What Is The Name Of The Surgery Involving Rod Insertion For Severe Right Hip Osteoarthritis?

my son was diagnosed with bad right hip osteoarthritis. it is recommended for surgery. not hip replacement, but insertion of a rod. what is this procedure called? he is a 49 yr old male, active at the gym. works out daily. has had thigh/femur pain and lower right upper buttock pain for about 1 yr. what is the procedure the orthopedic surgeoun is recommending? its not hip replacement.