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Randomized Controlled Trial
, 12, 174

Algometry With a Clothes Peg Compared to an Electronic Pressure Algometer: A Randomized Cross-Sectional Study in Pain Patients

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Randomized Controlled Trial

Algometry With a Clothes Peg Compared to an Electronic Pressure Algometer: A Randomized Cross-Sectional Study in Pain Patients

Niklaus Egloff et al. BMC Musculoskelet Disord.

Abstract

Background: Hypersensitivity of the central nervous system is widely present in pain patients and recognized as one of the determinants of chronic pain and disability. Electronic pressure algometry is often used to explore aspects of central hypersensitivity. We hypothesized that a simple pain provocation test with a clothes peg provides information on pain sensitivity that compares meaningfully to that obtained by a well-established electronic pressure algometer. "Clinically meaningful" was defined as a medium (r = 0.3-0.5) or high (r > 0.5) correlation coefficient according to Cohen's conventions.

Methods: We tested 157 in-patients with different pain types. A calibrated clothes peg was applied for 10 seconds and patients rated the pain intensity on a 0 to 10 numerical rating scale. Pressure pain detection threshold (PPdt) and pressure pain tolerance threshold (PPtt) were measured with a standard electronic algometer. Both methods were performed on both middle fingers and ear lobes. In a subgroup of 47 patients repeatability (test-retest reliability) was calculated.

Results: Clothes peg values correlated with PPdt values for finger testing with r = -0.54 and for earlobe testing with r = -0.55 (all p-values < 0.001). Clothes peg values also correlated with PPtt values for finger testing with r = -0.55 (p < 0.001). Test-retest reliability (repeatability) showed equally stable results for clothes peg algometry and the electronic algometer (all r-values > 0.89, all p-values < 0.001).

Conclusions: Information on pain sensitivity provided by a calibrated clothes peg and an established algometer correlate at a clinically meaningful level.

Figures

Figure 1
Figure 1
Measurement of the Clamping Force of a Clothes Peg. We selected clothes pegs in which the spread of 5 mm (controlled with a caliper) could be reached with a force of 10 Newton in vertical direction (controlled with a spring scale).
Figure 2
Figure 2
The Two Compared Algometric Methods. a shows the measurement of pressure pain sensitivity with an electronic algometer. b and c show the pain provocation test with a calibrated clothes peg.
Figure 3
Figure 3
Pain Characteristics of the Two Clinical Groups. Our aim was to compare the two algometric test methods in a wide range of pain types. Therefore we recruited patients from the orthopaedic department and the medical-psychosomatic department. a illustrates the distribution of the baseline pain values (NRS) in both groups. b illustrates the distribution of the pain sensitivity values (NRS) of the ear lobe provoked by clothes pegs. The box-and-whisker-plots show the median with interquartile range (box: 25th and 75th percentile) and 5th and 95th percentile (whiskers) of the data distribution.
Figure 4
Figure 4
Repeatability of Clothes Peg Algometry. a illustrates the test-retest reliability of the clothes peg test at the middle finger. b illustrates the test-retest reliability of the clothes peg test at the ear lobe. Both plots reflect the statistical agreement between the two clinical measurements following the Bland Altman technique [11]. Test-retest difference was not related to pain intensity. The null line stands for identical test and retest values. According to the British Standards Institution, at least 95% of the differences between test and retest are expected to be within two standard deviations from the null line to assume good repeatability http://www.bsigroup.com. All methods of measurement fulfilled this criterion; 100% of the differences were within these limits (maximum and minimum distances from the null line are indicated). In addition, no linear relation between pain intensity and test-retest difference was visible.
Figure 5
Figure 5
Repeatability of Clothes Peg Algometry Controlled for the Time Between the Two Measurements. a b Test-retest difference was neither related to pain intensity nor to time between test and retest. There is no linear relation between test-retest time and test-retest difference.

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