Original Research
Sonographic Measurements of the Ulnar Nerve at the Elbow With Different Degrees of Elbow Flexion Prutha Patel, MD, John W. Norbury, MD, Xiangming Fang, PhD Objective: To determine whether there were differences in the cross-sectional area (CSA) and the flattening ratio of the normative ulnar nerve as it passes between the medial epicondyle and the olecranon at 30 of elbow flexion versus 90 of elbow flexion. Design: Bilateral upper extremities of normal healthy adult volunteers were evaluated with ultrasound. The CSA and the flattening ratio of the ulnar nerve at the elbow as it passes between the medial epicondyle and the olecranon were measured, with the elbow flexed at 30 and at 90 , by 2 operators with varying ultrasound scanning experience by using ellipse and direct tracing methods. The results from the 2 different angles of elbow flexion were compared for each individual operator. Finally, intraclass correlations for absolute agreement and consistency between the 2 raters were calculated. Setting: An outpatient clinic room at a regional rehabilitation center. Participants: Twenty-five normal healthy adult volunteers. Main Outcome Measurement: The mean CSA and the mean flattening ratio of the ulnar nerve at 30 of elbow flexion and at 90 of elbow flexion. Results: First, for the ellipse method, the mean CSA of the ulnar nerve at 90 (9.93 mm2) was slightly larger than at 30 (9.77 mm2) for rater 1. However, for rater 2, the mean CSA of the ulnar nerve at 90 (6.80 mm2) was slightly smaller than 30 (7.08 mm2). This was found to be statistically insignificant when using a matched pairs t test and the Wilcoxon signed-rank test, with a significance level of .05. Similarly, the difference between the right side and the left side was not statistically significant. The intraclass correlations for absolute agreement between the 2 raters were not very high due to different measurement locations, but the intraclass correlations for consistency were high. Second, for the direct tracing method, the mean CSA at 90 (7.26 mm2) was slightly lower than at 30 (7.48 mm2). This was found to be statistically nonsignificant when using the matched pairs t test and the Wilcoxon signed-rank test with a significance level of .05. There was no significant difference in the average flattening ratio between the 2 angles for the left arm (0.54 at 30 vs 0.56 at 90 ; P ¼ .619 for the matched pairs t test and .274 for the Wilcoxon signed-rank test). However, for the right arm, the flattening ratio at 90 was significantly higher than that at 30 (0.58 at 90 vs 0.50 at 30 ; P ¼ .007 for both the matched pairs t test and the Wilcoxon signed-rank test). Conclusions: The mean CSA of the ulnar nerve at the elbow at 30 was not significantly different than at 90 . However, the average flattening ratio at 90 was found to be significantly higher than at 30 for the right arm. PM R 2014;-:1-5
J.W.N. Department of Physical Medicine and Rehabilitation, Brody School of Medicine, Greenville, NC Disclosure: nothing to disclose
INTRODUCTION Ulnar nerve neuropathy at the elbow (UNE) is the second most frequent entrapment of the ulnar nerve in the upper limb [1]. Trauma from repeated elbow flexion that increases pressure on the ulnar nerve is thought to cause damage to the nerve [2,3]. It usually is diagnosed with nerve conduction studies and electromyography. These studies are painful, invasive (the use of a needle during electromyography), and uncomfortable. Also, the sensitivity of electrodiagnosis for UNE ranges only from 37% to 80% [4], which is much lower than for carpal tunnel syndrome. This is likely due to technical problems, including improper elbow positioning, which gives inaccurate nerve length measurements [5,6]. PM&R 1934-1482/13/$36.00 Printed in U.S.A.
P.P. Department of Physical Medicine and Rehabilitation, Brody School of Medicine, 925-10 Spring Forest Road, Greenville, NC 27834. Address correspondence to: P.P.; e-mail: [email protected] Disclosure: nothing to disclose
X.F. Department of Biostatistics, East Carolina University, Greenville, NC Disclosure: nothing to disclose A research poster was presented at the Association of Academic Physiatrists annual Meeting February 27-March 4, 2012 in Las Vegas, NV. Submitted for publication December 1, 2012; accepted December 18, 2013.
