Surgical needle abstract
A combined surgical needle-suture device of controlled suture release
characteristics and a method for manufacturing the device employ
a shrinkable tubing to connect the needle to the suture. The tip
of the suture which is connected to the needle possesses a reduced
cross section relative to the remainder of the suture, such reduced
cross section being capable of rupture by applying an amount of
force therto, e.g., a sharp tug, within a predetermined range thus
effecting needle separation.
Surgical needle claims
What is claimed is:
1. A method for attaching a surgical needle to a suture to provide
a combined surgical needle-suture device exhibiting a predetermined
range of average pull-out force for a suture of given size which
comprises:
a) providing a surgical needle having a shank end of reduced cross-section
and a suture having a region of reduced cross section at its tip;
b) placing a shrinkable tubing around the reduced diameter shank
of the needle and the tip of the suture having the region of reduced
cross section with a portion of the reduced cross section region
extending beyond the shrinkable tubing; and,
c) applying energy to the shrinkable tubing to bring the tubing
into engagement with the needle shank and suture thereby providing
a combined surgical needle-suture device in which the force required
to achieve rupture of the suture at its region of reduced cross
section with consequent separation of the needle from the suture
falls within a predetermined average value.
2. The method of claim 1 wherein the predetermined average value
of the rupture for a particular size of suture is as follows:
3. The method of claim 1 wherein the cross section of the tip of
the suture is reduced by at least 10% relative to the cross section
of the remaining suture.
4. The method of claim 1 wherein the suture is a monofilament suture.
5. The method of claim 1 wherein the suture is a multifilament
suture.
6. The method of claim 1 wherein the step of applying energy further
comprises applying energy to bring the tubing into engagement with
the needle shank and thereafter applying energy to shrink the shrinkable
tubing into engagement with the tip of the suture.
7. A combined surgical needle-suture device which comprises:
(a) a needle having a shank of reduced cross-section;
(b) a suture having a region of reduced cross section at its tip;
and,
(c) a shrinkable tubing around said needle shank and a portion
of the region of reduced cross section of the tip of the suture
to couple the same without swaging or crimping, the force required
to achieve rupture of the suture at its region of reduced cross
section and consequently, separation of the needle from the suture,
falling within a predetermined average value.
8. The combined surgical needle-suture device of claim 7 wherein
the predetermined average value of the rupture force for a particular
size of suture is as follows:
9. The combined surgical needle-suture device of claim 7 wherein
the cross section of the tip of the suture is reduced by at least
10% relative to the cross section of the remaining suture.
10. The combined surgical needle-suture device of claim 7 wherein
the suture is a monofilament suture.
11. The combined surgical needle-suture device of claim 7 wherein
the suture is a multifilament suture.
12. The combined surgical needle-suture device of claim 7 wherein
said suture is a non-absorbable material selected from the group
consisting of silk, nylon, polyester, polypropylene, linen and cotton.
13. The combined surgical needle-suture device of claim 7 wherein
said suture is a braided multifilament.
14. The combined surgical needle-suture device of claim 7 wherein
said suture is a monofilament.
15. The combined surgical needle-suture device of claim 7 wherein
said suture is an absorbable material selected from the group consisting
of gut and synthetic materials including polymers and copolymers
of glycolic and lactic acids.
16. The combined surgical needle-suture device of claim 15 wherein
said suture is a braided multifilament.
17. The combined surgical needle-suture device of claim 7 wherein
said suture portion is tipped with an adhesive or resinous coating.
18. The combined surgical needle-suture device of claim 7 wherein
said shrinkable tubing is manufactured from a memory metal or a
shrinkable plastic material.
19. The combined surgical needle-suture device of claim 18 wherein
said shrinkable plastic material is a polyvinylidene fluoride material.
20. The combined surgical needle-suture device of claim 7 wherein
the shank is provided with a texturized surface to facilitate gripping
by said shrinkable tubing.
21. The combined surgical needle-suture device of claim 20 wherein
the shank is scored, ribbed, or threaded in whole or in part.
22. The combined surgical needle-suture device of claim 7 wherein
the shank of reduced cross section forms a shoulder with a remainder
of said needle.
23. The combined surgical needle-suture device of claim 22 wherein
said shank is tapered in a direction towards said shoulder, such
that a distal end of said shank is of greater cross-sectional diameter
than cross-sectional diameter of said shank in a region of said
shoulder.
