- Email: [email protected]
Biomechanics of a new atraumatic surgical needle holder
The Journal of Emergency
Medicine,
Vol. 9, pp 477485,
Printed in the USA
1991
. Copyright
0 1991 Pergamon Press plc
BIOMECHANICS OF A NEW ATRAUMATIC SURGICAL NEEDLE HOLDER Michael A. Towler, MSME,* Norman C. Chen, BA,* Felice P. Moody, BS,* Walter McGregor, John G. Thacker, POD,+ George T. Rodeheaver, PhD,*Richard F. Edlich, MD, PhD*
MBA,*
*Department of Plastic Surgery, University of Virginia School of Medicine and the +Department of Mechanical and Aerospace Engineering, Charlottesville, Virginia Reprint address: Richard F. Edlich, MD, PhD, University of Virginia School of Medicine, Department of Plastic Surgery, Box 332, Charlottesville, VA 22908
0 Abstract - It is the purpose of this report to design, develop, and evaluate a needle holder whose jaws improve needle-holding security without altering the geometry of the curved surgicai needle. The configuration of the jaws of this new needle holder is curved, conforming to the curvature of the surgical needle. A biomechanical study of this curved surgical needle holder demonstrates that it holds the curved needle securely without needle deformation.
tories in tissue, which interfere with the physician’s ability to achieve meticulous coaptation of tissue without inadvertent injury to contiguous tissues (4). Consequently, it is the purpose of this report to design, develop, and evaluate a needle holder whose jaws improve needle holding security without altering the geometry of the curved surgical needle. The configuration of the jaws of this new needle holder is curved, conforming to the curvature of the surgical needle. A biomechanical study of this curved surgical needle holder demonstrates that it holds the curved needle securely without needle deformation. These curved jaws provide a greater resistance to needle rotation than flat needle holder jaws. Because the curved needle holder jaws can permit improved manipulation of the needle without bending, this new needle holder should enhance surgical precision, permitting meticulous wound closure.
0 Keywords - needle holder; curved jaws; deformation; surgical needles
INTRODUCTION
During the last decade, our research on the biomechanits of surgical needles has led to dramatic improvements in surgical needle design and alloy composition (l-6). Our research has now been expanded to search for a scientific basis for selecting surgical needle holders. The purpose of the surgical needle holder is to securely hold the curved surgical needle during its passage through tissue without altering the needle geometry. Because the surfaces of standard needle holder jaws are flat, they do not conform to the configuration of curved surgical needles. The flat needle holder jaws will irreversibly bend and flatten the curved surgical needle if the jaw closing forces are excessive (7). Such needle deformation leads to unpredictable needle trajec-
~ =
MATERIAL
AND METHODS
Needle Holder The two Crile Wood (Snowden-Pencer, Inc., Tucker, GA) needle holders used in this study exerted comparable clamping forces on the needles at each ratchet setting, and differed only in the configuration of the faces of the jaws that held the needle (Table 1). The jaws of one needle holder had standard smooth tungsten carbide inserts. In the new needle holder, these smooth inserts were replaced by curved jaw inserts that
Techniques and Procedures features practical, “how-to” articles of interest to all practicing This section is coordinated by George Sternbach, MD, Stanford University Medical Center.
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1991; ACCEFTED:8 February
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478
M. A. Towler et al.
Table 1. Needle Holder Speclflcatlons
Jaw
Length
Type Flat Curved
(cm)
LL* (cm)
LJ+ (cm)
Mechanical* Advantage
13.5 13.5
11.0 11.0
2.5 2.5
4.4 4.4
Jaw Widths (cm) 0.20 0.20
‘Length of the handle from the fulcrum to the site at which force is applied to the ringlets. ‘Length of the jaw from the fulcrum to the point at which the jaw holds the needle 2 mm from the tip of the jaw. SLL/L,. $2 mm from the needle holder jaw tip.
had apposable convex and concave clamping surfaces with a radius of curvature of 6 mm (Figure 1). These curved jaw inserts closed to approximate the circular curvature of surgical needles.
Needles
Three different curved surgical needles were supplied by the same manufacturer (Ethicon, Inc., Somerville, NJ) (Table II). All needles had a similar radius of curvature, varying from 5 .O to 6.8 mm. They differed predominantly in their diameters, varying from 0.36 to 0.66 mm. All needles were manufactured from the same stainless steel alloy (American Society For Testing Materials 45500).
Biomechanical Pe$ormance
The biomechanical performance of a needle holder is judged by its clamping moment, needle deformation, and needle holding security. The needle holder is an instrument designed to hold a curved surgical needle (Figure 2). It consists of two first class levers that rotate on a common fulcrum. The portions of the levers that grasp the needle are distal to the fulcrum and are called the jaws. The remaining portion of the lever, that portion which is held by the physician, is called the handle. On the end of the handle portion of each
shank is a ringlet through which a finger tip can be placed. The force placed on the ringlets (FF) is related directly to the force applied to the interface between the apposing jaws (F,). The force resulting from the closure of the jaws is directly proportional to length of handles and inversely related to the length of the jaws; it can be calculated by the following equation: r, FJ = Fpy J
where FJ = Force applied by jaws of needle holder, FF = Force applied by finger ringlets of the needle
holder, L, = Length of the shank from fulcrum to site at which force is applied to ring, LJ = Length of the jaw from the fulcrum to point at which jaws hold the needle (usually 2 mm from needle holder tip), and L,_lLJ = Mechanical advantage of the needle holder.
