OA has become a major public health challenge, and with the increasing ageing of the global population, this burden is gradually increasing, especially among women . The present study showed that the prevalence of knee OA in pastoralist areas of Xinjiang was 23.1%, significantly higher than in other regions of China. This may be associated with long-term exposure to kneeling or squatting and climbing in patients living in pastoralist areas. Verbeek et al. conducted a meta-analysis of case-control studies of osteoarthritis of the knee and found that exposure to kneeling or squatting, lifting and climbing all had an elevated risk, with a dominance ratio between 1.4 and 1.7 . The pathogenesis of osteoarthritis of the knee in relation to work is not clear, but studies have shown that high knee flexion increases the risk of meniscal damage, which further increases the risk of knee OA . Herders in Xinjiang's pastoral areas graze their livestock between 1500-3600m above sea level for long periods of time and mainly engage in activities such as kneeling, squatting and climbing, which may be the main reason for the high prevalence of OA in herders.
Previous studies have shown that age is a major risk factor for OA pairs[11-12] . The present study also confirms this finding. The prevalence of knee OA increases progressively with age, especially after 40, and is significantly higher in women than in men, although the exact pathogenesis is not known. The increase in adiposity and associated metabolic changes with age can lead to age-related inflammation, a chronic low-grade systemic pro-inflammatory state. Previous studies have shown that osteoarthritis is associated with low-grade systemic and local inflammation, so the chronic low-grade systemic pro-inflammatory state caused by ageing may be involved in the development of osteoarthritis[13-15] . In addition, age-related changes in cellular functions such as: mitochondrial function, ROS levels and alterations in energy metabolism may be involved in the development of OA by interfering with cellular signaling and function . Therefore, further research into the mechanisms of ageing and OA and the development of targeted intervention programmes may help to delay or prevent the onset of OA.
Women have also been recognised as a risk factor for knee OA. The present study also shows that women are an independent risk factor for knee OA, but the underlying mechanisms are unclear. Although the association of oestrogen with osteoarthritis was proposed as early as 1925, there is currently controversy regarding the association of oestrogen with osteoarthritis. Some studies have suggested that oestrogen can inhibit type II collagen catabolism, enhance glycosaminoglycan synthesis, antioxidant effects and reduce metalloproteinase synthesis involved in cartilage protection[17-19] , while other studies have shown that oestrogen has the potential to increase chondrocyte apoptosis through other studies suggest that estrogen is involved in the development of osteoarthritis by increasing chondrocyte apoptosis, inhibiting proteoglycan synthesis, increasing pro-inflammatory factors, and increasing metalloproteinase synthesis and cartilage destruction[20-25] .
The present study shows that BMI is an independent risk factor for knee OA, which is consistent with the findings of previous studies[26-27] . It is now generally accepted that obesity is associated with the development of knee OA and that increased abnormal loading of weight-bearing joints is a major factor in the progression of knee OA, and a recent population-based cohort study conducted in the Netherlands also showed that obesity-related mechanical stress is the most important risk factor for osteoarthritis of the knee . Obesity can also be involved in the pathogenesis of OA through inflammatory pathways. Studies on the etiology of obesity-associated arthritis in animal models generally agree that inflammation is the main cause of obesity-associated arthritis, and Larranaga Vera A et al showed that high fat diet induced synovial lipodystrophy increased synovitis in osteoarthritis in mice[29-31] . A homogeneous diet with a high intake of meat products and high calorie intake in Xinjiang pastoral areas may contribute to the high prevalence of knee OA.
In addition to the above factors, coronary heart disease and hypertension were found to be independent risk factors for knee OA in this study. Up to now some studies have suggested an association between OA and atherosclerosis-related diseases, and some common co-pathogenesis of osteoarthritis and cardiovascular disease, such as fat metabolism and the innate immune system have been suggested . A meta-analysis showed that one or more of these co-morbidities or other chronic diseases, such as diabetes or cardiovascular disease, predicted a worse prognosis for OA . However, the exact mechanisms need to be further explored.
The effects of smoking and alcohol consumption on knee OA have been controversial. Some studies have shown that smoking prevents the development of osteoarthritis and reduces chondrocyte catabolism when nicotine concentrations are close to those of smokers, thus suggesting that smoking may have a protective role in the development of OA[34-36] , but some studies have concluded that smoking is not relevant in osteoarthritis of the knee . Some studies have suggested that alcohol consumption is a protective factor for osteoarthritis of the knee[38-39] . However, some clinical studies have found a significant association between excessive alcohol consumption and OA, while low and moderate alcohol consumption is not associated with the development of knee OA . This study did not find a correlation between smoking and alcohol consumption and knee OA. This may be related to the low prevalence of smoking and alcohol consumption in the local population, and the fact that smoking and alcohol consumption were not quantified in this study may lead to some discrepancies in the findings.
Limitations of the current study: this is a cross-sectional study and cannot show the causal link between influencing factors and the disease; secondly, this survey was only conducted in Bozidun Township, Xinjiang region, and a large scale survey study is still needed to investigate the overall disease situation and its influencing factors in other pastoral areas of Xinjiang.
It is clear from this survey that the overall prevalence of knee OA in the pastoral areas of Xinjiang is significantly higher than in other provinces of China, with an increasing trend in prevalence with age and a higher prevalence in females than in males, where factors such as age, female, obesity and pastoralists may be related to the onset of knee OA.