Hallux rigidus is a condition where the big toe (the hallux) joint is excessively rigid than it should be. As the joint becomes stiffer, it can become more painful and impairs the way you walk. The primary cause is osteoarthritis and is generally painful. Treatment is usually directed at medications. https://podiatryfaq.com/knowledge-base/what-is-the-difference-between-hallux-rigidus-and-hallux-valgus/