Neural and psychosocial contributions to sex differences in knee osteoarthritic pain

Correlation Between Pain, Disease Activity, and Rheumatoid Factor Positivity in Patients with Chikungunya Arthritis

Chikungunya fever (CHIKF) is an acute viral disease caused by the chikungunya virus (CHIKV) transmitted by Aedes mosquitoes. The acute phase presents with limited symptoms and low mortality, but approximately half of cases progress to more chronic illness with persistent and disabling joint symptoms. To better characterize the burden of chronic disease, we analyzed the relationship between pain intensity, the Disease Activity Index by DAS28-ESR, rheumatoid factor (RF) positivity, sex, and age in a retrospective cohort of 133 patients with chikungunya arthritis (CHIKA). We assessed all subjects by clinical evaluations, and laboratory testing, including the Pain Visual Analog Scale (VAS), the Disease Activity Score (DAS28-ESR), and RF measurement. We observed that pain intensity increased significantly with disease activity (ρ = 0.416 and p-value < 0.05) and with age (ρ = 0.259 and p-value = 0.003). Despite a predominance of women in our cohort, sex/gender was not associated with increased pain risk. Our study demonstrated a strong correlation between pain and disease activity, but assessment of these variables in a larger, prospective cohort should be undertaken to further characterize risk variables and improve therapy for patients with CHIKA.

Effect of central sensitization inventory on the number of painful sites and pain severity in a Japanese regional population cohort

BACKGROUND

To investigate the association between the central sensitization inventory (CSI), a screening tool for central sensitization, and the number of painful sites and the severity of pain in locomotive organs in an epidemiological study in the elderly.

METHODS

A total of 379 individuals who underwent musculoskeletal disease screening were enrolled in this study. The CSI was used to assess symptoms of central sensitization. The number and location of painful sites and the severity of pain were evaluated using pain mapping and a numerical rating scale (NRS) at 37 sites. We investigated the association between the number of painful sites and CSI score, and the association between the severity of low back pain or knee pain and CSI score.

RESULTS

There was a positive correlation between CSI score and the number of painful sites. The CSI score was significantly higher in those with significant low back pain than in those without pain, and the high-CSI group tended to have a greater number of painful sites. Comparison of CSI scores between participants with low back pain alone and those with low back pain and posterior lower leg pain showed that the latter group had a significantly higher CSI score than the former group. The CSI score in participants with radiographic evidence of knee osteoarthritis was significantly higher in those with knee pain than in those without pain.

CONCLUSIONS

The results of this study suggest that participants with significant low back pain and a higher number of painful sites are more susceptible to the influence of central sensitization. In addition, CSI score was higher in participants with low back pain and posterior lower leg pain than in those with low back pain alone, suggesting that the spread of pain may be due to central sensitization.

Factors Influencing Pain Response Following Patient Education and Supervised Exercise in Male and Female Subjects With Hip Osteoarthritis

OBJECTIVE

To understand factors associated with pain intensity responder status following nonsurgical hip osteoarthritis (OA) intervention, according to sex.

METHODS

Data were from individuals with hip OA participating in the Danish Good Life With Osteoarthritis in Denmark 8-week education and exercise program. The following factors were recorded at program entry: age; education; mental well-being; comorbidities; body mass index; symptoms in hip, knee, and low back; and program-specific factors including education sessions, former participant lectures, and supervised exercise sessions. Pain intensity was recorded at baseline and at month 3 (post-program) on a 0-100-mm visual analog scale. Response was defined as pain intensity improvement of ≥30% from baseline to post-program. Logistic regression was used and conducted separately in male and female subjects.

RESULTS

The sample included 791 men and 2,253 women. Female subjects had a mean baseline pain score of 47.2 of 100 (95% confidence interval [95% CI] 46.4-48.1) and male subjects had a score of 41.7 (95% CI 40.3-43.1). By post-program, the proportion of pain responders was 50.4% among women and 45.8% among men (difference P = 0.025). Among women, program-specific factors (attending former participant lectures and more supervised exercise sessions) were positively associated with pain response, as were better mental well-being and fewer comorbidities, while symptoms in other joints/sites were associated with a decreased likelihood of response. Among men, program-specific factors were not associated with response, while better mental well-being and fewer comorbidities were associated with being a responder.

