Surgical needle abstract
A combined surgical needle-suture device and a method for manufacturing
the device employ a shrinkable tubing to connect the needle to a
suture possessing a weakened segment. Separation of the needle from
the suture is achieved by providing a weakened suture segment and
applying a rupturing force to the suture within a predetermined
range.
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 which comprises:
a) providing a surgical needle possessing a shank end of reduced
cross-section and a suture possessing a weakened segment adjacent
its tip region;
b) placing a shrinkable tubing around the reduced diameter shank
end of the needle and the tip of the suture such that the weakened
segment of the suture is positioned beyond, but proximate to, the
tubing; and,
c) applying energy to the shrinkable tubing to bring the tubing
into engagement with the needle shank and the tip of suture thereby
providing the combined surgical needle-suture device.
2. The method of claim 1 wherein the weakened segment of the suture
is obtained by irradiating the suture in the region of the segment
with a suture-weakening dosage of radiation.
3. The method of claim 2 wherein the average force required to
rupture the irradiation-weakened suture segment is within the following
range for the suture indicated
4. The method of claim 2 wherein the suture is fabricated from
a fiber-forming material selected from the group consisting of cellulose,
cellulose ester, polyolefin, vinyl polymer, acrylic polymer, lactide
homopolymer, lactide copolymer, glycolide polymer and glycolide
copolymer.
5. The method of claim 1 wherein the suture is a monofilament suture.
6. The method of claim 1 wherein the suture is a braided suture.
7. The method of claim 1 wherein the weakened segment of the suture
is obtained by forming a suture-weakening notch in the segment.
8. The method of claim 7 wherein the average rupture force required
to rupture the notch-weakened suture segment is within the following
range for the suture indicated
9. The method of claim 7 wherein the suture is fabricated from
a fiber-forming material selected from the group consisting of collagen,
silk, cotton, linen, nylon, polypropylene, polyethylene terephthalate,
lactide homopolymer, lactide copolymer, glycolide homopolymer and
glycolide copolymer.
10. The method of claim 1 wherein the shrinkable tubing is a memory
metal or shrinkable plastic.
11. The method of claim 1 wherein the shrinkable tubing is a shrinkable
polyvinylidene fluoride material.
12. The method of claim 1 wherein the step of applying energy further
comprises applying energy to shrink the shrinkable tubing into engagement
with the needle shank and thereafter applying energy to shrink the
shrinkable tubing into engagement with the tip of the suture.
13. A combined surgical needle-suture device which comprises:
a) a surgical needle possessing a shank end of reduced cross-section;
b) a suture possessing a weakened segment adjacent its tip region;
c) a shrinkable tubing around the reduced diameter shank end of
the needle and the tip of the suture such that the weakened segment
of the suture is positioned beyond, but proximate to the tubing;
the tubing being shrunk around the reduced diameter shank end of
the needle and the tip region of the suture thereby providing the
combined surgical needle-suture device.
14. The combined surgical needle-suture device of claim 13 wherein
the weakened segment of the suture is obtained by irradiating the
suture in the region of the segment with a suture-weakening dosage
of radiation.
15. The combined surgical needle-suture device of claim 14 wherein
the average force required to rupture the irradiation-weakened suture
segment is within the following range for the suture indicated
16. The combined surgical needle-suture device of claim 14 wherein
the suture is fabricated from a fiber-forming material selected
from the group consisting of cellulose, cellulose ester, polyolefin,
vinyl polymer, acrylic polymer, lactide homopolymer, lactide copolymer,
glycolide polymer and glycolide copolymer.
17. The combined surgical needle-suture device of claim 13 wherein
the suture is a monofilament suture.
18. The combined surgical needle-suture device of claim 13 wherein
the suture is a braided suture.
19. The combined surgical needle-suture device of claim 13 wherein
the weakened segment of the suture is obtained by forming a suture-weakening
notch in the segment.
20. The combined surgical needle-suture device of claim 19 wherein
the average rupture force required to rupture the notch-weakened
suture segment is within the following range for the suture indicated
21. The combined surgical needle-suture device of claim 19 wherein
the suture is fabricated from a fiber-forming material selected
from the group consisting of collagen, silk, cotton, linen, nylon,
polypropylene, polyethylene terephthalate, lactide homopolymer,
lactide copolymer, glycolide homopolymer and glycolide copolymer.
