Can a twisted ankle be the cause of swollen lymph nodes in the groin?

Not usually: Groin nodes enlarge when the body is trying to clear an inflammation or infection of the limb they drain. An ankle sprain could causes unilaterally swelling (one side only). But one must rule out another cause first (infection particularly) before attributig it t an ankle injury.

Doubtful: After obtaining a medical history, examination and any needed studies - your physician may be able to shed more life on your inguinal lymphadenopathy.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells/digested food. Lymph nodes "taste" the lymph everywhere for bad stuff like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.