Surgical needle abstract
An improved surgical needle of the type having a simple main cutting
edge extending across the needle and formed by the intersection
of two planar surfaces for use in cutting through hard body tissue
material. The forward end of the needle includes a relatively small
third substantially planar surface having an acute angle of convergence
with the axis of the needle and intersecting at substantially equal
acute angles with the other two planar surfaces. The surgical needle
is preferably curved in the reference plane defined by the main
cutting edge and the axis of the needle. Such an improved surgical
needle results in an extremely sharp needle with a high resistance
to burring.
Surgical needle claims
We claim:
1. A surgical instrument comprising a body portion and a cutting
portion, a pair of intersecting first and second planar surfaces
forming a single main cutting edge extending from one side of the
cutting portion of the instrument to a point at the end of the instrument,
a third planar surface having an acute angle of convergence with
the longitudinal axis of the instrument and extending from the opposite
side of the cutting portion of the instrument to the point thereof,
secondary cutting edges formed by the intersection of the third
planar surface with said pair of first and second planar surfaces,
the point at the end of the instrument being on the single main
cutting edge so that the end portions of both the main and secondary
cutting edges extend to the end point of the instrument.
2. A surgical insstrument as claimed in claim 1 wherein said surgical
instrument is curved in the reference plane defined by said main
cutting edge and said axis.
3. A surgical instrument as claimed in claim 1 wherein said main
cutting edge forms an acute angle with said third surface.
4. A surgical instrument as claimed in claim 1 wherein the angle
of convergence between said third planar surface and said axis is
within the range of 20.degree. to 35.degree., inclusive.
5. A surgical instrument as claimed in claim 4 wherein the angle
of slope of said main cutting edge is less than 20.degree..
6. A surgical instrument as claimed in claim 5 wherein said first
and second planar surfaces form at said main cutting edge a sharpness
angle that is within the range of 40.degree. to 50.degree., inclusive.
7. A surgical instrument as claimed in claim 6 wherein said angle
of slope is approximately 18.degree., said sharpness angle is approximately
43.degree. and said angle of convergence is approximately 30.degree..
8. A surgical instrument as claimed in claim 1 wherein said third
surface forms corresponding acute angles with said first and second
surfaces.
Surgical needle description
FIELD OF THE INVENTION
This invention relates to surgical cutting instruments and in particular
relates to an improved surgical needle for suturing through calcified
tissue, cartilage, or bone.
DESCRIPTION OF THE PRIOR ART
A surgical cutting instrument, as is well known, has the concomitant
requirements of being as sharp as possible in order to perform its
function properly and of being resistant to burr formation caused
by an insufficient amount of metal at the extreme tip portion of
the needle. In the previous Kurtz U.S. Pat. Nos. 2869550 and 3094123
issued Jan. 20 1959 and June 18 1963 respectively, a sharp surgical
needle was disclosed, which needle has a single main cutting edge
formed by the intersection of two planar surfaces such that the
main cutting edge extends from one side of the needle to the other
side thereof. In this type of needle, greater sharpness is obtained
by decreasing the slope angle of the main cutting edge relative
to the needle axis. However, as discussed in the Kurtz U.S. Pat.
No. 3636955 issued Jan. 25 1972 as the slope angle is decreased,
a point is reached at which so little material is left at the point
that the point lacks sufficient structural integrity to effectively
penetrate the tissue without the tip of the point burring or otherwise
deforming.
In the Kurtz U.S. Pat. No. 3094123 the concept of blunting the
tip of the needle to avoid deformation of the tip, even when using
a fairly sharp slope angle, was disclosed. The Kurtz U.S. Pat. No.
3636955 discloses the concept of adding a third planar surface
at the extreme tip so as to form a chisel-type forward cutting edge
at the intersection of the third planar surface with one of the
first two planar surfaces. Unfortunately, as the structural strength
of the tip portion of the needle has been increased by providing
more metal at this area by using either a rounded tip or a chisel-type
tip, the amount of force to obtain needle penetration has been increased,
particularly when calcified tissue must be penetrated. Thus, there
exists a need for a surgical needle having a very sharp point and
which is still strong enough to retain its structural integrity
when used to cut through bone or other hard tissue.