ª 2014 by the American Academy of Physical Medicine and Rehabilitation Vol. -, 1-5, --- 2014 http://dx.doi.org/10.1016/j.pmrj.2013.12.011
1
2
Patel et al
SONOGRAPHIC MEASUREMENTS OF ULNAR NERVE AT THE ELBOW
Given the low sensitivity of electrodiagnostics for UNE, we need other methods that would improve the reliability of its diagnosis. Ultrasound (US) is a diagnostic modality that is noninvasive, painless, and affordable. The use of US in the diagnosis of UNE will become an excellent tool for a rapid and painless diagnosis [7]. Analysis of research results showed that there is a positive correlation between an increase in the cross-sectional diameter of the ulnar nerve and entrapment neuropathy. Recently, studies that used US also established normal values for the cross-sectional area (CSA) of several peripheral nerves, including the ulnar nerve [8]. However, the measurements were not done at different degrees of elbow flexion, nor did they take into account the morphologic changes that occur in the ulnar nerve. For performing conduction studies, it has been well established that the position of the elbow strongly influences the calculated conduction velocity. Ulnar nerve conduction studies performed in the extended elbow position often show artifactual slowing of conduction velocity due to underestimation of the true nerve length. This is because, in the extended elbow position, the ulnar nerve is slack, with some redundancy. It is important to determine whether the CSA of the ulnar nerve varies with the position of the elbow as well just as its length [9]. In addition, calculating the flattening ratio by using short-axis and long-axis radii gives information regarding morphologic changes. If variations are found in the CSA and the flattening ratio due to elbow positioning, then establishing normal values for the CSA at different elbow positions will be helpful in determining normal versus abnormal conditions at a given degree of elbow flexion. Previous studies that used indirect measures of the CSA by means of the ellipsoid formula showed lower diagnostic accuracy (Fig 1) [10]. Because the shape of the ulnar nerve around the elbow is not round but rectangular, most literature indicates that measurement of the CSA is best assessed by direct tracing (Fig 2) [11]. Similarly, although a few studies have included the hyperechoic epineurium in the CSA measurements, there is consensus in the literature that more precise measurement of the CSA is obtained along the inner hypoechoic border [12,13]. The goal of this study was to determine whether there were differences in the CSA and the flattening ratio of the normative ulnar nerve at 30 of elbow flexion versus 90 of elbow flexion when using US as a diagnostic tool. The CSA was obtained by 2 operators (P.P., J.W.N.) by using the ellipse method and the direct tracing method.
Figure 1. Transverse scan of the ulnar nerve at the retroepicondylar groove. CSA measured with ellipse method.
if they exhibited no symptoms of neuropathy. Exclusion criteria included signs or symptoms in the upper extremities that resemble peripheral nervous system dysfunction (paresthesias, numbness, weakness), any history of risk factors for polyneuropathy (including but not limited to diabetes mellitus), previous elbow surgery, medial elbow pain, and acute trauma to the elbow. For each participant, we obtained a transverse scan of the ulnar nerve at the elbow as it passes between the medical epicondyle and the olecranon to calculate CSA measurements by using the ellipse method and the direct tracing method. We performed US evaluation of the ulnar nerve CSA at 30 of elbow flexion and at 90 of elbow flexion of both upper extremities for all the participants. Measurements were done while the subjects were in
METHODS The study protocol was approved by the institutional review board, and all participants gave written informed consent. We enrolled 25 healthy adult participants who were >18 years old and who volunteered to participate in the study (18 women and 7 men). Participants were considered only
Figure 2. Transverse scan of the ulnar nerve at the retroepicondylar groove. CSA measured using direct tracing excluding the epineurium.
