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Periacetabular Osteotomy is a hip preserving procedure performed to correct a congenital deficiency of the acetabulum: acetabular dysplasia.

Acetabular dysplasia is a condition defined by inadequate development of an individual's acetabulum. The resulting acetabulum is shallow and "dish shaped" rather than "cup shaped". The upper portion (roof) of the acetabulum is obliquely inclined outward rather than having the normal horizontal orientation. Because of these abnormalities, the superior and usually anterior femoral head are incompletely covered by this dysplastic acetabulum.

Individuals with acetabular dysplasia usually develop through childhood and adolescence without symptoms or knowledge of their abnormality. By the age of 30 however the patient typically experiences pain from their hip and they often seek medical evaluation and an X-ray discloses the abnormality (acetabular dysplasia). Other patients may have been treated for hip problems as an infant or child.

Acetabular dysplasia is often also associated with abnormalities in the shape of the upper femur which may contribute to the patient's hip symptoms.

Acetabular dysplasia is associated with an abnormally high stress on the outer edge (rim) of the acetabulum which leads to degeneration of the articular cartilage (arthritis). It is also possible for breakdown of the acetabular labrum (rim cartilage of the acetabulum) or a fatigue fracture of the rim of the acetabulum to occur as a result of this rim overload. Any one or a combination of these conditions can cause hip pain sufficient for the patient to seek medical evaluation and treatment.

When the diagnosis of acetabular dysplasia is made, the X-ray also usually shows a sign of arthritis which is most commonly an acetabular cyst though increased bone density, a femoral head cyst, osteophytes (bone spurs), and/or cartilage thinning may also be present. If the dysplasia is left uncorrected worsening of the arthritis is predictable and often progresses to a severe status within a few years and sometimes even a few months. For the patient, this means increasing hip pain, progressive loss of hip motion, and worsening functional capabilities.

Periacetabular Osteotomy (PAO) is a surgical treatment for acetabular dysplasia that preserves and enhances the patient's own hip joint rather than replacing it with an artificial part. The goal is to alleviate the patient's pain, restore function, and maximize the functional life of their dysplastic hip.

PAO is a procedure that was developed and first performed in 1984 in Bern, Switzerland by Professor Reinhold Ganz with the assistance of Jeffrey Mast, M.D. (an American surgeon from Sparks, Nevada who was spending a year's sabbatical leave with Prof. Ganz). Dr. Joel Matta's personal association with Prof. Ganz and Dr. Mast made him aware of the very good initial results of this innovative procedure.

Two parts comprise the hip joint: a ball on the upper end of the thigh bone (femur), called the head of the femur, and a socket in the pelvis known as the acetabulum. The hip joint, like other joints, is made up of specialized structural elements that serve as precisely fitting moving parts. The head of the femur rotates freely within the smooth, concentric surface of the acetabulum. An extremely low friction tissue, hyaline cartilage, lines this joint as well as others in the human body. The friction between two hyaline cartilage surfaces is much less than the best man-made bearing.

Outer (left) and inner (right) views ot the right side of the pelvis (the innominate bone). The acetabulum is seen on the outer aspect of the bone. The red line indicates where the bone is cut for PAO.

A normal acetabulum "covers" the upper (superior) portion of the head of the femur as well as a partial portion of the front (anterior) and back (posterior) of the femoral head.



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Front and side views of the pelvis and hip joint in the body