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

The efficacy and safety of a fixed-dose combination of apocynin and paeonol, APPA, in symptomatic knee OA: A double-blind, randomized, placebo-controlled, clinical trial

OBJECTIVE

Apocynin (AP) and paeonol (PA) are low molecular weight phenolic compounds with a broad array of anti-inflammatory and immunoregulatory effects. This study assessed of a fixed-dose combination of APPA in people with symptomatic knee osteoarthritis (OA).

METHODS

A multi-center, randomized, placebo-controlled, double-blind phase 2a trial enrolled participants with radiographic knee OA (Kellgren-Lawrence, KL, grades 2-3) and pain ≥40/100 on WOMAC pain subscale, and evaluated the efficacy and safety of oral APPA over a 28-day period. APPA 800 mg or matching placebo was administered twice daily in a 1:1 ratio. Post-hoc analyses explored the response to APPA in sub-groups with more severe pain and structural severity.

RESULTS

The two groups were comparable at baseline; 152 subjects were enrolled and 148 completed the trial. There was no statistically significant difference between groups with respect to the primary outcome, WOMAC pain (mean difference between groups was -0.89, 95% CI: -5.62, 3.84, p = 0.71), nor WOMAC function or WOMAC total. However, predefined subgroup analyses of subjects with symptoms compatible with nociplastic/neuropathic pain features showed a statistically significant effect of APPA compared to placebo. Adverse events (mainly gastrointestinal) were mild to moderate.

CONCLUSION

Treatment with APPA 800 mg twice daily for 28 days in subjects with symptomatic knee OA was not associated with significant symptom improvement compared to placebo. The treatment was well-tolerated and safe. While the study was not powered for such analysis, pre-planned subgroup analyses showed a significant effect of APPA in subjects with nociplastic pain/severe OA, indicating that further research in the effects of APPA in appropriate patients is warranted.

The impact of diabetes status on pain and physical function following total joint arthroplasty for hip and knee osteoarthritis: variation by sex and body mass index

Few studies have examined diabetes impact on total joint arthroplasty (TJA) outcomes, with variable findings. We investigated the association between diabetes and post-TJA physical function and pain, examining whether diabetes impact differs by sex and BMI. Patient sample completed questionnaires within 3 months prior to hip or knee TJA for osteoarthritis (OA) and 1-year post-surgery. Surgical 'non-response' was defined as < 30% improvement in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physical function at 1-year. Two adjusted logistic regression models were estimated: (1) excluding, (2) including an interaction between diabetes, sex and BMI. The sample (626 hip, 754 knee) was 54.9% female, had mean BMI of 30.1, 13.0% reported diabetes. In adjusted models excluding an interaction, diabetes was not associated with non-response. However, a significant 3-way interaction (physical function: p = 0.003; pain: p = 0.006) between diabetes, sex, and BMI was found and was associated with non-response: non-response probability increased with increasing BMI in men with diabetes, but decreased with increasing BMI in women in diabetes. Findings suggest uncertainty in diabetes impact may be due to differential impacts by sex and BMI. A simple consideration of diabetes as present vs. absent may not be sufficient, with implications for the large TJA population.

EEG-Based Cortical Alterations in Individuals With Chronic Knee Pain Secondary to Osteoarthritis: A Cross-sectional Investigation

Chronic painful knee osteoarthritis (OA) is a disabling physical health condition. Alterations in brain responses to arthritic changes in the knee may explain persistent pain. This study investigated source localized, resting-state electroencephalography activity and functional connectivity in people with knee OA, compared to healthy controls. Adults aged 44 to 85 years with knee OA (n = 37) and healthy control (n = 39) were recruited. Resting-state electroencephalography was collected for 10 minutes and decomposed into infraslow frequency (ISF) to gamma frequency bands. Standard low-resolution electromagnetic brain tomography statistical nonparametric maps were conducted, current densities of regions of interest were compared between groups and correlation analyses were performed between electroencephalography (EEG) measures and clinical pain and functional outcomes in the knee OA group. Standard low-resolution electromagnetic brain tomography nonparametric maps revealed higher (P = .006) gamma band activity over the right insula (RIns) in the knee OA group. A significant (P < .0001) reduction in ISF band activity at the pregenual anterior cingulate cortex, whereas higher theta, alpha, beta, and gamma band activity at the dorsal anterior cingulate cortex, pregenual anterior cingulate cortex, the somatosensory cortex, and RIns in the knee OA group were identified. ISF activity of the dorsal anterior cingulate cortex was positively correlated with pain measures and psychological distress scores. Theta and alpha activity of RIns were negatively correlated with pain interference. In conclusion, aberrations in infraslow and faster frequency EEG oscillations at sensory discriminative, motivational-affective, and descending inhibitory cortical regions were demonstrated in people with chronic painful knee OA. Moreover, EEG oscillations were correlated with pain and functional outcome measures. PERSPECTIVE: This study confirms alterations in the rsEEG oscillations and its relationship with pain experience in people with knee OA. The study provides potential cortical targets and the EEG frequency bands for neuromodulatory interventions for managing chronic pain experience in knee OA.

Total Hip Arthroplasty Versus Education and Exercise: A Propensity-Matched Analysis of 266 Patients Who Have Hip Osteoarthritis

BACKGROUND

Total hip arthroplasty (THA) for osteoarthritis (OA) is a major health system cost. Education and exercise (Edu + Ex) programs may reduce the number of THAs needed, but supporting data are limited. This study aimed to estimate the treatment effect of THA versus Edu + Ex on pain, function, and quality of life outcomes 3 and 12 months after treatment initiation for hip OA.

METHODS

Patients who had hip OA who underwent THA or an Edu + Ex program were included in this propensity-matched study. In 778 patients (Edu + Ex, n = 303; THA, n = 475), propensity scores were based on pretreatment characteristics, and patients were matched on a 1:1 ratio. Between-group treatment effects (pain, function, and quality of life) were estimated as the mean difference (MD) in change from pretreatment to 3-month and 12-month follow-up using linear mixed models.

RESULTS

The matched sample consisted of 266 patients (Edu + Ex, n = 133; THA, n = 133) who were balanced on all pretreatment characteristics except opioid use. At 12-month follow-up, THA resulted in significantly greater improvements in pain (MD 35.4; 95% confidence interval [CI] 31.4 to 39.4), function (MD 30.5; 95% CI 26.3 to 34.7), and quality of life (MD 33.6; 95% CI 28.8 to 38.4). Between 17% and 30% of patients receiving Edu + Ex experienced a surgical threshold for clinically meaningful improvement in outcomes, compared to 84% and 90% of THA patients.

CONCLUSIONS

A THA provides greater improvements in pain, function, and quality of life. A notable proportion of Edu + Ex patients had clinically meaningful improvements, suggesting Edu + Ex may result in THA deferral in some patients, but confirmatory trials are needed.

Neuropathic pain in patients with osteoarthritis of the hip before and after total hip arthroplasty

OBJECTIVES

The pain associated with osteoarthritis (OA) was thought to be nociceptive; however, neuropathic pain is also observed. We investigated the relationship between hip OA and neuropathic pain using the PainDETECT questionnaire (PDQ).

METHODS

A total of 159 hips of 146 consecutive patients who underwent total hip arthroplasty (THA) with a diagnosis of OA were enrolled in this study. The prevalence of each pain phenotype was evaluated preoperatively and at 6 months postoperatively using the PDQ. Patient characteristics and numerical rating scale (NRS) scores were compared between a group with possible neuropathic pain (NP group) and a group with nociceptive pain (non-NP group).

RESULTS

Before THA, neuropathic, unclear, and nociceptive pain was observed in 18, 36, and 105 hips, respectively. The prevalence in the NP group was 54 hips, accounting for approximately one-third of all hips, which decreased significantly to seven hips after THA. A significantly higher NRS score was observed in the NP group, both before and after THA.

CONCLUSION

Approximately one-third of the patients with hip OA had neuropathic pain. Therefore, neuropathic pain should be considered when treating patients with hip OA.

Neuropathic pain is a feature in patients with symptomatic femoral acetabular impingement

Femoral acetabular impingement syndrome (FAIS) is a cause of hip pain thought to be nociceptive, although pain phenotypes e.g., burning, pain attacks, prickling, numbness etc., are reported, mimicking neuropathic pain. Although no lesion to the somatosensory system is identified, neuropathic pain (NeP) may explain why nociceptive-focussed treatments are not always successful.

OBJECTIVE

To identify NeP in patients with FAIS and investigate if related to poorer outcomes.

DESIGN

A secondary analysis of the Femoral Acetabular Impingement Trial (FAIT). Outcome of interest: PainDETECT questionnaire; secondary outcomes of interest; International Hip Outcome Tool (iHOT33), Hospital Anxiety and Depression Scale (HADS) and VAS 'average pain over a month', at baseline and 8 months follow-up. Intervention (surgery or physiotherapy) were pooled.

