U.S. patent application number 13/312626 was filed with the patent office on 2012-05-24 for axial tension screw.
Invention is credited to Randall J. Huebner.
Application Number | 20120130433 13/312626 |
Document ID | / |
Family ID | 38621715 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120130433 |
Kind Code |
A1 |
Huebner; Randall J. |
May 24, 2012 |
AXIAL TENSION SCREW
Abstract
A screw having a root and threads formed on the root. The screw
is configured to generate and/or maintain axial compression between
threads formed in leading and trailing sections of the screw either
by virtue of pitch differential in the threads or the way in which
the screw is installed.
Inventors: |
Huebner; Randall J.;
(Portland, OR) |
Family ID: |
38621715 |
Appl. No.: |
13/312626 |
Filed: |
December 6, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11329368 |
Jan 9, 2006 |
8070786 |
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13312626 |
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10162397 |
Jun 3, 2002 |
6984235 |
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11329368 |
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09483076 |
Jan 14, 2000 |
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10162397 |
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09305841 |
May 5, 1999 |
6017347 |
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09483076 |
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09157783 |
Sep 21, 1998 |
6120505 |
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09305841 |
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08457624 |
Jun 1, 1995 |
5810825 |
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09157783 |
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09375306 |
Aug 16, 1999 |
6299615 |
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09483076 |
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09019135 |
Feb 5, 1998 |
5976134 |
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09375306 |
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08847820 |
Apr 28, 1997 |
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09019135 |
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08587210 |
Jan 11, 1996 |
5624440 |
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08847820 |
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08622368 |
Mar 26, 1996 |
5665087 |
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09483076 |
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09318437 |
May 25, 1999 |
6162224 |
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08622368 |
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09318669 |
May 25, 1999 |
6171309 |
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09318437 |
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08636326 |
Apr 22, 1996 |
5662649 |
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09318437 |
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08636326 |
Apr 22, 1996 |
5662649 |
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09318669 |
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08389056 |
Feb 15, 1995 |
5545162 |
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08636326 |
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08715017 |
Sep 17, 1996 |
5658283 |
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09483076 |
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08759075 |
Dec 2, 1996 |
5697934 |
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08715017 |
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29063695 |
Dec 13, 1996 |
D404128 |
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08759075 |
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08773968 |
Dec 26, 1996 |
5702472 |
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29063695 |
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09034046 |
Mar 3, 1998 |
5964768 |
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08773968 |
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08781471 |
Jan 10, 1997 |
5871486 |
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09034046 |
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08792988 |
Feb 3, 1997 |
5868789 |
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08781471 |
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08506469 |
Jul 25, 1995 |
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08781471 |
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08332445 |
Oct 31, 1994 |
5562672 |
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08506469 |
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08007196 |
Jan 21, 1993 |
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08332445 |
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PCT/US94/00738 |
Jan 19, 1994 |
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08781471 |
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09157783 |
Sep 21, 1998 |
6120505 |
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09483076 |
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08457624 |
Jun 1, 1995 |
5810825 |
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09157783 |
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08986717 |
Dec 8, 1997 |
5944721 |
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09483076 |
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09093415 |
Jun 8, 1998 |
6001099 |
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08986717 |
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09216316 |
Dec 18, 1998 |
6030162 |
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09093415 |
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09263141 |
Mar 5, 1999 |
6077271 |
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09216316 |
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60077168 |
Mar 6, 1998 |
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Current U.S.
Class: |
606/300 |
Current CPC
Class: |
A61B 2017/00004
20130101; A61B 17/863 20130101; A61B 17/864 20130101; A61B
2017/0648 20130101; A61B 17/8645 20130101; A61B 17/8635 20130101;
A61B 2017/0646 20130101; A61B 17/1686 20130101; A61B 17/8863
20130101 |
Class at
Publication: |
606/300 |
International
Class: |
A61B 17/84 20060101
A61B017/84 |
Claims
1. A method of compressing a bone, comprising: boring a hole
through a first bone fragment, across a fracture, and into a second
bone fragment; placing a leading end of a fastener into the hole,
where the fastener has a root portion, the root portion having a
leading end, a trailing end, and an elongate axis extending
therebetween, and a single continuous thread formed on the root
portion and extending between the leading end and the trailing end
of the root portion, the thread having an outside diameter which,
moving from the leading end toward the trailing end, increases over
several revolutions, then decreases, then increases again, wherein
the pitch of the thread measured between corresponding points on
consecutive threads near the leading end is larger than the pitch
of the threads near the trailing end; and driving the fastener into
the hole such that the thread spans the fracture.
Description
CROSS-REFERENCES
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/329,368, filed Jan. 9, 2006, issued as U.S.
Pat. No. 8,070,786 on Dec. 6 2011, which in turn is a continuation
of U.S. patent application Ser. No. 10/162,397, filed Jun. 3, 2002,
issued as U.S. Pat. No. 6,984,235 on Jan. 10, 2006, which in turn
is a continuation of U.S. patent application Ser. No. 09/483,076,
filed Jan. 14, 2000, now abandoned.
[0002] U.S. patent application Ser. No. 09/483,076 is a
continuation-in-part of U.S. patent application Ser. No.
09/305,841, filed May 5, 1999, issued as U.S. Pat. No. 6,017,347 on
Jan. 25, 2000, which is a continuation-in-part of U.S. patent
application Ser. No. 09/157,783, filed Sep. 21, 1998, issued as
U.S. Pat. No. 6,120,505 on Sep. 19, 2000, which is a
continuation-in-part of U.S. patent application Ser. No.
08/457,624, filed Jun. 1, 1995, issued as U.S. Pat. No. 5,810,825
on Sep. 22, 1998.
[0003] U.S. patent application Ser. No. 09/483,076 is also a
continuation-in-part of U.S. patent application Ser. No.
09/375,306, filed Aug. 16, 1999, issued as U.S. Pat. No. 6,299,615
on Oct. 9, 2001, which is a continuation-in-part of U.S. patent
application Ser. No. 09/019,135, filed Feb. 5, 1998, issued as U.S.
Pat. No. 5,976,134 on Nov. 2, 1999, which is a continuation-in-part
of U.S. patent application Ser. No. 08/847,820, filed Apr. 28,
1997, which is a continuation-in-part of U.S. patent application
Ser. No. 08/587,210, filed Jan. 11, 1996, now issued as U.S. Pat.