CONCLUSION

Findings suggest that the influence of some factors on pain response differ for male and female subjects and point to a potential need for targeted approaches for men and women who may require different key messages/approaches from health care providers.

Gender and Sex Are Key Determinants in Osteoarthritis Not Only Confounding Variables. A Systematic Review of Clinical Data

Many risk factors for osteoarthritis (OA) have been noted, while gender/sex differences have been understated. The work aimed to systematically review literature investigating as primary aim the relationship between gender/sex related discriminants and OA. The search was performed in PubMed, Science Direct and Web of Knowledge in the last 10 years. Inclusion criteria were limited to clinical studies of patients affected by OA in any joints, analyzing as primary aim gender/sex differences. Exclusion criteria were review articles, in vitro, in vivo and ex vivo studies, case series studies and papers in which gender/sex differences were adjusted as confounding variable. Of the 120 records screened, 42 studies were included. Different clinical outcomes were analyzed: morphometric differences, followed by kinematics, pain, functional outcomes after arthroplasty and health care needs of patients. Women appear to use more health care, have higher OA prevalence, clinical pain and inflammation, decreased cartilage volume, physical difficulty, and smaller joint parameters and dimensions, as compared to men. No in-depth studies or mechanistic studies analyzing biomarker differential expressions, molecular pathways and omic profiles were found that might drive preclinical and clinical research towards sex-/gender-oriented protocols.

Sex- and Gender-Related Differences in Common Functional Gastroenterologic Disorders

Functional gastrointestinal (GI) disorders (FGIDs) result from central and peripheral mechanisms, cause chronic remitting-relapsing symptoms, and are associated with comorbid conditions and impaired quality of life. This article reviews sex- and gender-based differences in the prevalence, pathophysiologic factors, clinical characteristics, and management of functional dyspepsia (FD) and irritable bowel syndrome (IBS) that together affect approximately 1 in 4 people in the United States. These conditions are more common in women. Among patients with IBS, women are more likely to have severe symptoms and coexistent anxiety or depression; constipation or bloating and diarrhea are more common in women and men, respectively, perhaps partly because defecatory disorders, which cause constipation, are more common in women. Current concepts suggest that biological disturbances (eg, persistent mucosal inflammation after acute gastroenteritis) interact with other environmental factors (eg, abuse) and psychological stressors, which influence the brain and gut to alter GI tract motility or sensation, thereby causing symptoms. By comparison to a considerable understanding of sex-based differences in the pathogenesis of visceral hypersensitivity in animal models, we know less about the contribution of these differences to FGID in humans. Slow gastric emptying and colon transit are more common in healthy women than in men, but effects of gonadal hormones on colon transit are less important than in rodents. Although increased visceral sensation partly explains symptoms, the effects of sex on visceral sensation, colonic permeability, and the gut microbiome are less prominent in humans than rodents. Whether sex or gender affects response to medications or behavioral therapy in FD or IBS is unclear because most patients in these studies are women.

Female Team Physician Representation in Professional and Collegiate Athletics

BACKGROUND

Although a sex-based balance in US graduate medical education has been well-documented, a discrepancy remains in orthopaedic surgery. In orthopaedic sports medicine, the representation of women as team physicians has not previously been characterized.

PURPOSE

To quantify the sex-related composition of team physicians of select National Collegiate Athletic Association (NCAA) Division I collegiate and professional teams. Additionally, the authors assess the sex-related composition of orthopaedic surgeon team physicians specifically and compare these proportions to the sex-related composition of orthopaedic surgeon membership of the American Orthopaedic Society for Sports Medicine (AOSSM).

STUDY DESIGN

Cross-sectional study.

METHODS

Publicly available sex-related data were collected for team physicians in select NCAA Division I collegiate conferences and professional sports organizations. Subspecialty characteristics and sex distribution were described by use of percentages. Chi-square tests were used to assess whether sex distributions of team physicians in collegiate and professional sports were (1) representative between the populations of female and male physicians compared with the general public and (2) representative of the sex-based composition of orthopaedic surgeons nationally.

