Reverse Thread Bone Screw

Abstract

A reverse-thread bone screw, more specifically a reverse-thread bone screw having a helix angle that slopes upwards to the left such that counterclockwise rotation promotes forward axial advancement of the screw.

Description

[Technical field]

[0001] Embodiments of the present invention relate generally to reverse thread bone screws, and more particularly to reverse thread bone screws having a left-upward sloping helix angle such that counterclockwise rotation promotes forward axial advancement of the threads. [Background technology]

[0002] There are certain anatomical locations and fracture patterns where the clockwise rotational forces generated during insertion of a conventional threaded screw can compromise fracture reduction.

[0003] Rotational forces generated during screw insertion can be particularly problematic when placing lag screws, including both techniques with overdrilling of the nearby fragment and lag with full-threaded screws or designs with partially threaded screws. During lag screw insertion, there is no leverage of the threads in the nearby fragment, and therefore, when the screw threads engage the distant fragment, a rotational force differential is concentrated at the fracture site. This concentrated force can be strong enough to cause failure of fracture reduction with rotational deformity of the fracture, even when the lag screw trajectory is perfectly perpendicular to the fracture plane.

[0004] The typical human anatomy has a femoral neck anteversion of 15° to 20°. During fixation of left femoral neck, neck base, trochanteric and some subtrochanteric hip fractures, clockwise rotational forces during insertion of conventional threaded lag screws can cause fracture extension deformity. This can result in fracture malreduction with increased risk of construct failure, sometimes necessitating additional surgery and compromised clinical outcome. During fixation of right hip fractures, the same clockwise rotational forces during insertion of conventional threaded lag screws can impart a bending force across the fracture. This bending force does not usually result in unfavorable bending deformity during fixation of right hip fractures due to femoral neck anteversion, and displacement of the proximal head fragment in the direction of bending is resisted by contact with and even compression against the more posterior bone.

[0005] Alternative techniques to counteract clockwise rotational forces during conventional threaded lag screw insertion for fixation of left sided hip fractures include the following. Use of a separate "derotational screw." A smaller diameter screw is placed in the fracture prior to placement of the primary hip lag screw to help withstand the rotational forces generated during lag screw insertion. This approach can be used with a sliding hip screw construct but not a cephalomedullary nail construct because the proximal portion of the nail blocks the trajectory of the derotational screw. Use of a derotational screw with a sliding hip screw construct increases the risk of iatrogenic lateral femoral cortical fracture, which may require the addition of a trochanteric stabilization plate to the sliding hip screw construct or even conversion to a cephalomedullary nail construct. b. Placement of an additional k-wire into the fracture prior to lag screw insertion to increase pseudofracture stability and withstand the rotational forces generated during lag screw insertion. This approach is technically more challenging with the cephalomedullary nail construct but can be performed successfully with both the sliding hip screw and cephalomedullary nail constructs. c. Use of bone hooks, ball spikes, or larger diameter k-wires, or Schanz pins to manipulate the proximal segment of the fracture and withstand the rotational forces generated during lag screw insertion. d. Placement of a clamp across the fracture to stabilize the fracture reduction and withstand the rotational forces generated during lag screw insertion, which is more challenging than with the percutaneous techniques commonly used for surgical fixation of hip fractures. e. Tapping on the lag screw and / or combined insertion and removal of the lag screw while using additional techniques to control rotational forces as described above. This reduces the leverage of the lag screw in the bone and therefore reduces the deforming rotational forces generated during lag screw insertion, however, this also sacrifices the quality of implant fixation. f. Use of an auxiliary plate to further stabilize the fracture prior to lag screw insertion. This technique may be used during an open approach to femoral neck fractures, such as high energy, high angle femoral neck fractures in young adults, where the plate also works in this fracture pattern and can serve a buttress function to withstand shear forces that contribute to construct failure, and therefore may be used in the surgical treatment of both left and right sided hip fractures. Summary of the Invention [Problem to be solved by the invention]

[0006] Accordingly, embodiments of the present invention are directed to a reverse thread bone screw that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[0007] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. [Means for solving the problem]

[0008] To achieve these and other advantages, and in accordance with the purpose of the present invention, as embodied and broadly described, a reverse thread bone screw includes a generally cylindrical body having a longitudinal axis, a reverse angle thread formed about a distal end of the body, a unique drive connection formed at a proximal end of the body, and a predetermined radiographic identifier bonded or embedded in the body.