Clamping and Yield Moments
The clamping moment is a property of the needle holder that determines the magnitude of the stress on the clamped surgical needle (7). When a circular needle is clamped between the flat jaws of a needle holder, the needle contacts the jaws at three different sites
Table 2. Needle Speclflcatlons Needle Designation
Needle Mfgr
RBl PS4 CP5
Ethicon Ethicon Ethicon
Needle Diam.
Needle Length
Radius of Curvature
O-r-@
(mm)
(mm)
ASTM Alloy
11.0 10.3 13.5
17.5 16.0 21.0
5.5 5.0 6.8
45500 45500 45500
Chord Length
(mm)
Curvature in degrees + 5”
0.36 0.58 0.66
180 175 180
Atraumatic Surgical Needle Holder
Figure 1. Curved surgical needle holder Jaw Inserts.
(Figure 3). At midpoint in one jaw, a clamping force (F,) is applied to one site on the convex surface of the needle. Each edge of the opposing jaws surface applies separate and equal forces to the concave surface of the needle. The magnitude of each of these forces is exactly half the total clamping force (FJ2). Under this loading configuration, the maximum stress to which the needle is subjected occurs at the point where the applied clamping moment is greatest, which coincides with the site at which F, is applied to the convex needle surface. At this point, each F,/2 force applied to the concave needle surface exerts counterbalancing bending moments to keep the needle in static equilibrium. Consequently, the maximum clamping moment (M,) to which a needle under this loading configuration is subjected is expressed as: M, = F,/2
x WI2 = F, W/4.
Note that the F, force applied to the convex needle surface acts at the point of maximum clamping moment. Its moment arm is therefore zero, and it does not contribute to the total clamping moment.
479
The yield moment of a curved surgical needle is a material property defined as the maximum moment that can be applied to the surgical needle without causing permanent deformation (3). The ultimate moment is defined as the maximum bending moment after 90’ of needle deformation and is also an indication of needle strength. Using the curved surgical needle bend tester developed previously (3), the yield and ultimate moments for each of the needles used in this study were determined. The above equation that calculates the clamping moment (M,) was validated by observing that curved needles with yield moments less than the applied clamping moments exerted by needle holders were permanently deformed, while needles with yield moments greater than the applied clamping moments underwent reversible deformation (7). Reversible deformation refers to the elastic bending of a needle that resumes its original circular shape following removal from the needle holder. When a circular needle is clamped by a curved jaw needle holder, surface contact is made at all points along the needle body. As a result, FJ is distributed throughout the contacting jaw surface. Each component of F, on one side of the needle creating a clamping moment is counterbalanced by an equal F, component acting on the opposite side of the needle. Because all contributing clamping moments are counterbalanced, the effective clamping moment is zero. The clamping forces (F,) exerted by the flat and curved needle holder jaws were recorded at specific ratchet settings. During measurements of the clamping forces, PS4 and RBl needles were positioned 2 mm
Figure 2. Descriptive lnformatlon used to characterize the operatlon of the needle holder: FJ Is force applied to jaws of needle holder; F, Is force applled to rlnglets; L, Is the length of the shank from the fulcrum to site at which force Is spplled to the ring. LJ Is the length of the jaw from the fulcrum to the point at which the jaws hold the needle. The first [l], second [2], and third [3] lnterlocklng teeth of one ratchet are ldentlfled In the lllustratlon.
480
M. A. Towler et al.
DEFORMED SUTURE
NEEDLE
UNDEFORMED
to the ringlets slightly disengaged the interlocking teeth, after which the movement of the crosshead was stopped. As the direction of the crosshead was reversed, the force applied to the needle holder ringlet (FF) was recorded until the teeth in the specified ratchet setting reengaged. The maximal force encountered just before engagement of the interlocking teeth was judged to be the force required for engagement at the specified ratchet setting. Using the force (FF) placed on the ringlets, the clamping force (FJ) was calculated by multiplying it by the mechanical advantage (L/L,) of the needle holder. This measurement was repeated 8 times for each ratchet setting using the PS4 and RBl needles, after which the clamping moments were calculated.
NEEDLE
Needle Deformation
Permanent deformation of curved surgical needles due to the needle holder clamping is measured as an increase in needle chord length, which can be detected by a linear profile projector (Nikon Profile Projector Model No. 6c, Tokyo, Japan) (7). Needle chord length is the linear distance measured from the swage to the point of the needle. The flat- and curved-jaw needle holders were tested with PS4 and RBl needles. The initial chord length of each test needle was measured using the profile projector. The needle was then clamped 2 mm from the curved needle holder jaw tip for one minute. The resulting percent changes in chord length were noted. This measurement was repeated 8 times at each ratchet setting using a new needle for each test.
