Pain in the groin often originates from the hip joint itself but may also come from other processes including nerve compression, and some internal problems. It is possible that due to the knee surgery your gait has been altered in a way that it is increasing the forces on your hip now causing you to expereince the pain, but you should speak to your orthopedist concerning this new complaint.
About Clifton Bingham, III, MD
Professor of Medicine
Director - Johns Hopkins Arthritis Center