The Contribution of Age and Obesity to the Number of Painful Joint Sites in Individuals Reporting Osteoarthritis

A Population-Based Study

Elizabeth M. Badley; Jessica M. Wilfong; Calvin Yip; Dov B. Millstone; Anthony V. Perruccio

Disclosures

Rheumatology. 2020;59(11):3350-3357. 

In This Article

Abstract and Introduction

Abstract

Objective: To investigate the association of OA risk factors with number of painful joint sites in a representative population sample.

Methods: Analysis of the 2009 Survey on Living with Chronic Diseases in Canada – Arthritis Component (n = 1614) for respondents reporting symptomatic OA. Variables: painful joints sites (hands, wrists, elbows, shoulders, hips, knees, ankles, feet, back, neck), joint symptom duration, sociodemographic characteristics, smoking, comorbidities and BMI. Zero-truncated negative binomial regressions were used to investigate the association between number of painful joint sites and the variables. Generalizability of findings was assessed by a similar analysis in a clinical hip/knee OA sample.

Results: The sample comprised 73% women and 56% were aged <65 years. The mean number of painful joint sites was 3.8: 84% reported pain at ≥2 sites, and 45% at ≥4 sites. Age, BMI, education and smoking were not associated with the number of joint sites. Significant associations were found with being female [rate ratio (RR) = 1.23, 95% CI 1.09, 1.39], having more comorbidities (RR = 1.11, 95% CI 1.07, 1.15) and longer symptom duration (RR = 1.16, 95% CI 1.09, 1.24), although the increase in joint sites with duration was small. Similar regression results were found with the clinical OA sample.

Conclusion: The lack of an association of age and BMI (obesity) with number of painful joint sites in OA raises questions about the role of these risk factors and our understanding of OA as a multi-joint disease. Filling this knowledge gap is critical to making progress with defining OA phenotypes and identifying potential aetiological mechanisms.

Introduction

OA is one of the most frequently reported chronic physical health conditions, characterized by pain and stiffness in the joints, and a major cause of disability.[1–3] Medical care use data suggests upwards of 10% of the population has symptomatic OA.[4,5] Most research on OA, both clinical and epidemiological, focuses on a single joint site regardless of whether other sites are affected. The knee is overwhelmingly the most studied joint, followed by the hip and hand.[6] OA in other joints, including the spine, has received very little attention.

Multiple joint OA (MJOA) is often referred to as generalized OA (GOA), a term first proposed by Kellgren and Moore.[7] A recent systematic review of literature published from 1952 to 2017 found only 30 eligible studies that included a clear definition of MJOA and found little consensus between study definitions.[8] Hand joints were included in the definition of MJOA in all but two of the 27 studies that included specific joints in their definition, and all but four specified the knee. Other joints were less consistently included. As can be inferred by the small number of papers meeting criteria for this review, MJOA is not well characterized either clinically or epidemiologically.

Despite general recognition that OA can affect multiple joints, relatively few studies have reported on the frequency of MJOA in representative population-based samples. A study of adults aged ≥50 years surveyed with a joints homunculus indicated that more than half had joint pain consistent with OA, of whom 70% reported pain at two or more joint sites (out of seven).[9] Similarly, a community survey showed 39% of the population aged >55 years reported joint pain, of whom 80% reported pain in two or more joints out of eight sites.[10] European clinical studies of patients with OA have shown that >50% of patients had OA at multiple joint sites.[11,12] Finally, analysis of data from the Osteoarthritis Initiative (OAI) and Multicenter Osteoarthritis Study (MOST) population-based cohort studies of knee OA showed that 79.6% of those with bilateral knee pain, and 63.8% of those with unilateral knee pain had pain in other joints.[13] While generally neglected, the impact of having MJOA is considerable. No matter how it is defined or what outcomes are considered, clinical and community studies that have investigated the impact of having multiple joint vs single joint OA consistently show a more negative impact for MJOA with greater disability and reduced quality of life.[8,10,14–17]

It is surprising, particularly given the high prevalence and impact of MJOA, that there have been few previous studies of the risk factors for having pain at multiple joint sites. A Canadian survey of a representative sample of people with self-reported OA, including sites of painful joints, provided us with the opportunity to study this. Age, sex, education (as an indicator of socioeconomic status), smoking and BMI are established risk factors for OA.[1–3] These are also risk factors for many chronic conditions that are associated with OA.[18] Our assumption was that risk factors for OA generally and at individual joint sites would also be risk factors for a greater number of painful joints in OA.

In particular, we hypothesized that increasing age and higher BMI would be associated with a higher number of painful joints sites in OA. Separate epidemiological studies of knee OA, hip OA and hand OA have consistently reported that the prevalence of these conditions increases with age.[19,20] Given this, it seems likely that the probability of having OA in two or more of these joints should also increase with age. Overweight and obesity are well-established risk factors for OA, particularly the knee,[21–23] but also to a lesser extent for the hip and hand.[24–26] Indeed, the association of obesity with OA at the hand, a non-weight-bearing joint, has contributed to the developing body of literature suggesting that OA might have a metabolic component.[27–29] In addition to a mechanical contribution to knee OA,[21,30,31] a postulated mechanism for the role of obesity in OA is that adipokines released by adipose tissue act as systemic inflammatory mediators that cause a low-grade inflammatory state involving damage to joints and other tissues.[32] If this is a mechanism associated with obesity and OA, one might speculate that the inflammatory processes would affect all joints and that MJOA should be more frequent in overweight or obese individuals. Therefore, the purpose of this study was to investigate the association of OA risk factors, including age and obesity (BMI), with the number of sites of symptomatic joint pain in a representative sample of the population with self-reported OA.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....