Note: Descriptions are shown in the official language in which they were submitted.
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`, TRANSCUTANEO~J5 PIN FOR FIXATION OF A
.. BONE PART OR FRAGMENT
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i~Transcutaneous pins have been known for many years
-~and are used in bone surgery, particularly in external
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osteosynthesis. Such pins pass through the flesh and
bone and, in general, are used with the type of
external skeletal fixation appliances developed by Dr.
Hoffmann. These external skeletal fixation appliances
comprise swivel joints, connecting bars, sliding bars,
articulations, and anchorage clamps intended to hold
and position the transcutaneous pins. The ~offmann
external fixation devices comprise an assembly
framework placed around a part or member of the human
body and arranged to hold bones or bone fragments in
place ~rom the exterior with the aid of pins or groups
of transcutaneous pins.
There are many types of transcutaneous pins on the
market today. These pins generally comprise a threaded
portion with a tapping portion at the end arranged to
cut a thread when it is screwed into a bone part or
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fragment. Before the pin is installed, the bone or
bone fragment is first drilled to the desired diameter,
which is substantially equal to or greater than the
inner diameter of the thread. The end of the pin is
then inserted in the drilled hole and the threaded
portion of the pin is screwed into the hole. During
this operation, the tap provided at the end of the pin
cuts the thread in the previously drilled hole. To
screw the pin into the hole, use is commonly made of a
chuck engaging a portion of polygonal cross section,
for example a square cross section located at one end
of the pin. In the pins of the prior art, the end of
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1 329081
64680-398
the threaded portion mlght take a form like the point of a
drilling bit or take different conflgurations known to those
skilled in the art.
There i~ also a type of pin, known as a transfixing pin,
in which the threaded portion is preceded hy a rod having a drill
` tip at its free end~ Transfixing pins may be in~talled without
!, previously drilling a hole in ~he bone. In the ca~e of a
transfixiny pin, the hole is drilled by the extremity of ~he tip
and the thread is tapped by a tappiny portion provided at the
beginning of the ~hread.
; The transcutaneous pins of the prior art do not afford a
~ drilling or a tapping of very high quality. As in any drilling or
`s tapping operation, the te~perature rises at the place of the
operation, which can cause necroses and deteriorations in ~he bone
tissues. Moreover, the prior art pins do not produce tapped
surfaces of good quality. The surfaces are torn out in placeR,
thus failing to provide a good quality of anchorage between the
bone fragment and the pin when the latter has been installed.
Finally, the prior art pins, by reason of their poor performance
in the drilllng or tapping operation, can cause undue stre~ses in
the bone when they are in place.
The objeat of the present invention is to propo~e a
transcutaneou~ pln assuring a drilllng or a tapplng of good
quallty, while ensuring a minimal ~emperature rise during
insertion.
According ko the present invention, there is provided a
transcutaneous pln having a centerline and a tap, said pin for
fixation of a bone part or fragmen~ and said pin havi-ng a tap
comprisiny a threaded portion with at least one flute at the
~ 30 anterior end of the threaded portion adapted to perform a tapping
:~ operation when said anterlor end of the threaded portion
penetrate~ the bona part or fragmentr with the at lea~t one flute
each taking the form of a notch creating a cutting edge of the tap
across the thread, and a clearance relief being provided behlnd
the cutting edge of the tap which approaches the centerllne of the
~ pin until it reaches the following notch, thereby forming a
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64680-398
clearance angle, wherein said at least one flute is disposed
helicoidally in relation to the axis of the thread, with the helix
and the thread beiny pitched in the same direction.
The presence of the clearance relief permits a tapping
of good quality and an easier penetration of the pin into the
bone. Furthermore, since the chips do not remain inside the bone
during the procedure and thus present no obstacle to the following
cutting edge, the temperature ri~e is much less than with the pins
of the prior art.
The anterior portion of the threading of the pin may
take the form of a leading cone, with the fllltes defining the
cut~ing edges extending over the leading cone of the threading and
over the beginning of the central cylindrical portion of said
threading.
Various modificationx may be adopted in producing ~he
flutes forming the cutting edges. The flutes may take the form of
a notch formed by two suhstantially perpendiculax surfaces, or a
notch having a rounded shape in cross ~ection. The fluting is
preferably accomplished by grinding, after the threading with its
; 20 leadlng cone have been made.
