Musannaf Ibn Abi Shayba 18:442

Abu Bakr narrated to us, he said: Muhammad bin Bakr narrated to us, from Ibn Jurayj, he said: Ibn Abi Najih informed me, from Mujahid, he said: If the spine is injured or broken and it is set, and his semen is cut off, then the full blood money (diyah) is due. And if the semen is not cut off, and there is a curvature in the back, then he (the judge) shall exercise his discretion regarding it.