ORTHOPEDIC IMPLANT SYSTEM FOR VARIABLE ANGLE LOCKING HAVING ENGINEERED MATING THREAD ENGAGEMENT

Abstract

The invention relates to an orthopedic implant system comprising an implant including a threaded aperture which receives either a first non-locking bone fastener or a second threaded variable axis locking fastener. The threaded aperture includes interruptions to form sections having a thread segment. The variable axis locking fastener has a threaded head configured to cause the threads to wedge against the female threads of the aperture as the fastener is tightened into the aperture in an off-axis orientation. In a further embodiment, the aperture includes a concentric annular groove to form flexible threaded fines.

Claims

1. An orthopedic implant system, comprising: a plate including a first surface and a second surface, the implant including at least one aperture, the aperture including one or more female threads which a define a thread crest angle T1, and a thread root and at least two recesses within the threads which interrupt the threads to define at least two sections having a thread crest segment; and at least one screw including an elongate shaft and a head member having a head configuration including male locking threads, the male locking threads of the head member define a thread trough angle, T2, and the male locking threads of the fastener head member and the female threads of the aperture having a differing thread configuration; wherein the at least one screw is configured for insertion within at least one threaded aperture at a plurality of different insertion angles while achieving a locking engagement between the threaded head and the threaded aperture.

2. An orthopedic implant system as set forth in claim 1, wherein T1 is different than T2.

3. An orthopedic implant system as set forth in claim 2, wherein T1 is from 15° to 45° larger than T2.

4. An orthopedic implant system as set forth in claim 1, wherein the aperture is a compound opening including an annulus having an annulus configuration and joined to a mouth in at least one of the first surface and the second surface.

5. An orthopedic implant system as set forth in claim 4, wherein the annulus configuration is different from the head configuration.

6. An orthopedic implant system as set forth in claim 5, wherein the annulus configuration is cylindrical and the head configuration decreases in diameter along a vertical axis.

7. An orthopedic implant system as set forth in claim 5, wherein the annulus configuration decreases in diameter along a vertical axis and the head configuration decreases in diameter along a vertical axis at a different rate that the annulus configuration.

8. An orthopedic implant system as set forth in claim 7, wherein the annulus configuration is tapered at an angle of 4° to 20° and the head is tapered at an angle of from 25° to 60°

9. An orthopedic implant system as set forth in claim 8, wherein the annulus configuration is cylindrical and the head configuration decreases in diameter along a vertical axis.

10. An orthopedic implant system as set forth in claim 1, wherein the thread root of the aperture describes a helix.

11. An orthopedic implant system as set forth in claim 10, wherein the thread root defines a helix for at least 120° of the circumference of the aperture.

12. An orthopedic implant system as set forth in claim 11, wherein the thread root defines a helix for at least 180° of the circumference of the aperture.

13. An orthopedic implant system as set forth in claim 1, wherein the helix is cylindrical or tapered and wherein the female locking threads of the aperture have a thread crest that describes a first configuration and the male locking threads of the head member

14. An orthopedic implant system as set forth in claim 1, wherein the male locking threads of the screw head are tapered between a proximal end of the threaded head and a distal end of the threaded head.

15. An orthopedic implant system as set forth in claim 14, wherein male locking threads define a conical helix for at least 120° of the circumference of the screw head.

16. An orthopedic implant system as set forth in claim 15, wherein the male locking threads are at least a double lead thread.

17. An orthopedic implant system as set forth in claim 1, wherein there are 2-6 recesses that interrupt the threads.

18. An orthopedic implant system as set forth in claim 1, wherein T2 is larger than T1.

19. An orthopedic implant system as set forth in claim 18, wherein the value of T2 is at least 1.25× the value of T1.

20. An orthopedic implant system with an implant having an aperture with a thread or threads including a thread crest which describe a helix and having from 2 to 6 recesses which interrupt the thread crest in a radially symmetric geometry to form sections having a segment of a thread crest and a locking fastener having a head which has a thread or threads including a thread crest that describe a helix and wherein the thread crest of the aperture has an angle T1 which is different than the angle T2 of the thread recess of the screw head and the value of T2 is at least 1.3× the value of T1.

