Screw and rod fixation assembly and device

ES 2 342 008 T3

DESCRIPTION

Screw and rod fixing assembly and device.

Cross reference with related requests

The present patent application is a continuation application in part of US patent application Serial No. 10 / 823,369, filed April 13, 2004 and published as US 2004/0193160 A1, which is a continuation of the US Patent Application Serial No. 10 / 124,945, filed April 18, 2002 and published as US 2003/0199873 A1, now US Patent No. 6,740,086.

Background of the invention

1. Technical field

The present invention relates to a locking mechanism according to the preamble of claim 1.

2. Previous technique

Various techniques and systems have been developed to correct and stabilize the spine and to facilitate fusion at various levels of the spine. Stabilization of the spine in various states, including degenerative disc disease, scoliosis, spondylolisthesis, and spinal stenosis, often requires spinal attachment implants and then attachment of the implants to spinal rods. Such spinal fixation devices can immobilize the vertebrae of the spine and can alter the alignment of the spine in a large number of vertebrae by connecting at least one elongated rod to the sequence of selected vertebrae. These rods can span a large number of vertebrae, such as three or four. The anatomy of the spine, however, rarely allows three or more implants to be directly in line. In order to allow for this irregularity, the rod must surround the coronal plane.

Fixation of the spine has become a common approach in the fusion of the vertebrae and the treatment of fractures and disorders of the spine noted above. A common device used for spinal fixation is a bone fixation plate assembly. Typical bone fixation plate assemblies have a relatively flat rectangular plate with a plurality of openings therethrough. Additional assemblies include an implant fixation system that locks a rod to multiple vertebrae. In these assemblies, as in other spinal fixation systems, various fasteners, such as bone screws, are used to secure the bone fixation plate assembly or implant fixation assembly to the desired and target vertebrae of the patient. These screws vary in design and shape depending on your desired location and use of the screws.

In particular, polyaxial locking screws are used with these devices. The key in the polyaxial screws used with these systems is to make the screw head grip firmly to the vertebrae and the whole of the screw. Therefore, polyaxial screws should be used in conjunction with a type of screw head clamping device that provides firm locking of the polyaxial screw. Any movement of the screw can be detrimental to the healing process of the spine. In addition, additional damage can occur if there is movement of the screw once it has been attached to the vertebrae. Therefore, screw movement must be minimized or eliminated.

There are currently numerous polyaxial screws on the market and known in the prior art. Additionally, there are numerous devices that provide a clamping means to lock the polyaxial screw. For example, US Patent No. 5,554,157, US Patent No. 5,549,608, and US Patent No. 5,586,984 all to Errico et al. disclose polyaxial locking screws and coupling element devices for use with a rod fixation apparatus. The 5,554,157 patent discloses a coupling element that includes an inner axial passage having an inner surface that is curved inwardly at the bottom thereof, such that it comprises a bushing for polyaxially retaining a spherical head of a screw. The coupling element further includes a pair of opposing vertically oriented channels extending downwardly from the top of the coupling element, defining therebetween a rod housing seat. The channel further provides top walls to a pair of upwardly extending members, each including an external thread disposed on the uppermost portion thereof to accommodate a lock nut. During implantation of the assembly, the locking nut is sealed against the top of the rod which, in turn, sits on top of the screw head. The nut causes the rod to lock between the nut and the bolt and the bolt to lock into the socket.

The '5,549,608 patent discloses a modification in which a locking ring is disposed around the outside of the bottom of the coupling element and provides an inward force on an outwardly tapering portion by moving it downward. As a result, the crushing of the inner chamber locks a screw head therein eliminating the polyaxial nature of the screw element engagement.

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The 5,586,984 patent discloses a polyaxial orthopedic device that includes a coupling element having a tapered bottom portion having a slotted inner chamber in which a curved head of a screw is initially polyaxially disposed. The coupling element includes a recess for receiving a rod of the implant apparatus. A locking ring is disposed around the bottom of the coupling member and provides an inward force on the outward tapering portion by moving it downward. The vertical slots are closed and squashed, thus locking the screw head within the interior chamber of the screw.

US Patent No. 6,280,442 to Barker et al. discloses a complex locking mechanism having a screw head with complex head geometry, a crown element, and an external rigid body. Locking occurs by compressing the crown element against the complex head, which compresses the head against the rigid seat. This compression crushes the machined splines in the head and holds the screw inside.

Another example of a common locking mechanism is a type of collar that has a spherical seat with a flexible portion that is designed to flex around the screw. By compressing the flexible part against a rigid outer wall, the collar is compressed against the head causing it to lock inside. Examples of these necklaces are found in numerous patents. For example, US Patent No. 6,053,917 to Sherman et al. discloses a multiaxial bone screw assembly that includes a bone screw having a partially spherical head. Additionally, the assembly includes a housing element having a central bore defining a tapered recess for housing a contraction collar carrying the head of the bone screw. The collar defines a partially spherical recess to accommodate the bone screw head and includes deflectable fingers that substantially surround the screw head. When a set screw is tightened in the housing element, the set screw compresses the rod against the collar, which presses the collar into the tapered recess in the housing element, thereby biasing the fingers of the collar against the bone screw head.

Another patent, US Patent No. 5,964,760 to Richelsoph, discloses a spinal implant fixation assembly that includes a bone fixation element. A rod housing seat is operatively connected to the bone fixture for seating a portion of a rod therein. A locking mechanism, in the form of a nut and lock ring, engages the rod housing seat to force an inner wall of the rod housing seat to be encircled and to engage the rod that sits inside and to lock and securing the rod with respect to the internal housing. The assembly further includes a screw head housing insert for containing a screw head therein. The insert can move within the assembly between a locked position that traps the screw head and an unlocked position where the screw head enters or exits.

Other patents on polyaxial screws using a similar collar are disclosed in US Patent No. 6,010,503 to Richelsoph, US Patent No. 5,910,142 to Tatar (which discloses the use of a spherical collar that compresses between the screw head and rod) and US Patent No. 5,891,145 to Morrison et al. (which discloses the use of a very complex double wedge locking mechanism).

More specifically, the Tatar patent 5,910,142 discloses a polyaxial pedicle screw device for use with a rod implant apparatus, utilizing a rod-mounted splint. The device further includes a screw having a curved head and a rod housing body. The body has a rod housing channel and an axial bore into which the screw head is inserted. The rod-mounted ferrule sits in a small curved recess in the top of the screw head so that the rod can enter the body at a variety of angles while maintaining a firm seat against the screw head. The upper set screw insert compresses the splint downward, locking the rod in place and the screw head. In addition, the body locks into position, fully holding the assembly.