Figure 3. Anatomy of surgical needle holder clamplng.
from the needle holder jaw tip. This positioning was accomplished using an aluminum block with a 0.64-cm diameter hole drilled to a 2-mm depth. After setting the needle across the hole, the needle holder jaws were inserted to the prescribed depth of the hole and clamped about the needle 2 mm from the tip of the jaw. Each needle was clamped between the needle holder jaws at a site approximately 110” from the needle point. At this specified distance (2 mm) from the tip, the jaw width (W) was measured using calipers. The needle holder was then placed in a machinist’s vise on top of a compression load cell. The crosshead of the In&on@ Universal Tensile Tester (Canton, MA) was then lowered at 10 mm/min until the force applied
Needle Holding Security The needle-holding security of the flat- and curved-jaw
needle holders was determined by measuring the torque required either to rotate or to twist a CP5 needle held in the jaws of each needle holder (8). The CP5 needle was chosen because the magnitude of its yield moment was large enough to resist bending when the needleholding security tests were performed. Weak needles with low yield moments twist or bend before enough torque can be applied to the needle holder to cause needle slippage between the jaw surfaces. Using the aluminum block with the 2-mm hole, each needle holder was locked to the first ratchet setting about a CP5 needle at a position approximately 110” from the needle point. During each measurement, the CP5 nee-
Atraumatic
Surgical Needle Holder 481
Figure 4. The instrument used to measure rotational moment of the needle In the needle holder.
TO INSTRON
Figure 5. The instrument employed for measurlng the twisting moment of the needle In the needle holder.
482
M. A. Towler et al.
PS4 AND RBl NEEDLES
CLAMPED
2mm FROM
65.4 5?*6
0:4
62.t 5 * 45.6
074
TIP
?? 1st RATCHET SETTING
0:4
0
II-I RBl
PS4 CURVED JAW NEEDLE HOLDER
2nd
RATCHET SETTING
3rd
RATCHET SETTING
-
FLAT JAW NEEDLE HOLDER
Figure 6. The clamping forces (F.,) exerted by flat and curved needle holder jaws on PS4 and RBl needles.
dles were held securely in a clamping fixture by a vise, with the body of the needle projecting outward from the vise. Rotation of the needle holder occurred when the needle holder turned about the needle on its central axis (Figure 4). Before measuring the torque required to rotate the needle, a cable was attached to the needle holder ratchet and passed by a pulley to the load cell of the Model 1122 Instrot Tensile Tester. The moment arm length multiplied by the force detected by the load cell was the rotational moment. The variation in
PS4 AND RBl NEEDLES
moment length was small (f 0.5 mm). This test was repeated 8 times for each needle holder. The twisting needle axis is defined as the axis lying in the planes formed by the needle handles and rings that is perpendicular to the rotation axis and jaw face (Figure 5). Before measuring the twisting moments, a cable was attached to the ratchet mechanism because it was the central point of application of the force. Care was taken to ensure that the needle holder jaw did not contact the top of the vise as the needle holder twisted about the needle. This test was repeated 8 times for the
CLAMPED
2mm
FROM
TIP
3.27 2.53
0:2
2.03 0.6 ‘3 0.62
RBl CURVED JAW NEEDLE HOLDER
I
Es4
11
FLAT JAW NEEDLE HOLDER
Flgure 7. The clamplng moments (A&) exerted by flat and curved needle holder jaws on PS4 and FtBl needles.
483
Atraumatic Surgical Needle Holder
IO.6
mean and standard deviation of the data. The statistical significance of all data was determined by the Student’s t test.
0!2 ;r,
II-
8.8
IO-
of2
s-
RESULTS 8-
As judged by the clamping forces applied by the jaws (F,), the mechanical performance of the flat- and curvedjaw needle holders did not differ significantly (Figure 6). Advancing the ratchet setting from the lst, 2nd, and 3rd interlocking teeth of each needle holder resulted in significant increases in their jaw closing forces (P CO.01). The magnitude of the jaw closing forces was significantly influenced by the diameter of the needle clamped between the jaws. When needle holder jaws clamped PS4 (diameter 0.58 mm) needles at the site 2 mm from their jaw tips, the needle holder jaw clamping forces were significantly greater than those on the smaller diameter needles (RBl) (diameter 0.36 mm) (P -=C0.01). When the clamping moment was used as a measure of needle holder mechanical performance, there were dramatic differences between the performance of the flat and curved jaw needle holders (Figure 7). The clamping moments for the curved-jaw needle holder was not measurable, regardless of needle diameter or ratchet setting. In contrast, measurable clamping moments were calculated for the flat-jaw needle holder at each ratchet setting with each surgical needle. The
2.3 0:2
RBl
PS4
RBl
CP5
YIELD MOMENT
PS4
CP5
ULTIMATE
MOMENT
Figure 8. Needle yield and ultlmate moments were proportional to needle diameter.
flat- and curved-jaw needle holders. The needle holder clamping moments, twisting moments, rotational moments, needle yield moments, and percent chord length changes were expressed as the
PS4
AND RBI NEEDLES
CLAMPED
2mm
FROM TIP
0.92 0:6 0.08
0.05 0.10 0.08
PS4
0.12
O.!3
o.10
0.14 018
ff2$ I
RBl
CURVED JAW NEEDLE HOLDER
PS4 FLAT NEEDLE
JAW HOLDER
Figure 9. Needle deformation, a8 measured by change In needle chord length, followlng clamping by flat- and curved-jaw needle holders.
M. A. Towler et al.
484 CP5 NEEDLES
CLAMPED
2mm FROM
TIP
3.03 4
3
1.83 E Y Z
2
cd-3
surgical needles (PS4) with yield moments greater than the applied clamping moments of the flat-jaw needle holder were not significantly deformed by needle holder clamping, regardless of ratchet setting. The curved-jaw needle holder exhibited excellent needle holder security (Figure 10). Its rotational moment for the CP5 needle was significantly greater than that of the flat-jaw needle holder using the same needle type (P < 0.05). The twisting moments for the CP5 needles in the flat- and curved-jaw needle holders did not differ significantly.
