A Fractured Epidural Needle: Case Report and Study Steven M. Dunn, MD, Robert B. Steinberg, MD, PhD, Patricia s. O’Sullivan, EdD, Wade T. Goolishian, MD, and Evelyn A. Villa,
MD
Department of Anesthesiology, Baystate Medical Center, Tufts University School of Medicine, Springfield, Massachusetts
E
pidural blocks are most commonly performed using a 17-gauge needle to permit easy passage of the catheter. The durability of these largegauge needles can be inferred by the lack of any reports of breakage other than separation at the hub-needle shaft junction (1). Recent improvements in catheter technology and the availability of smaller gauge catheters have generated increased interest in using smaller needles for both epidural and continuous spinal anesthesia. We report a case of a midshaft fracture of an 18-gauge Tuohy needle during an attempted administration of epidural anesthesia.
Case Report A healthy 18-yr-old, 114-kg, 170-cm woman, gravida 2, para 1, at term was admitted to the labor suite in active labor. At 6-7-cm cervical dilatation, consent was obtained for epidural anesthesia. A CA-3 anesthesiology resident in the fourth month of an obstetric anesthesia subspecialty rotation attempted the block. The bony landmarks were difficult to palpate owing to obesity, so the patient was placed in the sitting position, and the skin was painted with an antiseptic solution and draped in the usual manner. The L3-4 interspace was approximated, and an 18-gauge, thinwalled Tuohy needle (American Medical Instruments, New Bedford, Mass.) was advanced until resistance was encountered. The stylet was removed, and a Pulsator syringe (ConcordPortex, Keene, N.H.) filled with 0.9% saline was attached. The needle was advanced with constant pressure on the syringe plunger. After inserting the needle an additional 1 cm, the resistance to advancement increased. The resident thought that this was due to calcified ligament, and the resistance was overcome with a transient increase in the pressure applied to the needle. The needle was then advanced to the hub with no perceived loss of resistance. On attempting to withdraw the needle, moderate resistance was encountered followed by a sudden release. The needle had fractured at the midshaft, leaving a 4.5-cm fragment in the patient. Epidural placement was Accepted for publication July 14, 1992. Address correspondence to Dr. Dunn, Department of Anesthesiology, Baystate Medical Center, 759 Chestnut Street, Springfield, MA 01199.
1050
Anesth Analg 1992;75:105&2
abandoned. The patient was positioned on her side for the remainder of her labor and delivery without problems. After delivery, the patient was brought to the operating room, and the needle fragment was located by a neurosurgeon using fluoroscopy. The needle was lateral to the midline and had encountered the lamina of L4 rather than the interspinous ligament or the spinous process. Under local anesthesia, a small incision was made, and the fragment was grasped with a forceps and removed. Postoperatively, the patient complained of localized back pain with no radiation or signs of nerve injury. We postulated that as the axial force on the needle against the bone increased, it bowed and eventually kinked. After this kink occurred, the resistance to forward movement decreased. This was misinterpreted as the “give” when a needle is passed over a vertebral spine, and the needle continued to bend as it was advanced to the hub. The action of withdrawing the needle caused it to break at the kink point. Our initial perception was that the needle involved in this incident might have been defective. However, studies of additional 18-gauge Tuohy needles from the same manufacturer revealed that they kinked easily when axial force was applied to the needle without the stylet in place. In view of this, we initiated a more systematic study of the stiffness and malleability of epidural needles to see whether there were differences among manufacturers. Sample lots of ten 18- and 17-gauge epidural needles were obtained from seven manufacturers for comparison (Table 1).The outer diameter of each needle was measured at its midpoint using a micrometer. The needles were placed in a Luer lock fitting and compressed at a fixed rate of speed by an Instron Universal Testing Device (Instron Corporation, Canton, Mass.). This machine applies a variable axial force to the needle (Figure 1).Buckling force, the force applied when the needle first began to bend, was chosen as an index of needle stiffness. Malleability was assessed by measuring the distance (displacement) by which the needle was compressed in the axial direction when kinking first occurred. Descriptive statistics were obtained for each type of needle. To determine the association among selected variables, correlation coefficients were calculated. Comparisons among different groupings of needle types were made with nonparametric analysis of variance. The outer diameters, buckling forces, and displacements for the different needles are displayed in Table 1. Each 01992 by the International Anesthesia Research Society 0003-2999/921$5.00
ANESTH ANALG
1051
CASE REPORTS
1%2;75 1050-2
Table 1. Epidural Needle Measured Outer Diameters, Buckling Forces, and Displacements Needle tvue"
Outer diameter (in.)
