Injections to put medication into the joint itself should always be done under a real-time form of x-ray that helps to ensure accuracy of needle placement. The concern with the hip joint is that there is a lot of soft tissue between the skin and the joint itself which contain arteries, veins and nerves, so performing this injection blind is not advisable. In addition, striking the bone with the needle can be very painful for the patient. The post the surgeon is aiming for is also extremely small, probably about 5mm in diameter, so some guidance with the xray is helpful. Once the joint is reached, some harmless dye is injected to check the needle is actually inside the joint. Upon this confirmation, the steroid is injected along with some local anaesthetic and the procedure is concluded.
image courtesy of HSS site