PM&R
Vol.
a supine position with a pillow under the extremity being scanned for comfort and ease of scanning. The degree of elbow flexion was measured by using a goniometer while the wrists were in a supinated position. All images were acquired by using a US device with a 12/5-MHz linear array transducer for all the participants (GE LOGIQ E Ultrasound System, GE Healthcare, Fairfield, CT). To address the possible effect of measurement errors on the outcome of the study, we had 2 individuals (rater 1 [P.P.] and rater 2 [J.W.N.]) take 2 independent measurements of CSA on the same US image of the ulnar nerve. The CSA (in square millimeters [mm2]) was obtained by using the US machine’s automatic ellipse tool by rater 1, which included the hypoechoic epineurium, whereas rater 2 did not include the hypoechoic epineurium. We compared the measurements obtained with the ellipse method for the different degrees of elbow flexion by using the matched pairs t test and the Wilcoxon signed-rank test for both raters. Also, intraclass correlations between the 2 raters for absolute agreement and consistency were calculated. In addition, we compared measurements for the 2 angles obtained with the direct tracing method by rater 2 in a similar manner. Finally, the flattening ratio (F ¼ a e b/a, where a is the long-axis radius and b is the short-axis radius) for the direct tracing measurements was calculated and compared for the 2 angles. All analyses were conducted by using IBM SPSS 20 (IBM Corp, Armonk, NY). A P value of 90 , the shape of the ulnar nerve changes and the CSA decreases [22,23]. In our study, we tried to determine whether ulnar nerve CSA and the flattening ratio would change with elbow flexion 90 . Measurements were done by 1 operator (rater 1) with less than 1 year of US experience and by another operator (rater 2) with more than 3 years of experience, which makes our results highly reliable and consistent. In this study, we used 2 different tracing methods. In the ellipse method, the nerve CSA was approximated with an elliptical shape that was used to approximate the borders of the nerve. In the direct tracing method, the nerve was traced inside the hyperechoic rim to yield a CSA measurement. The significant differences between the values obtained by the 2 methods may be related to the fact that an overestimate of nerve area was found with the ellipse because it was difficult to include the entire nerve without capturing an “extra” area with the ellipse method. To compare the measurements of 2 raters and to calculate intraclass correlations, the ellipse method was used because it is more reproducible and therefore ideal for use when calculating intraclass correlations [2]. Our study revealed that, even though the mean CSA of the ulnar nerve at 90 was slightly different from that at 30 , the difference was not statistically significant for the ellipse method or the direct tracing method. This indicates that the ulnar nerve size
Table 2. Flattening ratios and CSA using the direct tracing method (n ¼ 24) P Value for Comparing 2 Angles Arm Right
Variable Flattening ratio CSA (mm2)
Left
Flattening ratio CSA (mm2)
Average
Flattening ratio CSA (mm2)
Angle
30 90 30 90 30 90 30 90 30 90 30 90
Mean ± SD
Median
Matched Pairs t test
Wilcoxon Signed-Rank Test
0.50 0.60 6.94 7.25 0.54 0.55 7.83 7.89 0.52 0.57 7.48 7.26
.007*
.007*
.248
.290
.619
.274
.565
.617
.045*
.049*
.243
.259
0.50 0.58 7.60 7.19 0.54 0.56 8.58 8.33 0.52 0.57 8.09 7.76
0.13 0.15 2.74 3.20 0.12 0.10 2.96 3.41 0.09 0.10 2.60 3.10
CSA ¼ cross-sectional area; SD ¼ standard deviation. *Statistically significant difference at the level of .05 Flattening ratio ¼ a e b/a, where a is the long-axis radius and b is the short-axis radius. One subject’s data had to be eliminated because the measurements did not have enough significant figures to convert square centimeters (cm2) to square millimeters (mm2).
PM&R
likely does not change with elbow movement of 30 to 90 flexion. In addition, the flattening ratio of the ulnar nerve was calculated and compared for the 2 angles to evaluate the morphologic changes that occur during elbow flexion. The difference in the average flattening ratio for the left arm was not statistically significant. However, for the right arm, the flattening ratio at 90 was significantly higher than at 30 . It is possible that dominant handedness influenced these results. The dominant upper extremity is usually involved with increased repetitive motion, which might make the nerve more pliable. However, future studies will be needed to assess this theory. Using a ratio of ulnar nerve CSA to cubital tunnel area measurements with different degrees of elbow flexion would be another measurement that could be used in future studies because repeated changes in the tunnel size during elbow flexion would have the same impact as changes in ulnar nerve size. Our study had several limitations. A clear limitation is the small sample size. Furthermore, although a thorough history was performed to exclude subjects with symptoms of ulnar neuropathy, electrodiagnostic tests to rule out ulnar entrapment at the elbow would have been ideal.
