WO2015050900A1

WO2015050900A1 - Scaphoid screws and fasteners

Info

Publication number: WO2015050900A1
Application number: PCT/US2014/058472
Authority: WO
Inventors: Lloyd P. Champagne; Jozef Zoldos; Walter BALFOUR
Original assignee: Exsomed Holding Co LLC
Current assignee: Exsomed Holding Co LLC
Priority date: 2013-10-02
Filing date: 2014-09-30
Publication date: 2015-04-09
Anticipated expiration: 2016-04-02

Abstract

Disclosed are embodiments of screws that can be used to compress broken fragments of a bone at the fracture point to help enable them to heal properly.

Description

Scaphoid Screws and Fasteners

Field of the Invention

[001] The present invention relates to screws and fasteners that could be used for fractures in the scaphoid bone, or for any suitable bone repair.

Background of the Invention

[002] A variety of screw apparatuses and methods have been developed for use in compression of various materials, particularly in the fields of orthopedics, podiatry, and chiropody. The prior art includes various types of screws for placement into bone for compressing bone fragments across a fracture line. During use to compress two spaced-apart materials such as bone fragments, holes can be drilled in the bone to accept the screw, and a driver can be used to thread into place the screw across the fracture line. As such, it is well known to utilize a screw for placement across a fracture or osteotomy in order to compress, or as is referred to in the field, fixate a fracture to promote the healing process.

[003] As used herein, the following terms have the following meanings: (1) pitch diameter means the diameter of the threads on a screw, as measured along the axis of the thread, (2) screw diameter means the diameter of the screw, including threads, measured along an axis perpendicular to the longitudinal axis of the screw, and (3) pitch means the distance between individual, adjacent threads of a screw.

[004] Apparatuses and methods known in the medical field for reducing, fixing, and generally assisting the healing of fractured bones within the body typically require surgical intervention. Open reduction internal fixation (ORIF) is a method or technique developed for surgically repairing fractured bone generally involving the use of plates and screws or an intramedullary (IM) rod to stabilize fractured bone. Many complications typically exist, however, with this technique that prevent successful or optimal outcomes in all cases.

Treatment methods can also significantly impact healing time, pain, and functional outcomes. Moreover, the necessity of reducing operative time is driven both by patient risk of infection, anesthetic complications, and health care costs. As a result, efforts are continuously made to improve surgical techniques and fixation devices to improve surgical outcomes, costs, and operative times.

[005] Despite the prior art compression screw apparatuses and methods, room for improvement remains for easily and effectively achieving compression of suitable materials, particularly for compression of bone fragments across a fracture line. Summary of the Invention

[006] Embodiments of the invention provide simple and novel structures of screws (or fasteners, hereafter collectively "screws") used to repair fractured bones, and that can compress bone segments along a fracture; the compression helping to ensure the proper healing of the bone. Each of the screws is preferably cannulated to fit over a guide wire or structure, such as a k-wire.

Brief Description of the Drawings

[007] Figure 1 shows perspective device in accordance with various aspects of the invention.

[008] Figure 1A shows a side view of the device of Figure 1.

[009] Figure IB shows a front view, from the end of the device opposite the heads of the device of Figure 1.

[0010] Figure 2 shows another device in accordance with various aspects of the invention.

[001 1] Figure 3 shows another device in accordance with various aspects of the invention that has threads that increase in diameter moving from the distal to the proximal end.

[0012] Figure 4 shows a side view of another device in accordance with various embodiments of the invention.

[0013] Figure 4A shows a side, perspective partial view of the device of Figure 4.

[0014] Figure 4B shows a partial, side view of the device of Figure 5.

[0015] Figure 5 shows a side, partial view of another device in accordance with the invention.

[0016] Figure 6 shows a method for using the device of Figure 5.

[0017] Figure 7 also shows a method for using the device of Figure 5.

[0018] Figure 8 shows a side view of another device in accordance with the invention.

[0019] Figure 9 shows a tool that can be used with certain devices in accordance with aspects of the invention. [0020] Figures 10-1 OB show how the tool of Figure 9 is used with a device according to Figure 8.

[0021] Figure 1 1 shows a side view of another device in accordance with aspects of the invention.

[0022] Figure 1 1A shows a partial, cross-sectional view of the device of Figure 11 and front view of a first driver used with the device.

[0023] Figure 1 IB shows a partial, cross-sectional view of the device of Figure 1 1 and front view of a second driver used with the device.

