Self adjusting, high strength, screw system

ES 2 249 449 T3

DESCRIPTION

High resistance self-regulating screw system.

Field of the invention

The field of the invention is constituted by mechanical fastening elements, mainly for orthopedic use, for high vibration environments and for substrates subjected to erosion.

Background and summary of the invention

Screws are used to hold various materials together and generally depend on the wedge penetration of the threads and the screw shank into the substrate into which the screw is pushed to obtain a secure joint. However, this wedge action applies resultant forces and stresses to the substrate, which, under certain circumstances, accelerate the deterioration of the substrate at, or adjacent to, the interface or interface between the screw and the substrate, and this can lead, in turn, to loosening of the screw.

An example of this effect occurs in orthopedic screws that are pushed into the bone. These screws can damage bone cells at and in the vicinity of the bone-screw interface, causing the bone to slowly back away from the screw and eventually causing the screw to loosen or loosen. Another example occurs in wood, where wedge forces crush the wood adjacent to the interface between the wood and the screw. Also stone and concrete frequently crack as a result of the wedge forces of normal screws and bolts, especially where they are located close to the edges. In metal fabrication, where the wedging action of a screw being tightened into a metal substrate can alter the metallurgy of the substrate immediately adjacent to the interface or interface between the screw and the substrate. This metallurgical alteration can, under certain circumstances, accelerate the rate of corrosion and ultimately lead to fastener failure.

In many cases, there is a very limited elastic path or gap in the substrate into which the screw is tightened. Any setback of the substrate with respect to the initial interface between the substrate and the screw will result in a drastic reduction in the wedge force on which the screw depends for its grip and clamping, since the reaction forces exerted by the rigid substrate fall rapidly with the substrate recoil.

One method currently used to increase the holding capacity of the screw is to fix a spring washer below the head of the screw, which increases the friction and wedge forces between the screw thread and the substrate in the one in which the screw is inserted by tightening. The difficulty of this solution lies in the fact that the elastic washer pulls the screw out of the internal cavity or bore into which it has been pushed, instead of pushing it into it. If the screw does, in effect, become loose for any reason, this pulling force can act to accelerate further loosening of the screw. An added difficulty with this method is that it often exerts uneven pressure on the various parts of the screw thread. This uneven pressure application can result in lower total friction being available to hold the screw securely in the substrate, and also, in some cases, in increased substrate damage, which in turn time, they can cause additional loosening.

What is needed is a screw system that does not rely critically on wedge forces to maintain its grip and hold within the substrate.

What is also needed is a screw system that tends to push the screw into the substrate into which it is pushed in, rather than pulling it out.

What is also needed is a screw system that evenly distributes the friction forces along the interface between the screw and the thread, over which it slides.

What is also required is a screw system that is capable of maintaining stationary clamping forces, even as the substrate recoils away from the screw.

Document WO-A-0175315 (prior art under Art. 54 (3) of the EPC) describes various means to satisfy the above-stated requirements. The present invention resides in the fastener assemblies according to claim 1 or claim 2, which allow higher clamping forces to be maintained and, in some preferred embodiments, do not require adhesives to hold the screw and helix of the system together. for applying torque and radial load to the propeller prior to insertion.

The present invention consists of a screw system that maintains grip and hold on the substrate, by maintaining a relatively small and constant force perpendicular to the longitudinal axis of the screw, even in the event that the substrate recedes away from the separation surface. or interface between the screw and the substrate, and as it does so. This force perpendicular to said longitudinal axis of the screw can be kept relatively constant and can be set in advance for various specific purposes, in order to avoid unnecessary damage to the substrate into which it is inserted. Also, the screw system expands as the substrate recedes, thereby maintaining intimate contact between the two. Additionally, the screw system can apply a controlled and relatively constant force, parallel to the longitudinal axis of the screw, which pushes the screw into the hole into which it is tightened, and increases the friction between the screw and the thread within. from which it is tightened, thereby reducing the possibility of the screw reversing out of the hole.

A preferred embodiment of the invention consists of a system composed of a screw and a helix or helical turn (the terms have the same meaning in this patent). Both the screw and the helix are inserted into the substrate. The helical coil is a helix usually formed of metal wire, although it may have been formed from any material to which some elasticity may have been imparted, including plastic and biodegradable plastic. The screw is screwed into the center of the propeller, whose turns or turns, by the surface in2

ES 2 249 449 T3, describe the thread that engages or engages with the screw threads. The outside of the helix also forms a thread that can be threaded, in turn, inside an incised or cut thread in the internal walls of a hole made in the substrate into which the screw system is inserted by tightening and propeller. In the event that the hole walls have not been prepared with a thread, the propeller can still be threaded into the hole so that the propeller itself will press or cut thread threads that will engage with those thread threads (formed by the propeller turns) existing on the outside of the propeller.