The 5,891,145 patent to Morrison et al. discloses a spinal fixation assembly that includes a bone latch and an elongated element such as a spinal rod. The fixation assembly is a multiaxial assembly that allows fixation of the bone latch to the spinal rod at any continuous angle range relative to the rod in three-dimensional space. The fastening assembly includes a housing element having a hole through it, the walls of which are tapered near the bottom, and a channel communicating with the hole and having an upper opening in the upper part of the mounting element. accommodation for inserting a spinal rod. An outer wedge element and an inner wedge element are also included. Both elements have the general shape of a washer and a hole through them. In each wedge element, the respective bore is not parallel to the central axis of the respective wedge element. Additionally, the outer surfaces of the wedge elements may be tapered and the respective perforations may be tapered to mutually lock when seated and tightened. The bone latch fits within the bore of the inner wedge member, which in turn fits within the bore of the outer wedge member, which in turn fits within the tapered sides of the housing member. When the desired position of the bone latch is achieved in three-dimensional space, the components are seated to achieve a tight friction fit.

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US Patent No. 6,063,089 to Errico et al. discloses a polyaxial orthopedic device for use with a rod implant apparatus that includes a screw with a head, a tubular body having holes in the top, side, and bottom thereof, and a rod coupling element. The head of the screw is disposed in the body, with the shaft of the screw extending outside the lower hole, so that the body and the screw can initially rotate with respect to each other. The rod coupling element has a ball-shaped end that sits in the body, the remainder of the rod coupling element extending out of the side hole of the body so that the rod coupling element and the body are initially polyaxially coupled with respect to each other. The ball end of the rod coupling element is arranged on top of the screw head. A set screw is provided in the upper part of the body, the tightening of which causes the ball, head and body to lock by mutual crushing, thus preventing further relative movement.

A pedicle screw with a locking device for fixing elastic rod elements is known from US 2005/0096659 A1. A device for immobilizing a connecting rod in a bone anchoring element of a spinal implant is disclosed in US 2005/0027292 A1. A further osteosynthesis device is described in DE 199 51 145 A1. US 2002/0120272 A1 relates to a device for holding rods for the spine. Furthermore, document US 2005/0080419 A1 discloses a device for connecting a longitudinal element to a bone.

In all of the existing prior art, particularly that described herein, polyaxial screws use a complex locking mechanism and additional locking pieces to prevent movement of the polyaxial screw. Typically, the more complex the locking mechanism, the larger components and higher manufacturing costs are required. Locking and achieving high holding values ​​are more difficult with more parts. In addition, the sizes of the various fixation plates and fixation sets are critical in these types of surgery. Bulky components can cause soft tissue irritation, as well as putting the facet joints at risk at the end of a fusion. Minimizing implants used in spinal surgery is critical. Soft tissue irritation as a result of implant extensions happens frequently. Many times, it is caused because the implant is thick in relation to its surroundings. For example, implants may be too thick to be sufficiently covered by muscle tissue. Therefore, a reduction in the overall thickness of the implant is a critical advantage.

Accordingly, an object of the present invention is to provide a screw head clamping mechanism or device that provides a strong, effective and firm locking of the screw head in its desired position. Additionally, a further object of the invention is to provide a screw head clamping mechanism or device having a minimum size and a reduced number of components to provide a simpler, more efficient and less troublesome device for fixing screws.

Summary of the invention

According to the present invention, these objects are achieved by a locking mechanism according to claim 1. Additional preferred embodiments of the locking mechanism are set forth in the dependent claims.

Description of the drawings

Other advantages of the present invention are readily appreciated when better understood with reference to the following detailed description considered in connection with the accompanying drawings, in which:

Figure 1 is a cross-sectional view of one embodiment of a locking mechanism in which Figure 1A shows a screw head (indicated by the circle) that is freely movable within a non-gripping portion of the locking mechanism and Figure 1B shows the screw head firmly fixed within a gripping portion of the inner surface wall of the fixing mechanism of the present invention;

Figure 2 is a detailed cross-sectional view of one embodiment of a screw and rod fixation assembly;

Figure 3 is a detailed cross-sectional view of one embodiment of the locking mechanism, wherein the locking mechanism is tapered inward at a distal end;

Figure 4 illustrates another embodiment of the screw and rod fixation assembly in which the screw head is firmly fixed within the fixation mechanism, in which a minimal amount of material is used for the fixation mechanism in order to minimize X-ray obstruction;

Figure 5 illustrates another embodiment of the locking mechanism that uses composite polymeric material in the outer layer with an internal metal component to form a hybrid load sharing structure to securely fix the screw head within the locking mechanism;

ES 2 342 008 T3 Figure 6 is a perspective view of a substantially annular ring used in an embodiment of the screw and rod fixation assembly in which the substantially annular ring has a spherical indentation and a flat portion, as well as a hole pitch and insert can be of any shape to provide mechanical and / or frictional force to the screw head;

Figure 7 is a perspective view of a rod seat mechanism including a tapered and / or cylindrical outer surface having flexible extension portions for engaging a spinal rod as a locking mechanism is tightened. on the flexible extension parts, thus deflecting the flexible extension parts around the rod located inside;

Figure 8 is a cross-sectional view of the rod seat mechanism shown in Figure 7;

Figure 9 is a perspective view of the locking mechanism (a set screw) for use with the rod seating mechanism shown in Figure 7, in which the locking mechanism has an interior chamber or spherical portion within it. which engages the flexible extension parts of the locking mechanism to ensure that the flexible extension parts deflect inwardly and surround the rod seated therein;

Figure 10 is a perspective view of one embodiment of the screw and rod fixation assembly that includes a screw, a fixation mechanism, the rod seat mechanism, and the locking mechanism, in which the screw head is textured. to improve screw head locking within the locking mechanism;

Figure 11 is a perspective line drawing of the screw and rod fastening assembly illustrated in Figure 10;

Figure 12A is an enlarged side view of the rod seat mechanism of one embodiment of the present invention, in which the rod seat mechanism seats the rod therein and the flexible extension portions of the rod seat mechanism are in an extended state, while Figure 12B is a cross-sectional view illustrating the rod seating mechanism with the flexible extension portions in a compressed state surrounding and engaging against the rod therein;

Figure 13 is a perspective side view illustration of another embodiment of the screw and rod fixation assembly including a solid, substantially annular ring;

Figure 14 is a side perspective view of the screw and rod fixation assembly including a substantially annular ring that is split to allow maximum flexibility of the substantially annular ring within the fixation mechanism;

