Correction to: The effect of mobile-app-based instruction on the physical function of female patients with knee osteoarthritis: a parallel randomized controlled trial - Seyed Sajad Arfaei Chitkar; Hamid Reza Mohaddes Hakkak; Hassan Saadati; Seyed Hamid Hosseini; Yasaman Jafari; Reza Ganji (BMC, 2021)