RESULTS

173 data sets at baseline; 123 at 8 months follow-up. Baseline painDETECT identified three groups: 69% nociceptive, 19% unclear and 12% neuropathic pain phenotypes. Baseline, median scores were higher for the neuropathic group compared to the nociceptive group demonstrating borderline anxiety (9.5(5.3 to 14.2), 5(3 to 8), higher normal values for depression (7.5(2.3 to 11.8), (4(2 to 9), higher average pain (7 (6 to 8), 5(4 to 6) and lower iHOT33 14.2(9 to 21.1), 38.4(26.2 to 55.7). Post treatment, there was a median change in the neuropathic score in both iHOT33 (40.8 (25 to 76.5) with a median difference of 24.13 (CI 95% 10.46 to 45.92) and average pain 4.5(1.5 to 7) with a median difference of 2 (CI 95% 1 to 5) but to a lesser amount than the nociceptive group, iHOT33 (64(38.2 to 86.6) with a median difference of 15.50 (CI 95% 6.41 to 21.82) and average pain 3(1 to 5.7) with a median difference of 1 (CI 95% 0.5 to 1).

CONCLUSION

NeP exists in symptomatic FAIS patients and is associated with increased average pain, and functional limitations. Nociceptive-targeted treatment improves hip function and pain but with less improvement in the NeP group when compared to the nociceptive group. Pain phenotyping before intervention may improve outcomes. CONTRIBUTION OF PAPER.

Fibrocyte Phenotype of ENTPD1+CD55+ Cells and Its Association with Pain in Osteoarthritic Synovium

Osteoarthritis (OA) is a prevalent degenerative joint disorder characterized by cartilage erosion, structural changes, and inflammation. Synovial fibroblasts play a crucial role in OA pathophysiology, with abnormal fibroblastic cells contributing significantly to joint pathology. Fibrocytes, expressing markers of both hematopoietic and stromal cells, are implicated in inflammation and fibrosis, yet their marker and role in OA remain unclear. ENTPD1, an ectonucleotidase involved in purinergic signaling and expressed in specific fibroblasts in fibrotic conditions, led us to speculate that ENTPD1 plays a role in OA pathology by being expressed in fibrocytes. This study aimed to investigate the phenotype of ENTPD1+CD55+ and ENTPD1-CD55+ synovial fibroblasts in OA patients. Proteomic analysis revealed a distinct molecular profile in ENTPD1+CD55+ cells, including the upregulation of fibrocyte markers and extracellular matrix-related proteins. Pathway analysis suggested shared mechanisms between OA and rheumatoid arthritis. Correlation analysis revealed an association between ENTPD1+CD55+ fibrocytes and resting pain in OA. These findings highlight the potential involvement of ENTPD1 in OA pain and suggest avenues for targeted therapeutic strategies. Further research is needed to elucidate the underlying molecular mechanisms and validate potential therapeutic targets.

Frequency of multisite non-hand joint involvement in patients with thumb-base osteoarthritis, and associations with functional and patient-reported outcomes

Purpose

In OA studies, the focus often is on an index-joint; other affected joint sites are often overlooked. In this thumb-base OA study, we documented the frequency of symptomatic non-hand joint sites and investigated whether their count was associated with thumb-specific functional and patient-reported outcome measures.

Design

Patients seeking care for thumb-base OA (conservative or surgical) were included. A patient-completed questionnaire captured sociodemographic and health characteristics, symptomatic hand and non-hand joint sites, and outcome measures (thumb-base pain intensity, symptoms and disability (TASD) and upper-extremity disability/symptoms (quickDASH)). Grip and pinch strength were measured. Linear regressions examined the association between each outcome and symptomatic joint site count, adjusted for several covariates.

Results

The mean age of the 145 patients was 62 years, 72% were female. Mean symptomatic non-hand joint site count was 3.6. Ten percent reported only their hands as symptomatic; 30% reported 2-3 other symptomatic sites, and 49% reported 4+. From cross-sectional multivariable analyses, a higher symptomatic non-hand joint site count was associated with worse scores for all patient-reported outcomes and grip strength. Every unit increase in joint site count (49% had a 4+ count) was associated with a 2.1-3.3 unit increase (worse) in patient-reported outcome scores (all p ​< ​0.02).

Conclusions

In this sample, nearly 80% of patients had 2+ symptomatic non-hand joint sites. These symptoms were associated with worse thumb- and hand-specific outcomes, suggesting a need for awareness of whole body OA burden, with implications for outcome score interpretations, study designs, and provision of care in thumb-base OA.

Preoperative Pain Catastrophizing and Neuropathic Pain Do Not Predict Length of Stay and Early Post-Operative Complications following Total Joint Arthroplasty

BACKGROUND

Both pain catastrophizing and neuropathic pain have been suggested as prospective risk factors for poor postoperative pain outcomes in total joint arthroplasty (TJA).

OBJECTIVE

We hypothesized that pain catastrophizers, as well as patients with pain characterized as neuropathic, would exhibit higher pain scores, higher early complication rates and longer lengths of stay following primary TJA.

METHODS

A prospective, observational study in a single academic institution included 100 patients with end-stage hip or knee osteoarthritis scheduled for TJA. In pre-surgery, measures of health status, socio-demographics, opioid use, neuropathic pain (PainDETECT), pain catastrophizing (PCS), pain at rest and pain during activity (WOMAC pain items) were collected. The primary outcome measure was the length of stay (LOS) and secondary measures were the discharge destinations, early postoperative complications, readmissions, visual analog scale (VAS) levels and distances walked during the hospital stay.

RESULTS

The prevalence of pain catastrophizing (PCS ≥ 30) and neuropathic pain (PainDETECT ≥ 19) was 45% and 20.4%, respectively. Preoperative PCS correlated positively with PainDETECT (rs = 0.501, p = 0.001). The WOMAC positively correlated more strongly with PCS (rs = 0.512 p = 0.01) than with PainDETECT (rs = 0.329 p = 0.038). Neither PCS nor PainDETECT correlated with the LOS. Using multivariate regression analysis, a history of chronic pain medication use was found to predict early postoperative complications (OR 38.1, p = 0.47, CI 1.047-1386.1). There were no differences in the remaining secondary outcomes.

CONCLUSIONS

Both PCS and PainDETECT were found to be poor predictors of postoperative pain, LOS and other immediate postoperative outcomes following TJA.

Therapeutic exercise interventions in rat models of arthritis

Arthritis is the leading cause of musculoskeletal pain and disability worldwide. Nearly 50% of individuals over the age of 65 have arthritis, which contributes to limited function, articular pain, physical inactivity, and diminished quality of life. Therapeutic exercise is often recommended in clinical settings for patients experiencing arthritic pain, however, there is little practical guidance regarding the use of therapeutic exercise to alleviate arthritic musculoskeletal pain. Rodent models of arthritis allow researchers to control experimental variables, which cannot be done with human participants, providing an opportunity to test therapeutic approaches in preclinical models. This literature review provides a summary of published findings in therapeutic exercise interventions in rat models of arthritis as well as gaps in the existing literature. We reveal that preclinical research in this field has yet to adequately investigate the impact of experimental variables in therapeutic exercise including their modality, intensity, duration, and frequency on joint pathophysiology and pain outcomes.

Presence of Night Pain, Neuropathic Pain, or Depressive Disorder Does Not Adversely Affect Outcomes After Total Knee Arthroplasty: A Prospective Cohort Study

BACKGROUND

A considerable proportion of patients warranting total knee arthroplasty (TKA) have night pain, neuropathic pain, and/or depressive disorder, which may not be resolved by TKA. This prospective, longitudinal cohort study aimed to document the prevalence of night pain, neuropathic pain, and depressive disorder in patients with advanced knee osteoarthritis undergoing TKA and to determine whether the specific coexisting pain and/or disorder at the time of TKA adversely affected postoperative outcomes.

METHODS

In this study, 148 patients undergoing TKA were longitudinally evaluated. The presence of night pain, neuropathic pain (determined using Douleur Neuropathique 4 [DN4]) and depressive disorder (determined using the Patient Health Questionnaire-9 [PHQ-9]) was determined before and 6 weeks, 3 months and 1 year after TKA. In addition, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and EuroQol-5 Dimension (EQ-5D) scores were assessed before and 1 year after TKA. Potential associations of night pain, neuropathic pain, and/or depressive disorder with pre- and postoperative WOMAC and EQ-5D scores were examined in subgroup analyses.

RESULTS

Preoperatively, 72% (n = 106) of patients reported night pain, and the prevalences of neuropathic pain and depressive disorder were 15% and 17%, respectively. Preoperatively, compared with patients without night pain, those with night pain had significantly poorer preoperative WOMAC scores, but no significant difference was seen between groups 1 year after TKA. Preoperatively, the WOMAC, EQ-5D, and EQ-5D health scores of patients with neuropathic pain were not significantly different from those of patients without neuropathic pain, and there was no difference in clinical outcome scores 1 year after TKA between these groups. Preoperatively, the patients with depressive disorder showed significantly poorer preoperative WOMAC, EQ-5D, and EQ-5D health scores than those without depressive disorder, but no significant differences in scores were observed 1 year after TKA between these groups.

CONCLUSION

This study revealed a considerable prevalence of night pain, neuropathic pain, and depressive disorder in patients undergoing TKA and that patients with these specific conditions reported poorer functional and quality of life scores preoperatively. However, such adverse effects disappeared after TKA. Our study findings suggest that TKA can provide satisfactory outcomes for patients with these specific conditions.

