Study of 31,265 Twins Finds More Knee Arthritis in Women

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Researchers in Sweden used the largest registry of twin siblings in the world to identify the differences in the etiology of knee osteoarthritis (OA). Their study, “Nature vs nurture in knee osteoarthritis – the importance of age, sex and body mass index,” appears in the April 2019 edition of Osteoarthritis and Cartilage.

Co-author Karin Magnusson, Ph.D., P.T., post doc in the Clinical Epidemiology Unit, Orthopedics, Department of Clinical Sciences at Lund University in Sweden, explained the rationale behind her study, “Familial factors such as genetics and body weight are well-known risk factors for knee OA for men and women. However, the association between the genetic contribution to knee OA and body weight for men and women across the life span had not been previously studied.”1

“Also, patients generally are convinced that their OA has genetic rather than lifestyle causes. This strong belief may prevent patients from changing behavior to reduce their symptoms although we know that weight reduction reduces knee pain.”1

The study included 10,092 identical and 21,153 non-identical pairs of twin siblings with a follow-up period off 27 years.

“By studying the largest twin registry in the world, including more than 60,000 identical and fraternal twins, we observed that the genetic contribution to having arthroplasty due to knee OA, was stronger for women than for men. In women, the genetic contribution was high, around 80%, from age 50 independent of body mass index. In men the genetic contribution was relatively low (50%) and varied with age and body mass index.”1

“The differences in genetic contribution across age for men and women provide new insights into the etiology of severe end-stage knee OA. It can be hypothesized from our results that mainly non-shared, individual factors account for knee OA surgery in men up to age 68, with examples of causes being knee injury and/or individual adult lifestyle or occupational factors not shared by the twins.”1

“For women, our results imply genetics is of great relevance in the etiology of knee OA, however, we cannot exclude the relevance of shared hormonal factors related to the menopause, which should be further studied. Health practitioners should be aware of these potential sex differences in the etiology of knee OA and encourage both men and women to maintain a healthy body weight.”1

“Our study shows that the interaction between genetics and lifestyle factors in knee OA is complex and dependent on age and sex. We would like orthopedic surgeons to know that although knee OA may be highly genetically driven at least for women and for older men, this does not exclude any preventive effect of keeping a healthy body weight.”1

The study sheds light on the interesting differences between men and women who experience knee osteoarthritis and should be considered as new treatment methods for the disease develop.

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  1. Hofheinz, E. (2019, April 23). 31,265 Twins Study Finds More Knee Osteoarthritis in Women. Retrieved December 11, 2019, from
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