ORIGINAL RESEARCH
Association Between Gender, Body Mass Index, and Ulnar Nerve
Entrapment at the Elbow: A Retrospective Study
Aslihan Uzunkulao
glu,* Sevgi Ikbali Afsar,† and Metin Karatas¸†
*
Department of Physical Medicine and Rehabilitation, Faculty of Medicine, Ufuk University, Ankara, Turkey; and†Department of Physical Medicine and Rehabilitation, Faculty of Medicine, Baskent University, Ankara, Turkey.
Introduction: Entrapment of the ulnar nerve is the second most common compression neuropathy in the upper extremity, but the etiology is multifactorial and still not clearly understood. The authors aimed to determine whether gender and body mass index (BMI) are risk factors for ulnar nerve entrapment (UNE) at the elbow. Methods: Results of electrodiagnostic studies performed on patients with UNE between January 2008 and February 2013 were examined retrospectively. Patients with BMI#22 were considered slender, those with a BMI between 22 and 29, normal, and those with a BMI.29, overweight. The authors compared the data for patients with and without UNE. Results: A total of 622 subjects were studied; 295 were UNE cases (154 men, 141 women) and 327 were controls (110 men,
217 women). There was no difference between control and UNE groups in terms of BMI. In univariate analysis, age and gender are independent risk factors for UNE, but when included in a stepwise Cox regression model, only gender was a significant factor. Male gender was found to be a risk factor for UNE.
Conclusions: Male gender is a risk factor for developing UNE, but age and BMI are not significant risk factors. Further studies which examine BMI and gender differences with data about occupational risk factors are required.
Key Words: Gender, Body mass index, Ulnar nerve. (J Clin Neurophysiol 2016;33: 545–548)
E
ntrapment of the ulnar nerve is the second most common compression neuropathy in the upper extremity (Bozentka, 1998; Robertson and Saratsiotis, 2005). This entrapment can occur at five sites around the elbow: the arcade of Struthers, the medial intermuscular septum, the medial epicondyle, the cubital tunnel, and the deep flexor pronator aponeurosis. Because of the anatomic positioning of the ulnar nerve, the most common site of entrapment is in the elbow region (Ochiai et al., 2001).The etiology of ulnar nerve entrapment (UNE) at the elbow is multifactorial and still not clearly understood. According to one study, the annual UNE incidence is 20.9/100,000 with an incidence that increases with age. The incidence in men was twice as high as in women and higher in geographic regions in which manual labor is common (Mondelli et al., 2005). Furthermore, both high and low extremes of body mass index (BMI) have been reported to be risk factors for UNE (Buschbacher, 1999; Warner et al., 1994; Warner et al., 1999). However, there is limited data about the effect of BMI on UNE. From this point of view, to clarify the gap in the knowledge, we aimed to determine whether gender and BMI are, in fact, risk factors for UNE.
METHODS
Study Population
Electrodiagnostic reports of patients with UNE and controls were obtained from an electronic database of electrodiagnostic study results performed between January 2008 and February 2014. After approval from our institutional review board, we retrospectively analyzed the results of previously completed electrodiagnostic studies.
Medical records of patients who underwent electroneuro-myographic studies with an initial diagnosis of UNE were examined. Patients clinically and electrophysiologically diag-nosed with UNE were included in the study group (UNE group); and patients with normal electroneuromyographic parameters were included in the control group. Exclusion criteria for both groups included other mononeuropathy, polyneuropathy, diabe-tes mellitus, upper extremity trauma or fracture, cervical radiculopathy or plexopathy, severe neurological disorder, a his-tory of surgery for ulnar entrapment neuropathy, or any abnormal median nerve response.
The reports include the following information which was used for analysis: patient age, gender, height, and weight; nerve conduction parameters; and, if available, results of needle electro-myography. Body mass index was calculated for each subject. Patients with BMI#22 were considered slender, those with a BMI between 22 and 29, normal, and those with a BMI.29, overweight.
Electroneuromyographic Studies
Medelec Synergy multimedia electromyograph instrument (Oxford Instruments, Surrey, England) was used for all patients both in UNE and control groups. All electrophysiological examinations were conducted at temperatures above 258C. The
The authors declare no conflicts of interest.
