Personal influencing factors for pressure pain threshold in healthy people: A systematic review and meta-analysis

Trigemino-autonomic activation in a human trigeminal pain model

BACKGROUND

Autonomic symptoms are mandatory for making the diagnosis of a trigemino-autonomic cephalalgia (TAC). These symptoms can occasionally also occur in migraine and facial pain disorders. This leads to the question whether the trigeminal pain itself can induce autonomic symptoms also in healthy subjects.

METHODS

We enrolled healthy subjects without a history of migraine or a TAC and provoked severe trigeminal pain by injection of 0.05 ml capsaicin (0.01%) into the right forehead. Autonomic symptoms occurring at the right eye or right nostril were registered until they disappeared. We also calculated an autonomic score for the frequency and duration of autonomic symptoms in an individual.

RESULTS

We enrolled 60 healthy volunteers (30 male, 30 female; mean age 28 +/- 5 years). All but two subjects developed at least one autonomic symptom after injection of capsaicin. One minute after injection, the pain was rated as 9.2 +/- 1.1 and 8.5 +/- 1.2 (scale from 0 to 10) in female and male subjects, respectively. The autonomic score was 4.4 +/- 1.6 and 1.7 +/- 0.9 for female and male subjects, respectively. All differences between female and male subjects were significant. Pain rating and autonomic score showed a significant positive correlation which remained significant even after adjusting for sex.

CONCLUSIONS

Severe trigeminal pain was accompanied by autonomic symptoms in almost all subjects in this experiment. The pain rating and the severity of autonomic symptoms were significantly higher in female subjects than in male. The higher the pain the more severe was this autonomic activation. We conclude that activation of autonomic symptoms is an unspecific consequence of severe trigeminal pain. This does, however, not exclude the possibility that primary headache disorders might have an independent anatomic pathway to induce autonomic symptoms because these symptoms can, although very rarely, also occur without pain.

Correlation between pressure pain threshold and L4-5 supraspinous ligament biomechanics after cesarean delivery under spinal anesthesia

Background

Localized low back pain is a frequent complaint after spinal anesthesia for cesarean delivery (CD).

Objectives

This study aimed to examine the pressure pain threshold (PPT) and biomechanical properties (stiffness, elasticity, relaxation time, and creep) of the L4-5 supraspinous ligament at the spinal anesthesia needle insertion site in women who had CD. These measurements were compared with those from the controls who never had pregnancy or anesthesia, and correlations between the variables were explored.

Methods

A retrospective cohort study involved 44 women, divided into two groups. Group A: 22 women experienced spinal anesthesia for CD, and Group B: 22 women represented the controls. L4-5 supraspinous ligament's PPT was measured using pressure algometry, and its biomechanical properties were assessed with the MyotonPRO device.

Results

Significant differences were found in PPT between the two groups (P = 0.0001), but non-significant differences were observed in stiffness, elasticity, relaxation time, or creep (P = 0.318, 0.344, 0.241, and 0.227, respectively). There were also non-significant correlations between PPT and biomechanical properties.

Conclusion

Women who experienced spinal anesthesia for CD showed increased tenderness and lower PPT at the L4-5 site, 6–12 weeks postpartum, with minor changes in supraspinous ligament biomechanics. The relationship between PPT and these properties was negligible.

Correlation between pressure pain threshold and L4-5 supraspinous ligament biomechanics after cesarean delivery under spinal anesthesia

BackgroundLocalized low back pain is a frequent complaint after spinal anesthesia for cesarean delivery (CD).ObjectivesThis study aimed to examine the pressure pain threshold (PPT) and biomechanical properties (stiffness, elasticity, relaxation time, and creep) of the L4-5 supraspinous ligament at the spinal anesthesia needle insertion site in women who had CD. These measurements were compared with those from the controls who never had pregnancy or anesthesia, and correlations between the variables were explored.MethodsA retrospective cohort study involved 44 women, divided into two groups. Group A: 22 women experienced spinal anesthesia for CD, and Group B: 22 women represented the controls. L4-5 supraspinous ligament's PPT was measured using pressure algometry, and its biomechanical properties were assessed with the MyotonPRO device.ResultsSignificant differences were found in PPT between the two groups (P = 0.0001), but non-significant differences were observed in stiffness, elasticity, relaxation time, or creep (P = 0.318, 0.344, 0.241, and 0.227, respectively). There were also non-significant correlations between PPT and biomechanical properties.ConclusionWomen who experienced spinal anesthesia for CD showed increased tenderness and lower PPT at the L4-5 site, 6-12 weeks postpartum, with minor changes in supraspinous ligament biomechanics. The relationship between PPT and these properties was negligible.

