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 bone nail for the heel comprising: a front portion insertable into one or more bones or bone fragments of the heel and having a tip; an arc-shaped main portion extending from the front portion and having a rear end; wherein the main portion includes a tapered shape, such that a cross sectional diameter of at least a first section of the main portion increases towards the rear end.

2. The bone nail according to claim 1, wherein the tapered shape is a conical shape.

3. The bone nail according to claim 1, wherein the arc-shaped main portion has a radius of curvature of at least 130 mm;

4. The bone nail according to claim 3, wherein the radius of curvature is 240 mm or less.

5. The bone nail according to claim 1, wherein the cross-sectional diameter of the main portion continuously increases along the entire length of the main portion towards the rear end.

6. The bone nail according to claim 1, further comprising a first bore formed therein for receiving a locking bone anchor, wherein the first bore extends from the rear end of the main portion to an opening formed in an outer surface of the main portion to allow locking of the bone nail in the calcaneus and talus when the bone nail is inserted in a bore formed through the heel.

7. The bone nail according to claim 6, wherein the bone nail has an arc-shaped central axis extending from the tip to the rear end, and the first bore has a longitudinal axis that intersects the central axis at or near the rear end of the main portion at an angle of at most 20 degrees.

8. The bone nail according to claim 7, wherein the bone nail is curved within a single plane, and wherein the longitudinal axis of the first bore extends in the single plane.

9. (canceled)

10. The bone nail according to claim 1, wherein the front portion has a second section that is conically shaped and has a cross-sectional diameter that increases in a direction away from the tip and towards the rear end of the main portion, and wherein an increase of the cross-sectional diameter per unit length of the second section is greater than that of the first section of the main portion.

11. The bone nail according to claim 1, wherein the tip of the front portion is provided with a rounded shape.

12. The bone nail according to claim 1, wherein an entire length of the bone nail measured from the tip to the rear end is at least 110 mm.

13. (canceled)

14. The bone nail according to claim 6, further comprising the locking bone anchor for locking the bone nail, the locking bone anchor comprising: an engagement end provided with an engagement portion for receiving an engagement tool; and a shank provided with an outer thread section configured to be screwed into the bone material.

15. The bone nail according to claim 14, wherein a threadless section extends between the engagement end and the outer thread section of the locking bone anchor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Further advantages and aspects will become apparent from the detailed description of embodiments taken in conjunction with the drawings. Therein:

[0017] FIG. 1 shows a perspective view of the bone nail and a locking bone nacho according to an embodiment in an assembled state.

[0018] FIG. 2 shows the same as FIG. 1, but in an explosion view;

[0019] FIG. 3 shows the same as FIG. 1, but in a cross-sectional view;

[0020] FIG. 4 shows the same as FIG. 1, but in an implanted state in the hindfoot;

[0021] FIG. 5 shows the bone nail of FIG. 1 with a partial cross-sectional view of its rear end;

[0022] FIG. 6 shows a side view of the bone nail as seen from the right side of FIG. 5;

[0023] FIG. 7 shows a perspective view of the locking bone anchor shown in FIG. 1;

[0024] FIG. 8 shows the same as FIG. 7, but with a partial cross-sectional view of a head portion of the bone anchor;

[0025] FIG. 9A shows a perspective view of a closing cap;

[0026] FIG. 9B shows a side view of the closing cap;

[0027] 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;

[0028] FIG. 11 shows a first step of mounting the bone nail to an adapter in a perspective view;

[0029] FIG. 12 shows a second step of mounting the bone nail to an adapter in a perspective view;

[0030] FIG. 13 shows a cross sectional view of the assembly shown in FIG. 12;

[0031] 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;

[0032] FIG. 15 shows the assembly of FIG. 12 in a step after the bone nail has been driven into the bore via a hammer;

[0033] FIG. 16 shows a step of applying a drill jig pin to form a bore for receiving the locking bone anchor;

[0034] FIG. 17 shows a step of inserting the locking bone anchor;

[0035] 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

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 inner thread 10 close to its opening towards the rear end 5, and further has a flat surface towards the opening 8 in the outer surface 9 of the main portion 4.

[0050] 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.

[0051] 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.

[0052] 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, 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.

[0053] 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.

[0054] 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. 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 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.

[0060] 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.

[0061] 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.

[0062] As shown in FIG. 16, a drill jig pin 140 having a tubular portion, an engagement portion 142 and a thread portion 144 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.