No. 5,624,440 on Apr. 29, 1997, and also a continuation-in-part of
U.S. patent application Ser. No. 08/622,368, filed Mar. 26, 1996,
now issued as U.S. Pat. No. 5,665,087 on Sep. 9, 1997, and a
continuation-in-part of U.S. patent application Ser. No.
09/318,437, filed May 25, 1999, issued as U.S. Pat. No. 6,162,224
on Dec. 19, 2000 and U.S. patent application Ser. No. 09/318,669,
filed May 25, 1999, issued as U.S. Pat. No. 6,171,309 on Jan. 9,
2001. The '224 and '309 patents are continuations-in-part of U.S.
patent application Ser. No. 08/636,326, filed Apr. 22, 1996, now
issued as U.S. Pat. No. 5,662,649 on Sep. 2, 1997, which is a
continuation-in-part of U.S. patent application Ser. No.
08/389,056, filed Feb. 15, 1995, now issued as U.S. Pat. No.
5,545,162 on Sep. 2, 1997.
[0004] U.S. patent application Ser. No. 09/483,076 is also a
continuation-in-part of U.S. patent application Ser. No.
08/715,017, filed Sep. 17, 1996, now issued as U.S. Pat. No.
5,658,283 on Aug. 19, 1997, and a continuation-in-part of U.S.
patent application Ser. No. 08/759,075, filed Dec. 2, 1996, now
issued as U.S. Pat. No. 5,697,934 on Dec. 16, 1997, and also a
continuation-in-part of U.S. Design Patent Application Ser. No.
29/063,695, filed Dec. 13, 1996, and a continuation-in-part of U.S.
patent application No. 08/773,968, filed Dec. 26, 1996, now issued
as U.S. Pat. No. 5,702,472 on Dec. 30, 1997, and also a
continuation-in-part of U.S. patent application Ser. No.
09/034,046, filed Mar. 3, 1998, issued as U.S. Pat. No. 5,964,768
on Oct. 12, 1999, which is a continuation-in-part of U.S. patent
application Ser. No. 08/781,471, filed Jan. 10, 1997, and also a
continuation-in-part of U.S. patent application Ser. No.
08/792,988, filed Feb. 3, 1997. U.S. patent application Ser. No.
08/781,471 is (A) a continuation-in-part of U.S. patent application
Ser. No. 08/506,469 filed Jul. 25, 1995, which is a
continuation-in-part of U.S. patent application Ser. No. 08/332,445
filed Oct. 31, 1994, which is a continuation of U.S. Patent
Application Serial No. 08/007,196, filed Jan. 21, 1993, and (B) a
continuation-in-part of PCT Patent Application Ser. No.
PCT/US94/00738, filed Jan. 19, 1994, which claims priority from
U.S. patent application Ser. No. 08/007,196, filed Jan. 21,
1993.
[0005] U.S. patent application Ser. No. 09/483,076 is also a
continuation-in-part of 09/157,783, filed Sep. 21, 1998, which is a
continuation-in-part of U.S. patent application Ser. No.
08/457,624, filed Jun. 1, 1995, now issued as U.S. Pat. No.
5,810,825 on Sep. 22, 1998.
[0006] U.S. patent application Ser. No. 09/483,076 is also a
continuation-in-part of U.S. patent application Ser. No.
08/986,717, filed Dec. 8, 1997, issued as U.S. Pat. No. 5,994,721
on Aug. 31, 1999, and also a continuation-in-part of U.S. patent
application Ser. No. 09/093,415, filed Jun. 8, 1998, issued as U.S.
Pat. No. 6,001,099 on Dec. 14, 1999.
[0007] U.S. patent application Ser. No. 09/483,076 is also a
continuation-in-part of U.S. patent application Ser. No.
09/216,316, filed Dec. 18, 1998, issued as U.S. Pat. No. 6,030,162
on Feb. 29, 2000, and U.S. patent application Ser. No. 09/263,141,
filed Mar. 5, 1999, issued as U.S. Pat. No. 6,077,271 on Jun. 20,
2000 which claims priority from U.S. Provisional Patent Application
Ser. No. 60/077,168, filed Mar. 6, 1998.
[0008] All of the above patents and applications are hereby
incorporated by reference.
Field of the Invention
[0009] The present invention relates to fasteners and more
particularly to a screw adapted to create axial tension along its
length.
BACKGROUND OF THE INVENTION
[0010] Screws have long been used to secure objects to one another.
Depending on the requirements of a particular application, the
screw may take on many different shapes and sizes. Although screws
have been produced in enormous variety, the vast majority create
axial compression along the length of the screw by virtue of
drawing the lower surface of a head down against the surface of one
object using threads embedded in an adjacent object, as, for
instance, occurs in a wood screw.
[0011] Although traditionally configured screws are suitable for
most purposes, in some instances the presence of the head is
unacceptable for functional, structural or cosmetic reasons.
Various types of headless screws have been developed to address
some of the applications where a traditional screw is less than
optimal. One early example of such a screw is shown in U.S. Pat.
No. 187,023 to Russell which employs a variable pitch thread to
generate compression without relying on a head. Although the screw
of Russell will generate some compression, its effectiveness is
limited by the fact that the threads disposed toward the trailing
end achieve little purchase because of the stripping that occurs
due to the preceding threads of different pitch. U.S. Pat. No.
4,175,555 to Herbert overcomes Russell's problem of reaming of
female threads by subsequent threads on the screw. In particular,
the Herbert screw has a region of large pitch and small diameter
thread near the leading end and a region of smaller pitch and
larger diameter thread near the trailing end, with the regions
being separated by an unthreaded section. Unfortunately, the
Herbert screw suffers from a number of other disadvantages. In the
Herbert screw, the leading threads have a smaller diameter than the
trailing threads. This is necessary to permit the leading threads
to pass through the relatively large bore in the near bone fragment
and engage the smaller bore in the remote bone fragment. The larger
trailing threads then engage the larger bore in the near bone
fragment. As a result of this arrangement, any stripping of the
threads cut into the bones during installation of the screw occurs
in the remote bone. If the stripping occurred in the bore in the
near bone fragment, a screw having a head thereon could still be
used to compress the fracture even though the near bore was
stripped; however, when stripping occurs in the bore in the remote
bone, a standard screw with the head thereon cannot be used and
another bore must be drilled.
[0012] Further, the Herbert screw must be correctly positioned,
i.e., it is imperative that the fracture intersect the unthreaded
central portion of the Herbert bone screw when the same is
installed. Thus, the Herbert screw is not suitable for treating
fractures that are very near the surface of the bone where the hole
is to be drilled. In addition, because the Herbert screw is not
threaded entirely along the length thereof, the purchase obtained
by the screw in the bone is not as good as with a screw threaded
along the entire length. Also, two bores of different sizes must be
drilled to install the Herbert screw rather than a single bore.