Different Prevalence of Neuropathic Pain and Risk Factors in Patients with Knee Osteoarthritis at Stages of Outpatient, Awaiting and after Total Knee Arthroplasty

Objective

Neuropathic pain (NP) plays an important role in patients with knee osteoarthritis (KOA). However, the prevalence of NP at different treatment stages including outpatient, awaiting and after total knee arthroplasty (TKA) have not been compared. The understanding of this issue and identify risk factors can help physicians develop individualized strategies to manage the pain of KOA. Therefore, the aim of the study is to investigate the prevalence and risk factors of NP at different treatment stages of KOA.

Methods

Patients diagnosed as KOA between August 2016 and August 2020 were enrolled in this cross‐sectional study and divided into three groups according to treatment stage, including outpatient stage, awaiting TKA stage (pre‐TKA) and after TKA stage (post‐TKA). A numeric rating scale (NRS) and PainDETECT questionnaire were used to evaluate nociceptive pain and NP. Patient demographics, radiological assessments using Kellgren–Lawrence (K‐L) grade, and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores were analyzed. Data analysis and statistics were processed using SPSS 20.0 and examined by ANOVA with/without Bonferroni correction or Kruskal–Wallis test. A chi‐square test was used to determine cross‐table data and calculate the odds ratio (OR) value.

Results

Of the 921 patients, the prevalence of possible and likely NP was 17.5% (56/320) and 2.5% (8/320) in the pre‐TKA group compared with 3.4% (8/233) and 0.4% (1/233) in the outpatient group and 1.4% (5/368) and 0.5% (2/368) in the post‐TKA group, respectively. In the pre‐TKA group, higher NRS (NRS >3; OR = 10.65, 95% CI: 3.25–34.92, P < 0.001) and WOMAC pain score (score > 10; OR = 4.88, 95% CI: 2.38–10.01, P < 0.001) conferred an increased risk of unclear pain. Age, gender, BMI and K‐L grade showed no significant differences among the unlikely, possible and likely NP groups.

Conclusion

Prevalence of NP is different at stages of out‐patient, awaiting and after TKA in patients with KOA. Patients awaiting TKA have the highest prevalence of NP compared with patients in outpatient and post‐TKA groups. In the patients waiting for TKA, higher NRS (NRS >3) and WOMAC pain scores (score > 10) are risk factors of NP.

Selective block of sensory neuronal T-type/Cav3.2 activity mitigates neuropathic pain behavior in a rat model of osteoarthritis pain

BACKGROUND

Peripheral and central nociceptive sensitization is a critical pathogenetic component in osteoarthritis (OA) chronic pain. T-type calcium channel 3.2 (Ca_V3.2) regulates neuronal excitability and plays important roles in pain processing. We previously identified that enhanced T-type/Ca_V3.2 activity in the primary sensory neurons (PSNs) of dorsal root ganglia (DRG) is associated with neuropathic pain behavior in a rat model of monosodium iodoacetate (MIA)-induced knee OA. PSN-specific T-type/Ca_V3.2 may therefore represent an important mediator in OA painful neuropathy. Here, we test the hypothesis that the T-type/Ca_V3.2 channels in PSNs can be rationally targeted for pain relief in MIA-OA.

METHODS

MIA model of knee OA was induced in male and female rats by a single injection of 2 mg MIA into intra-knee articular cavity. Two weeks after induction of knee MIA-OA pain, recombinant adeno-associated viruses (AAV)-encoding potent Ca_V3.2 inhibitory peptide aptamer 2 (Ca_V3.2iPA2) that have been characterized in our previous study were delivered into the ipsilateral lumbar 4/5 DRG. Effectiveness of DRG-Ca_V3.2iPA2 treatment on evoked (mechanical and thermal) and spontaneous (conditioned place preference) pain behavior, as well as weight-bearing asymmetry measured by Incapacitance tester, in the arthritic limbs of MIA rats were evaluated. AAV-mediated transgene expression in DRG was determined by immunohistochemistry.

RESULTS

AAV-mediated expression of Ca_V3.2iPA2 selective in the DRG-PSNs produced significant and comparable mitigations of evoked and spontaneous pain behavior, as well as normalization of weight-bearing asymmetry in both male and female MIA-OA rats. Analgesia of DRG-AAV-Ca_V3.2iPA1, another potent Ca_V3.2 inhibitory peptide, was also observed. Whole-cell current-clamp recordings showed that AAV-mediated Ca_V3.2iPA2 expression normalized hyperexcitability of the PSNs dissociated from the DRG of MIA animals, suggesting that Ca_V3.2iPA2 attenuated pain behavior by reversing MIA-induced neuronal hyperexcitability.

CONCLUSIONS

Together, our results add therapeutic support that T-type/Ca_V3.2 in primary sensory pathways contributes to MIA-OA pain pathogenesis and that Ca_V3.2iPAs are promising analgesic leads that, combined with AAV-targeted delivery in anatomically segmental sensory ganglia, have the potential for further development as a peripheral selective T-type/Ca_V3.2-targeting strategy in mitigating chronic MIA-OA pain behavior. Validation of the therapeutic potential of this strategy in other OA models may be valuable in future study.

Correlation between CD163 expression and resting pain in patients with hip osteoarthritis: Possible contribution of CD163+ monocytes/macrophages to pain pathogenesis

Expression of CD163, a scavenger receptor specifically expressed by monocytes and macrophages, is elevated in the synovial tissue of patients with knee osteoarthritis (OA) compared with healthy controls. However, the association between CD163 expression in the synovium and pain in OA patients is unclear. We investigated the correlation between synovial CD163 expression and resting and active pain levels in patients with hip osteoarthritis (HOA). To investigate the possible contribution of CD163+ subsets to pain pathogenesis, we compared pain-related cytokine expression and M1/M2 macrophage marker expression in CD163+ and CD163- cells. We performed flow cytometric analysis to study the CD163+ cell population. We also examined pain-related cytokine expression and M1/M2 macrophage marker expression on CD163+ CD14^high and CD163+ CD14^low cells using cell sorting. Synovial CD163 expression significantly correlated with resting pain levels (p = 0.006; R = 0.321), but not active pain levels (p = 0.155; R = 0.169). Expression of the M1 macrophage marker CD80 was significantly higher in CD163+ than CD163- cells (p = 0.010), as was the expression of M2 macrophage markers CD206 and IL10 (CD206, p = 0.014; IL10, p = 0.005), and TNFA and IL1B (TNFA, p = 0.002; IL1B, p = 0.001). TNFA expression was significantly higher in CD163+ CD14^low than CD163+ CD14^high cells, while IL1B, IL10, and CD206 expression were comparable among these subsets. Our findings suggest that CD163 expression is associated with higher resting pain scores. As TNF-α plays a role in the pain process, CD163+ CD14^low cells expressing TNFA may be a potent contributor to the pathogenesis of resting pain in HOA.

Phenotypic classification of knee osteoarthritis according to pain mechanisms; a clinical observational study

BACKGROUND

Pain in knee osteoarthritis is considered to be nociceptive. Recently, involvement of neuropathic pain and psychosocial factors in knee osteoarthritis has been reported. However, the following details are unclear: 1) How often are neuropathic pain and psychosocial factors involved? And 2) Which patients are associated with neuropathic pain and psychosocial factors?

METHODS

In 104 patients with knee osteoarthritis, we evaluated neuropathic pain factor with a painDETECT questionnaire and catastrophic thinking using the pain catastrophizing scale. Pain intensity was assessed using the visual analog scale; patients with scores below the median were defined as low-pain group and others as high-pain group. Radiographic severity was categorized according to the Kellgren-Lawrence classification, with grades I-II and III-IV defined as low- and high-grades, respectively. We compared the painDETECT and pain catastrophizing scale scores between the low- and high-pain groups and low- and high-grade groups. Furthermore, the painDETECT and pain catastrophizing scale scores were compared among the following four groups: low-grade/low-pain, low-grade/high-pain, high-grade/low-pain, and high-grade/high-pain.

RESULTS

Neuropathic pain factor and catastrophic thinking were found in 16% and 34% of patients, respectively. There were no significant differences in both painDETECT and pain catastrophizing scale scores between the two pain intensity groups. Between the two groups of radiographic severity, there was no significant difference in the painDETECT scores; however, the pain catastrophizing scale score was significantly high in the low-grade group. In addition, there was no significant difference in the painDETECT scores among the four groups; however, the pain catastrophizing scale scores were significantly higher in low-grade/high-pain than in high-grade/low-pain patients.

CONCLUSIONS

Therefore, 64% had only nociceptive pain factor. Catastrophic thinking was strong in patients with low radiographic severity, especially in those with high pain intensity. Patients with neuropathic pain factor could not be identified from radiographic severity and pain intensity.

