Exploration of the Extent of Somato-Sensory Impairment in Patients with Unilateral Lateral Epicondylalgia

The Journal of Pain, Vol 10, No 11 (November), 2009: pp 1179-1185 Available online at www.sciencedirect.com

Exploration of the Extent of Somato-Sensory Impairment in Patients with Unilateral Lateral Epicondylalgia Josue´ Ferna´ndez-Carnero,*yx Ce´sar Ferna´ndez-de-las-Pen˜as,*yx Michel Sterling,z Tina Souvlis,z Lars Arendt-Nielsen,x and Bill Vicenzinoz * Department of Physical Therapy, Occupational Therapy, Rehabilitation and Physical Medicine, Universidad Rey Juan Carlos, Alcorco´n, Madrid, Spain. y Esthesiology Laboratory of Universidad Rey Juan Carlos, Alcorco´n, Madrid, Spain. z Division of Physiotherapy and National Health and Medical Research Council Centre for Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, The University of Queensland, Australia. x Centre for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.

Abstract: There is evidence suggesting an important role of nociceptive sensitization in lateral epicondylalgia (LE). Our aim was to explore somato-sensory changes in patients with unilateral LE to better understand this musculoskeletal condition. Twelve patients (6 female) with LE with a mean (SD) age 47 (10) years, and 16 controls (7 female), aged 41 (9) years were tested. The following somato-sensory parameters were assessed: pressure-pain threshold (PPT), heat- and cold-pain thresholds, thermal, cold- and vibration-detection thresholds. All these tests were bilaterally assessed over the lateral epicondyle (affected/unaffected in patients; dominant/nondominant in controls) and at the dorsal-lateral surface of the wrist in all patients and controls. The results showed that patients with unilateral LE not only exhibited substantial reductions in PPT on the affected side compared to the unaffected side (mean difference and 95% confidence intervals: 219 kPa [136.8 to 301.1 kPa] but also when compared to controls (581.1 kPa [340.5 to 821.7 kPa]), showing bilateral pressurepain hyperalgesia. These differences represented an effect size (ie, standardized mean difference) of 1.23 and .94, respectively. In the same cohort, there were no such deficits in cold and heat pain, cold- and warm-detection thresholds, and vibration-detection thresholds, either between affected and unaffected sides in patients with LE or between patients and controls. Effect sizes for the sensory-detection tests were small, which were generally less than the pain tests. Our data imply that LE is largely characterized by peripheral and central mechanical pain hyperalgesia. Perspective: This article reveals the presence of bilateral pressure-pain hypersensitivity in patients with unilateral LE. On the contrary, thermal and vibration tests were not significantly different from controls. ª 2009 by the American Pain Society Key words: Lateral epicondylalgia, quantitative sensory testing, hyperalgesia.

L

ateral epicondylalgia (LE) is characterized by local pain and mechanical hyperalgesia at the lateral epicondyle, referred pain,6 and decreased force production of the wrist extensor muscles.23 It is a relatively common disorder of the upper limb that affects 1 to 3% of the general population and 15% of workers.3,24 This condition is a frequent complaint in primary care, Received November 3, 2008; Revised March 26, 2009; Accepted April 20, 2009. Address reprint requests to Professor Bill Vicenzino, Division of Physiotherapy, St Lucia Campus, University of Queensland 4067, Australia. E-mail: [email protected] 1526-5900/$36.00 ª 2009 by the American Pain Society doi:10.1016/j.jpain.2009.04.015

and is generally associated with work-related activities showing a substantial impact on participation at work.31 Although the aetiology of LE is not completely understood, there is recent evidence that it involves sensitization of the nociceptive system. It is generally accepted that the tendon of the extensor carpi radialis brevis muscle is the most likely source of pain in LE.18 Alfredson et al1 reported higher levels of glutamate but not inflammatory markers (eg, prostaglandin E2) at the origin of the extensor carpi radialis brevis muscle in LE patients as compared to healthy controls. In addition, studies that used inmunoreactive marker techniques to identify receptors and nerve fibers at the origin of the extensor carpi radialis brevis muscle have reported evidence that other algogenic 1179

