AU757039B2

AU757039B2 - Bone screw

Info

Publication number: AU757039B2
Application number: AU54052/99A
Authority: AU
Inventors: Roger Berger; Piet Reynders
Original assignee: Synthes AG Chur
Current assignee: Synthes GmbH
Priority date: 1999-09-08
Filing date: 1999-09-08
Publication date: 2003-01-30
Anticipated expiration: 2019-09-08
Also published as: ES2228085T5; ES2228085T3; JP4145044B2; EP1210019B2; AU5405299A; KR100656573B1; ATE279887T1; CA2405230C; NZ517314A; CN1367665A; KR20020035642A; CN1261082C; CA2405230A1; EP1210019A1; WO2001017447A1; TW466310B; EP1210019B1; JP2003508147A; DE59910917D1

Abstract

The invention relates to a bone screw that is provided with a head (1), a shaft (2), a central longitudinal axis (3), a screw point (4), a surface area (5) an external thread (6) and an entire length (L). A bore (7) that is open in the direction towards the head (1) and extends coaxially in relation to the longitudinal axis (3) is provided. Said bore is connected to the surface area (5) via at least one channel (8) which extends crosswise in relation to the longitudinal axis (3). The bore reaches the outside in the form of at least one perforation (9) through the surface area (5) and is closed in the direction towards the screw point (4). The advantage of the bone screw is that osteocementum can be introduced into the adjacent bone in such a way that an artificial coaxial cement bed for the thread of the bone screw is embodied. The cement bed is only laterally adjacent to the screw such that said screw can be axially screwed further into the forward direction even after the osteocementum has hardened.

Description

1- Bone screw The invention relates to a bone screw.

DE-OS-3,508,759 discloses a hip screw with a continuous central bore which opens into the open screw tip and has lateral perforations between the thread walls. This hip screw is intended to anchor the overdimensioned and pointed thread in the bone and at the same time, by means of bone cement being injected into the central bore and emerging into the lateral perforations, to strengthen the weakened bone material.

The main disadvantage of this known hip screw is that, once the cement has hardened, it cannot be screwed any further forwards in the axial direction since the cement which has emerged through the open tip of the hip screw and hardened no eoee longer permits this.

oo: JP-07051292-A as well as JP-07222752-A disclose bone o •screws being provided with central through bore, but which comprise perforations over the whole length, meaning from the screw tip to the screw head. The disadvantage of these two ee 20 screws consists therein that bone cement also leaks in the proximal section of the screw what is clinically unwelcome.

The above discussion of background art is included to explain the context of the invention. It is not to be taken as an admission or suggestion that any of the documents or other material referred to was published, known or part of the common general knowledge in Australia at the priority date of any one of the claims of this specification.

The invention is intended to remedy this situation. In particular, it would be desirable to make available a partially bored bone screw through which bone cement can be introduced into the surrounding bone in such a way that an artificial, coaxial bed of cement forms for the thread of the bone screw, iSpci\662043.doc 2which bed of cement, however, only adjoins the screw along the sides, with the result that the screw can be screwed further forwards in the axial direction (tightened) even after the cement has hardened.

Broadly, the invention provides a bone screw having a head, a shank, a central longitudinal axis, a screw tip, a jacket surface, an external thread, and a total length with a bore being provided which is coaxial with the longitudinal axis and open towards the head and which is connected to the jacket surface via at least one channel extending transversely to the longitudinal axis and opens towards the outside in the form of at least one perforation through the jacket surface, wherein the bore is closed towards the screw tip, and wherein the central axes of the perforations, measured on the eeoc 1 5 longitudinal axis, are at a distance of at most 0.5 L from the screw tip.

ee It is thus possible to obtain the advantage, desirable in particular for the securing of bone plates, that the bone screw which has already been fixed can be tightened even after the oooo 20 artificial bed of cement has hardened, because no bone cement can emerge through the closed screw tip and possibly block the axial movement of the bone screw.

In a preferred embodiment of the invention, the flank eeoc angle of the external thread of the bone screw is expediently greater than 250, and preferably lies in the range of 290 to 610.

The central axes of the perforations, measured on the longitudinal axis, should be at a distance of at most 0.5 L from the screw tip.

The diameter of the external thread should be at most mm and preferably lie in the range of 3.0 to 7.5 mm.

