This study aimed to analyze the external factors associated with the prevalence of OA in the Brazilian population with a description of 60,202 individuals as assessed by the PNS in 2013. The results showed that most of the analyzed outcomes showed significant associations with the prevalence of OA, with greater representation in the female gender, in the middle-age range, performing less habitual activities and having poor self-perception of health.
The OA prevalence in this study was similar to that found in the National Household Sample Survey (PNAD)[17] in 2008, in which arthritis or rheumatism ranked third among chronic conditions, second only to arterial hypertension and back diseases[12]. This fact was also confirmed in a recent study[18].
Variables such as gender, age and weight are individual factors which are widely described in the literature[19–21]. Most studies confirm the prevalence of OA with a two-fold increase for women compared to men[22, 23] and at older ages[24], similar to what was found in this study. This fact may be linked to hormonal issues, especially when it occurs in middle age around 50 years, in which women go through the climacteric and menopause process and are more exposed to metabolic and joint disorders due to the decrease in the estrogen hormone[25, 26]. Another aspect which may be associated is the volume of articular cartilage, which is considerably lower in women[27]. Regarding age, it is known that the aging process generates a natural and progressive wear on the structures which compose the joints, leading to physical and functional consequences of individuals, as in osteoarthritis[24]. Such a progressive effect was confirmed by the gradual increase in the prevalence of OA with increasing age.
It was also observed in this study that OA showed a gradient of increasing prevalence of association with BMI. This finding is supported by a systematic review, which found a positive risk of high BMI for OA in all 36 studies which were part of the review[28]. Among the modifiable factors, it is known that overweight and obesity cause mechanical overload on the joints which support the body, especially the knees and hips, which are normally the most affected regions[29]. However, another study showed that the relationship of obesity in OA is beyond the biomechanical cause, showing that there is a direct influence of metabolic and inflammatory aspects that are present in these cases[30].
Although it was confirmed in this study that OA was strongly associated with the female gender, advanced ages and body weight above the ideal limits (other variables little discussed so far) also presented relevant results. It was observed that failure to perform habitual activities in the internal environment, such as domestic services and external activities such as going to work or shopping are associated with a higher prevalence of OA. This fact may be related to sedentary behavior and the consequent disuse of muscles and joints, which may accelerate the tissue degeneration process due to muscle weakness and immobility. On the other hand, after adjusting the multivariate model, lower practice of physical activity became a factor associated with the decrease in the prevalence of OA; although this decrease is small (around 7%), it is believed that such an attitude is associated with a protective factor assumed by individuals who already have OA and therefore they avoid practicing physical activity for fear of generating more pain and then is the consequence of low adherence of these individuals to regular physical activity programs.
The prevalence of OA was associated with a greater presence of comorbidities. According to a study[18], hypertension, diabetes, kidney problems and depression stood out as the most frequent. The latter was also associated with a higher prevalence of OA in the Brazilian population, suggesting that the multifactorial impact of the disease may influence mental health.
The self-perception of the limitation degree shows a high level of agreement with the individual’s clinical condition[31]. In a study which classified the limitation degree as intense or very intense for habitual activities in chronic diseases, OA occupied the third position behind mental illness and stroke sequelae[11]. This fact reveals a general concern for society, as there is a general increase in the limitations of habitual activities in chronic diseases due to the reduced functional capacity and little knowledge about diagnostic and treatment methods. This generates a relevant social and economic impact[32].
The individual’s perception of feeling sick is not just a result of physical sensations, but of the social and psychological consequences of the disease[33]. The self-perceived health assessed in this study showed a strong concentration gradient for the categories bad and very bad, corroborating with a study[34] which evaluated the impact of osteoarthritis on the ability to work and activities of daily living, and showed a strong association with worse physical health; it is also related to reports of pain at higher levels.
Among the associated factors, age and gender target groups are at greater risk for developing this chronic condition and therefore need strategic health promotion actions and preventive measures such as screening for early diagnosis of this condition. However, modifiable factors should be considered such as overweight and poor health perception, as these factors can be changed or minimized through specific strategic and political actions, since they are not purely individual or biological factors, but involve a variety of health determinants and conditions. In addition, a sedentary lifestyle and immobility suggest isolation and consequent diagnosis of depression, making supportive measures relevant for greater social participation and physical activity.
In this study we can see that other factors are involved in OA, however the cross-sectional study design limits the analysis because it does not enable for an inference of reverse causality. Another limitation in this study was the diagnostic method adopted in this study following the PNS assessment instrument, in which it does not differentiate the type of arthritis or rheumatism pointed out by the interviewee. In addition, it would be pertinent to investigate other conditions and characteristics of the population with this disease, such as knowledge about the disease and measures used for treatment. Thus, it is suggested that prospective studies be developed to better manage cases and reduce the magnitude of social impacts on the lives of people with OA observed in this study.