21. An orthopedic implant system of claim 17, wherein the aperture and the fastener head each has a double lead thread.

22. An orthopedic implant system, comprising: a plate including a first surface and a second surface, the implant including at least one aperture having a central aperture axis, the aperture including one or more female threads which a have a crest a defining a helical spiral and having a thread crest angle T1, and a thread root and at least two recesses within the threads which interrupt the threads to define at least two areas of threads; and at least one screw including an elongate shaft and a head member along a longitudinal screw axis including male locking threads, the male locking threads of the head member having a thread root defining a conical or hemispherical helical spiral and a thread trough angle, T2, wherein the at least one screw is configured for insertion within at least one threaded aperture at a plurality of different insertion angles while achieving a locking engagement between the threaded head and the threaded aperture, and the plate thread has a crest, and the plate thread crest forms an interference fit onto the thread root of the screw head member so as to lock the orientation of the screw when the longitudinal screw axis is not co-axial with the central aperture axis.

23. An orthopedic implant system as set forth in claim 22, wherein T1 is not equal to T2.

24. An orthopedic implant system as set forth in claim 23, wherein the female thread crests of the aperture define a helical spiral that describes a first configuration and the male thread troughs of the screw head define a helical spiral that describes a second configuration and the first configuration is not the same as the second configuration.

25. An orthopedic implant system as set forth in claim 24, wherein the first configuration has a diameter that decreases and the second configuration has a diameter that decreases and the first configuration decreases at a greater rate than the second configuration.

26. An orthopedic implant system as set forth in claim 25, wherein the first configuration is a taper and the second configuration is a taper and the taper of the first configuration has a greater taper angle than the taper of the second configuration.

27. An orthopedic implant having a first surface and a second surface and aperture between the first surface and the second surface which includes an annulus having male threads and from 2 to 8 recesses which interrupt the male threads to form sections having at least one thread segment and one of the first or the second surfaces including an concentric annular groove exterior to the aperture and the aperture including from 2 to 8 recesses in the threads of the aperture which extend radially inward into the annular groove so as to form a series of flexible threaded sections in the aperture.

28. An orthopedic implant as set forth in claim 27, wherein there is an implant thickness defined between the first surface and the second surface and the annular groove extends at least 30% of the implant thickness.

29. An orthopedic implant as set forth in claim 27, wherein the annular groove extends at least 50% of the implant thickness.

30. An orthopedic implant as set forth in claim 27, wherein the male threads define a cylindrical helix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 shows a top side view of the orthopedic implant system of the present invention having a variable axis locking screw in a normal orientation in an implant which is shown in cross-section;

[0013] FIG. 2 shows a side cross-sectional view of the orthopedic implant system of FIG. 1;

[0014] FIG. 3 shows top side view of an implant with three embodiments of the aperture of the present invention;

[0015] FIG. 4 is a top view of the implant of FIG. 3;

[0016] FIG. 5 is bottom view of the of the implant of FIG. 4;

[0017] FIG. 6 a detail of the variable locking screw shown at a normal axis orientation in an aperture of the implant of the present invention in cut-away form;

[0018] FIG. 7 is a detail of the variable locking screw shown at an oblique axis orientation in an aperture of the implant of the present invention in cut-away form;

[0019] FIG. 8 a detail of the variable locking screw shown at a normal axis orientation in an aperture of the implant of the present invention in cut-away form and illustrating the thread angle mismatch;

[0020] FIG. 9 is a detail in cross-section of the torque driving recess of the implant of the present invention;

[0021] FIG. 10 is a top side view of the of the torque driving recess of the implant of FIG. 9;

[0022] FIG. 11 shows a side view of the implant of the present invention in cross-section, but with a non-locking screw in an on-axis orientation and showing different embodiments of the apertures in the implant;

[0023] FIG. 12 is a detail illustrating the cylindrical aperture of the implant of the present invention;

[0024] FIG. 13 is a detail showing the cross-section of a second embodiment of the implant of the present invention;

[0025] FIG. 14 is a side view of the implant system of FIG. 13 showing the screw in side view and the implant as a partial section;

[0026] FIG. 15 is a cross section of the plate of FIG. 14;

[0027] FIG. 16 illustrates a cross-section of an implant aperture for a third embodiment of the invention; and