CONCLUSION In this study, when ulnar nerve CSA measurements were taken with US at 2 different angles of elbow flexion by 2 operators by using 2 different measuring methods, there was no statistically significant difference found between the 2 angles. The flattening ratio of the ulnar nerve, however, was significantly higher at 90 than at 30 for the right arm. Future studies could be conducted by recording dominant handedness, which may influence the ulnar nerve’s compressibility during elbow flexion. Results from this study may be helpful when conducting future studies that confirm or refute our results. We suggest that future US ulnar nerve studies be performed according to a protocol that includes elbow position and the method of measurements at the time of scanning.
REFERENCES 1. Campbell WW, Pridgeon RM, Riaz G, Astruc J, Sahni KS. Variations in anatomy of the ulnar nerve at the cubital tunnel: Pitfalls in the diagnosis of ulnar neuropathy at the elbow. Muscle Nerve 1991;14:733-738. 2. Abdel-Salam A, Eyres KS, Cleary J. Driver’s elbow: A cause of ulnar neuropathy. J Hand Surg 1991;16:436-437. 3. Bozentka DJ. Cubital tunnel syndrome pathophysiology. Clin Orthop Relat Res 1998;351:90-94. 4. Beekman R, Schreuder AH, Rozeman CA, Koehler PJ, Uitdehaag BMJ. The diagnostic value of provocative clinical tests in ulnar neuropathy at the elbow is marginal. J Neurol Neurosurg Psychiatry 2009;80:1369-1374.
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5. Wiesler ER, Chloros GD, Cartwright MS, Shin HW, Walker FO. Ultrasound in the diagnosis of ulnar neuropathy at the cubital tunnel. J Hand Surg Am 2006;31:1088-1093. 6. Yoon JS, Walker FO, Cartwright MS. Ulnar neuropathy with normal electrodiagnosis and abnormal nerve ultrasound. Arch Phys Med Rehabil 2010;91:318-320. 7. Yoon JS, Hong SJ, Kim BJ, et al. Ulnar nerve and cubital tunnel ultrasound in ulnar neuropathy at the elbow. Arch Phys Med Rehabil 2008;89:887-889. 8. Cartwright MS, Passmore LV, Yoon JS, Brown ME, Caress JB, Walker FO. Cross-sectional area reference values for nerve ultrasonography. Muscle Nerve 2008;37:566-571. 9. Preston DC, Shapiro BE. Ulnar neuropathy at the elbow. In: Preston DC, Shapiro BE, eds. Electromyography and Neuromuscular Disorders. 2nd ed. Philadelphia, PA: Elsevier; 2005, 297. 10. Bayrak IK, Bayrak AO, Tilki HE, Nural MS, Sunter T. Ultrasonography in carpal tunnel syndrome: Comparison with electrophysiological stage and motor unit number estimate. Muscle Nerve 2007; 35:344-348. 11. Wong SM, Griffith JF, Hui AC, Tang A, Wong KS. Discriminatory sonographic criteria for the diagnosis of carpal tunnel syndrome. Arthritis Rheum 2002;46:1914-1921. 12. Moran L, Perez M, Esteban A, Bellon J, Arranz B, del Cerro M. Sonographic measurement of cross-sectional area of the median nerve in the diagnosis of carpal tunnel syndrome: Correlation with nerve conduction studies. J Clin Ultrasound 2009;37:125-131. 13. Kaymak B, Ozçakar L, Cetin A, Candan Cetin M, Akinci A, Hasçelik Z. A comparison of the benefits of sonography and electrophysiologic measurements as predictors of symptom severity and functional status in patients with carpal tunnel syndrome. Arch Phys Med Rehabil 2008; 89:743-748. 14. Duncan I, Sullivan P, Lomas F. Sonography in the diagnosis of carpal tunnel syndrome. AJR Am J Roentgenol 1999;173:681-684. 15. Beekman R, Schoemaker MC, Van Der Plas JP, et al. Diagnostic value of high-resolution sonography in ulnar neuropathy at the elbow. Neurology 2004;62:767-773. 16. Beekman R, Van Der Plas JP, Uitdehaag BM, Schellens RL, Visser LH. Clinical, electrodiagnostic, and sonographic studies in ulnar neuropathy at the elbow. Muscle Nerve 2004;30:202-208. 17. Park GY, Kim JM, Lee SM. The ultrasonographic and electrodiagnostic findings of ulnar neuropathy at the elbow. Arch Phys Med Rehabil 2004;85:1000-1005. 18. Gelberman RH, Yamaguchi K, Hollstien SB, et al. Changes in interstitial pressure and cross-sectional area of the cubital tunnel and of the ulnar nerve with flexion of the elbow. An experimental study in human cadavers. J Bone Joint Surg Am 1998;80:492-501. 