Welcome to health care magic.
1.The history suggest the possible cause of the lesion at the site of the previous
injury could be infective collection.
2.Though there is no history mentioned about pain or
fever infective aetiology to be ruled out.
3.Other possible cause could be lipomatous lesion - fat content.
4.The
Ultrasound examination is the investigation of choice in this case, ultrasound will help to evaluate the nature of the lump,its source and extensions.
5.First thing one has to examine the lump, i do not think there is much to worry as there is no pain on touch.
Good luck.
Hope i have answered your query,
any thing to ask ? do not hesitate to ask.
http://doctor.healthcaremagic.com/doctors/dr-ganesh/62888