Dyplasia means malformation. Hip dyplasia means a malformation of the hip joint.  The malformation can be of the socket (acetabulum) or the ball (femoral head) or of both bones. In a normal hip the ball and socket fit together so there is coverage of the femoral head by the acetabulum. This keeps the cartilage healthy, the shape of the bones rounded, and good motion of the hip. In a dysplastic hip the ball isn't covered by the socket so the femoral head and acetabulum become mis-shaped and there is often cartliage that isn't covered by the opposing bone. The hip doesn't move as well because the two sides of the joint don't fit together.

Hip dysplasia is described by the area of the bone affected. In all types the labrum can become stretched and tear or detach.

• Anterior acetabular dysplasia - the front portion of the socket isn't formed completely so the front of the ball isn't covered by the socket
• Lateral acetabular dysplasia - the outside portion of the socket isn't formed completely so the outside aspect of the ball isn't covered by the socket.
• Coxa vara - the femoral head is formed at an angle that causes the inner portion of the head to remain uncovered by the socket
• Coxa valga - the femoral head is formed at an angle that causes the outer portion of the head to remain uncovered by the socket

X-ray image of hip dysplasia of both hips. There is Legg-Calve-Perthes on the left side and acetabular dysplasia on the right side.