19. Jacob D, Creteur V, Courthaliac C, et al. Sonoanatomy of the ulnar nerve in the cubital tunnel: A multicenter study by the GEL. Eur Radiol 2004;14:1770-1773. 20. Kim YS, Yeh LR, Trudell D, Resnick D. MR imaging of the major nerves about the elbow: Cadaveric study examining the effect of flexion and extension of the elbow and pronation and supination of the forearm. Skeletal Radiol 1998;27:419-426. 21. Okamoto M, Abe M, Shirai H, Ueda N. Morphology and dynamics of the ulnar nerve in the cubital tunnel. Observation by ultrasonography. J Hand Surg 2000;25:85-89. 22. Kutlay M, Colak A, Simsek H, et al. Use of ultrasonography in ulnar nerve entrapment surgery: A prospective study. Neurosurg Rev 2009; 32:225-232. 23. Ozturk E, Sonmez G, Colak A, et al. Sonographic appearance of the normal ulnar nerve in the cubital tunnel. J Clin Ultrasound 2008;36: 325-329.
Sonographic Measurements of the Ulnar Nerve at the Elbow With Different Degrees of Elbow Flexion Prutha Patel, MD, John W. Norbury, MD, Xiangming Fang, PhD Objective: To determine whether there were differences in the cross-sectional area (CSA) and the flattening ratio of the normative ulnar nerve as it passes between the medial epicondyle and the olecranon at 30 of elbow flexion versus 90 of elbow flexion. Design: Bilateral upper extremities of normal healthy adult volunteers were evaluated with ultrasound. The CSA and the flattening ratio of the ulnar nerve at the elbow as it passes between the medial epicondyle and the olecranon were measured, with the elbow flexed at 30 and at 90 , by 2 operators with varying ultrasound scanning experience by using ellipse and direct tracing methods. The results from the 2 different angles of elbow flexion were compared for each individual operator. Finally, intraclass correlations for absolute agreement and consistency between the 2 raters were calculated. Setting: An outpatient clinic room at a regional rehabilitation center. Participants: Twenty-five normal healthy adult volunteers. Main Outcome Measurement: The mean CSA and the mean flattening ratio of the ulnar nerve at 30 of elbow flexion and at 90 of elbow flexion. Results: First, for the ellipse method, the mean CSA of the ulnar nerve at 90 (9.93 mm2) was slightly larger than at 30 (9.77 mm2) for rater 1. However, for rater 2, the mean CSA of the ulnar nerve at 90 (6.80 mm2) was slightly smaller than 30 (7.08 mm2). This was found to be statistically insignificant when using a matched pairs t test and the Wilcoxon signed-rank test, with a significance level of .05. Similarly, the difference between the right side and the left side was not statistically significant. The intraclass correlations for absolute agreement between the 2 raters were not very high due to different measurement locations, but the intraclass correlations for consistency were high. Second, for the direct tracing method, the mean CSA at 90 (7.26 mm2) was slightly lower than at 30 (7.48 mm2). This was found to be statistically nonsignificant when using the matched pairs t test and the Wilcoxon signed-rank test with a significance level of .05. There was no significant difference in the average flattening ratio between the 2 angles for the left arm (0.54 at 30 vs 0.56 at 90 ; P ¼ .619 for the matched pairs t test and .274 for the Wilcoxon signed-rank test). However, for the right arm, the flattening ratio at 90 was significantly higher than that at 30 (0.58 at 90 vs 0.50 at 30 ; P ¼ .007 for both the matched pairs t test and the Wilcoxon signed-rank test). Conclusions: The mean CSA of the ulnar nerve at the elbow at 30 was not significantly different than at 90 . However, the average flattening ratio at 90 was found to be significantly higher than at 30 for the right arm. PM R 2014;-:1-5
J.W.N. Department of Physical Medicine and Rehabilitation, Brody School of Medicine, Greenville, NC Disclosure: nothing to disclose