This screw and helix combination is well known in the art. US Patent No. 4,712,955, Reece et al., Describes a screw and helical turn system in which the screw is larger than the helical turn and forces the helical turn out perpendicular to the longitudinal axis of the helix and of the screw, with the use of threaded threads as a ramp, arranged on the screw, and of receivers arranged inside the propeller. This action creates very strong wedge forces that hold the screw and helix assembly within the hole in the substrate. This method, while suitable for some purposes, is unsuitable in the event that the substrate is likely to recede away from the initial helix-substrate interface. As explained above, even though the wedge forces are very high, they are maintained over a small distance perpendicular to the longitudinal axis of the propeller and screw, and they drop drastically when the substrate retracts and moves away from said interface. .

The preferred embodiment of the invention includes a screw and screw system, although the screw tends, by various means, to expand once it has been inserted into a substrate independently, and not by being forced to do so by another element of the screw system. fixation. These media are referred to herein as "expansion media." While expansion is desirable, it should not come at the cost of loosening the screw from the substrate as the helix travels away from the screw in response to the helix following the substrate recoil. WO-A-0175315, Unsworth and Waram, referred to above, describes a means to ensure that the joint between screw and helix is ​​maintained under these conditions, and these means can be combined with the preferred embodiments described herein to accomplish the same purpose.

Unlike the wedge action of the conventional screw or the conventional screw and helix combination, the helix will expand radially over a relatively large distance, following any recoil of the substrate as it moves away from the initial interface between the substrate and the helix, and , specifically, if a super-elastic shape memory alloy (SMA) material is used for the propeller, the forces exerted by the expanding helix on the interface substrate into which the screw and helix are tightened will be relatively uniform, predictable, and repeatable. The expanding screw and helix combination will also maintain, by various means described below, the gripping and holding of the screw and helix combination on the internal cavity or bore of the substrate into which said combination is pressed.

A preferred embodiment of the invention includes means that tend to increase the friction between the propeller and the screw, and, at the same time, drive the screw further into the bore of the substrate into which the screw is being tightened and inserted. the propeller. These means are referred to herein as "torque applying means" and "corrugation means".

Preferred embodiments of the invention may incorporate either the features that tend to expand the helix once it is within the substrate, or features that tend to increase the friction between the helix and the screw, and drive the screw into said cavity. interior, or both.

The expansion means involve both arranging the helix around the screw, wrapping it, and then introducing new conditions that allow it to expand. The first of such means consists in starting with a helix that has a certain elasticity and that, in its unloaded state, has an internal cavity or bore diameter that is greater than the external diameter of the screw around which it will be screwed. Once the propeller has been arranged around the screw, wrapping it tightly, so that the turns or turns of the propeller are located between the double interleaved threads of the screw so that they engage or mesh, the propeller will adopt a larger diameter. compact and, if it is confined by some means in this compact form, it will expand when the confinement means is further removed. The elastic material will include conventional or super-elastic elastic metalloplastic material, the latter of which is a shape memory alloy (SMA) material that is above its end austenitic temperature, both in its compressed and in its compressed form. expanded form.

The second means to carry out the expansion of this helix consists of using a helix that is made of shape memory alloy material (SMA - "shape memory alloy") whose shape has been fixed at high temperature so that it forms a helix having an inner cavity diameter that is greater than the outer diameter of the screw around which it is to be wrapped. Once the propeller has cooled below its final martensitic temperature, that is, it is capable of bending or folding, it is arranged around the outer diameter of the screw, wrapping it tightly, in such a way that the turns of the propeller are between the Interleaved double threads of the screw, so that they mesh or fit together. The propeller will then adopt a diameter more compact than its hot-set size, before cooling. When the helix is ​​then heated to a temperature equal to or greater than its final austenitic temperature, it will recover to the high temperature or larger diameter shape and the helix will expand.

Torque applying means may be imparted to the propeller in a similar manner. The application of torque occurs when a certain kink is imparted to the wire, along the longitudinal axis of the wire that forms the helix, or, in the case of a helix made from a tube, when the twist is imparted to the tubular member that forms the helix, along its longitudinal tube axis.