[0009] In another aspect, the reverse thread bone screw includes a reverse thread hip lag screw comprising a generally cylindrical body having a longitudinal axis with reverse angle threads formed about a distal end of the body and a drive coupling formed at a proximal end of the body, and a predetermined radiographic indicator bonded or embedded in the body.

[0010] In another aspect, a reverse thread screw comprises a generally cylindrical body having a longitudinal axis, the reverse angle thread formed about a distal end of the body, the reverse angle thread extending the length of the body so as to terminate near the proximal end of the body, the reverse angle thread formed at the proximal end of the body, and a predetermined radiographic identification portion bonded or embedded in the body.

[0011] In another aspect, a reverse thread screw kit includes a generally cylindrical body having a longitudinal axis, the body having a reverse angle thread formed about a distal end of the body, the reverse angle thread extending the length of the body to terminate near the proximal end of the body, and a drive coupling formed at the proximal end of the body; a reverse thread screw having a predetermined radiographic identification bonded or embedded into the body; a reverse thread tap configured to provide threads complementarily configured to engage with the threads of the reverse thread screw; and a reverse thread drive mechanism complementarily configured to engage with the unique drive coupling of the reverse thread screw.

[0012] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.

[0013] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a side view of a related art threaded screw. [Diagram 2] FIG. 1 is a side view of a related art threaded hip lag screw. [Diagram 3] FIG. 1 is a side view of a reverse thread screw according to one embodiment of the disclosed subject matter. [Figure 4] FIG. 1 is a side view of a reverse thread hip lag screw, according to an embodiment of the disclosed subject matter. [Diagram 5] FIG. 13 is a plan view of the end of a head of a reverse threaded screw having a uniquely configured drive connection in accordance with one embodiment of the disclosed subject matter. [Figure 6] FIG. 13 is a plan view of the head end of a reverse threaded screw having a uniquely configured drive connection in accordance with another embodiment of the disclosed subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Typically, conventional threaded bone screws have a helix angle that slopes upwards to the right, such that a clockwise rotation promotes forward axial advancement of the screw. However, embodiments of the present invention provide a reverse thread bone screw with a helix angle that slopes upwards to the left, such that a counterclockwise rotation promotes forward axial advancement of the screw. The screw dimensions and thread pitch may be the same or similar to the conventional thread bone screw equivalent, as shown in Figures 1-4.

[0016] The implementation of a reverse-threaded hip lag screw for fixation of proper left-sided hip fractures is a novel approach that converts the extension deformity causing clockwise rotational forces generated during insertion of a conventionally threaded lag screw into a more favorable counterclockwise rotational force that is better resisted by normal hip joint anatomy and is better tolerated. The generation of counterclockwise rotational forces during lag screw insertion for fixation of left-sided hip fractures obviates the use of additional procedures described for many, if not most, of these fractures. Not having to use additional techniques to maintain fracture reduction may further benefit patient care and treatment costs through reduced operative time and potentially fewer implants.

[0017] Reverse thread bone screws must have a unique radiographic identity so that they can be identified in situ by x-ray alone. a. The typical thread pitch of hip lag screws is small enough that x-rays must be carefully scanned to distinguish between conventional and reverse thread hip lag screws in situ. b. Prevent interpretation errors resulting from inadvertent image inversion or labeling errors. c. If implant removal is necessary, it is particularly important to avoid inadvertently advancing the screw instead of withdrawing it, which can result in serious iatrogenic damage, i.e., damage caused by the surgeon. d. The unique radiographic identification can take several forms including, but not limited to, a carbide ring or a bead of increased radiographic density at the base of the threads.

[0018] Additional Instrumentation to Accompany Reverse Thread Bone Screws: e. A reverse thread tap must accompany the reverse thread bone screw, where the helix angle slopes left upwards so that counterclockwise rotation promotes forward axial advancement, and the dimensions and thread pitch of the reverse thread tap are the same as the corresponding conventional thread tap. f. A unique coupling mechanism or screwdriver for insertion or extraction of reverse thread bone screws can be used as an additional fail-safe against the surgeon improperly advancing or extracting the screw when both conventional and reverse thread bone screws are available in a set. g. No additional instrumentation or modifications are required to use a reverse-thread hip lag screw with most existing sliding hip screw and cephalomedullary nail systems. One exception is Smith+Nephew's Trigen Intertan Intertrochanteric Antegrade Nail system, which requires fabrication of a reverse-thread compression screw for use with a reverse-thread hip lag screw.

