The main risk of hip replacement or hip surgery is Blood Clots that can form in the veins of your legs after hip surgery.
The blood clot becomes dangerous because it can break off and travel to your lungs, heart and even sometimes but rarely can travel to your brain.
Other less severe complications of hip surgery are infections of the joint, joint dislocation and even uneven leg length as in one leg may be shorter than the other leg but only by a little bit.
Joint replacement surgery is pretty safe and rarely do people experience any complications especially severe complications after hip surgery.