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Biomechanical performance of cutting edge surgical needles
The Journal of Emergency Medicme. Vol IS, No 5, pp 679 -68.5. lYY7 copyright 0 1997 Eisevie~ Science Inc. Prilltcd ill the US.\. All rights reserwi 1J73h-.ih79!‘U $17 00 1~ (H) ELSEVIER
PI1 SO736-4679(97)00149-2
BWMCHAMCAL Frederick
H. Watkins,
PERFORMANCE MD,*
OF CUTTING EDGE SURGICAL
Scott D. London, rm,t Jeffrey G. Neal, ES,* John G. Thacker, Richard F. Edlich, MD, PhD*
ES Pm,$ and
’ Department of Plastic Surgery, University of Virginia School of Medicine, tDepartment of Mechanical and Aerospace Engineering, and *Department of Otolaryngology and Head and Neck Surgery, University of Virginia, Charlottesville, Virginia Reprint Address: Richard F. Edlich, MD, PhD, Department of Plastic Surgery, Box 332, University of Virginia School of Medcine, Charlottesville, Virginia 22908
q Abstract-The purpose of thii study was to compare the biomechanical performance of cutting edge needles made of S45500 stainless steel alloy to Surgalloy stainless steel. The new high-nickel stainless steel alloy, Surgalloy, has superior performance characteristics over that of the other highnickel stainless steel alloy, S45500. The Surgalloy needle is produced from a stronger stainless steel alloy than the S45500 needle. The Surgalloy needle has considerably greater resistance to bending than the needle produced from S4550@alloy. In addition, Surgalloy stainless steel has almost a twofold greater resistance to fracture than the S45500 stainless steel alloy. 0 1997 Elsevier Science Inc.
than low-nickel stainless steel, such as S42000, which is the most commonly used alloy for manufacturing surgical needles(3). BecauseS45500 stainless steel alloy has such considerable resistance to bending and fracturing, the geometry of its point can be narrowed to enhance sharpnesswithout risk of inadvertent breakage. A new high-nickel stainless steel, Surgalloy (U. S. Surgical Corp., Norwalk, CT), has been used recently to manufacture cutting edge needles. It is the purpose of this investigation to comparethe biomechanical performance of cutting edge needles made of S45.500stainless steel alloy to that of Surgalloy stainless steel.
0 Keywords-stainless steel; nickel; cutting edge needle; resistance to bending; ductility; sharpness
MATERIALS INTRODUCTION
Surgical Needles
Surgical needle manufacturersprovide needle dimension tables that relate their needles to comparable needles produced by other manufacturers(Table 1). Using these data, two separategroups of comparably sized, reverse cutting edge needles were selected for measurementof their biomechanical performance. The dimensions of a surgical needle are characterizedby many distinct measurements. The curvature of the needle is described in degreesof the subtendedarc. The radius of the needle is the distance from the center of the circle to the body of the needle, if the curvature of the needle was continued
Each type of needle point is designed to penetrate a specific type of tissue (1). In general, there are needles with cutting edges, taper points, or a combination of both. Because most wounds in the emergency department are lacerations, cutting edge needles are used to reapproximate the divided edges of skin. Cutting edge needles have at least two opposing edges that are designed to penetrate tough, dense tissue. A high-nickel stainless steel alloy, such as S4.5500,has been successfully used to manufacture cutting edge needles (2). This alloy exhibits a greater resistanceto bending and fracture
RECIEVED: ACCEPTED:
19 August 1996; FINAL 9 December 1996
SUBMISSION
AND METHODS
RECEIVED:
5 November 1996: 679
F. H. Watkins et al.
680
Table 1. Needle
Specifications Needle
Needle Manufacturer Lot no. NDL code Wire diameter (mm) Radius (mm) Chord length (mm) Curve degrees Needle length (mm) Swage length 0-W Bodv_ tvpe _. Tip style Point length (mm)
P-l 2 (Surgalloy)
ussc A4G22 SL-3627 4-O BSA
PS-2 (S45500) Ethicon HG9031 J496 4-O BSA
0.58 8.0
0.60 8.4
15.2 140
15.2 130
19.6
18.7
0.9
5.4 Triangular portion of Point with ribbed bodv Reverse cutting ’
Trianaular bodv Reverse cutting 3.9
3.4
to make a full circle. Chord length is the linear distance measuredfrom the central point of the needle swage to the point of the needle. The needle diameter is the width of the original circular wire utilized in the manufacturing processfor the production of the needle.Needle length is the arc length of the needle measuredat the center of the wire’s cross section. The point of the needle extends from the tip of the needle to the maximum cross section of the body. Each needle swagehas a hole or linear slit drilled into the needle body that allows attachmentof the suture. The depth of the slit or hole in the needle swage can be measuredin millimeters.
