The hip is susceptible to damage, deterioration, and subsequently arthritis due to a variety of conditions. Arthritis is just a catch-all term for the joint wearing out. It is characterized by painful restricted motion and, when severe enough, can benefit from a hip replacement.
The labrum and articular cartilage are the two main structures that can be damaged, causing pain and eventually leading to arthritis. Both of these are actually types of cartilage. The labrum is like a gasket seal or O-ring around the acetabulum (socket). Its most important function is to help evenly distribute weightbearing forces across the surface of the hip. Uneven distribution with hotspots of contact leads to uneven wear and arthritis. It also has some importance in enhancing stability of the joint. The labrum is richly innervated with pain-sensing nerve endings so that labral tears tend to be quite painful. The articular cartilage lines the acetabulum and the femoral head (ball part of the ball-and-socket joint) like a thick Teflon coating creating a smooth, frictionless surface. Breakdown of the articular cartilage represents the earliest stages of arthritis, and it is the progressive wear of this cartilage surface that characterizes advancing arthritis. The articular cartilage has few nerve endings, so early on damage may not cause much pain. Only once extensive erosion occurs does this part start to be more noticeable.
A normal, healthy hip joint is a very durable structure that can withstand hard use. Most commonly when injury or damage occurs, there is some underlying abnormality of the way the joint is formed making it more susceptible to damage. By far, the most common cause is femoroacetabular impingement (FAI). Second on the list is dysplasia. However, some patients can present with a hybrid condition of both dysplasia and impingement that must both be carefully weighted to determine which or what combination of treatment strategies must be employed.
There are also inflammatory types of arthritis that do not necessarily involve bony structural abnormalities of the joint. The synovium is a membrane that lines the hip, normally producing synovial fluid that lubricates the joint, providing nutrition. With inflammatory types of arthritis, the synovium grows out of control, eroding the articular cartilage leading to arthritis. Occasionally, arthroscopy for resecting the synovium (synovectomy) can be beneficial. This is not frequently necessary because in recent years pharmacological management to control the synovium have made significant advancements.