24. The combined surgical needle-suture device of claim 23 wherein
said shank is tapered in a direction away from said shoulder, such
that a distal end of said shank is of smaller cross-sectional diameter
than cross-sectional diameter of said shank in a region of said
shoulder.
Surgical needle description
BACKGROUND OF THE INVENTION
The present invention relates to a method for attaching a surgical
needle to a suture to provide a combined surgical needle-suture
device possessing controlled suture release characteristics and,
more particularly, to such a method in which a shrinkable tubing
is employed to secure the needle to the suture.
For many years, surgeons have employed needle-suture combinations
in which a suture or ligature is attached to the shank end of a
needle. Such needle-suture combinations are provided for a wide
variety of monofilament and braided suture materials, both absorbable
and non-absorbable, e.g., catgut, silk, nylon, polyester, polypropylene,
linen, cotton, and absorbable synthetic materials such as polymers
and copolymers of glycolic and lactic acids.
Needle-suture combinations fall into two general classes: standard
needle attachment and removable or detachable needle attachment.
In the case of standard needle attachment, the suture is securely
attached to the needle and is not intended to be separable therefrom,
except by cutting or severing the suture. Removable needle attachment,
by contrast, is such that the needle is separable from the suture
in response to a force exerted by the surgeon. Minimum acceptable
forces required to separate a needle from a suture (for various
suture sizes) are set forth in the United States Pharmacopoeia (USP).
The United States Pharmacopoeia prescribes minimum individual pull-out
forces and minimum average pull-out forces as measured for five
needle-suture combinations. The minimum pull-out forces for both
standard and removable needle-suture attachment set forth in the
United States Pharmacopoeia are hereby incorporated by reference.
One typical method for securing a suture to a needle involves providing
a cylindrical recess in the shank end of a needle and securing a
suture therein. For example, U.S. Pat. No. 1558037 teaches the
addition of a cement material to such a substantially cylindrical
recess to secure the suture therein. Additional methods for bonding
a suture within a needle bore are described in U.S. Pat. Nos. 2928395
(adhesives) and 3394704 (bonding agents). Alternatively, a suture
may be secured within an axial bore in a needle by swaging the needle
in the region of the recess. See, e.g., U.S. Pat. No. 1250114.
Additional prior art methods for securing a suture within a needle
bore include expansion of a catgut suture through the application
of heat (U.S. Pat. No. 1665216), inclusion of protruding teeth
within the axial bore to grasp an inserted suture (U.S. Pat. No.
1678361) and knotting the end of the suture to be inserted within
the bore to secure the suture therein (U.S. Pat. No. 1757129).
Methods for detachably securing a suture to a needle are also well
known. For example, U.S. Pat. Nos. 3890975 and 3980177 teach
swaging a suture within a needle bore such that the suture has a
pull-out valve of 3 to 26 ounces. Alternative detachable attachment
methods include providing a weakened suture segment (U.S. Pat. No.
3949756), lubricant tipping the end of a suture to be inserted
in the axial bore of a needle (U.S. Pat. No. 3963031) and pre-tensioning
a suture that is swaged within an axial needle bore (U.S. Pat. No.
3875946). See also, U.S. Pat. Nos. 3799169; 3880167; 3924630;
3926194; 3943933; 3981307; 4124027; and, 4127133.
Another method for attaching a suture to a needle involves the
use of tubing which is secured to the shank end of the needle and
to the suture. For example, U.S. Pat. No. 1613206 describes the
use of a tubing (preferably silver) which is secured to the shank
end of a needle and to a ligature. It is suggested that the tube
may be attached to the needle by pressure or soldering and to the
ligature by pressure or cementing. It is also suggested that the
shank of the needle be of reduced cross section and that the furthest
extremity of the reduced diameter shank section be provided with
a spike or point upon which the suture may be secured prior to tube
application.
U.S. Pat. No. 2240330 describes a tubing attachment method whereby
the tubing and suture are releasably secured to the needle. In particular,
the needle and tubing are provided with cooperating catch and abutment
means which are released one from the other by rotating the needle
90.degree. relative to the tubing (or vice versa). The tubing is
manufactured from spring-tempered carbon steel or chrome nickel
steel and is secured to the suture by heating the tubing and then
swaging to the suture.
