Neuromuscular Function in Painful Knee Osteoarthritis

Adaptive Force of hamstring muscles is reduced in patients with knee osteoarthritis compared to asymptomatic controls

BACKGROUND

Quadriceps strength deficits are known for patients with knee osteoarthritis (OA), whereas findings on hamstrings are less clear. The Adaptive Force (AF) as a special neuromuscular function has never been investigated in OA before. The maximal adaptive holding capacity (max. isometric AF; AFisomax) has been considered to be especially vulnerable to disruptive stimuli (e.g., nociception). It was hypothesized that affected limbs of OA patients would show clear deficits in AFisomax.

METHODS

AF parameters and the maximal voluntary isometric contraction (MVIC) of hamstrings were assessed bilaterally comparing 20 patients with knee OA (ART) vs. controls (CON). AF was measured by a pneumatically driven device. Participants were instructed to maintain a static position despite an increasing load of the device. After reaching AFisomax, the hamstrings merged into eccentric action whereby the force increased further to the maximum (AFmax). MVIC was recorded before and after AF trials. Mixed ANOVA was used to identify differences between and within ART and CON (comparing 1st and 2nd measured sides).

RESULTS

AFisomax and the torque development per degree of yielding were significantly lower only for the more affected side of ART vs. CON (p ≤ 0.001). The percentage difference of AFisomax amounted to - 40%. For the less affected side it was - 24% (p = 0.219). MVIC and AFmax were significantly lower for ART vs. CON for both sides (p ≤ 0.001). Differences of MVIC between ART vs. CON amounted to - 27% for the more, and - 30% for the less affected side; for AFmax it was - 34% and - 32%, respectively.

CONCLUSION

The results suggest that strength deficits of hamstrings are present in patients with knee OA possibly attributable to nociception, generally lower physical activity/relief of lower extremities or fear-avoidance. However, the more affected side of OA patients seems to show further specific impairments regarding neuromuscular control reflected by the significantly reduced adaptive holding capacity and torque development during adaptive eccentric action. It is assumed that those parameters could reflect possible inhibitory nociceptive effects more sensitive than maximal strengths as MVIC and AFmax. Their role should be further investigated to get more specific insights into these aspects of neuromuscular control in OA patients. The approach is relevant for diagnostics also in terms of severity and prevention.

Association of Mu opioid receptor (A118G) and BDNF (G196A) polymorphisms with rehabilitation-induced cortical inhibition and analgesic response in chronic osteoarthritis pain

Background/objective

Chronic pain due to osteoarthritis (OA) is a prevalent cause of global disability. New biomarkers are needed to improve treatment allocation, and genetic polymorphisms are promising candidates.

Method

We aimed to assess the association of OPRM1 (A118G and C17T) and brain-derived neurotrophic factor (BDNF [G196A]) polymorphisms with pain-related outcomes and motor cortex excitability metrics (measured by transcranial magnetic stimulation) in 113 knee OA patients with chronic pain. We performed adjusted multivariate regression analyses to compare carriers versus non-carriers in terms of clinical and neurophysiological characteristics at baseline, and treatment response (pain reduction and increased cortical inhibitory tonus) after rehabilitation.

Results

Compared to non-carriers, participants with polymorphisms on both OPRM1 (A118G) and BDNF (G196A) genes were less likely to improve pain after rehabilitation (85 and 72% fewer odds of improvement, respectively). Likewise, both carriers of OPRM1 polymorphisms (A118G and C17T) were also less likely to improve cortical inhibition (short intracortical inhibition [SICI], and intracortical facilitation [ICF], respectively). While pain and cortical inhibition improvement did not correlate in the total sample, the presence of OPRM1 (A118G) and BDNF (G196A) polymorphisms moderated this relationship.

Conclusions

These results underscore the promising role of combining genetic and neurophysiological markers to endotype the treatment response in this population.

The beneficial role of companion animals in translational pain research

The use of spontaneous painful disease in companion pet animals has been highlighted as one of the changes that could be made to help improve translation of basic science to new therapeutics, acting as a bridge between preclinical and clinical studies, with the goal of accelerating the approval of new therapeutics. This review focuses on the utility of companion pet dogs for translational research by reviewing what outcome measures can be measured, and importantly, the relevance of these outcome measures to human translational research. It also details the practical considerations involved in incorporating companion dogs into human therapeutic development.