[0013] Yet another problem with the Herbert screw is the stripping
that can occur if additional tightening occurs after the screw has
drawn the bone fragments together. While the bone fragments are
being drawn together, trailing threads K.sub.6 all follow a single
path through the near fragment. Similarly, leading threads J.sub.6
all follow a single path through the remote fragment. When,
however, the bone fragments make contact, the two sets of threads
can no longer move independently. Further rotation of the Herbert
screw after contact between the fragments can cause the leading
threads to strip out as they attempt to move forward through the
distal bone fragment faster than the trailing threads will allow.
See The Herbert Bone Screw and Its Applications in Foot Surgery,
The Journal of Foot and Ankle Surgery, No. 33, Vol. 4., 1994, pages
346-354, which reports on a study that found compression of 10 kg
after only two complete turns of the trailing threads engaged in
the near bone fragment. Each subsequent revolution lead to a
decrease in compressive force. Thus, care must be taken not to
over-tighten the Herbert screw.
[0014] The various problems of the Herbert screw are addressed by
the screw shown in U.S. patent application Ser. No. 08/781,471,
filed Jan. 10, 1997, to Huebner, which is herein incorporated by
reference. The Huebner screw, sold under the trademark ACUTRAK, in
most versions, is fully threaded and has a changing pitch over the
entire length. The outside diameter of the thread tapers from front
to rear so that as the trailing threads ream the tracks left by the
leading threads due to the pitch change, the trailing threads are
expanding outward into undisturbed material. The ACUTRAK screw can
be driven in as far as desired without reduction in compression
because of the expanding thread diameter along its length. In
addition, the screw generates compression over the entire length,
rather than only at the tip and tail as with Herbert. Thus, the
ACUTRAK screw can be used to repair fractures anywhere along its
length. Although the ACUTRAK screw was a major improvement over the
Herbert screw, installation of the ACUTRAK screw requires careful
attention. In particular, the screw is typically installed in a
tapered hole that has been pre-drilled. Drilling this tapered hole
can be difficult because the tapered drill bit sometimes clogs with
bone and tapered bits require more pressure to feed than a similar
straight drill. Moreover, for best results, the depth of the hole
should generally match the length of the screw, requiring the
surgeon to drill the hole accurately. The other area of concern
during installation is the torque needed to drive the screw. When
the screw reaches the point where the root and hole taper match,
the driving force increases substantially. Similarly, in dense
bone, the driving force may make installation difficult.
SUMMARY OF THE INVENTION
[0015] The present disclosure describes a bone screw having a root
and threads formed on the root. The screw is configured to generate
and/or maintain axial compression between threads formed in leading
and trailing sections of the screw either by virtue of pitch
differential in the threads or the way in which the screw is
installed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a side elevational view of a screw constructed
according to the present invention.
[0017] FIG. 2 is a perspective view of a self-cutting tip on the
screw of FIG. 1.
[0018] FIG. 3 is a cross-sectional view of the screw of FIG. 1.
[0019] FIG. 4 is a perspective view of a drill for use with the
screw of FIG. 1.
[0020] FIG. 5 shows the step of placing a guide wire into a bone in
preparation for utilizing the screw of FIG. 1.
[0021] FIG. 6 shows use of a depth gauge to measure the length of
screw required.
[0022] FIG. 7 shows use of the drill of FIG. 4.
[0023] FIG. 8 shows the screw of FIG. 1 driven partially into the
bone.
[0024] FIG. 9 shows the screw of FIG. 1 in its final placement.
[0025] FIG. 10 shows another screw constructed according to the
present invention.
[0026] FIG. 11 shows the screw of FIG. 10 mounted to a sleeve and
drive handle and partially installed in a fractured bone.
[0027] FIG. 12 shows the bone of FIG. 11 after reduction of the
fracture by rotating the sleeve.
[0028] FIG. 13 shows the bone of FIG. 11 after reduction by
rotating the sleeve and screw.
[0029] FIG. 14 shows the bone of FIG. 11 as the screw leaves the
sleeve.
[0030] FIG. 15 shows a screw according to the present invention
with an unthreaded intermediate section.
[0031] FIG. 16 shows a screw according to the present invention
with an unthreaded intermediate section.
[0032] FIG. 17 shows another screw according to the present
invention.
[0033] FIG. 18 shows a screw according to the present invention
with a cylindrical trailing section.
[0034] FIG. 19 shows a screw according to the present invention
with a smoothly changing outside diameter.
[0035] FIG. 20 shows a screw according to the present invention
with unthreaded leading and trailing extensions.
[0036] FIG. 21 shows a headed screw according to the present
invention.
[0037] FIG. 22 shows a screw according to the present invention
with a stepped, tapered outside diameter.
DETAILED DESCRIPTION
[0038] A screw according to one embodiment of the present invention
is shown at 10 in FIG. 1. Screw 10 extends between a front end 12
and a back end 14 and includes root portion 16. Root portion 16 has
a leading end 18 and a trailing end 20, which, in the embodiment of
FIG. 1, are coextensive with the leading and trailing ends of the
screw.
[0039] In other embodiments, the screw could extend beyond either
end of the root portion.
[0040] A screw thread 22 is formed on root portion 16 and extends
as a single continuous thread from the leading end to the trailing
end. Screw thread 22 includes multiple thread revolutions 23, which
are spaced apart on the root by an interthread spacing 25. It
should be noted that the interthread spacing in combination with
the thread depth establishes the pitch of the thread revolutions.
In particular, increasing the interthread spacing or the thread
depth (except in the case of perpendicular thread faces) increases
the pitch. In screw 10, the interthread spacing is varied to avoid
large pitch changes when reducing the outside diameter while at the
same time maintaining a relatively constant root diameter. The
reduced outside diameter and/or relatively constant root diameter
helps to minimize the driving force required to advance the screw.
It should also be noted that the thread land, the flat at the
outside end of the thread, could also be varied to accommodate
changing pitch.
[0041] One method of manufacturing screws according to the present
invention is to use a computer-controlled screw machine or lathe.
