Bone fixation device

Abstract

A bone fixation device (1) comprises an elongated member (2) and a washer (3) assembled in a manner to prevent relative longitudinal displacement at the same time allowing axial rotation of the washer (3) with respect of the elongated member (2). The elongated member (2) comprises a proximal head (4) and an elongated shaft (5). The proximal head (4) comprises at least a distal spherical portion (8) having a diameter (D) and defining a maximum transversal dimension (Dh) of the proximal head (4). The washer (3) has a central cavity (14) configured to seat the proximal head (4) and comprising a central spherical portion (15) having the same diameter (D) of the distal spherical portion (8) of the proximal head (4). The central spherical portion (15) extends between a distal rim (16) and a proximal rim (17). The distal rim (16) has a distal transversal dimension (Dd) larger than a maximum transversal dimension (d) of the elongated shaft (5) and smaller than the maximum transversal dimension (Dh) of the proximal head (4). The proximal rim (17) has a proximal transversal dimension (Dw) larger than the maximum transversal dimension (d) of the elongated shaft (5) and slightly smaller than the maximum transversal dimension (Dw) of the proximal head (4). The proximal transversal dimension (Dw) of the proximal rim (17) is larger than the distal transversal dimension (Dd) of the distal rim (16). The proximal rim (17) is configured to be elastically deformable by pressing the proximal head (4) through the proximal rim (17).

Claims

1. A bone fixation device comprising an elongated member and a washer suitable for being assembled in a manner to prevent relative longitudinal displacement at the same time allowing axial rotation of the washer with respect of the elongated member, wherein the elongated member comprises a proximal head and an elongated shaft extending from the proximal head along a shaft axis towards a distal end of the elongated member, the proximal head comprising at least a distal spherical portion having a diameter and defining a maximum transversal dimension of the proximal head with respect to the shaft axis, wherein the washer has a central cavity configured to seat the proximal head and comprising a central spherical portion having the same diameter of the distal spherical portion of the proximal head, the central spherical portion extending along a washer axis between a distal rim and a proximal rim, the distal rim having a distal transversal dimension larger than a maximum transversal dimension of the elongated shaft and smaller than the maximum transversal dimension of the proximal head, with respect to the washer axis and the shaft axis, the proximal rim having a proximal transversal dimension larger than the maximum transversal dimension of the elongated shaft and slightly smaller than the maximum transversal dimension of the proximal head, with respect to the washer axis and the shaft axis, wherein the proximal transversal dimension of the proximal rim is larger than the distal transversal dimension of the distal rim and wherein the proximal rim is configured to be elastically deformable by pressing the proximal head through the proximal rim along the shaft axis and washer axis; wherein the maximum transversal dimension of the proximal head is smaller than the diameter of the spherical portion of the proximal head.

2. The bone fixation device according to claim 1, wherein the distal rim is disposed at a side of the washer facing the elongated shaft when assembled with the washer.

3. The bone fixation device according to claim 1, wherein the central cavity of the washer comprises a conical diverging portion outwardly extending from said distal rim along the washer axis towards said elongated shaft, when assembled with the washer.

4. The bone fixation device according to claim 1, wherein the central cavity of the washer comprises a cylindrical portion outwardly extending from said proximal rim along the washer axis.

5. The bone fixation device according to claim 1, wherein the proximal head comprises a proximal conical portion extending proximally along the shaft axis, the proximal conical portion having a maximum transversal dimension defined by the maximum transversal dimension of the proximal head and a minimum transversal dimension defining a proximal surface of the proximal head, with respect to the shaft axis.

6. The bone fixation device according to claim 5, wherein the proximal conical portion comprises at the proximal surface a tool receiving seat suitable for receiving an insertion tool.

7. The bone fixation device according to claim 5, wherein the proximal head comprises a central cylindrical portion extending proximally from the distal spherical portion along the shaft axis at the maximum transversal dimension of the proximal head and wherein proximal conical portion extends proximally from the central cylindrical portion along the shaft axis.

8. The bone fixation device according to claim 1, wherein the proximal head comprises a central cylindrical portion extending proximally from the distal spherical portion along the shaft axis at the maximum transversal dimension of the proximal head.

9. The bone fixation device according to claim 1, wherein the elongated member is a cannulated screw having a length up to 180 mm for trauma applications or being shorter for SI-Joint arthrodesis and comprising a single or dual lead thread.

10. The bone fixation device according to claim 1, wherein interference between washer and proximal head is 0.005-0.2 mm.