Restricting Branched-Chain Amino Acids within a High-Fat Diet Prevents Obesity

Obesity is a global pandemic, but there is yet no effective measure to control it. Recent metabolomics studies have identified a signature of altered amino acid profiles to be associated with obesity, but it is unclear whether these findings have actionable clinical potential. The aims of this study were to reveal the metabolic alterations of obesity and to explore potential strategies to mitigate obesity. We performed targeted metabolomic profiling of the plasma/serum samples collected from six independent cohorts and conducted an individual data meta-analysis of metabolomics for body mass index (BMI) and obesity. Based on the findings, we hypothesized that restriction of branched-chain amino acids (BCAAs), phenylalanine, or tryptophan may prevent obesity and tested our hypothesis in a dietary restriction trial with eight groups of 4-week-old male C57BL/6J mice (n = 5/group) on eight different types of diets, respectively, for 16 weeks. A total of 3397 individuals were included in the meta-analysis. The mean BMI was 30.7 ± 6.1 kg/m2, and 49% of participants were obese. Fifty-eight metabolites were associated with BMI and obesity (all p ≤ 2.58 × 10-4), linked to alterations of the BCAA, phenylalanine, tryptophan, and phospholipid metabolic pathways. The restriction of BCAAs within a high-fat diet (HFD) maintained the mice's weight, fat and lean volume, subcutaneous and visceral adipose tissue weight, and serum glucose and insulin at levels similar to those in the standard chow group, and prevented obesity, adipocyte hypertrophy, adipose inflammation, and insulin resistance induced by HFD. Our data suggest that four metabolic pathways, BCAA, phenylalanine, tryptophan, and phospholipid metabolic pathways, are altered in obesity and restriction of BCAAs within a HFD can prevent the development of obesity and insulin resistance in mice, providing a promising strategy to potentially mitigate diet-induced obesity.

Does weight-bearing versus non-weight-bearing pain reflect different pain mechanisms in knee osteoarthritis?: the Multicenter Osteoarthritis Study (MOST)

OBJECTIVE

Knee osteoarthritis (OA) is predominantly characterized by pain with weight-bearing activities. Pain at rest also occurs but the mechanisms for this are not clear. We evaluated the relations of nociceptive signal alterations to weight-bearing and non-weight-bearing pain in knee OA.

DESIGN

We used data from a NIH-funded longitudinal cohort of older adults with or at risk of knee OA. We evaluated quantitative sensory testing (QST) measures (pressure pain threshold (PPT) at patellae and the wrist; mechanical temporal summation (TS); conditioned pain modulation (CPM)). Each WOMAC pain question was dichotomized as having at least moderate pain, and we further categorized them as weight-bearing pain and non-weight-bearing pain. We evaluated the relation of QST measures to each pain outcome using logistic regression, adjusting for potential confounders.

RESULTS

2,749 participants (5,479 knees) were included (mean age 64 ± 11, 57% female). Each SD unit decrease in patellar PPT was associated with greater odds of both weight-bearing pain (OR 1.51 (95% CI 1.27, 1.79)) and non-weight-bearing pain (OR 1.46 (1.20-1.77)), while wrist PPT was associated with greater odds of weight-bearing pain (OR 1.27 (1.15, 1.39)) but only with pain during sitting/lying (OR 1.20 (1.01, 1.43)). TS was significantly associated with greater odds of pain with walking and stairs (OR 1.11 (1.01, 1.23), 1.11 (1.03, 1.20), respectively). CPM was not associated with any pain outcomes.

CONCLUSIONS

Our findings challenge the hypothesis that non-weight-bearing pain may reflect greater pain sensitization and/or inefficient CPM than weight-bearing pain in knee OA, suggesting other mechanisms are likely responsible.

High Prevalence of Pain Sensitization in Knee Osteoarthritis: A Meta-Analysis with Meta-Regression

OBJECTIVE

The aim of this meta-analysis was to study the evidence on pain sensitization in knee osteoarthritis (OA), providing a quantitative synthesis of its prevalence and impact. Factors associated with pain sensitization were also investigated.

METHODS

Meta-analysis; PubMed (MEDLINE), Cochrane Central Register (CENTRAL), and Web of Science were searched on February 2021. Level I to level IV studies evaluating the presence of pain sensitization in patients with symptomatic knee OA, documented through a validated method (questionnaires or quantitative sensory testing), were included. The primary outcome was the prevalence of pain sensitization. Factors influencing the prevalence were also evaluated, as well as differences in terms of pain thresholds between knee OA patients and healthy controls.

RESULTS

Fifty-three articles including 7,117 patients were included. The meta-analysis of proportion documented a prevalence of pain sensitization of 20% (95% confidence interval [CI] = 16%-26%) with a significant heterogeneity of results (I² = 89%, P < 0.001). The diagnostic tool used was the main factor influencing the documented prevalence of pain sensitization (P = 0.01). Knee OA patients presented higher pain sensitivity compared with healthy controls, both in terms of local pressure pain threshold (standardized mean difference [SMD] = -1.00, 95% CI = -1.67 to -0.32, P = 0.007) and distant pressure pain threshold (SMD = -0.54, 95% CI = -0.76 to -0.31, P < 0.001).

CONCLUSIONS

Knee OA pain presents features that are consistent with a significant degree of pain sensitization. There is a high heterogeneity in the reported results, mainly based on the diagnostic tool used. The identification of the best methods to detect pain sensitization is warranted to correctly evaluate and manage symptoms of patients affected by knee OA.

REGISTRATION

PROSPERO CRD42019123347.

How does hip osteoarthritis differ from knee osteoarthritis?

Hip and knee osteoarthritis (OA) are leading causes of global disability. Most research to date has focused on the knee, with results often extrapolated to the hip, and this extends to treatment recommendations in clinical guidelines. Extrapolating results from research on knee OA may limit our understanding of disease characteristics specific to hip OA, thereby constraining development and implementation of effective treatments. This review highlights differences between hip and knee OA with respect to prevalence, prognosis, epigenetics, pathophysiology, anatomical and biomechanical factors, clinical presentation, pain and non-surgical treatment recommendations and management.

Altered brain activity in end-stage knee osteoarthritis revealed by resting-state functional magnetic resonance imaging

INTRODUCTION

Knee osteoarthritis (KOA) is characterized by a degenerative change of knee cartilage and secondary bone hyperplasia, resulting in pain, stiffness, and abnormal walking gait. Long-term chronic pain causes considerable cortical plasticity alternations in patients. However, the brain structural and functional alterations associated with the pathological changes in knee joints of end-stage KOA patients remain unclear. This study aimed to analyze the structural and functional connectivity alterations in end-stage KOA to comprehensively understand the main brain-associated mechanisms underlying its development and progression.

METHODS

In this study, 37 patients with KOA and 37 demographically matched healthy controls (HCs) were enrolled. Alternations in gray matter (GM) volume in patients with KOA were determined using voxel-based morphometry. The region with the largest GM volume alteration was selected as the region of interest to calculate the voxel-wise resting-state functional connectivity (rs-FC) in the two groups. Pearson's correlation coefficient was used to analyze the correlation between clinical measures and GM volume alternations in patients with KOA.

RESULTS

Compared with HCs, patients with KOAs exhibited significantly decreased GM volumes in the left middle temporal gyrus (left-MTG) and the left inferior temporal gyrus. Results of the voxel-wise rs-FC analysis revealed that compared with HCs, patients with KOA had decreased left-MTG rs-FC to the right dorsolateral superior frontal gyrus, left middle frontal gyrus, and left medial superior frontal gyrus. GM volume in the left-MTG was negatively correlated with the Western Ontario and McMaster Universities Arthritis Index in patients with KOA (r = -0.393, p = .016).

CONCLUSION

Structural remodeling and functional connectivity alterations may be one of the central brain mechanisms associated with end-stage KOA.

BoNT/A alleviates neuropathic pain in osteoarthritis by down-regulating the expression of P2X4R in spinal microglia

Neuropathic pain in osteoarthritis is one of the reasons why the pain is difficult to treat, and P2X4R plays an important role in neuropathic pain. In addition, BoNT/A has been proven to have analgesic effects on both neuropathic pain and osteoarthritis, but its exact mechanism is still unknown. This study aims to investigate the relationship between the analgesic effect of BoNT/A on osteoarthritis and the expression of P2X4R in spinal cord microglia. The analgesic effect was compared between BoNT/A and compound betamethasone. Western blot analysis was used to examine the expression of P2X4R and BDNF proteins in the spinal cord. Immunohistochemistry was used to determine the cellular location of P2X4R. Mechanical allodynia and weight asymmetry were identified using the hind paw withdrawal threshold and weight bearing test. The results showed that intra-articular injection of MIA induced persistent mechanical allodynia and weight asymmetry in rats. Both BoNT/A and betamethasone could relieve pain behavior in rats, but BoNT/A had a more obvious effect and lasted longer. Furthermore, BoNT/A could reverse the MIA-induced overexpression of BDNF and P2X4R in the spinal dorsal horn. To sum up, BoNT/A is more effective than betamethasone in relieving MIA-induced osteoarthritis pain in rats, and its analgesic effect may be related to the regulation of P2X4R-mediated BDNF release in spinal microglia and the relief of neuropathic pain in osteoarthritis.

Neuropathic pain in the IMI-APPROACH knee osteoarthritis cohort: prevalence and phenotyping

Objectives

Osteoarthritis (OA) patients with a neuropathic pain (NP) component may represent a specific phenotype. This study compares joint damage, pain and functional disability between knee OA patients with a likely NP component, and those without a likely NP component.

Methods

Baseline data from the Innovative Medicines Initiative Applied Public-Private Research enabling OsteoArthritis Clinical Headway knee OA cohort study were used. Patients with a painDETECT score ≥19 (with likely NP component, n=24) were matched on a 1:2 ratio to patients with a painDETECT score ≤12 (without likely NP component), and similar knee and general pain (Knee Injury and Osteoarthritis Outcome Score pain and Short Form 36 pain). Pain, physical function and radiographic joint damage of multiple joints were determined and compared between OA patients with and without a likely NP component.