[0028] FIG. 17 is a top edge view of a section of the aperture of FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention relates to an orthopedic implant system 10 which includes an implant 9, such as a member having two major opposing, and typically co-extending, or concentric surfaces, which will be referred to as a “top surface” 11, meaning the surface intended to face out relative to the affected bone, and a “bottom surface” 8, meaning the surface that is configured to contact, or face toward the affected bone and a side edge 15 including a long edge 9. Plates have typically been configured in a curved blade-like configuration where the curve is meant to accommodate the long radiused surfaces of bone they are meant to support, such as the femur, fibula, radius or humerus. However, as orthopedic implants have become increasingly sophisticated, the outlines and profiles have evolved in more complex shapes with generalized curves or bends to accomplish certain medical goals. In addition, sometimes implants will also include portions that are intended to project into the bone, rather than sitting against it, and these areas tend to be more cylindrical and less “plate-like” in order to support the bone from the intramedullary channel.

[0030] The implant, or plate 12, has at least one threaded compound aperture 14 which includes a necked area or annulus 13 having internal or female threads 17. More typically the implant has multiple apertures 14, which in a first embodiment, has a cylindrical configuration in the annular portion, meaning that throughout at least 50%, and preferably 75%, and most preferably 85% of the depth of the annulus 13 as measured from one surface of the plate to the opposing surface there is a constant major diameter in the annulus portion of the aperture and a constant minor diameter in the annulus portion of the aperture (as defined by a line at which intersections the edges of the major diameter and the minor diameter shown in cross-section or alternatively, the threads, or more specifically, the thread crest follow a cylindrical helical path for at least 120° radially, and preferably 180°, and preferably 270° radially, depending on whether the threads are single or multiple leads, and preferably double lead). This means that the thread edges at the major diameter subscribes a portion of a cylinder for at least a portion of the height of the aperture, likewise, so may the thread root. The aperture 14 includes one or more counterbores or chamfers 33 joined to the annulus 13, to allow for a wider angulation or to accommodate the screw head member 22. The internal thread 17 is preferably a double lead thread which will lock with less thread deformation since the locking head does not seat fully in the aperture as the bottom threads are not in the way try to force the screw back on-axis (and therefore causes less need for thread deformation in that bottom-left corner).

[0031] In a further embodiment of the variable locking system of the present invention, the annulus portion 13 of the plate aperture 14 as considered at the thread root or thread crest, has a diameter that decreases along the central axis of the aperture from the top of the plate to the bottom of the plate. In particular, the configuration of the plate aperture differs from the configuration of the screw head where both configurations are defined at the thread crests. This could mean tapering conical configurations at differing angles, such as the screw head having a taper of from 5° to 30°, and preferably from 12° to 20° (or 15°+/−7° or 5°) and the plate aperture has a taper that is from 5° to 40°, and preferably 25° to 35° (or 10°+/−7° or 5°), in difference as measured by the angle between a line at the thread crest and the central longitudinal axis of the relative configuration, with the thread of the aperture forming a greater angle of from 25° to 60°, and preferably from 30° to 50° (or 40°+/−7° or 5°). Alternatively, the differing configurations could be rounded or hemispherical shapes of differing diameters.

[0032] The invention further includes a first fastener, which is variable locking screw 16 which has a shaft 18 including a distal portion 19 that has a cortical bone thread 20 extending from the shaft 18 which defines the minor diameter of the cortical thread to the thread crest 23 which defines the major diameter of the cortical thread, and a proximal portion 21 that includes a head member 22 which is convexly rounded, tapered or conical in shape and which includes external or male threads 24. The threads 24 run from a top surface 26 of the screw head member 22 to a necked portion 28 which joins the head member 22 to the shaft 18. At the distal portion 25 of the head member 22, the screw includes at least one, and preferably two or three cutting flutes 29. The distal portion 19 of the screw can also include cutting flutes. The proximal portion 27 of the screw 16 includes a top surface 26 of the screw, which has a torque driving recess 30 which can be a hexalobe shape, and preferably can include an internal taper to enable a press fit with a mating torque driver head. The cutting flutes are provided to bore a countersink into the bone to accommodate a deeper screw head in a thinner plate. Thus, the countersink helps to minimize prominence above the bone by sinking part of the screw head below the bottom surface of the plate into the bone and to reduce the number of operative steps, the cutting flutes would help automatically countersink any bone that gets in the way.