11. A bone fixation kit comprising a bone fixation device (1) according to claim 1 and an assembling device (22) configured to overcome the interference between the proximal head (4) and the proximal rim (17) and to push the proximal head (4) into the central cavity (14) of the washer (30).

12. A]bone fixation kit according to claim 11, wherein the assembling device (22) comprises a seat (23) suitable for receiving the washer (3).

13. The bone fixation device according to claim 1, wherein the interference between washer and proximal head is 0.005-0.08 mm.

Description

(1) The present invention is further illustrated by way of the attached figures which are described in detail in the following section and of which

(2) FIG. 1 shows a side view of an embodiment of a bone fixation device according to the present invention;

(3) FIG. 2 shows a cross-section partial view of the bone fixation device of FIG. 1 in an assembling configuration;

(4) FIG. 3a shows an enlarged detail of FIG. 1 in a possible configuration;

(5) FIG. 3b shows a cross section view of the detail of FIG. 3a

(6) FIG. 3c shows a cross section view A-A of the bone fixation device of FIG. 1;

(7) FIG. 4 shows a perspective view of the bone fixation kit according to the present invention;

(8) FIG. 5 shows a perspective view of an embodiment of a bone fixation device according to the present invention;

(9) FIG. 6 shows a side view of the bone fixation device of FIG. 5;

(10) FIG. 7 shows a cross section view B-B of the bone fixation device of FIG. 6;

(11) FIG. 8 shows a perspective view of an embodiment of a bone fixation device according to the present invention;

(12) FIG. 9 shows a side view of the bone fixation device of FIG. 8;

(13) FIG. 10 shows a cross section view C-C of the bone fixation device of FIG. 9.

(14) A bone fixation device 1 has been shown in FIG. 1 and comprises an elongated member 2 and a washer 3 assembled in a manner to prevent relative longitudinal displacement at the same time allowing axial rotation of the washer 3 with respect of the elongated member 2.

(15) Embodiment of FIGS. 1 and 3c is related in particular to trauma applications. The elongated member 2 is longer than 100 mm.

(16) With reference to the following description, the term proximal has been used with reference to those parts/components near the surgeons and the tool used for implanting the bone fixation device and the term distal has been used with reference to those parts/components far from the surgeons and the tool used for implanting the bone fixation device.

(17) The elongated member 2 comprises a proximal head 4 and an elongated shaft 5 extending from the proximal head along a shaft axis 6 towards a distal end 7 of the elongated member 2.

(18) The proximal head 4 comprises at least a distal spherical portion 8 having a diameter D and defining a maximum transversal dimension Dh of the proximal head 4 with respect to the shaft axis 6.

(19) In particular the maximum transversal dimension Dh of the proximal head 4 is smaller than the diameter D of the spherical portion 8 of the proximal head 4.

(20) The proximal head 4 comprises a proximal conical portion 9 extending proximally along the shaft axis 6. The proximal conical portion 9 has a maximum transversal dimension defined by the maximum transversal dimension Dh of the proximal head 4 and a minimum transversal dimension Dmin defining a proximal surface 10 of the proximal head 4, with respect to the shaft axis 6.

(21) The proximal conical portion 9 comprises at the proximal surface 10 a tool receiving seat 12 suitable for receiving an insertion tool (not shown).

(22) The proximal head 4 comprises a central cylindrical portion 13 extending proximally from the distal spherical portion 8 along the shaft axis 6 at the maximum transversal dimension Dh of the proximal head 4.

(23) The proximal conical portion 9 extends proximally from the central cylindrical portion 13 along the shaft axis 6.

(24) Preferably the elongated member 2 is a cannulated screw comprising a axial channel 20 extending along the shaft axis 6 through the proximal head 4 and the elongated shaft 5 and opening out into the exterior through a fenestrations 21 arranged at the distal end 7 of the elongated shaft 5.

(25) Through the axial channel 20 can pass a guide wire in order to put the elongated member 2 in position. Moreover the axial channel 20 can be used to insert bone cement through fenestrations 21 and a distal aperture 22 to improve fixation. A fluid preparation of bony cement is injected by a cannula that fits into the axial channel 20, from here the cement can overflow through the lateral fenestrations 21 and when it dries it acts as additional fixation between the screw and bone.

(26) When bone cement is not used, fenestrations 21 and the distal aperture 22 are useful for the bone growing. The bone tissue is expected to grow around the implant as a consequence of the surgical injury. The bony tissue can grow inside fenestrations and through, to build an additional anchoring of the screw to the bone

(27) In particular the elongated shaft 5 has a smooth portion 5a disposed in a proximal portion of the elongated shaft 5, starting from the head 4, and a threaded portion 5b which has preferably a dual lead thread. In this case the pitch can be greater than 4 mm.

