Surgical needle abstract
A non-magnetic surgical needle. The needle is made from Type 316
stainless steel or ERSTE 4456CA stainless steel and is work hardened
to have mechanical properties substantially equivalent to a surgical
needle made from conventional magnetic stainless steel. The needle
is useful in the magnetic field of a magnetic resonance imaging
diagnostic apparatus.
Surgical needle claims
We claim:
1. A non-magnetic surgical needle comprising an elongated member
having a distal piercing tip and a proximal suture mounting end,
said needle comprising Type 316 stainless steel, wherein said needle
is work-hardened and has the following mechanical characteristics:
a modulus of elasticity (E) of at least 25.times.10.sup.6 pounds
per square inch;
an ultimate tensile strength of at least 250000 pounds per square
inch;
a yield strength of at least 200000 pounds per square inch;
a bending strength of about 7.5.times.10.sup.-5 inch-pounds to
about 8.8 inch-pounds; and,
sufficient ductility to such that the needle can be effectively
be bent from a resting shape through an arc of 90 degrees, and rebent
in the reverse direction an additional 90 degrees back to the resting
shape,
wherein said needle is non-magnetic in the magnetic field of a
1.5 Telsa magnet.
2. A non-magnetic surgical needle comprising an elongated member
having a distal piercing tip and a proximal suture mounting end,
said needle comprising ERSTE Type 4456 CA stainless steel alloy,
wherein said needle is work hardened and has the following mechanical
characteristics:
a modulus of elasticity (E) of at least 25.times.10.sup.6 pounds
per square inch;
an ultimate tensile strength of at least 250000 pounds per square
inch;
a yield strength of at least 200000 pounds per square inch;
a bending strength of about 7.5.times.10.sup.-5 inch pounds to
about 8.8 inch-pounds; and,
sufficient ductility to such that the needle can be effectively
be bent from a resting shape through an arc of 90 degrees, and rebent
in the reverse direction an additional 90 degrees back to the resting
shape,
wherein said needle is non-magnetic in the magnetic field of a
1.5 Telsa magnet.
3. A method of suturing tissue in the magnetic field of an MRI
diagnostic unit, said method comprising:
passing a surgical needle and attached suture through tissue a
sufficient number of times to effectively approximate the tissue,
said surgical needle comprising:
a non-magnetic surgical needle having an elongated member having
a distal piercing tip and a proximal suture mounting end, said needle
comprising Type 316 stainless steel, wherein said needle is work
hardened and has the following mechanical characteristics:
a modulus of elasticity (E) of at least 25.times.10.sup.6 pounds
per square inch;
an ultimate tensile strength of at least 250000 pounds per square
inch;
a yield strength of at least 200000 pounds per square inch;
a bending strength of about 7.5.times.10.sup.-5 inch-pounds to
about 8.8 inch-pounds; and,
sufficient ductility to such that the needle can be effectively
be bent from a resting shape through an arc of 90 degrees, and rebent
in the reverse direction an additional 90 degrees back to the resting
shape,
wherein said needle is non-magnetic in the magnetic field of a
1.5 Telsa magnet.
4. A method of suturing tissue in the magnetic field of an MRI
diagnostic unit, said method comprising:
passing a surgical needle and attached suture through tissue a
sufficient number of times to effectively approximate the tissue,
said surgical needle comprising:
a non-magnetic surgical needle having an elongated member having
a distal piercing tip and a proximal suture mounting end, said needle
comprising ERSTE 4456 CA stainless steel alloy, wherein said needle
is work hardened and has the following mechanical characteristics:
a modulus of elasticity (E) of at least 25.times.10.sup.6 pounds
per square inch;
an ultimate tensile strength of at least 250000 pounds per square
inch;
a yield strength of at least 200000 pounds per square inch;
a bending strength of about 7.5.times.10.sup.-5 inch-pounds to
about 8.8 inch-pounds; and,
sufficient ductility to such that the needle can be effectively
be bent from a resting shape through an arc of 90 degrees, and rebent
in the reverse direction an additional 90 degrees back to the resting
shape,
wherein said needle is non-magnetic in the magnetic field of a
1.5 Telsa magnet.
Surgical needle description
TECHNICAL FIELD
The field of art to which this invention relates is surgical needles,
in particular, non-magnetic stainless steel surgical needles.