1180 substances (eg, calcitonin gene-related peptide and substance P) are present in these patients.19,20 These findings suggest an important role of the nociceptive system processes in this musculoskeletal condition. Some authors have reported that LE is characterised by mechanical, but not thermal hyperalgesia.33 A preliminary study by Smith and Wright28 showed that the mechanical pain of LE is likely signalled by afferent input along myelinated neurons. Taken in combination, the findings from these studies have led to the proposal that LE represents a secondary hyperalgesia33 and that sensitization of central pathways may be involved in LE.26 If central sensitization is present in patients with LE, then sensibility in other body regions distant to the affected lateral epicondyle might be altered. Supporting this proposition to some extent is a study by Leffler et al17 who found lower thermal-detection threshold in the forearm (ie, muscle referred pain area) in LE after pain provocation, but not prior to pain provocation. In support of this proposition of central nervous system involvement in LE are findings that referred muscle pain is clinically relevant to pain perception in patients with LE.6 Specifically, stimulation of a trigger point (TrP) in the extensor carpi radialis brevis muscle resulted in a larger referral area of pain in patients, with pain referral to the lateral epicondyle (proximally), to the dorso-lateral aspect of the forearm, and, sometimes, to the wrist.6 In addition, we have recently found the presence of bilateral muscle TrPs in strictly unilateral LE, supporting the role of, at least, a contralateral segmental sensitization in this musculoskeletal condition.7 Further, support for a broad involvement of the central nervous system in this condition is evidenced by sensory-motor dysfunction in unilateral LE in the form of bilateral impediment in reaction time and speed of movement,22 as well as bilateral impaired wrist angle during grip strength testing.2 Several quantitative sensory tests (pressure-pain threshold,4,25 thermal-pain10,35 or detection34 thresholds, or vibration-detection threshold15) have been previously used for assessing impairments of the nociceptive system in several chronic conditions, eg, whiplash,30 repetitivestrain injury,12 nonspecific arm pain,13 or fibromyalgia.5 In the present study, we used a number of quantitative sensory tests, measured both locally at the elbow and at a distant site (wrist), to provide further information that may improve our insight into the pain-processing mechanisms underlying LE. Our aim was to compare pressure-pain threshold (PPT), thermal (warm, cold) detection/pain threshold, and vibration-detection thresholds bilaterally over the lateral epicondyle and dorsal aspect of the wrist (distant area) between patients with LE and controls.

Methods Subjects Six females and 6 males with unilateral LE, aged 34 to 56 years old (mean: 47 6 10 years), and 16 healthy controls (7 females and 9 males) aged 32 to 56 (mean: 41 6 9 years), without upper extremity symptoms participated

Somatosensory Impairment in Lateral Epidondylalgia in this study. Both patients and controls were recruited by newspaper advertisements from Brisbane metropolitan and suburban areas. Each subject underwent a physical examination, conducted by a physical therapist experienced in musculoskeletal examination, to assess inclusion and exclusion criteria. Patients were selected for inclusion if, during physical examination 2 or more of the following criteria were identified: 1) unilateral pain over lateral side of the elbow present for at least 6 weeks; 2) pain provocation to manual palpation over the lateral epicondyle; 3) elbow pain with gripping; 4) clinically related decreased grip strength on the affected elbow; or 5) elbow pain with resisted static contraction or stretching of the extensor muscles.14 Patients were excluded if they exhibited any of the following: 1) multiple diagnoses (arm fracture, disease of bone, muscle or nervous system) or had evidence of any systemic disease; 2) seeking litigation; 3) received corticosteroid injection or any therapy within the year prior to the study; or 4) undergone a surgical intervention in the elbow area. Healthy controls were excluded if they exhibited a history of upper extremity or cervical pain in the last 6 months, fractures or neurological disorders, prior wrist extensor training or any consumption of analgesic or anti-inflammatory drugs. The research project was done at the Division of Physiotherapy of the University of Queensland and approved by the University of Queensland Medical Research Ethics Committee. All subjects signed an informed consent prior to their inclusion.

Procedure Patients registered on an 11-point numerical pain rating scale16 (NPRS: range; 0 = no pain, 10 = maximum pain) the current level of lateral elbow pain and the level of worst lateral elbow pain experienced in the preceding week. Further, patients were asked to draw the location of their symptoms on a body diagram. Following the clinical examination, both patients and controls underwent the same experimental procedure and completed the following tests: vibration detection; thermal (warm, cold) detection and pain thresholds; and pressure-pain threshold, in a randomized order. All these tests were bilaterally assessed over the lateral epicondyle (ie, affected or unaffected in patients, dominant or nondominant within controls) and in the dorso-lateral aspect of the wrist (distant pain area) in both patients and controls.