The threads are cut in repeated passes, typically with a single
tool. The shape of the tool determines the thread face angle and
the width at the tip of the tool determines the minimum interthread
spacing. For larger interthread spacing, the position of the tool
is shifted along the length of the screw on subsequent cutting
passes to cut a wider interthread space. It should be noted that
dimensions such as the interthread spacing and land are measured to
a theoretical perfectly sharp corner even though, in practice, the
corners may be rounded slightly or significantly.
[0042] The screw thread has a leading section 24 disposed toward
the leading end, a trailing section 26 disposed toward the trailing
end, and an intermediate, medial or waist section 28 disposed
between the leading and trailing sections. The leading section has
pitch which is larger at the leading end and decreases toward the
trailing end. It should be noted that pitch, as used herein, is
defined as the distance between corresponding points on consecutive
threads as indicated at Pin FIG. 1. With this pitch arrangement,
the leading section generates axial compression between its ends as
it is driven in. The outside diameter of the thread in the leading
section tapers from a smaller diameter near the leading end to a
larger diameter toward the trailing end at an angle of
approximately 1.2 degrees relative to the elongate axis of the
screw. The tapered outside diameter helps to prevent and/or
mitigate the stripping of the leading threads in the object being
secured that naturally occurs with threads of variable pitch or
that may occur due to tension along the length of the screw.
Typical taper angles or rates would generally be between 0.5 and 5
degrees.
[0043] Medial section 28 extends back from the end of leading
section 24, but has an outside diameter that is reduced relative to
the outside diameter of the thread at the trailing end of the
leading section. The pitch of the medial section thread is less
than the average pitch in the leading section and preferably,
although not necessarily, approximately equal to the pitch at the
back end of the leading section. This causes the medial section
thread to maintain any compression or reduction generated by the
leading section until the trailing section engages. The outside
diameter of the thread can have a constant diameter, as
illustrated, or may taper slightly outward toward the trailing end
to accommodate any stripping that may occur because of the pitch
difference between the leading section and the medial section. It
should be noted that the medial section threads could be eliminated
in favor of an unthreaded root, as described below.
[0044] The trailing section threads may be of constant diameter or
may taper outwardly toward the trailing end. As with the leading
section, the taper helps to reduce the effect of stripping because
of changing pitch. The pitch of the threads in the trailing section
is smaller than the pitch in the leading section so that as the
screw moves forward, axial compression is generated along the
length of the root. The pitch in the trailing section can be
constant, as illustrated, or variable.
[0045] The root diameter tapers outwardly with the threads through
the leading section and is constant in the medial and trailing
sections, with the diameter through the trailing section being
somewhat larger than the diameter through the medial section.
Although the described root configuration is desirable to reduce
the driving torque, the shape of the root can take many other forms
essentially independent of the outside diameter of the threads.
Screw 10 includes a drive socket 30 at the trailing end and a
self-drilling tip 32 at the leading end. See FIGS. 2 and 3. A
central bore 34 extends through the screw to facilitate
installation of the screw over a guide wire. The self-drilling tip
includes a plurality of teeth 36 disposed in a circular pattern
around the periphery of the leading end, as shown in FIG. 2. Teeth
36 cut a path for the screw as it is advanced. A notch 37 in the
threads at the front of the leading section may be provided to
facilitate the thread on the screw tapping a female thread in the
object to be fastened.
[0046] The leading section includes a termination zone 80 in which
the thread diminishes rapidly to a starting point 82 on the root,
as shown in FIG. 2. It should be noted that the root diameter is
not diminishing commensurately with the thread diameter in the
termination zone as occurs in a gimlet point screw. Although not
essential to the present invention, the benefit of the depicted
arrangement is that the thread diameter, and thus its holding
power, is maintained to the end of the thread. This can be
important where the joint to be secured falls near the front end of
the screw.
[0047] Both the self-cutting tip and termination zone could be used
on any of the screws described herein. Alternatively, the tip of
any of the screws could be pointed like more traditional screws to
allow for self-starting with or without a pilot hole.
[0048] Screw 10, as shown, is particularly adapted for repair of
bone fractures. In this application, screw 10 is formed of
titanium, stainless steel, a resorbable substance, or some other
biocompatible material. The screw may also incorporate an
osteoductive substance to promote bone healing or growth. The
osteoductive substance may be resorbable and form the structure of
the screw or it may be a compound carried in the screw and
delivered for instance through ports formed in the screw. As
depicted, screw 10 has a length of approximately 20 millimeters.
Typical lengths in the range from a few millimeters to ten
centimeters or more may be applicable to medical applications with
the most common sizes ranging from about 10 to 40 millimeters. In
non-medical uses, the length and size would be chosen to suit the
particular application. The outside diameter of the leading section
of screw 10 tapers from about 3.5 millimeters at the front to about
3.6 millimeters at the back, while the root tapers from about 2.4
to 2.5 millimeters over the same area. The root is cylindrical in
the intermediate section with a diameter of 2.5 millimeters and
cylindrical in the trailing section with a diameter of 2.8
millimeters. The outside diameter of the threads in intermediate
and trailing sections is 3.2 and 4.1 millimeters, respectively.
[0049] In a typical screw, the pitch in the trailing section would
be between 10 and 90 percent of the pitch in the leading section,
with a pitch change around 50 percent, for example, being a typical
value in orthopedic applications. It should be understood that
greater or lesser pitch changes may be effective depending on the
compression and reduction required for any particular application.
In orthopedic applications, the pitch would typically fall in the
range of between 10 and 100 thousandths of an inch.
[0050] In the disclosed embodiment, a drill used to bore a hole to
receive screw 10 is shown at 50 in FIG. 4. Drill 50 includes a
cylindrical shank 52 to which a handle or motor, not shown, may be
attached to allow manual or powered drilling. A cutting section 54
is formed on the leading end of the drill to create a hole of
appropriate shape and size for the screw. The cutting section has a
leading end 56 with cutting teeth 58, followed by a first
cylindrical section 60, typically about 6-12 millimeters long, with
a cutting flute 62. Adjacent the trailing end of the first
cylindrical section, the cutting section tapers outward to a second
cylindrical section 64 with a cutting flute 66. The diameter of the
first cylindrical section is slightly, i.e., 0.005 inches, larger
than the diameter of the root portion at the trailing end. The
diameter of the second cylindrical section is approximately 0.020
inches larger than the diameter of the root section at the trailing
end. The second section is larger because it is designed to form a
slightly larger hole in the hard cortex shell of a bone so that
passage of the trailing section of threads does not require
excessive torque. A depth groove 68 is formed at the trailing end
of the second cylindrical portion to be used as a gauge of proper
hole depth during drilling. Drill 50 is cannulated so that it can
be used over a guide wire.