U.S Pat. No. 3311100 relates to a flexible composite suture having
a tandem linkage. The needle is secured to a flexible suture leader
manufactured from a readily sterilizable plastic such as nylon,
linear polyethylene, isotactic polypropylene, polyester, silk or
other proteinaceous material, e.g., by inserting and crimping the
leader within an axial bore in the needle shank. The opposite end
of the suture leader is crimped within a connector sleeve of a thin
walled metal tubing, e.g., stainless steel. The opposite end of
the tubing is crimped around a stiff suture, e.g., monofilament
stainless steel.
U.S. Pat. No. 3918455 describes a needle-suture attachment wherein
a hollow suture portion is secured to the shank end of a needle
which is of reduced cross-section as compared to the remainder of
the needle.
Additional patents which describe the use of tubing to effect suture-needle
attachment include U.S. Pat. Nos. 4672734 (forming needle from
U-shaped metal plate around suture), 4359053 (silicone tubing),
3835912 (laser welding of metal tube to needle), 2814296 2802468
(chamfered tubing ends), 2302986 2240330 1981651 (needle
and tubing screw threaded), 1960117 and 1591021.
Numerous disadvantages exist with methods used heretofore to effect
needle-suture attachment. For example, those methods which involve
the formation and use of an axial bore in the shank end of the needle
require the use of expensive hole forming equipment. Moreover, it
is difficult to maintain the bore concentric with the center-line
of the needle and to control the depth (and diameter) of the bore
when drilling the needle shank, whether using conventional drilling
equipment or laser drilling. Another disadvantage is the possibility
that foreign substances may inadvertently or uncontrollably be introduced
into the needle bore, e.g., oil used during drilling or silicone
from the needle silconization process. Safeguards employed in an
attempt to prevent the introduction of such foreign materials, e.g.,
water blocking during needle silconization, are inconvenient adding
time, effort and cost to the needle production process.
Attachment processes which employ bored needle shanks also limit
the range of materials from which needles may be fabricated in a
cost effective fashion. For example, it is exceedingly difficult
to drill Series 300 stainless steel (laser drilling is required)
and, once drilled, it is difficult to swage Series 300 stainless
steel in a consistent and reliable manner. For this reason, Series
300 stainless steel is not employed for the vast majority of needled
suture products despite its advantageous combination of strength
and ductility characteristics as compared to conventionally employed
Series 400 stainless steel.
Additional disadvantages associated with needle-suture attachment
methods which employ bored needle shanks include the weakness imparted
to the bored section of the needle, particularly after swaging,
and the attendant increased possibility that the needle will fracture
in this region. It is also difficult to provide a specialized surface
finish to the needle shank to assist in needle attachment, e.g.,
a texturized surface and/or a tapered bore. Swaging equipment used
in such needle-suture attachment methods is also maintenance intensive.
Needle-suture attachment methods which have employed tubings heretofore
also exhibit numerous disadvantages. Methods which employ metal
tubings greatly diminish the flexibility of the needle-suture combination
in the attachment region. Such diminished flexibility has a deleterious
effect in many surgical procedures. Swaging of the tubing to the
needle and the suture is also undesirable in that swaging is time-consuming,
maintenance intensive, and subject to variability in attachment
force.
Moreover, needle-suture attachment methods which have employed
tubings heretofore have necessarily required the use of tubing having
an inner diameter essentially equal to the outer diameters of the
needle shank and suture tip to be attached. Too large a difference
between the aforesaid inner and outer diameters inhibits the attachment
process, and prevents a tight, secure interface between needle (and/or
suture) and tubing. The limited tolerance between the tubing inner
diameter and the needle shank/suture outer diameters in such methods
make these dimensions critical, thereby making the attachment process
more difficult and time-consuming, and increasing the likelihood
of attachment failure and/or rejected materials.