1.43 o:,
DISCUSSION II-
0,-
l-k ROTATION MOMENT
MOMENT
Figure 10. Twisting and rotational moments for the flat- and curved-jaw needle holders.
magnitude of the clamping moment for the flat-jaw needle holder was significantly influenced by the size of the needle and the ratchet setting of the needle holder. The needle holder clamping moments on the larger diameter needles (PS4) were significantly greater than those on the smaller diameter needles (RBl) (P < 0.01). Similarly, advancing the ratchet setting resulted in significant incremental increases in the clamping moments (P < 0.01). As expected, the yield moment, which signifies the greatest applied load that results in reversible needle deformation, was significantly less than the ultimate moments for the same needle (P < 0.01) (Figure 8). The most important determinant of the magnitude of the yield moments for the curved surgical needle was the needle diameter. The yield moment of the curved surgical needle was proportional to its needle diameter. Because the curved-jaw needle holder had no measurable clamping moment, it imparted no significant permanent needle deformation, regardless of needle diameter or ratchet setting (Figure 9). The needle deformation caused by the flat-jaw needle holder correlated with the needle holder clamping moment and surgical needle yield moment. When the applied clamping moment of the flat-jaw needle holders exceeded the yield moment of the surgical needle (RBl), there was permanent needle deformation that increased incrementally with advancement of the ratchet setting. In contrast,
The most important consideration in the selection of a needle holder with flat jaws for use with a designated curved needle are the clamping moment of the needle holder and the yield moment of the needle (7). Ideally, the physician should select a needle holder in which the clamping moment is less than the needle yield moment. If the needle holder clamping moment exceeds that of the needle yield moment, clamping the needle between the jaws of the needle holder will result in irreversible bending of the needle. Because the manufacturers of needle holders and surgical needles provide no information regarding the clamping and yield moments, the physician has no scientific basis for selecting surgical needle holders and needles for wound closure. Consequently, a new curved-jaw surgical needle holder has been developed that has superior biomechanical performance properties compared to the standard flatjaw design. When this curved-jaw needle holder was used with surgical needles, it caused no significant needle deformation, regardless of needle diameter or ratchet setting. An additional advantage of the curved-jaw needle holder is that it holds the surgical needle more securely than a comparable flat-jaw needle holder. With the advent of a curved-jaw needle holder, the physician may now hold a surgical needle securely without deformation, ensuring a predictable needle passage through tissue.
CONCLUSION It is the purpose of this investigation to design, develop, and evaluate a new, atraumatic surgical needle holder whose jaws improve needle-holding security without altering the geometry of curved surgical needles. The configuration of the jaws of this new needle holder is curved and utilizes apposable convex and concave
485
Atraumatic Surgical Needle Holder
clamping surfaces, which conform to the circular curvature of surgical needles. The biomechanical performance of this new curved-jaw needle holder was compared to that of a comparable flat-jaw needle holder. The performance of these needle holders was evaluated by quantitating their jaw clamping forces and moments as well as their needle holding security. Measurement of the jaw clamping forces by an Instron Tensile Tester demonstrated comparable clamping forces for the curved- and flat-jaw needle holders. In contrast, the clamping moment for the curved-jaw needle holder was zero, while it ranged from 1.7 to 3.3 N-cm for the flat-jaw needle holder. Using an optical comparator, permanent needle deformation was demonstrated with the flat-jaw needle holder, while the curved-jaw needle holder did not alter needle geometry. Such needle de-
formation will lead to unpredictable needle trajectories in tissue, which interferes with the physician’s ability to achieve meticulous coaptation of tissue without inadvertent injury to contiguous tissues. An additional benefit of the curved-jaw needle holder is that it significantly increased needle-holding security (28%) as measured by its rotational jaw clamping moment when compared to the standard flat jaw design (P < 0.01). With the advent of a curved-jaw needle holder, a physician secures a surgical needle without deformation, ensuring a predictable needle passage through tissue.
Acknowledgement - This research was supported by a generous gift from the Texaco Philanthropic Foundation, White Plains, New York.
REFERENCES 1. Towler MA, McGregor W, Rodeheaver GT, et al. Influence of cutting edge configuration on surgical needle penetration forces. J Emerg Med. 1988;6:475-8 1. 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 Biomed Mat Res. 1989;23:129-43. 4. Abidin MR, Towler MA, Nochimson GD, Rodeheaver GT, Thacker JG, Edlich RF. A new quantitative measurement for surgical needle ductility. Ann Emerg Med. 1989;18:64-68. 5. Kaulbach HC. Towler MA, McClelland WA, et al. A beveled,
conventional cutting edge surgical needle: A new innovation in wound closure. J Emerg Med. 1990;8:253-63. 6. McClelland WA, Towler MA, Kaulbach HC, et al. Biomechanical performance of cardiovascular suture needles. Am Surg. 1990; 56:632-X. 7. Edlich RF, Towler MA, Rodeheaver GT, Becker DG, Lombardi SA, Thacker JG. Scientific basis for selecting surgical needles and needle holders for wound closure. Clin Plast Surg. 1990;17: 5X3-602. 8. Abidin MR. Dunlap JA, Towler MA, et al. Metallurgically bonded needle holder jaws: a technique to enhance needle holder security without sutural damage. Am Surg. 1990;56:643-7.