Address correspondence and reprint requests to Aslihan Uzunkulaoglu, MD, Department of Physical Medicine and Rehabilitation, Faculty of Medicine, Ufuk University, Konya Yolu, Mevlana Bulvarı No: 86-88, Balgat, Ankara 06490, Turkey; e-mail: aslihanseyrek@gmail.com.
CopyrightÓ 2016 by the American Clinical Neurophysiology Society ISSN: 0736-0258/16/3306-0545
DOI 10.1097/WNP.0000000000000288
distal skin temperature of each participant was measured at the hand dorsum and was maintained above 328C. Conventional motor and sensory conduction studies of the median and ulnar nerves and sensory conduction studies of the radial nerve were performed. Filter settings were 3 to 10 kHz for motor conduction studies and 20 to 2 kHz for sensory conduction studies. The compound muscle action potentials (CMAPs) were recorded using 9 mm disc surface cup (Ag/AgCl) electrodes (TECA Accessories; Medelec, Oxford Instruments, Old Woking, United Kingdom) placed over the motor point of the abductor pollicis brevis muscle for the median nerve and over the abductor digiti minimi muscle for the ulnar nerve. In motor conduction studies, the ulnar nerve was stimulated 8 cm proximal to the active electrode (wrist), approximately 3 to 4 cm distal to the medial epicondyle (below the elbow), and 10 to 12 cm proximal to the below elbow (BE) site (above the elbow). The elbow was flexed to 908 and wrist maintained in a neutral position. Ulnar nerve distal motor latencies, CMAP amplitudes, and motor conduction velocities at the forearm and above elbow (AE)-BE segments were calculated. Sensory nerve conduction studies were performed antidromically. The ulnar nerve was stimulated at the wrist 12 cm from to the active electrode, approximately 3 to 4 cm distal to the medial epicondyle (BE), and then 10 to 12 cm proximal to that site (AE). Ulnar nerve distal sensory latencies, sensory nerve action potential amplitudes, and sensory conduction velocities of the forearm and elbow segments were recorded from thefifth digit using ring electrodes. After at least 20 supramaximal stimulation periods, minimum F latencies were recorded. Latencies are expressed in milliseconds (ms), CMAP amplitudes as millivolts (mV), and sensory nerve action potential amplitudes as microvolts (mV). Nerve conduction velocities (NCVs) were calculated as ms21. Electrophysiological diagnosis of UNE was performed according to the following criteria; (1) an absolute NCV AE to BE of ,50 m/s, (2) an AE to BE conduction velocity .10 m/s slower (or a 20% slowing) compared with the BE to wrist segment, (3) a decrease in CMAP peak amplitude from BE to AE of.20%, (4) a significant change in CMAP configuration at the AE site compared with the BE site (American Academy of Neurology, American Association of Electrodiagnostic Medicine, American Academy of Physical Medicine and Rehabilitation 1999). When a diagnosis of UNE was considered, needle electromyography was performed with
patient consent. Denervation presence in the abductor digiti minimi muscle was recorded.
In the control group, the same techniques were used, but needle electromyography was not performed on any of the individuals. All the individuals in the control group demonstrated normal ulnar nerve conduction parameters across the elbow.
Statistical Analysis
Data were analyzed using SPSS version 20 for Windows (IBM SPSS Inc, Chicago, IL). Normal distribution of the data was examined with Kolmogorov–Smirnov test. Numerical variables with a normal distribution are shown as mean6 SD, and other data are reported as median (minimum–maximum). Categorical variables are shown as the number of cases and percent of total (%). The comparisons between the patients and controls were calculated using Student t-test or the non-parametric Mann–Whitney U test. When comparing the three BMI groups, analysis of variance test was used for normally distributed variables and Kruskal–Wallis H test for nonnormal variables. For comparing categorical variables, x2 or Fisher
exactx2test were used. Univarite Cox regression analysis was
used for determining the effects of potential prognostic factors on UNE. Factors which were found statistically significant were included in a stepwise Cox regression model and used to determine independent predictors. A P-value ,0.05 was deemed to indicate statistical significance.
