A bursa is a thin-walled sac filled with a very small amount of fluid that is usually found over bony prominences and functions to help soft tissues to glide over these prominences.
The trochanteric bursa lies over the bony greater trochanter in the upper outer thigh. Trochanteric bursitis, sometimes called Greater trochanteric pain syndrome, causes pain in this region that can vary from mild pain to disabling pain that requires the use of crutches to walk.
It can be caused by a number of things. Anything that causes an alteration in the way that a person walks can cause the condition. This includes anything that causes a limp, such as a foot injury, foot surgery, knee problems etc. It can also be caused by a fall directly onto the greater trochanter. As an overuse injury it can also occur in runners and other sports-active people. It can also occur in people who have had hip surgery, for example a hip replacement.
The condition can occur in association with iliotibial band (ITB) syndrome, where pain is felt along the outer thigh especially at the outer aspect of the knee. The pain occurs along the path of the fibrous iliotibial band which is a structure that is important in knee movements.