Vibration Stimulus Detection The vibration threshold was tested with a vibrameter (Somedic AB, Ho¨rby, Sweden). A frequency of 120 Hz was used to supply the stimulus to both elbows (affected or unaffected in patients, dominant or nondominant in controls) and both wrists (dorsal surface, over the trapezoid-capitate bone). Tissue displacement brought about by the vibrating probe (1 cm) was displayed digitally. The same investigator was used to take all measures. A pressure display of 0 to 1,000 g enabled the applied pressure of the hand-held stimulator probe to be calibrated to 500 g before use with each subject. The range of

Ferna´ndez-Carnero et al

1181

Table 1. Somato-Sensory Pain Thresholds Mean Data (Standard Deviation [SD]) for Control (n = 16) and Lateral Epicondylalgia (n = 12) and the Between Group Mean Differences (Upper And Lower 95% Confidence Interval [CI]) that are Bonferroni Adjusted for Multiple Comparisons LATERAL EPICONDYLALGIA (SD) PPT elbow (kPa) Dominant/affected Nondominant/unaffected PPT wrist (kPa) Dominant/affected Nondominant/unaffected HPT elbow ( C) Dominant/affected Nondominant/unaffected HPT wrist ( C) Dominant/affected Nondominant/unaffected CPT elbow ( C) Dominant/affected Nondominant/unaffected CPT wrist ( C) Dominant/affected Nondominant/unaffected

CONTROL (SD)

MEAN DIFFERENCE (CI)

SMD

303.2 (97) 527.5 (178)

884.3 (394.9) 813.1 (350.6)

–581.1 (–821.7 to –340.5)* –285.6 (–513.6 to –57.7)*

.94y .49

661.3 (288.6) 704.8 (267.3)

974.4 (354.4) 919.1 (348.2)

–313.1 (–570.8 to –55.5)* –214.3 (–462.7 to 34.2)

.47 .62y

44.8 (3) 43.9 (3.6)

42.9 (3) 43.9 (3.1)

1.9 (–.4 to 4.3) –.1 (-2.7 to 2.5)

.63 .03

45 (3.9) 43.4 (3.3)

43.9 (3.4) 43.3 (3.2)

1.1 (–1.8 to 4) .1 (–2.4 to 2.7)

.32 .03

20.2 (12) 11.1 (7.4)

13.8 (9.6) 9 (4.7)

6.4 (–2 to 14.8) 2.1 (–2.7 to 6.8)

.67y .45

10.9 (7.3) 12.0 (7.3)

9 (5.2) 10.8 (6)

1.9 (–2.9 to 6.7) 1.2 (–3.9 to 6.4)

.37 .20

Abbreviations: CPT, cold-pain threshold; HPT, heat-pain threshold; PPT, pressure-pain threshold; SMD, standardized mean difference. NOTE. The SD and standardized mean difference (SMD) for the comparisons are also presented. *Confidence intervals that do not contain 0 are statistically significant to the P < .05 level. ySMD of reasonable magnitude (moderate effect size).

amplitude for the vibration stimulus was .1 to 130 mm, and the rate of change was .5 mm/second. All subjects were naive to the test procedure and performed the assessment with eyes closed once the technique had been fully explained and demonstrated to them. Onset amplitude was defined as the amplitude (mm) when subjects were able to perceive the vibration stimuli, while the offset amplitude was the amplitude at which the vibration sensation was no longer perceived by the subject. Both onset and offset measurements were repeated 3 times. The vibration threshold (VIBT) was calculated as the mean of both onset and offset amplitudes and considered for main analysis. Previous studies have established the validity and reliability of this equipment and procedure.10,11

Thermal Stimulus Tests Both warm/cold perception and heat/cold pain thresholds were tested with a Thermotest System (Somedic AB). The Thermotest System is calibrated to 6.2 C with a control resolution of greater than .2 C. A Peltier thermode of 2.5  5 cm was applied directly to the skin in both lateral epicondyle and the dorso-lateral aspect of the wrist regions of either arm. From a baseline of 30 C, the thermode either increased in temperature at a rate of 1 C/second up to a maximum cut-out temperature of 50 C; or decreased temperature at a rate of 1 C/second to a minimum cut-out temperature of 4.5 C. Park et al21 demonstrated a good reliability of thermal-pain thresholds at the dorsal aspect of the forearm in healthy subjects. For warm-detection (WDT) and cold-detection (CDT) thresholds, participants were asked to press a hand switch as soon as they perceived warm or cold sensation.