Results

OA patients with painDETECT scores ≥19 had statistically significant less radiographic joint damage (p≤0.04 for Knee Images Digital Analysis parameters and Kellgren and Lawrence grade), but an impaired physical function (p<0.003 for all tests) compared with patients with a painDETECT score ≤12. In addition, more severe pain was found in joints other than the index knee (p≤0.001 for hips and hands), while joint damage throughout the body was not different.

Conclusions

OA patients with a likely NP component, as determined with the painDETECT questionnaire, may represent a specific OA phenotype, where local and overall joint damage is not the main cause of pain and disability. Patients with this NP component will likely not benefit from general pain medication and/or disease-modifying OA drug (DMOAD) therapy. Reserved inclusion of these patients in DMOAD trials is advised in the quest for successful OA treatments.

Trial registration number

The study is registered under clinicaltrials.gov nr: NCT03883568.

Does the Presence of Neuropathic Pain Influence the Response to Hyaluronic Acid in Patients with Knee Osteoarthritis?

OBJECTIVES

Up to 50% of patients with symptomatic knee osteoarthritis (OA) present with neuropathic pain (NP) features. We assessed the impact of NP according to DN4 (Douleurs Neuropathiques 4 questions) score on the response to intra-articular (IA) hyaluronic acid (HA) injections and the effects of HA injections on NP.

MATERIALS AND METHODS

We conducted a post hoc analysis from a multicenter, randomized, double-blind, noninferiority trial comparing the efficacy of 2 HA in symptomatic knee OA at 24 weeks. At baseline, demographic, anthropometric, radiologic data, and symptoms were recorded. The symptomatic effect of HA was assessed by VAS pain, patient global assessment (PGA), WOMAC, DN4, and OMERACT-OARSI response.

RESULTS

A total of 187 patients were included. NP according to DN4 score was present in 20 patients (10.7%) at baseline. Most common positive DN4 items were tingling (36.9%) and burning (36.4%). NP was associated with WOMAC pain score (P = 0.02). The presence of NP at baseline did not affect the symptomatic improvement after HA injections according to the VAS pain (P = 0.71), PGA (P = 050), WOMAC pain (P = 0.89), WOMAC function (P = 0.52), and rate of OMERACT-OARSI responders (P = 0.21). The prevalence of patients with NP decreased by 50% (n = 10) at 24 weeks after HA injections. Most improved DN4 items were itching (90%), hypoesthesia to pinprick (88%), and burning (50%).

CONCLUSION

In our study, NP was associated with pain severity, but did not influence the response to IA HA. On the other hand, HA injections reduced some NP features, especially itching, sting hypoesthesia, and burning.

Mechanism of Chronic Pain of Symptomatic Hip Osteoarthritis by Association of its Distribution, Nociceptive, Neuropathic, Nociplastic, or Mixed-pain Screening, and the Prevalence of Lumbar Spinal Stenosis: A Cross-sectional Study

OBJECTIVES

The pain of hip osteoarthritis (OA) is generally recognized as nociceptive in origin because of the local pathology. However, some patients with OA experience a neuropathic pain component as an essential part of some nociplastic pain subtype. Here, we sought to examine the mechanism of chronic pain of symptomatic hip OA by the association of its distribution, complex pain mechanism screening, and the prevalence of lumbar spinal stenosis.

MATERIALS AND METHODS

We conducted a prospective cross-sectional study of 100 hips in 100 patients with symptomatic hip OA in a chronic state. We examined all baseline clinical characteristics including clinical and functional score, location of pain and numbness, and pain score (PainDETECT questionnaire and the Leeds Assessment of Neuropathic Symptoms and Signs), and magnetic resonance imaging of the hip and lumbar spine.

RESULTS

The PainDETECT questionnaire and Leeds Assessment of Neuropathic Symptoms and Signs revealed that 23% of the patients had a neuropathic pain component. There were 24 variations of the pain pattern. By contrast, the pain localized around the hip joint was only 15%. Pain distal to the thigh and any numbness was significantly more frequent in the group with neuropathic pain (P<0.001). Lumbar spinal stenosis grade was not significantly different between patients with nociceptive pain and those with neuropathic pain. Pain score was significantly correlated with the pain in clinical and functional scores.

DISCUSSION

Among patients with symptomatic hip OA, the distribution of pain was various, and about 23% of patients had neuropathic, nociplastic, or mixed pain as a possibility for somatosensory system disturbances.

Adverse Effects of Higher Preoperative Pain at Rest, a Central Sensitization-Related Symptom, on Outcomes After Total Hip Arthroplasty in Patients with Osteoarthritis

Background

In patients with hip osteoarthritis (OA), pain at rest, unlike pain on activity, is due to pain mechanisms that cannot be explained by nociceptive pain. However, it remains unclear whether central sensitization (CS) is one of the causes of exacerbated pain at rest in patients with hip OA. Therefore, we investigated the differences in causative factors and postoperative course of total hip arthroplasty (THA) between preoperative pain at rest and on activity in patients with hip OA.

Methods

In total, 120 patients (125 hips, 22 men and 98 women, aged 64.5±1.0 years) with hip OA were included. Preoperative pain at rest and on activity and CS were assessed using the visual analog scale (VAS) and CS Inventory (CSI), respectively. Postoperative assessments were evaluated using the Japanese Orthopedic Association Hip Disease Evaluation Questionnaire (JHEQ); pain, satisfaction, function, and mental scores were evaluated 6 and 12 months after THA.

Results

Multivariate regression analysis indicated the CSI score as affecting VAS for pain at rest (β=0.067, P=0.002) but not VAS for pain on activity (β=0.036, P=0.073). VAS for pain at rest had a weak negative correlation with satisfaction and pain scores at both 6 and 12 months after THA (satisfaction, r=-0.309, -0.278; pain, r=-0.202, -0.22). VAS for pain on activity was not correlated with JHEQ. The CSI score had a weak or moderate negative correlation with three scores other than the function score at both 6 and 12 months after THA (satisfaction, r=-0.266, -0.213; pain, r=-0.332, -0.203, mental, r=-0.427, -0.370). The function score was weakly correlated with the CSI score only 6 months after THA (function, r=-0.231, -0.190).

Conclusion

A higher level of preoperative pain at rest, a CS-related symptom, may affect postoperative pain persistence and dissatisfaction in patients with hip OA.

Possible Neuropathic Pain in Patients with Osteoarthritis of the Knee Before and After Total Knee Arthroplasty

Purpose

Although the pain of osteoarthritis (OA) is traditionally considered to be nociceptive, some patients also have neuropathic pain. The objective of this study was to evaluate the presence of neuropathic pain in the knees of OA patients using the painDETECT questionnaire (PDQ).

Methods

A total of 180 knees in 158 consecutive patients who underwent total knee arthroplasty (TKA) were enrolled prospectively. The prevalence of neuropathic pain, unclear pain, and nociceptive pain in the knee was determined before and after TKA using a numerical rating scale (NRS). All patients were evaluated preoperatively and 6 months postoperatively. Neuropathic pain and unclear pain were grouped together as possible neuropathic pain. The relationship between possible neuropathic pain and pain intensity was evaluated.

Results

Before TKA, neuropathic pain and unclear pain were found in 10 and 30 knees, respectively. The remaining 140 knees were categorized as nociceptive pain. After TKA, the numbers of knees with neuropathic and unclear pain decreased to one and five, respectively. The prevalence of possible neuropathic pain decreased significantly from 22.2% to 3.3% after surgery. Among the six knees with possible neuropathic pain postoperatively, four had possible neuropathic pain preoperatively as well, while the remaining two patients had been classified as nociceptive pain preoperatively. Knees with possible neuropathic pain postoperatively had higher postoperative NRS scores than those with nociceptive pain.

Conclusion

Although the prevalence of possible neuropathic pain decreased significantly after TKA, the preoperative presence of possible neuropathic pain might be associated with the development of persistent postoperative pain following TKA.

Osteoarthritis Progression: Mitigation and Rehabilitation Strategies

Osteoarthritis is the most common form of arthritis and is a substantial burden for patients with the disease. Currently, there is no cure for osteoarthritis, but many emerging therapies have been developed to aid in the mitigation of disease progression. When osteoarthritis reaches the end-stage of disease many patients undergo total joint arthroplasty to improve quality of life, yet some experience persistent pain and mobility limitations for extended periods following surgery. This review highlights recent therapeutic advancements in osteoarthritis treatment consisting of pharmacologics, nutraceuticals, biologics, and exercise while emphasizing the current state of post-arthroplasty rehabilitation.

Synovitis is associated with constant pain in knee osteoarthritis: a cross-sectional study of OMERACT knee ultrasound scores

OBJECTIVE

To examine the association between ultrasound (US)-detected knee inflammation and intermittent and constant pain experiences in patients with knee osteoarthritis (OA).

METHODS

Participants with radiographically early- (KL ≤ 2) and late-stage (KL ≥ 3) disease and frequent symptoms underwent musculoskeletal US measures of inflammation using the OMERACT knee US scoring system. Pain experiences were captured using the Intermittent and Constant OA Pain (ICOAP) tool. We assessed the association between US-synovitis and ICOAP pain experiences using a series of linear, logistic, or multinomial logistic regression models (as appropriate for each variable), while adjusting for age, sex, body mass index (BMI), and radiographic stage. Secondary analyses were performed similarly by radiographic stage.