Commonly assigned, copending U.S. patent application Ser. No. 413240
filed Sept. 27 1989 of which the present application is a continuation-in-part,
describes and claims a combined surgical needle-suture device and
surgical needle-suture attachment method which overcomes the aforementioned
drawbacks of the previously known needle-suture combinations and
needle-suture attachment methods. In accordance with said application,
a combined surgical needle-suture device is provided in which a
surgical needle having a shank of reduced cross-section is attached
to a suture through a shrinkable tubing, or microferrule, which
is fitted about the needle shank and a portion of the suture. Application
of energy to the shrinkable tubing brings the tubing into engagement
with both the needle shank and the suture. The physical and chemical
characteristics of the shrinkable tubing material, the relative
diameters of the tubing, the needle shank and the suture, and the
amount of energy applied to the tubing may be controlled to provide
a needle-suture combination having a desired pull-out force. It
is thus possible to produce standard needle-suture combinations
and removable needle-suture combinations using a single attachment
process and a common inventory of materials.
Minimum average pull-out forces for various sizes combined surgical
needle-suture devices are set forth in the United States Pharmacopoeia
and are as follows:
______________________________________ Average Pull-Out Suture
Size Force/Ounces ______________________________________ 8/0 2.39
7/0 3.20 6/0 5.92 5/0 7.97 4/0 15.97 3/0 23.63 2/0 38.80 1/0 52.89
1 63.48 2 and larger 63.48 ______________________________________
U.S. Pat. No. 3875946 referred to supra, describes needle-suture
combinations said to exhibit suture pull-out values that are substantially
less than those given by the United States Pharmacopoeia as set
forth above. According to U.S. Pat. No. 3875946 employing the
procedure described therein, combined surgical needle-suture devices
can be obtained with the following average pull out forces:
______________________________________ Average Pull-Out Suture
Size Force/Ounces ______________________________________ 8/0 1-2
7/0 1-3 6/0 2-5 5/0 3-7 4/0 3-15 3/0 3-23 2/0 3-26 1/0 10-26 1 10-26
2 and larger 10-26 ______________________________________
These pull-out forces are obtained by prestressing the suture,
i.e., by applying tension to the suture after the tip of the suture
has been inserted into an axial bore, or recess, formed in the blunt
end of the needle and the needled suture has been swaged so that
the force required to pull the suture out of the recess exceeds
the minimum limits on needle attachment set forth in the United
States Pharmacopoeia but is less than the actual tensile strength
of the suture used. As the suture is pulled from the needle during
application of the tensioning force, the force required to move
the suture relative to the swaged section decreases. When the tensioning
force required to move the end of the suture relative to the needle
recess drops to the desired pull-out value, the tension is released.
The foregoing procedure is said to permit better control of the
resulting needle-suture device in that the force required to separate
a suture of a particular size from its attached needle is uniform.
In the approach to achieving controlled needle-suture separation
described in aforementioned U.S. Pat. No. 3926194 the contents
of which are incorporated by reference herein, a suture having a
reduced diameter or cross section at its tip is inserted into the
recess formed in the blunt end of the needle. This reduced suture
material region results in a rupture strength which is lower than
the rupture strength in other portions of the suture and lower than
the force necessary to pull the suture tip out of the needle recess.
The rupture strength can be controlled to a value which results
in the separation of the needle from the suture by a sharp tug which
can fall within the range of average pull-out forces set forth above,
i.e., 1 to 26 ounces depending on suture size.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a method
for attaching a surgical needle to a suture to provide a combined
surgical needle-suture device exhibiting a predetermined range of
average rupture force to effect separation of the needle from the
suture which comprises:
a) providing a surgical needle having a shank end of reduced cross-section
and a suture having a region of reduced cross section at its tip;
b) placing a shrinkable tubing around the reduced diameter shank
of the needle and the tip of the suture having the region of reduced
cross section with a portion of the reduced cross section region
extending beyond the shrinkable tubing; and,
c) applying energy to the shrinkable tubing to bring the tubing
into engagement with the needle shank and suture thereby providing
a combined surgical needle-suture device in which the force required
to achieve rupture of the suture at its region of reduced cross
section with consequent separation of the needle from the suture
falls within a predetermined average value.
