Reliability and minimal detectable difference of pressure pain thresholds in a pain-free population

Selective nociceptive modulation using a novel prototype of transcutaneous kilohertz high-frequency alternating current stimulation: a crossover double-blind randomized sham-controlled trial

BACKGROUND

Kilohertz high-frequency alternating current (KHFAC) stimulation has demonstrated to induce rapid and reversible nerve blocks without causing nerve damage. Previous studies have explored frequency-dependent effects using a transcutaneous approach in humans from 5 to 20 kHz. Nevertheless, its application in humans is limited by the lack of stimulators approved for frequencies above 20 kHz. Therefore, this study aimed to assess the effects and safety of transcutaneous KHFAC stimulation using a novel prototype stimulator, comparing interventions at 30, 40, and 50 kHz to sham stimulation on experimental pain, sensory, motor, and neurophysiological outcomes.

METHODS

A randomized, double-blind, sham-controlled crossover study involving 34 healthy participants was conducted. Four interventions (30, 40, 50 kHz, and sham) were administered, and stimulation was applied for 20 min to the median nerve of the non-dominant hand. A prototype stimulator capable of delivering frequencies between 1 and 50 kHz, with a maximum peak-to-peak output current intensity of 400 mA was designed. The intensity applied during the stimulation was below motor threshold, evoking a 'strong but comfortable' tingling sensation. Primary outcomes included heat pain threshold (HPT), pressure pain threshold (PPT), and adverse effects. The secondary outcomes included static two-point discrimination sensitivity, isometric pinch strength, and median sensory nerve action potential (SNAP).

RESULTS

Compared with the sham stimulation, all the active interventions exhibited a significantly greater increase in the PPT during and immediately after the stimulation, while only a significant increase was observed at 40 kHz (4.1 N/cm2; 95%CI 0.3 to 7.9) at 15 min post-intervention. Compared to sham stimulation, the 40 kHz intervention had a significantly greater effect on the HPT at all time points, with the greatest difference (1.4 °C; 0.6 to 2.1) occurring immediately post-intervention. Adverse effects during active interventions included petechiae, erythema, and itching, which resolved at 24 h post-intervention. For secondary outcomes, only a significant reduction in the median SNAP velocity was observed in the sham stimulation group compared to the 50 kHz group.

CONCLUSIONS

Active KHFAC stimulation, particularly at 40 kHz, delivered through a novel stimulator, effectively increased the PPT and HPT without affecting tactile or motor outcomes, inducing mild skin-related adverse effects. These findings have potential implications for people with pain-related pathologies.

TRIAL REGISTRATION

NCT05230836.

Regional Sensorimotor Effects of Chiropractic Spinal Manipulation: Preliminary Results From an Experimental Study

OBJECTIVE

The purpose of this study was to assess the effects of different spinal manipulation (SM) techniques and target segments on a specific dermatome and myotome, when compared with a remote spinal cord segment that served as a control location.

METHODS

Twenty-nine healthy volunteers were randomized to receive instrumental (Activator IV, Activator Methods International Ltd) or manual SM at the C6, C1, and T4 vertebral segments in 3 independent sessions. Pressure pain thresholds (PPTs) and muscle strength were examined at the C6 (test) and L4 (control) dermatomes and myotomes, at baseline and after intervention. Linear mixed-effects models were used to analyze changes over time and interindividual variability.

RESULTS

Pressure pain thresholds significantly increased at both proximal and distal C6 dermatome locations (P < .05), irrespective of the technique and segment of application (P > .2). No significant changes were observed at the L4 dermatome. Muscle strength remained unchanged throughout the study. Multilevel modeling revealed significant associations between increased PPTs along the C6 dermatome (P < .001), whereas the combination of technique and target segment predicted PPT increases at the proximal C6 dermatome.

CONCLUSION

These findings support regional, rather than segmental mechanisms underlying the sensory effects of SM. Specifically, significant increases in PPTs along the C6 dermatome suggest localized effects on pain sensitivity, which may depend on the target spinal region. Further investigation is needed to better understand these regional changes of SM and their potential clinical implications.

The effect of six-week regular stretching exercises on regional and distant pain sensitivity: an experimental longitudinal study on healthy adults

BACKGROUND

Stretching exercises are widely used for pain relief and show positive effects on musculoskeletal, nociplastic and neuropathic pain; the magnitude of altered pain sensitivity responses following regular stretching is currently unknown. This study aimed to investigate the effect of six weeks of regular stretching exercise on regional and widespread pain sensitivity and range of motion and the effect of stretching cessation on regional and widespread pain sensitivity and range of motion.

METHODS

An experimental single-blind longitudinal repeated measures study. Twenty-six healthy adults were recruited. Regional and distant pressure pain thresholds and passive knee extension range of motion were measured at three points: before (baseline) and after six weeks (post-stretch) of daily bilateral hamstring stretching exercises and following four weeks of cessation (post-cessation) from stretching exercises.

RESULTS

Participants had a mean ± standard deviation (range) age of 23.8 ± 2.1 (21-30) years. There was a 36.7% increase in regional (p = 0.003), an 18.7% increase in distant pressure pain thresholds (p = 0.042) and a 3.6% increase in range of motion (p = 0.002) between baseline and post-stretch measures. No statistically significant differences were found for regional (p = 1.000) or distant pressure pain thresholds (p = 1.000), or range of motion (p = 1.000) between post-stretch and post-cessation. A 41.2% increase in distant pressure pain thresholds (p = 0.001), a 15.4% increase in regional pressure pain thresholds from baseline to post-cessation (p = 0.127) and a 3.6% increase in passive knee extension range of motion (p = 0.005) were found from baseline to post-cessation.

CONCLUSIONS

Six weeks of regular stretching exercises significantly decreased regional and widespread pain sensitivity. Moreover, the results showed that the hypoalgesic effect of stretching on regional and widespread pain sensitivity persisted following four weeks of cessation. The results further support the rationale of adding stretching exercises to rehabilitation efforts for patients experiencing nociceptive, nociplastic, and neuropathic pain. However, further research is needed to investigate how the long-term effects of stretching exercises compare with no treatment in clinical populations.

TRIAL REGISTRATION

The trial was registered June 1st, 2021 at ClinicalTrials.gov (Trial registration number NCT04919681).

Personalized pain management: The relationship between clinical relevance and reliability of measurements

Reliability is a topic in health science in which a critical appraisal of the magnitudes of the measurements is often left aside to favour a formulaic analysis. Furthermore, the relationship between clinical relevance and reliability of measurements is often overlooked. In this context, the aim of the present article is to provide an overview of the design and analysis of reliability studies, the interpretation of the reliability of measurements and its relationship to clinical significance in the context of pain research and management. The article is divided in two sections: the first section contains a step-by-step guide with simple and straightforward recommendations for the design and analysis of a reliability study, with a relevant example involving a commonly used assessment measure in pain research. The second section provides deeper insight about the interpretation of the results of a reliability study and the association between the reliability of measurements and their experimental and clinical relevance. SIGNIFICANCE: Reliability studies quantify the measurement error in experimental or clinical setups and should be interpreted as a continuous outcome. The assessment of measurement error is useful to design and interpret future experimental studies and clinical interventions. Reliability and clinical relevance are inextricably linked, as measurement error should be considered in the interpretation of minimal detectable change and minimal clinically important differences.