Medicine,
Vol. 9, pp 477485,
Printed in the USA
1991
. Copyright
0 1991 Pergamon Press plc
BIOMECHANICS OF A NEW ATRAUMATIC SURGICAL NEEDLE HOLDER Michael A. Towler, MSME,* Norman C. Chen, BA,* Felice P. Moody, BS,* Walter McGregor, John G. Thacker, POD,+ George T. Rodeheaver, PhD,*Richard F. Edlich, MD, PhD*
MBA,*
*Department of Plastic Surgery, University of Virginia School of Medicine and the +Department of Mechanical and Aerospace Engineering, Charlottesville, Virginia Reprint address: Richard F. Edlich, MD, PhD, University of Virginia School of Medicine, Department of Plastic Surgery, Box 332, Charlottesville, VA 22908
0 Abstract - It is the purpose of this report to design, develop, and evaluate a needle holder whose jaws improve needle-holding security without altering the geometry of the curved surgicai needle. The configuration of the jaws of this new needle holder is curved, conforming to the curvature of the surgical needle. A biomechanical study of this curved surgical needle holder demonstrates that it holds the curved needle securely without needle deformation.
tories in tissue, which interfere with the physician’s ability to achieve meticulous coaptation of tissue without inadvertent injury to contiguous tissues (4). Consequently, it is the purpose of this report to design, develop, and evaluate a needle holder whose jaws improve needle holding security without altering the geometry of the curved surgical needle. The configuration of the jaws of this new needle holder is curved, conforming to the curvature of the surgical needle. A biomechanical study of this curved surgical needle holder demonstrates that it holds the curved needle securely without needle deformation. These curved jaws provide a greater resistance to needle rotation than flat needle holder jaws. Because the curved needle holder jaws can permit improved manipulation of the needle without bending, this new needle holder should enhance surgical precision, permitting meticulous wound closure.
0 Keywords - needle holder; curved jaws; deformation; surgical needles
INTRODUCTION
During the last decade, our research on the biomechanits of surgical needles has led to dramatic improvements in surgical needle design and alloy composition (l-6). Our research has now been expanded to search for a scientific basis for selecting surgical needle holders. The purpose of the surgical needle holder is to securely hold the curved surgical needle during its passage through tissue without altering the needle geometry. Because the surfaces of standard needle holder jaws are flat, they do not conform to the configuration of curved surgical needles. The flat needle holder jaws will irreversibly bend and flatten the curved surgical needle if the jaw closing forces are excessive (7). Such needle deformation leads to unpredictable needle trajec-
~ =
MATERIAL
AND METHODS
Needle Holder The two Crile Wood (Snowden-Pencer, Inc., Tucker, GA) needle holders used in this study exerted comparable clamping forces on the needles at each ratchet setting, and differed only in the configuration of the faces of the jaws that held the needle (Table 1). The jaws of one needle holder had standard smooth tungsten carbide inserts. In the new needle holder, these smooth inserts were replaced by curved jaw inserts that
Techniques and Procedures features practical, “how-to” articles of interest to all practicing This section is coordinated by George Sternbach, MD, Stanford University Medical Center.
RECEIVED:28
January
1991; ACCEFTED:8 February
1991
emergency
0736-4679/91 477
physicians.
$3.00 + .OO
478
M. A. Towler et al.
Table 1. Needle Holder Speclflcatlons
Jaw
Length
Type Flat Curved
(cm)
LL* (cm)
LJ+ (cm)
Mechanical* Advantage
13.5 13.5
11.0 11.0
2.5 2.5
4.4 4.4
Jaw Widths (cm) 0.20 0.20
‘Length of the handle from the fulcrum to the site at which force is applied to the ringlets. ‘Length of the jaw from the fulcrum to the point at which the jaw holds the needle 2 mm from the tip of the jaw. SLL/L,. $2 mm from the needle holder jaw tip.
had apposable convex and concave clamping surfaces with a radius of curvature of 6 mm (Figure 1). These curved jaw inserts closed to approximate the circular curvature of surgical needles.
Needles
Three different curved surgical needles were supplied by the same manufacturer (Ethicon, Inc., Somerville, NJ) (Table II). All needles had a similar radius of curvature, varying from 5 .O to 6.8 mm. They differed predominantly in their diameters, varying from 0.36 to 0.66 mm. All needles were manufactured from the same stainless steel alloy (American Society For Testing Materials 45500).
Biomechanical Pe$ormance
The biomechanical performance of a needle holder is judged by its clamping moment, needle deformation, and needle holding security. The needle holder is an instrument designed to hold a curved surgical needle (Figure 2). It consists of two first class levers that rotate on a common fulcrum. The portions of the levers that grasp the needle are distal to the fulcrum and are called the jaws. The remaining portion of the lever, that portion which is held by the physician, is called the handle. On the end of the handle portion of each
shank is a ringlet through which a finger tip can be placed. The force placed on the ringlets (FF) is related directly to the force applied to the interface between the apposing jaws (F,). The force resulting from the closure of the jaws is directly proportional to length of handles and inversely related to the length of the jaws; it can be calculated by the following equation: r, FJ = Fpy J
where FJ = Force applied by jaws of needle holder, FF = Force applied by finger ringlets of the needle
holder, L, = Length of the shank from fulcrum to site at which force is applied to ring, LJ = Length of the jaw from the fulcrum to point at which jaws hold the needle (usually 2 mm from needle holder tip), and L,_lLJ = Mechanical advantage of the needle holder.