In addition to the foregoing surgical needle-suture attachment
method, the present invention includes the resulting combined surgical
needle-suture device.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more apparent from the following
detailed description taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a side cross-sectional view of a surgical needle possessing
a shank of reduced diameter and a suture possessing a region of
reduced diameter at its tip with a shrinkable tubing positioned
around the needle shank and the suture tip (prior to engagement
of the tubing with the needle and suture);
FIG. 2 is a side cross-sectional view of the needle and suture
combination of FIG. 1 following shrinking of the tubing to effect
engagement of the needle and suture;
FIG. 3 is a side view of the combined surgical needle-suture device
of FIG. 2;
FIG. 4 is a side view of an alternative embodiment of the present
invention in which the shank of the needle is scored;
FIG. 5 is a side view of an alternative embodiment of the present
invention in which the needle shank is ribbed;
FIG. 6 is a side view of an alternative embodiment of the present
invention in which the needle shank is threaded;
FIG. 7 is a side view of an alternative embodiment of the present
invention in which the needle shank is flared in a direction away
from a remainder of the needle; and
FIG. 8 is a side view of an alternative embodiment of the present
invention in which the needle shank is tapered in a direction towards
the remainder of the needle.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a combined surgical needle-suture
method and resulting surgical needle-suture device featuring controlled
suture release. The invention has application to any suture material
whether absorbable or non-absorbable, natural or synthetic, braided
or monofilament, and to any needle material and configuration whether
straight or curved.
Referring to FIGS. 1-3 needle 10 has a reduced cross-sectional
diameter at its shank end 12 relative to the remainder of needle
14. The diameter of shank end 12 can be reduced by any conventional
means, e.g., by machining on a lathe. Typically, shank end 12 has
a diameter from 10 to 65% smaller than the remaining portion 14
of the needle, and preferably from 25 to 50% smaller. It is also
possible to provide shank end 12 with a texturized surface to facilitate
gripping by shrinkable tubing 20. For example, shank end 12 can
be scored, ribbed or threaded, in whole or in part (FIGS. 4-6 respectively).
It may also be desirable to taper shank end 12 such that its butt,
or distal, end 16 is of greater cross-sectional diameter than the
cross-sectional diameter of shank end 12 in the region of shoulder
18 or vice versa (FIGS. 7 and 8 respectively). Shank end 12 is
placed within tubing 20 as shown in FIG. 1.
The sutures suitable for use in the preparation of the notched
needle-suture combination herein include both monofilaments and
multifilament structures such as braided, twisted and covered sutures.
Suitable suture materials include collagen (including catgut and
extruded collagen), silk, cotton, linen and synthetic polymers including
nylon, polypropylene and polyesters such as polyethylene terephthalate
and homopolymers and copolymers of lactide and glycolide.
With multifilament sutures, the entire cross-sectional area of
the suture is not made up of suture material since there is, of
necessity, some free space between the suture strands. The proportion
of the total cross-sectional area of a suture which is occupied
by the suture strands is called "suture density". As disclosed
is aforementioned U.S. Pat. No. 3926194 the suture densities
of braided structures and suture densities in general are calculated
from the volume of the sample of the suture and the volume of the
fiber therein in accordance with the formula: ##EQU1## in which
S is the volume of the suture, F is the volume of the fiber, and
D is the suture density.
For convenience, it is best to determine volumes in samples at
fixed lengths of 9000 meters, r 9.times.10.sup.5 centimeters. This
is convenient because fiber denier is defined as weight in grams
per 9000 meters. At this length, the volume of the suture in cubic
centimeters is: ##EQU2## where d is the diameter of the suture in
centimeters. The volume in cubic centimeters of the individual fibers,
F. at the same length would be: ##EQU3## or ##EQU4## where r is
the density of the suture material in grams per cubic centimeter.
As further disclosed in U.S. Pat. No. 3926194 the load at which
reduced tip suture 30 will rupture within its region of reduced
diameter can be estimated from the equation: ##EQU5## wherein
P is the rupture load, in pounds;
T is the tensile strength of the suture material, in pounds per
square inch;
A is the area, in square inches, of the reduced diameter portion
of the suture;
D is the suture density of the suture, being unity in the case
of a monofilament; and,
K is a constant factor, empirically determined and representing
the degree of weakening at the reduced tip portion of the suture
over and above the weakening to be expected from its reduced area.