[0033] The locking threads 24 of the head member 22 are preferably dual lead threads, with a start point 180° apart, and have a major diameter 32 and a minor diameter 34 with a locking thread crest 36 at the junction of a bottom thread face 38 and a top thread face 40 which together define a thread cut-out angle 42 as shown in FIG. 8. The screw head member 22 configuration includes a decreasing diameter, or more specifically, a taper, meaning that lines connecting the major diameters converge toward the screw axis in the distal direction and that lines connecting the minor diameters converge toward the screw axis in the distal direction as can be seen in FIG. 2. A taper angle A can be defined between the longitudinal axis 39 of the screw and the outer diameter at the crest of the locking threads of the screw head member 22. Although any suitable taper angle A can be used, suitable taper angles A can be between about 2° and about 35°, and more particularly between about 5° and about 25°, such as about 15°+/−5°. Similarly to the corresponding definition of the cylindrical annulus, the screw head is considered tapered as marked by the following concepts: the edge of the thread or threads, i.e., the thread crest, or the edge of the minor diameter, i.e., the thread root, in the case of multiple lead threads at the major diameter subscribe a portion of a cone, and define for at least 120°, and preferably at least 180°, or 270° or 360° or for an at least 75% of an entire diameter or preferably for at least a fully turn of the screw head, the threads follow the path of a helical cone.

[0034] In contrast, the annulus 13 of the plate aperture 14 has a deliberately mis-matched configuration that differs from the configuration of the screw head, such as being generally cylindrical with a tapered screw head (aside from any chamfers or other reliefs), and has a diameter that is intermediate the widest major diameter of the screw head 22 and the narrowest major diameter 32. In a first embodiment, the threads 17 of the plate 12 follow a cylindrical (non-tapered) helical path while the thread 24 of the screw head member 22 follows a tapered helical path that increases in diameter as it travels up proximally on the screw head 22. Thus, in a mating cooperation the trailing (upward) surfaces of the plate threads support the screw while the crests of the screw threads press radially outward on the plate's thread major as the screw's advanced until it binds as is shown in FIG. 7. The present invention utilizes a tapered locking screw head member and a cylindrical threaded locking aperture, which has the advantage over a system using a tapered locking aperture which tends to re-orient an off-axis screw orientation back to center.

[0035] In a further embodiment, the configuration of the annulus of the aperture varies from the configuration of the screw head in that both may have a decreasing diameter, but which decreases at a different rate in the direction of the central axis from the top to the bottom respectively. In addition, the thread angle of the aperture and of the screw head differ so as to present an intended mis-match of 15 degrees in either direction between the mating thread surfaces. This allows for 30 degrees of conical freedom in the angulation but still provides for locking by means of the tapered mismatch on the thread crest of the plates onto the thread valley of the screw.

[0036] As illustrated in FIG. 2, the threaded apertures 14 can define a longitudinal axis 50 extending through the threaded aperture 14 between the first surface 11 and the second surface 8 of the bone plate 12. The longitudinal axis 50 can represent the “centerline” of the threaded aperture 14 and is therefore dependent on the orientation in which the threaded aperture 14 is formed in the bone plate 12. In various examples, the threaded aperture 14 can be formed in the bone plate 12 such that it extends generally perpendicular to the first surface 11 and the second surface 8, or the threaded aperture 14 can be formed in the bone plate 12 such that it extends at an oblique or non-perpendicular angle relative to the first surface 11 and the second surface 8. Regardless of the orientation of the threaded aperture 14, the longitudinal axis 50 defines only one of the axes along which the variable locking fastener can be inserted. Thus, the threaded aperture 14 and the locking fastener 16 can define a “variable axis locking” or “polyaxial” fastening system wherein the locking fastener 16 can be inserted into the threaded aperture 14 in a plurality of different insertion angles relative to the longitudinal axis 50 of the aperture while achieving a locking engagement between the thread head 22 and the threaded aperture 14. An example of this variable axis locking capability is illustrated in FIG. 7, wherein the elongate shaft 18 of the locking fastener 16 does not extend along the longitudinal axis 50 of the corresponding threaded aperture 14, but instead forms an angle with the longitudinal axis 50 while maintaining a locking connection between the externally threaded head member 22 and the internally threaded aperture 14.