Biomechanical Per$ormance Tests
The biomechanical performance of these surgical needles was determined by the following parameters: 1) sharpness,2) resistance to bending, and 3) ductility. A combined needle penetration force and needle strength test machine has been interfaced with newly developed computer software (4). The test machine rotates a curved surgical needle through the designated membrane and measuresthe resistanceforce encounteredby the needle. Because the point regions of many surgical needles do not follow true circular arcs, the test instrument compensates automatically for the change in radius so that the needle follows a truly circular arc asit passesthrough the membrane.Eleven major hardware componentsmake up the needle penetration test instrument and include the following: motor-driven rotary table, centering X-Y micrometer positioning table, needle clamp, synthetic membrane holder with index head, vertical load cell;
X-Y micrometer positioning table; ,Z positioning slide with analogue readout, air table, horizontal load cell; 25MHz, 386 computer, 1lo-MB hard drive; VGA monitor, and laser jet printer. A curved surgicalneedleis clampedin a fixture attached to the X-Y centeringtable, which rotatesabouta horizontal axis. The computercontrols a rotary steppingmotor, which rotatesthe needlethrough a precisecircular arc. The speed of needlerotation is 0.33”/s. The arc is dependenton the needleradius and is controlled by manual micrometeradjustmentson the X-Y centeringtable. The computer directs the stepping motor to rotate the table through an arc of 40”, which in turn rotates the needle through the membranebeing tested. Adjustment of the X-Y positioning table allows precise horizontal plane alignment of the needle with the membraneholder. The membrane holder has 24 indexing positions for multiple needle puncture testing and exerts constant uniform tension on the membranebeing tested. The membrane holder is attached to the top of the vertical load cell, which measuresthe vertical penetration force exerted on the membraneby the needle during the rotation of the needle.Needlesthat are not completely circular (as is often the case in the point region) will also exert a horizontal force on the membraneduring the penetration run. A horizontal load cell measuresthe horizontal force exerted by the needle against the needle track within the membrane.A computer feedbackloop holds the horizontal force to acceptablylow levels during testing, which is accomplishedby the computer that continually monitors the horizontal force and directs the horizontal stepping motor to move the needle horizontally to hold the horizontal side force within an acceptablerange. During a test run, the computer plotted the vertical force exerted on the membrane versus the degrees of needle rotation. The penetration force data typically showed an initial penetration force peak followed by an even higher maximum force. The initial force peak representsthe first point at which the needle actually penetrates the membrane. The maximum force peak, however, is reached as the wider needle body follows the tapered point through the channel created in the membrane. The additional force is due to the frictional drag forces placed on the needle by the designatedmembrane as the needle body widens the channel created by the point. Needle Sharpness
The sharpnessof the points of these surgical needleswas determined by measuring the initial and maximum vertical force required to push them through a thin, laminated synthetic membrane (Medpar 1220@,3M Center,
681
Cutting Edge Surgical Needs
St. Paul, MN) (5). Previously reported investigations have demonstrated that this synthetic membrane is a reliable and reproducible substitute for human skin in needle sharpness testing (2). This laminated membrane, called Medpar 1220@,has a thickness of 0.002 inches. It consists of a 0.0005-inch layer of Mylar@ film bonded to a 0.0015inch sheet of modified polyethylene. Square samples (3 X 3 inch) of Medpar@ were cut using a paper cutter. Each sample was then mounted in the membrane holder with its dull polyethylene side facing up toward the needle point. The tension applied to stretch the membrane over the rotary table was adjusted by the clamping ring of the holding device. The four screws that secured the clamping ring were torqued down together to ensure a uniform tension on the membrane. If a wrinkle developed in the membrane, it was discarded and a new membrane placed in the membrane holder. Fifteen needles of each type were tested. The means of the initial and maximum penetration force measurements for each needle were recorded and the standard deviations were calculated.
the classic 0.2% offset strain method commonly used in tensile testing. The 2” offset yield technique was accomplished by drawing a line parallel to the initial elastic loading region, except offset horizontally by 2” of‘ needle deformation. This 2” value was chosen because it represents a distinct point of demarcation from the linear line. The yield moment was identified at the intersection 01’ this offset line with the test curve. Tests performed during this study in which the applied bending moments were less than the yield moments result in elastic deformations that were completely recoverable. whereas applied bending moments greater than the yietd moments caused plastic or irreversible deformation. The ultimate moment was defined as the greatest bending moment on the curve, with the maximum angle of bend for the curved surgical needle being 90” due to limitation imposed by the test apparatus. Fifteen needles of each type were tested. The means of the yield moments and the ultimate moments for each curved surgical needle were determined, and the standard deviation was calculated.
DuctiliQ Resistunce to Bending With the advent of the electronic load cell transducer, the bending resistance of the surgical needle can generate a force-deflection curve that allows quantitation of the resistance to needle bending (3). In these tests, the bending forces were sensed by the strain gauge load cell transducer and recorded on a strip chart recorder. The speed of the recorder was fixed at 10 cm/min, and the angular rotation speed of the curved surgical needle was set at 1.5”/s. The bending force needed to deform the curved needle was recorded as a function of the angular deformation of the needle. The vertical axis on the strip chart recorder was calibrated to record force, whereas the horizontal axis was linearly related to the angular rotation of the needle. Because the moment arm remained constant, the bending force was proportional to the bending moment or torque. During each test, bending of the needle in a counterclockwise direction resulted in an angular deformation versus bending moment curve that was analyzed to give a yield moment (torque) and an ultimate bending moment (torque) for all needles tested. Typically, the curve exhibits an initial linear elastic deformation region, followed by a nonlinear plastic deformation region. Because there is no clear distinction for some needles between the elastic and plastic regions of this bending curve. it was difficult to identify the applied moment at which permanent deformation occurs. To identify a reproducible yield moment for this test, a 2” offset yield technique was used that followed the same principle as
Ductility or resistance to surgical needle breakage was measured by determining the work required to completely fracture a surgical needle (6). After 90” of deformation from the bend test, the rotational direction was reversed and the bend forces were recorded as the needle was deformed approximately back to its original curvature. These bend cycles were repeated continuously until the needle was broken. Consequently, bend forces were recorded as each test needle was cyclically bent clockwise and counterclockwise through an arc of 90’. To obtain the work required for needle breakage, the area under the moment deflection curve was measured. The total work to cause the plastic deformation of the needle was obtained by subtracting the elastic work of deformation, which was recovered as the needle direction was reversed from the total work imparted to the needle. The total amount of work required to bend the needle back and forth through a 90” arc until fracture was the measurement of needle ductility. The mean and standard deviation of the ductility measurements for each needle type were calculated. The statistical significance for all of the measurements of the biomechanical needle performance parameters was determined by the Student’s 1 test.