The extent of the diameter, or cross-sectional area, reduction
of tip region 31 will be such as to result, following attachment
of the needle and suture as described below, in an average rupture
force within a predetermined range. For example, a suitable range
of rupture force in ounces and in pounds for various suture sizes
can be as follows:
______________________________________ Average Rupture Force Suture
Size Ounces Pounds ______________________________________ 8/0 1-2
.0625-.125 7/0 1-3 .0625-.1875 6/0 2-5 .125-.3125 5/0 3-7 .1875-.4375
4/0 3-15 .1875-.9375 3/0 3-23 .1875-1.4375 2/0 3-26 .625-1.625 1/0
10-26 .625-1.625 1 10-26 .625-1.625 2 and larger 10-26 .625-1.625
______________________________________
Selecting, e.g., an average rupture value P of 0.8 pounds provides
leeway for differences in individual sutures and for differences
in the reduction of their tips and assures rupture strengths within
the desired range for most of the reduced tip sutures. The value
of constant factor K can be experimentally determined for each suture
material by comparing the actual breaking strength of a reduced
diameter suture to the strength calculated on the basis of the tensile
strength of the material and the diameter of the reduced tip. For
example, a sample of chromic catgut is known to have a tensile strength
of from 45000-65000 psi with an average tensile strength of 55000
psi. A size 5/0 catgut would accordingly be expected to have a breaking
strength of 1.85 pounds. When the tip of a 2/0 catgut is reduced
to size 5/0 however, the breaking strength is determined to be
1.4 pounds, and a value for K is computed as 1.85/1.4 or 1.3. Values
of K for other suture materials are readily determined in a like
manner.
In general, tip 31 will be reduced in cross section by at least
about 10% relative to remaining region 32 of suture 30. Reduction
of the material in the tip region of suture 30 to provide the region
of reduced cross-section at tip 31 can be accomplished in a variety
of ways, e.g., as described in U.S. Pat. No. 3926194. Thus, the
suture tip can be ground down to the desired diameter and to the
desired length of the cutaway portion. The grinding can be carried
out by known techniques and in known equipment such as in a jeweler's
lathe or in a grinding machine as described in British Patent No.
1180276. Another tip reduction method which is applicable to monofilament
sutures is to produce a continuous monofilament with spaced segments
of reduced diameter, each such segment being cut to provide two
reduced diameter suture ends. A continuous filament of this type
can be prepared by providing pulsation during the extrusion of the
monofilament, or periodic partial slowdown of the rate of polymer
feed to the extrusion orifices.
The procedure for attaching needle 10 to suture 30 employing shrinkable
tubing 20 will now be described.
Suture 30 is positioned within shrinkable tubing 20 with suture
tip 31 abutting or separated a short distance from distal end 16
of shank 12. Prior to insertion into tubing 20 tip region 31 of
suture 30 can, if desired, be tipped with an adhesive or resinous
agent as disclosed, e.g., in Canadian Patent No. 1009532 to prevent
brooming, particularly for multifilament braided sutures, and/or
to facilitate attachment of the needle using the shrinkable tubing
of the present invention.
After shrinkable tubing 20 is placed around shank end 12 of needle
10 and suture tip region 31 energy is applied to tubing 20. In
response to this energy, tubing 20 contracts or shrinks and engages
shank end 12 and suture 30. The overall length of tubing 20 may
also be affected by the application of energy, e.g., the length
of tubing 20 may reduce. Thus, the shrinking of tubing 20 brings
the inner surface of tubing 20 into engagement with shank end 12
and suture 30 thereby securing suture 30 to needle 10. Suitable
energy sources include heat (convective or conductive), radiation,
microwave energy, etc.
As shown in FIGS. 1-2 shrinkable tubing 20 is simultaneously placed
around both suture 30 and shank end 12 of needle 10 in one embodiment
of the present invention. It is preferable, however, to sequentially
secure tubing 20 to the shank end 12 of needle 10 and thereafter
to tip 31 of suture 30. Thus, in a preferred embodiment of the present
invention, shrinkable tubing 20 is initially secured to shank end
12 through the localized application of energy to tubing 20 in the
region surrounding shank end 12. After tubing 20 has been brought
into engagement with shank end 12 tip region 31 of suture 30 is
inserted into tubing 20 and additional energy is applied thereto.
Sequential shrinkage of tubing 20 makes it possible to vary the
amount of energy used in securing tubing 20 to shank end 12 and
suture tip 31 respectively, and to limit the exposure of suture
30 to energy during the attachment process. It may also be desirable
to cool suture 30 in the region outside tubing 20 to prevent any
undesirable degradation thereof, e.g., employing a cold air curtain.
