It is estimated that knee osteoarthritis (OA) affects around 23 per cent of the global population aged 40 years and over, with the individual lifetime risk for symptomatic knee OA as much as 45 per cent. 

Knee OA is a leading cause of disability that also comes at a high cost; in Australia, $3.5 billion is spent annually on treating it and it results in a yearly productivity loss of $424 billion. 

Identifying its potential risk factors is a priority for researchers looking at preventive measures. 

Dr Vicky Duong APAM is a physiotherapist and researcher at the Kolling Institute in the Faculty of Medicine and Health, University of Sydney; and Associate Professor Christina Abdel Shaheed is a pharmacist and researcher based at the School of Public Health, University of Sydney. 

They were keen to discover what new data is available on the risk factors for knee OA by carrying out what they believe is the largest systematic review and meta-analysis of research from across the globe. 

‘Many of the previous reviews would focus on one risk factor and collate the evidence solely on that factor,’ says Christina. 

‘But when we looked at the area closely, we noticed that there hadn’t really been one review that brought together all the possible risk factors for developing knee OA.’ 

Seven electronic databases and three registries were searched for longitudinal cohort studies or randomised controlled trials that evaluated participants for incident symptomatic and/or radiographic knee OA. 

More than 150 risk factors were identified in 131 studies, with data then ranked according to the certainty of evidence using GRADE (Grading of Recommendations, Assessment, Development and Evaluation). 

‘Rather than randomised controlled trials, most of the data in the systematic review was based off cohort studies, where they follow people who don’t have knee OA over a really long time and try to see what sort of risk factors could lead to them developing knee OA,’ says Vicky. 

‘It’s much easier to address this sort of research question in the cohort study type, either retrospectively or prospectively, than in a randomised controlled trial due to feasibility issues of time and cost.’ 

Vicky and Christina’s analysis identified, with moderate to high certainty of evidence, that overweight/obesity, previous knee injury, higher femoral neck and lumbar spine bone mineral density and occupational physical activity are associated with an increased risk of incident radiographic knee OA. 

There was also low to moderate certainty of evidence of female sex and older age being associated with an increased risk of incident knee OA. 

While activity is known to help alleviate the symptoms of knee OA, an interesting finding was that it depends on the kind of activity. 

‘When we separated out the types of physical activity, categorising them into leisure time and occupational physical activity, we found that the latter, such as doing shiftwork for more than 20 years or heavy manual handling, increased the risk of knee OA considerably,’ says Christina. 

‘Although the evidence was not strong, so this is an important area for future research.’ 

Their findings illustrated that there are ways for people to lower their risk of developing knee OA. 

‘We found the things that were helpful were a Mediterranean diet, a diet high in fibre, healthy cereals and for men— not for women, apparently—drinking four cups of green tea a day,’ says Christina. 

Click here to read the research.