[0019] FIG. 1 is a side view of a related art threaded screw. In FIG. 1, a conventional threaded screw 100, i.e., forward or right-hand threaded screw 100, is shown having threads 110 about an inner core 120, the threads 110 having a helix angle α that slopes from left to right upwards. The diameter of the threads 110 is larger than the diameter of the inner core 120. The inner core 120 includes a conical forward distal end 125 and a head 130 at a proximal end opposite the end of the cone. The head 130 further includes a drive mechanism in a proximal end 135 configured to engage a driving tool, e.g., a screwdriver. Clockwise rotation of the conventional threaded screw 100 facilitates axial movement of the conventional threaded screw 100 into an object. The threads 110 extend substantially the entire length of the inner core 120, from near the conical forward end 125 to near the distal end of the head 130.

[0020] FIG. 2 is a side view of a related art threaded hip lag screw. In FIG. 2, a conventional threaded hip lag screw 200, i.e., forward or right-hand threaded hip lag screw 200, is shown having threads 210 about an inner core 220, the threads 210 having a helix angle α that slopes from left to right upward. The diameter of the threads 210 is larger than the diameter of the inner core 220. The inner core 220 includes a conical forward distal end 225 and a head 230 at a proximal end opposite the end of the cone. The head 230 further includes a drive mechanism 237 in a proximal end 235 that is configured to engage a driving tool, such as a screwdriver. Clockwise rotation of the conventional threaded screw 200 facilitates axial movement of the conventional threaded screw 200 into an object. The threads 210 extend only a portion of the length of the inner core 220 , from near the conical forward end 225 to approximately ¼ to ½ of the length of the inner core 220 .

[0021] FIG. 3 is a side view of a reverse thread screw according to one embodiment of the disclosed subject matter. In FIG. 3, a reverse thread screw 300, i.e., a reverse or left-handed threaded screw 300, is shown having a reverse thread 310 about an inner core 320, the reverse thread 310 having a helix angle α that slopes from right to left upward. The diameter of the reverse thread 310 is larger than the diameter of the inner core 320. The inner core 320 includes a conical forward distal end 325 and a head 330 at a proximal end opposite the end of the cone. To aid in identifying the type of screw prior to surgery, a radiological marker, such as but not limited to, one or more carbide bands 327, may be attached to the inner core 320 near the base of the reverse thread 310 distal to the conical forward distal end 325. Alternatively, or in addition to the carbide bands 327, one or more radiologic beads 329 may be attached along the inner core 320. The head 330 can further include a uniquely configured drive connection (see FIGS. 5 and 6 for exemplary embodiments of drive connections) at the proximal end 335 of the reverse-threaded screw 300 that is configured to engage a complementary shaped drive tool, e.g., a uniquely shaped screwdriver and / or other drive tool. Counterclockwise rotation of the reverse-threaded screw 300 facilitates axial movement of the reverse-threaded screw 300 into the object. The reverse threads 310 extend substantially the entire length of the inner core 320 from near the conical forward end 325 to near the distal end of the head 330.

[0022] 4 is a side view of a reverse thread hip lag screw, according to one embodiment of the disclosed subject matter. In FIG. 4, a reverse thread hip lag screw 400, i.e., a reverse or left-handed threaded hip lag screw 400, is shown having a reverse thread 410 about an inner core 420, the reverse thread 410 having a helix angle α that slopes from right to left upward. The diameter of the reverse thread 410 is larger than the diameter of the inner core 420. The inner core 420 includes a conical anterior distal end 425 and a head 430 at a proximal end opposite the end of the cone. To aid in identification of the type of screw prior to surgery, a radiological marker, such as but not limited to, one or more carbide bands 427, may be attached to the inner core 420 near the base of the reverse thread 410 distal to the conical anterior distal end 425. Alternatively, or in addition to the carbide band 427, one or more radioactive beads 429 may be attached along the inner core 420. The head 430 may further include a uniquely configured drive connection (see FIGS. 5 and 6 for exemplary embodiments of drive connections) at a proximal end 435 of the reverse-threaded screw 400 that is configured to engage with a driving tool, for example, a screwdriver and / or other driving tool. Counterclockwise rotation of the reverse-threaded screw 400 facilitates axial movement of the reverse-threaded screw 400 into the object. The reverse threads 410 extend only a portion of the length of the inner core 420, from near the conical forward end 425 to approximately ¼ to ½ of the length of the inner core 420.