RESULTS

Pain and synovitis measures from 248 patients (453 knees) were included. Worse synovitis was associated with higher ICOAP constant pain scores (β 8.05 [95%CI 0.67, 15.43]), but not intermittent pain scores. Moderate-to-severe synovitis was associated with a 4.73-fold increased relative risk [95%CI 1.06, 8.80] of a constant pain pattern. In secondary analyses, moderate-to-severe synovitis in early radiographic OA was associated with 2.70-higher odds [95%CI 1.04, 7.02] of any constant pain, 3.28-higher odds [95%CI 1.43, 7.52] of any intermittent pain, and with higher intermittent (β 10.47 [95%CI 1.03, 19.91]) and constant (β 12.62 [95%CI 3.02, 22.23]) pain scores. No associations identified for synovitis in those with late radiographic OA.

CONCLUSION

In patients with knee OA, moderate-to-severe synovitis is most strongly associated with constant pain. Inflammation may play context-specific roles across pain experiences, especially in earlier radiographic stages of knee OA.

Systematic review and meta-analysis of the prevalence of neuropathic-like pain and/or pain sensitization in people with knee and hip osteoarthritis

OBJECTIVE

To determine the prevalence of neuropathic-like pain (NP) and pain sensitization (PS) defined by self-report questionnaires in knee and hip osteoarthritis, and whether prevalence is potentially explained by disease-severity or affected joint.

DESIGN

MEDLINE, EMBASE, CINAHL were systematically searched (1990-April 2020) for studies describing the prevalence of NP and PS in knee and hip osteoarthritis using self-report questionnaires. Random-effects meta-analysis was performed. Statistical heterogeneity between studies and sub-groups (affected joint and population source as a proxy for disease severity) was assessed (I² statistic and the Chi-squared test).

RESULTS

From 2,706 non-duplicated references, 39 studies were included (2011-2020). Thirty-six studies reported on knee pain and six on hip pain. For knee osteoarthritis, the pooled prevalence of NP was: using PainDETECT, possible NP(score ≥13) 40% (95%CI 32-48%); probable NP(score >18) 20% (95%CI 15-24%); using Self-Report Leeds Assessment of Neuropathic Symptoms and Signs, 32% (95%CI 26-38%); using Douleur Neuropathique (DN4) 41% (95% CI 24-59%). The prevalence of PS using Central Sensitization Inventory (CSI) was 36% (95% CI 12-59%). For hip osteoarthritis, the pooled prevalence of NP was: using PainDETECT, possible NP 29% (95%CI 22-37%%); probable NP 9% (95%CI 6-13%); using DN4 22% (95%CI 12-31%) in one study. The prevalence of possible NP pain was higher at the knee (40%) than the hip (29%) (difference 11% (95% CI 0-22%), P = 0.05).

CONCLUSIONS

Using self-report questionnaire tools, NP was more prevalent in knee than hip osteoarthritis. The prevalence of NP in knee and hip osteoarthritis were similar for each joint regardless of study population source or tool used. Whether defining NP using self-report questionnaires enables more effective targeted therapy in osteoarthritis requires investigation.

Correlation between pain severity and levels of anxiety and depression in osteoarthritis patients: a systematic review and meta-analysis

OBJECTIVES

Osteoarthritis (OA) is a chronic degenerative musculoskeletal disease that causes articular damage and chronic pain, with a prevalence of up to 50% in individuals >60 years of age. Patients suffering from chronic painful conditions, including OA, also frequently report anxiety or depression. A systematic review and meta-analysis were performed to assess the correlation between pain severity and depressive and anxious symptomatology in OA patients.

METHODS

A systematic search was conducted using four databases (PubMed, Medline, Scopus, and Web of Science) from inception up to 14th January of 2020. We included original articles evaluating pain severity and anxiety and/or depression severity in OA-diagnosed patients. Detailed data were extracted from each study, including patients' characteristics and pain, anxiety, and depression severity. When available, the Pearson correlation coefficient between pain and depression severity and pain and anxiety severity was collected and a meta-analysis of random effects was applied.

RESULTS

This systematic review included 121 studies, with a total of 38085 participants. The mean age was 64.3 years old and subjects were predominantly female (63%). The most used scale to evaluate pain severity was the Western Ontario and the McMaster Universities Osteoarthritis Index, while for anxiety and depression, the Hospital Anxiety and Depression Scale was the most used. The meta-analysis showed a moderate positive correlation between pain severity and both anxious (r = 0.31, p < 0.001) and depressive symptomatology (r = 0.36, p < 0.001).

CONCLUSIONS

Our results demonstrate a significant correlation between pain and depression/anxiety severity in OA patients, highlighting the need for its routine evaluation by clinicians.

Comparison of Predisposing Factors Between Pain on Walking and Pain at Rest in Patients with Knee Osteoarthritis

Purpose

Patients with knee osteoarthritis (OA) complain of various types of pain, divided into two main categories: pain on movement and pain at rest. A thorough understanding of pain is essential for managing knee OA; however, few studies have investigated the mechanisms underlying the two different types of pain. This study aimed to clarify the predisposing factors for pain in patients with knee OA with a focus on differences between pain on walking and pain at rest.

Patients and Methods

This study involved 93 patients, aged 44–90 years, with knee OA, including 74 women. We assessed demographic variables (sex, age, body mass index [BMI], side), visual analogue scale (VAS) score on walking, VAS score at rest, Kellgren and Lawrence (KL) grade on radiograph, synovitis score and bone marrow lesion (BML) score on magnetic resonance imaging, and pressure pain threshold (PPT), and used univariate and multiple regression analyses to investigate factors predisposing patients to pain at rest or pain on walking.

Results

In the univariate analyses, we found significant correlations between VAS score on walking and BMI (r=0.31, p<0.01), KL grade (r=0.40, p<0.01), synovitis score (r=0.26, p=0.01), and BML score (r=0.36, p<0.01), whereas VAS score at rest correlated with PPT (r=−0.23, p=0.02) and BMI (r= 0.26, p=0.01). Multiple regression analysis showed that significant explanatory factors for VAS score on walking were BMI (β=0.22, p=0.03) and KL grade (β=0.27, p=0.03). By contrast, PPT was the only significant explanatory factor for VAS score at rest (β=−0.27, p=0.01).

Conclusion

Predisposing factors were significantly different between pain on walking and pain at rest, indicating that different pain mechanisms exist in the two types of pain. Pain on walking was more strongly associated with mechanical and structural factors, while pain at rest was associated with mechanical hyperalgesia of the knee.

Clinical Registration

University Hospital Medical Information Network Clinical Trials Registration number; 000041190.

Pain-Reducing Effects of Physical Therapist-Delivered Interventions: A Systematic Review of Randomized Trials Among Older Adults With Dementia

BACKGROUND AND PURPOSE

Pain is common among older adults with dementia. There are nonpharmacological options for managing pain in this population. However, the effects of physical therapist-delivered interventions have not been summarized. The purpose of this systematic review was to summarize the literature on physical therapist-delivered interventions in randomized trials for reducing pain among older adults with dementia.

METHODS

A systematic search of MEDLINE/PubMed, CINAHL, PsycINFO, and Web of Science was conducted for randomized trials of pain management in individuals 60 years or older with medically diagnosed dementia of any severity. Included studies addressed the effects of nonpharmacological physical therapist-delivered interventions on pain outcomes. Pain outcomes included patient or caregiver self-report, observational or interactive measures. Independent reviewers extracted relevant data and assessed methodological quality using the PEDro scale.

RESULTS AND DISCUSSION

Three studies (total = 222 participants; mean age range = 82.2-84.0 years; 178 [80.2%] females) met inclusion criteria. PEDro scores ranged from 4 to 8/10. Interventions included passive movement and massage. Pain outcomes included the observational measures Pain Assessment Checklist for Seniors with Limited Ability to Communicate (PACSLAC), Pain in Advanced Dementia (PAINAD), and Doloplus-2 Scale. Passive movement did not show better results when compared with no treatment, while massage showed pain-reducing effects in 1 study compared with no treatment.

CONCLUSIONS

The evidence supporting pain-reducing physical therapy interventions for patients with dementia is limited. There is a clear gap in knowledge related to evidence-based physical therapy for managing pain in this population. Future studies should examine active physical therapist-delivered interventions and utilize interactive pain measures.

Neuropathic-Like Pain Symptoms in a Community-Dwelling Sample with or at Risk for Knee Osteoarthritis

OBJECTIVE

To characterize neuropathic-like pain among individuals with or at risk for knee osteoarthritis.

SUBJECTS

One hundred eighty-four individuals who self-identified as non-Hispanic black or non-Hispanic white and presented with unilateral or bilateral knee pain.

DESIGN

Neuropathic-like pain was assessed using the painDETECT, and those with high vs low neuropathic-like pain were compared on clinical pain, psychological symptoms, physical function, and quantitative sensory testing. Analyses were unadjusted, partially and fully adjusted for relevant covariates.

RESULTS

Thirty-two (17.4%) participants reported experiencing neuropathic-like pain features above the painDETECT clinical cut-score. The neuropathic-like pain group reported significantly greater pain severity on all measures of clinical pain and higher levels of psychological symptoms when fully adjusted for covariates, but no differences emerged for disability and lower extremity function. The neuropathic-like pain group also reported greater overall heat pain ratings during the heat pain threshold and increased temporal summation of heat pain in the fully adjusted model. Additionally, those with neuropathic-like pain symptoms reported greater painful after-sensations following heat pain temporal summation in all analyses. No significant group differences in pressure pain threshold emerged at any of the testing sites. In contrast, temporal summation of mechanical pain was significantly greater at both the index knee and the ipsilateral hand for the neuropathic-like pain group in all analyses.