The diameter of the central bore and of the perforations should lie in the range of 0.9 to 3.3 mm.

W:\Gcorgio\PWG Spci\662043.doc 3 The number of perforations can be from 1 to 8; relative to the longitudinal axis, they should preferably be arranged on one to three planes oriented at right angles thereto.

The opening of the bore opening out in the head of the bone screw can be designed as a polygonal cavity which can receive a corresponding polygonal screwdriver. The opening can be designed as a socket connection for an adapter for coupling to a bone cement syringe.

The ratio D:F between external thread diameter D in mm and the total exit area F of the perforations in mm 2 should either be in the range of 0.1 to 0.9 mm 1 or in the range of 1.1 to 2.9 mm and the ratio D:d between external thread diameter D and the diameter d of the bore should be in the range of 2.0 to 2.9.

The perforations expediently reach into the area of the thread walls.

The bone screw according to the invention can be used in a known manner for fixing bone plates which have a plurality of continuous plate bores.

The invention and developments of the invention are explained below in greater detail with reference to the partially diagrammatic representation of an illustrative embodiment.

4 Fig. 1 shows a longitudinal section through the bone screw according to the invention.

The bone screw with the central longitudinal axis 3 and the total length L has a head 1 which is adjoined by a shank 2 with a screw tip 4. The jacket surface 5 of the shank 2 has an external thread 6.

Extending coaxially with the longitudinal axis 3 is a bore 7 which is open towards the head 1 and which is connected to the jacket surface 5 of the shank 2 via a channel 8 extending transversely to the longitudinal axis 3 and opens towards the outside in the form of two perforations 9 through the jacket surface 5. The bore 7 is closed towards the screw tip 4.

The central axes 10 of the two perforations 9, measured on the longitudinal axis 3, are at a distance of about 0.28 L from the screw tip 4.

The opening of the bore 7 opening out in the head 1 of the bone screw is designed as a hexagonal cavity, which can receive a corresponding screwdriver.

Claims

2. Bone screw according to Claim 1, wherein the flank 15 angle of the external thread is greater than 250, and preferably lies in the range of 290 to 610.
3. Bone screw according to Claim 2, wherein the central axes of the perforations, measured on the longitudinal axis, are ""at a distance of at most 0.5 L from the screw tip. oooo 20 4. Bone screw according to any one of Claims 1 to 3, oo oo wherein the diameter of the external thread is at most 7.5 mm. oeoeo Bone screw according to any one of Claims 1 to 4 wherein the diameter of the perforations lies in the range of 0.9 to 3.3 mm.
6. Bone screw according to any one of Claims 1 to wherein the number of perforations lies in the range of 1 to 8.
7. Bone screw according to Claim 6, wherein the perforations relative to the longitudinal axis, are arranged on one to three planes oriented at right angles thereto.
8. Bone screw according to any one of Claims 1 to 7, wherein the opening of the bore opening out in the head is designed as a socket connection, for an adapter for coupling to a bone cement syringe. W:\Gcorgi\PWG Speci662043.doc
9. Bone screw according to any one of Claims 1 to 8, wherein the ratio D:F between external thread diameter D in mm and the total exit area F of the perforations in mm 2 is in the range of 0.1 to 0.9 mm
10. Bone screw according to any one of Claims 1 to 9, wherein the ratio D:F between external thread diameter D in mm and the total exit area F of the perforations in mm 2 is in the range of 1.1 to 2.9 mm
11. Bone screw according to any one of Claims 1 to wherein the ratio D:d between external thread diameter D and the diameter d of the bore lies in the range of 2.0 to 2.9. S12. Bone screw according to any one of Claims 1 to 11, wherein the perforations reach into the area of the thread ""walls. oo 15 13. Bone screw according to any one of Claims 1 to 12 with an adapter for coupling to a bone cement syringe.
14. Fixation system with at least two bone screws according to any one of Claims 1 to 15, wherein it includes a bone plate *with a plurality of plate bores for receiving the bone screws. 20 15. Bone screw substantially as herein described with ooooo reference to the accompanying drawings.
16. Fixation system substantially as herein described with reference to the accompanying drawings. Dated: 26 November 2002 PHILLIPS ORMONDE FITZPATRICK Attorneys for: SYNTHES AG CHUR