BACKGROUND OF THE INVENTION
The recent use of Magnetic Resonance Imaging (MRI) diagnostic equipment
has provided the medical professional with an important, non-invasive
diagnostic tool. Magnetic Resonance Imaging operates by placing
a patient in a strong magnetic field. The magnetic field excites
the protons in tissue to their resonant frequency. Gradient fields
tune the frequencies for special differentiation. Radio frequency
signals are then transmitted through the tissue to detect resonance
differences that distinguish tissue types to make up an image.
Heretofore, it has been difficult to view real time diagnostic
images during surgery. X-ray, ultrasound and other forms of imaging
all have significant limitations. for most surgical procedures,
surgeons had access only to images taken at some time prior to the
surgery, hence limiting their usefulness. Advances in the design
of MRI equipment have made it possible for a surgeon to stand inside
the Magnetic Resonance (MR) magnet and perform surgery while viewing
a real time image of the anatomy of interest. Accurate location
of internal anatomical structures is important in many surgical
procedures, including neurological and gynecological lesion biopsy,
orthopaedic endoscopy, laparoscopy, and catheterizations.
Typical surgical procedures already being performed while the patient
is in an MRI unit to provide precise visualization include craniotomies
in neurosurgery, laminectomies in orthopaedics, and endoscopic sinus
procedures in plastic surgery. Other procedures under development
include laparoscopies and thoracoscopies. In most of these procedures
there is a need to perform suturing as part of the surgical procedure.
However, special non-magnetic medical devices and surgical needles
must be used because of the extreme strength of the magnetic field
in the MRI unit, which can dislodge or otherwise disturb the position
of magnetic objects. Conventional stainless steel surgical needles
cannot be used in an MRI procedure since they are magnetic. There
is a need in this art for non-magnetic surgical needles which can
be used in the magnetic field of an MRI.
Non-magnetic surgical needles are known in this art, but are know
to have disadvantages. For example, Japanese Patent JP 03284264
A2 911213 discloses a non-magnetic ceramic surgical needle for use
in a magnetic resonance imaging magnetic field. However, it is known
that such needles are brittle and do not have the mechanical characteristics
of conventional stainless steel surgical needles. Non-magnetic needles
made from Nickel-Titanium alloys are disclosed in U.S. Pat. No.
5219358. Such needles are expensive and difficult to manufacture
and may not have the desired physical characteristics. In addition,
non-magnetic needles made from Tungsten are disclosed in U.S. Pat.
No. 5415707. Such needles are difficult to manufacture.
There is a need in this art for non-magnetic stainless steel surgical
needles having the mechanical characteristics of conventional stainless
steel needles which can be used in MRI magnetic fields.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to provide
a non-magnetic stainless steel surgical needle which can be used
in the magnetic field of an MRI diagnostic unit.
It is yet a further object of the present invention to provide
a surgical needle which is non-magnetic and which is made from Type
316 stainless steel alloy or ERSTE Type 4456 CA stainless steel
alloy.
It is still yet a further object of the present invention to provide
a surgical needle made from Type 316 stainless steel alloy or ERSTE
Type 4456 CA stainless steel alloy having the mechanical characteristics
of a surgical needle made from conventional stainless steel alloys.