As shown in FIGS. 2-3 the shrinkage of tubing 20 typically compresses
suture 30 to some extent. This is particularly true where the suture
is a braided, multifilament material having void spaces in its structure.
For example, tubing 20 may compress suture 30 by as much as 30 to
35% for a braided, synthetic absorbable suture and by a minimal
amount for a relatively stiff material such as a monofilament surgical
gut.
Shrinkable tubing 20 can be manufactured from any material which
shrinks, i.e., reduces in diameter, in response to the application
of energy. Suitable materials include "memory metals,"
e.g., nickel-titanium mixtures, nickel-iron-titanium mixtures, or
copper based materials, as are well known in the art (see, e.g.,
U.S. Pat. Nos. 3759552 3801954 4198081 and 4773680),
and shrinkable plastic materials, such as polyvinylidene fluoride
materials available from Raychem Corporation, Menlo Park, California,
under the tradename Kynar. In the case of shrinkable plastic materials,
the tubing is typically extruded such that the inner diameter is
less than the final desired inner diameter, i.e., the inner diameter
of the tubing after energy application in the attachment method
of the present invention. Thereafter, the extruded tubing is expanded
radially outward through radial expansion means to provide a tubing
of expanded inner diameter as shown, for example, by tubing 20 in
FIG. 1. Such plastic tubing is thus adapted to shrink, or "recover",
to its original extruded inner diameter in response to the application
of a predetermined amount of energy.
The amount of energy applied to the tubing to effect the desired
attachment, i.e., diameter reduction, depends upon the chemical
characteristics of the tubing material and the relative dimensions
of the tubing, the shank end of the needle and the suture. For example,
one polyvinylidene fluoride material available from Raychem Corporation
(RT-850) shrinks at temperatures greater than 175.degree. C. and
is adapted to recover to about 50% of its radially expanded inner
diameter. In such case, tubing 20 can be brought into engagement
with shank end 12 of needle 10 and tip 31 of suture 30 either simultaneously
or sequentially, by heating tubing 20 to a temperature above 175.degree.
C. Tubing 20 can be heated through contact with a hot gas stream
or with heated dies, or by other heating means. Typically, the outer
diameters of shank end 12 and suture tip region 31 (in the region
inserted into tubing 20) are greater than the fully recovered diameter
of tubing 20 e.g., greater than 50% of the initial inner diameter
of tubing 20 for the RT-850 material such that tubing 20 engages
shank end 12 and suture tip 31. It is preferred that the attachment
conditions be controlled such that the tubing remains secured to
the needle once the suture is detached.
The foregoing surgical needle-suture attachment procedure has many
advantages over previous attachment methods. Machining of the needle
to provide a reduced diameter needle shank is much easier and more
controllable than drilling processes, and permits the use of needle
alloys which have previously been impractical, e.g., Series 300
stainless steel and MP35N (available from SPS Technologies). These
heretofore impractical alloys have advantageous strength and ductility
characteristics as compared to conventionally used Series 400 stainless
steels. Moreover, an unreliable, expensive and maintenance intensive
swaging process is replaced by a sterile, controllable and relatively
inexpensive energy supply. The tubing used in the present invention
may be color coded to designate suture material, standard versus
detachable attachment, etc., particularly where a plastic tubing
is employed.
The attachment method is also much more efficient from a processing
and inventory control standpoint. For example, the tubing can be
removed from a needle and the needle attached to a fresh suture
as may be the case where the suture and/or attachment properties
of the initial suture-needle combination are outside specifications.
In many instances, the suture can also be recovered and reused thereby
greatly reducing processing waste. The range of acceptable suture
diameters is greatly expanded due to the ability of the tubing to
recover or shrink to varying degrees thereby minimizing the likelihood
that suture production will be rejected for inability to attach
several needle sizes because the shrinkable tubing is capable of
recovering or shrinking to varying degrees. This greatly simplifies
inventory considerations. Moreover, the needle-suture combinations
are atraumatic and advantageously exhibit flexibility in the attachment
region.
While the above description contains many specifics, these specifics
should not be construed as limitations on the scope of the invention,
but merely as exemplifications of preferred embodiments thereof.
Those skilled in the art will envision many other possible variations
that are within the scope and spirit of the invention as defined
by the claims appended hereto.
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