[0024] Figures 12-12C show how the device of Figure 1 1 is preferably mounted in a bone.

[0025] Figure 13 shows a side view of another device in accordance with aspects of the invention.

[0026] Figure 13A shows a partial, cross-sectional view of the device of Figure 11 and front view of a first driver used with the device.

[0027] Figure 13B shows a partial, cross-sectional view of the device of Figure 1 1 and front view of a second driver used with the device.

[0028] Figure 14 shows a side view of another device in accordance with aspects of the invention.

[0029] Figure 15 shows a side view of another device in accordance with aspects of the invention.

[0030] Figure 16 shows a side view of another device in accordance with aspects of the invention.

[0031] Figure 17 shows a side view of another device in accordance with aspects of the invention.

[0032] Figure 18-18C show a method for inserting a device according to any of Figures

14-16 into a bone.

[0033] Figure 19 shows a side view of another device in accordance with aspects of the invention. [0034] Figure 20-20A shows a side view of the device of Figure 19 being inserted into a bone.

[0035] Figure 21 shows a side view of the device of Figure 19 inserted into a bone.

[0036] Figure 22 shows a side view of another device in accordance with aspects of the invention.

[0037] Figure 23 shows a side view of another device in accordance with aspects of the invention.

[0038] Figure 23 A shows a side view of the device in Figure 22 in use.

[0039] Figure 23B shows a side view of the device in Figure 22 in use.

[0040] Figure 24 shows a side view of another device in accordance with aspects of the invention.

[0041] Figure 25 shows a side view of another device in accordance with aspects of the invention.

[0042] Figure 26 shows a side view of another device in accordance with aspects of the invention.

[0043] Figure 27 shows a side perspective view of a device according to the invention and a tool that can be used with the device.

Detailed Description of Preferred Embodiments

[0044] Turning now to the figures where the purpose is to describe preferred embodiments of the invention and not to limit same, Figures 1-lB show a screw 10 with a shaft 12, cutting threads 14 and a distal tip 16. In this embodiment, cutting threads 14 have a pitch angle of preferably 5°-40° and most preferably between 15°-30°. The threads 14 may have any suitable pitch angle or pitch, and the pitch may vary among threads as may the pitch diameter. The threads 14 are preferably triangular, but could also be of other shapes, such as hexagonal or rectangular, as long as they have sharp cutting edges. Screw threads of this type can be used or any screw according to aspects of the invention where practical.

[0045] For each of the screws defined herein, the pitch, pitch angle and pitch diameter of the threads may vary in any suitable way for the particular screw design.

[0046] Figure 2 shows a screw 20 with a shaft 22, threads 24 and distal tip 26. In this embodiment, the screw threads 24 are random in pitch and/or pitch diameter and/or pitch angle. The purpose of these one or more variations is for many or all of the threads 24 to thread into a section of bone not already carved away by another thread having passed through it. Threads 24 may be present along all or part of shaft 22 and may be used on any screw according to aspects of the invention where practical.

[0047] Figure 3 shows a screw 30 positioned inside of a predrilled hole 14 in a bone. Screw 30 has a head 32 with a driver opening 34, a shaft 36, threads 38, a distal tip 40 and a cannula 42 running through the entire length of screw 30. In this embodiment, the threads 38 start near distal tip 40 and extend across about 50% of the length of shaft 36, although they could extend across any suitable portion of the shaft. The threads 38 are of the same pitch angle and increase in pitch diameter moving from the distal tip 40 towards the head 32. A cannula, such as cannula 42, is preferably included on every screw according to embodiments of the invention. Threads 38 may be used on any screw according to the invention where practical.

[0048] Figures 4-4B show screw 30 and aspects of head 32. Head 32 is thin and has cutting blades 32A, which could be of any suitable shape or dimension to cut into bone.

Preferably, the cutting blades 32A are sufficient so that head 32 can be countersunk 2 mm into the bone by a tool that drives screw 30 via driving opening 34. Head 32 and/or cutting blades 32A may be used on any screw according to the invention where practical.

[0049] Figure 5 shows a screw 50 with a shaft 52, threads 54 and a distal tip 56. In this embodiment, the threads 54 each have self-tapping notches 54A. Notches 54A can all be aligned at the same general position on each thread as shown or can be aligned at different positions on each thread 54 or some threads 54. Threads 54 and/or self-tapping notches may be used on any screw according to the invention where practical.