For heat-pain (HPT) and cold-pain (CPT) thresholds, each subject was instructed to press a hand-controlled switch as soon as the pain was perceived. The mean of 3 trials at each site was calculated and used for further analysis. A pause of at least 5 seconds was allowed between tests.

Pressure-Pain Threshold Assessment An electronic pressure algometer (Somedic AB) with a 1-cm2 rubber-tipped plunger mounted on a force transducer was used to measure the pressure-pain thresholds (PPT). PPT is defined as the minimal amount of pressure where a sense of pressure first changes to pain.8 The subjects were instructed to push a button to stop the pressure stimulation when the sensation first changed from pressure to pressure and pain. Pressure was applied at a rate of 30 kPa per second. Three measurements, with 30-second intervals between each one, were taken and the mean was used for further analysis.

Statistical Analysis Data were analyzed with SPSS v11.0 for Macintosh (SPSS Inc, Chicago, IL). Baseline demographic characteristics between the groups were evaluated with independent Student t-tests for continuous data and c2 tests for categorical data. The effects of LE on each of the somato-sensory measures taken in this study were first evaluated with an omnibus mixed 3-way analysis of variance (ANOVA) with group (patients or controls) as the between-subjects factor, and side (affected/dominant or unaffected/nondominant) and site (elbow or wrist) as the within-subjects factors. An alpha rate of .05 was adopted for these analyses. Tests of simple effects for the pairwise comparisons of interest were undertaken

1182

Somatosensory Impairment in Lateral Epidondylalgia

Figure 1. Individual (raw) and group (mean and standard deviation) data for the pain-threshold measures in patients and controls at the 2 test sites of lateral elbow and wrist. Note that only the elbow data for cold (CPT) and wrist data for heat (HPT) are provided, as the alternate data was unremarkable (Tables 3 and 4). Horizontal lines indicate statistical significance (P < .05). Diamonds represent dominant limb in controls, squares represent nondominant in controls, triangles represent the affected side of patients and circles represent unaffected side of patients with lateral epicondylalgia. with the experiment alpha rate of .05 Bonferonni adjusted. Mean differences and 95% confidence intervals (CI) are presented to demonstrate the magnitude and significance of any pairwise difference. A significant mean difference was defined as one that did not contain 0 within its confidence intervals. The standardized mean difference or effect size (Cohen’s d) (mean difference/ standard deviation), was also calculated to facilitate a decision regarding the relative magnitude of pairwise differences between the somato-sensory variables that were measured. In this way, point estimates of effect for measurements in different units could be directly compared. Effect size classification is referenced as trivial (0 to .2), small (.2 to .6), moderate (.6 to 1.2), and large (> 1.2). Finally, the Spearman’s rho (rs) test was used to analyse the association between somato-sensory tests and the clinical variables relating to elbow pain.

Results Demographic and Clinical Data of the Patients All subjects with LE reported an insidious onset of their symptoms. Patient’s pain was located in the lateral

epicondyle (100%), the dorso-lateral aspect of the forearm (90%) and the wrist (85%). Eight patients (67%) in the LE group were right-handed and the remaining 4 (33%) were left-handed. The dominant arm was the affected arm in all patients. Within the control group, 11 subjects (69%) were right-handed and the remaining 5 (31%) left-handed, which was not significantly different to the LE group. Lateral elbow pain history ranged from 10 to 52 months (mean duration 6 SD: 25 6 16 months). The worst level of pain the day of the examination was 4.4 (range: 2 to 6), whereas the worst level of lateral elbow pain experienced in the preceding week was 5.3 (range: 1 to 7). From all tests, only PPT showed significant correlations with clinical pain features: 1) PPT scores over the affected elbow were correlated with the worst level of pain on the day of the examination and the worst level of pain experienced in the preceding week (both, rs = –.7; P < .001); 2) PPT levels over the unaffected elbow also were correlated with both levels of elbow pain (both, rs = –.4; P < .001); and 3) PPT over the affected wrist was correlated with the worst level of pain experienced in the preceding week (both, rs = –0.4; P = .03). In such a way, the greater the pain level, the lower was the PPT levels.

