Hallux rigidus is when the big toe (the hallux) joint is excessively rigid than it should be. As the joint becomes stiffer, it becomes more painful and affects the way you walk. The most common cause is osteoarthritis and is generally painful. Treatment is typically directed at medications. https://podiatryfaq.com/knowledge-base/what-is-the-difference-between-hallux-rigidus-and-hallux-valgus/