[0051] To install screw 10 to repair a fractured bone, a surgeon
will first place a guide wire 72, checking position and depth in
the bone through x-ray as illustrated in FIG. 5. Next, the depth of
the wire is measured using a template 74 which fits over the wire
as shown in FIG. 6. Knowing the depth allows the surgeon to select
a screw of the proper length. The drill is then installed over the
guide wire and advanced until the depth groove reaches the surface
of the bone. See FIG. 7. The screw is then slid over the wire, as
shown in FIG. 8, and driven into the bone with the variable pitch
generating axial compression along the length of the screw. The
screw should be seated so that the trailing end is approximately
0.1 inches below the surface of the bone to avoid interference with
surrounding tissues. See FIG. 9. The screw is driven in with a
cannulated driver 76 having a driving tip 78, a handle 80 and a
drive shank 82 extending between.
[0052] FIG. 10 shows another screw according to the present
invention. Screw 110 includes a front end 112, a back end 114 and a
root portion 116. The root portion includes a leading end 118 and a
trailing end 120. Screw 110 has a screw thread 122 formed thereon
in a leading section 124 and a trailing section 126, with an
unthreaded section 128 therebetween. The screw has a drive socket
130 and a drilling tip 132, similar to tip 32 on screw 10. As
illustrated, the pitch of the screw thread in the leading and
trailing sections is constant over each section, but the pitch
could also vary over either or both sections depending on the type
of compression sought. Screw 110 includes a central bore or
cannulation 134.
[0053] Screw 110 is adapted for installation using a placement
sleeve 140 as shown in FIGS. 11-14. Sleeve 140 includes a gripping
structure 142 with a knurled perimeter 144 adapted to be gripped by
an operator. Extending forward from the gripping structure is a
shaft 146 leading to a contact tip 148. Contact tip 148 is
preferably smooth and slightly rounded to allow it to rotate with
minimal friction when pressed against an object. It is also
possible, although not shown, that the tip could include some type
of bearing connection to the shaft to eliminate the need for the
tip to slide on the objection. The shaft includes an internal bore
150 which is threaded to match the threads in leading section 124
of screw 110. An elastomeric ring 152 is disposed inside bore 150
to frictionally connect the placement sleeve to the drive shank so
that both turn as a unit unless the gripping structure is utilized
to restrain the sleeve. In use, the trailing end of screw 110 is
screwed partially into bore 150, as shown in FIG. 11. The drive
shank of the driver is then inserted into the bore from the
opposite end. Mild pressure on the driver is sufficient to urge the
shank through the elastomeric ring, although once the driver is
slid into place, the ring prevents the sleeve from slipping off the
driver. The screw, with the sleeve attached, is driven into the
object to be secured until the leading section is buried and tip
148 contacts the surface of the object. Upon subsequent rotation of
the driver and sleeve, tip 148 acts like the head of a standard
screw and compression is generated along the axis of the screw, as
shown by comparing FIGS. 11 and 13. This compression continues to
build as long as the sleeve turns with the driver. To generate
additional compression without driving the screw further into the
object, the operator can rotate the sleeve using the gripping
structure while holding the driver still, thus generating
additional compression or reduction, as illustrated by the change
between FIGS. 11 and 12. Once the desired compression/reduction is
established, the operator holds the gripping structure while
continuing to turn the driver, thus driving the trailing section
threads out of the bore and into the member to be secured. See FIG.
14. The tension originally carried at the tip of the sleeve is
thereby transferred to the trailing section threads.
[0054] It should be noted that the outside diameter of the threads
in the leading and trailing sections of screw 110 is tapered. This
taper, although not essential, is beneficial in that it makes the
threads strip-tolerant. These sections of threads are
strip-tolerant because the diameter of the threads expands toward
the rear of the section. The expanding thread diameter brings all
of the threads into contact with undisturbed material anytime the
screw is moving forward in the object. Thus, even if the screw was
momentarily stalled, stripping the female thread in the object, as
soon as the screw starts to move forward, all of the threads find
new purchase.
[0055] In a screw with a straight outside diameter, after any
stripping occurs, only the threads at the leading end move into
undisturbed material, leaving the remainder of the threads without
purchase until they move forward far enough to pass the entire
region where stripping occurred. Thus, a screw with a straight
leading end is subject to abrupt and nearly complete loss of
compression should any stripping occur. Moreover, the loss of
compression is not recovered by simply driving the screw forward.
This effect is manifest in the screw shown in Herbert, with which
sudden loss of compression due to stripping of the leading threads
is known to occur. In the case of Herbert, as with many of the
screws disclosed herein, the stripping occurs due to the difference
in pitch between threads in leading and trailing sections. In the
case of screw 110 with the same pitch in both sections, stripping
might occur as tension is created after the tip of the sleeve
contacts the surface of the object.
[0056] FIG. 15 shows a screw 210 similar to screw 110, but having a
larger pitch in a leading section 224 and a smaller pitch in a
trailing section 226 with an unthreaded medial section 228 in
between. Although the pitch is different in each section, the pitch
over each section is constant. Screw 210 can be used with sleeve
140 as described for screw 110, but can also generate compression
without the sleeve because of the pitch differential. Although
screw 210 is depicted with taper in the leading and trailing
sections, taper could be used in only one of the sections depending
upon the particular application. Moreover, the relative lengths of
the two sections and the unthreaded section could be varied to suit
the particular application. FIG. 16 shows a screw 310 similar to
screw 110, but having a variable pitch in a leading section 324 and
a constant pitch in a trailing section 326. As with screw 210,
screw 310 can be used with or without the sleeve. The variable
pitch threads in leading section 324 have a decreasing pitch moving
toward the trailing end of the screw. Thus, the leading section
threads develop some internal compression, in addition to the
compression created between the leading and trailing sections,
which may be beneficial where additional compression or reduction
is desired near the leading end.
[0057] It should be understood that the screws of the various
embodiments shown herein could also have a variable pitch in the
trailing section to create additional compression. As long as the
pitch change was not too large, such screws could still be used
with the sleeve by providing a slightly looser fit to the threads
in the sleeve or a sleeve with an interior surface which is soft
enough to be deformed by the threads on the screw.
[0058] FIG. 17 shows a screw 410 having a leading section 424, a
trailing section 426 and an intermediate section 428. Each section
is threaded and has the same pitch pattern as shown in screw 10.