INTRODUCTION Ulnar nerve neuropathy at the elbow (UNE) is the second most frequent entrapment of the ulnar nerve in the upper limb [1]. Trauma from repeated elbow flexion that increases pressure on the ulnar nerve is thought to cause damage to the nerve [2,3]. It usually is diagnosed with nerve conduction studies and electromyography. These studies are painful, invasive (the use of a needle during electromyography), and uncomfortable. Also, the sensitivity of electrodiagnosis for UNE ranges only from 37% to 80% [4], which is much lower than for carpal tunnel syndrome. This is likely due to technical problems, including improper elbow positioning, which gives inaccurate nerve length measurements [5,6]. PM&R 1934-1482/13/$36.00 Printed in U.S.A.
P.P. Department of Physical Medicine and Rehabilitation, Brody School of Medicine, 925-10 Spring Forest Road, Greenville, NC 27834. Address correspondence to: P.P.; e-mail: [email protected] Disclosure: nothing to disclose
X.F. Department of Biostatistics, East Carolina University, Greenville, NC Disclosure: nothing to disclose A research poster was presented at the Association of Academic Physiatrists annual Meeting February 27-March 4, 2012 in Las Vegas, NV. Submitted for publication December 1, 2012; accepted December 18, 2013.
ª 2014 by the American Academy of Physical Medicine and Rehabilitation Vol. -, 1-5, --- 2014 http://dx.doi.org/10.1016/j.pmrj.2013.12.011
1
2
Patel et al
SONOGRAPHIC MEASUREMENTS OF ULNAR NERVE AT THE ELBOW
Given the low sensitivity of electrodiagnostics for UNE, we need other methods that would improve the reliability of its diagnosis. Ultrasound (US) is a diagnostic modality that is noninvasive, painless, and affordable. The use of US in the diagnosis of UNE will become an excellent tool for a rapid and painless diagnosis [7]. Analysis of research results showed that there is a positive correlation between an increase in the cross-sectional diameter of the ulnar nerve and entrapment neuropathy. Recently, studies that used US also established normal values for the cross-sectional area (CSA) of several peripheral nerves, including the ulnar nerve [8]. However, the measurements were not done at different degrees of elbow flexion, nor did they take into account the morphologic changes that occur in the ulnar nerve. For performing conduction studies, it has been well established that the position of the elbow strongly influences the calculated conduction velocity. Ulnar nerve conduction studies performed in the extended elbow position often show artifactual slowing of conduction velocity due to underestimation of the true nerve length. This is because, in the extended elbow position, the ulnar nerve is slack, with some redundancy. It is important to determine whether the CSA of the ulnar nerve varies with the position of the elbow as well just as its length [9]. In addition, calculating the flattening ratio by using short-axis and long-axis radii gives information regarding morphologic changes. If variations are found in the CSA and the flattening ratio due to elbow positioning, then establishing normal values for the CSA at different elbow positions will be helpful in determining normal versus abnormal conditions at a given degree of elbow flexion. Previous studies that used indirect measures of the CSA by means of the ellipsoid formula showed lower diagnostic accuracy (Fig 1) [10]. Because the shape of the ulnar nerve around the elbow is not round but rectangular, most literature indicates that measurement of the CSA is best assessed by direct tracing (Fig 2) [11]. Similarly, although a few studies have included the hyperechoic epineurium in the CSA measurements, there is consensus in the literature that more precise measurement of the CSA is obtained along the inner hypoechoic border [12,13]. The goal of this study was to determine whether there were differences in the CSA and the flattening ratio of the normative ulnar nerve at 30 of elbow flexion versus 90 of elbow flexion when using US as a diagnostic tool. The CSA was obtained by 2 operators (P.P., J.W.N.) by using the ellipse method and the direct tracing method.
