What should a man do who abandoned prayer, was afflicted by an accident that rendered his knee immobile, and now wishes to return to prayer, knowing that he performed ghusl from janabah without observing the sunnah of ghusl?

Neglecting prayer is one of the major sins. The one who abandons it must offer sincere repentance and perform ghusl (definition) if they are in a state of ritual impurity (junub). The obligatory ghusl suffices by pouring water over the entire body. As for their inability to bend their knee, they should pray according to their condition, and what they are unable to do is waived for them. They should gesture for prostration if they are unable to perform it. Regarding the obligation to make up prayers that were intentionally missed, making them up is obligatory, and this is the view of the majority of scholars.