(28) The washer 3 is a single part, in the shape of a disc, of various sizes (external diameters). The washer 3 has a central cavity 14 configured to seat the proximal head 4 and comprising a central spherical portion 15 having the same diameter D of the distal spherical portion 8 of the proximal head 4.

(29) The central spherical portion 15 extends along a washer axis 6 between a distal rim 16 and a proximal rim 17.

(30) The distal rim 16 has a distal transversal dimension Dd larger than a maximum transversal dimension d of the elongated shaft 5 and smaller than the maximum transversal dimension Dh of the proximal head 4, with respect to the washer axis 6 and the shaft axis 6.

(31) The proximal rim 17 is designed to have an interference with the central cylindrical portion 13 of the proximal head 4. In particular the proximal rim 17 has a proximal transversal dimension Dw larger than the maximum transversal dimension d of the elongated shaft 5 and slightly smaller than the maximum transversal dimension Dh of the proximal head 4, with respect to the washer axis 6 and the shaft axis 6.

(32) The proximal transversal dimension Dw of the proximal rim 17 is larger than the distal transversal dimension Dd of the distal rim 16. The proximal rim 17 is configured to be elastically deformable by pressing the proximal head 4 through the proximal rim 17 along the shaft axis 6 and washer axis 6.

(33) With reference to the above mentioned definition of the words distal and proximal the distal rim 16 is disposed at a side of the washer 3 facing the elongated shaft 5 when assembled with the washer 3.

(34) The central cavity 14 of the washer 3 comprises a conical diverging portion 18 outwardly extending from said distal rim 16 along the washer axis 6 towards the elongated shaft 5, when assembled with the washer 3.

(35) The central cavity 14 of the washer 3 comprises a cylindrical portion 19 outwardly extending from the proximal rim 17 along the washer axis 3.

(36) FIG. 4 shows a bone fixation kit comprising a bone fixation device 1 as disclosed above and an assembling device 22 configured to overcome the interference between the proximal head 4 and the proximal rim 17 and to push the proximal head 4 into the central cavity 14 of the washer 3. The assembling device 22 comprises a seat 23 suitable for receiving the washer 3. In FIG. 4 the assembling device 22 is a plier allowing to overcome the interference and to push the head into the spherical seat of the washer. The plier accommodates the washer 3 in one extremity 24a while pressing the proximal head 4 with the opposite extremity 24b.

(37) When assembled, thanks to the spherical coupling of the relevant surfaces the proximal head 4 and the washer 3 can freely rotate and tilt and, due to the interference, the parts cannot be disassembled unless an appropriate force is intentionally applied.

(38) With the device and kit according to the invention, the washer 3 can be mounted on the elongated member by the distal end of the latter, and slid along the elongated shaft until the proximal rim 17 touches the distal spherical portion 8 of the proximal head 4. At this point, the proximal head 4 can be seated into the washer 3 by using the assembling device 22.

(39) Thanks to the above mentioned features it is possible to intraoperative chose the combination between the elongated member 2 and the washer 3 and assemble the bone fixation device 1 during the surgery.

(40) In order to be able to intraoperative assemble the washer together with the head the tolerance between the two components are very strict. In particular interference between washer and head is 0.005-0.08 mm or 0.005-0.2 mm.

(41) It is further possible to choose between washers suitable for different maximum transversal dimension Dh of the proximal head 4. The washers will be designed in different sizes, with a diameters larger than Dh by 2 to 15 mm or 2 to 25 mm. For example if the screw has a maximum transversal dimension Dh of 10 mm, the relevant washers can be designed in a diameter range of 12 to 25 mm, or between 12 and 35 mm.

(42) FIGS. 5-7 are related to a bone fixation device 1 for trauma applications, like the preceding embodiment, in which the elongated member 2 is long about 180 mm. Reference numbers are identical with the reference numbers used in the preceding embodiment. Characterizing features of the head 4 and washer 3 are the same.

(43) FIGS. 8-10 are related to a bone fixation device 1 for SI-Joint Arthrodesis. The elongated member 2 is shorter with respect to the preceding embodiments and does not have a smooth portion or has a very short smooth portion. The threaded portion has a dual lead thread. Fenestrations 21 are elongated along the axis 6. Reference numbers are identical with the reference numbers used in the preceding embodiment. Characterizing features of the head 4 and washer 3 are the same.

(44) The embodiments disclosed above can be provided with a screw having a single lead thread.