An osteotomy is a surgical procedure that involves cutting and reshaping of a bone. Pelvic osteotomy involves reshaping a shallow hip socket so that it accommodates the ball of the hip joint (femoral head).
Pelvic osteotomy is indicated in various hip disorders such as developmental dysplasia of the hip involving acetabular dysplasia, subluxation and dislocation, avascular necrosis of the capital femoral epiphysis (Legg-Calve-Perthes-Disease), and neuromuscular hip instability.
A characteristic feature of hip dysplasia is increased stress at the edge of the steep, shallow acetabulum (hip socket) because of point loading. Pelvic osteotomy can reduce the load by enhancing the contact area between the femoral head and the acetabulum. It also helps to improve the femoral head coverage by correcting the defect in the acetabulum.
Pelvic osteotomies can be categorized into three main groups based on the surgical technique – redirectional, reshaping and salvage/augmentation osteotomies.
Redirectional osteotomies such as the Salter, Sutherland, Dega, and periacetabular osteotomies (Steel, Tonnis, and Ganz) alter the orientation of the acetabulum.
Reshaping osteotomies such as Pemberton, Pembersal, and San Diego, involve changing the shape and volume of the acetabulum.
Salvage or augmentation osteotomies are designed to improve the coverage of the defective femoral head. They include the Chiari osteotomy and the shelf procedure.
The Salter, Dega and Pemberton osteotomies are performed in cases of mild to moderate hip dysplasia whereas the steel osteotomy is considered for severe dysplasia. In cases of dysplasia that persists even after skeletal maturity, Ganz osteotomy is preferred. The Dega, Chiari and shelf osteotomy procedures are used to treat neuromuscular hip instability.
Salter osteotomy is recommended in children between the ages of 18 months and 6 years.
In this procedure, the acetabulum is rotated such that the articular cartilage is repositioned above the femoral head. The technique involves exposure of the pelvic bone through an ilioinguinal approach. A skin incision is made that begins from the middle of the iliac crest and runs parallel to the inguinal ligament. The underlying subcutaneous fat and muscles are retracted to expose the ilium. A transverse cut (osteotomy) is made in the iliac bone just above the roof of the acetabulum. Then the distal pelvic fragment is rotated laterally so that the acetabulum covers the femoral head. This corrected position is made secure by inserting a wedge-shaped bone graft taken from the anterior iliac wing into the gap created by osteotomy and stabilizing it with two threaded wires.
Dega osteotomy is performed in conditions where the socket is too wide and shallow.
A two-inch-long incision is made in front of the pelvis where the hip bone can be felt. After exposure of the pelvic bone, a surgical cut is made in the bone just above the acetabulum. Then the lower part of the pelvis is bent downwards to form a well-defined cup that covers the femoral head.
A bone graft is placed over the space created by osteotomy in the pelvis.
Steel triple pelvic osteotomy is performed in a similar manner as the Salter osteotomy but is more complicated because it involves two incisions and three separate osteotomies. A diagonal skin incision is made across the ischial tuberosity to gain access to the ilium and a second incision, ilioinguinal incision, is made to approach the pubis. The three osteotomies are performed through these incisions:
On the lower portion of the ischium
On the ilium above the acetabulum
On the pubic ramus
In this procedure, the acetabulum is repositioned by rotating the fragment created by these osteotomies.
Ganz osteotomy is performed in children, adolescents and young adults in whom growth plate closure around the hip socket has taken place.
In Ganz osteotomy, five bone cuts are made in the pelvic bone around the socket. Then the pelvic bone along with the hip socket is rotated to cover the femoral head in an adequate manner. Once the position is corrected, it is maintained with the help of 2 to 3 small cortical screws.
Pemberton osteotomy is the treatment of choice for bilateral, moderate to severe hip dysplasia in children under 6 years old. In this procedure, the acetabulum is rotated down through the triradiate cartilage to change the direction and increase the depth of the socket.
Osteotomy cuts are made around the acetabulum (pericapsular osteotomy). Then the cut margins of the acetabulum are rotated downwards to cover the femoral head. This position is maintained by a wedge of bone taken from the iliac crest.
Chiari osteotomy is performed in cases of severe acetabular dysplasia in which other repositional osteotomies have failed to achieve adequate coverage of the femoral head. It is also a salvage procedure used to treat hip subluxation and early osteoarthritis.
In this procedure, osteotomy of the ilium is performed at the level of the anterior inferior iliac spine following which the acetabulum is displaced medially. Consequently, the ilium joins the superior and lateral capsule, thus forming a shelf to cover the femoral head.
Shelf procedure is done in cases of residual hip dysplasia where there is no adequate coverage of the femoral head. It improves support of the femoral head by widening the roof of the acetabulum over the joint capsule and thus prevents subluxation. In this procedure, iliac crest bone grafts are placed into the lateral portion of the ilium at the acetabular margin, to augment the acetabulum.
Risks and Complications.
Pelvic osteotomies, although the best option for hip dysplasias, are associated with certain risks and complications. The complications of pelvic osteotomies are rare but can include the following:
Injuries to the nerves and blood vessels
Delayed union between bone grafts
Heterotopic ossification: Formation of bone in places where it normally does not occur, usually in soft tissues.