Figure 1. Transverse scan of the ulnar nerve at the retroepicondylar groove. CSA measured with ellipse method.
if they exhibited no symptoms of neuropathy. Exclusion criteria included signs or symptoms in the upper extremities that resemble peripheral nervous system dysfunction (paresthesias, numbness, weakness), any history of risk factors for polyneuropathy (including but not limited to diabetes mellitus), previous elbow surgery, medial elbow pain, and acute trauma to the elbow. For each participant, we obtained a transverse scan of the ulnar nerve at the elbow as it passes between the medical epicondyle and the olecranon to calculate CSA measurements by using the ellipse method and the direct tracing method. We performed US evaluation of the ulnar nerve CSA at 30 of elbow flexion and at 90 of elbow flexion of both upper extremities for all the participants. Measurements were done while the subjects were in
METHODS The study protocol was approved by the institutional review board, and all participants gave written informed consent. We enrolled 25 healthy adult participants who were >18 years old and who volunteered to participate in the study (18 women and 7 men). Participants were considered only
Figure 2. Transverse scan of the ulnar nerve at the retroepicondylar groove. CSA measured using direct tracing excluding the epineurium.
PM&R
Vol.
a supine position with a pillow under the extremity being scanned for comfort and ease of scanning. The degree of elbow flexion was measured by using a goniometer while the wrists were in a supinated position. All images were acquired by using a US device with a 12/5-MHz linear array transducer for all the participants (GE LOGIQ E Ultrasound System, GE Healthcare, Fairfield, CT). To address the possible effect of measurement errors on the outcome of the study, we had 2 individuals (rater 1 [P.P.] and rater 2 [J.W.N.]) take 2 independent measurements of CSA on the same US image of the ulnar nerve. The CSA (in square millimeters [mm2]) was obtained by using the US machine’s automatic ellipse tool by rater 1, which included the hypoechoic epineurium, whereas rater 2 did not include the hypoechoic epineurium. We compared the measurements obtained with the ellipse method for the different degrees of elbow flexion by using the matched pairs t test and the Wilcoxon signed-rank test for both raters. Also, intraclass correlations between the 2 raters for absolute agreement and consistency were calculated. In addition, we compared measurements for the 2 angles obtained with the direct tracing method by rater 2 in a similar manner. Finally, the flattening ratio (F ¼ a e b/a, where a is the long-axis radius and b is the short-axis radius) for the direct tracing measurements was calculated and compared for the 2 angles. All analyses were conducted by using IBM SPSS 20 (IBM Corp, Armonk, NY). A P value of 90 , the shape of the ulnar nerve changes and the CSA decreases [22,23]. In our study, we tried to determine whether ulnar nerve CSA and the flattening ratio would change with elbow flexion 90 . Measurements were done by 1 operator (rater 1) with less than 1 year of US experience and by another operator (rater 2) with more than 3 years of experience, which makes our results highly reliable and consistent. In this study, we used 2 different tracing methods. In the ellipse method, the nerve CSA was approximated with an elliptical shape that was used to approximate the borders of the nerve. In the direct tracing method, the nerve was traced inside the hyperechoic rim to yield a CSA measurement. The significant differences between the values obtained by the 2 methods may be related to the fact that an overestimate of nerve area was found with the ellipse because it was difficult to include the entire nerve without capturing an “extra” area with the ellipse method. To compare the measurements of 2 raters and to calculate intraclass correlations, the ellipse method was used because it is more reproducible and therefore ideal for use when calculating intraclass correlations [2]. Our study revealed that, even though the mean CSA of the ulnar nerve at 90 was slightly different from that at 30 , the difference was not statistically significant for the ellipse method or the direct tracing method. This indicates that the ulnar nerve size