Clamping and Yield Moments
The clamping moment is a property of the needle holder that determines the magnitude of the stress on the clamped surgical needle (7). When a circular needle is clamped between the flat jaws of a needle holder, the needle contacts the jaws at three different sites
Table 2. Needle Speclflcatlons Needle Designation
Needle Mfgr
RBl PS4 CP5
Ethicon Ethicon Ethicon
Needle Diam.
Needle Length
Radius of Curvature
O-r-@
(mm)
(mm)
ASTM Alloy
11.0 10.3 13.5
17.5 16.0 21.0
5.5 5.0 6.8
45500 45500 45500
Chord Length
(mm)
Curvature in degrees + 5”
0.36 0.58 0.66
180 175 180
Atraumatic Surgical Needle Holder
Figure 1. Curved surgical needle holder Jaw Inserts.
(Figure 3). At midpoint in one jaw, a clamping force (F,) is applied to one site on the convex surface of the needle. Each edge of the opposing jaws surface applies separate and equal forces to the concave surface of the needle. The magnitude of each of these forces is exactly half the total clamping force (FJ2). Under this loading configuration, the maximum stress to which the needle is subjected occurs at the point where the applied clamping moment is greatest, which coincides with the site at which F, is applied to the convex needle surface. At this point, each F,/2 force applied to the concave needle surface exerts counterbalancing bending moments to keep the needle in static equilibrium. Consequently, the maximum clamping moment (M,) to which a needle under this loading configuration is subjected is expressed as: M, = F,/2
x WI2 = F, W/4.
Note that the F, force applied to the convex needle surface acts at the point of maximum clamping moment. Its moment arm is therefore zero, and it does not contribute to the total clamping moment.
479
The yield moment of a curved surgical needle is a material property defined as the maximum moment that can be applied to the surgical needle without causing permanent deformation (3). The ultimate moment is defined as the maximum bending moment after 90’ of needle deformation and is also an indication of needle strength. Using the curved surgical needle bend tester developed previously (3), the yield and ultimate moments for each of the needles used in this study were determined. The above equation that calculates the clamping moment (M,) was validated by observing that curved needles with yield moments less than the applied clamping moments exerted by needle holders were permanently deformed, while needles with yield moments greater than the applied clamping moments underwent reversible deformation (7). Reversible deformation refers to the elastic bending of a needle that resumes its original circular shape following removal from the needle holder. When a circular needle is clamped by a curved jaw needle holder, surface contact is made at all points along the needle body. As a result, FJ is distributed throughout the contacting jaw surface. Each component of F, on one side of the needle creating a clamping moment is counterbalanced by an equal F, component acting on the opposite side of the needle. Because all contributing clamping moments are counterbalanced, the effective clamping moment is zero. The clamping forces (F,) exerted by the flat and curved needle holder jaws were recorded at specific ratchet settings. During measurements of the clamping forces, PS4 and RBl needles were positioned 2 mm
Figure 2. Descriptive lnformatlon used to characterize the operatlon of the needle holder: FJ Is force applied to jaws of needle holder; F, Is force applled to rlnglets; L, Is the length of the shank from the fulcrum to site at which force Is spplled to the ring. LJ Is the length of the jaw from the fulcrum to the point at which the jaws hold the needle. The first [l], second [2], and third [3] lnterlocklng teeth of one ratchet are ldentlfled In the lllustratlon.
480
M. A. Towler et al.
DEFORMED SUTURE
NEEDLE
UNDEFORMED
to the ringlets slightly disengaged the interlocking teeth, after which the movement of the crosshead was stopped. As the direction of the crosshead was reversed, the force applied to the needle holder ringlet (FF) was recorded until the teeth in the specified ratchet setting reengaged. The maximal force encountered just before engagement of the interlocking teeth was judged to be the force required for engagement at the specified ratchet setting. Using the force (FF) placed on the ringlets, the clamping force (FJ) was calculated by multiplying it by the mechanical advantage (L/L,) of the needle holder. This measurement was repeated 8 times for each ratchet setting using the PS4 and RBl needles, after which the clamping moments were calculated.
NEEDLE
Needle Deformation
Permanent deformation of curved surgical needles due to the needle holder clamping is measured as an increase in needle chord length, which can be detected by a linear profile projector (Nikon Profile Projector Model No. 6c, Tokyo, Japan) (7). Needle chord length is the linear distance measured from the swage to the point of the needle. The flat- and curved-jaw needle holders were tested with PS4 and RBl needles. The initial chord length of each test needle was measured using the profile projector. The needle was then clamped 2 mm from the curved needle holder jaw tip for one minute. The resulting percent changes in chord length were noted. This measurement was repeated 8 times at each ratchet setting using a new needle for each test.