The invention can be adapted to various types of pins,
whether pins requirlng a pre-drilled hole or sel~-drilling pins.
In the latter case, the pin advantageously is provlded with a
drill tip at least indirectly adjacent the beginning of the
leading cone of the thread.
The invention likewise comprises a transfixing pin in
which the leading cone of the thread is preceded by
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a rod of a diameter equal to or less than the inner
diameter of the thread of the threaded portion, with
said rod terminating in a flat ogive-shaped drill tip.
The flat ogive-shaped tip may have two clearance
cutouts placed opposite each other on its upper
portion.
;~ The flat ogive-shaped tip may have a cross section
in the shape of an elongated parallelogram defining two
opposed cutting surfaces, each followed by a surface
~ forming a clearance angle, said cutting and clearance
r'~'' surfaces forming together a cutting edge, and the
cutting surfaces having an elongated spoon-shaped
; depression next to the cutting edge so as to modify the
r' cutting angle to bring it to zero or to a positive
value.
The accompanying drawings show, by way of example,
.r:~ several embodiments of the transcutaneous pin according
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to the invention.
In the drawings:
FIG. 1 is a side view showing a first embodiment
of a transcutaneous pin;
~` FIG. 2 is a side view showing a second embodiment
of a transcutaneous pin, i.e. a transfixing pin;
FIG. 3 is an enlarged view of the end of the pin
shown in FIG. 1 as seen at III, in a first embodiment
of a pin installed after the bone has been drilled to a
$ suitable diameter; such a pin is commonly called a
blunt tip half-pin;
FIG. 4 is a view similar to FIG. 3 in a second
embodiment of a transfixing pin serving additionally to
drill the hole before making the tapping, and referred
- to as a self-drilling and self-tapping half-pin;
!~' FIG. 5 is an enlarged view of the anterior end of
~x~i the threading of a transfixing pin, in a first
-, - embodiment;
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FIG. 6 is a view similar to FIG. 5, in a second
; embodiment;
FIG. 7 is a section view taken along the line
VII-VII in FIG. 5;
FIG. 8 is a section view taken along the line
VIII-VIII in FIG. 6;
FIG. 9 is an enlarged detail view of the tip of
: the pin of FIG. 2, as indicated by the arrow IX; and
FIG. 10 is a section view taken through the tip in
.,:. FIG. 9, along the line X-X.
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The transcutaneous pin 1 shown in FIGS. 1 and 3
comprises a threaded portion 2, which is the anterior
portion of the pin, and a posterior portion 3 which is
-~ referred to as the smooth portion 3. The pin 1 is a
,~ cylindrical pin of small diameter compared to its
,~ length, and the posterior or smooth portion 3 is
`'~! provided with a groove 4 and a four-sided terminal
portion 5. The terminal portion 5 enables use of a
: chuck to drive the pin 1 into a bone part or fragment,
~. while the groove 4 serves fo~. retention of the chuck.
.:";: The anterior portion 2 of the pin 1 (see in particular
~i FIG. 3) comprises a thread 6 whose anterior portion
`. takes the form of a truncated leading cone 7 terminated
by a substantially planar face 8 perpendicular to the
centerline of the pin.
In FIGS. 3, 5 and 6, three flutes 9 are placed
:~. 120 apart over the circumference of the anterior end
: of the pin, to perform the tapping operation. These
~^'f~'` flutes 9 take the form of two perpendicular surfaces 10
and 11, with surface 10 defining the cutting edge 12 of
. the tap at its free end (see also the cross section of
FIG. 7). Each of the cutting edges 12 is followed! in
.~ the direction of rotation of the pin, by a clearance
relief 13 which approaches the centerline of the pin
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until it intersects the surface 11 of the following
flute 9.
The flutes 9 are preferably realized by grinding.
The grinding operation is performed with a circular
grinder moved tangentially over the end of the thread
6. Grinding of the flutes 9 provides a good surface
quality at the cutting edge and obviates a subsequent
finishing operation. The clearance relief 13 is made
in the same manner by bringing a grinder up to the end
of the pin and rotating the latter while bringing the
grinder closer to the centerline of the pin.
Although the creation of the flutes 9 and of the
clearance relief by grinding has given very good
results, it will be apparent to those skilled in the
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`~ art that it may also be done by milling or by any other
~ suitable means.