[0050] Figures 6 and 7 show a method of inserting the screw of Figure 5, which has a head according to Figures 4-4B, into a fractured scaphoid bone. First a K-wire is positioned through the bone fragments on either side of the fracture. Then a cannulated drill is positioned over the K-wire to drill a hole H. Screw 50 is threaded into hole H using a driver (not shown). As the threads 54 of screw 50 enter the distal part of the fractured bone, they pull the fractured bone fragments together and compress them. Then, by applying more torque to the screw 50A via the driver placed in opening 34, the cutting blades 32A (not shown) in head 32 bore into the proximal bone fragment, preferably at a depth of about 2 mm.

[0051] Figure 8 shows a screw 60 positioned in a drilled hole H, with a head 62, a driver opening 64, a shaft 66, interference ridges 68, and self-tapping threads 70 (like those on the screw of Figure 5), cutting openings 70A and a distal end 72. On screw 60 threads 70 increase in pitch diameter moving from distal end 72 towards head 62, and threads 70 extend across about 50% of the outer surface of shaft 66. Interference ridges 68 as shown are waved, annular rings that have alternating raised 68A and depressed portions 68B (which can depress to the level of the outer surface of shaft 66, or higher or lower). The raised portions 68A preferably raise about 1 -2 mm above the outer surface of shaft 66, although any suitable height is acceptable. The purpose of interference ridges 68 is to stabilize the screw 60 in hole H without the need for the additional torque required by adding more threads. Any suitable structure for interference ridges (other than threads that thread into the bone) may be used, such as raised dimples of any shape, such as rounded or pyramidal, smooth continuous annular rings, or other structures. The interference ridges may be present on any portion of shaft 66 and at any location(s). Interference ridges may be used on any screw according to the invention where practical.

[0052] Figure 9 shows a tool 100 that performs two functions: it (1) measures the length (or depth) of the drilled hole so the length of the screw needed can be determined, and (2) includes a section that bores out a counter sink for a screw head to fit into the hole. Tool 100 has a handle 102 that records the length or depth of the hole, a body portion 104, and an extension or awl portion 106 that extends into drilled hole H to measure its length. At the distal end of body portion 104 is a cutting portion 108 and a stop 1 10. Cutting portion 108 can be any suitable structure for cutting bone, and as shown is helical blades. Stop 110 prevents cutting structure 108 from cutting too deep into the bone and most preferably limits the countersink hole formed by structure 108 to 2-4 mm.

[0053] Figures 10 and 10A show the use of a tool 100 to measure the length of a drilled hole and to cut a countersink opening in the bone. Figure 10B shows a screw 60 according to Figure 8 positioned in the hole with the head 62 retained in the countersink opening formed by tool 100.

[0054] Figure 1 1 shows a screw 120 having a shaft 122, a first (or proximal) end 124, a second (or distal) end 126, a first driver opening 128, a second driver opening 130, a cannular 132 extending through screw 120, a first set of threads 134 extending from the distal end 126, a second set of threads 136 near proximal end 124, and a third set of threads 138 on the head 140 of the screw at proximal end 124. In use, as shown in Figures 12-12C, screw 120 is threaded into a predrilled opening H and is guided by a K-wire that is received in cannula 132.

[0055] A first driver 142 passes through second driver opening 130 and is received in first driver opening 128. Then the first driver 142 can turn screw 120 so that threads 134 thread into the distal end of the fractured bone fragment as shown in Figures 12 and 12A. Head 140 remains outside of the bone so the tightening of screw 120 using first driver 142 pulls the distal end of the broken bone fragment towards the proximal end and compresses them as shown in Figure 12A. Next, second driver 144 is positioned in driver opening 130, as shown in Figure 12B, and threaded into the bone over threads 136 (head 140 has edges 150, or alternatively interior threads, that thread onto threads 136). Threads 138 are of a type that thread into bone or alternatively a second hole may be drilled for them.

[0056] After head 140 is positioned inside of the bone, the bone fragments may be further compressed, as shown in Figure 12C, by using first driver 142 to tighten threads 134 and pulls the distal end of screw 120 towards the proximal end.

[0057] Figures 13-13B show a screw 160 that is in all respects like screw 120 except that it has internal threads 131 inside of second driving opening 130. The internal threads thread onto the threads on the shaft adjacent the head when an appropriate driver is used to sink the head into the bone. This structure may be used on any suitable embodiment disclosed herein.