ES 2 249 449 T3

The application of torque can occur simply by compressing the coil spring or pulling it along the longitudinal axis of the original or starting coil (as opposed to the longitudinal axis of the coil forming member). The application of torque can also take place in a more direct way, by grasping and twisting a part or parts of the helix spring, along the axis that runs longitudinally through the wire or tubular member that forms the helix. This special way of imparting torque to the spring is referred to in this patent as "camber".

For example, the helix may be made of wire with a rectangular cross section, rather than the usual round, so that the smaller sides form the outer and inner surfaces of the helix, and the larger sides constitute the facing surfaces between the helix. turns or turns of the propeller. Such a propeller will look like a "Slinky-Toy^TM”(“ Winding toy ”). These turns, of the "Slinky-Toy", for example, are flat and have the longitudinal axis of their rectangular cross sections approximately perpendicular to the longitudinal axis of the primitive helix. Now, if said cross sections of these turns, unlike a "Slinky-Toy^TM”, Were arranged at an angle, in their unloaded state, in such a way that their longitudinal axes form an angle of 45 degrees with respect to the plane that passes perpendicularly through the longitudinal axis of the primitive propeller, each turn of the propeller (if this consisted of a solid loop or loop) would adopt a cone-like disk shape. This shape would be similar to, but not coincident with, a Belleville washer. If the propeller were made of an elastic material, each turn of the propeller would act as a Belleville washer in the event that force was applied to move the turns, or else its cross sections would be tilted relative to its unloaded configuration, at an angle. and in the shape of a disk like a cone, up to its flat loaded configuration (or some configuration that has a different angle than the discharged configuration). Any propeller can be angled, although the most convenient are those with cross sections that provide grip points, such as a rectangle, diamond, cam, or triangle.

The tilting means (the special way of applying torque as described above) can be brought into effect, similar to the expansion means, in two physically related paths. The first way consists of inclining the turns of the helix of an elastic material as described in the immediately preceding paragraph, and then removably or removably fix the turns of the helix along all or part of their surface on the screw, such that, when the fastening restraints are removed, the turns of the propeller thus treated will unload and spring back, tending to drive the screw further into the substrate into which it is being pushed, by reacting against the threads of the interior cavity of the substrate, on the one hand, and against the threads of the screw, on the other hand. The elastic material that makes up the helix can include conventional elastic metal or plastic, or super-elastic material, the latter of which is a shape memory alloy (SMA) material that is above its final austenitic temperature. , both in its compressed form and in its expanded form.

The second way is to make the propellers from a shape memory alloy (SMA) material and impart to them, at an elevated temperature, typically in the range of 400-500 ° C for nitinol, for example, a sectional shape. that will be recovered once the propeller has cooled down to a temperature equal to or lower than the final martensitic temperature, and then heating them to a temperature equal to or greater than their final austenitic temperature. The shape thus conferred will be such that, when it is confined below the initial martensitic temperature and then subsequently heated to or above the final austenitic temperature, it will present a certain inclination imparted to the turns of the propeller. As the SMA material has been heated to or above the final austenitic temperature, it will be super-elastic and analogous to a spring or spring, and will therefore be able to spring back and, as in the preceding example, it will tend to push the screw on which it is rotated forward, driving it into the substrate. If the shape of the cross-section at high temperature is the same as in the previous example, that is, the longitudinal axis of the propeller cross-section, in its unloaded state, is arranged at an angle of 45 degrees with respect to the plane. passing perpendicularly through the longitudinal axis of the primitive or starting turn, and while being flattened while below the final martensitic temperature, in such a way that the same longitudinal axis of the cross section of the helix is ​​parallel to the plane that passes perpendicularly through the longitudinal axis of the primitive helix; and if the turn is then confined in such a way as to maintain said flattened cross section, when the helix is ​​heated to or above its final austenitic temperature, it will be tilted. Once tilted, the propeller, being now super-elastic and spring-like, will spring back and, as in the previous example, will tend to push the screw forward, making it penetrate the substrate.

