Experimental pain phenotyping in community-dwelling individuals with knee osteoarthritis

Current concepts in joint pain in knee osteoarthritis

Joint pain attributable to osteoarthritis (OA) is complex and influenced by a myriad of factors beyond local joint pathology. Current practice continues to predominantly adopt a biomedical approach to OA despite emerging evidence of the importance of a more holistic approach. This paper will summarise evidence for the presence of multidimensional pain profiles in knee joint pain and the presence of subgroups characterized by systemic features such as psychological distress, high comorbidity load or sensitisation of the nervous system. These factors have the potential to influence patient outcomes making them relevant for clinicians and highlighting the necessity of a broader multifactorial approach to assessment and treatment. This review describes the current state of the evidence for treatments of people with knee OA-related pain, including those receiving strong recommendations from current clinical guidelines, namely exercise, weight loss, self-management advice and pharmacological approaches. Other pain-modulating treatment options are emerging such as sleep and psychological interventions, pain education and multisensory retraining. The evidence and rationale for these newer therapeutic approaches is discussed. Finally, this review will highlight some of the limitations of current international guidelines for the management of OA and make recommendations for future research.

The Relationship Between β-Endorphin and Experimental Pain Sensitivity in Older Adults With Knee Osteoarthritis

Osteoarthritis (OA) is the most common cause of pain in people aged >45 years, and the knee is the most commonly affected joint. There is a growing interest in understanding the biological factors that influence pain among older adults, but few studies have examined the relationship between β-endorphin and experimental pain sensitivity in older adults with knee OA pain. The purpose of this study was to investigate the relationship between resting plasma levels of β-endorphin and experimental pain sensitivity. This study was a secondary analysis of data for 40 adults with knee OA pain in whom quantitative sensory testing was used to measure experimental sensitivity to heat- and mechanically induced pain. The mean age of the sample was 60 years (SD = 9 years), and approximately half were female (53%). Regression analyses indicated that β-endorphin level was negatively related to pressure pain threshold (β = -17.18, p = .02) and positively related to punctate mechanical pain (β = 17.13, p = .04), after controlling for age, gender, and OA severity. We did not find a significant relationship between β-endorphin and heat pain tolerance. The results suggest that higher circulating levels of β-endorphin at rest are associated with increased sensitivity to mechanical pain in older adults with knee OA. These findings add to the literature regarding biological factors associated with pain sensitivity in older adults with chronic pain. Additional studies are needed to identify mediators of the relationship between β-endorphin and pain sensitivity in OA and other musculoskeletal pain conditions.

Midfoot osteoarthritis: potential phenotypes and their associations with demographic, symptomatic and clinical characteristics

OBJECTIVE

To investigate the demographic, symptomatic, clinical and structural foot characteristics associated with potential phenotypes of midfoot osteoarthritis (OA).

DESIGN

Cross-sectional study of 533 community-dwelling adults aged ≥50 years with foot pain in the past year. Health questionnaires and clinical assessments of symptoms, foot structure and function were undertaken. Potential midfoot OA phenotypes were defined by the pattern of radiographic joint involvement affecting either the medial midfoot (talonavicular, navicular-1^st cuneiform, or cuneiform-1^st metatarsal joint), central midfoot (2^nd cuneiform-metatarsal joint), or both medial and central midfoot joints. Multivariable regression models with generalised estimating equations were used to investigate the associations between patterns of midfoot joint involvement and symptomatic, clinical and structural characteristics compared to those with no or minimal midfoot OA.

RESULTS

Of 879 eligible feet, 168 had medial midfoot OA, 103 central midfoot OA, 76 both medial and central midfoot OA and 532 no/minimal OA. Having both medial and central midfoot OA was associated with higher pain scores, dorsally-located midfoot pain (OR 2.54, 95%CI 1.45, 4.45), hallux valgus (OR 1.76, 95%CI 1.02, 3.05), flatter foot posture (β 0.44, 95%CI 0.12, 0.77), lower medial arch height (β 0.02, 95%CI 0.01, 0.03) and less subtalar inversion and 1^st MTPJ dorsiflexion. Isolated medial midfoot OA and central midfoot OA had few distinguishing clinical characteristics.