Also like screw 10, screw 410 includes a self-drilling tip 432 and
a central bore 434. Screw 410 differs from screw 10 in that the
outside diameter of the screw tapers outward even in the
intermediate section. In particular, as shown, screw 410 tapers at
around 2 degrees over the leading and trailing sections and about
1/2 degree over the intermediate section. The reduction in taper
angle over the intermediate section reduces the driving force
required to install the screw while providing some additional grip
in the intermediate section relative to screw 10. It should be
noted that the intermediate section could also have no taper or
taper in toward the trailing end.
[0059] Dashed line 438 indicates the shape of a surface of
revolution of the threads about an elongate axis 440 of the screw,
as similarly illustrated on other embodiments. It can be seen that
the surface of revolution has a constriction or steps in slightly
in the area 442 of the transition between the leading section and
the intermediate section. The surface is then steps out in the area
of the transition between the intermediate section and the trailing
section.
[0060] FIG. 18 shows a screw 510 having a leading section 524 and a
trailing section 526. The leading section has variable pitch which
is larger near the front end of the screw and decreases back toward
the trailing section. The threads in the trailing section are
constant pitch and start at the same pitch as at the trailing end
of the leading section. The leading section is shorter than the
trailing section and constitutes approximately 1/3 of the length of
the threaded sections. The outside diameter or surface of
revolution of the threads at transition between the leading section
and trailing section makes a convex transition. The trailing
section is depicted with constant outside diameter, but could
alternatively have a taper. Similarly, while the pitch is depicted
as constant, variable pitch could be used, depending on the
compression desired.
[0061] FIG. 19 shows a screw 610 having a leading section 624, a
trailing section 626 and an intermediate or waist portion 628. A
single continuous screw thread 622 extends over all three sections
and has a pitch which changes relatively constantly over the entire
length. As before, other pitch patterns could be used, such as
constant pitch in the leading and trailing sections and variable
pitch in the intermediate section. The thread revolutions on screw
610, as with the other screws disclosed herein, can be considered
to form a surface of revolution about an elongate axis 640 of the
screw, the surface being indicated by dashed line 638. The surface
of revolution of screw 610 smoothly changes with no abrupt
discontinuities in slope or diameter. The surface of revolution is
convex in the area of the transition between the leading and
intermediate sections and is concave in the area of the transition
to the trailing section. Screw 610 includes a central bore 634 and
a self-drilling tip 632.
[0062] FIG. 20 shows a screw 710 similar to screw 10, but having an
unthreaded leading extension 742 and an unthreaded trailing
extension 744. The unthreaded extensions are useful to resist
bending loads along the axis of the screw, such as where two
elongate members are secured together. Screw 710 is thus useful in,
for instance, interphalangeal fusion procedures. Although the
extensions are illustrated on a screw such as screw 10, it should
be understood that they could be applied to any of the other screws
depicted herein.
[0063] FIG. 21 illustrates a screw 810 similar in profile to screw
10, but further including a head 846. Screw 810 includes a leading
section 824 of constant pitch, a trailing section 826 of constant
but smaller pitch and an intermediate section 828 of variable pitch
connecting the leading and trailing sections. It should be
understood that this pitch pattern and outside diameter profile is
not specific to or required by a headed screw according to the
present invention and other embodiments shown herein could be
equipped with a head. Although the head creates the disadvantage
that the screw cannot be driven in below the surface of the objects
to be fastened, it may be useful under some circumstances, such as
where the screw may serve as an anchor or hold down a plate.
[0064] FIG. 22 depicts a screw 910 having a leading section 924, a
trailing section 926 and an intermediate or waist section 928. The
leading section is frustro-conical in shape and tapers at an angle
of approximately 2 degrees relative to an elongate axis 940 of the
screw. The thread revolutions in the intermediate section have an
outside diameter which is stepped down from the trailing end of the
leading section to approximately the starting diameter of the
leading section. The outside diameter of the thread revolutions in
the intermediate section then tapers outward smoothly into the
trailing section. The intermediate and trailing sections thus have
a frustro-conical profile, again at an angle of approximately 2
degrees. The leading section represents about 1/3 of the length of
the screw, although other ratios could of course be used. As
depicted, the pitch of the threads in the leading section is
constant. The pitch of the threads in the intermediate and trailing
section is also constant, but smaller than the pitch in the leading
section. The pitch of the threads in any or all of the leading,
intermediate and trailing sections could also be variable.
[0065] Although the various screws according to the present
invention disclosed herein are described with particular reference
to orthopedic applications, it should be understood that screw
designs according to the present invention could be used for other
fastening purposes as well. For instance, screws according to the
present invention could be used to fasten wood flooring to
subfloors, sheathing or gypsum board to studs, and many other
non-medical uses. Generally, screws according to the present
invention are particularly useful where compression is needed or
two objects must be secured together, but where the head of a
standard screw or nail would be undesirable for functional or
cosmetic reasons.
EXAMPLE
[0066] This example describes further aspects of the present
invention, presented without limitation as a set of numbered
paragraphs.
[0067] 1. A fastener comprising (A) a root portion, the root
portion having a leading end, a trailing end and an elongate axis
extending therebetween; and (2) a single continuous thread formed
on the root portion and extending between the leading end and the
trailing end of the root portion, the thread having an outside
diameter which, moving from the leading end toward the trailing
end, increases over several revolutions, then decreases, then
increases again, wherein the pitch of the thread measured between
corresponding points on consecutive threads near the leading end is
larger than the pitch of the threads near the trailing end.
[0068] 2. The fastener of paragraph 1, wherein the root portion
includes a bore extending along the elongate axis from the leading
end to the trailing end.
[0069] 3. The fastener of paragraph 1, wherein the thread includes
an interthread spacing between revolutions of the thread on the
root portion and further wherein the interthread spacing varies
along the root portion.
[0070] 4. The fastener of paragraph 3, wherein the thread includes
an intermediate region disposed generally between the leading end
and the trailing end, and further wherein the interthread spacing
is larger in the intermediate region than near the trailing
end.
[0071] 5. The fastener of paragraph 1 further including a
self-drilling tip disposed at the leading end of the root
portion.
[0072] 6. The fastener of paragraph 1, wherein the thread includes
an intermediate portion where the outside diameter is decreased and
over which the outside diameter of the threads is substantially
constant.
[0073] 7. A screw comprising a leading section having a plurality
of thread revolutions, a trailing section having a plurality of
thread revolutions and an unthreaded intermediate section between
the leading and trailing sections, the thread revolutions in the
leading section having a greater average pitch and smaller average
outside diameter than the thread revolutions in the trailing
section, and where the outside diameter of the thread revolutions
in the leading section generally increases toward the trailing
section.