Figure 15 is a perspective view of the locking mechanism in which an outer surface is made of a polymeric, composite or other material, and the locking mechanism includes a ball screw seat that is located within the gripping portion of the inner surface wall that also allows deflection inside;

Figure 16 is a side view of the clamp mechanism and rod seat mechanism of the present invention in which the rod seat mechanism deflects onto the rod when pushed into the clamp mechanism body and tabs. openings or indentations are hooked on the side of the rod seat mechanism in the body of the fixation mechanism to ensure that the rod seat mechanism remains locked;

Figure 17 is a perspective view of another embodiment of the locking mechanism in which a threaded locking mechanism is pressed into the substantially tubular body of the locking mechanism after the rod has been inserted into the locking mechanism therein that engages a groove in the inner surface wall and the locking mechanism is tightened to lock the entire screw and rod fixation assembly;

Figure 18 is a cross-sectional view of one embodiment of the screw and rod fixation assembly in which the head of a frame, as opposed to a screw, is within the gripping portion of the fixation mechanism, and the movement from the head of the structure further into the gripping part blocks the screw and rod fixing assembly;

Figure 19 is a cross-sectional view of one embodiment of the screw and rod fixation assembly in which the locking mechanism is a non-threaded cap;

Figure 20 is a cross-sectional view of one embodiment of the screw and rod fixation assembly in which the locking mechanism is an unthreaded tapered cap;

Figure 21 is a cross-sectional view of one embodiment of the screw and rod fixation assembly in which the locking mechanism is an unthreaded tapered, slotted cap;

Figures 22A-E are side views of a cam for use in the locking mechanism of the present invention;

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Figure 23 is a cross-sectional view of one embodiment of the screw and rod fixation assembly in which the locking mechanism is a non-threaded cam lock cap.

Detailed description of the invention

A screw and rod fixation assembly constructed in accordance with the present invention is indicated generally by 10 in the figures. In general, the screw and rod fixation assembly 10 fixes and / or locks a screw, a rod, or both. Additionally, the screw and rod fixation assembly 10 includes various components in different combinations. For example, the screw and rod fixation assembly 10 may include any of, all, or combinations of a screw, fixation mechanism, substantially annular ring, rod seat mechanism, and locking mechanism.

The present invention provides for the locking of a screw head without any manipulation of the screw fixing mechanism. The fixation mechanism inherently grips the screw head rigidly, preventing movement of the screw head, which can occur due to movement of the vertebrae, without application of force or manipulation of the fixation mechanism as required to ensure fixed grip. Instead, insertion of the screw head into the locking or gripping portion of the fixation mechanism causes locking to occur around the screw head by compressive force thereon. Basically, the locking mechanism is a passage that includes side walls and an inherent locking mechanism to grip and lock the screw head as the screw head enters through the passage and into the locking mechanism. The passage can be a substantially tubular body and be composed of semi-flexible material.

The present invention has numerous advantages over the prior art. These advantages include, but are not limited to, simplifying currently existing polyaxial screw fixation assemblies. For example, an expensive collar or other similar screw head holding mechanism is not used with the present invention. Additionally, the present invention is significantly smaller in size, diameter, circumference, and overall dimensions than other prior art devices. Since the present invention does not use any additional components such as a collar, crown or cap that exceeds the diameter of the screw head, the size of the present invention is greatly reduced. Therefore, the present invention and, in particular, the locking mechanism, only has to be large enough to allow the screw to enter or seat therein. Another advantage of the present invention is that the screw and / or the screw head are clamped more uniformly and in a more controlled manner.

Additionally, tolerance problems for collar design geometries, crowns, caps, and complex screw retention mechanisms are eliminated. Furthermore, the screw positioned in the present invention can be firmly locked without any internal mechanism creating a fixed screw. An instrument can easily push the screw down to the proper seating position to create a locked screw at any desired angle, even after removing the instrument. The term "elastic deformation zone" as used herein is the stress limit within which deformation of a body of material disappears completely after removal of stress, tension and / or force on the body of material. Elasticity is the ability of a material to return to its original dimensions after removal of stress, tension, or force applied to the material. However, once the stress, tension or forces exceed the elastic deformation zone, the material cannot return to its original dimensions and is deformed forever. The term "zone of deformation" as used herein means the excessive amount of fatigue, force or load outside the zone of elastic deformation from which the deformation is maintained and the body of material can no longer return to its original dimensions. Basically, deformation occurs when a change in shape occurs by external forces or loads acting on the body of material.

The term "screw" 12 as used herein means a simple inclined plane type machine that includes a solid spirally slotted cylinder and a correspondingly slotted hollow cylinder into which it fits. Screw 12 can be any type of screw such as a set screw and can be of any size, shape, or design, as is known to those skilled in the art. In certain cases, it may be desirable for the screw 12 to have a screw head 14 of another shape and / or size.

The term "rod" 16 as used herein means a substantially cylindrical body having a desired length. As regards the present invention, rod 16 is typically a rod 16 used within a human body to aid in the alignment of bones, particularly the vertebrae.

An important feature of the screw fixation assembly 10, and more particularly the fixation mechanism, is the use of a semi-flexible material as opposed to a rigid material. As is known to those skilled in the art of strength of materials, materials such as metals and composites thereof have an elastic deformation zone and a deformation zone. For example, if a sample of a material is put under tension and is not allowed to exceed the elastic deformation zone, the sample will elongate.

Elastic elongation occurs in such a way that, by relaxing the tension, the material will return to its original dimensions. By adapting this property to the present invention, the wall of the locking mechanism acts as a controllable spring that can be used effectively to exert a uniform compressive load on a head portion of a screw, shank, or other component. Elastic elongation occurs by introducing a part of

ES 2 342 008 T3 head that is larger than the inside dimensions of the locking mechanism. This forces the clamping mechanism to expand to accept the head portion. In a similar way to a spring, the locking mechanism would return to its original dimensions when the head part was removed. However, while the head portion is within the locking mechanism, the locking mechanism exerts a compressive force on the head portion. Thus, the locking mechanism works by inherently gripping the screw head rigidly, preventing movement of the screw head without the application of force or manipulation of the locking mechanism by other means.

This property of the wall expansion of the clamping mechanism within this elastic deformation zone and the resulting inward generated force around the head portion is called "spring reaction". Outside of this elastic deformation zone, the material is permanently deformed and will not return to its original dimensions. Therefore, it is essential to stay within the elastic deformation zone of the material in order to have a controllable reaction in which to use the compressive forces created within it.

