Hip pain can be caused by many different reasons. It could be that there is some wear and tear within the joint itself, or perhaps a slight tear of the capsule that the joint sits in. Sometimes it isn't the hip joint at all. There are many pelvic stabilsing muscles around the hip, which if strained, can cause hip pain. Strained muscles around the hip can unfortunately irritate the fluid filled cushions around the muscles, called Bursas. This can then lead to Bursitis.
Pelvis problems, lower back problems and knee problems can also cause pain to manifest around the hip.