EEG theta and beta bands as brain oscillations for different knee osteoarthritis phenotypes according to disease severity

This study aims to investigate the multivariate relationship between different sociodemographic, clinical, and neurophysiological variables with resting-state, high-definition, EEG spectral power in subjects with chronic knee osteoarthritis (OA) pain. This was a cross-sectional study. Sociodemographic and clinical data were collected from 66 knee OA subjects. To identify associated factors, we performed independent univariate and multivariate regression models by frequency bands (delta, theta, alpha, beta, low-beta, and high-beta) and by pre-defined regions (frontal, central, and parietal). From adjusted multivariate models, we found that: (1) increased frontocentral high-beta power and reduced central theta activity are positively correlated with pain intensity (β = 0.012, 95% CI 0.004-0.020; and β = - 0.008; 95% CI 0.014 to - 0.003; respectively); (2) delta and alpha oscillations have a direct relationship with higher cortical inhibition; (3) diffuse increased power at low frequencies (delta and theta) are associated with poor cognition, aging, and depressive symptoms; and (4) higher alpha and beta power over sensorimotor areas seem to be a maladaptive compensatory mechanism to poor motor function and severe joint degeneration. Subjects with higher pain intensity and higher OA severity (likely subjects with maladaptive compensatory mechanisms to severe OA) have higher frontocentral beta power and lower theta activity. On the other hand, subjects with less OA severity and less pain have higher theta oscillations power. These associations showed the potential role of brain oscillations as a marker of pain intensity and clinical phenotypes in chronic knee OA patients. Besides, they suggest a potential compensatory mechanism of these two brain oscillators according to OA severity.

Increased motor cortex inhibition as a marker of compensation to chronic pain in knee osteoarthritis

This study aims to investigate the associative and multivariate relationship between different sociodemographic and clinical variables with cortical excitability as indexed by transcranial magnetic stimulation (TMS) markers in subjects with chronic pain caused by knee osteoarthritis (OA). This was a cross-sectional study. Sociodemographic and clinical data were extracted from 107 knee OA subjects. To identify associated factors, we performed independent univariate and multivariate regression models per TMS markers: motor threshold (MT), motor evoked potential (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). In our multivariate models, the two markers of intracortical inhibition, SICI and CSP, had a similar signature. SICI was associated with age (β: 0.01), WOMAC pain (β: 0.023), OA severity (as indexed by Kellgren–Lawrence Classification) (β: − 0.07), and anxiety (β: − 0.015). Similarly, CSP was associated with age (β: − 0.929), OA severity (β: 6.755), and cognition (as indexed by the Montreal Cognitive Assessment) (β: − 2.106). ICF and MT showed distinct signatures from SICI and CSP. ICF was associated with pain measured through the Visual Analogue Scale (β: − 0.094) and WOMAC (β: 0.062), and anxiety (β: − 0.039). Likewise, MT was associated with WOMAC (β: 1.029) and VAS (β: − 2.003) pain scales, anxiety (β: − 0.813), and age (β: − 0.306). These associations showed the fundamental role of intracortical inhibition as a marker of adaptation to chronic pain. Subjects with higher intracortical inhibition (likely subjects with more compensation) are younger, have greater cartilage degeneration (as seen by radiographic severity), and have less pain in WOMAC scale. While it does seem that ICF and MT may indicate a more acute marker of adaptation, such as that higher ICF and MT in the motor cortex is associated with lesser pain and anxiety.

Quantitative Sensory Testing Protocols to Evaluate Central and Peripheral Sensitization in Knee OA: A Scoping Review

OBJECTIVE

This scoping review analyzed various quantitative sensory testing methodologies used in the assessment of sensitization and how sensitization is defined in people with knee osteoarthritis.

DESIGN

A scoping review.

SETTING

All clinical and research settings.

SUBJECTS

Non-surgical adults with knee osteoarthritis.

METHODS

This scoping review was guided by existing scoping review methodologies. Relevant studies were extracted from the following electronic databases: Medical Literature Analysis and Retrieval System Online, Excerpta Medica Database, Allied and Complementary Medicine Database and the Cumulative Index to Nursing Allied Health Literature. Abstract and full article screening and data extraction were performed in pairs. Information on quantitative sensory testing techniques and parameters was extracted and summarized in tables. General and technique specific definitions of sensitization were extracted from included texts.

RESULTS

Our search yielded 4199 articles, of which 50 were included in our review. The most common quantitative sensory test was pressure pain threshold. In total 28 unique testing sites were found speaking to the high degree of variability between studies. Sensitization was poorly defined with only 8 studies fully operationalizing it, 22 partially, and the remainder did not provide sufficient information to meet our criteria.

CONCLUSION

This scoping review has provided an overview of the most common methods of quantitative sensory testing being implemented in the assessment of nervous system sensitization to nociceptive signaling in people with knee osteoarthritis. This study provides a foundation for future development of quantitative sensory testing methodology for research and clinical practice in the osteoarthritis population.