Compressive forces created by expansion of the locking mechanism wall can be easily controlled by altering the material, material thickness, coatings, or otherwise modifying the material of the locking mechanism. The head part can also be altered to be of any material and hardness. A softer material would allow better compensation of tolerances with respect to the dimensions of the components, while a harder material could provide a more controlled expansion of the clamping mechanism.

The introduction of the screw head into the gripping or locking portion of the clamping mechanism causes gripping or locking to occur around the screw head by compressive force thereon. Generally, the locking mechanism is a passage that includes side walls and an inherent locking mechanism to grip and lock the screw head as the screw head enters through the passage and into the locking mechanism. The passage is a substantially tubular body, while the locking mechanism is inherently a semi-flexible part of the side wall. Another way to describe the locking mechanism is that it is a single wall receptacle made of semi-flexible material.

The present invention can be constructed from any suitable material known to those skilled in the art. Preferably, the present invention is constructed from material that is compatible with its use in the environments in which it is placed. The present invention can be constructed of a variety of metallic materials including, but not limited to, titanium, stainless steel, and any other suitable metallic alloy known to those skilled in the art. Additional materials can also be used either individually or in combination with the above-described metallic materials. For example, various plastics, fibers, and other polymers can be used in conjunction with the various metallic materials. These combinations can be used to construct various components or parts of the present invention. In addition, other types of coatings can be placed on various parts of the present invention in order to improve the durability, strength and usability thereof. However, normally any material used to construct the present invention must be very strong, non-reactive, and non-antigenic to biological systems if used in that environment. If the present invention is used outside of biological systems, however, the aforementioned features are not necessarily required.

There are numerous embodiments of the present invention. As such, similar structures in the various embodiments are shown by apostrophic numbers in the various figures. Although numerous embodiments are disclosed and described herein, each of the embodiments includes a variation of the attachment mechanism of the present invention.

The screw and rod fixation assembly 10 includes a screw 12 with a screw head 14. The screw and rod fixation assembly 10, and more specifically the fixation mechanism 18, grips and holds the screw head 14. Optionally, the screw and rod fixation assembly fixes a rod 16. The screw and rod fixation assembly 10 includes the fixation mechanism 18 for fixing the screw head 14 against movement relative to the screw and rod fixation assembly 10. The attachment mechanism 18 includes an interior surface wall 20 having a gripping portion 22 and a non-gripping portion 24. Clamping mechanism 18 operatively engages screw head 14 and ultimately screw 12. The locking mechanism is basically a single wall passage or receptacle made of semi-flexible material. As described above, the clamping mechanism 18, and more particularly the gripping portion 22, firmly grips the screw head 14 through compression forces generated by the spring reaction of the semi-flexible material. To reiterate, the spring reaction occurs from the screw head 14 elongating the grip portion 22 beyond its original dimensions, but within the elastic deformation zone of the material. Therefore, the gripping portion 22 has a spring reaction to return to its original dimensions which results in the creation of compressive forces on the screw head 14. As a result, the screw head 14 is firmly gripped within the gripping portion 22.

The screw and rod fixation assembly 10 includes a substantially annular ring 26 to guide and provide mechanical and frictional force to the screw head 14. In addition, the screw fixation assembly 10 includes a rod seat mechanism 28 operatively engaged to the screw head 14 and has at least one flexible portion 46 that can be compressed against the rod 16 seated within the seat mechanism 28 of the screw. dipstick. The rod seating mechanism 28 also includes a tapered outer surface end 34. Alternatively, the rod seating mechanism 28 may be cylindrically shaped.

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The screw and rod fixation assembly 10 includes a locking mechanism, generally shown at 36 in the figures. The locking mechanism 36 engages the rod 16 and the rod seating mechanism 28. The locking mechanism 36 includes a biasing mechanism 38 to bias at least a flexible portion 46 of the rod seating mechanism 28 against and around the rod 16 as the locking mechanism 36 further engages at least a flexible portion 46 of the rod seating mechanism 28. The biasing mechanism 38 specifically engages and biases the tapered outer surface end 34 therein.

Fixation mechanism 18 includes a substantially tubular body 40. As noted above, the locking mechanism 18 includes the gripping portion 22 and the non-gripping portion 24. It is this attachment mechanism 18 that is included in all of the various embodiments described herein. As described above, the locking mechanism 18, specifically the grip portion 22, uses semi-flexible material that creates compressive forces on the screw head 14 that is engaged with the grip portion 22 when the grip portion 22 is further elongated. past its original dimensions and returns to its original dimensions. Gripper portion 22 is a substantially tubular body portion 40 that grips and holds screw head 14 once screw 12 has been inserted into grip portion 22. The gripping portion 22 grips and holds the screw head 14 by the spring reaction of the material that makes up the clamping mechanism 18. Thus, the screw head 14 of the screw 12 extends the inner surface wall 20 into its elastic deformation zone so that it is not permanently deformed. As a result of the elasticity of the material in the inner surface wall 20, the spring reaction of the material creates sufficient force on the screw head 14 to firmly fix the screw head 14 and ultimately the screw 12 in place.

As for the non-gripping portion 24, the screw 12 and the screw head 14 do not extend the inner surface wall 20 therein. Instead, the screw 12 and the screw head 14 are free to move within their area surrounded by the non-gripping portion 24 of the inner surface wall 20 of the locking mechanism 18. The gripping portion 22 and the non-gripping portion 24 of the inner surface wall 20 may be made of the same material or different materials depending on the design. For example, the gripping portion 22 may have an added coating or material in order to provide added strength and / or flexibility. Preferably, the entire locking mechanism 18 is made of semi-flexible material, especially at the end of the grip portion 22. Naturally, the non-gripping portion 24 can also be made of a semi-flexible material. The semi-flexible material includes, but is not limited to, metal, plastics, alloys, polymers, fibers, combinations thereof, and any other similar material having a desired elasticity and zone of elastic deformation. Thus, the locking of the screw head 14 does not require any other manipulation of the clamping mechanism other than the introduction of the screw head 14 into the grip portion 22 of the substantially tubular body 40.

The substantially tubular body 40 of the locking mechanism 18 can be of various designs. Although a substantially tubular body 40 is used with the present invention, any other similar body shape known to those skilled in the art can be used with the present invention. The substantially tubular body 40 also varies in its overall dimensions depending on the intended use thereof. Furthermore, the substantially tubular body 40 can be segmented so that parts of the substantially tubular body 40 can be detached. Furthermore, the substantially tubular body 40 can be threaded or smooth. The threading can be on the outer surface or the inner surface thereof. Threading is useful when the locking mechanism 18 is used in conjunction with a similarly threaded locking mechanism 36, as described in more detail below.

