The big toe joint is stiff and painful, limiting its ability to bend.
Because this condition is rated as severe hallux valgus, the evidence that matters most is whatever shows your big toe meets that level of severity. Medical records documenting the degree of stiffness or rigidity at the metatarsophalangeal joint are central. X-ray findings showing structural changes at the joint can support a severe characterization. Range-of-motion measurements from a VA or private examination showing significantly restricted movement help establish how limiting the condition is. Your examiner's clinical findings about pain, gait disturbance, and weight-bearing difficulty are also relevant. Statements from you or people who observe you daily — describing how the stiffness affects standing, walking, or work tasks — can round out the picture of functional loss tied to the severity criteria.
Conditions that are often caused or made worse by this one. If you have any of these, they may be claimable as secondary service connection.