Buckling force (N)
0.0502 t 0.000025 0.0530 0.000042 0.0532 t 0.000025 0.0499 t 0.000017 0.0502 f 0.000035 0.0532 t 0.000021 0.0498 f 0.000032 0.0577 0.000032 0.0583 t 0.000032 0.0589 t 0.000063
27.07 4 0.38 38.69 4 0.57 40.32 t 0.73 28.58 4 0.67 29.49 4 0.67 38.26 4 0.76 30.56 2 0.17 40.62 4 0.38 0.43 50.02 57.49 0.69
*
*
*
6o
1
rn BN(17)
Displacement (mm) 15.34 16.60 22.28 21.53 14.18 16.64 22.54 24.37 18.90
H
0.25 0.24 2 0.11 f 0.14 t 0.33 f 0.30 f 0.22 22.54 f 0.18 ?
a
BD(17)
?
AMI, American Medical Instruments, New Bedford, Mass.; BD, Becton Dickinson, Franklin Lakes, N.J.; BN, Burron Medical Inc., Bethlehem, Pa.; BR, Baxter International Inc., Deerfield, Ill.; K, Kendall Healthcare Products Company, Mansfield, Mass.; M, Manan Medical Products Inc., Northbrook, Ill.; S, Sherwood Medical Company, St. Louis, Mo. Values are expressed as mean SEM; n = 10. 'Numbers in parentheses are gauges.
-
0 LL
20
0.050
I
0.054
0.056
0.058
0.060
Figure 2. The needle buckling force (stiffness) plotted against measured needle outer diameter. Numbers in parentheses are gauges. Each buckling force and diameter measurement represents the mean of 10 samples. Abbreviations as in Table 1.
Overhead
Adapter Luer Lock Fitting
Needle Sample
&I3
0.052
Outer Diameter (inches)
*
*
K(17)
f 0.17 f 0.21
24
l
0
A
-
BD(18ga)
E
E -
K(17ga)
0
0
18-
.-
0
s(18ga) BR(18ga)
-
Base
entry in the table represents the mean of 10 samples with the standard error of the mean. The measured diameters stratified the needles into three different groups, as seen in Figure 2. The 17-gauge needles had an average diameter of 0.058 in. The 18-gaugeneedles fell into two distinct groups, with mean diameters of 0.053 and 0.050 in. Figure 2 also shows how the buckling force correlates with the measured outer diameter (Y = 0.93; P = 0.0001). The three groupings of points differed significantly from each other with respect to buckling force (P < 0.02; Kruskal-Wallis nonparametric analysis of variance). Figure 3 shows the mean displacement plotted against the mean outer diameters for each brand of needle. Displacement did not correlate significantly with needle diameter (Y = 0.41; P = 0.24). The Becton Dickinson, Burron, and Manan needles (Figure 3, solid dots) had displacement values significantly higher than the others (P < 0.008; Mann-Whitney U test).
BN(17ga)
20-
16
Figure 1. A schematic representation of the Instron Universal Testing Device.
0
BN(18ga)
M(18)
v
a
0
UJ
Polyethylene
BD(17ga)
o AMl(18ga)
14
K(18ga) I
.
I
.
I
.
I
.
I
.
