You should be able to walk with the new rod in situ although you will need crutches for the 1st few weeks and ultimately your surgeon should tell your how much weight he is happy for your to put through the leg. If you are simply having a rod exchange and not open bone grafting
then the pain should be less severe than after your surgery to treat your initial fracture
. Ask your surgeon about a femoral nerve block
or epidural to help with the pain post op.