What could cause a swollen lymph node in the groin area when there is no infection in the body?

Leg trauma: Enlarged inguinal lymph nodes are very common and related to the multiple minor injuries, cuts and scratches for example, that we get on the legs all the time. The nodes should not be tender and should not be bigger than about 1 cm in size. Pain, redness, progressive enlargement, or size over 1 cm should be evaluated by a doctor.

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.