Figure 3. Anatomy of surgical needle holder clamplng.
from the needle holder jaw tip. This positioning was accomplished using an aluminum block with a 0.64-cm diameter hole drilled to a 2-mm depth. After setting the needle across the hole, the needle holder jaws were inserted to the prescribed depth of the hole and clamped about the needle 2 mm from the tip of the jaw. Each needle was clamped between the needle holder jaws at a site approximately 110” from the needle point. At this specified distance (2 mm) from the tip, the jaw width (W) was measured using calipers. The needle holder was then placed in a machinist’s vise on top of a compression load cell. The crosshead of the In&on@ Universal Tensile Tester (Canton, MA) was then lowered at 10 mm/min until the force applied
Needle Holding Security The needle-holding security of the flat- and curved-jaw
needle holders was determined by measuring the torque required either to rotate or to twist a CP5 needle held in the jaws of each needle holder (8). The CP5 needle was chosen because the magnitude of its yield moment was large enough to resist bending when the needleholding security tests were performed. Weak needles with low yield moments twist or bend before enough torque can be applied to the needle holder to cause needle slippage between the jaw surfaces. Using the aluminum block with the 2-mm hole, each needle holder was locked to the first ratchet setting about a CP5 needle at a position approximately 110” from the needle point. During each measurement, the CP5 nee-
Atraumatic
Surgical Needle Holder 481
Figure 4. The instrument used to measure rotational moment of the needle In the needle holder.
TO INSTRON
Figure 5. The instrument employed for measurlng the twisting moment of the needle In the needle holder.
482
M. A. Towler et al.
PS4 AND RBl NEEDLES
CLAMPED
2mm FROM
65.4 5?*6
0:4
62.t 5 * 45.6
074
TIP
?? 1st RATCHET SETTING
0:4
0
II-I RBl
PS4 CURVED JAW NEEDLE HOLDER
2nd
RATCHET SETTING
3rd
RATCHET SETTING
-
FLAT JAW NEEDLE HOLDER
Figure 6. The clamping forces (F.,) exerted by flat and curved needle holder jaws on PS4 and RBl needles.
dles were held securely in a clamping fixture by a vise, with the body of the needle projecting outward from the vise. Rotation of the needle holder occurred when the needle holder turned about the needle on its central axis (Figure 4). Before measuring the torque required to rotate the needle, a cable was attached to the needle holder ratchet and passed by a pulley to the load cell of the Model 1122 Instrot Tensile Tester. The moment arm length multiplied by the force detected by the load cell was the rotational moment. The variation in
PS4 AND RBl NEEDLES
moment length was small (f 0.5 mm). This test was repeated 8 times for each needle holder. The twisting needle axis is defined as the axis lying in the planes formed by the needle handles and rings that is perpendicular to the rotation axis and jaw face (Figure 5). Before measuring the twisting moments, a cable was attached to the ratchet mechanism because it was the central point of application of the force. Care was taken to ensure that the needle holder jaw did not contact the top of the vise as the needle holder twisted about the needle. This test was repeated 8 times for the
CLAMPED
2mm
FROM
TIP
3.27 2.53
0:2
2.03 0.6 ‘3 0.62
RBl CURVED JAW NEEDLE HOLDER
I
Es4
11
FLAT JAW NEEDLE HOLDER
Flgure 7. The clamplng moments (A&) exerted by flat and curved needle holder jaws on PS4 and FtBl needles.
483
Atraumatic Surgical Needle Holder
IO.6
mean and standard deviation of the data. The statistical significance of all data was determined by the Student’s t test.
0!2 ;r,
II-
8.8
IO-
of2
s-
RESULTS 8-
As judged by the clamping forces applied by the jaws (F,), the mechanical performance of the flat- and curvedjaw needle holders did not differ significantly (Figure 6). Advancing the ratchet setting from the lst, 2nd, and 3rd interlocking teeth of each needle holder resulted in significant increases in their jaw closing forces (P CO.01). The magnitude of the jaw closing forces was significantly influenced by the diameter of the needle clamped between the jaws. When needle holder jaws clamped PS4 (diameter 0.58 mm) needles at the site 2 mm from their jaw tips, the needle holder jaw clamping forces were significantly greater than those on the smaller diameter needles (RBl) (diameter 0.36 mm) (P -=C0.01). When the clamping moment was used as a measure of needle holder mechanical performance, there were dramatic differences between the performance of the flat and curved jaw needle holders (Figure 7). The clamping moments for the curved-jaw needle holder was not measurable, regardless of needle diameter or ratchet setting. In contrast, measurable clamping moments were calculated for the flat-jaw needle holder at each ratchet setting with each surgical needle. The
2.3 0:2
RBl
PS4
RBl
CP5
YIELD MOMENT
PS4
CP5
ULTIMATE
MOMENT
Figure 8. Needle yield and ultlmate moments were proportional to needle diameter.
flat- and curved-jaw needle holders. The needle holder clamping moments, twisting moments, rotational moments, needle yield moments, and percent chord length changes were expressed as the
PS4
AND RBI NEEDLES
CLAMPED
2mm
FROM TIP
0.92 0:6 0.08
0.05 0.10 0.08
PS4
0.12
O.!3
o.10
0.14 018
ff2$ I
RBl
CURVED JAW NEEDLE HOLDER
PS4 FLAT NEEDLE
JAW HOLDER
Figure 9. Needle deformation, a8 measured by change In needle chord length, followlng clamping by flat- and curved-jaw needle holders.
M. A. Towler et al.
484 CP5 NEEDLES
CLAMPED
2mm FROM
TIP
3.03 4
3
1.83 E Y Z
2
cd-3
surgical needles (PS4) with yield moments greater than the applied clamping moments of the flat-jaw needle holder were not significantly deformed by needle holder clamping, regardless of ratchet setting. The curved-jaw needle holder exhibited excellent needle holder security (Figure 10). Its rotational moment for the CP5 needle was significantly greater than that of the flat-jaw needle holder using the same needle type (P < 0.05). The twisting moments for the CP5 needles in the flat- and curved-jaw needle holders did not differ significantly.