[0074] 8. The screw of paragraph 7, wherein the outside diameter of
the thread revolutions in the leading section tapers outward toward
the trailing section at an angle of 0.5 to 2.5 degrees relative to
an elongate axis of the screw.
[0075] 9. The screw of paragraph 7, wherein the leading section
includes at least three thread revolutions.
[0076] 10. The screw of paragraph 7, wherein the pitch of the
thread revolutions in the leading section decreases toward the
trailing section.
[0077] 11. The screw of paragraph 7, wherein the outside diameter
of the thread revolutions in the trailing section generally
increases away from the leading section.
[0078] 12. The screw of paragraph 7, wherein the intermediate
section has a smaller average diameter than the leading
section.
[0079] 13. The screw of paragraph 7, wherein the pitch of the
thread revolutions in the trailing section is constant.
[0080] 14. The screw of paragraph 7, wherein the screw includes a
central bore extending through the screw along an elongate
axis.
[0081] 15. The screw of paragraph 7, wherein the screw is
headless.
[0082] 16. A screw comprising a leading end, a leading section
proximal to the leading end and having a plurality of thread
revolutions, a trailing end, a trailing section proximal the
trailing end and having a plurality of thread revolutions, and a
waist section having at least one thread revolution disposed
between the leading and trailing sections, the thread revolutions
in the leading section having a greater average pitch and smaller
average outside diameter than the thread revolutions in the
trailing section, and wherein the minimum outside diameter of the
at least one thread revolution in the waist section is less than
the maximum outside diameter of the thread revolutions in the
leading section.
[0083] 17. The screw of paragraph 16, wherein the outside diameter
of the thread revolutions in the leading section is smaller toward
the leading end and larger toward the trailing end.
[0084] 18. The screw of paragraph 16, wherein the pitch of the
threads in the leading section is larger toward the leading end and
smaller toward the trailing end.
[0085] 19. The screw of paragraph 16, wherein the minimum outside
diameter in the waist region is at least five percent smaller than
the maximum outside diameter in the leading section.
[0086] 20. The screw of paragraph 16 further including a root
portion on which the thread revolutions are formed and where the
thread revolutions are the only part of the screw with a larger
diameter than the root portion.
[0087] 21. The screw of paragraph 20, wherein the thread depth
measured between the root portion and the outside diameter of the
thread revolutions is at least as large near the leading end as the
change in outside diameter of the thread revolutions between the
leading and trailing sections.
[0088] 22. The screw of paragraph 20, wherein the thread depth in
the leading section is at least substantially as large as the
radius of the root portion in the leading section.
[0089] 23. The screw of paragraph 20, wherein the root portion is
substantially cylindrical over at least one of the sections.
[0090] 24. The screw of paragraph 16, wherein the maximum diameter
of the thread revolutions is at least equal to the largest diameter
of any part of the screw.
[0091] 25. The screw of paragraph 16, wherein, at least along part
of the screw, the pitch gradually decreases as the outside diameter
gradually increases.
[0092] 26. The screw of paragraph 16, wherein the pitch changes
substantially continuously over the majority of the threaded
sections.
[0093] 27. A screw comprising a leading section having a plurality
of thread revolutions, a trailing section having a plurality of
thread revolutions and an intermediate section between the leading
section and the trailing section, the thread revolutions in the
leading section having a greater average pitch and smaller average
outside diameter than the thread revolutions in the trailing
section, the intermediate section having a smaller average outside
diameter than the leading or trailing sections and where the
outside diameter of the thread revolutions in the leading section
generally increases from revolution to revolution toward the
trailing section.
[0094] 28. The screw of paragraph 27, wherein the intermediate
section includes a plurality of thread revolutions.
[0095] 29. The screw of paragraph 28, wherein the thread
revolutions in the leading, intermediate and trailing sections form
a single continuous thread.
[0096] 30. The screw of paragraph 28, wherein the outside diameter
of the thread revolutions in the intermediate section is
substantially constant.
[0097] 31. The screw of paragraph 28, wherein the outside diameter
of the thread revolutions in the leading section tapers outward
toward the trailing section at an average angle of approximately
0.8 to 3 degrees.
[0098] 32. The screw of paragraph 27, wherein the average pitch of
the thread revolutions in the trailing section is less than about
90 percent of the average pitch of the thread revolutions in the
leading section.
[0099] 33. The screw of paragraph 27, wherein each section covers
at least 10 percent of the length of the screw.
[0100] 34. The screw of paragraph 27, wherein the screw has an
elongate axis and includes a bore extending through the screw along
the elongate axis.
[0101] 35. The screw of paragraph 27, wherein the outside diameter
of the thread revolutions in the leading section tapers at an angle
of between 0.5 and 5 degrees relative to an elongate axis of the
screw.
[0102] 36. The screw of paragraph 27, wherein the pitch of the
thread revolutions in the leading section is substantially
constant.
[0103] 37. The screw of paragraph 27, wherein the pitch of the
thread revolutions in the trailing section is substantially
constant.
[0104] 38. The screw of paragraph 27, wherein the average pitch of
the thread revolutions in the trailing section is at least
substantially half of the average pitch of the thread revolutions
in the leading section.
[0105] 39. The screw of paragraph 27, wherein the intermediate
section is unthreaded.
[0106] 40. The screw of paragraph 39, wherein the intermediate
section covers at least 20 percent of the length of the screw.
[0107] 41. The screw of paragraph 27, wherein the pitch of the
thread revolutions in the leading section decreases toward the
trailing section.
[0108] 42. The screw of paragraph 27, wherein the pitch of the
thread revolutions in the trailing section increases toward the
leading section.
[0109] 43. The screw of paragraph 27, wherein the outside diameter
of the thread revolutions in the trailing section decreases toward
the leading section.
[0110] 44. The screw of paragraph 27 further comprising an
unthreaded extension projecting from an end of the leading section
opposite the trailing section.
[0111] 45. The screw of paragraph 27 further comprising an
unthreaded extension projecting back from an end of the trailing
section opposite the leading section.
[0112] 46. A screw comprising (A) a root portion having a leading
end and a trailing end and a longitudinal axis extending
therebetween; and (B) thread means formed on the root portion for
generating axial compression along the longitudinal axis of the
root portion as the screw is driven into an object.
