The structure of the hip joint

The hip joint (Articulatio coxae) is the second largest joint in the human body after the knee. It is a ball and socket joint. These joints have the advantage that they can move in three dimensions, which explains the high mobility of the hip (e.g. flexion, extension, splaying, internal and external rotation).

The main structures of the hip are the 5 cm thick head (Caput femoris) of the thigh (femur) and the acetabulum of the pelvis. To prevent friction between these two joint halves, both the head and the acetabulum are covered with a smooth layer of cartilage of just a few millimeters thickness, which in patients with arthrosis, for example, can have massive defects.

The margin of the acetabulum is surrounded by a cartilaginous lip (Labrum acetabuli), similar to a sealing ring, which closes the intra-articular space. Note: Tears in the labrum (e.g. as a result of falling on the hip or natural wear) can be responsible for severe pain in the hip or groin region.