Hallux rigidity is when the big toe (the hallux) joint is excessively rigid than it should be. As the joint gets stiffer, it becomes more painful and impairs 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/