Accordingly, a nonmagnetic surgical needle is disclosed. The surgical
needle has an elongated body, a distal piercing point, and a proximal
suture mounting end. The surgical needle is made from Type 316 stainless
steel alloy which is sufficiently work-hardened such that it has
an ultimate tensile strength of at least 250000 pounds per square
inch, and a bending strength in the range of about 7.5.times.10.sup.-5
inch-pounds to about 8.8 inch-pound over the range of common needle
sizes. The needle has a modulus of elasticity (E) of at least 25.times.10.sup.6
pounds per square inch and a yield strength of at least 200000
pounds per square inch. The needle has sufficient ductility to effectively
permit it to be bent from a resting configuration through an arc
of 90 degrees, and rebent in the reverse direction an additional
90 degrees to the original resting shape.
Yet another aspect of the present invention is a nonmagnetic surgical
needle. The surgical needle has an elongated body, a distal piercing
point, and a proximal suture mounting end. The surgical needle is
made from ERSTE Type 4456 CA stainless steel alloy which is sufficiently
work-hardened such that it has an ultimate tensile strength of at
least 250000 pounds per square inch, and a bending strength in
the range of about 7.5.times.10.sup.-5 inch-pounds to about 8.8
inch-pounds over the range of common needle sizes. The needle has
a modulus of elasticity (E) of at least 25.times.10.sup.6 pounds
per square inch and a yield strength of at least 200000 pounds
per square inch. The needle will have sufficient ductility to effectively
permit it to be bent from a resting configuration through an arc
of 90 degrees, and rebent in the reverse direction an additional
90 degrees to the original resting shape.
Yet another aspect of the present invention is a method of using
the above-described non-magnetic surgical needles in a surgical
procedure in the magnetic field of an MRI.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of a taper point surgical needle of the present
invention.
FIG. 2 is a side view of a taper point surgical needle of FIG.
1.
FIG. 3 is a cross-sectional view of the needle of FIG. 2 taken
along View Line 3--3.
FIG. 4 is a cross-sectional view of the surgical needle of FIG.
2 taken along View Line 4--4.
FIG. 5 is a top view of a cutting edge surgical needle of the present
invention.
FIG. 6 is a side view of the cutting edge needle of FIG. 5.
FIG. 7 is a cross-sectional view of the surgical needle of FIG.
6 taken along View Line 7--7.
FIG. 8 is a cross-sectional view of the surgical needle of FIG.
6 taken along View Line 8--8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In most cases, metallic needles are used in the martensitic state.
This is true for martensitic, precipitation hardening and 300 grade
stainless steel. The martensite in martensitic stainless steel is
formed as a result of heat treatment, the martensite in precipitation
hardening stainless steel forms athermally and the martensite in
300 grade stainless steels forms as a result of transformation during
deformation. The reason is that stainless steel inn the martensitic
condition exhibits the best combination of strength and ductility.
The martensite content of the needles makes them magnetic. This
is of little or no consequence since the majority of surgical procedures
are done in an open environment. If, however, the surgical procedure
is done under a magnetic active environment, then the martensite
content and resulting magnetism may be a problem.
If the surgical needles are used in a magnetic environment the
needles must possess sufficient strength to be practical and still
remain non-magnetic. The most likely candidate are the 300 grade
stainless steels. These stainless steel alloys contain approximately
18 percent chromium and 8 percent nickel. This grade is non-magnetic
in the annealed or soft condition. This is because the microstructure
of the alloy is austenite. The strength of the alloy is too low
to be practical as a surgical needle. The tensile strength in the
annealed condition is about 80000 pounds per square inch (psi).
In order to strengthen the 300 grade stainless steels it is necessary
to subject it to deformation at or near room temperature. This is
type of deformation is called cold-working and is usually done by
wire drawing. As the amount of cold work increases the strength
of the alloy decreases. This is the result of two phenomena. The
first is the storage of some part of the energy in microstructure
of the alloy. This energy acts as a strengthening mechanism. The
second is the conversion of the austenite to martensite. The martensite
has a higher strength then the austenite. The stored energy, as
seen if deformed grains in the microstructure, does not effect the
magnetism of the alloy. The conversion to martensite, however, changes
the microstructure from non-magnetic to magnetic. For most austenitic
stainless steel, the magnetism or the tensile strength can be used
as a measurement of the amount of cold-work in a metallic object.
