I had fracture pelvis near the hip joint sincr one year and till noe I have loew backache and bilateral knee joint pain what is the causes and treatme?

Pain after pelvis fx. I would suspect other injuries. You are young, and it takes a good deal of trauma to fracture a young pelvis. Proper evaluation would require xrays of the spine and pelvis at the time of injury, and likely repeat xrays now due to continued pain. You may have injured your sacrum, iliosacral ligaments, sacroiliac joints, etc. Energy that fractures the pelvis can also be transferred through knees.
Cause of fx. Hard to say. Walking differently because of pain will cause back and knee pain.