An example of the locking mechanism 18 is illustrated in Figures 1A and 1B. In this embodiment, the locking mechanism 18 utilizes a relatively thin-walled, substantially tubular body 40. The substantially tubular body 40 has an outer diameter and an inner diameter such that a portion of the inner diameter is less than the diameter of the screw head 14 (ie, the gripping portion 22 of the inner surface wall 20). When the screw head 14 is pushed down into the substantially tubular body 40, the screw head 14 causes the smaller internal diameter to expand, but remains within its elastic deformation zone. As the inner surface wall 20 remains elastic, the spring reaction of the inner surface wall 20 at the gripping portion 22 creates a considerable compressive force as the inner surface wall 20 naturally returns from a state. deformed to its original condition. This spring or force reaction is equivalent to a mechanical variant of a pressure socket that creates a circumferential stress in the inner surface wall 20. As long as this stress is maintained within the elastic deformation zone of the material of the inner surface wall 20, the load or force on the screw head 14 remains constant. Furthermore, the force exerted on the screw head 14 is directly related to the ability of the gripping portion 22 of the inner surface wall 20 to resist deflection or expansion in this case. Therefore, the thicker the inner surface wall 20 in the gripping portion 22, the more spring reaction and compression forces will be generated and applied to the screw head 14. Naturally, the further the screw head 14 has to be pushed into the smaller diameter area (gripping part 22) and the thicker the inner surface wall 20 therein, the more force will be required to drive the head 14 bolt further into the smallest diameter area (grip part 22).

For one skilled in the art, there are various ways to narrow the internal diameter of the locking mechanism 18. One method is to reduce the internal diameter using simple drilling techniques (Figures 1A and 1B). Additionally, multiple molds can be created to form the same design.

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In another embodiment of a locking mechanism 18 ', the inner surface wall is tapered inwardly therein and the inner surface wall 20' is also threaded 25 (FIG. 2). As shown in Figure 2, the attachment mechanism 18 'is a substantially tubular body or single-walled receptacle. The locking mechanism 18 ', more particularly the gripping portion 22', is made of the semi-flexible material described above. The grip portion 22 ', due to the semi-flexible material, creates sufficient compressive force on the screw head 14 to secure it therein as the grip portion 22' is elongated beyond its original dimensions by the screw head 14. Gripping portion 22 'has a spring reaction when it returns to its original dimensions after being temporarily deformed by screw head 14 after screw head enters the inside of gripping portion 22' therein .

The interior of the gripping portion 22 'of the fixing mechanism 18' is spherically shaped 23 therein. Thus, as the locking mechanism 36 is inserted into the locking mechanism 18 ', the screw head 14 engages the spherically shaped gripping portion 22' therein. The further the screw head 14 is pushed into it, the more interference will be generated, which is compensated for by expanding the tubular structure to create the compressive force on the screw head 14 (eg, spring reaction). In this embodiment, the locking mechanism 18 'includes a pair of spaced, substantially parallel arms 42 that extend from the substantially tubular body 40'. These arms 42, as shown in FIG. 2, may optionally be detached from the substantially tubular body 40 'upon completion of the assembly of the screw fixation assembly 10'.

Another embodiment of the locking mechanism 18 "is illustrated in Figure 3. This embodiment is similar to the embodiment illustrated in Figure 2; however, this embodiment of the locking mechanism 18 "has a threaded outer surface 27 as opposed to a threaded inner surface 25. Again, the locking mechanism 18 "and, more particularly, the gripping part 22", is made of the semi-flexible material described above, with the gripping part 22 "creating compressive forces on the screw head 14 when the part 22" grip returns to its original dimensions after being lengthened by the screw head 14 inserted therein. The embodiment of the locking mechanism 18 "illustrated in Figure 3 uses a different locking mechanism 36" that is similar to a nut or other device. The embodiment of the locking mechanism 18 "in FIG. 3 also includes a pair of spaced, substantially parallel arms 42 'extending from the substantially tubular body 40" thereof.

In yet another embodiment of the attachment mechanism 18 "'(Figure 4), metal or metal and composite material (eg, polymers) are used. The composite material can be mixed with the metal or used as an external cladding layer. The composite material remains semi-flexible so that compression forces are generated as the grip portion 22 "'elongates, but returns to its original dimensions. In addition, the gripping portion 22 "'of the attachment mechanism 18"' illustrated therein uses a minimal amount of material to minimize X-ray obstruction, while providing sufficient spring reaction to secure the head of the device. screw inside. The screw head 14 used with this particular locking mechanism 18 "'is spherically shaped.

Figure 5 illustrates another embodiment of the locking mechanism 18 "" such that a composite material is used. The 18 "" attachment mechanism includes an outer composite / polymer layer having an internal metal component to form a hybrid charge sharing structure. Again, the locking mechanism 18 "" and, more particularly, the grip portion 22 "", uses semi-flexible material so that sufficient compressive forces are generated on the screw head 14 when the grip portion 22 "" returns. to its original dimensions after being lengthened by the screw head 14 inserted therein. The locking mechanism 18 "", as shown in Figure 5, is basically a single-walled passageway or receptacle that can house the screw head 14 therein.

In Figure 15, another embodiment of the locking mechanism 18 "" 'is shown. The 18 "" 'fixing mechanism is made of a semi-flexible polymer. The locking mechanism 18 "" 'includes a substantially tubular body 40 ""' with a metal ring at the location of the screw head 14. As described above, the semi-flexible locking mechanism 18 "" 'and, more specifically, the gripping portion 22 ""', generates compressive forces on the screw head 14 as the gripping portion 22 "" 'returns to its position. original dimensions after being elongated by the screw head 14. The locking mechanism 18 "" 'further includes a ball screw seat 23. Ball screw seat 23 is generally machined into substantially tubular body 40 "" 'therein. Ball screw seat 23 allows deflection and grip. This embodiment is very useful in cases where the substantially tubular body 40 "" 'is not strong enough to provide a large spring reaction or force on the screw head 14 or sufficient frictional holding force. This is an example of a composite load sharing structure.

Optionally, the screw and rod fixation assembly 10 may further include a substantially annular ring 26 having an edge portion 30 that extends about a centered axis. Annular ring 26 acts in conjunction with attachment mechanism 18 which includes a substantially tubular body 40 forming a passageway or receptacle described herein. Although the clamping mechanism 18 creates sufficient compression forces due to the spring reaction of the material that makes up the clamping mechanism 18 and, more specifically, the gripping part 22 (the spring reaction generates compression forces when the gripping part is returning to its original dimensions after being elongated), there are times when additional frictional and / or mechanical forces are required.