Table 2. Flattening ratios and CSA using the direct tracing method (n ¼ 24) P Value for Comparing 2 Angles Arm Right
Variable Flattening ratio CSA (mm2)
Left
Flattening ratio CSA (mm2)
Average
Flattening ratio CSA (mm2)
Angle
30 90 30 90 30 90 30 90 30 90 30 90
Mean ± SD
Median
Matched Pairs t test
Wilcoxon Signed-Rank Test
0.50 0.60 6.94 7.25 0.54 0.55 7.83 7.89 0.52 0.57 7.48 7.26
.007*
.007*
.248
.290
.619
.274
.565
.617
.045*
.049*
.243
.259
0.50 0.58 7.60 7.19 0.54 0.56 8.58 8.33 0.52 0.57 8.09 7.76
0.13 0.15 2.74 3.20 0.12 0.10 2.96 3.41 0.09 0.10 2.60 3.10
CSA ¼ cross-sectional area; SD ¼ standard deviation. *Statistically significant difference at the level of .05 Flattening ratio ¼ a e b/a, where a is the long-axis radius and b is the short-axis radius. One subject’s data had to be eliminated because the measurements did not have enough significant figures to convert square centimeters (cm2) to square millimeters (mm2).
PM&R
likely does not change with elbow movement of 30 to 90 flexion. In addition, the flattening ratio of the ulnar nerve was calculated and compared for the 2 angles to evaluate the morphologic changes that occur during elbow flexion. The difference in the average flattening ratio for the left arm was not statistically significant. However, for the right arm, the flattening ratio at 90 was significantly higher than at 30 . It is possible that dominant handedness influenced these results. The dominant upper extremity is usually involved with increased repetitive motion, which might make the nerve more pliable. However, future studies will be needed to assess this theory. Using a ratio of ulnar nerve CSA to cubital tunnel area measurements with different degrees of elbow flexion would be another measurement that could be used in future studies because repeated changes in the tunnel size during elbow flexion would have the same impact as changes in ulnar nerve size. Our study had several limitations. A clear limitation is the small sample size. Furthermore, although a thorough history was performed to exclude subjects with symptoms of ulnar neuropathy, electrodiagnostic tests to rule out ulnar entrapment at the elbow would have been ideal.
CONCLUSION In this study, when ulnar nerve CSA measurements were taken with US at 2 different angles of elbow flexion by 2 operators by using 2 different measuring methods, there was no statistically significant difference found between the 2 angles. The flattening ratio of the ulnar nerve, however, was significantly higher at 90 than at 30 for the right arm. Future studies could be conducted by recording dominant handedness, which may influence the ulnar nerve’s compressibility during elbow flexion. Results from this study may be helpful when conducting future studies that confirm or refute our results. We suggest that future US ulnar nerve studies be performed according to a protocol that includes elbow position and the method of measurements at the time of scanning.
REFERENCES 1. Campbell WW, Pridgeon RM, Riaz G, Astruc J, Sahni KS. Variations in anatomy of the ulnar nerve at the cubital tunnel: Pitfalls in the diagnosis of ulnar neuropathy at the elbow. Muscle Nerve 1991;14:733-738. 2. Abdel-Salam A, Eyres KS, Cleary J. Driver’s elbow: A cause of ulnar neuropathy. J Hand Surg 1991;16:436-437. 3. Bozentka DJ. Cubital tunnel syndrome pathophysiology. Clin Orthop Relat Res 1998;351:90-94. 4. Beekman R, Schreuder AH, Rozeman CA, Koehler PJ, Uitdehaag BMJ. The diagnostic value of provocative clinical tests in ulnar neuropathy at the elbow is marginal. J Neurol Neurosurg Psychiatry 2009;80:1369-1374.
Vol.
-,
Iss.
-,
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