[0058] Figures 14-17 are variations of the screw of Figure 1 1 and 13 except that when the proximal end is embedded and mates with the distal end they mate and lock so the entire screw turns. Figures 18-18C show screws of this type being inserted into a bone. Figure 19 shows a screw 400 with a spring biasing device 402. Figures 20-21 show the screw 400 of Figure 19 being threaded into a fractured bone.

[0059] Figures 22-23B show versions of headless screws according to the invention.

[0060] Figures 24-26 show screws according to the invention, each with four sets of threads.

[0061] Figure 27 shows a screw and tool wherein the screw head has open slots and the tool for driving the screws has ridges (or blades) that fit into the slots. As the tool turns the screw, the screw advances into the bone until the ridges of the tool protruding through the slots reach the bone and form an opening to receive the screw head. This structure may be used on any suitable embodiment disclosed herein.

Some specific examples of the invention are as follows:

1. A screw having (a) a body with a cannula, an outer surface, a distal end, a proximal end, and a first driver receiving opening and (b) a head rotably attached to the proximal end and a second driver receiving opening, the second driver receiving opening being larger than the first.

(i) a first set of threads at the distal end;

(ii) a second set of threads at the proximal end; and (iii) a third set of threads on the head;

wherein the distal end and proximal end are threaded into a drilled opening in the bone by using a first driver that is received in the first driver receiving opening, the distal and proximal end tightened until the bone fragments at a fracture are compressed, and then a second driver is used to thread the head over the second set of threads and the third set of threads into the bone.

2. The screw of example 1 wherein the pitch and diameter of the at least some of the first set of threads varies.

3. The screw of example 1 wherein the head has a cross-sectioned area greater than the body of the screw and an inner edge to thread to the second set of threads.

4. The screw of example 1 wherein the head has a cross-sectional area greater than the body of the screw and a fourth set of threads on the inner portion of the head to thread onto the second set of threads.

5. The screw of examples 1 or 2 wherein the pitch and diameter of the second set of threads is less than the pitch and diameter of the first set of screws.

6. The screw of any of examples 1, 2 or 5 wherein the diameter of the third set of threads is greater than the diameter of the first set of threads.

7. The screw of any of examples 1, 2, 5 or 6 wherein the pitch of the threads of the third set of threads is different than the pitch of the second set of threads.

8. The screw of any of examples 1-2 or 5-7 wherein the first set of threads covers 30- 50% of the length of the body.

9. The screw of any of examples 1-2 or 507 wherein the first set of threads covers 40% of the length of the body.

10. The screw of any of examples 1-2 or 5-9 wherein the threads on the first section of threads are self-cutting.

11. The screw of any of examples 1-2 or 5-10 wherein the threads on the third section of threads are self-cutting.

12. The screw of any of examples 1-2 or 5-1 1 wherein each thread on the first section of threads increases in diameter moving from the distal to the proximal end.

13. The screw of any of examples 1-2 or 5-12 wherein each thread on the third section of threads increases in diameter moving from the distal to the proximal end.

14. A screw having (a) a body with a cannula, a body with an outer surface, a distal end and a proximal end and (b) a head connected to the proximal end and

(i) a first set of threads on the distal end, and (ii) cutting structures on the head to permit it to bore into bone.

15. The screw of example 1 wherein the diameter of the head is greater than the diameter of the first set of screws.

16. The screw of any of claims 1-15 wherein at least some of the threads on the first set of threads are triangular.

17. The screw of example 1 1 wherein adjacent ones of the at least some of the triangular threads are offset.

18. The screw of any of the examples herein that has a shaft with an outer surface and the outer surface has interference ridges.

19. The screw of example 18 wherein the ridges extend 1 mm - 2 mm beyond the outer surface.

20. The screw of example 18 or 19 wherein the ridges are present on 10%-50% of the length of the shaft.

21. The screw of any of examples 18-20 wherein the ridges are annular rings.

22. The screw of any of examples 18-20 wherein the ridges are waved annular rings.

23. The screw of any of examples 18-20 wherein the ridges are a plurality of raised dimples.

24. A tool for use in placing a screw into a bone, the tool comprising (a) a device for measuring the length of a hole in the bone, and (b) a cutting structure for cutting an opening larger than the hole in the bone wherein the opening is in communication with the hole.

25. The tool of example 24 that further includes a stop adjacent the cutting structure and that limits the depth of the cutting structure can cut into the bone.