CONCLUSIONS

Distinct phenotypes of midfoot OA appear challenging to identify, with substantial overlap in symptoms and clinical characteristics. Phenotypic differences in symptoms, foot posture and function were apparent in this study only when both the medial and central midfoot were involved.

Pain Susceptibility Phenotypes in Those Free of Knee Pain With or at Risk of Knee Osteoarthritis: The Multicenter Osteoarthritis Study

OBJECTIVE

It is not clear why some individuals develop pain with knee osteoarthritis (OA). We undertook this study to identify pain susceptibility phenotypes (PSPs) and their relationship to incident persistent knee pain (PKP) 2 years later.

METHODS

We identified individuals free of PKP from the Multicenter Osteoarthritis Study, a longitudinal cohort of older adults with or at risk of knee OA. Latent class analysis was used to determine PSPs that may contribute to development of PKP apart from structural pathology. These included widespread pain, poor sleep, and psychological factors as well as pressure pain threshold and temporal summation (TS) as determined by quantitative sensory testing (QST). We used logistic regression to evaluate the association of sociodemographic factors with PSPs and the relationship of PSPs to the development of PKP over 2 years.

RESULTS

A total of 852 participants were included (mean age 67 years, body mass index 29.5 kg/m² , 55% women). Four PSPs were identified, primarily characterized by varying proportions (low/absent, moderate, or high) of the presence of pressure pain sensitivity and of facilitated TS, reflecting different measures of sensitization. Subjects in the PSP with a high proportion of pressure pain sensitivity and a moderate proportion of facilitated TS were twice as likely to develop incident PKP over 2 years (odds ratio 1.98 [95% confidence interval 1.07-3.68]) compared with subjects in the PSP having a low proportion of sensitization by both measures.

CONCLUSION

Four PSPs were identified, 3 of which were predominated by QST evidence of sensitization and 1 of which was associated with developing PKP 2 years later. Prevention or amelioration of sensitization may be a novel approach to preventing onset of PKP in OA.

The impact of multisite pain on functional outcomes in older adults: biopsychosocial considerations

Multisite pain, or pain that occurs simultaneously at >1 anatomical site, is more prevalent than single-site pain. While multisite pain affects over half of older adults, it remains an understudied pain entity that may have important functional implications in an aging population. Greater understanding of this complex pain entity from a biopsychosocial perspective is critical for optimizing clinical and functional outcomes in older adults with pain. Therefore, the primary purpose of this review is to summarize the relationship between multisite pain and functional outcomes in older adults to further elucidate the impact of multisite pain as a distinct entity within this population. A comprehensive literature search revealed 17 peer-reviewed articles. Multisite pain in older individuals is associated with reductions in several physical function domains: 1) lower-extremity mobility; 2) upper-extremity impairments; 3) balance and increased fall risk; and 4) general disability and poor physical function. Further, multisite pain in older individuals is associated with psychological dysfunction (eg, anxiety and depressive symptoms) and social factors (eg, income and education). Overall, this review highlights the scant literature investigating the functional implications of multisite pain in an aging population. Further, while multisite pain appears to have functional consequences, the neurobiological mechanisms contributing to this relationship are unknown. Thus, how this pain characteristic may contribute to the variability in pain-related functional outcomes among older adults is not clear. Future investigations are strongly warranted to advance the understanding of multisite pain and its broad impact on physical and psychosocial function in older adults.