[0037] FIG. 8 illustrates the threads 17 of the plate aperture 14. The threads can be thrust threads having a truncated V-shape defining a series of roots 60 and crests 62 and having an internal thread angle T1 at 63. The internal thread angle T1 is 60°+/−20°, and preferably +/−15° or 10°. A thread height H1 of the threads of the internally threaded surface 14 can be defined between one of the roots 60 and an adjacent one of the crests 62. The roots 60 and/or the crests ° can be truncated to avoid the formation of a “sharp” V-shape, or a trough. A perfectly sharp 60° V-thread generally includes a thread height equal to about 0.866 of the pitch. However, with truncated threads, the thread height decreases. In an example, the thread height H1 can be between about 0.008 inches and about 0.015 inches, such as about 0.0118 inches. The screw threads have an external thread angle T2, 42, at the thread crest which is about 30°+/−20° preferably +/−15° or 10°. T1 is different than T2, and is preferably 30°. preferably +/−15° or 10° inclusively (meaning including both sides of the thread crest or trough.)

[0038] FIG. 16 illustrates that the angle T2 of the screw head has a differential on both sides of the crest (i.e. the leading and trailing surfaces) which are smaller than the corresponding thread trough on the female threads of the screw head. The difference on one of the two sides T3 is equal to the one half of the available conical angle of variability for the variable locking aspect of the screw in the aperture.

[0039] The threads 17 of the annulus 13 of the aperture 14 include one or more recesses 78 (78′,79″) circumferentially spaced around the annulus 13 so as to define a plurality of threaded sections 79 (78′, 79″) having at least one thread segment on a section. In an example, the one or more recesses 78 can be formed by creating radially symmetrical hemicylindrical cuts in the internally threaded surface of the threaded aperture 14. Preferably, there are 2-6 recesses, and more preferably 4, 5 or 6 recesses as is illustrated in FIGS. 3-5. The cuts 78, 78′ and 78″ can have a depth sufficient to completely remove the threads in the area of the recesses such that a substantially smooth recessed surface is created to cause an interruption to the threads crest and at varying degrees to the thread trough such that the vertical edges of the interruptions are not aligned but spiral about the edge of the annulus 13. The effect of the recesses is to form sections with a thread crest 79 and multiple thread troughs on the side wall of the aperture between the recesses. Alternatively, the recess 78 can be formed to a depth that retains the thread segment in the area of the recess 78, albeit at a reduced height (between a root and a crest of the thread) but still sufficient to create the interruption to the thread.

[0040] The locking screw head member 22 has a 2-start thread which mates with the female locking threads 17 of the aperture, but the plate's male thread form is sharper (i.e., a 20°-45°, and preferably 30°+/−5° triangular cross-section) than the screw head's female cutout (i.e., a 50°-85°, and preferably 60°+/−10° or 5° triangular cross-section) to facilitate off-axis cross-threading without damaging the threads and so as to avoid generating tailings or metal debris. The locking screw head threads are on a conical taper (smallest diameter at bottom) to facilitate engagement with the plate at various angles and to prevent the screw from being advanced all the way through the plate. To minimize the plate thickness and overall height of the screw/plate assembly over the bone, the underside of the locking screw's head/neck area has a cutting feature which cuts into bone if the screw protrudes too far under the plate. The one or more external threads 20 on the elongate shaft 18 can have double the pitch and the same lead as the locking threads 24 of the head member 22.

[0041] FIG. 11 illustrates a non-locking screw 16′ in the aperture 14′. In this example, the non-locking screw 16′ has a head 22′ with a rounded proximal portion that extends into a tapered necked portion 28′ which enable the screw to have a wide angle at which it extends through the aperture 14′.

[0042] A further embodiment of the implant of the present invention is shown having a trepanned aperture 14″. In this embodiment, the aperture includes a concentric outer annular groove 90 which extends vertically up from a surface, and preferably the bottom surface of the implant more that 25%, and preferably more than 50% of the thickness of the implant such that the columns of tabs 79″ of threads become independent from the greater plate material to create tines that can flex radially to better accommodate the off-axis external threads of the fastener.

[0043] The bone plate 12 and the locking fastener 16 can be formed from any suitable medical-grade material. Exemplary materials can include, but are not limited to, stainless steel, titanium, and cobalt based alloys and coated or anodized versions of these materials. The bone plate 12 and the locking fastener 16 can be formed from the same material or at least partially from different materials.