The principal factors determining the amount of force required
in needle penetration of tissue include the force required for the
engagement of the tip of a needle and for the widening of the hole.
The widening of the hole is effected either by the blunt dilatation
of a conventional taper point needle or by a very sharp cutting
action, as occurs with a needle of the type disclosed in the Kurtz
U.S. Pat. No. 2869550 or by the relatively sharp cutting action
as with a conventional cutting edge needle, or with a combination
of the three. With a taper point needle, after the tip is engaged,
a hole is made by pure blunt dilatation with no cutting action whatsoever.
After the hole is fully developed, the rest of the shaft slides
through and the suture, attached to the needle, follows. On the
other hand, with a needle of the type disclosed in the Kurtz U.S.
Pat. No. 2869550 a hole is produced by initially engaging the
tip. The cutting edge of this needle then enlarges the hole. Finally,
the remainder of the hole size is made by blunt dilatation with
no cutting edge being present. When the hole is fully developed,
the rest of the shaft slides through with friction as the major
resistance component. Still further, with a conventional cutting
edge needle, the relatively sharp edges slide through, after the
tip is engaged, until there is a fully developed hole. After the
hole is developed, the shaft slides through with the major resistance
component being only friction.
The dilatation per unit time is a direct reflection of the work
required, and hence the force required, for the needle to make the
fully developed hole. With a taper point, the included angle (at
the apex of the cone) is approximately 12.degree.. When the needle
included angle is more acute, less work per unit time would be required
to make a fully developed hole. However, the more acute the angle,
the more fragile the tip with resultant possible bending over and
burr formation. Burr formation obviously destroys the sharpness
of the needle. When the angle is greater than 12.degree., the dilatation
per unit time must be faster and the needle appears to be more blunt
because of the necessity for rapid dilatation.
With respect to the needle of the type disclosed in U.S. Pat. No.
2869550 it is obvious that the longer the knife blade, the less
metal there is at the tip and the greater the danger of turning
the tip with burr formation. In the past, when this type needle
had to be used for hard tissue material, the tip edge was blunted
as disclosed in the Kurtz U.S. Pat. No. 3094123 in order to allow
a long cutting action. Similar reasoning applies for the conventional
cutting edge needles of the type fully discussed in the Kurtz U.S.
Pat. No. 2869550. The longer the edge which slip through tissue
on entering, the sharper the needle and the less required force
per unit time to make a completely developed hole. The reasons for
desiring an extremely sharp needle with structural integrity is
discussed in detail in the aforecited Kurtz U.S. patents. A sharper
needle results in a smaller opening and a minimization of trauma.
Obviously, needles which break or bend while in use or which tear
through tissue are undesirable. On the other hand, it is very desirable
to have needles which require minimum force when penetrating tissue.
SUMMARY OF THE INVENTION
Thus, a purpose of the present invention is to provide a surgical
cutting instrument which is both sharp enough and strong enough
to cut through hard body tissue without burring or otherwise becoming
deformed at its point and which requires a minimum amount of force
in its use.
According to the present invention, there is provided a surgical
cutting instrument having a main cutting edge extending from one
side of the needle to a point near the other side thereof and passing
through the axis of the needle, the main edge being formed by the
intersection of two planar surfaces. As a matter of convention,
the side of the needle having the main cutting edge is referred
to as the "bottom" of the needle and the plane defined
by the main cutting edge and the axis of the needle point or tip
is referred to as the "reference plane," so that when
the main edge is on the bottom, the reference plane is vertical.
It is apparent, however, that the needle could assume any orientation
in practice.
It is an object of the present invention to form a new improved
surgical cutting needle for cutting through bone or other hard tissue
which overcomes the disadvantages of previously known surgical cutting
needles. It is also an object of the present invention to provide
a surgical needle that has sufficient metal at the tip to minimize
the danger of burr formation, has a long knife blade, has longer
edges which slip through the tissue on entering, and requires less
force per unit time to make a completely developed hole.
A surgical needle according to the present invention has an extremely
long cutting edge formed by the intersection of two substantially
planar surfaces and a secondary cutting edge having a different,
sharper angle and which is located proximate to the tip of the needle.