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.

Quantitative Sensory Testing Protocols to Evaluate Central and Peripheral Sensitization in Knee OA: A Protocol for a Scoping Review

BACKGROUND

Quantitative sensory testing (QST) methods have become widely used for the assessment of nervous system sensitization to nociceptive signalling in studies of people with knee osteoarthritis (OA). However, few standardised QST protocols have been developed. Variability in their execution may lead to differences in their interpretation.

OBJECTIVE

The proposed scoping review will seek to identify various QST methodologies being used in the assessment of sensitization and how sensitization is being defined in people with knee OA. Methods and Analysis: This scoping review will be guided by existing scoping review methodologies. Relevant studies will be extracted from the following electronic databases: Medical Literature Analysis and Retrieval System Online, ExcerptaMedica Database, Allied and Complementary Medicine Database and the Cumulative Index to Nursing Allied Health Literature. Independent screening of the abstracts and full articles and data extraction will be performed in pairs. Information extracted will focus on qualitative and quantitative data relevant to the content of the protocols from included studies. Data will be summarised in order to draw conclusions on the common elements used in QST protocols and definitions of sensitization for knee OA.

CONCLUSION

This scoping review will provide insight into the most common methods of QST used in the assessment of nociceptive signaling in people with knee OA. This will potentially identify areas where a systematic review or other primary research may be required in order to develop fixed evidence-based protocols for QST in patients with knee OA.

Comorbidity of Fibromyalgia in Primary Knee Osteoarthritis: Potential Impact on Functional Status and Quality of Life

BACKGROUND

Knee osteoarthritis (OA) is a painful condition with peripheral and central pain transmission. Fibromyalgia (FM) is the role model of central sensitization of pain perception.

AIM

To assess the frequency of FM in knee OA patients and evaluate the impact of FM on mental health and the quality of life in knee OA patients.

PATIENTS AND METHODS

A total of 121 female patients were recruited and divided into 3 groups: group I of 59 patients with knee OA only, group II of 32 patients with knee OA and FM, and group III of 30 FM patients. Patients underwent history taking, examination, investigations, and radiological evaluation of both knees. The assessment of visual analog scale (VAS), Pittsburgh Sleep Quality Index (PSQI), Pain Anxiety Symptom Scale Short Form 20 (PASS20), Beck Depression Inventory (BDI-II), and PCASEE questionnaire were done for all patients. Lequesne index of knee OA and radiological Kellgren and Lawrence score severity were done for all OA patients. Fibromyalgia Impact Questionnaire (FIQ) was assessed for all FM patients.

RESULTS

FM was diagnosed in 35.5% of knee OA patients. Group II patients had higher VAS, PASS-20, PSQI, and lower quality of life than either groups I and III, elevated Lequesne index score than group I, significant correlation between VAS and BMI (p=0.002), Lequesne index score (p<0.001), PASS20 (p=0.006), BDI-II score (p=0.002), and FIQ (P<0.001), and a negative correlation was found between VAS and physical (p<0.001), anxiety (p=0.046), and social (p=0.026) QoL parameters. Univariable regression analysis showed a higher age, VAS, PSQI, PASS20, and FIQ were associated with lower QoL in group II. A higher PASS20 was the only predictor of lower QoL in multivariable analysis.

CONCLUSION

Fibromyalgia coexists frequently in knee OA patients and has implications on their mental health, functional activity, and quality of life.

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.

Spontaneous painful disease in companion animals can facilitate the development of chronic pain therapies for humans

OBJECTIVE

To outline the role that spontaneous osteoarthritis (OA) in companion animals can play in translational research and therapeutic pharmacological development.

OUTLINE

Narrative review summarizing the opportunities and limitations of naturally occurring, spontaneous OA as models of human OA pain, with a focus on companion animal pets. The background leading to considering inserting spontaneous disease models in the translational paradigm is provided. The utility of this model is discussed in terms of outcome measures that have been validated as being related to pain, and in terms of the potential for target discovery is outlined. The limitations to using companion animal pets as models of human disease are discussed.

CONCLUSIONS

Although many steps along the translational drug development pathway have been identified as needing improvement, spontaneous painful OA in companion animals offers translational potential. Such 'models' may better reflect the complex genetic, environmental, temporal and physiological influences present in humans and current data suggests the predictive validity of the models are good. The opportunity for target discovery exists but is, as yet, unproven.

Association of Pain Catastrophizing With Static Balance, Mobility, or Functional Capacity in Patients With Knee Osteoarthritis: A Blind Cross-sectional Study

OBJECTIVE

The aim of this study was to investigate whether catastrophizing is associated with static balance, mobility, and functional capacity in patients with knee osteoarthritis.