[0023] FIGURE 5 is a plan view of the head end of a reverse-threaded screw having a uniquely configured drive connection, according to one embodiment of the disclosed subject matter. In FIGURE 5, head 530 of reverse-threaded screw 500, which may include, for example, but is not limited to, reverse-threaded screw 300 of FIGURE 3, reverse-threaded hip lag screw 400 of FIGURE 4, reverse-threaded Smith+Nephew's Trigen Intertan Intertrochanteric Antegrade Nail System, etc. Head 530 includes a uniquely configured connection mechanism 537, shown here as a 3 / 4 circle shaped connection mechanism 537, which requires a complementary shaped drive mechanism (not shown) that can mate with and rotate the uniquely configured connection mechanism 537.

[0024] 6 is a plan view of the head end of a reverse-threaded screw having a uniquely configured drive connection in accordance with another embodiment of the disclosed subject matter. In FIG. 6, head 630 of reverse-threaded screw 600, which may include, for example, but is not limited to, reverse-threaded screw 300 of FIG. 3, reverse-threaded hip lag screw 400 of FIG. 4, reverse-threaded Smith+Nephew's Trigen Intertan Intertrochanteric Antegrade Nail System, etc. Head 630 includes a uniquely configured connection mechanism 637, shown here as an elongated hexagonal shaped connection mechanism 637, which requires a complementary shaped drive mechanism (not shown) that can mate with and rotate the uniquely configured connection mechanism 637.

[0025] Alternatively, other embodiments may include a uniquely configured interlocking mechanism having at least two different depth levels, with each depth level having a different configuration to prevent the screw from being advanced or removed by the complementary shaped drive mechanism unless the complementary shaped drive mechanism is fully inserted into the interlocking mechanism having the differently configured depth level. The above two shapes of Figures 5 and 6, as well as the multiple possible depth levels, are merely examples of possible shapes for the uniquely configured interlocking mechanism, and numerous other shapes and configurations are contemplated.

[0026] In various configurations and embodiments, a reverse thread tap accompanies a reverse thread bone screw, where the helix angle is ramped upwards to the left such that counterclockwise rotation promotes forward axial advancement, and the dimensions and thread pitch of the reverse thread tap are the same as the corresponding conventional thread tap.

[0027] A reverse thread hip lag screw is an exemplary embodiment of the application of a reverse thread bone screw, for example, a reverse thread hip lag screw used in sliding hip screw and cephalomedullary nail constructs for osteosynthesis of selected hip fractures. For fixation of left hip fractures, a reverse thread hip lag screw, in which counterclockwise rotation promotes anterior axial advancement, creates more favorable bending forces at the fracture (as occurs during conventional thread lag screw insertion in fixation of right hip fractures), thus preventing the fixation implant from contributing to poor reduction, and is expected to improve fracture healing and clinical outcomes. This statement applies to hip lag screws used in both sliding hip screw and cephalomedullary nail constructs. This statement may be extended to dual lag screw cephalomedullary nails, often referred to as "reconstruction nails" or "recon nails," and cannulated screw systems used to treat some femoral neck fracture patterns.

[0028] Alternative configurations include reverse thread hip lag screws for sliding hip screw constructs, reverse thread hip lag screws for cephalomedullary nail constructs, reverse thread hip lag screws for dual lag screw cephalomedullary nail constructs, fully threaded and partially threaded reverse thread cannulated screws.Embodiments of the present invention can be readily applied to other anatomical sites and / or fracture patterns where conversion of clockwise rotational forces to counterclockwise rotational forces is beneficial.

[0029] In some instances, careful intraoperative monitoring with fluoroscopy, and possibly even direct visualization of the fracture, may be preferred during implant insertion for fixation of a hip fracture to ensure maintenance of reduction.