The Relationship between Acculturation and Experimental Pain Sensitivity in Asian Americans with Knee Osteoarthritis

Multiple studies in healthy populations and clinical samples have shown that ethnic minorities have greater pain sensitivity than their majority counterparts. Acculturation is speculated to be one of the sociocultural factors contributing to pain sensitivity since cultural beliefs and practices can influence the way patients perceive and respond to pain. However, the relationship of acculturation to pain sensitivity in minority populations remains poorly understood. Therefore, in this cross-sectional study, we examined the relationship between acculturation and experimental pain sensitivity in 50 Asian Americans residing in North Central Florida with knee osteoarthritis pain. The Suinn-Lew Asian Self Identity Acculturation Scale was used to assess acculturation, and multimodal quantitative sensory testing was performed to measure experimental sensitivity, including heat pain tolerance, pressure pain threshold, and punctate mechanical pain. Descriptive and regression analyses were performed. Participants' mean age was 55.7 years, and about half of this sample were Korean American (56%). The participants had lived in the United States for 21 years on average. Regression analyses indicated that lower acculturation to American culture may contribute to greater experimental pain sensitivity. Asian Americans who were more acculturated to the American culture had higher heat pain tolerance (beta = 0.61, P=0.01), higher pressure pain threshold (beta = 0.59, P=0.02), and lower ratings of punctate mechanical pain (beta = -0.70, P < 0.01). These findings add to the literature regarding sociocultural factors associated with pain in Asian Americans; additional research with a larger and more diverse sample of Asian Americans is warranted for cross-validation.

Pressure Pain Phenotypes in Women Before Breast Cancer Treatment

OBJECTIVES

To explore associations between quantitative sensory testing (QST) and pretreatment pain, physical, and psychological characteristics in women with breast cancer.

SAMPLE & SETTING

41 women with treatment-naive stage 0-III breast cancer at the University of Michigan Comprehensive Cancer Center in Ann Arbor.

METHODS & VARIABLES

Participants completed self-report surveys and QST within the month before breast surgery. Pressure pain thresholds (PPTs) were measured bilaterally at each trapezius with a manual QST algometer. PPT values were split, yielding low, moderate, and high pain sensitivity subgroups. Subgroup self-reported characteristics were compared using Spearman's correlation, chi-square, and one-way analysis of variance.

RESULTS

Lower PPT (higher sensitivity) was associated with higher levels of pain interference and maladaptive pain cognitions. The high-sensitivity group reported higher pain severities, interference, and catastrophizing and lower belief in internal locus of pain control than the low-sensitivity group.

IMPLICATIONS FOR NURSING

Individualized interventions for maladaptive pain cognitions before surgery may reduce pain sensitivity and the severity of chronic pain developed after surgery.

Traits associated with central pain augmentation in the Knee Pain In the Community (KPIC) cohort

This study aimed to identify self-report correlates of central pain augmentation in individuals with knee pain. A subset of participants (n = 420) in the Knee Pain and related health In the Community (KPIC) baseline survey undertook pressure pain detection threshold (PPT) assessments. Items measuring specific traits related to central pain mechanisms were selected from the survey based on expert consensus, face validity, item association with underlying constructs measured by originating host questionnaires, adequate targeting, and PPT correlations. Pain distribution was reported on a body manikin. A "central pain mechanisms" factor was sought by factor analysis. Associations of items, the derived factor, and originating questionnaires with PPTs were compared. Eight self-report items measuring traits of anxiety, depression, catastrophizing, neuropathic-like pain, fatigue, sleep disturbance, pain distribution, and cognitive impact were identified as likely indices of central pain mechanisms. Pressure pain detection thresholds were associated with items representing each trait and with their originating scales. Pain distribution classified as "pain below the waist additional to knee pain" was more strongly associated with low PPT than were alternative classifications of pain distribution. A single factor, interpreted as "central pain mechanisms," was identified across the 8 selected items and explained variation in PPT (R = 0.17) better than did any originating scale (R = 0.10-0.13). In conclusion, including representative items within a composite self-report tool might help identify people with centrally augmented knee pain.

Is osteoarthritis one disease or a collection of many?