There is, however, a class of austenitic stainless steels which
does not convert to martensite during cold work. This group, exemplified
by alloy Type 316 SS, strengthens only by the deformation of the
grains during cold-work and no by the transformation to martensite.
Because of this, Type 316SS alloy remains non-magnetic even at very
high amounts of cold-work. This alloy has the further advantage
of being biologically non-reactive with the human body.
Alloy 316SS is a molybdenum-bearing austenitic stainless steel
with nickel increased over the level in the plain 18-8 type stainless
steel. The elemental composition of Type 316SS alloy is shown in
Table 1. Another austenitic alloy composition which shows good strength
and is non-magnetic in the cold worked state is ERSTE 4456 CA alloy.
This alloy replaces the nickel in the Type 316SS alloy with manganese
at a two to one ratio. The chemical composition of 4456 CA is also
shown in Table 1.
TABLE 1 ______________________________________ Chemical Composition
(Weight %) 316SS 4456CA ______________________________________ Chromium
16.00-18.00 16.00-20.00 Nickel 10.00-14.00 0.30 max Molybdenum 2.00-3.00
1.80-2.50 Carbon 0.08 max 0.10 max Manganese 2.00 max 16.00-20.00
Phosphorus 0.045 max 0.050 max Sulfur 0.030 max 0.050 max Silicon
1.00 max 1.00 max Nitrogen -- 0.70-1.00 Iron Balance Balance ______________________________________
The use of iron based alloy, such as Type 316SS, has the advantage
over non-ferrous materials which are also non-magnetic because of
its tensile strength and Modulus of Elasticity (E). The tensile
strength of cold worked 316SS can be as high as 300000 psi. Non-ferrous
alloys, such as those based on aluminum or titanium, do not usually
reach this level. Additionally, the Modulus of Elasticity of 316SS
is about 29.times.10.sup.+6 psi. For aluminum and titanium alloy
the Modulus of Elasticity is from 10 to 15.times.10.sup.+6. This
is important since E is a measure of how much the surgical needle
will defect under load. During surgery it is disadvantage for a
needle to deflect at low loads.
A taper point surgical needle 5 of the present invention is seen
in FIGS. 1-4. The needle 5 is seen to have a conventional configuration
having elongated body 10 distal piercing point 20 and proximal
suture mounting end 30. A cutting edge needle 50 of the present
invention is seen in FIGS. 5-8. Needle 50 has a conventional configuration
having elongated body 60 distal piercing point 70 proximal suture
mounting end 80 and cutting edges 90.
Methods of manufacturing taper point and cutting edge needles are
disclosed in U.S. Pat. No. 5477604 and U.S. patent application
Ser. No. 08/149435 filed on Nov. 1 1993 which are incorporated
by reference.
As mentioned above, the needles of the present invention are manufactured
from conventional Type 316 stainless steel alloy or ERSTE Type 4456
CA stainless steel alloy. The needles will typically be made from
conventional wire sizes having diameters ranging from about 0.00145
inches to about 0.071 inches.
The needles of the present invention are sufficiently work-hardened
to effectively impart mechanical characteristics which are substantially
equivalent to the mechanical characteristics of magnetic stainless
steel alloys such as types 302 420 and 455 stainless steels, but
yet remain nonmagnetic. The terms work-hardened and cold-hardened
are interchangeable and are defined to mean the process of increasing
a material's strength by forming, stretching or otherwise causing
it to undergo plastic, or permanent, deformation, without the addition
of heat.
The needles of the present invention are typically work-hardened
using the following process. Initially, Type 316SS or ERSTE 4456
CA stainless steel alloy wire rod with a diameter of approximately
0.250 inches is drawn down to progressively smaller diameters into
a wire used in the needles manufacturing process. During the reduction
process, the metal becomes harder due to a molecular reorientation
that takes place, until it becomes too brittle for further drawing.
