The process of degeneration, or breakdown, of a hip joint is a gradual one but may proceed at different speeds depending upon the cause. When one part of the hip is affected by disease or injury, it can affect the function of the entire joint.
The part most often affected is the articular cartilage. In a healthy joint, the friction between two moving surfaces is less than between two ice cubes sliding against one another. When the cartilage is damaged or starts to wear down, the joint can no longer move smoothly.
A defect in the surface of the articular cartilage will wear against the opposite side of the joint and cause damage to that area as well. The joint surfaces collapse and the underlying bone is affected. It may become deformed. The joint loses range of motion and weight bearing forces in the joint are altered.
At the same time, the lining tissues within the joint become inflamed. The soft tissues around the joint such as the joint capsule may become tightened and contracted. The muscles that move the joint may become weakened. When all this happens, the hip joint can no longer function normally.
Many disease processes can damage the hip joint. Most are related to some form of arthritis.
There are five major causes of hip disease:
- Osteoarthritis
- Rheumatoid arthritis
- Post-traumatic arthritis
- Avascular necrosis
- Arthritis secondary to childhood hip disease Some of the secondary less common causes include:
- Prior infection
- Hemophilia
- Ankylosing spondylitis
- Gaucher’s disease
- Sickle cell anemia
- Paget’s disease
Each of these conditions is different in how it changes the anatomy and biology of the normal hip joint. All of them can create the need for hip replacement.