He had a car accident and damaged his cervical vertebrae, paralyzing him from the neck down
素早い回復を願います。
質問者様のお求めの英語は「He had a car accident and damaged his cervical vertebrae, paralyzing him from the neck down」になります。
首から下は「From the neck down」と言います。
動けなくなることは「Paralyze」されると言います。