RESULTS

Women represented 12.7% (112/879) of all team physicians and 6.8% (30/443) of all orthopaedic surgeons (P < .0001). More than half (53.9%; 413/767) of male and 26.8% (30/112) of female team physicians were orthopaedic surgeons. In collegiate athletics, women comprised 18.1% of all team physicians and 7.7% of orthopaedic surgeon team physicians. In professional sports, women comprised 6.7% of all team physicians and 6.3% of orthopaedic surgeon team physicians, with the greatest proportion in the Women's National Basketball Association (31.3%).

CONCLUSION

Women comprise a minority of team physicians in select NCAA Division I collegiate and professional sports organizations. When compared with the composition of AOSSM orthopaedic surgeon membership, expected female orthopaedic surgeon representation varies between conferences and leagues with little statistical significance. Although efforts have been made to increase sex-based diversity in orthopaedic surgery, results of this study suggest that barriers affecting female orthopaedic surgeons as team physicians should be identified and addressed.

Clinical outcome, functional outcome and patient satisfaction after cruciate retaining total knee arthroplasty for stiff arthritic knee - A short term outcome study

Background

Various authors have shown that Cruciate Retaining (CR) Total Knee Arthroplasty (TKA) has better long-term survivorship compared to Posterior Stabilized (PS), however most arthroplasty surgeons tend to use PS knees in patients with severe deformity and stiffness. There is limited data correlating stiffness and CR versus PS design. The aim of our study was to assess the outcome of CR TKA for patients with stiff arthritic knee.

Materials & methods

We evaluated the results of 30 knees with osteoarthritis and inflammatory arthritis and preoperative stiffness (ROM 15-90°), who had been treated with CR TKA with a mean follow up of 2 years. The primary outcome variable measures were improvement in the flexion, flexion deformity (FFD) and overall improvement in the arc of motion. Patients were also evaluated by Knee Society Score (KSS), WOMAC score and 5-point Likert scale for patient satisfaction.

Result

At the time of final follow-up, the mean arc of motion improved from 75° preoperatively to 108° postoperatively and it was statistically significant (p < 0.001). Similar improvement was noted for FFD (15.43° to 0.83° (p < 0.001)), maximum flexion from 90.9° to 109.1° (p < 0.001), KSS clinical from 37.67 to 87.47 (p < 0.001), KSS functional from 58.5 to 93.83 (p < 0.001), WOMAC from 76.73 to 7.63 (p < 0.001). Further, the Likert Scale for patient satisfaction was excellent for 90% of the patients.

Conclusion

This study clearly shows that the routine use of PS design for complex stiff knees has questionable scientific intent and standard CR TKA design in stiff knees can produce excellent outcome. Since there is slight preponderance of data pointing towards improved longevity with CR design, it would be a better option for the patients with longer life expectancy.

Sex differences in pain and opioid mediated antinociception: Modulatory role of gonadal hormones

Sex-related differences in pain and opioids has been the focus of many researches. It is demonstrated that women experience greater clinical pain, lower pain threshold and tolerance, more sensitivity and distress to experimentally induced pain compared to men. Sex differences in response to opioid treatment revealed inconsistent results. However, the etiology of these disparities is not fully elucidated. It is, therefore, conceivable now that this literature merits to be revisited comprehensively. Possible multifaceted factors seem to be associated. These include neuroanatomical, hormonal, neuroimmunological, psychological, social and cultural aspects and comorbidities. This review aims at providing an overview of the substantial literature documenting the sex differences in pain and analgesic response to opioids from animal and human studies within the context of the modulatory effects of the aforementioned factors. A detailed and critical discussion of the cellular and molecular signaling pathways underlying the modulatory actions of gonadal hormones in the sexual dimorphism in pain processing and opioid analgesia is extensively presented. It is indicated that sexual dimorphic activation of certain brain regions contributes to differential pain sensitivity between females and males. Plausible crosstalk between sex hormones and neuroimmunological signaling pertinent to toll-like and purinergic receptors is uncovered as causal cues underlying sexually dimorphic pain and opioid analgesia. Conceivably, a thorough understanding of these factors may aid in sex-related advancement in pain therapeutic management.

Sex differences in negative affect and postoperative pain in patients undergoing total knee arthroplasty

Background

Knee osteoarthritis (OA) is among the most common and disabling persistent pain conditions, with increasing prevalence in the developed world, and affects women to a greater degree than men. In the USA, the growth of knee OA has been paralleled by an increase in rates of total knee arthroplasty (TKA), a surgical treatment option for late-stage knee OA. While TKA outcomes are generally good, postoperative trajectories of pain vary widely, with some patients reporting a complete absence of pain, but with a significant minority reporting worsening pain. Biopsychosocial factors, including anxiety and depression, are known to contribute importantly to the experience of joint pain, with women reporting a higher degree of negative affective symptoms.

