Protocol for a randomised, placebo-controlled, double-blinded clinical trial on the effect of oestrogen replacement on physical performance to muscle resistance exercise for older women with osteoarthritis of knee joint: the EPOK trial

Background: Knee osteoarthritis (KOA) is highly prevalent in older women, and previous studies suggest the involvement of hormonal factors play a role in the pathogenesis of osteoarthritis. KOA causes musculoskeletal impairment, resulting in decreased physical activity, muscle mass, and strength, which leads to sarcopenia and further increases the burden on healthcare systems. Oestrogen replacement therapy (ERT) improves joint pain and muscle performance in early menopausal women. Muscle resistance exercise (MRE) is a non-pharmacological method that preserves the physical functions of patients with KOA. However, data on short-term oestrogen administration combined with MRE in postmenopausal women, especially in those aged > 65 years, are limited. Therefore, this study presents a protocol of a trial aimed to examine the synergistic effect of ERT and MRE on lower-limb physical performance in older women with KOA. Methods: We will conduct a double-blinded, randomised placebo-controlled trial in 80 Japanese women aged > 65 years living independently with knee pain. The participants will be randomly categorised into two groups: (1) 12-week MRE programme with transdermal oestrogen gel containing 0.54 mg oestradiol per push and (2) 12-week MRE programme with placebo gel. The primary outcome measured using the 30-s chair stand test, and secondary outcomes (body composition, lower-limb muscle strength, physical performance, self-reported measure of knee pain, and quality of life) will be measured at baseline, 3 months, and 12 months, and these outcomes will be analysed based on the intention-to-treat. Discussion: The EPOK trial is the first study to focus on the efficacy of ERT on MRE among women aged > 65 years with KOA. This trial will provide an effective MRE to prevent KOA-induced lower-limb muscle weakness, confirming the benefit of short-term oestrogen administration. Trial registration: Japan Registry of Clinical Trials: jRCTs061210062. Registered 17th December 2021, https://jrct.niph.go.jp/en-latest-detail/jRCTs061210062.