Hallux rigidus is when the big toe (the hallux) joint is more rigid than it should be. As the joint gets stiffer, it can become more painful and impairs the way you walk. The primary cause is arthritis of the bones and is almost always painful. Treatment is typically directed at pharmacological interventions. https://podiatryfaq.com/knowledge-base/what-is-the-difference-between-hallux-rigidus-and-hallux-valgus/