Dear Editor,

Here, we reply to the letter to the editor about our study [1]. As pointed out, the original article written by Ueno [2], which we cited, does not define the threshold value of joint space width for classification. However, the original article was written in Japanese, and Takatori et al. [3] translated it to English. Additionally, Takatori et al. [3] recommended the modified staging classification in this translated article. It was recommended that the classification criteria should involve the joint space width in order to divide stage 2 (early stage) and stage 3 (advanced stage). Clinically, the classification of hip osteoarthritis is often used as a modified version, but a unified consensus has not yet been reached by the Japanese Orthopedic Association (JOA) Committee. In our study, we used the modified classification. However, we made an incorrect citation and should have cited the translated article by Takatori et al. with the modified classification in addition to the original article by Ueno. Therefore, our citation misled the reader and caused confusion to the authorized people of JOA. We would like to take this opportunity to apologize and correct the citation.