ES 2 342 008 T3

Edge portion 30 of annular ring 26 has a frusto-conical surface tapered outward toward edge portion 30 to engage a screw head 14, while allowing a portion of screw 12 to pass through. The substantially annular ring 26 guides the screw head 14 and provides additional frictional and mechanical forces on the screw head 14. The screw and rod fixation assembly 10 requires both mechanical and frictional locking. Holding the rod 16 requires mostly frictional locking, while holding the screw head 14 requires both mechanical and frictional locking. The various materials used to make up the locking mechanism 18 may not necessarily provide sufficient frictional and mechanical locking force. Thus, by using a smaller substantially annular ring 26 within the locking mechanism 18, sufficient frictional and mechanical locking force can be provided therein. The blockage can be spread over the metal portion of the substantially annular ring 26, while the fiber / polymer reinforced portion creates a stronger interconnection. The use of the substantially annular ring 26 is optional. Thus, the screw and rod fixation assembly 10 may include it. Alternatively, one embodiment of the screw and rod fixation assembly 10 may exclude it, so that the screw and rod fixation assembly 10 includes only a screw 14, a fixation mechanism 18, a rod seat mechanism 28, and a mechanism. 36 lock.

A rod seat mechanism 28 is operatively engaged with the fixation mechanism 18. The rod seat mechanism 28 further includes at least one flexible portion 46 that can be compressed against the rod 16 seated within the rod seat mechanism 28. The flexible portion 46 has a tapered outer surface end 34. The rod seat mechanism 28 has a body portion 44. In the embodiments shown in Figures 7, 10-14, and 16, there are two flexible portions or arms 46 that are substantially parallel to each other. In those situations, the two flexible portions 46 and the body portion 44 form a substantially U-shaped interior wall 32 that defines the first seat 30 therein. In addition, the flexible portions 46 include a tapered outer surface end 34.

The at least one flexible portion 46 of the rod seat mechanism 28 firmly engages the rod 16 within it surrounding the circumference or outer surface of the rod 16. The rod seat mechanism 28 is altered to allow the deflectable flexible portions 46 engage rod 16 as locking mechanism 36 is tightened on it (Figures 7 and 8). Thus, as the locking mechanism 36, as illustrated in Figure 9, advances into the locking mechanism 18, the flexible parts are pushed onto the top of the rod 16 thus increasing the contact area of ​​the parts. 46 flexible on the rod 16 and further increasing the friction force thereon (Figures 12A and 12B). Figure 12A illustrates the rod seating mechanism 28 in which the rod 16 is seated therein and the flexible portions 46 extend above the rod 16. Figure 12B illustrates the rod seating mechanism 28 with the parts Flex 46 compressed against and around rod 16 as a result of locking mechanism 36 being tightened around flex portions 46. The flexible portions 46 are biased inward by the locking mechanism 36 in order to compress the flexible portions 46 around and against the rod 16. In Figures 12A and 12B, the locking mechanism 36 is not shown for the purpose of clarification. and further illustrate the bending of the flexible portions 46.

As mentioned above, it is possible to add a substantially annular ring 26 or inner sleeve 26 to improve the grip or to act as a spacer between the locking mechanism 18 and the screw head 14 therein. When grip is improved, a material with a softer or different composition than that of the outer surface wall 21 of the substantially tubular body 40 can be placed on the inner surface wall 20 so that the screw head 14 is compressed against, in instead of directly against the outer surface wall 21. For example, a purely commercial soft substantially annular ring 26 or sleeve 26 is within a stronger body of Ti-6AI-4V. In this case, the outer surface 21 acts like a tubular spring, but the softer interior, which would potentially be too weak to allow spring reaction, will allow the screw head 14 to penetrate the softer material for a screw lock. improved (Figures 13 and 14). In addition, for fabrication, it may be advantageous to excessively bore the interior of the substantially tubular body 40 and add a substantially annular ring 26 or sleeve 26. Such a sleeve 26 may be a solid, thin wall or a split wall having a gap 29 as shown in Figures 13 and 14, respectively. The partition or space 29 allows the sleeve 26 to flex without interfering with the outer surface 21 of the substantially tubular body 40. Sleeve 26 may be press fit or have some clearance for easier mounting. A semi-flexible polymeric or composite material can be used for the substantially tubular body 40 and a different material such as titanium can be used for the sleeve 26 to provide either additional reinforcement, better screw lock 12, and / or a rod engagement. 16 improved.

With respect to the locking mechanism 36, the locking mechanism 36 engages a rod 16 and a rod receiving mechanism 28. The locking mechanism acts in conjunction with the locking mechanism 18, the locking mechanism 18 normally being a substantially tubular body 40 which can house the locking mechanism 36 therein. Again, the locking mechanism 18 is basically a single-walled passage or receptacle made of semi-flexible material. The clamping mechanism 18, through the gripping part 22, applies compression forces on the screw head 14 as a result of the spring reaction created when the gripping part 22 returns to its original dimensions after being elongated within its elastic deformation zone by means of the screw head 14 inserted therein. The locking mechanism 36 holds and tightens the entire screw and rod fixation assembly 10. The locking mechanism 36 includes a biasing mechanism 38 for biasing at least one flexible portion 46 of the rod seating mechanism 28 against and around the rod 16 as said locking mechanism 36 further engages the at least one flexible portion 46 mechanism 28 of

ES 2 342 008 T3 rod seat. The biasing mechanism 38 can be an internal surface or part of the locking mechanism 36 itself. The biasing mechanism 38 further engages the tapered outer surface 34 therein.

The locking mechanism 36 may be a nut, screw, set screw, or other similar locking mechanism 36 as is known to those skilled in the art. The locking mechanism 36 is usually threaded onto at least one surface thereof. Figures 9, 14, 10, 11, 13, 14 and 19 to 23 illustrate embodiments of locking mechanisms 36, 36 ". As noted, the locking mechanism 36 is preferably a set screw that includes a threaded outer surface 48 for operatively engaging a threaded inner surface 25 of the locking mechanism 18. Alternatively, the locking mechanism 36 may be a locking nut that includes a threaded inner surface 50 for operatively engaging a threaded outer surface 27 of the locking mechanism 18 as disclosed herein.

The locking mechanism 36 may further include a spherical inner chamber 39 to house at least one flexible portion 46 of the rod seating mechanism 28 when the at least one flexible portion 46 surrounds the rod 16 located therein. The spherical inner chamber 39 can also be useful to house any type of instrument.