OA is a multifaceted and heterogeneous syndrome that may be amenable to tailored treatment. There has been an increasing focus within the OA research community on the identification of meaningful OA phenotypes with potential implications for prognosis and treatment. Experimental and clinical data combined with sophisticated statistical approaches have been used to characterize and define phenotypes from the symptomatic and structural perspectives. An improved understanding of the existing phenotypes based on underlying disease mechanisms may shed light on the distinct entities that make up the disease. This narrative review provides an updated summary of the most recent advances in this field as well as limitations from previous approaches that can be addressed in future studies.

Women Undergoing Third Line Overactive Bladder Treatment Demonstrate Elevated Thermal Temporal Summation

PURPOSE

We sought to determine whether women with overactive bladder who required third line therapy would demonstrate greater central sensitization, indexed by temporal summation to heat pain stimuli, than those with overactive bladder.

MATERIALS AND METHODS

We recruited 39 women with overactive bladder from the urology clinic who were planning to undergo interventional therapy for medication refractory overactive bladder with onabotulinumtoxinA bladder injection or sacral neuromodulation. We also recruited 55 women with overactive bladder who were newly seen at our urology clinic or who responded to advertisements for study participation. Participants underwent quantitative sensory testing using a thermal temporal summation protocol. The primary study outcome was the degree of temporal summation as reflected in the magnitude of positive slope of the line fit to the series of 10 stimuli at a 49C target temperature. We compared the degree of temporal summation between the study groups using linear regression.

RESULTS

Women in the group undergoing third line therapy showed significantly higher standardized temporal summation slopes than those in the nontreatment group (β = 1.57, 95% CI 0.18-2.96, t = 2.25, p = 0.027). On exploratory analyses a history of incontinence surgery or hysterectomy was associated with significantly greater temporal summation.

CONCLUSIONS

In this study the degree of temporal summation was elevated in women undergoing third line overactive bladder therapy compared to women with overactive bladder who were not undergoing that therapy. These findings suggest there may be pathophysiological differences, specifically in afferent nerve function and processing, in some women with overactive bladder.

Pain Adaptability in Individuals With Chronic Musculoskeletal Pain Is Not Associated With Conditioned Pain Modulation

Healthy humans can be divided into the pain adaptive (PA) and the pain nonadaptive (PNA) groups; PA showed a greater decrease in pain rating to a cold pressor test (CPT) than PNA. This study examined if the dichotomy of pain adaptability existed in individuals with chronic musculoskeletal pain. CPTs at 2°C and 7°C were used to assess the status of pain adaptability in participants with either chronic nonspecific low back pain or knee osteoarthritis. The participants' potency of conditioned pain modulation (CPM) and local inhibition were measured. The strengths of pain adaptability at both CPTs were highly correlated. PA and PNA did not differ in their demographic characteristics, pain thresholds from thermal and pressure stimuli, or potency of local inhibition or CPM. PA reached their maximum pain faster than PNA (t₄₁ = -2.76, P < .01), and had a gradual reduction of pain unpleasantness over 7 days whereas PNA did not (F_6,246 = 3.01, P = .01). The dichotomy of pain adaptability exists in musculoskeletal pain patients. Consistent with the healthy human study, the strength of pain adaptability and potency of CPM are not related. Pain adaptability could be another form of endogenous pain inhibition of which clinical implication is yet to be understood.

PERSPECTIVE

The dichotomy of pain adaptability was identified in healthy humans. The current study confirms that this dichotomy also exists in individuals with chronic musculoskeletal pain, and could be reliably assessed with CPTs at 2°C and 7°C. Similar to the healthy human study, pain adaptability is not associated with CPM, and may reflect the temporal aspect of pain inhibition.