1
Discussion Epidural needles are often subjected to a substantial degree of axial force. This is due to the combination of the size and dullness of the needle, as well as the firmness of the interspinous ligaments and frequent impingement on bone. The standard procedure for placement of an epidural needle requires the removal of the stylet after the needle is advanced into the interspinous ligament. This allows the use of the loss of resistance or hanging drop technique to detect
1052
ANESTH ANALG 1992;751050-2
CASE REPORTS
entry into the epidural space. With the stylet removed, the stiffness of the needle decreases, making it easier to buckle. After some critical amount of bending without the stylet in place, the shaft will kink, occluding the lumen. Once this kinking occurs, if the needle is then bent back toward its original shape, it is very likely to break. We cannot be certain that the fracture mechanism we propose, and partially verified in the laboratory, represents the events in our case. In vivo, the tissues surrounding the needle may apply forces in a nonaxial direction; if the patient should move, or if the needle is "walked off" the spinous process improperly, significant lateral or twisting forces may result. Buckling force was proportional to the outer diameter of the needle, whereas displacement correlated poorly with diameter. Among needles of a given diameter, variations in displacement values probably arise from differences in the composition of the alloy from which the needle is constructed and from differences in wall thickness. We did not attempt to quantify these two variables. In conclusion, we report a case of midshaft fracture of an 18-gauge epidural needle. As a result of this case, we studied epidural needles from seven manu-
facturers and found significant variation in their stiffness and malleability, as assessed by buckling force and displacement, respectively. The needle that failed in our case has the lowest buckling force and the second lowest displacement value of the needles we tested. This would suggest that this needle is more likely to bend than the others and will kink very soon after it begins to bend. Stiffness correlates with the measured needle diameter but malleability does not. Although midshaft fracture of an epidural needle occurs infrequently, this is a serious complication, because the retained needle fragment, being rigid and sharp, ought to be removed. The potential for further injury is obvious. If needle fractures indeed occur as we postulate, the needles that have the best combination of resistance to buckling and greater malleability once buckling occurs should be least likely to break.
Reference 1. Schlake I T,Peleman RR, Winnie AP. Separation of the hub from the shaft of a disposable epidural needle. Anesthesiology 1988;68:611-3.
MD
Department of Anesthesiology, Baystate Medical Center, Tufts University School of Medicine, Springfield, Massachusetts
E
pidural blocks are most commonly performed using a 17-gauge needle to permit easy passage of the catheter. The durability of these largegauge needles can be inferred by the lack of any reports of breakage other than separation at the hub-needle shaft junction (1). Recent improvements in catheter technology and the availability of smaller gauge catheters have generated increased interest in using smaller needles for both epidural and continuous spinal anesthesia. We report a case of a midshaft fracture of an 18-gauge Tuohy needle during an attempted administration of epidural anesthesia.
Case Report A healthy 18-yr-old, 114-kg, 170-cm woman, gravida 2, para 1, at term was admitted to the labor suite in active labor. At 6-7-cm cervical dilatation, consent was obtained for epidural anesthesia. A CA-3 anesthesiology resident in the fourth month of an obstetric anesthesia subspecialty rotation attempted the block. The bony landmarks were difficult to palpate owing to obesity, so the patient was placed in the sitting position, and the skin was painted with an antiseptic solution and draped in the usual manner. The L3-4 interspace was approximated, and an 18-gauge, thinwalled Tuohy needle (American Medical Instruments, New Bedford, Mass.) was advanced until resistance was encountered. The stylet was removed, and a Pulsator syringe (ConcordPortex, Keene, N.H.) filled with 0.9% saline was attached. The needle was advanced with constant pressure on the syringe plunger. After inserting the needle an additional 1 cm, the resistance to advancement increased. The resident thought that this was due to calcified ligament, and the resistance was overcome with a transient increase in the pressure applied to the needle. The needle was then advanced to the hub with no perceived loss of resistance. On attempting to withdraw the needle, moderate resistance was encountered followed by a sudden release. The needle had fractured at the midshaft, leaving a 4.5-cm fragment in the patient. Epidural placement was Accepted for publication July 14, 1992. Address correspondence to Dr. Dunn, Department of Anesthesiology, Baystate Medical Center, 759 Chestnut Street, Springfield, MA 01199.
