Hallux valgus arises from an inherited predisposition to instability at the first metatarsophalangeal joint, on which mechanical factors — including footwear and biomechanical conditions such as flatfoot deformity — then act to accelerate progression. Footwear alone is rarely the underlying cause.
None — the terms describe the same condition. "Bunion" is the common name for the visible prominence; hallux valgus is the clinical term describing the underlying joint deformity that produces it.
No. Deformity grade, symptom severity, and rate of progression — not the presence of a bunion alone — determine whether surgery is appropriate. Many cases are managed effectively with non-surgical measures, particularly where the deformity is mild and symptoms are intermittent.