Alloy Composition The alloy composition of the surgical needles was compared with that of actual samples of American Society for Testing and Materials (ASTM) 45500 and Surgalloy
682
F. H. Watkins et al. Table 2. Elemental Analysis of Stainless Steel Alloys Alloy Type C s45500 Surgalloy
co.05 co.05
0Y.l 0.00
014 0.00
0:3 0:oo
1: 0.0
11.7 Cr 12.0
stainless steel alloys using a JSM 840A II electron microscope (JapanElectron Optics Laboratory, Tokyo, Japan) equipped with a PGT System 4 energy-dispersive x-ray spectrometerusing a beryllium window detector (Princeton GammaTechnology, Princeton, NJ). Elemental analysis by this technique can be performed quickly and efficiently. However, the absorption characteristics of the beryllium window usually do not permit the detection of elementswith atomic numbers smaller than 10. Minimum detection levels vary with the atomic number and excitation voltage; however, quantities smaller than a few 10th~ of a percent are generally not considered reliable. The analyseswere performed on the fractured surface of each needle as well as samplesof ASTM 45500 and Surgalloy stainless steel affixed to a carbon scanning electron microscopic stub to eliminate the influence of possible codings on either the needle or sample surface. Each spectrum was analyzed using a computer program basedon concentration ratios. This method is particularly suitable for materials such as alloys, in which the elements present are usually known. Furthermore, variables such as run time and probe current have little or no effect on the results.
Ni
Ti
8.5 9.0
1.1 0.9
CoandTa 0.00 0.00
Cu
MO
Nb
Fe
2.0 2.0
co.50 4.00
0.30 0.00
Balance Balance
8.5% and 9.0%, respectively (Table 2). In addition, both surgical needles were found to be true stainless steel alloys with a high content of chromium (S45500, 11.7%, and Surgalloy, 12.0%). The concentration of molybdenum was 4% in Surgalloy, a higher concentration than in S45500, which was ~0.5%. In contrast, small concentrations of some elements were found in S45500 (Mn, 0.5; P, 0.04; S, 0.03; Si, 0.5; and Nb, 0.3) that were not found in Surgalloy. There were also notable differences in needle dimensions and manufacturing processes.For example, all needlesmade of Surgalloy had laser-drilled swages, whereas the needles made from S45500 had channel swages. For the needles made of S45500, the swage accounted for 29% of the needle length. In contrast, the laser-drilled holes in the Surgalloy needles accounted for 4.8% of the entire needle length. Consequently, the length of the swage in the S45500 needles was approximately sixfold longer than those of the needles made of Surgalloy. Another important difference between these needles was the length of their needle point geometry. The point length of the needlesmade of Surgalloy was 0.5 mm longer than that of needlesmade of s45500.
Scanning Electron Microscopy Scanning Electron Microscopy
The energy level for scanning electron microscopy (model SR-50, International Scientific Instruments, Milipitas, CA) of the needles was 25 kV. Before examination, the needles were sputter-coatedwith gold to allow visualization without electric charging of any organic surface material. Polaroid PM film (Cambridge, MA) was used to photograph the needles at X50 magnification.
Scanning electron microscope photographs of the outer surfacesof these two different surgical needles showed notable differences. The width of the needle point of the S45500 needle appearedto be wider than that manufactured from Surgalloy stainless steel (Fig. 1). In addition, the length of the needle point of Surgalloy needles was longer than that of needles made from S45500 stainless steel. A scanning electron microscopic photograph of the profile of the needle made from Surgalloy clearly demonstrates that it has a slimmer needle point geometry than that of the needle made from S45500 alloy (Fig. 2).
RESULTS Alloy Composition Needle Sharpness
Elemental analysis of the alloy composition of the two different reverse cutting edge needlesrevealed that both the S45500and Surgalloy are high-nickel stainlesssteels,
Needle sharpnesswas judged by the initial and maximum penetration forces encounteredby the needlesdur-
Cutting Edge Surgical Needs
Figure 1. Scanning electron microscope photograph of the outer surface of the SurgaUoy needle (right) and the needle produced ‘from the EM5500 alloy (left). Note that the point of the Surgaffoy needle has a more narrow point geometry than the point of the S45500 needle.
ing passage through the membrane. The initial penetration force of the Surgalloy needles was remarkably similar to that of the needles manufactured from S4.5500 alloy (Fig. 3). The mean maximum penetration forces for the S45500 and the Surgalloy stainless steel needles were not different (Fig. 4).
;Veedle Resistance to Bending The resistance to bending of the needles produced from Surgalloy were found to be significantly greater than those manufactured from the S45500 alloy. The yield moment of the Surgalloy needle was significantly greater
8
0.14
$ !A
0.12
.b
0.1
2 ti;
0.08
5 a
0.06
m .Y
0.04
.g
0.02 0
Surgalloy Figure 3. Initial penetration force thrwrgh tkte &&@a@ membrane for the Surgafioy need& C&J not antty from that of the needles produced from the S46500 alloy.
than that of the needles produced by the S45500 alloy (P < 0.01) (Fig. 5). In addition, the ultimate bending moment of the Surgalloy needles was significantly greater than that of the needles manufactured from the S45500 alloy (P < 0.01) (Fig. 6).