Methods

This study investigated sex differences in TKA outcomes in age-matched groups of men and women at two academic medical centers. Pain and physical function were assessed in 100 patients (50 men and 50 women) during the perioperative period (preoperative visit—6 weeks postsurgical). The association of preoperative negative affect (anxiety and depression scores) to postoperative pain and function was evaluated, with specific attention to sex differences in this relationship.

Results

Overall, women reported more baseline pain-related physical dysfunction (although not higher baseline pain scores), as well as higher acute postoperative pain scores during the 2 weeks following TKA than their male counterparts. By 6 weeks postoperatively, sex differences in reported pain were no longer evident. Interestingly, although women reported higher preoperative levels of emotional distress than men, preoperative anxiety and depression scores were better predictors of severe postoperative pain among men than women, throughout the postoperative test period.

Conclusions

This study underlines the importance of considering sex and psychosocial factors, as well as their interaction, in understanding postsurgical pain trajectories.

Basics on the use of acid-sensing ion channels' inhibitors as therapeutics

Since the discovery of acid-sensing ion channels in 1997, their importance in the health of neurons and other non-neuronal cells has gained significant importance. Acid-sensing ion channels play important roles in mediating pain sensation during diseases such as stroke, inflammation, arthritis, cancer, and recently migraine. More interestingly, acid-sensing ion channels may explain the sex differences in pain between males and females. Also, the ability of acid-sensing ion channel blockers to exert neuroprotective effects in a number of neurodegenerative diseases has added a new dimension to their therapeutic value. The current failure rate of ~45% of new drugs (due to toxicity issues) and saving of up to 7 years in the life span of drug approval makes drug repurposing a high priority. If acid-sensing ion channels’ blockers undergo what is known as “drug repurposing”, there is a great potential to bring them as medications with known safety profiles to new patient populations. However, the route of administration remains a big challenge due to their poor penetration of the blood brain and retinal barriers. In this review, the promise of using acid-sensing ion channel blockers as neuroprotective drugs is discussed.

Neuropathic pain in end-stage hip and knee osteoarthritis: differential associations with patient-reported pain at rest and pain on activity

OBJECTIVE

We investigated whether pain at rest and pain on activity were differentially associated with neuropathic pain scores in individuals with end-stage hip and knee OA.

DESIGN

Study participants were 843 patients with hip or knee OA scheduled for total joint arthroplasty. In pre-surgery questionnaires, measures of socio-demographics, health status, medication use, neuropathic pain (painDETECT), pain at rest and pain on activity (WOMAC pain items), depression (HADS) and pain catastrophizing (PCS) were collected. Multivariable linear regression models were estimated for men and women separately to examine the association between neuropathic pain scores (outcome) and study measures, entered in blocks.

RESULTS

Sample mean age was 65.1 years (SD: 9.6); 57.1% were women. Mean painDETECT scores were significantly higher (P ≤ֹ 0.001) for women (11.2 ± 6.6 out of 38) than men (9.3 ± 7.0), with 35.6% of women and 27.7% of men meeting cut-offs for possible or likely neuropathic pain. In the final regression model for women, the coefficients for both types of pain were statistically significant, although the coefficient for pain at rest was 1.6 times greater than that for pain on activity. For men, only pain at rest was significantly associated with neuropathic pain scores.

CONCLUSIONS

Findings support that possible neuropathic pain is experienced by a notable proportion of patients with end-stage hip and knee OA and is more strongly associated with pain at rest than pain on activity, particularly in men. Clinical presentation of pain at rest may warrant more thorough evaluation for potential neuropathic pain and have implications for appropriate pain management.

Regular physical activity prevents development of chronic muscle pain through modulation of supraspinal opioid and serotonergic mechanisms

The current study shows that blockade of opioid receptors systemically in the periaqueductal gray and the rostral ventromedial medulla prevents analgesia by 8 weeks of wheel running in a chronic muscle pain model. We further show increases in serotonin transporter expression and reversal of hyperalgesia with a selective reuptake inhibitor in the rostral ventromedial medulla in the chronic muscle pain model, and exercise normalizes serotonin transporter expression.