CONCLUSIONS

Participants with or at risk for knee osteoarthritis who reported high neuropathic-like pain experienced significantly greater clinical pain and increased heat and mechanical temporal summation at the index knee and other body sites tested, suggesting central sensitization.

Co-existing patterns of MRI lesions were differentially associated with knee pain at rest and on joint loading: a within-person knee-matched case-controls study

BACKGROUND

To assess the association of co-existing MRI lesions with knee pain at rest or on joint loading.

METHODS

We included participants from Osteoarthritis Initiative whose pain score, measured by WOMAC sub-scales, differed by ≥1 point at rest (in bed at night, sitting/lying down) or on joint loading (walking, stairs) between two knees. Cartilage morphology, bone marrow lesions, meniscus extrusion, meniscus morphology, Hoffa's synovitis and synovitis-effusion were assessed using the compartment-specific MRI Osteoarthritis Knee Score. We performed latent class analyses to identify subgroups of co-existing MRI lesions and fitted a conditional logistic regression model to examine their associations with knee pain.

RESULTS

Among 130 eligible participants, we identified five subgroups of knees according to patterns of co-existing MRI lesions: I. minimal lesions; II. mild lesions; III. moderate morphological lesions; IV. moderate multiple reactive lesions; and V. severe lesions. Compared with subgroup I, the odds ratios (ORs) and 95% confidence intervals (CI) of greater pain in bed at night were 1.6 (0.3, 7.2), 2.2 (0.5, 9.5), 6.2 (1.3, 29.6) and 11.2 (2.1, 59.2) for subgroups II-V, respectively. A similar association was observed between aforementioned subgroups and pain with sitting/lying down. The ORs (95% CI) of greater pain with walking were 1.0 (reference), 1.7 (0.5, 6.1), 0.7 (0.2, 2.3), 5.0 (1.4, 18.6) and 7.9 (2.0, 31.5) for subgroup I-V, respectively. The corresponding analysis for pain on stairs showed similar results.

CONCLUSIONS

Distinct patterns of co-existing MRI lesions have different implications for the pathogenesis of osteoarthritic knee pain occurring with/without joint loading.

Central sensitization inventory scores correlate with pain at rest in patients with hip osteoarthritis: a retrospective study

Background

Patients with persistent pain due to osteoarthritis (OA) complain of multiple symptoms that cannot be explained solely by structural changes. A poor correlation exists between structural and inflammatory changes in OA and pain levels. Central sensitization (CS) has been identified as a factor that induces chronic pain in patients with OA. Although it is important to identify osteoarthritis patients with CS components, the prevalence and characteristics of CS, especially those in patients with hip OA, are not well understood. Thus, we aimed to determine the prevalence and characteristics of CS in patients with hip OA, in this study.

Methods

The CS Inventory (CSI), used as a non-invasive routine clinical tool to evaluate the presence of CS 1 month before surgery in 100 patients with hip OA, was measured at our outpatient clinic, and the data were retrospectively reviewed. We determined the number of patients with a CSI score of 40 points or higher and assessed the relationships between the CSI score and clinical factors (including age, duration of hip pain, degree pain at rest and on activity, by using the visual analogue scale [VAS] and the Harris Hip Score) using the Spearman’s correlation coefficient.

Results

The mean age of participants was 63.9 ± 11.6 years, and there were 15 men and 85 women. All patients had hip OA, categorised as advanced and terminal stage (Tönnis grade 2–3) on preoperative plain radiography. The mean duration of hip pain was 4.2 ± 4.4 years. The mean CSI score was 19.5 ± 11.3 and 5 (5.0%) of the patients had a score of 40 or more points. CSI scores correlated significantly only with VAS pain at rest (r = 0.348, P < 0.001).

Conclusion

In this study, 1 out of every 20 hip OA patients had CS components. CSI scores were significantly correlated with pain at rest in hip OApatients. CS approaches to hip OA may be one of the treatment options for pain at rest.

How Does Preoperative Central Sensitization Affect Quality of Life Following Total Knee Arthroplasty?

BACKGROUND

Central sensitization (CS) has been recently identified as a significant risk factor for persistent pain and patient dissatisfaction following total knee arthroplasty (TKA). However, it remains unclear as to whether the preoperative CS persists after the elimination of a nociceptive pain source by TKA, or how CS affects the quality of life after TKA.

METHODS

A total of 222 consecutive patients undergoing primary TKA were enrolled in the study. All patients were preoperatively screened for CS using the Central Sensitization Inventory (CSI) and categorized into either a CS (n = 55; CSI ≥ 40) or non-CS group (n = 167; CSI < 40). CSI, pain visual analog scale (VAS), Knee Society Score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index score, and satisfaction were recorded at postoperative 2 years.

RESULTS

Two years after TKA, preoperative CS remained unchanged; there was no difference between preoperative and postoperative CSI scores, and both preoperative and postoperative CSI severity levels were similar (P > .1). The CS group showed worse pain VAS, KSS, and Western Ontario and McMaster Universities Osteoarthritis Index scores than did the non-CS group (P < .01) and more patients in the CS group were dissatisfied with all activities (P < .01). However, a similar percentage of the CS group achieved the previously documented minimal clinically important difference in pain VAS and KSS, compared with the non-CS group. Multivariate regression analysis revealed that preoperative CSI scores were associated with dissatisfaction at postoperative 2 years.

CONCLUSION

Preoperative CS was persistent at 2 years after TKA. Although CS patients achieved comparable clinical improvement following TKA, CS patients had worse quality of life, functional disability, and dissatisfaction than non-CS patients.

Relationship between Pain Behavior and Changes in KCNA2 Expression in the Dorsal Root Ganglia of Rats with Osteoarthritis

Objective. To investigate the relationship between pain behavior and potassium voltage-gated channel subfamily A member 2 (KCNA2) expression in dorsal root ganglia (DRGs) of rats with osteoarthritis (OA). Methods. Male Sprague-Dawley rats were randomly divided into three groups: blank control group (group C), normal saline group (group S), and group OA. Paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were measured one day before injection and one, two, four, and six weeks after injection. At one, two, four, and six weeks after injection, pathological knee joint changes and activated transcription factor-3 (ATF-3) and KCNA2 expressions in DRGs were analyzed. Results. Compared with preinjection, PWMT and PWTL at two, four, and six weeks after injection were significantly decreased in the group OA (P<0.05 or 0.01). Compared with group C, PWMT and PWTL at two, four, and six weeks after injection were significantly decreased in the group OA (P<0.05 or 0.01). In the group OA, slight local articular cartilage surface destruction was found at week one. The cartilage surface destruction gradually developed, and the exacerbation of cartilage matrix reduction and bone hyperplasia were increasingly aggravated and eventually evolved into advanced OA in the second to sixth weeks. Compared with group C, ATF-3 expression was significantly increased, and KCNA2 expression was significantly decreased in the group OA at two, four, and six weeks after injection (P<0.05 or 0.01). Compared to baseline, ATF-3 expression was significantly increased, and KCNA2 expression was significantly decreased in the group OA (P<0.05 or 0.01). Conclusion. Pain behavior in OA rats was associated with decreased KCNA2 expression in DRGs.

Analgesic Effect of Duloxetine on an Animal Model of Monosodium Iodoacetate-Induced Hip Osteoarthritis

We investigated the efficacy of duloxetine on hyperalgesia, histopathological and radiographic findings, pain-related sensory innervation of dorsal-root ganglia (DRG), and spinal changes in a rat model of induced hip osteoarthritis (OA). The right hip joints of male Sprague-Dawley rats (n = 6 rats/group) in the Sham group were injected with 25 μl of sterile saline and 25 μl of sterile saline with 2 mg of monosodium iodoacetate (MIA) were injected to the MIA + Vehicle and MIA + Duloxetine groups. We injected duloxetine 20 mg/kg intraperitoneally in the MIA + Duloxetine group 28 days after injection, whereas rats in the MIA + Vehicle group were injected with 0.5 ml of 20% dimethyl sulfoxide. We assessed hyperalgesia, histopathological changes, immunoreactive (-ir) neurons for calcitonin gene-related peptide and activating transcription factor 3 in DRG, and immunoreactive neurons for ionized-calcium-binding adaptor molecule 1 (Iba1) in the dorsal horn of the spinal cord. MIA administration into the hip joint let to mechanical hyperalgesia of the ipsilateral hind paw (p < 0.05). A single injection of duloxetine significantly attenuated it in induced hip OA (p < 0.05) and suppressed the number of Iba1-ir microglia of the ipsilateral dorsal horn (p < 0.05). These results suggest that a single injection of duloxetine suppressed mechanical hyperalgesia and may influence the expression of Iba1 in the microglia of the ipsilateral dorsal horn in the MIA-induced hip OA. This finding implies the inhibitory effects of duloxetine against neuropathic pain, which may lead to a change of microglial activities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:422-430, 2020.