Alternatively, the locking mechanism 36 "may include an unthreaded outer surface 60. The locking mechanism 36 "includes a body 61 having an upper portion 62 and a lower portion 64. Preferably, both the upper part 62 and the lower part 64 have radially unthreaded outer surfaces 60. The locking mechanism 36 "may also include a latch portion 76 to engage the locking mechanism 18 of the assembly 10. The latch portion 76 ensures that the locking mechanism 36 "maintains proper placement within the assembly 10 and is secured relative thereto. The latch portion 76 may be a slot 78 that fits into a tab 80 in the locking mechanism 18. The locking mechanism 18 is preferably formed of a flexible material so as to allow a frustoconical movement of radial extension, thus allowing easier insertion of the locking mechanism 36 '. Alternatively, the latch portion 76 may be a tab 82 on the latch portion 76 that fits into a slot 84 located within the locking mechanism 18. In either case, the tab 80, 82 is any shape of protrusion that can be held within a slot 78, 84 through an interference fit. For example, the tab may be a circumferential tab on the outer surface 60 of the locking mechanism 36 "or a cam 36" '.

The locking mechanism 36 "also includes a spring charging device 66 located in the base 68 of the bottom 64. Spring charging device 66 is used to provide a biasing force between locking mechanism 36 and rod 16 in order to securely hold rod 16 within assembly 10. The spring charging device 66 can be any device known to those skilled in the art because it can provide a biasing force between the two parts. Examples of such devices include, but are not limited to, a Belleville washer, a spherical washer, a fixed spring charging device, or other similar devices. The washers 66 'can be of any size sufficient to provide the biasing force disclosed above. For example, the washer can be spherical or conical. Washer 66 'may be solid or it may include a central aperture that may be of any shape known to those skilled in the art to be effective, such as, but not limited to, round or square. Washer 66 'may have any thickness necessary for use of locking mechanism 36 "so that the thickness of washer 66' is directly related to the spring constant necessary to provide the desired biasing force to lock the assembly together. The washer 66 'can be formed with a solid thickness or the thickness can vary from the outer edge of the washer towards the inner section of the washer.

Washer 66 'sits in base 68 of lower body portion 64 61. Washer 66' is positioned within a notch 90 within base 68. Notch 90 is dimensioned to hold washer 66 'in position. so that the washer 66 'includes a concave portion 92 or is completely concave. The extent to which the washer 66 'concave depends on the use of the locking mechanism 36 ". The concave portion 92 of the washer 66 'engages the rod 16, thus creating a biasing force.

Alternatively, the spring charging device 66 may be fixed. In other words, the fixed spring loading device 66 'is machined directly into the base 68 of the bottom 64 of the locking mechanism 36 ".

The fixed spring charging device 66 'works in the same way as the previously described washer, however the fixed spring charging device 66' is integral with the base 68. The fixed spring charging device 66 'can be shaped according to required for the 36 ”locking mechanism in which it is machined. Examples of possible shapes for the fixed spring charging device 66 'include, but are not limited to, spherical, conical, rectangular, and cylindrical. As with the washer, the fixed spring biasing device 66 'can be formed to any thickness to provide the desired biasing force to lock the assembly together. Additionally, the thickness of the fixed spring charging device 66 'may be constant or it may vary.

In addition, the locking mechanism 36 "may include an opening 70 in the apex 72 of the top 62 of the locking mechanism 36". Opening 70 can be used for insertion and removal of locking mechanism 36 ". The opening 70 may include threads 74 or other mechanisms that are beneficial for the insertion and removal of the locking mechanism 36 ". Alternatively, opening 70 may be shaped so that a specific tool can be used to insert and remove locking mechanism 36 ".

ES 2 342 008 T3

The locking mechanism 36 'may include a number of tabs 82 as previously disclosed. For example, tab 82 'may be a cam lock 82' as shown in Figures 22 and 23. Preferably, tab 82 'is a partially circumferential tab that engages a partial slot 84' so that when the tab 82 'rotates or twists into place within slot 84', an axial force is generated that holds the entire assembly 10 together. The configuration of the tab 82 'may include an inclined plane or ramp configuration, or a bayonet configuration. The cam lock 82 'may include an opening 70' in an upper portion 72 'of the upper portion 62' of the lock mechanism 36 ". The opening 70 'may be used for insertion and removal of the locking mechanism 36 "'. Opening 70 'may include threads 74' or other mechanisms that are beneficial for insertion and removal of locking mechanism 36 ". Alternatively, the opening 70 'may be shaped so that a specific tool can be used to insert and remove the locking mechanism 36 ".

The locking mechanism 36 "may be a tapered locking cap 86, as shown in Figures 20 and 21. The tapered locking cap 86 is preferably a self-locking tapered section that fits into a tapered section 88 of fit on the outer surface 88 of the clamping mechanism 18. In other words, the outer surface 88 of the attachment means 18 is tapered as is the tapered locking cap 86 so that the two pieces fit and lock each other to keep the assembly 10 properly aligned. The tapered locking cap 86 may also include a latch portion 76 ". Latch portion 76 "is a device that ensures that tapered locking cap 86, and thus locking mechanism 36" ', maintains proper positioning within assembly 10. Latch portion 76 "may be a slot 78 "that fits into a tab 80" in the locking mechanism 18. Alternatively, the latch portion 76 "may be a tab 82" on the latch portion 76 "that fits into a slot 84" located within the locking mechanism 18. In either case, the tab 80 ", 82" is any shape of protrusion that can be held within a slot 78 ", 84" through an interference fit. For example, the tab 80 ", 82" may be a circumferential tab on the outer surface 60 "of the locking mechanism 36" '. The tapered locking cap 86 may include an opening 70 "in an upper portion 72" of the upper portion 62 "of the locking mechanism 36" '. The opening 70 "can be used for insertion and removal of the locking mechanism 36" '. The opening 70 "may include threads 74" or other mechanisms that are beneficial for insertion and removal of the locking mechanism 36 "'. Alternatively, the opening 70 "may be shaped so that a specific tool can be used to insert and remove the locking mechanism 36" '.

In other variations, a locking mechanism 36 is not included; instead, a different type of 28 ”” ”rod seat mechanism may be used. In this particular embodiment, the rod seating mechanism 28 "" "inserts directly into the locking mechanism 18" "". Rod seat mechanism 28 "" "operatively engages clamp mechanism 18" "". Again, the locking mechanism 18 "" "is made of semi-flexible material that generates compression forces that are applied to the screw head 14 when the locking mechanism 18 (more specifically the gripping portion 22" "") returns to its original dimensions after being elongated within its elastic deformation zone by the screw head 14 inserted therein.