[0030] It will be apparent to those skilled in the art that various modifications and variations can be made to the reverse thread bone screw of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. [Explanation of symbols]

[0031] 100 Conventional Threaded Screw 110 thread 120 Inner Core 125 Distal end 130 Head 135 Proximal end 200 Conventional Threaded Screw 210 thread 220 Inner Core 225 Distal end 230 Head 235 Proximal end 237 Driving Mechanism 300 reverse thread screw 310 reverse thread 320 Inner Core 325 Distal end 327 Carbide Band 329 Radiation Beads 330 Head 335 Proximal end 400 reverse thread screw 410 reverse thread 420 Inner Core 425 Distal end 427 Carbide Band 429 Radiation Beads 430 Head 435 Proximal end 500 reverse thread screw 530 Head 537 Connection mechanism 600 reverse thread screw 630 Head 627 Connection mechanism

Claims

1. It is a reverse threaded mountain bone screw, A main body having a longitudinal axis and a substantially cylindrical shape, wherein a reverse thread is formed around the distal end of the main body and a drive coupling is formed at the proximal end of the main body, A predetermined radiographic image identification unit is attached to or embedded in the main body, wherein the predetermined radiographic image identification unit helps to identify that a screw visible in situ by X-ray is a reverse-threaded crescent screw, A reverse-threaded crest screw.

2. The reverse threaded ridge screw according to claim 1, wherein the reverse threaded ridge screw is a reverse threaded hip lag screw.

3. The reverse thread hip lag screw according to claim 2, wherein the drive coupling portion is configured to receive a drive tool of complementary shape.

4. The reverse thread hip lag screw according to claim 3, wherein the complementary shaped drive tool is configured to drive and remove the reverse thread hip screw in the opposite direction to that of the forward thread hip screw.

5. The predetermined radiation image identification unit, A radiopaque ring connected to the base of the reverse thread, or One or more radiopaque beads connected to the main body. A reverse thread hip lag screw according to claim 2, comprising the features described in claim 2.

6. The reverse thread hip lag screw according to claim 2, wherein the reverse thread is formed over the fixed length of the distal end of the main body.

7. The reverse thread hip lag screw according to claim 6, wherein the fixed length of the distal end of the main body is less than 2.54 cm.

8. The reverse thread hip lag screw according to claim 6, wherein the fixed length of the distal end of the main body is less than 1.27 cm.

9. It is a reverse thread screw, A main body having a longitudinal axis and a substantially cylindrical shape, wherein a reverse thread is formed around the distal end of the main body, the reverse thread extends substantially along the entire length of the main body so as to terminate near the proximal end of the main body, and a drive coupling portion is formed at the proximal end of the main body, A predetermined radiation image identification unit is attached to or embedded in the main body, wherein the predetermined radiation image identification unit helps to identify that a screw visible in situ by X-ray is a reverse-threaded screw, A reverse-threaded screw equipped with this feature.

10. The reverse thread screw according to claim 9, wherein the drive coupling portion is configured to receive a drive tool of complementary shape.

11. The reverse threaded screw according to claim 10, wherein the complementary shaped drive tool is configured to drive and remove the reverse threaded hip screw in the opposite direction to that of the forward threaded hip screw.

12. The predetermined radiation image identification unit, A radiopaque ring connected to the outer circumference of the main body, or One or more radiopaque beads connected to the main body. A reverse thread screw according to claim 9, comprising the features described in claim 9.

13. The reverse thread screw according to claim 12, wherein the radiopaque ring is connected to the base of the reverse thread.

14. The reverse thread screw according to claim 12, wherein the plurality of radiopaque beads are arranged along the longitudinal direction of the main body.

15. The reverse thread screw according to claim 12, wherein the plurality of radiopaque beads are arranged along the circumferential direction of the main body.

16. It is a reverse thread screw, A main body having a longitudinal axis and a substantially cylindrical shape, wherein a reverse thread is formed around the distal end of the main body, the reverse thread extends substantially along the entire length of the main body so as to terminate near the proximal end of the main body, and a drive coupling portion is formed at the proximal end of the main body, and A predetermined radiation image identification unit attached to or embedded in the main body, wherein the predetermined radiation image identification unit helps to identify that a screw visible in situ by X-ray is a reverse-threaded screw. A reverse-threaded screw equipped with, A reverse thread tap configured to provide a thread that is complementary to the thread of the reverse thread screw, A reverse thread drive mechanism configured to engage with the drive coupling portion of the reverse thread screw, A screw kit with reverse threads.

Images