Bone cysts of this type are an indication of uneven or excessive weight-bearing load. If you have hip dysplasia, the hip socket or acetabulum is probably shallow with shortened margins.
The head of the femur (thighbone) is round and normally fits inside the acetabulum. The curved socket forms a shelf or roof over the femoral head to keep it from dislocating. With hip dysplasia, the round head of the femur isn't covered by the acetabulum. It can slip upward and even dislocate.
The cysts are a likely sign that there is uneven wear and load from the hip instability. The joint may be trying to cushion itself by forming cysts of this type.
In some patients, a procedure called a rotational acetabular osteotomy can be done for unstable hip dysplasia. The surgeon removes a wedge of bone and uses it to re-angle the joint. A small piece of bone is also used to improve the roof angle.
Studies show that cysts of the acetabulum or femoral head often disappear after this operation. Patients report decrease in pain and improved function.