22. The combined surgical needle-suture device of claim 13 wherein
the shrinkable tubing is a memory metal or shrinkable plastic.
23. The combined surgical needle-suture device of claim 13 wherein
the shrinkable tubing is a shrinkable polyvinylidene fluoride material.
24. The combined surgical needle-suture device of claim 13 wherein
the shank end of the needle is provided with a texturized surface
to facilitate gripping by said shrinkable tubing.
25. The combined surgical needle-suture device of claim 24 wherein
the shank end of the needle is scored, ribbed or threaded, in whole
or in part.
26. The combined surgical needle-suture device of claim 13 wherein
said shank end of reduced cross-section forms a shoulder with a
remainder of said needle.
27. The combined surgical needle-suture device of claim 26 wherein
said shank end is tapered to expand in a direction away from said
shoulder, such that a distal end thereof is of greater cross-sectional
diameter than cross-sectional diameter in a region of said shoulder.
28. The combined surgical needle-suture device of claim 26 wherein
said shank end is tapered to expand in a direction towards said
shoulder, and that a distal end thereof is of smaller cross-sectional
diameter than cross-sectional diameter 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 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 micro-ferrule, 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 of 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.
Other approaches to achieving controlled needle-suture separation
are described in aforementioned U.S. Pat. Nos. 3943933 and 3949756
the contents of which are incorporated by reference herein. According
to U.S. Pat. No. 3943933 a needle-suture combination provided
with a radiation-weakened suture segment adjacent the point of attachment
of the suture to the needle permits a surgeon to separate the needle
from the suture by a sharp tug. In U.S. Pat. No. 3949756 a suture
provided with a weakened segment in the form of a notch adjacent
the point of attachment of the suture to the needle likewise permits
separation of the needle from the suture by a sharp tug.
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 which comprises:
a) providing a surgical needle possessing a shank end of reduced
cross-section and a suture possessing a weakened segment adjacent
its tip region;
b) placing a shrinkable tubing around the reduced diameter shank
end of the needle and the tip of the suture such that the weakened
segment of the suture is positioned beyond, but proximate to, the
tubing; and,
c) applying energy to the shrinkable tubing to bring the tubing
into engagement with the needle shank and the tip of suture thereby
providing the combined surgical needle-suture device.
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 reduced shank and a suture possessing a radiation-weakened segment
adjacent its tip region with a shrinkable tubing positioned around
the reduced shank of the needle and the tip of the suture (prior
to engagement of the tubing with the needle and suture);
FIG. 2 is a side cross-sectional view of the needle-suture combination
of FIG. 1 following shrinking of the tubing to effect engagement
of the needle shank and the suture tip.
FIG. 3 is a side view of the combined surgical needle-suture device
of FIG. 2;
FIG. 4 is a side view of another embodiment of the combined surgical
needle-suture device of this invention in which the weakened suture
segment is provided as a pair of opposed notches;
FIG. 5 is a side of an alternative embodiment of the present invention
in which the needle shank is scored;
FIG. 6 is a side view of an alternative embodiment of an alternative
embodiment of the present invention in which the needle shank is
ribbed;
FIG. 7 is a side view of an alternative embodiment of the present
invention in which the needle shank is threaded;
FIG. 8 is a side view of an alternative embodiment of the present
invention in which the needle shank is tapered to expand in a direction
away from a remainder of said needle; and
FIG. 9 is a side view of an alternative embodiment of the present
invention in which the needle shank is tapered to expand 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. 5-7 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. 8 and 9 respectively). Shank end 12 is
placed within tubing 20 as shown in FIG. 1.
Suture 30 possesses a tip region 31 for subsequent engagement by
tubing 20 and adjacent to the tip region, a radiation-weakened segment
32 throughout region A of the suture. As disclosed in aforementioned
U.S. Pat. No. 3943933 the load at which suture 30 will rupture
at its radiation-weakened segment 31 i.e., within region A, can
be made to vary from 3 to 26 ounces depending upon the size of the
suture.