METHODS

A blind, cross-sectional study was conducted involving 60 volunteers (males and females), ages 40 to 80 years, with a diagnosis of knee osteoarthritis. Patients were recruited from a physical therapy clinic in the city of São Paulo, Brazil. The following measures were used for the evaluations: Pain-Related Self-Statement Scale, Functional Reach Test, Timed Up and Go Test, Lower Extremity Functional Scale, and Western Ontario and McMaster University Osteoarthritis Index. In statistical analysis, histograms were created to determine distribution of data. Spearman's correlation coefficients (r_s) were then calculated to determine the strength of the associations among the variables.

RESULTS

No significant correlation was found between the Pain-Related Self-Statement Scale score and the other clinical measures employed in the present study: Functional Reach Test (r_s = 0.151; P = .249), Timed Up and Go Test (r_s = -0.147; P =.264), Lower Extremity Functional Scale (r_s = 0.023; P = .860), and Western Ontario and McMaster University Osteoarthritis (r_s = -0.222; P = .088).

CONCLUSIONS

In this study, catastrophizing was not associated with static balance, mobility, or functional capacity in patients with knee osteoarthritis.

Acid-induced experimental knee pain and hyperalgesia in healthy humans

Inflammation and the related acidity in peri-articular structures may be involved in pain generation and hyperalgesia in knee osteoarthritis. This study investigated pain and associated hyperalgesia provoked by infusion of acidic saline into the infrapatellar fat pad. Twenty-eight subjects participated in two sessions in which acidic saline (AS, pH 5) or neutral saline (NS, pH 7.4) were infused into the infrapatellar fat pad for 15 min. Pain intensity, pain area, mechanical and thermal sensitivity, and maximal voluntary knee extension force were recorded. Repeated infusions were performed in 14 subjects. Infusion of AS caused significantly higher pain intensity, larger pain areas, induced hyperalgesia around the infused knee, and reduced extension force. No significant pain facilitation or spreading of hyperalgesia was found after repeated infusions as compared with single infusions. Acidic saline infused into the infrapatellar fat pad provoked pain and localized mechanical hyperalgesia. Thus, this acid-induced pain model may mimic the early-stage responses to tissue injury of knee osteoarthritis.

Vitamin D status and pain sensitization in knee osteoarthritis: a critical review of the literature

Diagnostic imaging of disease severity has been found thus far to be a relatively modest predictor of knee osteoarthritis (OA) pain and disability, suggesting that other factors likely contribute to clinical symptoms in this condition. Recent evidence suggests that sensitization of the peripheral and central pathways that process nociceptive information (i.e., pain sensitization) is an important contributor to knee OA clinical symptoms. Furthermore, low levels of vitamin D have been found to be associated with the presence of pain sensitization, as well as the overall experience of clinical pain severity in knee OA. African-Americans with knee OA may be at increased risk for poor clinical outcomes given evidence of lower vitamin D levels as well as greater pain sensitization compared with non-Hispanic whites. Whether vitamin D supplementation is effective for alleviating knee OA clinical symptoms is an important topic to be addressed in future research with racially diverse samples that include sufficient numbers of African-Americans.

Pain sensitization in people with knee osteoarthritis: a systematic review and meta-analysis

OBJECTIVE

Emerging evidence suggests that pain sensitization plays an important role in pain associated with knee osteoarthritis (OA). This systematic review and meta-analysis examined the evidence for pain sensitization in people with knee OA and the relationship between pain sensitization and symptom severity.

METHODS

A search of electronic databases and reference lists was carried out. All full text observational studies published between 2000 and 2014 with the aim of investigating pain sensitization in humans with knee OA using quantitative sensory testing (QST) measures of hyperalgesia and central hyperexcitability were eligible for inclusion. Meta-analysis of data was carried out using a random effects model, which included results comparing knee OA participants to controls, and results comparing high symptom severity to low symptom severity.

RESULTS

Fifteen studies were identified following screening and quality appraisal. For the meta-analysis, pressure pain threshold (PPT) and heat pain threshold (HPT) means and standard deviations were pooled using random effects models. The point estimate was large for differences in PPTs between knee OA participants and controls [-0.85; confidence interval (CI): -1.1 to -0.6], and moderate for PPT differences between knee OA participants with high symptom severity vs those with low symptom severity (0.51; CI: -0.73 to -0.30). A small point estimate was found for differences in HPTs between knee OA participants and controls (-0.42; CI: -0.87 to 0.02).

CONCLUSION

Evidence from this systematic review and meta-analysis suggests that pain sensitization is present in people with knee OA and may be associated with knee OA symptom severity.