Associations between biomarkers of bone and cartilage turnover, gender, pain categories and radiographic severity in knee osteoarthritis

Background

Excessive cartilage degradation is a known characteristic of osteoarthritis (OA). Biochemical markers, such as uCTX-II, have been shown to be associated with disease severity, yet the tissue origin of CTX-II has been disputed. This analysis investigates the association between OA knee joints at different radiographic stages and pain categories with levels of uCTX-II and biomarkers of bone resorption and formation.

Methods

Baseline data of two randomised clinical trials (NCT00486434 and NCT00704847) in patients with radiographic OA and presence of pain were analysed post hoc. A subgroup with available urine samples and evaluable radiographs for both knees (N = 1241) was analysed. Urine CTX-I, urine CTX-II and serum osteocalcin were analysed for associations with combined Kellgren-Lawrence (KL) scores, gender and pain for both knees to assess the contribution of joints at different stages.

Results

Pain, BMI, age, gender and KL grade were all significantly associated with uCTX-II. The association between pain and CTX-II appeared to be driven by weight-bearing pain. The level of uCTX-II incrementally increased with higher radiographic severity of each knee. Levels of bone markers CTX-I and osteocalcin were both significantly associated with BMI and gender, but neither were associated with radiographic severity. Biomarker levels between male or female groups of identical KL scores were found to be higher in females compared to males in some but not all KL score groups.

Conclusions

These results indicate that levels of uCTX-II are independently associated with radiographic severity of OA and pain intensity. CTX-II was associated with weight-bearing pain, but not non-weight-bearing pain, independent of co-variates. Bilateral OA knee joints appear to contribute to uCTX-II levels in an incremental manner according to radiographic severity of single joints. The data suggest that biomarker differences between genders should be taken into account when evaluating these markers in the context of structural features of OA.

[Expression of KCNA2 in the dorsal root ganglia of rats with osteoarthritis pain induced by monoiodoacetate]

OBJECTIVE

To investigate the changes in the expression of voltage-gated potassium channel subunit KCNA2 in the dorsal root ganglion (DRG) neurons of rats with osteoarthritis (OA) pain induced by sodium monoiodoacetate and explore the mechanism.

METHODS

A total of 156 adult male Sprague-Dawley rats were randomly divided into blank control group, saline group and intra-articular monoiodoacetate injection-induced OA group. The paw withdrawal mechanical threshold (PWMT) was measured before and at 1, 2, 4, and 6 weeks after monoiodoacetate injection. At 4 weeks after the injection, the pathological changes in the knee joints were analyzed using HE staining and Safranin O-Fast Green staining, and the expression of activating transcription factor 3 (ATF-3) and inducible nitric oxide synthase (iNOS) in the DRG neurons were detected by immunofluorescence staining. The expression of Kcna2 mRNA in the DRG neurons was detected by RT-qPCR at 1, 2, 4 and 6 weeks after the injection. The expression of KCNA2 in the DRG was measured by Western blotting, and the methylation level of Kcna2 promoter region was measured by MSPCR at 4 weeks after the injection.

RESULTS

The PWMT of the rats in OA group was significantly decreased at 2, 4, and 6 weeks after the injection as compared with the baseline (P &lt; 0.05 or P &lt; 0.001) as well as the control group (P &lt; 0.05 or P &lt; 0.001). Four weeks after the intra-articular injection, fractures and defects on the surface of the articular cartilage, bone hyperplasia, and blurred tidal line were observed in the rats in OA group, but no obvious pathological changes were detected in the control or saline groups. Compared with those in the control group, the expressions of ATF-3 and iNOS were significantly increased (P &lt; 0.01) at 4 weeks after injection; the expression of Kcna2 mRNA at 2, 4 and 6 weeks and the expression of KCNA2 protein at 4 weeks were all significantly decreased (P &lt; 0.05 or P &lt; 0.01), and the methylation level of Kcna2 gene was significantly increased at 4 weeks after the injection in OA group (P &lt; 0.01).

CONCLUSIONS

The expression of KCNA2 is decreased in the DRG neurons of rats with OA pain likely as a result of enhanced methylation of Kcna2 promoter region.

Neuropathic-like knee pain and associated risk factors: a cross-sectional study in a UK community sample

Background

Neuropathic-like knee pain (NKP) is often reported in individuals with knee pain (KP), but the contribution of specific central and peripheral risk factors to NKP has not been studied previously. The aims of the present study were to determine the prevalence of NKP in a community-derived sample with KP and to identify risk factors associated with NKP.

Methods

A cross-sectional study was undertaken (n = 9506) in the East Midlands community among responders (aged 40+ years) to a postal questionnaire. Questions included KP severity (numerical rating scale) and type (neuropathic versus nociceptive) using the modified painDETECT questionnaire, as well as age, body mass index (BMI), significant knee injury, widespread pain, pain catastrophising and fatigue. Multinomial regression analysis was used to determine ORs and 95% CIs. Risk factors were categorised into central and peripheral, and proportional risk contribution (PRC) and 95% CI were estimated using ROC.

Results

KP was reported in 28.2% of responders, of whom 13.65% had NKP (i.e., 3.9% of the total population). Women reported more NKP. After adjustment for age, gender, BMI and pain severity, definite NKP showed associations (aOR, 95% CI) with fibromyalgia (4.07, 2.49–6.66), widespread pain (1.93, 1.46–2.53), nodal osteoarthritis (1.80, 1.28–2.53), injury (1.50, 1.12–2.00), pain catastrophising (5.37, 2.93–9.84) and fatigue (5.37, 3.08–9.35) compared with non-NKP participants. Although only central risk factors contributed to NKP (PRC 8%, 95% CI 2.5–12.5 for central vs. PRC 3%, 95% CI −0.25 to 7.5 for peripheral), both central and peripheral risk factors contributed equally to non-NKP (PRC 10%, 95% CI 5–20 for both).

Conclusions

NKP appears to be driven largely by central risk factors and may require different prevention/treatment strategies.

Trial registration

ClinicalTrials.gov, NCT02098070. Registered on 27 March 2014.

Gender-related differences observed among immune cells in synovial fluid in knee osteoarthritis

OBJECTIVE

There is no existing comprehensive report on the cellular composition of synovial fluids (SFs) from knee osteoarthritis (OA). We therefore aimed to characterise the immune cell composition in SFs from knee OA (KOA) and in subgroups according to gender.

DESIGN

The immunophenotyping of monocyte/macrophage lineage cells, T and B cells, NK cells, neutrophils, dendritic and mast cells (MC) present in SFs from 53 patients (24 males/29 females) with KOA was performed using 6-colour flow cytometry.

RESULTS

SFs from patients with OA contained 90% hematopoietic cells. Lymphocytes were the predominant cell population (44.8%) in the SFs of OA patients, with CD4⁺ T lymphocytes being more prevalent than CD8⁺ T cells (CD4⁺/CD8⁺ ratio = 1.3). Within the monocyte/macrophage lineage gating, monocytes accounted for 33.9%, macrophages 14.8%, myeloid dendritic cells 16.4%. The rest of the hematopoietic cells were comprised of neutrophils (8%), NK cells (3.8%), T regulatory cells (1.2%), plasmacytoid dendritic cells (1.1%), mast cells (0.3%). In OA females, a higher percentage of CD4⁺ T cells (P = 0.023), macrophages (P = 0.012), and a lower percentage of monocytes (P = 0.008) and CD8⁺ T cells (P = 0.002) were detected in comparison to OA males.

CONCLUSIONS

Based on the immune cell composition of SFs, data mining analysis revealed distinct phenotypes (monocyte- and lymphocyte-predominant) within each gender group. This first study on the cellular complexity of SFs in KOA showed marked differences between male and female patients. The findings give a rational starting point for patient stratification according to their phenotypes, as is required for phenotype-specific treatment strategies.

Contralateral monoarthritis exacerbated chronic constriction injury-induced pain hypersensitivity through upregulating inducible nitric oxide synthase

Introduction

High comorbidity of osteoarthritis (OA) and neuropathic pain has been reported in aged patients. Evidence shows that central sensitization of pain processing occurs in late-phase OA and may facilitate the development of neuropathic pain. Few studies reveal whether acute monoarthritis (MA) aggravates neuropathic pain on the opposite side of the body from the injury.

Methods

To address whether neuropathic pain is affected by contralateral MA through distinct inflammatory pathway, MA was induced by intra-articular injection of complete Freund’s adjuvant (CFA) into the right tibiotarsal joint, and neuropathic pain was established by chronic constriction injury (CCI) of the left sciatic nerve.

Results

We observed that MA aggravated mechanical allodynia and thermal hyperalgesia in CCI rats. Furthermore, MA affected the other side of the spinal cord in multiple aspects, including the upregulation of iNOS mRNA and the enhancement of forskolin-induced facilitation of excitatory synaptic transmission in the spinal cord dorsal horn substantia gelatinosa neurons.

Discussion

Interestingly, intrathecal injection of 1400W, an antagonist of iNOS, attenuated intensity of pain behaviors in CCI rats with contralateral MA to similar levels in CCI rats without MA, and also normalized the facilitatory effect of forskolin on excitatory synaptic transmission in the spinal cord dorsal horn neurons in contralateral MA rats. Therefore, contralateral MA worsened CCI-induced pain hypersensitivity probably through upregulating iNOS and enhancing the facilitation of synaptic transmission following CCI.

Conclusion

Inhibiting the iNOS might be a potential therapeutic strategy for concurrent OA and neuropathic pain.