Hip Preservation Surgery for Adult Hip Dysplasia
Surgery to change the shape of the hip joint typically involve re-shaping the shallow hip socket (acetabulum) so it is in a better position to cover the ball of the hip joint (femoral head). Osteotomies may be performed on the hip socket side of the joint or on the ball side of the joint (upper thigh bone).
Surgeries are on the hip socket side are called “acetabular osteotomies” or “pelvic osteotomies”. The periacetabular osteotomy (PAO) is the most common type for young adults. This is also called the Ganz or Bernese osteotomy because it was developed by Professor Ganz in Berne, Switzerland.
When the top of the thigh bone is re-shaped (just below the hip joint on the ball side of the joint) these surgeries are called “femoral osteotomies” and may be “varus osteotomies,” or “valgus osteotomies” depending on the specific procedure being performed.
Surgery to restore the shape of the joint is currently more common on the hip socket side with a procedure, called a PAO.
Peri-Acetabular Osteotomy (PAO)
This surgery involves cutting the pelvis around the hip joint and shifting it into a better position to support the stresses of walking. After the hip is re-positioned, it is held in place with screws until the bone heals. After the bone heals, the screws can be removed, but this is not usually necessary.
As you might imagine, this operation is complex and is usually performed in specialized centers that do this procedure on a frequent basis. After the operation, patients should not put full weight on their leg for up to three months, so crutches or walkers are often recommended along with a wheel chair for longer distances until the bone has healed in its new position.
Determining Success Rates
The PAO operation is most likely to be successful in patients younger than 35 years and when the joint is shallow but has matching shapes on the ball and socket sides of the joint. This is called joint congruency and means that the curvature of the socket is the same as the curvature of the femoral head. When the joint space is thinner than 2mm thick (normal thickness is about 4 mm), then the joint may be too worn down for a PAO.
An MRI may be helpful to reveal whether the surface of the joint is healthy enough for the PAO to have a reasonable chance for success. There are a few techniques to look at cartilage health; on is called a dGEMRIC scan and another is called T2 mapping. dGEMRIC stands for delayed gadolinium-enhanced MRI of cartilage. When the dGEMRIC index is low, then the chance of success is decreased. The dGEMERIC index is not the only factor for predicting success, but it may help reveal when the joint surface is already damaged. More severe dysplasia when the top of the thigh bone is partly out of the hip socket also worsens the chances for success, but the PAO may still be the best choice for some patients.
Femoral osteotomy (the ball side of the joint) has also been reported with some success and is performed on a small percentage of patients. In this procedure, the upper femur is re-aligned to change the mechanics and allow weight-bearing on a fresh part of the femoral head. Femoral osteotomy is rarely used as the only procedure in the USA although promising results have been reported in Europe and other parts of the world. Usually, femoral osteotomy is combined with pelvic osteotomy when there is deformity of the upper femur from abnormal growth and development.
Other Pelvic Osteotomies
There are also other types of osteotomies on the hip socket side of the joint. In Japan, a modification of the PAO may be preferred. That modification cuts a circle around the hip socket and rotates the socket itself. This is called a “rotational” or “spherical” osteotomy. Other pelvic osteotomies that have had some success are the “triple innominate osteotomy,” “Chiari osteotomy,” and procedures that create a deeper socket or re-align the existing socket.
There are always risks to any operation, such as infection, blood clots, incomplete healing of the bone, nerve or artery injury. In addition, the hip may still develop arthritis over time even when the operation is successful.
Osteotomy is still the preferred treatment in young adults to postpone the need for hip replacement as long as possible.
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