Introduction:

It is generally believed that exercise produces its effects by activating central opioid receptors; there are little data that support this claim. The periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) are key nuclei in opioid-induced analgesia, and opioids interact with serotonin to produce analgesia.

Objectives:

The purpose was to examine central inhibitory mechanisms involved in analgesia produced by wheel running.

Methods:

C57/Black6 mice were given access to running wheels in their home cages before induction of chronic muscle hyperalgesia and compared with those without running wheels. Systemic, intra-PAG, and intra-RVM naloxone tested the role of central opioid receptors in the antinociceptive effects of wheel running in animals with muscle insult. Immunohistochemistry for the serotonin transporter (SERT) in the spinal cord and RVM, and pharmacological blockade of SERT, tested whether the serotonin system was modulated by muscle insult and wheel running.

Results:

Wheel running prevented the development of muscle hyperalgesia. Systemic naloxone, intra-PAG naloxone, and intra-RVM naloxone reversed the antinociceptive effect of wheel running in animals that had received muscle insult. Induction of chronic muscle hyperalgesia increased SERT in the RVM, and blockade of SERT reversed the hyperalgesia in sedentary animals. Wheel running reduced SERT expression in animals with muscle insult. The serotonin transporter in the superficial dorsal horn of the spinal cord was unchanged after muscle insult, but increased after wheel running.

Conclusion:

These data support the hypothesis that wheel running produced analgesia through central inhibitory mechanisms involving opioidergic and serotonergic systems.

Enhanced Pain Sensitivity Among Individuals With Symptomatic Knee Osteoarthritis: Potential Sex Differences in Central Sensitization

OBJECTIVE

Symptomatic knee osteoarthritis (OA) is a condition commonly associated with increased pain, disability, and functional limitations. Given the poor correspondence between radiographic evidence and clinical pain, central sensitization has been implicated as a potential mechanism underlying pain facilitation in knee OA. Sex may be a moderator of centrally mediated changes in knee OA pain; however, few studies have systematically assessed this. Therefore, the aim of this study was to examine differences in peripheral and central sensitization in men and women with symptomatic knee OA, as well as to determine whether these differences vary across age (middle age versus older age).

METHODS

Participants (n = 288) between the ages of 45 and 85 years completed a battery of quantitative sensory pain procedures assessing sensitivity to contact heat, cold pressor, mechanical pressure, and punctate stimuli. Differences in temporal summation (TS) were examined, as well as measures of clinical pain and functional performance.

RESULTS

When compared to men, women exhibited greater sensitivity to multiple pain modalities (i.e., lower heat, cold, pressure thresholds/tolerances, greater TS of pain); however, there were no sex differences in clinical pain, with the exception of greater widespread pain observed in women. Although there were select age-related differences in pain sensitivity, sex differences in pain varied minimally across the age cohort.

CONCLUSION

Overall, these findings provide evidence for greater overall sensitivity to experimental pain in women with symptomatic knee OA compared to men, suggesting that enhanced central sensitivity may be an important contributor to pain in this group.

Expanded Distribution of Pain as a Sign of Central Sensitization in Individuals With Symptomatic Knee Osteoarthritis

BACKGROUND

Expanded distribution of pain is considered a sign of central sensitization (CS). The relationship between recording of symptoms and CS in people with knee osteoarthritis (OA) has been poorly investigated.

OBJECTIVE

The aim of this study was to examine whether the area of pain assessed using pain drawings relates to CS and clinical symptoms in people with knee OA.

DESIGN

This was a cross-sectional study.

METHODS

Fifty-three people with knee OA scheduled to undergo primary total knee arthroplasty were studied. All participants completed pain drawings using a novel digital device, completed self-administration questionnaires, and were assessed by quantitative sensory testing. Pain frequency maps were generated separately for women and men. Spearman correlation coefficients were computed to reveal possible correlations between the area of pain and quantitative sensory testing and clinical symptoms.

RESULTS

Pain frequency maps revealed enlarged areas of pain, especially in women. Enlarged areas of pain were associated with higher knee pain severity (rs=.325, P<.05) and stiffness (rs=.341, P<.05), lower pressure pain thresholds at the knee (rs=-.306, P<.05) and epicondyle (rs=-.308, P<.05), and higher scores with the Central Sensitization Inventory (rs=.456, P<.01). No significant associations were observed between the area of pain and the remaining clinical symptoms and measures of CS.