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~i$ The type of pin shown in FIG. 3 is used more
~ specifically to be placed in bones in such a position
`~ that, at the exit rom the second cortex, the point of
s:~ the pin does not risk wounding the tissues near the
5~; bone.
In other applications, however, it may be
desirable to install a so-called transfixing pin, that
is a successively self-drilling and self tapping pin,
like those shown in FIGS. 2 and 4.
In FIC.. 4, as in the foregoing description, the
pin includes a thread 6 terminating on a truncated
:'r.~.~ conical portion 7. It nevertheless differs in that the
truncated cone 7 is extended by a cylindrical portion
28, which is terminated in turn by a tip 29 of
;~ generally conical shape. The cylindrical portion 28
permits avoidance of interference between the drilling
and tapping operations in cortical bone of ordinary
} thickness, which would render difficult the correct
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Y cutting of a thread in the bone. In this embodiment,
the pin includes two symmetrical flutes 30.
Alternatively, a transfixing pin such as shown in
FIG. 2 may be provided, cornprising, like the pin of
FIG. 1, a threaded portion 2, a posterior portion 3
i~ having an annular groove 4 adjacent its end, and a
-- four-sided end portion 5 intended to be received by a
feed chuck.
~?~ The threaded portion 2 includes a thread 6 with a
' leading cone 7 similar to the one detailed in FIG. 3
Here again, the tapping flutes 9 may be created by
means of a circular grinder which is moved tangentially
to the centerline of the pin, starting from the rod 16
preceding the truncated cone 7 and entering the
. threading 6. The rod 16 terminates anteriorly in a
cutting tip 17 adapted to drill a hole, which is shown
in more detail in FIG. 9.
The tip 17 at the end of the rod 16 of the
transfixing pin shown in FIG. 2 has the shape of an
ogive 22, the ogive having two clearance cutouts 23 in
its upper portion (FIG. 9). The oyive shaped tip 22
: has some particularly interesting design features which
~ are seen in FIG. 9 and in the cross section of FIG. 10
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~D~` showing an elongated parallelogram configuration
;. including two cutting surfaces 24 each defining a
;~ cutting edge 25 followed by a clearance surface 26. If
~`~ the tip is rotated in the directioil of rotation
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.~: indicated by the arrow F, it will be noted that-the
.~ surfaces 26 define a sufficiently large clearance angle
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to allow for the clearing of chips produced during
~; drilling of a bone with the ogive 22. On the other
:i:. hand, those skilled in the art will note in FIG. 9 that
~ the plane surfaces 24 define cutting surfaces having a
: negative cutting angle alpha. In order to modify this
:~. cutting angle alpha and bring it to zero or to a
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positive value, two elongated depressions 27 are
provided adjacent to the cutting edge 25. Thus the
cutting angle alpha may be corrected and selected
according to the user's preference by changing the
;~ depth of the depressions 27.
.''J.~ The tip of FIGS. 9 and 10, with its oyive shape,
its clearance surfaces 26, and its depressions 27
; bringing the cutting angle to zero or to a positive
value, affords drillings of very good quality compared
~ to prior art drill pins. The ogive-shaped tip is,
;~ moreover, especially suitable because i~ fixes itself
s in the bone and serves to drill a hole along an axis
~r~ ~ with no lateral deviation.
The pin just described with reference to FIGS. 1,
3 and 4 can vary between 75 and ZOO mm. in overall
1~ length, with diameters ranging from 3 to 6 mm. The
truncated cone typically has an inclination of 12
degrees.
~he pin according to the embodiment of FIG. 2,
with a central threaded portion, may be of from 175 to
~;` 350 mm. in overall length, with diameters likewise
ran~ing from 3 to 6 mm.. ~he anterior portion of the
pin shown in FIG. 2, comprising the rod 16, has a
diameter equal to or l~ss than the inner diameter of
the thread in the threaded portion 6. For a 3, 4, 5 or
6 mm. pin, the portion 16 may have a 2, 3~ 4 and 5 mm.
diameter, respectively. In the case of the pin of FIG.
2, it is advantageous to provide a 6 truncated leading
cone.
In the several examples given, the threading is a
single thread, but it is of course possible to
~'r alternatively provide multiple threads, the taps
~` passing successively in the same tapping flute several
times.
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