Needle Ductilit\ The ductility of the Surgalloy needles was significantly greater than that of the needles produced by the S45500
0.2
-0 !I I
Surgalloy Figure 2. Scanning etectron microscope photograph of me profiles of the Surgafioy needle (right) and the needle produced from tha 54e5800 alfey @ft). Note that the Surgailoy needbe haa a timer nwdfe point geometry man me needles produced from S45500 alloy.
Figure 4. The maximum
penetration
foroe through
me Med-
P8I@fWdWlBWforthO~-#dnot~*-
nificaMyfromthatoftheneedks alloy.
pmducedfromtheS45500
684
F. H. Watkins et al. bU
48.8 f3.2
I
Surgalloy
Surgalloy
Figure 5. The yield moment for the Surgalloy needles was significantly greater than that of the needles produced from the !34SXXI alloy.
alloy. The number of cycles neededto fracture the Surgalloy needles was approximately twofold greater than that required to fracture the needles produced by the S45500 alloy (P < 0.01) (Fig. 7). In addition, the work to fracture the Surgalloy needles was significantly greater than the work to fracture needlesproduced by the S45500 alloy (P < 0.01) (Fig. 8).
Figure 7. The number of cycles to fracture the Surgalloy needles was significantly greater than that required to fracture the needles produced from S455CKlalloy.
DISCUSSION The development of a high-nickel stainless steel representsa major advancein needle manufacture.A stainless steel, S45500, which contains 8.5% nickel, has been successfully used in the manufacture of surgical needles. Needles made from this stainless steel alloy are considerably stronger than stainless steels without nickel (3). Another high-nickel stainless steel, Surgalloy, which
624.8
94.5
f5.7 100-d
T
I
Surgalloy Figure 6. The ultimate bending moment for the Surgalloy needles was slgnifkantly greater than that of the needlee produced from the S45500 alloy.
I
Surgalloy Figure 8. The work to fracture the Surgalloy needles was signmcantly greater than that required to fracture the needles produced from s45500 alloy.
685
Cutting Edge Surgical Needs
contains 9% nickel, has been used recently to manufacture surgical needles. Our study of the biomechanical performance of Surgalley as compared to S45500 demonstrates that the Surgalloy has several superior characteristics over that of the S45500 alloy. Most importantly, it displays a greater resistance to bending than the S45500 alloy. Its superior resistance to bending allows Surgalloy needles to be manipulated close to their swages without the needle being inadvertently bent. Grasping the needle close to the swage between the jaws of the needle holder allows the emergency physician to manipulate the needle with considerable dexterity. This enhanced resistance to bending displayed by the Surgalloy needle is associated with considerable resistance to needle fracturing. The resistance to needle fracture of the Surgalloy needles is almost twofold greater than that of needles produced from S45500 alloy. The importance of a needle that resists breakage has implications both to the emergency physician and to the patient. The search for a broken needle fragment is often a futile quest that results in unnecessary damage to the wound. The presence of a dislodged needle fragment can be confusing to the patient, who may seek advice from an attorney rather than the physician. This enhanced strength of the Surgalloy needle allowed the manufacturer to narrow the point geometry of the needle without altering the resistance of the needle to bending. This narrowing of the point geometry of the cutting edge needle. however, does not enhance its
sharpness. The measured sharpness of needles with a wide point geometry is not significantly different from that of needles with a slim taper point geometry. The cost of the Surgalloy needle is comparable to that of the needle made of S45500 stainless steel alloy.
CONCLUSION
A new high-nickel stainless steel, Surpalloy. has been used to manufacture cutting edge surgical needles. The purpose of this investigation was to compare the biomechanical performance of the Surgalloy needle to that of another high-nickel stainless steel, S45500, used in the manufacture of surgical needles. Their biomechanical performance was judged by reproducible quantitative tests that measured sharpness, resistance to bending, and ductility. On the basis of these quantitative measurements, Surgalloy has several unique performance characteristics over the S45500 stainless steel alloy. Most importantly, the Surgalloy exhibits a stronger resistance to bending than the S45500 needles. In addition, the Surgalloy exhibits almost two times the resistance to fracture than do the needles produced from S45500 stainless steel alloy.
Acknowledgment-This research was supported by a generous gift from the Texaco Foundation. White Plains. NY
REFERENCES I. Edlich RF. Thacker JG, McGregor W, Rodeheaver GT. Past, present. and future for surgical needles and needle holders. Am J Surg. 1993; 166522-32. 2. Thacker JG. Rodeheaver GT. Towler MA, Edlich RF. Surgical needle sharpness. Am J Surg. 1989;157:334-9. 3. Abidin MR, Towler MA. Rodeheaver GT, Thacker JG, Cantrell RW. Edlich RF. Biomechanics of curved surgical needle bending. J Biomater Res. 1989;23: 129-43. 1. Manson TT, Bromberg WG. Thacker JG, McGregor W, Morgan
RF, Edlich RF. A new glove puncture detectcon system. J Emerg Med. 1995:13:357-64. 5. Towler MA. McGregor W, Rodeheaver GT. et al. Influence 01 cutting edge configuration on surgical needle penetration forces. J Emerg Med. 1988;6:475-81. 6. Abidin MR, Towler MA, Nochimson GD, Rodeheaver GT, Thacker JG, Edlich RF. A new quantitative measurement for surgical needle ductility. Ann Emerg Med. 1989:18:64-X.