A biopsychosocial approach to phenotyping people with knee osteoarthritis awaiting total knee arthroplasty: A secondary cohort analysis

BACKGROUND

Previous research showed chronic post-total knee arthroplasty (TKA) pain in 20% of people with knee osteoarthritis (KOA). Various preoperative biopsychosocial-related factors have been described, but phenotyping people with KOA awaiting TKA based on these factors is still lacking. This could be relevant to understanding differences in TKA surgery responses.

OBJECTIVE

To identify phenotypes in people with KOA awaiting TKA and differences in post-TKA pain based on preoperative biopsychosocial factors.

METHODS

People with KOA awaiting TKA in 4 hospitals in Belgium and the Netherlands were included. A cross-sectional latent profile analysis was conducted on structural, metabolic, functional, pain-related, psychological and social variables. Concurrent validity was tested using 3-step multinomial logistic regression. The difference in one-year post-TKA pain was examined with linear mixed model analysis.

RESULTS

Two hundred and seventeen participants were included in the latent profile analysis with a mean (SD) age of 65.5 (7.7) years, including 109 women. A model with 2 phenotypes differed in 14 out of 21 variables. Participants with phenotype 2 (28%) had a higher body mass index (BMI), higher chance of having less structural damage (KOA grade), lower mean quadriceps strength and physical function (Knee Society Scoring System functional and 30-second chair stand test), higher pain intensity, number of pain locations, and indices of central sensitisation (temporal summation, central sensitisation inventory score, and lower pressure pain thresholds), higher pain catastrophising, anxiety and depression, and higher post-TKA pain intensity compared to phenotype 1 (72%). Concurrent validity was confirmed in 3 out of 4 variables.

CONCLUSIONS

Phenotype 2 (28%) with nociplastic pain characteristics in combination with worse psychological factors, BMI, functional and structural factors, and phenotype 1 (72%) not representing these characteristics were identified. Phenotype 2 had worse pain intensity scores after TKA compared to phenotype 1. Attention to the characteristics of phenotype 2 is warranted concerning post-TKA pain.

DATABASE REGISTRATION

The protocol is registered at ClinicalTrials.gov (NCT05380648).

Effects of Apnea-Induced Hypoxia on Hypoalgesia in Healthy Subjects

INTRODUCTION

Exercise-induced hypoalgesia is a phenomenon in which exercise bouts induce a reduction in pain sensitivity. Apnea training involves similar characteristics that could potentially induce hypoalgesia.

OBJECTIVES

The objectives of this study are to explore the effect of apnea training on hypoalgesia; assess the correlation between conditioned pain modulation (CPM) response and apnea-induced hypoalgesia; and examine the association between hypoalgesia with hypoxemia, and heart rate (HR) during apnea.

METHODS

A randomized controlled trial was conducted comparing a walking protocol employing intermittent apnea compared with normal breathing in healthy volunteers. Hypoalgesia was tested with pressure pain thresholds (PPTs) and CPM. Oxygen saturation (SpO2) and HR were also tested.

RESULTS

Relevant but not significant changes were detected in the thumb (MD = 0.678 kg/cm2), and tibialis (MD = 0.718 kg/cm2) in favor of the apnea group. No significant differences were detected in CPM. The apnea group presented lower SpO2, but HR values similar to those of the control group during the intervention. Basal CPM and intrasession hypoxemia significantly correlated with the PPT response. However, HR did not correlate with the PPT response.

CONCLUSIONS

The current results suggest a trend, though not statistically significant, toward an improvement in the PPT in favor of apnea training compared to normal breathing. Nevertheless, subjects who presented greater basal CPM and lower oxygen saturation during the session presented a greater PPT response, suggesting the possibility of mediators of response. Future investigations should clarify this phenomenon.

Pressure and cold pain threshold reference values in a pain-free older adult population

Background

More sex-specific pain sensitivity normative values from population-based cohorts in pain-free older adults are required. The aims of this study were (1) to provide sex- and age-specific normative values of pressure and cold pain thresholds in older pain-free adults and (2) to examine the association of potential correlates of pain sensitivity with pain threshold values.