Propeller turns can also be corrugated rather than slanted. The propeller shall wind back and forth such that the ridges of the corrugations begin at the inner bore or cavity of the propeller and propagate or continue outward to the outer surface of the propeller, usually perpendicular to the longitudinal axis of the propeller. the helix, although other angles or curves may be used in some preferred embodiments, as described in the detailed description of the drawings below. This type of treatment will be applied, in some preferred embodiments of the invention, to the "Slinky-Toy" type propeller.^TM", That is, to one with an approximately square or rectangular cross section. This treatment could occur in addition to, or instead of, the tilting means referred to elsewhere. The means for carrying out this will be similar to those used for carrying out the above expansion means. The corrugated helix can be made of spring-like material and, in its unloaded state, can be flattened and confined by a releasable fastener provided on the screw. When unloaded, the propeller will relax until adop7

ES 2 249 449 T3 will retract its corrugated shape and will spring back, tending to drive the screw further into the hole into which it is inserted by tightening, by reacting against the thread threads of the interior cavity of the substrate, on the one hand, and against the screw threads, on the other hand. This spring-like material will include conventional elastic metallic plastic or super-elastic material, the latter of which is a shape memory alloy (SMA) material that is, at or above its final austenitic temperature, both in its compressed form as well as in its expanded form. Similarly, the material can be made of shape memory metallic (SMA) material, such that this method makes use of the shape recovery regime. The recovered shape can be corrugated. The corrugated helix can be flattened into its corrugated shape at a temperature equal to or lower than the final martensitic temperature, and fixed to the screw. When heated to or above its final austenitic temperature and confined in its flattened shape, the corrugated shape will rebound, load and be super-elastic, and when it is no longer confined it will spring back, thus tending to driving the screw further into the hole into which it is made to penetrate by clamping, by reacting against the threads of the internal cavity of the substrate, on the one hand, and against the screw threads, on the other hand. Instead of corrugating the helix, the helix can, of course, be a hollow tube and can have a compact and expanded effect by virtue of the same means as the corrugated helix, for the same purpose of providing elastic recoil that displaces the screw further within the substrate, and to increase the frictional forces that hold the screw in position.

Finally, tilting means may additionally be applied to any of the aforementioned methods or to any combination thereof, by rotating the screw within the helix while the turns or turns of the helix are confined by the threads. of the substrate into which the screw and the helix are inserted, and the forward progression of the screw is stopped by the screw head when it collides with said substrate, or by the tip of the screw when it hits a part of the substrate that prevents any further advancement of the screw. When this occurs, the screw threads will tend to pull on the inside of the helix, with which it forms a separation surface, in a direction opposite to the direction in which the screw is tightened into the hole in the substrate. This is especially the case if the turns of the helix are loosely nested between the interleaved double threads and / or the radial diameter of the turn is greater than the radial diameter of the most distant or distal thread, or closer. , or proximal, or both. When the screw is no longer rotated, and if said helix is ​​made of elastic material, the elastic recoil of said helix will tend to drive the screw further into the hole into which it is inserted by tightening, by reacting against the threads. of the internal cavity of the substrate, on the one hand, and against the threads of the screw, on the other hand.

As the propeller expands, it also unwinds, and therefore, in the event that a very long threaded section or length is required, it is preferable that a series of small propellers be placed end to end, in order to constitute the long stretch you want. This will reduce friction at the interface between the coil and the substrate, which could otherwise prevent the coil from unwinding and expanding. These small helixes could be independent or detachably fixed, in such a way that they separate once they are located inside the interior cavity of said hole in the substrate. The simplest means of releasing the helixes is to insert a groove or groove at intervals along the length of the helix wire so that separation will occur when the screw is turned as far as possible. sufficient to cause torsional forces to be imparted to the propeller.

Although the helix, provided with or without a spike, can be inserted into the substrate with the use of helical insertion devices well known in the art, the preferred embodiment loads the helix onto the screw prior to insertion into the substrate, as has been admitted in the foregoing. In the event that the helix is ​​inserted into the substrate with the use of an insertion tool, this will obviously require means for releasably securing the helix, similar to those used in the screw and helix combination being used. described herein in greater detail, as a consequence of which a preferred embodiment of this invention will include an insertion tool that will have the same characteristics as the screw and helix combination described herein.

These confinement means referred to in this patent require, in most cases, a removable or detachable fixation in one or more places along the interface between the helix and the screw, which are well known in the art and include a press fit, press weld, spot weld, adhesives, flexible adhesives and biodegradable adhesives, as well as water soluble adhesives, the last of which will be of particular use in orthopedics and in woodworking. Plastic fasteners or a plastic sleeve or sheath may also be employed, which could be biodegradable or simply peel off or peel, split, or be deformed as the helix and screw are pressed into the substrate. The preferred embodiment provides means for breaking the releasable fixture when the screw imparts sufficient torsional forces to the helix, as the screw is finally tightened and the helix is ​​deformed by the action of the screw. The materials of the junction points can also be biodegradable and dissolve over time in the presence of solvents such as water, or corrode by biochemical or electrochemical action, for example galvanic action. Adhesive materials or mechanical fasteners between the helix and the screw will be weaker across the axis of the helix wire or tube, rather than parallel to it, since the helix will more easily wind in the transverse direction in response to torque forces, than in the parallel direction, in which bending forces are required in the propeller. This allows the helix to be drawn into the substrate with a relatively weak bond between the helix and the screw, but once inside the substrate, only a relatively small torque action is required, which

ES 2 249 449 T3 causes the helix to wrap over the screw, to break the joint.