[0113] 47. The screw of paragraph 46, wherein the root portion
includes a central bore extending along the longitudinal axis
between the leading and trailing ends.
[0114] 48. A screw comprising a leading section having a plurality
of thread revolutions, a trailing section having a plurality of
thread revolutions and an intermediate section disposed between the
leading section and the trailing section and having a plurality of
thread revolutions, the outside diameter of the thread revolutions
forming a surface of revolution about an elongate axis of the
screw, the surface of revolution being convex in the transition
from the leading section to the intermediate section and concave in
the transition from the intermediate section to the trailing
section, and wherein the thread revolutions in the leading section
have a greater average pitch and smaller average outside diameter
than the thread revolutions in the trailing section.
[0115] 49. The screw of paragraph 48, wherein the surface of
revolution is generally conical in the leading section.
[0116] 50. The screw of paragraph 48, wherein the surface of
revolution is generally cylindrical in the trailing section.
[0117] 51. The screw of paragraph 48 further including a root
portion extending through the leading, intermediate and trailing
sections, wherein the diameter of the root portion is substantially
constant through the leading section and the intermediate
section.
[0118] 52. The screw of paragraph 51, wherein the root portion has
a leading end and a trailing end and a central bore extending
therebetween.
[0119] 53. The screw of paragraph 48, wherein the surface of
revolution tapers generally outward at an average angle of between
0.5 and 5 degrees relative to the elongate axis.
[0120] 54. The screw of paragraph 48 further including a root
portion, and further wherein there is a termination zone in the
thread revolutions in the leading section in which the thread
revolutions diminishes from approximately the average outside
diameter of the thread revolutions in the leading section down to a
starting point on the root portion, and wherein the diameter of the
root portion does not diminish substantially in the termination
zone and the outside diameter of the thread revolutions in the
leading section generally increases from revolution to revolution
outside the termination zone.
[0121] 55. The screw of paragraph 54, wherein the termination zone
includes less than one thread revolution.
[0122] 56. The screw of paragraph 48, wherein the surface of
revolution is generally conical in the trailing section.
[0123] 57. The screw of paragraph 48, wherein no part of the screw
has a larger diameter than maximum diameter of the thread
revolutions.
[0124] 58. The screw of paragraph 48, wherein the thread
revolutions in the three sections form a single, substantially
continuous thread.
[0125] 59. The screw of paragraph 48, wherein the surface of
revolution tapers outward at an angle of approximately 0.5 to 5
degrees in the leading section.
[0126] 60. The screw of paragraph 48, wherein the average pitch in
the leading section is at least 10% larger than the average pitch
in the trailing section.
[0127] 61. The screw of paragraph 48, wherein each section extends
for at least 15% of the total length of the three sections along
the elongate axis.
[0128] 62. The screw of paragraph 48, wherein the pitch of the
thread revolutions in the leading section is substantially
constant.
[0129] 63. The screw of paragraph 48, wherein the pitch of the
thread revolutions in the trailing section is substantially
constant.
[0130] 64. The screw of paragraph 48, wherein the pitch of the
thread revolutions in at least one of the sections is variable.
[0131] 65. The screw of paragraph 64, wherein the pitch is variable
in the intermediate section.
[0132] 66. The screw of paragraph 64, wherein the pitch is variable
in all three sections.
[0133] 67. The screw of paragraph 48 further comprising an
unthreaded leading extension disposed at an end of the leading
section opposite the trailing section.
[0134] 68. The screw of paragraph 48 further comprising an
unthreaded trailing extension disposed at the end of the trailing
section opposite the leading section.
[0135] 69. The screw of paragraph 48, wherein the screw is formed
of a biocompatible material.
[0136] 70. The screw of paragraph 69, wherein the screw is formed
of a resorbable material.
[0137] 71. The screw of paragraph 70, wherein the resorbable
material is osteoductive.
[0138] 72. The screw of paragraph 48, wherein the combined length
of the three sections is between 0.5 inches and 4 inches.
[0139] 73. The screw of paragraph 48 further comprising a root
portion on which the thread revolutions are formed, and wherein the
thread revolutions have an interthread spacing on the root portion,
and further wherein the interthread spacing on the root is not
constant over the three sections.
[0140] 74. The screw of paragraph 48 further comprising a
self-cutting tip disposed at the end of the leading section
opposite the trailing section.
[0141] 75. The screw of paragraph 48 further comprising a head.
[0142] 76. A screw comprising a leading section having a plurality
of thread revolutions and a trailing section having a plurality of
thread revolutions and forming a continuous extension of the thread
revolutions of the leading section, the outside diameter of the
thread revolutions forming a surface of revolution about an
elongate axis of the screw, the surface of revolution being convex
in the transition from the leading section to the trailing section,
and wherein the thread revolutions in the leading section have a
greater average pitch and smaller average outside diameter than the
thread revolutions in the trailing section and the length of the
leading section is less than the length of the trailing section,
the screw further including a root portion and wherein there is a
termination zone in the thread revolutions in the leading section
in which the thread revolutions diminish from approximately the
average outside diameter of the thread revolutions in the leading
section down to a starting point on the root portion, and wherein
the diameter of the root portion does not diminish substantially in
the termination zone whereby the screw has a relatively blunt
leading end.
[0143] 77. The screw of paragraph 76, wherein the outside diameter
of the thread revolutions in the leading section generally
increases from revolution to revolution outside the termination
zone.
[0144] 78. The screw of paragraph 77, wherein the surface of
revolution in the leading section tapers at an angle of between 0.5
and 5 degrees relative to the elongate axis of the screw outside
the termination zone.
[0145] 79. The screw of paragraph 76, wherein the pitch of the
thread revolutions gradually decreases in the leading section
toward the trailing section.
[0146] 80. The screw of paragraph 76, wherein the screw is
headless.
[0147] While the invention has been disclosed in its preferred
form, the specific embodiments thereof as disclosed and illustrated
herein are not to be considered in a limiting sense as numerous
variations are possible. Applicant regards the subject matter of
his invention to include all novel and non-obvious combinations and
subcombinations of the various elements, features, functions and/or
properties disclosed herein. No single feature, function, element
or property of the disclosed embodiments is essential. The
following claims define certain combinations and subcombinations
which are regarded as novel and non-obvious. Other combinations and
subcombinations of features, functions, elements and/or properties
may be claimed through amendment of the present claims or
presentation of new claims in this or a related application. Such
claims, whether they are broader, narrower or equal in scope to the
original claims, are also regarded as included within the subject
matter of applicant's invention.
* * * * *