Hip dysplasia is a developmental condition that is often recognized and treated in infancy. It is caused by an abnormal development of the hip joint. Normally, the hip socket or acetabulum develops its shape in response the head of the femur. If the head of the femur is positioned abnormally, the acetabulum can form with an angulated roof that slopes upward. This can lead to increased pressures on the cartilage of the hip as well as a persistent tendency for the femoral head to slide in and out of the hip with daily activities. This mechanical problem leads to a greater tendency to develop arthritis in middle age.(See Figure 1 )
Figure 1: Comparative radiographs of the pelvis from a 30 year old female with hip pain and early hip dysplasia (Left) and a 49 year old female with underlying hip dysplasia (Right) with progression to full-blown advanced hip osteoarthritis. This patient has since undergone hip replacement on both sides.
In younger patients, this abnormality can lead to increased pain in the hip as well as tears of the labrum. When this condition is diagnosed in adulthood and the hip is still in the non-arthritic phase, there is still a chance to intervene prior to full blown arthritis. Standard radiographs only show the damage in its final stages. Newer types of studies such as MRI (See Figure 2) can show early damage to the structures in the hip.
Figure 2: MRI of a hip with dysplasia showing much of the head uncovered by the bony roof (roof edge shown by large black arrow). The other structures of the joint such as the cartilage (large white arrows) and an enlarged labrum (small black arrows) can also be seen on the MRI image.
Our goal is to do something prior to the need for hip replacement because of our philosophy that your own joint is far superior to a mechanical joint regardless of what artificial material is used. Fortunately, there are some options available if the patient presents early enough.
The most successful, safe, and predictable of these operations is termed the "periacetabular osteotomy", also called the "PAO". It was developed by two ingenious surgeons, Professor Reinhold Ganz and Dr. Jeffrey Mast in the early 1980’s. An osteotomy is the surgical division of a bone and periacetabular described the application of the osteotomy "around" the hip socket or “acetabulum”. The procedure involves making a series of angular cuts on the pelvis, separating the hip socket from the pelvis and allowing free rotation of the socket in three dimensions. It has proven to be one of the most effective surgical procedures in the treatment of hip dysplasia in adults. The major advantage of the procedure is the flexibility of placement of the hip socket in essentially any position and the preservation of the stability of the pelvic ring. The ability to freely position the hip socket gives your surgeon the ability to customize the correction of the anatomy to the specific deficiencies of that pelvis.
Computer Assisted Preoperative Planning of PAO
We have been using three dimensional reconstructions to make a very precise computer model of the pelvis. (See Figure 3) With this information and a large database of normal pelvis models, we are able to plan the reorientation of the hip socket to as close a normal position as possible even before the operation. The preoperative computer plan is correlated with intraoperative xrays which allow for a very precise correction. The other benefit of the PAO is the innate stability of the hip socket at the end of the procedure.
Figure 3: Computer Generated Three-Dimensional Model of Pelvis With Hip Dysplasia both Before (Left) and After (Right) Simulated PAO.
Advantages of PAO
After PAO, patients can bear weight much earlier than with other procedures and females who undergo the procedure can have normal future vaginal deliveries rather than requiring a Cesarean section.
Recovery After PAO
Most patients require hospitalization for 3 to 4 days and can get up with physical therapy on the day after the procedure. Crutches or a walker are usually continued for 6 weeks until there is some evidence of healing of the osteotomy site. After the 6 to 8 week mark, if there is evidence of healing of the osteotomy site on the xrays, patients can resume weightbearing. In many cases, they may have some slight muscle weakness which responds well to physical therapy. By three to four months, nearly everyone walks without a cane. The most gratifying part of the operation is to see patients return to high level activities and occupations without even thinking about their hip.
Potential Complications After PAO
Although the PAO is a relatively major hip operation, in many ways, it is the safest in the long run. The biggest risks are from damage to the nerves, arteries, or veins that run in the pelvis. This risk is minimized by performing all the cuts with full xray guidance in the operating room as well as extensive experience with the operative procedure.