In orthopedic use, the use of a screw and helix combination makes it easier to remove the screw without damaging the bone tissue. The screw can be turned outward and the threads will slide along the turns of the helix, rather than scraping the bone along it. The helix can be removed by pulling on it with the use of helical extraction devices well known in the art, although, in most cases, it will remain in the bone, as the helix is ​​small and soon becomes embedded in the bone. bone as it grows.

For orthopedic use, if the propeller is made of a super-elastic material of shape memory alloy (SmA- "shape memory alloy"), the system that constitutes the object of this invention has the additional advantage of applying the forces of attachment by means of relatively constant forces over significant distances, even as the relative positions of the fixation system and of the bones are changed by the retreat and growth of the bones. This feature applies to all other uses as well.

The uniform and predictable forces exerted on the substrate by a propeller made of super-elastic material, for example, superelastic nitinol alloy, are primarily due to the relatively consistent discharge bending forces exerted by the turns of the propeller as radial forces on the substrate, as the confined "coiled" helix releases or elastically recoils, after or during installation of the screw / propeller assembly. All or some of the turns of a super-elastic helix are loaded in advance fundamentally when bending the screw-helix assembly before its installation, by virtue of the application of a certain bending moment, in such a way that the curvature of each preloaded turn it is increased with respect to the curvature of the turn in the unloaded state, in which no bending moment is applied. A possible load path during the preload of a turn of a super-elastic propeller is the ABD path of Figure 9, although there are many other load paths in which loading can occur up to a point between B and D, for example, C. During installation of the screw / helix assembly, the preloaded turns will unload, thereby experiencing radial expansion in response to substrate recoil or a decrease in substrate stiffness. This discharge can take place in a number of possible ways. One possible discharge path is the DEG path in Figure 9, although many other discharge paths can be taken to any point beyond D along the DEFGA path, for example discharge to a point F between E and G. In the case where the precharge was performed to a point between B and D in Figure 9, the discharge can occur to any point along numerous subordinate paths, an example of which is the CGA. It is also possible to facilitate the partial unloading of the super-elastic helix turns or turns following preload and prior to installation of the screw / helix assembly in the interior cavity of the substrate.

Similarly, elastic recoil from tilting or torque application of the propeller turns will provide a predictable, uniform thrust force that keeps the screw pushing to penetrate the interior cavity of the substrate, due to the super-elastic behavior of loading and unloading by twisting the turns of the propeller, in a manner similar to the super-elastic moment-bending bending behavior described above.

For orthopedic use, the helix can be designed to respond in the same way as the bone itself to loads and shocks, thereby reducing stress concentrations at the repair site. In the case where the screw system is used to hold two bones together, the resistance of the tilt and the magnitude of the expansion of the coil can be adjusted so that the optimum pressure required to hold the two bones together is obtained, in order to promote the growth and repair of bones. This feature applies to all other uses as well.

The system that is the subject of this patent is particularly suitable for environments with large temperature fluctuations or in which vibrations are present. Spatial structures that have huge temperature swings will benefit from the fixation system described here. The engines and airframes will also be capable of making use of the attachment system described herein.

Brief description of the drawings

The detailed description refers in particular to the accompanying drawings, in which:

Figure 1 is a perspective view of a propeller 1 having an approximately rectangular cross section.

Figure 2 is a cross-sectional view of a screw 4 having two interspersed helical threads 5a and 5b.

Figure 3 is a perspective view of said propeller 1, loaded around the screw 4 so that the threads 5a and 5b of the screw are located between the turns or turns 2 of the propeller.

Figure 4 is a cross-sectional view of the substrate 9, in which a hole has been drilled and threads 10 cut into the walls of the hole to provide accommodation for the helix 1 and screw 4.

Figure 5 is a cross-sectional view of screw 4 and helix 1, which have been threaded into an existing hole in substrate 9. The cross-sectional shape of helix 3, in this illustration, has been shaped roughly like a rectangle with a beveled angle, which, when combined with threads 5a and 5b, forms a single, more robust thread. Figure 5 also illustrates how the pair formed by the closest, or proximal, thread 5a and the most distant, or distal, thread, 5b, holds the turns of the helix in position with applied torque, preventing them from springing back. while it is radially loaded, before radial expansion.