PI1 SO736-4679(97)00149-2
BWMCHAMCAL Frederick
H. Watkins,
PERFORMANCE MD,*
OF CUTTING EDGE SURGICAL
Scott D. London, rm,t Jeffrey G. Neal, ES,* John G. Thacker, Richard F. Edlich, MD, PhD*
ES Pm,$ and
’ Department of Plastic Surgery, University of Virginia School of Medicine, tDepartment of Mechanical and Aerospace Engineering, and *Department of Otolaryngology and Head and Neck Surgery, University of Virginia, Charlottesville, Virginia Reprint Address: Richard F. Edlich, MD, PhD, Department of Plastic Surgery, Box 332, University of Virginia School of Medcine, Charlottesville, Virginia 22908
q Abstract-The purpose of thii study was to compare the biomechanical performance of cutting edge needles made of S45500 stainless steel alloy to Surgalloy stainless steel. The new high-nickel stainless steel alloy, Surgalloy, has superior performance characteristics over that of the other highnickel stainless steel alloy, S45500. The Surgalloy needle is produced from a stronger stainless steel alloy than the S45500 needle. The Surgalloy needle has considerably greater resistance to bending than the needle produced from S4550@alloy. In addition, Surgalloy stainless steel has almost a twofold greater resistance to fracture than the S45500 stainless steel alloy. 0 1997 Elsevier Science Inc.
than low-nickel stainless steel, such as S42000, which is the most commonly used alloy for manufacturing surgical needles(3). BecauseS45500 stainless steel alloy has such considerable resistance to bending and fracturing, the geometry of its point can be narrowed to enhance sharpnesswithout risk of inadvertent breakage. A new high-nickel stainless steel, Surgalloy (U. S. Surgical Corp., Norwalk, CT), has been used recently to manufacture cutting edge needles. It is the purpose of this investigation to comparethe biomechanical performance of cutting edge needles made of S45.500stainless steel alloy to that of Surgalloy stainless steel.
0 Keywords-stainless steel; nickel; cutting edge needle; resistance to bending; ductility; sharpness
MATERIALS INTRODUCTION
Surgical Needles
Surgical needle manufacturersprovide needle dimension tables that relate their needles to comparable needles produced by other manufacturers(Table 1). Using these data, two separategroups of comparably sized, reverse cutting edge needles were selected for measurementof their biomechanical performance. The dimensions of a surgical needle are characterizedby many distinct measurements. The curvature of the needle is described in degreesof the subtendedarc. The radius of the needle is the distance from the center of the circle to the body of the needle, if the curvature of the needle was continued
Each type of needle point is designed to penetrate a specific type of tissue (1). In general, there are needles with cutting edges, taper points, or a combination of both. Because most wounds in the emergency department are lacerations, cutting edge needles are used to reapproximate the divided edges of skin. Cutting edge needles have at least two opposing edges that are designed to penetrate tough, dense tissue. A high-nickel stainless steel alloy, such as S4.5500,has been successfully used to manufacture cutting edge needles (2). This alloy exhibits a greater resistanceto bending and fracture
RECIEVED: ACCEPTED:
19 August 1996; FINAL 9 December 1996
SUBMISSION
AND METHODS
RECEIVED:
5 November 1996: 679
F. H. Watkins et al.
680
Table 1. Needle
Specifications Needle
Needle Manufacturer Lot no. NDL code Wire diameter (mm) Radius (mm) Chord length (mm) Curve degrees Needle length (mm) Swage length 0-W Bodv_ tvpe _. Tip style Point length (mm)
P-l 2 (Surgalloy)
ussc A4G22 SL-3627 4-O BSA
PS-2 (S45500) Ethicon HG9031 J496 4-O BSA
0.58 8.0
0.60 8.4
15.2 140
15.2 130
19.6
18.7
0.9
5.4 Triangular portion of Point with ribbed bodv Reverse cutting ’
Trianaular bodv Reverse cutting 3.9
3.4
to make a full circle. Chord length is the linear distance measuredfrom the central point of the needle swage to the point of the needle. The needle diameter is the width of the original circular wire utilized in the manufacturing processfor the production of the needle.Needle length is the arc length of the needle measuredat the center of the wire’s cross section. The point of the needle extends from the tip of the needle to the maximum cross section of the body. Each needle swagehas a hole or linear slit drilled into the needle body that allows attachmentof the suture. The depth of the slit or hole in the needle swage can be measuredin millimeters.
