Please describe these protruding bones under my knee caps?

Tibial tuberosities; Part of the leg bone (tibia) these are prominences where the patellar tendon {tendon connecting the knee c to the leg bone, to move the leg into extension (ie to straighten it)}. Sometimes in growing kids they enlarge from too much activity and be painful. They remain enlarged forever then. The condition is called osgood-schlatter disease.