Eun Y, Yoo JE, Han K, et al. - The relationships between reproductive factors and joint replacement arthroplasty of the knee (TKRA) and hip (THRA) were investigated in a large nationwide population-based cohort study of 1,134,680 postmenopausal Korean women who participated in national health examinations in 2009.

• A total of 1,610 incident THRA cases and 60,670 incident TKRA cases were recorded during a median follow-up period of 8.2 years.

• Increased risk of TKRA for severe knee OA was observed in correlation with later age at menarche, longer breastfeeding, HRT and OC use, while there was a decreased risk in correlation with later age at menopause and longer reproductive span.

• With regard to THRA for severe hip OA, higher risk was recorded in correlation with later menarche, longer breastfeeding, HRT more than 5 years, and OC use more than 1 year.

• Overall, findings suggest correlation of shorter estrogen exposure with higher risk of TKRA due to severe knee OA.

• The associations were noted to be more pronounced in underweight and younger individuals.

• No robust association could be demonstrated between shorter estrogen exposure and THRA.