Biomechanical Per$ormance Tests
The biomechanical performance of these surgical needles was determined by the following parameters: 1) sharpness,2) resistance to bending, and 3) ductility. A combined needle penetration force and needle strength test machine has been interfaced with newly developed computer software (4). The test machine rotates a curved surgical needle through the designated membrane and measuresthe resistanceforce encounteredby the needle. Because the point regions of many surgical needles do not follow true circular arcs, the test instrument compensates automatically for the change in radius so that the needle follows a truly circular arc asit passesthrough the membrane.Eleven major hardware componentsmake up the needle penetration test instrument and include the following: motor-driven rotary table, centering X-Y micrometer positioning table, needle clamp, synthetic membrane holder with index head, vertical load cell;
X-Y micrometer positioning table; ,Z positioning slide with analogue readout, air table, horizontal load cell; 25MHz, 386 computer, 1lo-MB hard drive; VGA monitor, and laser jet printer. A curved surgicalneedleis clampedin a fixture attached to the X-Y centeringtable, which rotatesabouta horizontal axis. The computercontrols a rotary steppingmotor, which rotatesthe needlethrough a precisecircular arc. The speed of needlerotation is 0.33”/s. The arc is dependenton the needleradius and is controlled by manual micrometeradjustmentson the X-Y centeringtable. The computer directs the stepping motor to rotate the table through an arc of 40”, which in turn rotates the needle through the membranebeing tested. Adjustment of the X-Y positioning table allows precise horizontal plane alignment of the needle with the membraneholder. The membrane holder has 24 indexing positions for multiple needle puncture testing and exerts constant uniform tension on the membranebeing tested. The membrane holder is attached to the top of the vertical load cell, which measuresthe vertical penetration force exerted on the membraneby the needle during the rotation of the needle.Needlesthat are not completely circular (as is often the case in the point region) will also exert a horizontal force on the membraneduring the penetration run. A horizontal load cell measuresthe horizontal force exerted by the needle against the needle track within the membrane.A computer feedbackloop holds the horizontal force to acceptablylow levels during testing, which is accomplishedby the computer that continually monitors the horizontal force and directs the horizontal stepping motor to move the needle horizontally to hold the horizontal side force within an acceptablerange. During a test run, the computer plotted the vertical force exerted on the membrane versus the degrees of needle rotation. The penetration force data typically showed an initial penetration force peak followed by an even higher maximum force. The initial force peak representsthe first point at which the needle actually penetrates the membrane. The maximum force peak, however, is reached as the wider needle body follows the tapered point through the channel created in the membrane. The additional force is due to the frictional drag forces placed on the needle by the designatedmembrane as the needle body widens the channel created by the point. Needle Sharpness
The sharpnessof the points of these surgical needleswas determined by measuring the initial and maximum vertical force required to push them through a thin, laminated synthetic membrane (Medpar 1220@,3M Center,
681
Cutting Edge Surgical Needs
St. Paul, MN) (5). Previously reported investigations have demonstrated that this synthetic membrane is a reliable and reproducible substitute for human skin in needle sharpness testing (2). This laminated membrane, called Medpar 1220@,has a thickness of 0.002 inches. It consists of a 0.0005-inch layer of Mylar@ film bonded to a 0.0015inch sheet of modified polyethylene. Square samples (3 X 3 inch) of Medpar@ were cut using a paper cutter. Each sample was then mounted in the membrane holder with its dull polyethylene side facing up toward the needle point. The tension applied to stretch the membrane over the rotary table was adjusted by the clamping ring of the holding device. The four screws that secured the clamping ring were torqued down together to ensure a uniform tension on the membrane. If a wrinkle developed in the membrane, it was discarded and a new membrane placed in the membrane holder. Fifteen needles of each type were tested. The means of the initial and maximum penetration force measurements for each needle were recorded and the standard deviations were calculated.
the classic 0.2% offset strain method commonly used in tensile testing. The 2” offset yield technique was accomplished by drawing a line parallel to the initial elastic loading region, except offset horizontally by 2” of‘ needle deformation. This 2” value was chosen because it represents a distinct point of demarcation from the linear line. The yield moment was identified at the intersection 01’ this offset line with the test curve. Tests performed during this study in which the applied bending moments were less than the yield moments result in elastic deformations that were completely recoverable. whereas applied bending moments greater than the yietd moments caused plastic or irreversible deformation. The ultimate moment was defined as the greatest bending moment on the curve, with the maximum angle of bend for the curved surgical needle being 90” due to limitation imposed by the test apparatus. Fifteen needles of each type were tested. The means of the yield moments and the ultimate moments for each curved surgical needle were determined, and the standard deviation was calculated.
DuctiliQ Resistunce to Bending With the advent of the electronic load cell transducer, the bending resistance of the surgical needle can generate a force-deflection curve that allows quantitation of the resistance to needle bending (3). In these tests, the bending forces were sensed by the strain gauge load cell transducer and recorded on a strip chart recorder. The speed of the recorder was fixed at 10 cm/min, and the angular rotation speed of the curved surgical needle was set at 1.5”/s. The bending force needed to deform the curved needle was recorded as a function of the angular deformation of the needle. The vertical axis on the strip chart recorder was calibrated to record force, whereas the horizontal axis was linearly related to the angular rotation of the needle. Because the moment arm remained constant, the bending force was proportional to the bending moment or torque. During each test, bending of the needle in a counterclockwise direction resulted in an angular deformation versus bending moment curve that was analyzed to give a yield moment (torque) and an ultimate bending moment (torque) for all needles tested. Typically, the curve exhibits an initial linear elastic deformation region, followed by a nonlinear plastic deformation region. Because there is no clear distinction for some needles between the elastic and plastic regions of this bending curve. it was difficult to identify the applied moment at which permanent deformation occurs. To identify a reproducible yield moment for this test, a 2” offset yield technique was used that followed the same principle as
Ductility or resistance to surgical needle breakage was measured by determining the work required to completely fracture a surgical needle (6). After 90” of deformation from the bend test, the rotational direction was reversed and the bend forces were recorded as the needle was deformed approximately back to its original curvature. These bend cycles were repeated continuously until the needle was broken. Consequently, bend forces were recorded as each test needle was cyclically bent clockwise and counterclockwise through an arc of 90’. To obtain the work required for needle breakage, the area under the moment deflection curve was measured. The total work to cause the plastic deformation of the needle was obtained by subtracting the elastic work of deformation, which was recovered as the needle direction was reversed from the total work imparted to the needle. The total amount of work required to bend the needle back and forth through a 90” arc until fracture was the measurement of needle ductility. The mean and standard deviation of the ductility measurements for each needle type were calculated. The statistical significance for all of the measurements of the biomechanical needle performance parameters was determined by the Student’s 1 test.