RESULTS
A total of 622 subjects were studied; 295 were UNE cases (154 men, 141 women) and 327 were controls (110 men, 217 women). The mean age of patients with UNE and control group was 46.26 6 14.92 and 42.15 6 14.11, respectively. There was no difference between control and UNE groups in terms of BMI (Table 1). The presence of UNE was similar among slender, normal weight, and overweight patients for all subjects (Table 2).
Among slender patients, ulnar sensory NCV at the forearm segment was higher than within the normal weight and over-weight groups (slender 67.186 8.80 ms21vs. normal 63.496 8.73 ms21and overweight 64.516 8.24 ms21,P , 0.05). Ulnar
TABLE 1. Demographic Patient Characteristics of Control and UNE Groups
Variables Control Group, N ¼ 327 UNE Group, N ¼ 295 P
Age (mean6 SD), yr 42.156 14.11 46.266 14.92 0.001* Gender, % Male 110 (33.6) 154 (52.2) 0.001* Female 217 (66.4) 141 (47.8) BMI (mean6 SD) 26.306 4.43 25.936 4.31 0.299 BMI category, % #22.0 48 (14.7) 52 (17.6) 0.516 .22.0 and ,29.0 204 (62.4) 183 (62.0) $ 29.0 75 (22.9) 60 (20.3) *P , 0.05.
BMI, body mass index; UNE, ulnar nerve entrapment at the elbow.
A. Uzunkulaoglu, et al. Gender, Body Mass Index, and Ulnar Nerve
sensory NCV at the AE-BE segment was similar in slender and normal patients but lower in overweight patients (slender 50.966 8.90 ms21and normal patients 50.006 10.04 ms21vs. overweight 46.276 11.19 ms21,P , 0.05) (Table 3).
In univariate analysis, it was determined that age and gender are independent risk factors for UNE, but when included in a stepwise Cox regression model, only gender was a signif-icant factor. Male gender was found to be a risk factor for UNE (Table 4).
DISCUSSION
Ulnar nerve compression at the elbow is encountered frequently. Based mainly on clinical and surgical series, several risk factors have been identified. The etiology of UNE is multifactorial (Charness, 1992; Cutts, 2007). Individuals who work withflexed elbows at repetitive tasks, such as carpenters, artists, and musicians have a high-risk of developing UNE. Also, in some studies, it was found that gender differences can affect the development of ulnar nerve compression at the elbow (Bartels et al., 1998). The major finding in our study was that men were more likely to have an UNE than women. This result is consistent with a study conducted by Richardson of 112 UNE
cases and 104 controls (Richardson et al., 2001). But in Bartels and Verbeek’s study, gender and nerve compression were found not to be independent variables (Bartels and Verbeek, 2007). Compression less usually occurs under theflexor carpi ulnaris aponeurosis and is markedly increased with isometric contrac-tion of the flexor carpi ulnaris (Werner et al., 1985). Muscle mass and strength are significantly greater among men than women after the mid teen years (Barnekow-Bergkvist et al., 1996; Kanehisa et al., 1994). It is possible that men, with their thicker forearm musculature and greater grip strength, develop greater pressures over the ulnar nerve with hand usage and are therefore at increased risk for UNE. Another possible explana-tion is that men previously might have performed heavier labor than women. In our study, we did not record data about individuals’ jobs.
Some authors have found that women with a lower BMI had a greater likelihood of developing ulnar nerve compression (Chuman, 1985; Richardson et al., 2001), whereas others have reported that this occurred irrespective of BMI (Descatha et al., 2004). One study found that significantly more women with a BMI #22.0 had UNE compared with women with a BMI .22.0 (Richardson et al., 2001). In our study, there was no difference between the control and UNE groups in terms of BMI. This result is consistent with some reports (Bartels and Verbeek, TABLE 2. Ulnar Nerve Entrapment Presence in Relation to BMI Category
Variables £22.0, N ¼ 100 (%) .22.0 and ,29.0, N ¼ 387 (%) ‡29.0, N ¼ 135 (%) P UNE (1) 52 (52.0) 183 (47.3) 60 (44.4) 0.516 Male (n ¼ 264) 32 (32) 179 (46.3) 53 (39.3) 0.295 UNE (1) 22 (68.8) 99 (55.3) 33 (62.3) Control 10 (31.2) 80 (44.7) 20 (37.7) Female (n ¼ 358) 68 (68) 208 (53.7) 82 (60.7) 0.340 UNE (1) 30 (44.1) 84 (40.4) 27 (32.9) Control 38 (55.9) 124 (59.6) 55 (67.1) *P , 0.05.
