The hip is the largest “ball-and-socket” joint in the body. It is held together by ligaments, tendons, and a joint capsule. The ball is called the “femoral [fem-er-uhl] head,” which is the top of the femur or thigh bone.
The socket is called the “acetabulum” [as-i-tab-yuh-luhm] and is a part of the pelvis. The femoral head fits into the acetabulum creating the hip joint. The fit together so the ball can rotate freely in the socket.
Articular cartilage, a very smooth surface, covers the femoral head and the acetabulum so that the hip joint glides easily during motion.
The labrum, a type of cartilage, lines the edge of the acetabulum.
The labrum creates a seal of the hip joint and keeps a natural fluid called synovial fluid inside the hip joint. The labrum also helps stabalize the hip, along with the surrounding muscles, ligaments, tendons and joint capsule.
Orthopaedic surgeons at Wisconsin Bone & Joint use a variety of different terms for hip dysplasia depending on severity and time of occurrence. These names include:
- Hip Dysplasia
- Developmental Dislocation of the Hip (DDH)
- Hip Dislocation
- Developmental Dysplasia of the Hip (DDH)
- Acetabular Dysplasia
- Congenital Dislocation of the Hip (CDH)
Hip dysplasia means that the hip joint is the wrong shape, or that the hip socket is not in the correct position to completely cover and support the femoral head. This causes increased force, and abnormal wear on the cartilage and labrum.
The cartilage surface of the joint is made of large molecules trapped in a matted web of fibers called collagen. When the collagen fibers or the molecules break down, the joint surface wears out faster.
A joint that is out of place or shallow will wear out faster than one that has a more normal shape. Doctors often compare this is like the tread on a tire that is out of balance on a car. The tread wears out faster on a tire that is out of balance or out of alignment. However before the tire wears out completely, it can be rotated or re-balanced to increase the life of the remaining tread on the tire. Once the tread is gone, the tire needs to be replaced.
As in the tire example, certain changes can be made to preserve the life of the hip joint.
At present, there is no known way to re-grow the cartilage surface that is wearing out, although there are some incredibly brilliant researchers trying to solve this problem. Current methods rely on lifestyle changes and/or surgical treatments. using a cane, losing weight, or taking arthritis medication may help temporarily.
Non-operative methods do not provide a lasting solution because the joint itself is not properly formed. Therefore the condition usually gets worse over a time interval that depends on severity of the dysplasia.
Surgical methods to re-orient the acetabulum may decrease the possibility of the cartilage wearing out too fast.