I say, and with God's success: It is not a condition to tighten the splint while in a state of purity; to avoid hardship, and because wiping over the splint and similar items is like washing what is underneath it, it is not a substitute; because it is conditioned by the inability to wipe the actual place or wash it, unlike wiping over the socks, which is only permissible if they are worn in a state of purity. Refer to: Maraqi al-Falah and the commentary of al-Tahawi on it, pages 136-137, and 'Umdat al-Ri'ayah 1: 119, and Sharh al-Wiqayah page 120, and al-Hadiyyah al-Alaiyyah pages 42-43, and Nihayat al-Murad page 400, and God knows best.