Figure 6 is a cross-sectional view of the screw 4 and of the helix 1 as illustrated in Figure 5, although the substrate 9 has receded away, 15, from the initial interface or separation surface between the screw and substrate, and the helix, which was radially loaded, expands ha6

ES 2 249 449 T3 is located outside, 13, to maintain contact with the threads located on the inner walls of the hole made in the substrate. Figure 6 illustrates the helix in its partially expanded form, and in it the turns of the helix, 2a, have elastically retracted from their fully twisted position to push, 14, the screw 4 into the bore or interior cavity of the substrate 9. Figure 6 also illustrates the distal thread 5b and the proximal thread 5a, the latter of which allows the turns of the helix 2 to elastically retract as a consequence of its smaller size and, in some preferred embodiments, its curved surface 11.

Figure 7 is a perspective view of said propeller 1, loaded around a cross-sectional view of the screw 4, in such a way that the screw threads 5a and 5b lie between the turns 2 of the propeller. Figure 7 also shows a method for releasably or removably securing the proximal end of the helix to the screw 4, by applying a force 18 or 19 to a section or curved section 16 of the proximal end of the helix turn 2.

Figure 8 illustrates a helix 1 having a corrugated cross section 2c.

Figure 9 is a graph that illustrates the behavior of the bending moment as a function of the curvature of a bending member.

Detailed description of the drawings

Figure 1 illustrates a propeller 1, which may have one or more turns 2 and has the dimensions required for the use for which it is used. The cross section 3 can be any shape that provides a grip to the screw 4 that is illustrated in Figure and its threads 5a and 5b, which is threaded inside the internal cavity of said helix 1, as illustrated in Figure 3, and a certain grip on the thread or surface 10 located inside the substrate 9, both shown in Figure 4. The screw includes means 8 to make it rotate, in this case, a slot made in the head 7 of the screw 4. The cross section may include shapes such as beveled, rectangular, as shown in Figure 1, or any other shape that provides such a necessary grip to the substrate 9 and screw 4. The shape of the cross section 3 will depend largely on the mechanical properties of the substrate and, in particular, its resistance and its tendency to recede with time away from the initial interface or separation surface between helix 1 and substrate 9. In the same way, the cross-sectional shape of the screw 4 and of the threads 5a and 5b can be of any shape that fits or fits properly with the helix 1 and that allows the helix to expand and control the position of the screws. helices with respect to the screw 4 and the substrate 9. The height of the threads with respect to each other and the turns of the helix that they embrace, can vary depending on the demands of the substrate and the use.

The distinguishing feature of this invention is the double helical threads 5a and 5b that enclose helix 1. Figure 5 illustrates, for clarity of diagram, only two of the turns of helix 2. The preferred embodiment illustrated is only one of many combinations incorporating the invention disclosed herein. The relative sizes of the distal 5b and proximal 5a threads can vary, and their shape can vary, depending on the loads required and the substrate into which you insert the screw. It is to be appreciated that while the interleaved helical threads 5a and 5b are referred to as discrete threads, they may be manufactured as a single thread which then has, cut into it, a groove of various shapes intended to form a similar configuration.

The advantages of using a double thread to hug the propeller are numerous. First, if the propeller is made to spring back 12, as described above, and push screw 4 in direction 14, as shown in Figure 6, the clamping threads can hold the screw 4 together. helix in the loaded position, before appreciable radial expansion occurs, without having to resort to adhesives, and as long as the helix has some form of fixation to the screw at the distal and proximal ends, in order to avoid premature expansion; although it remains an option in some preferred embodiments of the invention releasably to fix the helix 1 to the distal and proximal threads, or both, at other points by various means. Once the substrate recoils and the radially loaded coil expands by the means described above, coil 2a is, as shown in Figure 6, free to elastically recoil and wrap over proximal thread 5a. The fact that the proximal thread 5a is shorter than the distal thread 5b, makes this elastic recoil rotation possible even though the turn of the helix 2 has expanded radially away from the screw 4 only by a small distance. This springback rotation can therefore push the screw 4 in the direction 14, and thereby more securely push the screw into the substrate, even at an early stage of the recession of the substrate 9 away from the screw. 4. The proximal thread 5a may also be curved, 11, as shown in the detail of Figure 2, in order to create the same effect. The curvature of the proximal thread allows it to be larger compared to the distal thread 5b, which, in some applications, can be an advantage. Both the relative size and shape of the distal and proximal threads can be modified accordingly by combining shapes and sizes to suit the screw system for the particular purpose.