BMI, body mass index; UNE, ulnar nerve entrapment at the elbow.
TABLE 3. Ulnar Nerve Electrophysiological Parameters in Relation to BMI Category in Patients with Ulnar Nerve Entrapment at the Elbow
Variables £22.0, N ¼ 52 .22.0 and ,29.0, N ¼ 183 ‡29.0, N ¼ 60 P
Distal motor latency (ms) 2.756 0.39 2.786 0.30 2.776 0.32 0.813
Distal sensory latency (ms) 2.856 0.22 2.946 0.28 2.946 0.23 0.069
Motor NCV forearm (ms21) 68.656 10.59 65.716 9.49 64.646 8.60 0.068 Motor NCV AE-BE (ms21) 46.536 9.58 47.536 9.27 45.606 7.25 0.330 Sensory NCV forearm (ms21) 67.186 8.80* 63.496 8.73 64.516 8.24 0.026† Sensory NCV AE-BE (ms21) 50.966 8.90 50.006 10.04 46.276 11.19* 0.026† Motor CMAP (mV) 9.10 (3–15) 8.80 (2–15) 9.0 (2–30) 0.858 Sensory SNAP (mV) 47.45 (2–128)* 27.90 (1–133) 30.71 (1–113) 0.001† Minimum F latency (ms) 26.366 2.24 26.996 2.39 27.006 2.51 0.225 Conduction block 2 (3.8%) 11 (6.0%) 7 (11.7%) 0.207 Denervation 8 (15.4%) 25 (13.7%) 10 (16.7%) 0.914
*Group showing statistically significant difference. †P , 0.05.
AE-BE, above elbow–below elbow; BMI, body mass index; CMAP, compound muscle action potential; NCV, nerve conduction velocity; SNAP, sensory nerve action potential.
Gender, Body Mass Index, and Ulnar Nerve A. Uzunkulaoglu, et al.
2007; Buschbacher, 1999) which found no association between BMI and UNE.
Because of biological and technical factors, various results on NCV can be determined. The experimental error inherent in the technique occurs primarily because of variability in measur-ing the latency and distance (Landau et al., 2002). Previously, obesity had been shown to result in higher measured ulnar AE-BE NCV values (Landau et al., 2005; Simmons et al., 1997). Our results were not consistent with these studies. Our results showed that ulnar AE-BE NCV is inversely proportional to BMI. That is, patients with higher BMIs had slower NCVs, and obesity was cited as a risk factor for UNE. Moreover, there was a correlation between BMI and ulnar forearm NCV; slender patients had higher ulnar nerve forearm sensory conduction velocities. It is not clear whether these correlations were due to biological or technical factors.
There were no data about individuals’ jobs or other occupational information in our study sample. This is a limitation of our study because it is known that occupations are associated with UNE (Bozentka, 1998). Furthermore, we cannot say that our control group was completely normal. The control group was composed of patients with symptoms that prompted the physician to perform ulnar nerve conduction studies across the elbow. These individuals may have had symptoms consistent with UNE, so differences between groups may not be determined effec-tively. However, large sample size and detailed electroneuromyo-graphic examination of median and ulnar nerve were the strengths of our study.
Finally, in our study, we determined that male gender is a risk factor for developing UNE, but BMI is not. Further studies which examine age, BMI, and gender differences along with data about occupational risk factors are required.
REFERENCES
American Academy of Neurology, American Association of Electrodiagnostic Medicine, American Academy of Physical Medicine and Rehabilitation. Practice parameter for electrodiagnostic studies in ulnar neuropathy at the elbow: summary statement. Muscle Nerve 1999;22:408–411.