1050
Anesth Analg 1992;75:105&2
abandoned. The patient was positioned on her side for the remainder of her labor and delivery without problems. After delivery, the patient was brought to the operating room, and the needle fragment was located by a neurosurgeon using fluoroscopy. The needle was lateral to the midline and had encountered the lamina of L4 rather than the interspinous ligament or the spinous process. Under local anesthesia, a small incision was made, and the fragment was grasped with a forceps and removed. Postoperatively, the patient complained of localized back pain with no radiation or signs of nerve injury. We postulated that as the axial force on the needle against the bone increased, it bowed and eventually kinked. After this kink occurred, the resistance to forward movement decreased. This was misinterpreted as the “give” when a needle is passed over a vertebral spine, and the needle continued to bend as it was advanced to the hub. The action of withdrawing the needle caused it to break at the kink point. Our initial perception was that the needle involved in this incident might have been defective. However, studies of additional 18-gauge Tuohy needles from the same manufacturer revealed that they kinked easily when axial force was applied to the needle without the stylet in place. In view of this, we initiated a more systematic study of the stiffness and malleability of epidural needles to see whether there were differences among manufacturers. Sample lots of ten 18- and 17-gauge epidural needles were obtained from seven manufacturers for comparison (Table 1).The outer diameter of each needle was measured at its midpoint using a micrometer. The needles were placed in a Luer lock fitting and compressed at a fixed rate of speed by an Instron Universal Testing Device (Instron Corporation, Canton, Mass.). This machine applies a variable axial force to the needle (Figure 1).Buckling force, the force applied when the needle first began to bend, was chosen as an index of needle stiffness. Malleability was assessed by measuring the distance (displacement) by which the needle was compressed in the axial direction when kinking first occurred. Descriptive statistics were obtained for each type of needle. To determine the association among selected variables, correlation coefficients were calculated. Comparisons among different groupings of needle types were made with nonparametric analysis of variance. The outer diameters, buckling forces, and displacements for the different needles are displayed in Table 1. Each 01992 by the International Anesthesia Research Society 0003-2999/921$5.00
ANESTH ANALG
1051
CASE REPORTS
1%2;75 1050-2
Table 1. Epidural Needle Measured Outer Diameters, Buckling Forces, and Displacements Needle tvue"
Outer diameter (in.)
Buckling force (N)
0.0502 t 0.000025 0.0530 0.000042 0.0532 t 0.000025 0.0499 t 0.000017 0.0502 f 0.000035 0.0532 t 0.000021 0.0498 f 0.000032 0.0577 0.000032 0.0583 t 0.000032 0.0589 t 0.000063
27.07 4 0.38 38.69 4 0.57 40.32 t 0.73 28.58 4 0.67 29.49 4 0.67 38.26 4 0.76 30.56 2 0.17 40.62 4 0.38 0.43 50.02 57.49 0.69
*
*
*
6o
1
rn BN(17)
Displacement (mm) 15.34 16.60 22.28 21.53 14.18 16.64 22.54 24.37 18.90
H
0.25 0.24 2 0.11 f 0.14 t 0.33 f 0.30 f 0.22 22.54 f 0.18 ?
a
BD(17)
?
AMI, American Medical Instruments, New Bedford, Mass.; BD, Becton Dickinson, Franklin Lakes, N.J.; BN, Burron Medical Inc., Bethlehem, Pa.; BR, Baxter International Inc., Deerfield, Ill.; K, Kendall Healthcare Products Company, Mansfield, Mass.; M, Manan Medical Products Inc., Northbrook, Ill.; S, Sherwood Medical Company, St. Louis, Mo. Values are expressed as mean SEM; n = 10. 'Numbers in parentheses are gauges.