Methods

This study investigated sex-specific pressure (lumbar spine, tibialis anterior, neck and dorsal wrist) and cold (dorsal wrist) pain threshold estimates for older pain-free adults aged 41-70 years. This cross-sectional study used participants (n = 212) from the Raine Study Gen1-26 year follow-up. The association of pain thresholds, with correlates including sex, test site, ethnicity, waist-hip ratio, smoking status, health-related quality of life, depression, anxiety and stress symptoms, sleep quality, socioeconomic status and physical activity levels, was examined.

Results

Values for pressure and cold pain thresholds for older pain-free adults are provided, grouped by vicennium, sex and test site (pressure). Statistically significant independent correlates of increased pressure pain sensitivity were test site, ethnicity and sex. Only lower waist/hip ratio was a statistically significant, independent correlate of increased cold pain sensitivity.

Conclusions

This study provides robust sex- and age-specific normative values for pressure pain threshold and cold pain threshold for an older adult pain-free population. Combined with existing values, these data provide an important resource in assisting interpretation of pain sensitivity in clinical pain disorders and provide insights into the complex association of pain sensitivity with correlates that can be used in research.

Long-Term Effects of Individualized Acupuncture for Chronic Neck Pain : A Randomized Controlled Trial

BACKGROUND

Long-term effects of individualized acupuncture in persons with chronic neck pain (CNP) remain unknown.

OBJECTIVE

To evaluate the efficacy and safety of pressure pain, sensory-based individualized acupuncture for relieving CNP.

DESIGN

A 24-week multicenter randomized controlled clinical trial. (ChiCTR1800016371).

SETTING

Outpatient settings at 4 clinical centers in China from May 2018 to March 2020.

PARTICIPANTS

716 participants with CNP.

INTERVENTION

Participants were randomly assigned to a waiting list (WL) group or to 1 of 3 interventions, which consisted of 10 sessions over 4 weeks: higher sensitive acupoints (HSA), lower sensitive acupoints (LSA), and sham acupoints (SA) acupuncture groups.

MEASUREMENTS

The primary outcome was the change in the visual analogue scale (VAS) score for neck pain (range, 0 to 100) from baseline to 4 weeks, with a difference of 10 points considered the minimum clinically important threshold. The VAS was also assessed every 4 weeks through 24 weeks.

RESULTS

The modified intention-to-treat population included 683 participants. The mean baseline VAS was 50.36, 50.10, 49.24, and 49.16 for HSA, LSA, SA, and WL, respectively. Compared with a mean baseline to week 4 change of -12.16 in the HSA group, the mean changes were -10.19 in the LSA group (net difference [ND], -1.97 [95% CI, -5.03 to 1.09]), -6.11 in the SA group (ND, -6.05 [CI, -9.10 to -3.00]), and -2.24 in the WL group (ND, -9.93 [CI, -12.95 to -6.90]). The intervention effects persisted at 24-week follow-up.

LIMITATION

Lack of complete blinding and limited generalizability.

CONCLUSION

Individualized acupuncture interventions using high- or low-sensitivity acupuncture points were more effective in reducing CNP than SA and WL control groups sustained through 24 weeks, but the magnitude of relative improvement did not reach a minimal clinically important difference.

PRIMARY FUNDING SOURCE

National Natural Science Foundation of China.

Application of the IASP Grading System to Identify Underlying Pain Mechanisms in Patients With Knee Osteoarthritis: A Prospective Cohort Study

OBJECTIVES

This study aimed to apply the International Association for the Study of Pain (IASP) grading system for identifying nociplastic pain in knee osteoarthritis (KOA) awaiting total knee arthroplasty (TKA) and propose criteria to fine-tune decision-making. In addition, the study aimed to characterize a "probable" versus "no or possible" nociplastic pain mechanism using biopsychosocial variables and compare both groups in their 1-year post-TKA response.

METHODS

A secondary analysis of baseline data of a longitudinal prospective study involving 197 patients with KOA awaiting total TKA in Belgium and the Netherlands was performed. Two approaches, one considering 4 and the other 3 pain locations (step 2 of the grading system), were presented. Linear mixed model analyses were performed to compare the probable and no or possible nociplastic pain mechanism groups for several preoperative biopsychosocial-related variables and 1-year postoperative pain. Also, a sensitivity analysis, comparing 3 pain mechanism groups, was performed.