Barnekow-Bergkvist M, Hedberg G, Janlert U, Jansson E. Development of muscular endurance and strength from adolescence to adulthood and level of physical capacity in men and women at the age of 34 years. Scand J Med Sci Sports 1996;6:145–155.
Bartels RH, Verbeek AL. Risk factors for ulnar nerve compression at the elbow: a case control study. Acta Neurochir (Wien) 2007;149:669–674. Bartels RHMA, Menovsky T, Van Overbeeke JJ, Verhagen WIM. Surgical management of ulnar nerve compression at the elbow: an analysis of the literature. J Neurosurg 1998;89:722–727.
Bozentka DJ. Cubital tunnel syndrome pathophysiology. Clin Orthop Relat Res 1998;351:90–94.
Buschbacher RM. Ulnar nerve motor conduction to the abductor digiti minimi. Am J Phys Med Rehabil 1999;78:9–14.
Charness ME. Unique upper extremity disorders of musicians. In: Millender LH, Louis DS, Simmons BD, eds. Occupational disorders of the upper extremity. New York: Churchill Livingstone, 1992:227–252.
Chuman MA. Risk factors associated with ulnar nerve compression in bedridden patients. J Neurosurg Nurs 1985;17:338–342.
Cutts S. Cubital tunnel syndrome. Postgrad Med J 2007;83:28–31. Descatha A, Leclerc A, Chastang J-F, Roquelaure Y; The Study Group on
Repetitive Work. Incidence of ulnar nerve entrapment at the elbow in repetitive work. Scand J Work Environ Health 2004;30:234–240. Kanehisa H, Ikegawa S, Tsunoda N, Fukunaga T. Crosssectional areas of fat
and muscle in limbs during growth and middle age. Int J Sports Med 1994;15:420–425.
Landau ME, Barner KC, Campbell WW. Effect of body mass index on ulnar nerve conduction velocity, ulnar neuropathy at the elbow, and carpal tunnel syndrome. Muscle Nerve 2005;32:360–363.
Landau ME, Diaz MI, Barner KC, Campbell WW. Changes in nerve conduction velocity across the elbow due to experimental error. Muscle Nerve 2002;26:838–840.
Mondelli M, Giannini F, Ballerini M, et al. Incidence of ulnar neuropathy at the elbow in the province of Siena (Italy). J Neurol Sci 2005;234:5–10. Ochiai N, Honmo J, Tsunjino A, Nisiura Y. Electrodiagnosis in entrapment neuropathy by the arcade of struthers. Clin Orthop Relat Res 2001;378:129–135.
Richardson JK, Green DF, Jamieson SH, Valentin FC. Gender, body mass and age as risk factors for ulnar mononeuropathy at the elbow. Muscle Nerve 2001;24:551–554.
Robertson C, Saratsiotis J. A review of compression ulnar neuropathy at the elbow. J Manipulative Physiol Ther 2005;28:345.
Simmons Z, Nicholson T, Wilde C, Manders EK. Variation of calculated ulnar motor conduction velocity across the elbow with body mass index. Muscle Nerve 1997;20:1607–1608.
Warner MA, Warner DO, Matsumoto JY, et al. Ulnar neuropathy in surgical patients. Anesthesiology 1999;90:54–59.
Warner MA, Warner ME, Martin JT. Ulnar neuropathy. Incidence, outcome, and risk factors in sedated or anesthetized patients. Anesthesiology 1994;81:1332–1340.
Werner CO, Ohlin P, Elmqvist D. Pressures recorded in ulnar neuropathy. Acta Orthop Scand 1985;56:404–406.
TABLE 4. Independent Predictors of Ulnar Neuropathy at the Elbow Variables Univariable Multivariable OR (95% CI) P OR (95% CI) P Age, yr 1.020 (1.010–1.031) 0.001* d d Gender (male) 2.155 (1.559–2.978) ,0.001* 1.922 (1.042–3.543) 0.036*
Multivariable logistic regression model summary: Nagelkerke R2¼ 0.802, P , 0.05.
*P , 0.05.
OR, odds ratio; 95% CI, 95% confidence interval.
A. Uzunkulaoglu, et al. Gender, Body Mass Index, and Ulnar Nerve