LIMITATIONS

Firm conclusions about the predictive role of pain drawings cannot be drawn. Further evaluation of the reliability and validity of pain area extracted from pain drawings in people with knee OA is needed.

CONCLUSION

Expanded distribution of pain was correlated with some measures of CS in individuals with knee OA. Pain drawings may constitute an easy way for the early identification of CS in people with knee OA, but further research is needed.

Sex differences in symptom severity and clusters in patients with stage C4 and stage C5 chronic venous disease

BACKGROUND

Multiple symptoms associated with chronic venous disease (CVD) are poorly understood, under-recognized, and ill-managed.

AIMS

The aim of this study was to determine whether there are differences in symptoms and symptom clusters between men and women with stage C4 and stage C5 CVD.

METHODS

Data were collected via interviews with 264 patients using a demographic survey and an 11-item VEINES-SYM questionnaire.

ANALYSIS

An intrinsic scoring algorithm was developed to calculate the overall t scores for each item by sex. Exploratory factor analysis identified symptom clusters using oblique rotation to account for correlations between factors.

RESULTS

The average age was 61.7 years; 54.5% of the patients were women, 58% were African American or black, and 60.6% had diabetes. The top three symptoms for women in order of frequency were achy legs, swelling, and pain; for men, these were swelling, achy legs, and heavy legs. For the total group, two symptom clusters emerged: distressful and discomfort. There was no statistically significant difference in factor score between the sexes. Different factor loadings for symptom clusters were observed: women reported hurting and annoying clusters; and men reported nagging and irritating clusters.

CONCLUSION

The data suggest differences in CVD symptoms and clusters by sex. Symptoms in the two clusters were different; however, there was consistency in the factors associated with each cluster. Co-morbid conditions and sex differences in pain responses may play a part in symptom presentation. This study supports the need for increased sex-delineated clinical assessment and consideration of the potential differences between the sexes in the management of CVD symptoms.

Prospective clinical observational study evaluating gender-associated differences of preoperative pain intensity

Previous studies reported conflicting results concerning different pain perceptions of men and women. Recent research found higher pain levels in men after major surgery, contrasted by women after minor procedures. This trial investigates differences in self-reported preoperative pain intensity between genders before surgery.Patients were enrolled in 2011 and 2012 presenting for preoperative evaluation at the anesthesiological assessment clinic at Charité University hospital. Out of 5102 patients completing a computer-assisted self-assessment, 3042 surgical patients with any preoperative pain were included into this prospective observational clinical study. Preoperative pain intensity (0-100 VAS, visual analog scale) was evaluated integrating psychological cofactors into analysis.Women reported higher preoperative pain intensity than men with median VAS scores of 30 (25th-75th percentiles: 10-52) versus 21 (10-46) (P < 0.001). Adjusted multiple regression analysis showed that female gender remained statistically significantly associated with higher pain intensity (P < 0.001). Gender differences were consistent across several subgroups especially with varying patterns in elderly. Women scheduled for minor and moderate surgical procedures showed largest differences in overall pain compared to men.This large clinical study observed significantly higher preoperative pain intensity in female surgical patients. This gender difference was larger in the elderly potentially contradicting the current hypothesis of a primary sex-hormone derived effect. The observed variability in specific patient subgroups may help to explain heterogeneous findings of previous studies.

Characterization of osteoarthritic human knees indicates potential sex differences

BACKGROUND

The prevalence of osteoarthritis is higher in women than in men in every age group, and overall prevalence increases with advancing age. Sex-specific differences in the properties of osteoarthritic joint tissues may permit the development of sex-specific therapies. Sex hormones regulate cartilage and bone development and homeostasis in a sex-dependent manner. Recent in vitro studies show that the vitamin D3 metabolite 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] also has sex-specific effects on musculoskeletal cells, suggesting that vitamin D3 metabolites may play a role in osteoarthritis-related sex-specific differences. The purpose of this study was to determine if sex-specific differences exist in synovial fluid and knee tissues isolated from male and female patients with severe knee osteoarthritis. We determined the presence of vitamin D3 metabolites, inflammatory cytokines, growth factors, and matrix metalloproteinases (MMPs) in synovial fluid and assessed responses of articular chondrocytes and subchondral osteoblasts to 17β-estradiol, dihydrotestosterone, and 1α,25(OH)2D3.