RESULTS

Thirty (15.22%-approach 4 pain locations) and 46 (23.35%-approach 3 pain locations) participants were categorized under probable nociplastic pain. Irrespective of the pain location approach or sensitivity analysis, the probable nociplastic pain group included more woman, was younger, exhibited worse results on various preoperative pain-related and psychological variables, and had more pain 1-year post-TKA compared with the other group.

DISCUSSION

This study proposed additional criteria to fine-tune the grading system for nociplastic pain (except for discrete/regional/multifocal/widespread pain) and characterized a subgroup of patients with KOA with probable nociplastic pain. Future research is warranted for further validation.

Does pain intensity after total knee arthroplasty depend on somatosensory functioning in knee osteoarthritis patients? A prospective cohort study

The objective of this study is to determine whether the change in pain intensity over time differs between somatosensory functioning evolution profiles in knee osteoarthritis (KOA) patients undergoing total knee arthroplasty (TKA). This longitudinal prospective cohort study, conducted between March 2018 and July 2023, included KOA patients undergoing TKA in four hospitals in Belgium and the Netherlands. The evolution of the Knee Injury and Osteoarthritis Outcome Score (KOOS) subscale pain over time (baseline, 3 months, and 1 year post-TKA scores) was the outcome variable. The evolution scores of quantitative sensory testing (QST) and Central Sensitization Inventory (CSI) over time (baseline and 1 year post-TKA scores) were used to make subgroups. Participants were divided into separate normal, recovered, and persistent disturbed somatosensory subgroups based on the CSI, local and widespread pressure pain threshold [PPT] and heat allodynia, temporal summation [TS], and conditioned pain modulation [CPM]. Linear mixed model analyses were performed. Two hundred twenty-three participants were included. The persistent disturbed somatosensory functioning group had less pronounced pain improvement (based on CSI and local heat allodynia) and worse pain scores 1 year post-TKA (based on CSI, local PPT and heat allodynia, and TS) compared to the normal somatosensory functioning group. This persistent group also had worse pain scores 1 year post-TKA compared to the recovered group (based on CSI). The study suggests the presence of a "centrally driven central sensitization" subgroup in KOA patients awaiting TKA in four of seven grouping variables, comprising their less pain improvement or worse pain score after TKA. Future research should validate these findings further. The protocol is registered at clinicaltrials.gov (NCT05380648).

Development and validation of machine learning based prediction model for postoperative pain risk after extraction of impacted mandibular third molars

Background

Predicting postoperative pain risk in patients with impacted mandibular third molar extractions is helpful in guiding clinical decision-making, enhancing perioperative pain management, and improving the patients' medical experience. This study aims to develop a prediction model based on machine learning algorithms to identify patients at high risk of postoperative pain after tooth extraction.

Methods

We conducted a prospective cohort study. Outpatients with impacted mandibular third molars were recruited and the outcome was defined as the NRS (Numerical Rating Scale) score of peak postoperative pain within 24 h after the operation ≥7, which is considered a high risk of postoperative pain. We compared the models built using nine different machine learning algorithms and conducted internal and time-series external validations to evaluate the model's predictive performances in terms of the area under the curve (AUC), accuracy, sensitivity, specificity, and F1-value.

Results

A total of 185 patients and 202 cases of impacted mandibular third molar data were included in this study. Five modeling variables were screened out using least absolute selection and shrinkage operator regression, including physician qualification, patient self-reported maximum pain sensitivity, OHI-S-CI, BMI, and systolic blood pressure. The overall performance of the random forest model was evaluated. The AUC, sensitivity, and specificity of the prediction model built using the random forest method were 0.879 (0.861-0.891), 0.857, and 0.846, respectively, for the training set and 0.724 (0.673-0.732), 0.667, and 0.600, respectively, for the time series validation set.

Conclusions

This study developed a machine learning-based postoperative pain risk prediction model for impacted mandibular third molar extraction, which is promising for providing a theoretical basis for better pain management to reduce postoperative pain after third molar extraction.