Differences in pain intensity in anti- and pro-nociceptive pain profile subgroups in patients with knee osteoarthritis

Aim: Facilitated temporal summation is one component of central sensitization. The aim of this exploratory study was to classify pro-, eu- and antinociceptive subgroups based on wind-up ratio cut-off scores in patients with knee osteoarthritis (OA). Patients & methods: A total of 56 patients with knee OA met the inclusion criteria. Temporal summation was measured and wind-up ratio was calculated. Reference values of 180 healthy subjects were used to define wind-up ratio cut-off scores. Results: Twenty-seven percent of patients showed a pro-nociceptive pain profile. Sixteen percent of patients showed an anti-nociceptive pain profile. A eu-nociceptive pain profile was present in 57% of patients. Conclusion: Central pain sensitization was present in approximately a third of knee OA patients. The results should be confirmed in larger studies.

Knee osteoarthritis phenotypes and their relevance for outcomes: a systematic review

OBJECTIVE

To systematically review the literature for studies investigating knee osteoarthritis (OA) phenotypes to examine what OA characteristics are relevant for phenotyping.

METHODS

A comprehensive search was performed in Medline, EMBASE, Web of Sciences, CINAHL, and Scopus databases from inception to September 2016. Inclusion was limited to observational studies of individuals with symptomatic knee OA that identified phenotypes based on any OA characteristics and assessed their association with clinically important outcomes. A descriptive synthesis of the data was performed.

RESULTS

Of the 2777 citations retrieved, 34 studies were included. Clinical phenotypes were investigated most frequently, followed by laboratory, imaging and aetiologic phenotypes. Eight studies defined subgroups based on outcome trajectories (pain, function and radiographic progression trajectories). Most studies used a single patient or disease characteristic to identify patients subgroups while five included characteristics from multiple domains. We found evidence from multiple studies suggesting that pain sensitization, psychological distress, radiographic severity, body mass index (BMI), muscle strength, inflammation and comorbidities are associated with clinically distinct phenotypes. Gender, obesity and other metabolic abnormalities, the pattern of cartilage damage, and inflammation may be implicated in delineating distinct structural phenotypes. Only a few studies investigated the external validity of the phenotypes or their prospective validity using longitudinal outcomes.

CONCLUSIONS

There is marked heterogeneity in the data selected by the studies investigating knee OA phenotypes. We identified the phenotypic characteristics that can be considered for a comprehensive phenotype classification in future studies. A framework for the investigation of phenotypes could be useful for future studies.

PROTOCOL REGISTRATION

PROSPERO CRD42016036220.

Physical performance and movement-evoked pain profiles in community-dwelling individuals at risk for knee osteoarthritis

BACKGROUND

Knee pain associated with osteoarthritis is a significant contributor to decreased physical function. Recent evidence supports the inter-individual heterogeneity associated with knee pain presentation, but whether there is similar heterogeneity in physical performance among these individuals has not been previously examined. The aim of the present study was to characterize the variability in physical performance profiles and the pain evoked by their performance (i.e., movement-evoked pain).

METHODS

In a secondary analysis of the community-based study Understanding Pain and Limitations in Osteoarthritic Disease (UPLOAD), individuals (n=270) completed functional, pain, psychological, and somatosensory assessments. Hierarchical cluster analysis was used to derive physical function profiles that were subsequently compared across several clinical, psychological and experimental pain measures.

RESULTS

Our results support the hypothesis that among persons with knee OA pain, three different physical performance profiles exist with varying degrees of movement-evoked pain. Even as all three groups experienced moderate to severe levels of spontaneous knee pain, those individuals with the most severe movement-evoked pain and lowest physical functional performance also had the least favorable psychological characteristics along with increased mechanical pain sensitivity and temporal summation.

CONCLUSIONS

Our findings support the need for the assessment and consideration of movement-evoked pain during physical performance tasks as these have the potential to increase the value of functional and pain assessments clinically. The identification of the mechanisms driving pain burden within homogeneous groups of individuals will ultimately allow for targeted implementation of treatments consistent with a biopsychosocial model of pain.