The radiation-weakening of suture segment 32 can be achieved by
exposure of region A of the suture which is adjacent its tip region
31 and is at or just beyond the end of shrinkable tubing 20 to a
sufficient dose of beta or gamma radiation to reduce the tensile
strength in the irradiated segment to a desired value. This irradiation
procedure will ordinarily be accomplished prior to providing the
needle-suture configuration shown in FIG. 1. The necessary dose,
or exposure, to achieve the desired weakening of suture segment
32 is dependent on the nature of the suture material and its diameter
and upon the degree of weakening desired. In the case of sutures
of small diameter which have rupture values within the desired range,
radiation-weakening is, of course, unnecessary.
For suture materials readily susceptible to radiation-weakening
in sutures of small diameters and requiring only slight weakening
to be within the desired range of rupture values, useful radiation-weakening
may be achieved with radiation doses as low as about 5 megarads.
For suture materials which are more difficult to weaken by irradiation
in sutures of larger diameter, it may be necessary to provide a
dose of 200 megarads, or more, before the rupture strength of the
suture is reduced to a practical value for easy separation of the
needle from the suture.
Thus, with increased radiation dosage, radiation-weakened segment
31 can be made to undergo rupture within the following average range
of force for the suture size indicated:
______________________________________ 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
______________________________________
The radiation used for localized suture weakening in accordance
with this invention can comprise either a high energy electron beam,
e.g., of the type produced by a linear electron accelerator, or
a high energy beam of electromagnetic radiation of extremely short
wave length, e.g., of the type generated by cobalt-60 or by a high
energy X-ray generator. These forms of radiation are conventionally
referred to as "beta" and "gamma" radiation,
respectively. An electron accelerator capable of delivering a large
dose of energy in a short time is preferred.
Radiation generators suitable for use in this invention include
those which have been used by manufacturers of needle-suture combinations
for sterilization purposes. For localized suture weakening, however,
the arrangement is altered so that the suture passes transversely
across the path of the beam instead of longitudinally, thereby isolating
the radiation effect to a small segment of the suture length, and
the arrangement is also modified to permit a plurality of passes
of the suture segment to be weakened under the radiation beam and
to thereby subject the segment to the cumulative dosage of such
a plurality of passes. The sutures may be aligned parallel to each
other in a grooved holder encased within a lead casing or other
suitable shielding except for an exposed open slot which permits
the radiation to pass through the casing and act upon a short segment
of each suture at or near its junction to its needle.
Fiber-forming materials suitable for sutures which are useful in
the practice of this embodiment of the invention include cellulose
and cellulose esters including cotton, linen, viscose rayon and
cellulose acetate; polyolefins including polypropylene and polyethylene;
vinyl polymers including polyvinyl alcohol, polyvinyl acetate and
polyvinylidene chloride; acrylic polymers such as polyacrylonitrile
and homopolymers and copolymers of lactide and glycolide.
As an alternative to a radiation-weakened suture segment and as
shown in FIG. 4 suture 30 can be provided with a mechanically weakened
segment 32 e.g., provided as a pair of opposed notches 17 and 19
as described in U.S. Pat. No. 3949756. Notching or similar mechanical
discontinuities can be formed in suture segment 32 by application
of at least one cutting edge thereto or by application of at least
one abrasive surface to the suture surface at the desired location
with relative movement between the abrasive and suture surfaces.
According to U.S. Pat. No. 3949756 a preferred notching device
has two parallel blades facing each other and firmly set with a
measured gap between them. As the suture is moved transversely to
the blade direction, two straight notches are formed facing each
other with a preset width of unnotched suture between them.
In another embodiment, also described in U.S. Pat. No. 3949756
the needle-suture combination is held within a groove and against
the bed thereof. A knife-edge is moved transversely into the area
of the groove with a stroke that is restricted by a stop so that
a desired distance is maintained between the bed of the groove and
the end of the knife stroke whereby a single notch is formed on
one side of the suture and a controlled portion of the suture on
the opposite side remains uncut, or unnotched.