METHODS

Samples from knee joints of 10 Caucasian male and 10 Caucasian female patients with advanced osteoarthritis aged 65 to 75 years were obtained from total knee arthroplasty. Vitamin D metabolites, cytokines, MMPs, and growth factors in the synovial fluid were measured. Primary cultures of chondrocytes were isolated from fibrillated articular cartilage adjacent to osteoarthritis lesions and minimally affected cartilage distal to the lesion. Osteoblasts were isolated from the subchondral bone. Expression of receptors for 17β-estradiol and 1α,25(OH)2D3 was assessed by real-time PCR. Chondrocytes and osteoblasts were treated with 10(-8) M 17β-estradiol, dihydrotestosterone, or 1α,25(OH)2D3 and effects on gene expression and protein synthesis determined.

RESULTS

Histology of the articular cartilage confirmed advanced osteoarthritis. Sex differences were found in synovial fluid levels of vitamin D metabolites, cytokines, and metalloproteinases as well as in the cellular expression of receptors for 17β-estradiol and 1α,25(OH)2D3. Male cells were more responsive to 1α,25(OH)2D3 and dihydrotestosterone, whereas 17β-estradiol-affected female cells.

CONCLUSIONS

These results demonstrate that there are underlying sex differences in knee tissues affected by osteoarthritis. Our findings do not address osteoarthritis etiology but have implications for different prevention methods and treatments for men and women. Further research is needed to better understand these sex-based differences.

Support for the Microgenderome: Associations in a Human Clinical Population

The 'microgenderome' provides a paradigm shift that highlights the role of sex differences in the host-microbiota interaction relevant for autoimmune and neuro-immune conditions. Analysis of cross-sectional self-report and faecal microbial data from 274 patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) suggests that commensal gut microorganisms may play both protective and deleterious roles in symptom expression. Results revealed significant sex-specific interactions between Firmicutes (Clostridium, Streptococcus, Lactobacillus and Enterococcus) and ME/CFS symptoms (including neurological, immune and mood symptoms), regardless of compositional similarity in microbial levels across the sexes. Extending animal studies, we provide support for the microgenderome in a human clinical population. Applied and mechanistic research needs to consider sex-interactions when examining the composition and function of human microbiota.

Mechanical hyperalgesia and reduced quality of life occur in people with mild knee osteoarthritis pain

OBJECTIVES

This study determined whether individuals with mild knee pain due to osteoarthritis (OA) experience hyperalgesia and central sensitivity by comparing them with age-matched and sex-matched control participants and determined whether these levels are associated with pain intensity. This study also determined whether these individuals experience significantly poorer quality of life than age-matched and sex-matched controls and whether pain and function predict quality of life.

METHODS

Quantitative sensory tests (QSTs), including punctate pain intensity (PPI), pressure pain threshold (PPT), and heat pain threshold, tolerance, and temporal summation, were measured in 75 individuals with mild knee OA pain and 25 age-matched and sex-matched controls. Pain intensity, walking function, and quality of life were also assessed.

RESULTS

Significant differences were found for PPI at all sites, for PPT at the affected knee, and for quality of life. QST measures significantly correlated with pain intensity. Pain, but not function, predicted quality of life.

DISCUSSION

Individuals with mild knee pain due to OA experience mechanical (but not thermal) hyperalgesia that relates to pain intensity. They have a reduced quality of life that is predicted by pain intensity. More aggressive pain management for mild knee OA pain is indicated to improve the quality of life for individuals who are not yet candidates for joint replacement.

Inflammation-induced pain sensitization in men and women: does sex matter in experimental endotoxemia?