26. The tool of example 24 or example 25 wherein the cutting structure is 2 mm to 4 mm in length.

27. A screw for use in compressing fragments of broken bone, the screw comprising:

(a) a first set of threads on distal end for threading into bone;

(b) a second set of threads at the proximal end not for threading into bone, the pitch diameter of the second set of threads being less than the pitch diameter of the first set of threads;

(c) a first driving opening at the proximal end;

(d) a head attached to the proximal end, the head having a cross-sectional area greater than the cross-sectional area of the shaft; (e) a second driving opening in the head, the second driving opening in communication with the first driving opening, the second driving opening larger than the first driving opening;

(f) a third set of threads on the head, the third set of threads for threading into bone, the third set of threads have a thread pitch diameter greater than the pitch diameter of the second set of threads; and

(g) a threading portion on a distal portion of the head for threading the head onto the second set of threads;

wherein the first driver is used in the first driver opening to thread the shaft into the fragment of a broken bone past the fracture and into a distal bone fragment and the head remains outside the bone so as the first driver turns the shaft, the first set of threads compress the bone fragments tougher, and then a second driver is used in the second driver opening to turn the head and thread it into the bone over the second set of threads.

28. The screw of example 27 that further include a cannula extending through the shaft. 29. The screw of example 27 wherein the threading portion is an inward-extending lip.

30. The screw of example 27 wherein the threading portion is mating threads.

31. The screw of any of examples 27-30 wherein the second opening comprises a fourth set of threads on its inner surface.

32. A screw for use in compressing fragments of broken bone, the screw having a shaft, a distal end and a proximal end that includes:

(a) a first set of threads at the distal end, the first set of threads for threading into bone;

(b) a middle region between the distal end and the proximal end, the middle region not having any threads and including a first driver opening; and

(c) a proximal end having a second driving opening larger than the first driving opening and in communication with the first driving opening, a second set of threads on its exterior surface, the second set of threads for threading into bone, and a third set of threads on the surface of the first opening;

wherein a first driver is positioned in the first driver opening and used to thread the distal end with first set of threads into a distal broken bone fragment, and as the distal end is rotated it compresses the broken bone fragments, and afterwards a second driver is positioned in the second driver opening to thread the proximal end over the middle region and into the bone under the proximal region is fully threaded onto the middle region at which point further rotation of the proximal region rotates the entire screw. 33. The example of example 32 wherein the middle region has a fourth set of threads that mate with the third set of threads.

34. The example of example 32 wherein there is no third set of threads inside the proximal region and the middle region has a set of threads, and the second driver threads the proximal region over the threads on the middle section until the proximal region reaches the end of the threads in the middle region at which point the entire screw rotates.

35. The screw of any of examples 32-34 wherein there is a physical stop in the middle portion that prevents the first end from tightening further and helps cause the entire screw to rotate.

36. A screw for use in compressing fragments of broken bone, the screw having a shaft, a distal end and a proximal end that includes:

wherein a first driver is positioned in the first driver opening and used to thread the distal end with first set of threads into a distal broken bone fragment, and as the distal end is rotated it compresses the broken bone fragments, and afterwards a second driver is positioned in the second driver opening to thread the proximal end over the middle region and into the bone under the proximal region is fully threaded onto the middle region at which point further rotation of the proximal region rotates the entire screw.

37. A screw for compressing fragments of a broken bone, the screw comprising:

(a) A distal section having a shaft having a first set of threads and a catch; and

(b) A proximal end comprising a spring, a catch bar and a driver opening;

Wherein a driver is inserted in the driver opening and compresses the spring as it rotates thereby driving the screw into a pre-drilled opening to compress the bone fragments together and the catch bar is received in the catch to hold the spring in a compressed position.

38. The screw of example 37 that further includes a center region having a sleeve with a center set of threads and a catch, the sleeve not being rotated under attached to the proximal end including the spring; wherein the driver is received in the driver opening and drives the spring and the distal end until the distal end threads into a distal fragment of broken bone and compresses the broken bone fragments as the driver rotates, and when the catch bar is received in the catch, further rotation of the driver rotates the entire screw including the center region and embeds it into the bone.

39. A device for attaching and compressing fragments of a broken bone, the device comprising:

(a) a screw having a distal end with threads and a proximal end with no head and a driving opening;

(b) a tool having a driver that is received in the driver opening and a stop comprising a screw head adjacent the driver opening, the stop being removable from the tool to become the head of the screw, and having a first set of external threads and a second set of internal threads;

wherein the driver inserts the screw into the bone until the screw head rests against the outsides of the bone causing rotation of the screw to compress broken bone fragments, and a second driver is used to thread the screw head into the bone and over the screw.

