner thread 10 of the bore 6 of bone nail 1.

(47) As shown in FIG. 16, a drill jig pin 140 having a tubular portion, an engagement portion 142, and a separate engagement structure (e.g., a thread portion 144) that is structured the same or substantially the same as the engagement structure of the guiding pin 90 (e.g., the outer thread section 91), may be inserted into the opening of the end face 141 of calcaneus 14 and immediately thereafter into the bore 6 of bone nail 1. The outer thread portion 144 is threaded into inner thread 10 of bore 6. Then, the inner cylindrical bore 143 of drill jig pin 140 defines an axis 150 for a drill tool in order to form a straight bore for receiving the locking bone anchor 7, as can be seen in FIG. 17.

(48) Thereafter, the drill jig pin 140 is removed and the locking bone anchor 7 is inserted and screwed into the bone and the inner thread 10. Finally, as shown in FIG. 18, the closing cap 76 is screwed with its thread portion 82 onto inner thread 85 formed within recess 78 of the bone anchor 7.

(49) It may be noted that above embodiment depicts detailed features, whereas the person skilled in the art readily recognizes that further modifications may be made without departing from the scope as set forth in the appended claims.

(50) For example, in the embodiments as illustrated above, the outer surface 9 of the main portion 4 and front portion 2 of bone nail 1 is formed with a pattern of grooves 24 and ribs there between. However, a smooth or otherwise structured surface may also be provided. Also alternating smooth regions and groove-and-rib patterns may be conceived.

(51) Further, in the embodiments above, a conically shaped section 21 of front portion 2 is distinguished from the conically shaped section 20 of main portion 4 by an abrupt transition in conicity, i.e., increase of diameter per unit length. However, a smooth transition with continuously varying conicity between both regimes may also be realized.

(52) In the above embodiments, substantially the entire length of the bone nail 1 is provided with some degree of conicity. However, it is also possible to apply a conical or curved shape only in a partial section, or in partial sections with regions of constant diameter arranged there between.

(53) In some of the above embodiments, the front portion 2 has a rounded tip 3 and a conically shaped portion 21. However, according to other embodiments, the conically shaped portion may also be tapered but non-conical, or may even be fully omitted such that the tip portion has a direct transition to the main portion, which has the tapered or even conical section.

(54) Further, the tip may not necessarily have a purely rounded shape. For example, the tip may be formed by a flat surface. Alternatively, the tip may also comprise multiple small flat surfaces arranged side by side to mimic a common obtuse tip.