Alloy Composition The alloy composition of the surgical needles was compared with that of actual samples of American Society for Testing and Materials (ASTM) 45500 and Surgalloy
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F. H. Watkins et al. Table 2. Elemental Analysis of Stainless Steel Alloys Alloy Type C s45500 Surgalloy
co.05 co.05
0Y.l 0.00
014 0.00
0:3 0:oo
1: 0.0
11.7 Cr 12.0
stainless steel alloys using a JSM 840A II electron microscope (JapanElectron Optics Laboratory, Tokyo, Japan) equipped with a PGT System 4 energy-dispersive x-ray spectrometerusing a beryllium window detector (Princeton GammaTechnology, Princeton, NJ). Elemental analysis by this technique can be performed quickly and efficiently. However, the absorption characteristics of the beryllium window usually do not permit the detection of elementswith atomic numbers smaller than 10. Minimum detection levels vary with the atomic number and excitation voltage; however, quantities smaller than a few 10th~ of a percent are generally not considered reliable. The analyseswere performed on the fractured surface of each needle as well as samplesof ASTM 45500 and Surgalloy stainless steel affixed to a carbon scanning electron microscopic stub to eliminate the influence of possible codings on either the needle or sample surface. Each spectrum was analyzed using a computer program basedon concentration ratios. This method is particularly suitable for materials such as alloys, in which the elements present are usually known. Furthermore, variables such as run time and probe current have little or no effect on the results.
Ni
Ti
8.5 9.0
1.1 0.9
CoandTa 0.00 0.00
Cu
MO
Nb
Fe
2.0 2.0
co.50 4.00
0.30 0.00
Balance Balance
8.5% and 9.0%, respectively (Table 2). In addition, both surgical needles were found to be true stainless steel alloys with a high content of chromium (S45500, 11.7%, and Surgalloy, 12.0%). The concentration of molybdenum was 4% in Surgalloy, a higher concentration than in S45500, which was ~0.5%. In contrast, small concentrations of some elements were found in S45500 (Mn, 0.5; P, 0.04; S, 0.03; Si, 0.5; and Nb, 0.3) that were not found in Surgalloy. There were also notable differences in needle dimensions and manufacturing processes.For example, all needlesmade of Surgalloy had laser-drilled swages, whereas the needles made from S45500 had channel swages. For the needles made of S45500, the swage accounted for 29% of the needle length. In contrast, the laser-drilled holes in the Surgalloy needles accounted for 4.8% of the entire needle length. Consequently, the length of the swage in the S45500 needles was approximately sixfold longer than those of the needles made of Surgalloy. Another important difference between these needles was the length of their needle point geometry. The point length of the needlesmade of Surgalloy was 0.5 mm longer than that of needlesmade of s45500.
Scanning Electron Microscopy Scanning Electron Microscopy
The energy level for scanning electron microscopy (model SR-50, International Scientific Instruments, Milipitas, CA) of the needles was 25 kV. Before examination, the needles were sputter-coatedwith gold to allow visualization without electric charging of any organic surface material. Polaroid PM film (Cambridge, MA) was used to photograph the needles at X50 magnification.
Scanning electron microscope photographs of the outer surfacesof these two different surgical needles showed notable differences. The width of the needle point of the S45500 needle appearedto be wider than that manufactured from Surgalloy stainless steel (Fig. 1). In addition, the length of the needle point of Surgalloy needles was longer than that of needles made from S45500 stainless steel. A scanning electron microscopic photograph of the profile of the needle made from Surgalloy clearly demonstrates that it has a slimmer needle point geometry than that of the needle made from S45500 alloy (Fig. 2).
RESULTS Alloy Composition Needle Sharpness
Elemental analysis of the alloy composition of the two different reverse cutting edge needlesrevealed that both the S45500and Surgalloy are high-nickel stainlesssteels,
Needle sharpnesswas judged by the initial and maximum penetration forces encounteredby the needlesdur-
Cutting Edge Surgical Needs
Figure 1. Scanning electron microscope photograph of the outer surface of the SurgaUoy needle (right) and the needle produced ‘from the EM5500 alloy (left). Note that the point of the Surgaffoy needle has a more narrow point geometry than the point of the S45500 needle.
ing passage through the membrane. The initial penetration force of the Surgalloy needles was remarkably similar to that of the needles manufactured from S4.5500 alloy (Fig. 3). The mean maximum penetration forces for the S45500 and the Surgalloy stainless steel needles were not different (Fig. 4).
;Veedle Resistance to Bending The resistance to bending of the needles produced from Surgalloy were found to be significantly greater than those manufactured from the S45500 alloy. The yield moment of the Surgalloy needle was significantly greater
8
0.14
$ !A
0.12
.b
0.1
2 ti;
0.08
5 a
0.06
m .Y
0.04
.g
0.02 0
Surgalloy Figure 3. Initial penetration force thrwrgh tkte &&@a@ membrane for the Surgafioy need& C&J not antty from that of the needles produced from the S46500 alloy.
than that of the needles produced by the S45500 alloy (P < 0.01) (Fig. 5). In addition, the ultimate bending moment of the Surgalloy needles was significantly greater than that of the needles manufactured from the S45500 alloy (P < 0.01) (Fig. 6).