Figure 5 illustrates how the lateral forces, which run from the distal end to the proximal end of the screw along its longitudinal axis, and which are applied by the screw 4 to the substrate 9 by virtue of the application of torque torque to the screw, are distributed between the distal 5b and proximal 5a threads and the turns of the helix 2. This makes the screw system much more robust and suitable for applications that require high torque loads on the screw.

The proximal thread 5a also prevents the turns or turns of the helix 2 from winding up and out of the distal thread 5b, in a direction opposite to the direction of elastic recoil 12, as the helix expands radially. This is the fundamental advantage of the system, which allows high torque loads to be applied to the screw while, at the same time, allowing the screw system to expand and follow the receding substrate. The fact that this can be achieved, in a preferred embodiment of the invention, with the use of a small proximal thread 5a, means that there is more substrate mass that has not been excessively displaced and is therefore available in 7

ES 2 249 449 T3 between the threads to hold the screw securely.

An additional advantage of the braced helix system is that the distances between the distal 5b and proximal 5a threads can be increased, allowing the turns or turns of the helix to rotate in direction 12, as illustrated in Figure 5 and Figure 6 , or that they turn in the opposite direction, allowing the application of torque in the turns of the propeller 2 by the operator to rotate the screw after the screw head contacts the substrate and the forward movement within the substrate has been thereby , stopped. Once the torque applied to the turns is adjusted in this way, the turns will spring back in direction 12 and thereby push screw 4 further into the substrate in direction 14, as shown in Figure 6. This method of imparting a twisting action to the threads is in addition to the other methods described herein, such that it is possible to use one or any of the methods in combination.

Figure 5 illustrates the system once the spring coil has been radially loaded or tilted, or both, and confined; either once it has been given a shape that will be restored with the application of heat, or all these things.

Figure 6 illustrates the system once the spring coil has been released from its restraints or has been heated to or above the austenitic end temperature, and has regained its largest diameter or slant shape, or both. The final turns of screw 4 may have been loaded with additional torque or tilt to the turns that will unwind or elastically retract in direction 12. Figure 6 also illustrates when the substrate 9 has receded from the initial interface between the helix and said substrate, and the approximately rectangular and beveled cross sections of the turns 2a of the helix 1 have followed the substrate in retreat and maintained the grip of the threads of the screw with the helix and, in turn, of the helix with the threads 10 of the substrate

9.

The substrate 9 can be of any material into which the screw and helix system can be inserted. This will include bone or cartilage for orthopedic uses, as well as metal and plastic and wood for structural or ornamental uses.

The system may include a number of propellers, rather than just one, located end to end. These may be in butt contact or may be separated from each other, depending on the circumstances. Figure 1 illustrates a helix that is releasably attached and detaches to form, in this example, three independent helixes. The grooves 6 made in the outer surface of the helix 1 so that the longitudinal axis of the helix wire runs around it approximately transversely, create lines of weakness that allow the helix to split when twisted or twisted. applies a torque, once located within the substrate 9. This twisting or torque application can occur when the screw is tightened in place, but it can also occur later, when the propeller begins to expand or release its torque application action, once the substrate begins to recoil. moving away from the initial interface between the helix and the substrate. This separation or division of the helix allows the helix to unwind along its longitudinal axis as it expands within the substrate, without excessive frictional resistance between the surface of the helix and the corresponding or conjugate surface 10 interface 9. These means of releasably attaching helixes, in the event that multiple helixes are used, are merely illustrative, and other methods of releasably attaching helixes are well known in the art, such as the use of adhesives or weld points, to mention two.

The means for fixing the screw 1 on the screw 4 will be explained in greater detail below, although, in order to enable the screw and the screw to be rotated together so that they penetrate the substrate, it will be necessary to at least fix the distal end of the helix to the distal end of the screw, so that said fixation may be removably fixable. Such releasable attachment can be made by use of adhesives, biodegradable adhesives, welds or mechanical bonds such as hooks or mortise and push-fit tendon, or other such means well known in the art. Once in place within the substrate, the fixation means, except perhaps for the distal end of the screw and the helix, should be removable, such that the helix is ​​free to expand with the interface receding between helix 1 and substrate 9. This detachment can occur, for example, due to the torque applied action that is imparted to the propeller by tightening the screw, or due to the biological degradation of the adhesive bond mentioned above. The methods for fixing the helix to the screw are described in that US Patent Application No. 09 / 541,508, Unsworth and Waram, referred to above, and all of these can be used for fixing the preferred embodiments of the invention. present invention. However, because the helix is ​​located between two helical threads interspersed in preferred embodiments of the present invention, the helix will, in many cases, only need to be releasably attached to the screw at the distal or proximal end, or for both.

