System for fusing joints

Details System for fusing joints System for fusing joints

1999-08-16

2001-10-09

Reip, David O. (Department: 3731)

Surgery

Instruments

Orthopedic instrumentation

Reexamination Certificate

active

06299615

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a bone screw for drawing together bone fragments separated by a fracture and more particularly to such a screw which draws the bone fragments together as a result of different-pitched threads on the screw.
BACKGROUND OF THE INVENTION
In healing bone fractures it is desirable to compress the fractures so that the fractured surfaces are pressed against one another. In the prior ark bone screws have been used to draw the fractured surfaces together and thereby optimize the healing process.
A number of prior art bone screws have been constructed in a fashion resembling wood screws. For example, some prior art bone screws include a threaded distal portion and a head with a relatively long unthreaded shank disposed between the head and the distal portion. A drill is used to create a bore through the fracture and the screw is threaded into the remote bone fragment with the head of the screw compressing the near fragment tightly against the remote bone fragment.
Other bone screws are threaded along the length thereof thus requiting a first drill bit to create a bore in both bone fragments extending across the fracture and a second bit to drill a larger bore in the near bone fragment so that the screw threads do not engage the near bone fragment Thereafter, the screw is tightened in the same manner as described above in connection with the screw having an unthreaded shank, thereby compressing the fragments together.
The operation of two prior art headed lag screws is illustrated in
FIGS. 8A-10D
. The operation of a lag screw A
1
with a head B
1
, and a shank C
1
is shown in
FIGS. 8A-D
. Shank C
1
of screw A
1
includes threads D
1
at the distal end and an unthreaded region E
1
proximal to head B
1
. The pitch of threads D
1
is constant.
FIG. 8A
shows screw A
1
partially engaged in a bore F
1
in a near bone fragment G
1
. The diameter of bore F
1
is less than the diameter of threads D
1
and therefore the threads engage the walls of the bore as the screw is twisted in.
FIG. 8B
shows screw A
1
as it starts threading into a bore H
1
in a remote bone fragment I
1
. At this point threads D
1
are engaged in both bores and moving forward at the same speed in both fragments so no compression between the fragments is achieved. Head B
1
has reached the top of fragment G
1
in
FIG. 8C
, as indicated schematically by the radiating “force” lines. Since threads D
1
are no longer engaged in fragment G
1
, screw A
1
rotates freely in the fragment without being drawn forward therein Subsequent rotation of screw A
1
draws fragment I
1
further up the screw. Because head B
1
prevents fragment G
1
from moving further up screw A
1
, fragment I
1
is drawn up against fragment G
1
and compression between the fragments is achieved as shown in
FIG. 8D
, with the head pulling down on the near fragment and the threads pulling up on the remote fragment.
The importance of the unthreaded region of screw A
1
is illustrated in
FIGS. 9A-d
. A lag screw A
2
including a head B
2
and a shank C
2
is shown partially engaged in a bore F
2
in a near fragment G
2
in FIG.
9
A. Shank C
2
includes threads D
2
running the entire length with no unthreaded region such as E
1
on screw A
1
. Rotating screw A
2
causes it to be drawn through fragment G
2
and pass into a bore H
2
in a remote fragment I
2
, as shown in FIG.
9
B. Further rotation of screw A
2
brings head B
2
down against the upper surface of fragment G
2
. See FIG.
9
C. At this point, threads D
2
are still engaged in bore F
2
of fragment G
2
and the interaction of the head on the surface of fragment G
2
impedes the further rotation of screw A
2
. To have additional rotation, head B
2
would have to be drawn down into fragment G
2
or the portion of threads D
2
in fragment G
2
would have to step out. Therefore a fully threaded screw, such as screw A
2
, would not be preferred for use in the fragment and bore configuration of
FIGS. 9A-D
.
The proper bore configuration for using screw A
2
is illustrated in
FIGS. 10A-D
. As shown in
FIG. 10A
, bore F
2
in fragment G
2
is enlarged to allow threads D
2
of screw A
2
to pass freely through the bore. Screw A
2
therefore slips into bore F
2
until it reaches fragment I
2
. At that point threads D
2
engage the walls of bore H
2
and draw screw A
2
down into fragment I
2
. See
FIGS. 10B-C
. When head B
2
reaches the upper surface of fragment G
2
, further rotation causes fragment I
2
to be drawn up into contact with fragment G
2
as shown in
FIGS. 10C-D
. No binding occurs between head B
2
and reads D
2
in the near fragment because of the large bore in fragment G
2
, and the screw functions as intended to draw the two fragments together.
FIGS. 11A-12D
illustrate the effect of substituting headless screws in the place of lag screws A
1
and A
2
.
FIG. 11A
, in particular, shows a headless screw A
3
partially installed in a bore F
3
in a near fragment G
3
. Screw A
3
includes threads D
3
extending along its entire length The pitch of threads D
3
is constant.
FIG. 11B
shows screw A
3
extending through fragment G
3
and just entering a bore H
3
in a remote fragment I
3
.
FIG. 11C
shows screw A
3
advanced further into fragment I
3
. It should be noted that, since the pitch of threads D
3
is constant, screw A
3
moves forward in fragments G
3
and I
3
by the same amount with each rotation. As shown in
FIG. 11D
, screw A
3
will pass through both fragments without altering their relative spacing or compressing them together. Thus, a headless screw such as screw A
3
will not work to draw the fragments together in the same way as lag screws A
1
and A
2
.
A variation of screw A
3
is shown at A
4
in FIG.
12
A. Screw A
4
includes threads D
4
of constant pitch extending along its entire length and differs from screw A
3
in that it tapers from a smaller outside diameter at the leading end to a larger outside diameter at the trailing end. Screw A
4
is shown because it incorporates tapering which is one of the features of the present invention, however, it is unknown whether such a screw is found in the prior art Screw A
4
is shown partially installed in a bore F
4
in a near fragment G
4
in FIG.
12
A. As screw A
4
is rotated, it moves through fragment G
4
and into a bore H
4
in a remote fragment I
4
, as shown in FIG.
12
B. Subsequent rotation simply carries screw A
4
further into and through fragment I
4
without any effect on the spacing between the fragments. See
FIGS. 12C-D
. With a constant pitch Dread, such as found on thread D
4
, the taper does not facilitate compression. Taper may, however, make a screw easier to start in a small pilot hole or even without a pilot hole. The threaded portion of many wood screws follows this general format, tapering to a sharp point, to allow installation without a pilot bole.
It can be seen from the above discussion that a headless screw of constant pitch does not achieve the desired compressive effect between the two fragments as win a lag screw with a head. It is, however, possible to draw two fragments together with a headless screw if it has valuing pitch.
FIG. 13A
shows a headless screw As with threads D
5
formed along its entire length. Such a screw is shown in U.S. Pat. No. 146,023 to Russell. The pitch of threads D
5
varies from a maximum at the leading end to a minimum at the trailing end It is expected that such a screw moves forward upon rotation in a fragment according to the approximate average pitch of the threads engaged in the fragment. Screw A
5
is shown in
FIG. 13A
with the leading threads engaged in a bore F
5
in a near fragment G
5
. Rotation of screw A
5
causes it to move forward into and through fragment G
5
and into a bore H
5
in a remote fragment I
5
, as shown in FIG.
13
B. Additional rotation after the leading threads engage fragment I
5
causes the two fragments to be drawn together. See
FIGS. 13C-D
. This is because the average pitch of the threads in fragment I
5
is greater than the average pitch o

Affiliated with

Also associated with

Rating

System for fusing joints does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with System for fusing joints, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for fusing joints will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2605274