Such a needle permits as long a cutting action as possible, yet
has a greatly decreased possibility for burr formation. Thus the
resultant needle has two differently shaped cutting edge points,
the main cutting edge being as long as possible and the secondary
cutting edge being blunter and confined close to the tip of the
needle.
In a presently preferred embodiment of the invention, the surgical
instrument comprises a curved body portion and a cutting tip portion.
The axis of the curved body portion defines a reference plane. The
cutting tip portion has a main cutting edge that is formed by the
intersection of first and second substantially planar surfaces,
the main cutting edge lying in the reference plane and on a line
which intersects the needle axis. A third planar surface intersects
the first and second planar surfaces so as to form corresponding
acute angles therewith and a forward end point that is located within
the fictive circumferential boundaries of the tip portion.
The foregoing and other objects and attendant advantages of the
present invention are discussed in or will become apparent from
the detailed description of the preferred embodiment hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings in which like numerals represent like elements
in the several views:
FIG. 1 illustrates the tip portion of a conventional surgical cutting
needle in side elevation.
FIG. 2 is a bottom view of the conventional surgical cutting needle,
the tip portion of which is depicted in FIG. 1.
FIG. 3 is a perspective view illustrating the tip portion of a
surgical cutting needle and showing the features of the present
invention.
FIG. 4 is a side elevational view of the surgical cutting needle
according to the present invention.
FIG. 5 is an elevational enlarged view of the cutting portion of
an actual surgical needle according to the present invention.
FIG. 6 is a top plan view of FIG. 5.
FIG. 7 is a bottom plan view of FIG. 5.
FIG. 8 is a cross-sectional view taken along line 8--8 of FIG.
4.
FIG. 9 is a cross-sectional view taken along line 9--9 of FIG.
4.
FIG. 10 is a cross-sectional view taken along line 10--10 of FIG.
4.
FIG. 11 is a cross-sectional view taken along line 11--11 of FIG.
4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIGS. 1 and 2 a prior art surgical needle as
disclosed in the Kurtz U.S. Pat. No. 3636955 is depicted at 20.
Needle 20 includes the two conventional planar surfaces 21 and 22
which form the main cutting edge 23 known heretofore. A third planar
surface 24 forms an angle other than 90.degree. with the reference
plane of the needle. Third surface 24 intersects planar surface
22 at its forward side to form a chisel-type forward cutting edge
25 and it intersects the first planar surface 21 at its second
or rearward side to form a rearward edge 26. The intersection of
third surface 24 with the outer periphery of needle 20 is shown
at 27. The plane of third surface 24 forms a complex angle with
the axis of the needle and is inclined rearwardly by an angle .alpha..
This will assure that the forward cutting edge 25 which as previously
indicated is formed by the intersection of the third surface 24
and the second planar surface 22 slopes rearwardly as well as downwardly.
Angle .alpha. can be approximately 45.degree.. Additionally, to
provide a slightly sharper point of introduction, third surface
24 is inclined rearwardly, the downward component being illustrated
by the angle .beta. in FIG. 1. The two arrows indicated by N.sub.1
and N.sub.2 represent the components of the lines normal to third
surface 24 taken in the vertical and horizontal planes, respectively.
Needle 20 is curved in an arc in the plan view of the needle such
that cutting edge 23 extends laterally. In addition, as seen in
FIG. 1 the tip of the needle 20 shown at 28 is on the periphery
of the needle. In effect then, planar surface 24 merely blunts the
end of needle 20 and does not provide a knife-type cutting edge,
but rather provides a chisel-type cutting edge.
A surgical needle 50 according to the present invention is illustrated
in FIGS. 3 through 11. Needle 50 includes a body portion 52 and
a cutting portion 54 and has a curved axis 56 which defines a reference
plane. A main cutting edge 58 is formed in a conventional manner
by the intersection of a first substantially planar surface 60 and
a second substantially planar surface 62 (FIG. 7). Thus it can be
seen that main cutting edge 58 lies in the reference plane as shown
in FIG. 4.
Cutting portion 54 includes an end portion 64 having a tip 66 and
a longitudinal axis 68 which is a continuation of needle axis 56.