Evolution of somatosensory processing signs after nociceptive targeted surgery in patients with musculoskeletal disorders: a systematic review

ABSTRACT

Surgery is often advised when conservative treatment fails in musculoskeletal pain conditions, but a substantial proportion still suffers chronic pain after surgery. Somatosensory processing system (SPS) signs were previously studied as potential predictors for chronic postsurgical pain, but results are inconsistent. Therefore, studying the evolution of SPS signs could be of added value. The aim was to summarize all studies that measured how SPS signs evolved after nociceptive targeted surgery in musculoskeletal disorders and to find preoperative, perioperative, and postoperative predictors for the evolution of these SPS signs. Data were summarized, and risk of bias and level of evidence and recommendation were determined. Twenty-one studies were included. Five scored a low, 3 a moderate, and 13 a high risk of bias. In general, no consistent evolution of SPS signs comparing preoperative and postoperative values and predictors for this evolution in musculoskeletal disorders could be found. In most cases, static quantitative sensory testing (QST) did not change or conflicting results were found. On the other hand, dynamic QST mostly improved after surgery. Worthfully mentioning is that worsening of SPS signs was only seen at a follow-up of <3 months after surgery, that conclusions are stronger when evaluating dynamic QST with a follow-up of ≥3 months after surgery, and that pain improvement postsurgery was an important predictor. Future high-quality research should focus on the evolution of SPS signs after nociceptive targeted surgery, accounting for pain improvement groups and focusing on preoperative, perioperative, and postoperative predictors of this evolution.

Age and Gender, but Not Pain are Associated with Pressure Pain Thresholds in Patients with Temporomandibular Disorders: A Cross-Sectional Study

PURPOSE

This study aims to explore the association of pressure pain thresholds (PPTs) with age, gender, and pain in patients with temporomandibular disorders (TMD).

PATIENTS AND METHODS

A total of 301 TMD patients (248 female and 53 male) were recruited and classified into the high and low age groups according to their median age of 26 years. Patients' demographics, pain-related variables, TMD-related variables, and PPTs of both left and right temporomandibular joints (TMJs), masseter, and temporalis were collected.

RESULTS

Pain duration and visual analog scale of pain (VAS) showed no significant correlations with PPTs (P>0.05). Multiple linear regression analysis revealed a significant positive association of PPTs of all six sites with males (β=0.41-0.72 kg·cm-2, 95% CI (0.19-0.38, 0.74-0.99), P<0.001), as well as with the high age group [β=0.28-0.36 kg·cm-2, 95% CI (0.07-0.20, 0.47-0.53), P<0.020]. Furthermore, PPTs of the left TMJ showed a significant negative association with left pain-related TMD (PT) [β=-0.21 kg·cm-2, 95% CI (-0.38, -0.04), P=0.026], but PPTs of the remaining sites did not show a significant association with PT (P>0.05). Stratified analysis showed that PPTs in females were associated with the high age group [β=0.25-0.37 kg·cm-2, 95% CI (0.04-0.20, 0.45-0.56), P<0.020] and that PPT of the left TMJ was associated with left PT [β=-0.21 kg·cm-2, 95% CI (-0.39, -0.03), P=0.043]. The remaining PPTs did not show a significant association with PT (P>0.05). In males, PPTs did not show significant correlations with age, PT and VAS (P>0.05).

CONCLUSION

PPTs in the orofacial region are associated with gender and age in TMD patients. Pain duration and intensity show no significant correlations with PPTs in TMD patients. Researchers and dentists should take age and gender into account when using PPTs as auxiliary diagnostic indicators for PT.

Effectiveness of spontaneous pain coping strategies for acute pain management: A laboratory study

The aim of the present study has been to analyze the relationship between the use of not previously trained, diverse acute pain coping strategies and levels of pain intensity and pain tolerance in a group of healthy participants. Previous research has analyzed the usefulness of the training of these strategies after several training sessions, but adequate patient training requires a great deal of time. Two hundred and forty healthy people participated in the study. Pain coping strategies was evaluated with a version of CSQ-S. Subsequently, the participants completed a cold pressor test and tolerance test. After that, subjects filled in the adaptation of the CSQ-S about the strategies which they had employed throughout the test. Correlation analyses showed a positive relationship between pain intensity and catastrophizing, distractor behaviors, hoping and ignoring the pain. Pain tolerance correlated with self-instructions, ignoring the pain, reinterpreting the pain, catastrophizing and faith and praying. Regression analyses showed that catastrophizing was found to be the strategy that most predicts the variance of pain intensity, and catastrophizing (negative) and ignoring the pain (positive) and praying (negative) were the most predictive ones for pain tolerance. This is the first laboratory study that identifies the more useful pain coping strategies which can be used by patients without previous training in an acute pain context. The results of this study could be useful in the development of protocols for nurses and other health professionals, especially for situations where potentially painful techniques are to be applied to patients.