Ferna´ndez-Carnero et al

Pain-Threshold Tests The intra-examiner reliability of pain-threshold test ranged from .86 to .95 for both patients and controls, suggesting high reliability. The only pain-threshold test to differentiate patients with LE from controls was PPT, both at the elbow and wrist sites (Table 1, Fig 1). This was demonstrated in the omnibus ANOVA, which revealed a significant 3-way interaction effect (group  side  site) for PPT (F(1,23) = 5.19, P = .032). Tests of simple effects revealed substantial between group mean differences of 581.1 (95% CI 340.5, 821.7) and 313.1 (95% CI 55.5, 570.8) at the elbow and wrist, respectively. In patients, PPT of the affected elbow was significantly lower than that of the unaffected elbow (–219 [95% CI –301.3, –136.8]), but this was not the case at the wrist (Table 2). There were no side-to-side differences in the control group. The next most remarkable finding was one of side-toside differences in CPT for both the LE (4.8 [95% CI 1.7, 7.9]) and control (9.7 [95% CI 4.1, 15.4]) groups (Tables 1 and 2, Fig 1). It would seem that there is a dominantside bias in CPT expression with CPT being higher in both affected (most were dominant-side affected) in patients and dominant elbow of the control group. Interestingly, HPT was lower at the wrist, but only within the LE patient group. However, the statistical significance of this pairwise difference should be viewed with caution as the P-level from the omnibus ANOVA did not reach the a priori set alpha of .05; this may have been a chance finding resulting from many pairwise comparisons in this study.

Sensory-Detection Tests Further, both thermal- and vibration-detection thresholds did not show significant differences between the LE and control groups and between the affected-unaffected sides (Tables 2 and 3).

Intermeasure Comparisons of Effect Size Substantial effects were observed for side-to-side comparisons in the elbows of patients [ie, PPT (1.23), CPT (1.31), WDT (.88)], implicating PPT, CPT, and WDT as characteristics of LE (Table 2). However, of these tests, only PPT demonstrated a moderate-sized effect for LE compared to controls (.94; Table 1) and CPT was similar between patients and controls (1.02). In addition to PPT differences between patients and controls, there was a strong effect for VDT at the elbow (1.14), but this was not the case between affected and unaffected sides (.46).

Discussion Our study found that patients with unilateral LE had bilateral increased pressure-pain sensitivity, not only in the affected area (elbow), but also in distant areas (wrist). On the contrary, both thermal and vibration pain and detection thresholds were not significantly different between patients and controls. Previous studies have demonstrated mechanical, but not thermal, hyperalgesia over the lateral epicondyle in

1183

The Mean Difference (95% Confidence Intervals [CI]), Standardized Mean Differences (SMD), Standard Deviation (SD) for Side-ToSide Comparisons (Affected-Dominant vs Unaffected-Nondominant) in Each Group (Lateral Epicondylalgia [LE] and Control)

Table 2.

MEASURE

SITE

GROUP

MEAN DIFFERENCE (CI)

SMD

PPT (kPa)

Elbow

LE Control LE Control LE Control LE Control LE Control LE Control LE Control LE Control LE Control LE Control LE Control LE Control

–219 (–301.3 to –136.8)* 71.2 (–4.9 to 147.2) –63 (–167.8 to 41.8) 55.3 (–24.4 to 135.1) .9 (–.7 to 2.4) –1 (–2.4 to .3) 1.6 (.3 to 2.9)* .6 (–.9 to 2) 9.7 (4.1 to 15.4)* 4.8 (1.7 to 7.9)* –.8 (–3.5 to 1.9) –1.8 (–3.6 to .1) .6 (–.05 to 1.3) .1 (–.2 to .5) .04 (–.08 to .2) –.01 (–.08 to .06) .7 (–.4 to 1.8) –.3 (–.9 to .4) –.9 (–2 to .2) –.2 (–.9 to .5) .2 (–.3 to .6) –.3 (–.9 to .4) .04 (–.4 to .5) –.2 (–1 to .6)

1.23y .2 .24 .16 .25 .32 .48 .19 1.31y 1.02y .11 .3 .46 .14 .13 .03 .88y .2 .45 .12 .29 .3 .05 .14

Wrist HPT ( C)

Elbow Wrist

CPT ( C)

Elbow Wrist

VDT (mm)

Elbow Wrist

WDT ( C)

Elbow Wrist

CDT ( C)

Elbow Wrist

*Statistically significant to .05 level. ySMD of reasonable magnitude.

