by Tracey Kellett, Online Health Advisor
More research needs to be done to better understand the difference between men and women with Osteoarthritis (OA). While there is no simple answer, several factors contribute to the disparity between the sexes, including life expectancy, hormones, joint shape (anatomy), body weight and genetics.
First, what is OA? Do you know someone with OA? Does sex have anything to do with your risk of OA? The NZ Health Survey tells us that an estimated 63% of those living with OA are women. What we couldn’t find was any information on gender-diverse people. The recent Waikato University Counting Ourselves health and well-being survey of trans and non-binary people did not collect data on medical conditions, so we can only compare the numbers of males and females.
Osteoarthritis is often referred to as ‘osteo’, ‘degenerative’, or ‘wear and tear’ arthritis. However, Dr Daniel O’Brien, senior lecturer in physiotherapy at AUT, says that none of these terms fully reflect the complexity of the disease. OA can affect most joints of the body but is usually found in the knees, hips, hands, feet and spine. The disease is characterised by the loss of cartilage in the joints, but it also affects the bone, ligaments, muscles and nerves around the joint. OA can affect all aspects of a person’s wellbeing or hauora and carries a significant health burden. Research shows that women are far more likely to be affected by OA as they get older, with women over the age of 65 almost twice as likely as men to have OA.
A 2005 meta-analysis (a type of study that reviews already-published research in this area to see if there is a consensus) of sex differences found differences in osteoarthritis sites of the body. They found greater incidence and prevalence of hand and knee OA and greater incidence of hip OA in women. Men under 55 had a greater risk for the prevalence of cervical spine OA.
Research has also shown that women sometimes experience more pain with OA than men. Although the difference in experiences of pain may not be so significant once certain pain behaviours that differ between the sexes are taken into account. However, there is research showing greater experiences of knee pain and research showing more severe radiographic knee OA, possibly supporting the pain differences experienced.
So, back to the question – why is OA more common in females?
Life expectancy
Dr O’Brien points out one simple answer: in Aotearoa New Zealand, like most places in the world, on average, women live longer than men. The likelihood of developing OA goes up as we age, so as women live longer, they are more likely to develop the condition. However, other factors leading to the discrepancy between the sexes are a little more complex.
Hormones
Women’s hormones change during menstruation and menopause, and there is evidence that hormones play a factor in the difference between rates of OA in women and men.
Sex differences in knee cartilage volume have been found to be greater after 50 years of age, suggesting a possible involvement of hormones. Differences in the prevalence of knee and hand OA after 55 years of age further suggest a role of menopause in OA development.
An analysis of 606 women post-menopause from the London Chingford Study found that Hormone Replacement Therapy (HRT) may have a protective effect against developing OA in the knee and hands. There is conflicting evidence, so no conclusions can be made about using HRT and OA yet; more research needs to be done in this area. Men were found to have more prevalent spine degradation over the age of 55, highlighting that although estrogen may have a modulating effect on risk factors, hormone-related effects are still poorly understood, and there may be other factors accounting for differences between the sexes and at different life stages.
Previous joint injuries
Injuries to joints are a significant risk factor for developing OA. One characteristic that is associated with increased injuries to joints is laxity. The difference between the sexes has been demonstrated in the knees, where laxity increases and decreases with the normal hormone fluctuations of the menstrual cycle. Joint laxity doesn’t appear to change in men. Researchers have linked knee joint laxity with the increased rate of anterior cruciate ligament (ACL) injuries in female athletes. People with a past ACL injury are about 4-6 times more exposed to developing knee OA. This is a rapidly –developing area of research.
Weight
Being overweight or obese is one of the most significant risk factors for OA in women and men. Being overweight can contribute to the development of OA in two main ways: Firstly, being heavier can lead to excessive joint loading, which can contribute to joint damage. Secondly, having a higher percentage of body fat can increase our susceptibility to inflammation within the body. Inflammation is part of the OA disease process. The latest New Zealand Health Survey shows that 36% of women are obese compared with 33% of men. And importantly, weight reduction can reduce the risk of symptomatic knee OA.
Anatomy
Dr. O’Brien says that the shape of our joints and the strength of the muscles supporting them can affect how likely we are to develop OA.
The way women tend to walk, run, and stand is affected by the difference in anatomy compared to men. The hips being wider than the knees puts more stress on the knees, which can cause OA over time in some women. One study found that the bony surfaces of females’ knees don’t fit together or move together as well as male’s. This may put more strain on the joint, resulting in more wear and tear.
Muscles move our joints and help to protect them from injury. Greater muscle strength has been associated with less symptoms for people with knee OA. On average, men have stronger muscles than women, which may have a protective element for them.
Shoes
A study looking at heeled shoes, typically worn by women, concluded that even 1.5-inch (3.8 cm) heeled shoes significantly alter knee joint forces that are related to the progression and development of OA. The researchers recommend that women avoid wearing these shoes, especially those with OA.
Genetics
When being diagnosed with OA, it is common to be asked about your family history, especially the experiences of mothers and grandmothers. OA may also affect women more so if they have female relatives who have it. Even the lubricant in joints (synovial fluid) differs between sexes. A study published in 2017 found that differences exist between male and female genetic expression of synovial fluid in the knee. They found that female synovial fluid in advanced OA has a much larger amount of genetic material differentially regulated than males and that the genetic material is involved in the estrogen signalling pathway and in joint-friendly processes. There is ongoing research on the genetic expression of both males and females as a possible way to slow down OA development.
Summary
The reason more women than men live with OA is multifactorial and complicated. Some factors, such as age, anatomy and genetics, are outside our control. But some factors are modifiable, to some extent, such as muscle strength and body weight. Visit our MyJointPain website for a comprehensive, individualised OA pain management plan.
Review and contributions by Dr Cathy Chapple, Senior Lecturer of physiotherapy, Otago University & Dr Daniel O’Brien, Senior lecturer of physiotherapy, Auckland University of Technology.