-
0 LL
20
0.050
I
0.054
0.056
0.058
0.060
Figure 2. The needle buckling force (stiffness) plotted against measured needle outer diameter. Numbers in parentheses are gauges. Each buckling force and diameter measurement represents the mean of 10 samples. Abbreviations as in Table 1.
Overhead
Adapter Luer Lock Fitting
Needle Sample
&I3
0.052
Outer Diameter (inches)
*
*
K(17)
f 0.17 f 0.21
24
l
0
A
-
BD(18ga)
E
E -
K(17ga)
0
0
18-
.-
0
s(18ga) BR(18ga)
-
Base
entry in the table represents the mean of 10 samples with the standard error of the mean. The measured diameters stratified the needles into three different groups, as seen in Figure 2. The 17-gauge needles had an average diameter of 0.058 in. The 18-gaugeneedles fell into two distinct groups, with mean diameters of 0.053 and 0.050 in. Figure 2 also shows how the buckling force correlates with the measured outer diameter (Y = 0.93; P = 0.0001). The three groupings of points differed significantly from each other with respect to buckling force (P < 0.02; Kruskal-Wallis nonparametric analysis of variance). Figure 3 shows the mean displacement plotted against the mean outer diameters for each brand of needle. Displacement did not correlate significantly with needle diameter (Y = 0.41; P = 0.24). The Becton Dickinson, Burron, and Manan needles (Figure 3, solid dots) had displacement values significantly higher than the others (P < 0.008; Mann-Whitney U test).
BN(17ga)
20-
16
Figure 1. A schematic representation of the Instron Universal Testing Device.
0
BN(18ga)
M(18)
v
a
0
UJ
Polyethylene
BD(17ga)
o AMl(18ga)
14
K(18ga) I
.
I
.
I
.
I
.
I
.
1
Discussion Epidural needles are often subjected to a substantial degree of axial force. This is due to the combination of the size and dullness of the needle, as well as the firmness of the interspinous ligaments and frequent impingement on bone. The standard procedure for placement of an epidural needle requires the removal of the stylet after the needle is advanced into the interspinous ligament. This allows the use of the loss of resistance or hanging drop technique to detect
1052
ANESTH ANALG 1992;751050-2
CASE REPORTS
entry into the epidural space. With the stylet removed, the stiffness of the needle decreases, making it easier to buckle. After some critical amount of bending without the stylet in place, the shaft will kink, occluding the lumen. Once this kinking occurs, if the needle is then bent back toward its original shape, it is very likely to break. We cannot be certain that the fracture mechanism we propose, and partially verified in the laboratory, represents the events in our case. In vivo, the tissues surrounding the needle may apply forces in a nonaxial direction; if the patient should move, or if the needle is "walked off" the spinous process improperly, significant lateral or twisting forces may result. Buckling force was proportional to the outer diameter of the needle, whereas displacement correlated poorly with diameter. Among needles of a given diameter, variations in displacement values probably arise from differences in the composition of the alloy from which the needle is constructed and from differences in wall thickness. We did not attempt to quantify these two variables. In conclusion, we report a case of midshaft fracture of an 18-gauge epidural needle. As a result of this case, we studied epidural needles from seven manu-
facturers and found significant variation in their stiffness and malleability, as assessed by buckling force and displacement, respectively. The needle that failed in our case has the lowest buckling force and the second lowest displacement value of the needles we tested. This would suggest that this needle is more likely to bend than the others and will kink very soon after it begins to bend. Stiffness correlates with the measured needle diameter but malleability does not. Although midshaft fracture of an epidural needle occurs infrequently, this is a serious complication, because the retained needle fragment, being rigid and sharp, ought to be removed. The potential for further injury is obvious. If needle fractures indeed occur as we postulate, the needles that have the best combination of resistance to buckling and greater malleability once buckling occurs should be least likely to break.
Reference 1. Schlake I T,Peleman RR, Winnie AP. Separation of the hub from the shaft of a disposable epidural needle. Anesthesiology 1988;68:611-3.