1.43 o:,
DISCUSSION II-
0,-
l-k ROTATION MOMENT
MOMENT
Figure 10. Twisting and rotational moments for the flat- and curved-jaw needle holders.
magnitude of the clamping moment for the flat-jaw needle holder was significantly influenced by the size of the needle and the ratchet setting of the needle holder. The needle holder clamping moments on the larger diameter needles (PS4) were significantly greater than those on the smaller diameter needles (RBl) (P < 0.01). Similarly, advancing the ratchet setting resulted in significant incremental increases in the clamping moments (P < 0.01). As expected, the yield moment, which signifies the greatest applied load that results in reversible needle deformation, was significantly less than the ultimate moments for the same needle (P < 0.01) (Figure 8). The most important determinant of the magnitude of the yield moments for the curved surgical needle was the needle diameter. The yield moment of the curved surgical needle was proportional to its needle diameter. Because the curved-jaw needle holder had no measurable clamping moment, it imparted no significant permanent needle deformation, regardless of needle diameter or ratchet setting (Figure 9). The needle deformation caused by the flat-jaw needle holder correlated with the needle holder clamping moment and surgical needle yield moment. When the applied clamping moment of the flat-jaw needle holders exceeded the yield moment of the surgical needle (RBl), there was permanent needle deformation that increased incrementally with advancement of the ratchet setting. In contrast,
The most important consideration in the selection of a needle holder with flat jaws for use with a designated curved needle are the clamping moment of the needle holder and the yield moment of the needle (7). Ideally, the physician should select a needle holder in which the clamping moment is less than the needle yield moment. If the needle holder clamping moment exceeds that of the needle yield moment, clamping the needle between the jaws of the needle holder will result in irreversible bending of the needle. Because the manufacturers of needle holders and surgical needles provide no information regarding the clamping and yield moments, the physician has no scientific basis for selecting surgical needle holders and needles for wound closure. Consequently, a new curved-jaw surgical needle holder has been developed that has superior biomechanical performance properties compared to the standard flatjaw design. When this curved-jaw needle holder was used with surgical needles, it caused no significant needle deformation, regardless of needle diameter or ratchet setting. An additional advantage of the curved-jaw needle holder is that it holds the surgical needle more securely than a comparable flat-jaw needle holder. With the advent of a curved-jaw needle holder, the physician may now hold a surgical needle securely without deformation, ensuring a predictable needle passage through tissue.
CONCLUSION It is the purpose of this investigation to design, develop, and evaluate a new, atraumatic surgical needle holder whose jaws improve needle-holding security without altering the geometry of curved surgical needles. The configuration of the jaws of this new needle holder is curved and utilizes apposable convex and concave
485
Atraumatic Surgical Needle Holder
clamping surfaces, which conform to the circular curvature of surgical needles. The biomechanical performance of this new curved-jaw needle holder was compared to that of a comparable flat-jaw needle holder. The performance of these needle holders was evaluated by quantitating their jaw clamping forces and moments as well as their needle holding security. Measurement of the jaw clamping forces by an Instron Tensile Tester demonstrated comparable clamping forces for the curved- and flat-jaw needle holders. In contrast, the clamping moment for the curved-jaw needle holder was zero, while it ranged from 1.7 to 3.3 N-cm for the flat-jaw needle holder. Using an optical comparator, permanent needle deformation was demonstrated with the flat-jaw needle holder, while the curved-jaw needle holder did not alter needle geometry. Such needle de-
formation will lead to unpredictable needle trajectories in tissue, which interferes with the physician’s ability to achieve meticulous coaptation of tissue without inadvertent injury to contiguous tissues. An additional benefit of the curved-jaw needle holder is that it significantly increased needle-holding security (28%) as measured by its rotational jaw clamping moment when compared to the standard flat jaw design (P < 0.01). With the advent of a curved-jaw needle holder, a physician secures a surgical needle without deformation, ensuring a predictable needle passage through tissue.
Acknowledgement - This research was supported by a generous gift from the Texaco Philanthropic Foundation, White Plains, New York.
REFERENCES 1. Towler MA, McGregor W, Rodeheaver GT, et al. Influence of cutting edge configuration on surgical needle penetration forces. J Emerg Med. 1988;6:475-8 1. 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 Biomed Mat Res. 1989;23:129-43. 4. Abidin MR, Towler MA, Nochimson GD, Rodeheaver GT, Thacker JG, Edlich RF. A new quantitative measurement for surgical needle ductility. Ann Emerg Med. 1989;18:64-68. 5. Kaulbach HC. Towler MA, McClelland WA, et al. A beveled,
conventional cutting edge surgical needle: A new innovation in wound closure. J Emerg Med. 1990;8:253-63. 6. McClelland WA, Towler MA, Kaulbach HC, et al. Biomechanical performance of cardiovascular suture needles. Am Surg. 1990; 56:632-X. 7. Edlich RF, Towler MA, Rodeheaver GT, Becker DG, Lombardi SA, Thacker JG. Scientific basis for selecting surgical needles and needle holders for wound closure. Clin Plast Surg. 1990;17: 5X3-602. 8. Abidin MR. Dunlap JA, Towler MA, et al. Metallurgically bonded needle holder jaws: a technique to enhance needle holder security without sutural damage. Am Surg. 1990;56:643-7.