Needle Ductilit\ The ductility of the Surgalloy needles was significantly greater than that of the needles produced by the S45500
0.2
-0 !I I
Surgalloy Figure 2. Scanning etectron microscope photograph of me profiles of the Surgafioy needle (right) and the needle produced from tha 54e5800 alfey @ft). Note that the Surgailoy needbe haa a timer nwdfe point geometry man me needles produced from S45500 alloy.
Figure 4. The maximum
penetration
foroe through
me Med-
P8I@fWdWlBWforthO~-#dnot~*-
nificaMyfromthatoftheneedks alloy.
pmducedfromtheS45500
684
F. H. Watkins et al. bU
48.8 f3.2
I
Surgalloy
Surgalloy
Figure 5. The yield moment for the Surgalloy needles was significantly greater than that of the needles produced from the !34SXXI alloy.
alloy. The number of cycles neededto fracture the Surgalloy needles was approximately twofold greater than that required to fracture the needles produced by the S45500 alloy (P < 0.01) (Fig. 7). In addition, the work to fracture the Surgalloy needles was significantly greater than the work to fracture needlesproduced by the S45500 alloy (P < 0.01) (Fig. 8).
Figure 7. The number of cycles to fracture the Surgalloy needles was significantly greater than that required to fracture the needles produced from S455CKlalloy.
DISCUSSION The development of a high-nickel stainless steel representsa major advancein needle manufacture.A stainless steel, S45500, which contains 8.5% nickel, has been successfully used in the manufacture of surgical needles. Needles made from this stainless steel alloy are considerably stronger than stainless steels without nickel (3). Another high-nickel stainless steel, Surgalloy, which
624.8
94.5
f5.7 100-d
T
I
Surgalloy Figure 6. The ultimate bending moment for the Surgalloy needles was slgnifkantly greater than that of the needlee produced from the S45500 alloy.
I
Surgalloy Figure 8. The work to fracture the Surgalloy needles was signmcantly greater than that required to fracture the needles produced from s45500 alloy.
685
Cutting Edge Surgical Needs
contains 9% nickel, has been used recently to manufacture surgical needles. Our study of the biomechanical performance of Surgalley as compared to S45500 demonstrates that the Surgalloy has several superior characteristics over that of the S45500 alloy. Most importantly, it displays a greater resistance to bending than the S45500 alloy. Its superior resistance to bending allows Surgalloy needles to be manipulated close to their swages without the needle being inadvertently bent. Grasping the needle close to the swage between the jaws of the needle holder allows the emergency physician to manipulate the needle with considerable dexterity. This enhanced resistance to bending displayed by the Surgalloy needle is associated with considerable resistance to needle fracturing. The resistance to needle fracture of the Surgalloy needles is almost twofold greater than that of needles produced from S45500 alloy. The importance of a needle that resists breakage has implications both to the emergency physician and to the patient. The search for a broken needle fragment is often a futile quest that results in unnecessary damage to the wound. The presence of a dislodged needle fragment can be confusing to the patient, who may seek advice from an attorney rather than the physician. This enhanced strength of the Surgalloy needle allowed the manufacturer to narrow the point geometry of the needle without altering the resistance of the needle to bending. This narrowing of the point geometry of the cutting edge needle. however, does not enhance its
sharpness. The measured sharpness of needles with a wide point geometry is not significantly different from that of needles with a slim taper point geometry. The cost of the Surgalloy needle is comparable to that of the needle made of S45500 stainless steel alloy.
CONCLUSION
A new high-nickel stainless steel, Surpalloy. has been used to manufacture cutting edge surgical needles. The purpose of this investigation was to compare the biomechanical performance of the Surgalloy needle to that of another high-nickel stainless steel, S45500, used in the manufacture of surgical needles. Their biomechanical performance was judged by reproducible quantitative tests that measured sharpness, resistance to bending, and ductility. On the basis of these quantitative measurements, Surgalloy has several unique performance characteristics over the S45500 stainless steel alloy. Most importantly, the Surgalloy exhibits a stronger resistance to bending than the S45500 needles. In addition, the Surgalloy exhibits almost two times the resistance to fracture than do the needles produced from S45500 stainless steel alloy.
Acknowledgment-This research was supported by a generous gift from the Texaco Foundation. White Plains. NY
REFERENCES I. Edlich RF. Thacker JG, McGregor W, Rodeheaver GT. Past, present. and future for surgical needles and needle holders. Am J Surg. 1993; 166522-32. 2. Thacker JG. Rodeheaver GT. Towler MA, Edlich RF. Surgical needle sharpness. Am J Surg. 1989;157:334-9. 3. Abidin MR, Towler MA. Rodeheaver GT, Thacker JG, Cantrell RW. Edlich RF. Biomechanics of curved surgical needle bending. J Biomater Res. 1989;23: 129-43. 1. Manson TT, Bromberg WG. Thacker JG, McGregor W, Morgan
RF, Edlich RF. A new glove puncture detectcon system. J Emerg Med. 1995:13:357-64. 5. Towler MA. McGregor W, Rodeheaver GT. et al. Influence 01 cutting edge configuration on surgical needle penetration forces. J Emerg Med. 1988;6:475-81. 6. Abidin MR, Towler MA, Nochimson GD, Rodeheaver GT, Thacker JG, Edlich RF. A new quantitative measurement for surgical needle ductility. Ann Emerg Med. 1989:18:64-X.