Figure 7 illustrates a mechanical method whereby helix 1 can be releasably attached to screw 4 at the proximal end. The space between the distal and proximal threads may be greater at the proximal end, so that space is provided at the proximal end of helix 1 so that it is curved and then joined by points, 17, by laser welding or other means. suitable well known in the art, to one of the threads, in this case the proximal thread 5a, as shown in detail 16a. The fixation point can be broken by simply rotating that part of the screw so that it penetrates the substrate 9, which will exert a force 18 on the curved section 16 located at the proximal end of the helix, which makes it straight or straight and moves said proximal end towards the distal thread 5b, as shown in details 16b and 16c of Figure 7. Alternatively, the operator can simply apply a force 19 that bends the distal curved tab, for example, with the use of gripping means, away from the thread to which it is releasably attached, thereby breaking the attachment and allows helix 1 to expand away

ES 2 249 449 T3 of screw 4. As shown at 16c, when helix 4 expands, the portion of turn 2 tends to move in direction 20.

It is to be appreciated that the various sections, segments or areas of the helix, regardless of their cross section, due to their flexibility, act with some independence and, consequently, an irregular recoil of the substrate 9 by the helix 1 can be allowed. , as the helix follows the threads 10 of the substrate 9 in reverse.

Fixation at the distal tip of screw 4 and at the distal end of helix 1 will, in most preferred embodiments, be removably fixable, although it may be permanent. This distal joint will be important when screwing the assembly into the substrate 9, since, once the first turns of the screw 4 and of the helix 1 are inside the substrate, the helix will be pulled in and the threads 10 of the substrate 9 will guide the next and proximal parts of the helix and screw.

There are various methods of providing heat in order to regain the shape of the propeller, in order to provide the torque and expansion of the propeller, as described above. It is possible to rely on the heat of the substrate itself if the substrate temperature is equal to or greater than the end austenitic temperature of the shape memory alloy material (SMA) and does not decrease to below the initial martensitic temperature of the alloy material with shape memory (SMA) (which would cause the propeller to lose its strength and shape). In order to prevent premature propeller activation, the substrate temperature can be temporarily lowered to below the austenitic initial temperature of the Shape Memory Alloy (SMA) material, during installation of the screw and propeller inside. from the interior cavity of the substrate, and then subsequently raised, by active or passive means, to or above the final austenitic temperature, once the screw and propeller are properly located within the interior cavity of the substrate. In the event that the shape memory alloy (SMA) material has an austenitic initial temperature, or possibly in some situations, an austenitic end temperature, equal to or lower than the ambient temperature of the transport, storage and environment environments. installation, the propeller can be cooled by some means such as refrigeration or immersion in liquid nitrogen, or its packaging in dry ice, after it has been manufactured and before its installation. For orthopedic use, this method will most often be used when the austenitic initial temperature, or, in some situations, the austenitic end temperature, of the shape memory alloy material (SMA) is equal to or less than the body temperature.

It is also to be appreciated that, for the sake of illustration simplicity, screws and helixes are not shown in a convergent or tapered shape at their distal tips, although this will normally be the case in most applications and will not alter the by no means the main features of the preferred embodiments described herein. It is also noteworthy that the drawings do not show all turns of the propeller or threads for the sake of illustration simplicity.

Although the description of the preferred embodiments combines the characteristics that favor the torque application action by the inclination of the turns 2 of the screw 4, in addition to the characteristics that cause the propeller 1 to expand, it is understood that certain embodiments of This invention may comprise all of these features together, or just some of them.

While the description of the helix includes a solid or hollow tube, it is to be understood that the helixes can be composed of a multiplicity of wires or tubes, or of both, woven or interlaced, in addition, with any composite material. It is also to be understood that it is possible to use a multiplicity of helices, rather than just one. These helices could be intertwined or braided with each other, for example in the shape of a double or triple helix.

Although the description speaks of a screw, it is to be understood that the member can include any fastening device that has a thread that can engage or engage with a helix, for example, a lag screw or a bolt and nut assembly, or a threaded substrate. . The helix may, for example, be releasably attached to a substrate, as discussed in the preferred embodiments described above, and the screw can then be screwed into the substrate and helix assembly; that is, this preferred embodiment may be just the reverse of the preferred embodiments described above.