The wire must then be annealed in order to undergo further diameter
reductions. By limiting the percent the diameter is reduced between
annealing steps to a range of about 90% to about 98%, and the percent
reduction after the final anneal to a range of about 93% to about
97%, it is possible to predict the ultimate tensile strength and
therefore produce wire that is capable of meeting both the strength
and ductility requirements of the needles made from it. Only a very
few specific, non-magnetic alloys are capable of undergoing such
processing.
The non-magnetic material processed into wire and subsequently
needles of the present invention will have the following mechanical
characteristics: an ultimate tensile strength of 250000 pounds
per square inch and a yield stress of at least 200000 pounds per
square inch. In addition, the needles will have a modulus of elasticity
(E) of at least 25.times.10.sup.6 pounds per square inch. The needles
will have a bending strength of about 7.5.times.10.sup.-5 inch-pounds
to about 8.8 inch-pounds over the range of typical needle sizing.
The magnetic field strength in a conventional MRI will range from
about 1.5 to about 3.0 Telsa. Accordingly, the nonmagnetic needles
of the present invention will have to remain nonmagnetic when subjected
to these magnetic fields.
The following examples are illustrative of the principles and practice
of the present invention, although not limited thereto.
EXAMPLE 1
Stainless steel needles of the present invention having conventional
taper point profiles were manufactured in the following manner.
The wire raw material was produced in a series of drawing and annealing
steps wherein the final drawing diameter reduction after annealing
was about 94% to about 96%. The needles were manufactured from the
wire in a series of conventional forming and grinding and finishing
steps familiar to one skilled in the art.
The needles had the following mechanical characteristics. For a
standard needle body cross-section, square in shape, fabricated
from Type 316 SS alloy wire with a diameter of 0.025 inches, and
cold-worked during the drawing process as described above, the bending
strength of the needle was 0.66 inch-pounds, and the ductility was
sufficient to permit the needle to be bent from a resting position
through an arc of 90 degrees and rebent in the reverse direction
another 90 degrees to its original shape (a conventional ductibility
test in the surgical needle arts). In addition, the needle was not
significantly influenced by a 1.5 Telsa magnet of the type standard
to MRI. For a needle with a round body cross-section fabricated
with Type 316 SS alloy wire having a diameter of 0.022 inches, and
cold-worked as described above, the bending strength was 0.64 inch-pounds
and ductility is as described above. This needle was also not significantly
influenced by a 1.5 Telsa magnet.
EXAMPLE 2
A surgical needle of the present invention is utilized by a surgeon
to perform a craniotomy procedure on a patient in a conventional
interventional MRI unit in the following manner. The surgeon makes
an incision in the skin an subcutaneous tissue of the scalp to expose
the cranium. A portion of the cranium is then removed and an additional
incision is made in the dura layer exposing the brain. When the
biopsy or other surgical procedure in the brain is completed, surgical
needles of the present invention having conventional surgical sutures
mounted thereto, are used by the surgeon to close the incision in
the dura and skin in a conventional manner by inserting the needles
through the tissue surrounding the incisions a sufficient number
of times to effectively approximate the tissue with the sutures.
The use of the non-magnetic needles of the present invention prevents
the needles from moving or otherwise being displaced by the magnetic
field of the MRI unit both when they are and are not being grasped
by the surgeon, as is routinely necessary in normal suturing practice.
It is surprising and unexpected that surgical needles can be made
from stainless steel alloys which are substantially non-magnetic
when placed in the magnetic field of a conventional MRI diagnostic
unit. It is surprising and unexpected that surgical needles made
from Type 316 and ERSTE 4456 CA stainless steel alloys can be work-hardened
to have similar mechanical characteristics to conventional stainless
steel alloy needles.
Although this invention has been shown and described with respect
to detailed embodiments thereof, it will understood by those skilled
in the art that various changes in form and detail thereof may be
made without departing from the spirit and scope of the claimed
invention.
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