patients with LE.29,33 Our results support this finding and suggest that mechanical hyperalgesia is clearly a somato-sensory characteristic of LE. Additionally, we also found that LE patients showed bilateral pressure-pain hyperalgesia in both the symptomatic area and in distant areas (wrist), which suggests contra-lateral segmental sensitization. Specific mechanical hyperalgesia, but not thermal- and vibration-detection thresholds, in LE patients may suggest that deep tissue (muscle) hyperalgesia is the first and cardinal abnormality in LE. Slater et al26 found that patients with LE reported more widespread pain and extended referred-pain areas compared with healthy controls in an experimental induced-pain model, suggesting a relevant role of central sensitization. In our previous studies, we found pressure-pain hyperalgesia and larger referred-pain areas elicited from muscle TrPs in LE compared to controls, suggesting an etiologic role of TrPs in LE.6,7 This evidence agrees with findings in animals where unilateral-musculoskeletal pain spreads contra-laterally,27 and suggests that early intervention is important in the treatment of localized musculoskeletal-pain conditions. These findings suggest that pain could lead to segmental central sensitization in the dorsal horn in patients with unilateral LE. In the present study, we found side-to-side differences in CPT within the LE patient group, but this finding was similar to the side-to-side differences in the control

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Somatosensory Impairment in Lateral Epidondylalgia

Somato-Sensory Detection Thresholds Mean Data (Standard Deviation [SD]) for Control (n = 16) and Lateral Epicondylalgia (n = 12) and the Between-Group Mean Differences (Upper And Lower 95% Confidence Interval [CI]) that are Bonferroni Adjusted For Multiple Comparisons

Table 3.

VDT elbow (mm) Dominant/affected Nondominant/unaffected VDT wrist (mm) Dominant/affected Nondominant/unaffected WDT elbow ( C) Dominant/affected Nondominant/unaffected WDT wrist ( C) Dominant/affected Nondominant/unaffected CDT elbow ( C) Dominant/affected Nondominant/unaffected CDT wrist ( C) Dominant/affected Nondominant/unaffected

LATERAL EPICONDYLALGIA (SD)

CONTROL (SD)

MEAN DIFFERENCE (CI)

SMD

1.8 (1.5) 1.2 (1.3)

1.1 (.7) .9 (.7)

.8 (–.1 to 1.6) .3 (–.5 to 1.1)

1.14y .43

.4 (.4) .4 (.3)

.4 (.3) .4 (.4)

–.004 (–.277 to .269) –.058 (–.309 to .193)

.01 .15

33.8 (1.6) 33.2 (.8)

33.4 (1.2) 33.7 (1.5)

.5 (–.6 to 1.5) –.5 (–1.5 to .5)

.42 .33

34.1 (1.5) 35 (2)

33.9 (1.5) 34.1 (1.7)

.2 (–1.0 to 1.4) .9 (–.6 to 2.4)

.13 .53

28.7 (.6) 28.5 (.7)

29 (1.1) 29.3 (1)

–.3 (–1.0 to .4) –.8 (–1.5 to –.04)*

.27 NA

28.7 (.7) 28.7 (.8)

29.3 (.8) 29.5 (1.4)

–.6 (–1.14 to –.06)* –.8 (–1.8 to .08)

NA .57

Abbreviations: CDT, cold-detection threshold; VDT, vibration-detection threshold; WDT, warm-detection threshold. NOTE. The SD and standardized mean difference (SMD) for the comparisons are also presented. *Confidence intervals that do not contain 0 are statistically significant to the P < .05 level. ySMD of reasonable magnitude (moderate effect size).

group, implying that LE may not be the determining factor, but rather something else, eg, hand dominance, given that most affected arms were dominant. It is interesting to note that previous studies17,33 did not include control groups and so may have not had sufficient data to show this dependency. We also found that vibration-detection threshold had a strong effect size (1.14) with only 1 more patient needed to show a difference between groups. However, the side-to-side comparison between affected and unaffected elbows within the LE group may have been underpowered, though the effect size was low (.49). This data may point to a dysfunction of large, sensory fibers or their processing. It is suggested that vibration-threshold assessment can detect some signs of minor neural irritation,12 since large, sensory (Ab) fibers, which mediate the sensation of vibration,9,10 are more vulnerable to ischaemia than other nerve fibers.12 Alternatively, impairments of vibration sensation are also considered an abnormal response of the central nervous system.32 Our results suggest, not confirm, that vibration-detection

thresholds may be also impaired in LE, although a greater sample size is needed. It should be noted that we included a small sample size in the present study. Population-based epidemiological studies with greater sample size are needed to permit a more generalized interpretation of our results. Finally, our sample size may represent chronic population of patients with LE, but we do not know if our findings might different in a cohort of acute LE patients. Further studies may investigate somatosensory differences between acute and chronic patients with LE.

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