In yet other embodiments, notching is achieved in a similar manner
except that a pair of rotating abrasive wheels or a single rotating
abrasive wheel is used in place of the knife edges, or knife edge(s).
Other embodiments provide for notching about the periphery of suture
30 by rotating the suture in contact with a knife edge or with a
grinding wheel until a circumferential notch of the desired depth
is formed.
The sutures suitable for use in the preparation of the notched
needle-suture combination of FIG. 4 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.
When suture 30 is notched, the remaining strength of the suture
is less than would be expected if the strength and cross-sectional
areas were directly proportional. Usually, the rupture strength
of the suture at the notched segment is only about 1/2.5 to about
1/2.0 times the rupture strength that would be expected based on
the relative areas of the original suture cross section and the
cross section of the notched portion of the suture at the location
of the notch or notches.
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" and generally
runs in braided sutures, for example, from about 0.70 to about 0.95
and most usually from about 0.80 to about 0.92.
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 herein 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## where r is the density
of the suture material in grams per cubic centimeter. The load at
which a notched suture will rupture may be estimated from the equation:
##EQU4## 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, remaining unnotched at the notched
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, initially determined empirically for each
suture material and represents the degree of weakening at the notched
portion of the suture over and above the weakening to be expected
from its reduced area. As a useful approximation, K may be taken
at values in the range of 2.0 to 2.5 for natural and synthetic polymeric
suture materials.
As in the case of the irradiated suture segment embodiment of FIGS.
1-3 it is usually desired that the notch-weakened suture of FIG.
4 be rupturable at its notched portion by a force of from about
1 ounce to about 26 ounces, or from about 0.0625 to about 1.625
pounds, and these limits may be inserted in the above equation as
the limiting values for rupture load P. Selecting an average value
for P of 0.8 pounds provides leeway for differences in individual
sutures and for difference in their notching and assures rupture
strengths within the desired range for most of the notched sutures.
In general, the specific rupture values for the notch-weakened
suture can be the same as those for the irradiated suture as set
forth above.
Returning to FIG. 1 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 and weakened suture segment 32 positioned
at, or a short distance beyond, the end of tubing 20. As shown in
FIG. 1 suture 30 may initially be of uniform cross-section throughout
its length. Alternatively, tip region 31 of suture 30 i.e., the
region inserted into tubing 20 may be of reduced cross-section
relative to the remainder of suture 30 e.g., by tipping the suture
tip with an adhesive or resinous tipping agent while suture 30 is
under tension. (See, e.g., Canadian Patent No. 1009532.) Resin
tipping may be desirable to prevent brooming of the suture, particularly
in the case of multifilament braided sutures, and/or to rigidify
the end of the suture to facilitate its handling during attachment.
Reducing the diameter of suture tip 31 as by tipping under tension,
may be desirable to allow a suture of larger diameter, i.e. a suture
diameter equal to the diameter of the needle to which it is attached,
to be more efficiently attached to the needle using the shrinkable
tubing of the present invention. It is not necessary according to
the present invention, however, to reduce the diameter of suture
tip region 31 to efficiently attach needle 10 to suture 30. Indeed,
it may be possible or desirable to apply a tipping agent to prevent
brooming without reducing suture diameter. As shown in FIG. 1 shrinkable
tubing 20 initially has an inner diameter that is larger than the
outer diameter of suture tip region 31 thereby minimizing the importance
of suture tipping.
After shrinkable tubing 20 is placed around shank end 12 of needle
10 and tip region 31 of suture 30 energy is applied to tubing 20.
In response to this energy, tubing 20 contracts or shrinks and engages
shank end 12 and suture tip 31. 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 tip 31 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 tip 31 and shank end 12 of needle 10 in one embodiment
of the present invention. It is preferable, however, to sequentially
secure tubing 20 to needle 10 and suture tip 31. 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 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., with a cold air curtain.
As shown in FIGS. 2-4 the shrinkage of tubing 20 typically compresses
tip region 31 of suture 30 to some extent. This is particularly
true where the suture is a braided, multi-filament material having
void spaces in its structure. For example, tubing 20 may compress
suture tip 31 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 and 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 suture tip 31 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 31 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,
e.g., in instances 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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