For occasions where two pieces have to be connected or reconnected to each other often threaded devices like screws or pins are used. They are inserted through both pieces by screwing into a predrilled hole or by self-tapping a hole during insertion thereby fixing the pieces together. Other types of threaded devices are used to attach something. In the medical field, screws or pins are used to fix the pieces of a broken bone together so that they could reconnect. In other cases threaded devices are used to attach a fixation plate to the bone or a suture thread to the bone for connecting soft tissue or ligaments.
Threaded devices like screws are made from all suitable materials dependent on their application. Mainly they are constructed of metal or any kind of plastics, in the medical field also from biodegradable materials.
For insertion of threaded devices a force is applied on the top so that the device is turning around its longitudinal axis, thereby getting screwed and anchored into the material below. If the material is rigid or the device gets stuck it could happen that the device could not stand the applied force and breaks due to torsion along the longitudinal axis. In most cases the screw breaks at the transition between the part including the opening for the screwdriver and the part that is already screwed into the material. Especially with regard to screws made from plastics this is a well-known problem.
For many applications it is desirable to have a threaded device that could be inserted without the risk of breaking due to torsion, especially for devices made from plastics. In addition it is desirable to have a threaded device that could be screwed into a material comprising a different elasticity of torsion than the material of the device.
The threaded device of the present invention overcomes the disadvantage described above by providing openings located distant from the centre of the body, preferably as far as possible at the outer margin of the screw body, for receiving an insertion instrument.
FIGS. 1 to 4 illustrate one example for a threaded device according to the present invention. In
The torque M of a turning body is defined as M=r×F. If M is constant it is valid for different r1, r2 , r3 . . . : M=r1×F=r2×F2=r3×F3(r—radius, F—force). For increasing values of r like r1(r2(r3 the force will behave like F1)F2)F3. Accordingly the application of force on a threaded, turning device is smaller the more distant the point of application of the force is from the central point (see
The body of the device described here could be basically cylindrical or tapered to satisfy the needs of the various applications within the medical field. The passageway(s) could be tapered or not, again dependent on the need of the various applications. It is also understood that the passageway(s) is (are) extending through a majority of the body. It is further understood that at least one passageway of the device is extending through the majority of the body of the device.
As shown in
The screw could comprise two openings as shown in
The threaded devices could either be self-tapping or could be screwed into pre-drilled holes. In addition to the threaded portion they could also comprises at least one non-threaded portion for special applications (see
Threaded devices according to the present invention could be used for all possible applications, in particular for applications with need of threaded devices made from polymers or from biodegradable polymers such as in the medical field including screws, pins, anchors and suture anchors. The threaded device according to the present invention could also comprise additional passageways for receiving a suture thread. In the medical field such a device could be used as a suture anchor to connect a soft tissue or a ligament to bone.
It might be necessary to design a special insertion instrument to fit exactly to the special proximal openings and the corresponding passageways extending through the body of the device. Such an instrument could also work as an thread cutter if the passageways are open at the side as shown in
As shown in
The device may be made from any suitable material. If the device should be applied in the medical area any biocompatible material is preferred to minimise anti-inflammatory response. It could be manufactured from titanium, magnesium, thallium, stainless steel, Nitinol or any other suitable metals or any suitable polymer. Advantageous is also the use of biodegradable polymers, if the device is implanted into the body. The device is then only needed for a limited time, e.g. until the pieces of a bone are reconnected. Preferred materials include polysaccharides, polylactides, polyglycolids, polydiaxanoles or other suitable biodegradable polymers or according copolymers or blends. Degradation of implants made from biodegradable polymers often leads to irritation of the surrounding tissue due to the release of substances like lactic acids. To limit this risk of irritation special compounds could be incorporated into the device material like antibiotics, immunosuppressiva, anti-inflammatory drugs or other suitable pharmaceuticals. If a biodegradable device is inserted into bone, incorporated bone growth factors could help to promote the ingrowth of the bone into the cavity left to replace the implant. A mixture of different compounds might be useful for special applications.
To change the characteristics of the device, e.g. the coefficient of friction, a coating could cover the device. When the surface has less friction, it is easier to insert the device. Implanted devices could also be covered by a biodegradable coating, eventually containing one or more compounds selected from the group of antibiotics, immunosuppressiva, anti-inflammatory drugs, bone growth factors or other suitable pharmaceutical to improve the acceptance of the implant.
For the manufacture of devices according to the present invention every suitable method could be applied, dependent on the material. Devices made from polymers could be manufactured by injection moulding, by extrusion combined with mechanical finish, by producing a casted block, which is subsequently machined, or by using a block produced by polymerisation, which is subsequently machined. The manufacture process of injection moulding could be controlled in a way to result in an orientation of the polymer, so that the device will relax after implantation and therefore will foreshorten and swell. This will then lead to additional anchoring of the device, e.g. into the bone. The density of the outer layer of the device could be influenced by different injection parameters as well, which results in different degradation times. To manufacture a device with incorporated compounds as discussed above devices could be incubated in a solution of the compound(s), so that there will be loaded a certain amount of compound into the device. Dependent on its characteristics the compound could be added to the polymer solution or the polymer resin prior to manufacturing of the device.
Another aspect of the invention is a method of inserting a threaded device into a tissue or structure that comprises the following steps. First, a device is provided that comprises a body having a proximal and distal end, a threaded portion adjacent to and positioned to lie between the proximal and distal portion and at least one passageway extending through the body, said passageway having at least one proximal opening for receiving an insertion instrument. The passageway is thereby orientated such that the torsion is reduced during insertion of the device by the insertion instrument. Second, a hole is eventually drilled into the tissue or structure. Finally the device is inserted into the tissue or structure via an insertion instrument with reduced torsion of the device.
It will be understood that the above-described device is only one example that illustrates the principle of the invention. Various modifications can be made by those skilled in the art without departing from the scope of this invention.
Number | Date | Country | Kind |
---|---|---|---|
02004444.2 | Feb 2002 | EP | regional |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP03/01793 | 2/21/2003 | WO |