A role of the innate immune system is increasingly recognized as a mechanism contributing to pain sensitization. Experimental administration of the bacterial endotoxin lipopolysaccharide (LPS) constitutes a model to study inflammation-induced pain sensitization, but all existing human evidence comes from male participants. We assessed visceral and musculoskeletal pain sensitivity after low-dose LPS administration in healthy men and women to test the hypothesis that women show greater LPS-induced hyperalgesia compared with men. In this randomized, double-blind, placebo-controlled crossover study, healthy men (n = 20) and healthy women using oral contraceptives (n = 20) received an intravenous injection of 0.4 ng/kg body weight LPS or placebo. Pain sensitivity was assessed with established visceral and musculoskeletal pain models (ie, rectal pain thresholds; pressure pain thresholds for different muscle groups), together with a heartbeat perception (interoceptive accuracy) task. Plasma cytokines (tumor necrosis factor-α and interleukin-6) were measured along with state anxiety at baseline and up to 6-hour postinjection. Lipopolysaccharide application led to significant increases in plasma cytokines and state anxiety and decreased interoceptive awareness in men and women (P < 0.001, condition effects), with more pronounced LPS-induced cytokine increases in women (P < 0.05, interaction effects). Although both rectal and pressure pain thresholds were significantly decreased in the LPS condition (all P < 0.05, condition effect), no sex differences in endotoxin-induced sensitization were observed. In summary, LPS-induced systemic immune activation leads to visceral and musculoskeletal hyperalgesia, irrespective of biological sex. These findings support the broad applicability of experimental endotoxin administration as a translational preclinical model of inflammation-induced pain sensitization in both sexes.

The dichotomized role for acid sensing ion channels in musculoskeletal pain and inflammation

Chronic muscle pain affects between 11 and 24% of the world's population with the majority of people experiencing musculoskeletal pain at some time in their life. Acid sensing ion channels (ASICs) are important sensors of modest decreases in extracellular pH that occur within the physiological range. These decreases in extracellular pH occur in response to inflammation, fatiguing exercise, and ischemia. Further, injection of acidic saline into muscle produces enhanced nociceptive behaviors in animals and pain in human subjects. Of the different types of ASICs, ASIC3 and ASIC1 have been implicated in transmission of nociceptive information from the musculoskeletal system. The current review will provide an overview of the evidence for ASIC3 and ASIC1 in musculoskeletal pain in both inflammatory and non-inflammatory models. This article is part of the Special Issue entitled 'Acid-Sensing Ion Channels in the Nervous System'.

Future directions in painful knee osteoarthritis: harnessing complexity in a heterogeneous population

This perspective article proposes a conceptual model for the pain experience for individuals diagnosed with knee osteoarthritis (OA). Pain in knee OA is likely a heterogeneous, multifactorial phenomenon that involves not only the OA disease process but also elements specific to patient psychology and pain neurophysiology. The relevant contributions to the pain experience for any individual patient remain difficult, if not impossible, to definitively determine, and the rationale for many clinical treatment decisions arises primarily from a mechanistic understanding of OA pathophysiology. The Osteoarthritis Research Society International (OARSI) recently identified "phenotyping" of OA pain as a research priority to "better target pain therapies to individual patients." This perspective article proposes that contributions from 3 domains--knee pathology, psychological distress, and pain neurophysiology--should be considered equally important in future efforts to understand pain phenotypes in knee OA. Ultimately, characterization of pain phenotypes may aid in the understanding of the pain experience and the development of interventions specific to pain for individual patients.

Clinical characteristics of pain originating from intra-articular structures of the knee joint in patients with medial knee osteoarthritis

Purpose

Although disease progression of osteoarthritis has been well documented, pain pathophysiology is largely unknown. This study was designed with two purposes: 1) to characterize patients with knee pain predominantly originating from intra-articular structures and 2) to describe the location and pattern of their pain.

Materials and methods

103 patients with medial knee osteoarthritis underwent an intra-articular injection of local anesthetics (joint block). At least 70% pain relief was defined as positive for the joint block, while less than 50% as negative. Pain characteristics in patients positive for joint block were evaluated in detail using a knee pain map.

Results

Sixty three knees (61%) were positive and 33 knees (32%) were negative. Patients negative for the joint block were significantly higher age, suffered for longer time, and complained more diffuse pain. Although pain at anterior medial area during walk was the most common finding, pain characteristics differed among different knee areas.

Conclusion

The characteristics of joint pain are widely variable even in patients with similar radiological features. Extra-articular sources are not negligible especially in older patients with a long history of diffuse pain. Differences in pain characteristics among knee areas should be taken into account when examining the pain source.

Addressing the gaps: sex differences in osteoarthritis of the knee

An introduction to the accompanying three papers.