Hallux rigidity 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 affects the way you walk. The primary cause is arthritis of the bones and is generally painful. Treatment is typically directed at pharmacological interventions. https://podiatryfaq.com/knowledge-base/what-is-the-difference-between-hallux-rigidus-and-hallux-valgus/