The hip joint is a deep ‘ball and socket’ joint that connects the leg to the pelvis. Confusion about the location of this joint is common. In common everyday usage, the term “hip” is applied to a bony ridge in the pelvis which is more accurately termed “iliac crest”, (eg., I carried the baby on my “hip”).
The hip is actually a joint that is located much lower. It can be found in the location of the groin crease where the leg attaches to the pelvis.
The ball of the hip joint is the “femoral head” which rests within the socket “acetabulum” of the pelvic bone. The surface of both the ball and socket is covered with a 3-4 millimeter thick layer of cartilage. The cartilage that lines the hip is an exceptional material. It is smoother than any man-made bearing. The cartilage has no nerve endings in it and, therefore, any motion between cartilaginous surfaces does not cause pain.
In a patient with arthritis, the cartilage wears away; debris is generated, producing pain. As the cartilage wears away, bone becomes exposed. The underlying bone does have nerve endings in it and is not a good bearing material. As the exposed bone ends rub against each other the nerve receptors in the bone are stimulated. This results in a greater pain sensation. Bone on bone pain is usually severe; the only solution at this point is some type of hip replacement.
You do not have to lose all of your cartilage in your joint to have severe pain, you just have to wear a section of the cartilage on both sides of the joint through. Often patients are told: “ you still have some cartilage left, so you don’t need an operation”. This, of course, is not true.