40. A screw for attaching and compressing broken bone fragments, the screw comprising four separate regions of threads, wherein each of the regions is separated by a region with no threads.

41. The screw of example 40 wherein at least two regions of threads has a separate pitch angle.

42. The screw of either example 40 or 41 wherein at least two regions of threads has a separate pitch diameter.

43. The screw of any of examples 40-42 wherein at least one region of threads has a different number of threads than at least one other region of threads.

[0062] Having thus described some embodiments of the invention, other variations and embodiments that do not depart from the spirit of the invention will become apparent to those skilled in the art. The scope of the present invention is thus not limited to any particular embodiment, but is instead set forth in the appended claims and the legal equivalents thereof. Unless expressly stated in the written description or claims, the steps of any method recited in the claims may be performed in any order capable of yielding the desired result.

Claims

What is claimed is:

(iv) a first set of threads at the distal end;

(v) a second set of threads at the proximal end; and

(vi) a third set of threads on the head;

2. The screw of claim 1 wherein the pitch and diameter of the at least some of the first set of threads varies.

3. The screw of claim 1 wherein the head has a cross-sectioned area greater than the body of the screw and an inner edge to thread to the second set of threads.

4. The screw of claim 1 wherein the head has a cross-sectional area greater than the body of the screw and a fourth set of threads on the inner portion of the head to thread onto the second set of threads.

5. The screw of claims 1 or 2 wherein the pitch and diameter of the second set of threads is less than the pitch and diameter of the first set of screws.

6. The screw of any of claims 1, 2 or 4 wherein the diameter of the third set of threads is greater than the diameter of the first set of threads.

7. The screw of any of claims 1, 2, 4 or 5 wherein the pitch of the threads of the third set of threads is different than the pitch of the second set of threads.

8. The screw of any of claims 1-2 or 4 wherein the first set of threads covers 30-50% of the length of the body.

9. The screw of any of claims 1-2 or 4 wherein the first set of threads covers 40% of the length of the body.

10. The screw of any of claims 1-2 or 4 wherein the threads on the first section of threads are self-cutting.

11. The screw of any of claims 1-2 or 4 wherein the threads on the third section of threads are self-cutting.

12. The screw of any of claims 1-2 or 4 wherein each thread on the first section of threads increases in diameter moving from the distal to the proximal end.

13. The screw of any of claims 1-2 or 4 wherein each thread on the third section of threads increases in diameter moving from the distal to the proximal end.

(iii) a first set of threads on the distal end, and

(iv) cutting structures on the head to permit it to bore into bone.

15. The screw of claim 4 wherein the diameter of the head is greater than the diameter of the first set of screws.

16. The screw of any of claims 14-15 wherein at least some of the threads on the first set of threads are triangular.

17. The screw of claim 14 wherein adjacent ones of the at least some of the triangular threads are offset.

18. The screw of any of claims 14-15 or 16 herein that has a shaft with an outer surface and the outer surface has interference ridges.

19. The screw of claim 18 wherein the ridges extend 1 mm - 2 mm beyond the outer surface.

20. The screw of claim 18 or 19 wherein the ridges are present on 10%-50% of the length of the shaft.

21. The screw of any of claims 18-19 wherein the ridges are annular rings.

22. The screw of any of claims 18-19 wherein the ridges are waved annular rings.

23. The screw of any of claims 18-19 wherein the ridges are a plurality of raised dimples.

25. The tool of claim 24 that further includes a stop adjacent the cutting structure and that limits the depth of the cutting structure can cut into the bone.

26. The tool of claim 24 or claim 25 wherein the cutting structure is 2 mm to 4 mm in length.

(a) a first set of threads on distal end for threading into bone; (b) a second set of threads at the proximal end not for threading into bone, the pitch diameter of the second set of threads being less than the pitch diameter of the first set of threads;

(c) a first driving opening at the proximal end;

(d) a head attached to the proximal end, the head having a cross-sectional area greater than the cross-sectional area of the shaft;

(e) a second driving opening in the head, the second driving opening in communication with the first driving opening, the second driving opening larger than the first driving opening;

28. The screw of claim 27 that further include a cannula extending through the shaft.

29. The screw of claim 27 wherein the threading portion is an inward-extending lip.

30. The screw of claim 27 wherein the threading portion is mating threads.

31. The screw of any of claims 27-30 wherein the second opening comprises a fourth set of threads on its inner surface.