The rod seat mechanism 28 "" "includes the same structural components as the rod seat mechanism 28 described above. Rod seating mechanism 28 "" "includes at least one flexible portion 46" "" having a tapered outer surface 34 "" "with at least one tab mechanism 31 extending radially from surface 34" " "Exterior tapered section to operatively engage and insert into at least one indentation 33 or aperture 35 located in wall 24" "" of interior surface of substantially tubular body 40 "" "of attachment mechanism 18" "". The size, shape and dimensions of the reed mechanism 31 vary according to a desired size of the overall structure of the rod housing mechanism 28 "" ". Also, indentation 33 or aperture 35 extending through interior surface wall 24 "" "varies by design (FIG. 16).

As the rod seat mechanism 28 ”” ”is inserted into the clamp mechanism 18” ”” and onto the screw head 14, the flexible portions 46 ”” ”of the rod seat mechanism 28” ”” surround and they compress the inserted rod 16 located therein due to deflection of the tongue mechanisms 31 caused by the interference created by the inner surface wall 24 "" "of the fixing mechanism 18" "". Once the reed mechanisms 31 engage with either the indentation 33 or the opening 35, the flexible portions 46 "" 'of the rod seat mechanism 28 ""' remain locked in a compressed state surrounding the rod 16. To release the rod seat mechanism 26 "" 'from the compressed state, an instrument simply has to be inserted between the rod seat mechanism 26 "" "and the locking mechanism 18" "".

In yet another variation, the rod seating mechanism 28 is eliminated and replaced by a different embodiment of the locking mechanism 36 "" "'in which the locking mechanism 36" ""' is a socket clamping mechanism 52 ( Figure 17) which is inserted into the screw and rod fixation assembly 10 and onto the rod 16 after inserting the rod 16 into the fixation mechanism 18 "" "'. As with the other embodiments, the locking mechanism 18 "" "'is made of semi-flexible material. Again, due to the semi-flexible material, the locking mechanism 18 "" "', and particularly the gripping portion 22" ""', generates compression forces that are applied to the screw head 14 once the portion 22 Grip ”” ”'returns to its original dimensions after being elongated within its elastic deformation zone.

Cap holding mechanism 52 may be any screw type device, such as a set screw 36 "" ". The bushing clamping mechanism 52 comes into contact with at least a piece or part of the rod

ES 2 342 008 T3 in order to firmly fix the rod 16 located inside it and the entire set 10 "" "'for fixing the screw and rod. Cap holding mechanism 52 is substantially cylindrical in shape and can be inserted into substantially tubular body 40 of clamping mechanism 18 "" "'. The socket clamping mechanism 52 also includes at least one outwardly tapering extension tab mechanism 55 for locking the socket clamping mechanism 53 on the rod 16. The extension tab mechanism 55 operatively engages at least an indentation 33 'or aperture 35' located within the substantially tubular inner surface wall 20 "" "'of the body 40" ""' of the attachment mechanism 18 "" "'. The size, shape and dimensions of the extension tab mechanism 55 vary according to a desired size of the overall structure of the attachment mechanism 18 "" "'. Also, the indentation 33 'in the inner surface wall 20 "" "' or the opening 35 'extending through the inner surface wall 20" ""' varies correspondingly (FIG. 17).

As the socket clamping mechanism 52 inserts into the clamping mechanism 18 "" "'and onto the rod 16, the socket clamping mechanism 52 compresses against the inserted rod 16 located within the first seat 30" ". ”'. Then, when the extension tab mechanisms 55 engage with either the indentation 33 'or the opening 35', the socket holding mechanism 52 remains locked in a compressed state on the rod 16.

Optionally, the socket clamping mechanism 52 further includes a threaded inner surface 53 for operatively engaging any additional type of screw 12 to further tighten the rod 16. Thus, a screw 12 may be inserted and screwed into the socket mechanism 52 . Alternatively, the outer surface 57 of the cap holding mechanism 52 may be threaded to engage the threaded inner surface wall 20 "" "'of the substantially tubular body 40" ""' of the attachment mechanism 18 "" "'.

The present invention is not limited to use simply with a bone screw 12. For example, the locking mechanism 18 "" "" can be extended to use with other types of screws, parts and / or mechanical structures. The 18 ”” ”” locking mechanism still uses, as with the other embodiments, semi-flexible material to create compression forces that are a result of the spring reaction created when the 18 ”” ”” locking mechanism returns to its original dimensions after to have elongated within its elastic deformation zone.

Other parts that can be used with the present invention include other implants, such as a ball joint 58 for a crossover connector that can be attached with the present invention (FIG. 18). In this situation, a ball head 54 is forced into a reduced diameter section 56 which exerts a force on the ball head 54 to firmly lock it. In Figure 18, the ball head is shown within the tube portion and movement of the ball head into the gripping portion 22 locks the entire assembly. Assembly 10 "" "" as shown in FIG. 18 may be further locked by locking mechanism 36 as described herein. Additionally, an instrument can be used to easily lock assembly 10. Simply pulling the two components with great force in opposite directions will lock the two components firmly as the wall expands and exerts compressive forces on the head portion as illustrated in figure 19.

The components for the screw fixation assembly and device disclosed and described herein can be manufactured by various methods known to those skilled in the art. For example, the assembly and device can be made by first stamping the outer shape of a round bar block. Then, by holding the threaded end or an extension of the threaded end, a hole is made in the opposite end. This hole is sized smaller with respect to the tapered section to allow cutting the tapered section with a single tool. While the part is turning on a lathe, a boring bar with a small cutting tip is inserted into the hole and the tapered section and recess are cut. The threads are then cut, any extensions removed by cutting, and either milled or notched cut to make it more compatible.

The various other components can be made by cutting the cylindrical outer shape with an extension for clamping on a lathe. A hole is drilled at one end and a drill rod with a small cutting tip is used to enter the hole and cut the ball seat. The outer notches and hinge details are cut either by gouging with a saw or wire.

Throughout this application, various publications are referenced by author and year. However, US patents are referenced by number and inventor. The full bibliography of the publications is listed below. The disclosures of these publications and patents are hereby incorporated in their entirety into this application by reference to more fully describe the state of the art to which this invention pertains.

The invention has been described in an illustrative manner and it is to be understood that the nature of the terminology that has been used is intended to be descriptive rather than limiting.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced in a manner other than that specifically described.