End portion 64 is comprised of a blunt cutting edge portion 70 (FIG.
6) which is formed by the intersection of a third substantially
planar surface 72 (FIG. 3) with first and second surfaces 60 and
62 thereby forming secondary cutting edges 74 and 76 (FIG. 6).
As seen in FIG. 4 main cutting edge 58 extends from the outer periphery
at point 78 of needle 50 forwardly toward tip 66 at the intersection
of third surface 72. Thus, main cutting edge 58 is truncated by
third surface 72 and if extended, as shown by dashed line 80 would
intersect with the outer periphery of needle 50 at fictive intersection
82. The longitudinal distance between fictive intersection 82 and
tip 66 represents the missing portions of needle 50.
First, second and third surfaces 60 62 and 72 are preferably
formed by grinding. In this way, the diameter of the point does
not become larger than the diameter of the rest of the needle. Other
advantages resulting from grinding the needle are discussed in the
three aforementioned Kurtz U.S. patents.
FIGS. 8 through 11 depict the cross-sectional shapes of needle
50 at various locations along body portion 52 and cutting portion
54. Needle 50 is generally round (FIG. 10) with a flat section at
84 (FIG. 4) to provide a needle holder (see e.g. Kurtz U.S. Pat.
No. 3265070). Cutting portion 54 begins at the rearward terminus
86 of surfaces 60 and 62. The rearward terminus of end portion 64
has a generally wedge-shape cross-section (FIG. 9) with an arcuate
top while the forward part of end portion 64 has a triangular wedge
shape cross-section (FIG. 8).
With reference to FIG. 4 the angle between main cutting edge 58
and the upper, outer periphery of needle 50 is identified as angle
"a" and is termed the angle of slope. This angle determines
the rate at which the tissues are cut to the diameter of the needle.
The angle shown as angle "b" in FIG. 8 is termed the sharpness
angle. This angle actually determines the sharpness of main cutting
edge 58. It is apparent that if the sharpness angle is made too
small, there is insufficient metal in the point to give the point
the necessary strength. Similarly, the angle of slope must be minimized
to provide for ease of passage of the needle through the tissue
and yet must be sufficiently large to preserve metal at the point
of tip 66 to give the needle rigidity. (See Kurtz U.S. Pat. No.
2869550 for ranges of the sharpness angle, and angle of slope).
In the present invention, it is preferable that the angle of slope
"a" be less than 20.degree. and preferably 18.degree..
The present needle 50 performs the best when the sharpness angle
is within the range of 40.degree. to 50.degree., inclusive, and
preferably is approximately 43.degree..
Third surface forms an acute angle of convergence "c"
with axis 68 resulting in tip 66 being within the fictive periphery
of end portion 64 the periphery being outlined by dashed lines
FIG. 4. Angle of convergence "c" can be from 20.degree.
to 35.degree. and is preferably 30.degree.. As third surface 72
is ground, the length of needle 50 is actually shortened as the
needle is advanced into the grinding wheel. The amount of advancement
of needle 50 is shown by the distance D in FIG. 4 and can be from
0.020 inch to 0.125 inch. As is clearly seen, the greater the amount
of advancement D at the same angle of convergence c, the lower will
be the resulting location of tip 66. It must be appreciated that
third surface 72 is relatively small with respect to first and second
surfaces 60 and 62. The resulting secondary cutting edges 74 and
76 are usually no more than one-fifth to one-sixth the length of
main cutting edge 58. Nevertheless, the addition of third surface
72 to a conventional single cutting edge needle adds a significant
amount of metal at the tip portion and amazingly provides a greatly
reinforced tip with a major resistance to burring when needle 50
is used in hard tissue. Thus, the provision of a blunter cutting
edge portion confined as close to tip 66 as possible and forming
an acute angle with main cutting edge 58 together with main cutting
edge 58 being as long as possible, results in a greatly improved
needle having a high resistance to burring, and a low insertion
and penetration force requirement, and thus creating a minimal amount
of trauma to the tissue.
Although the invention has been described in considerable detail
with respect to a preferred embodiment thereof, it should be apparent
that the invention is capable of numerous modifications and variations
by those skilled in the art without departing from the spirit and
scope of the invention.
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