Howard J Kapp, Orthopedic Surgeon

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Implants

The acetabulum is implanted with a cup named Converge (Zimmer, Warsaw Indiana). This cup has a rough surface called porous coating that allows the bone to grow into it. The cup is press-fit into the acetabular bone, and if the press fit is not secure enough to allow stabile fixation, then one or two screws can be added to augment the press-fit and hold the cup tight enough so that bone can grow into it. The position of the cup is of great importance to allow correct mating of the articulation surface and to provide stability of the hip joint. The insert is then placed into the metal shell and locked into position. The insert is the Durasul (cross-linked polyethylene) or Metasul (metal-on-metal) articulation surface.

The femur is most commonly implanted with the stem (anatomic porous replacement, Zimmer, Warsaw Indiana), which is a bone ingrowth stem. The stem has a porous coated surface on its top 1/3. Again, a press-fit is obtained at surgery. With the press-fit of the stem and that of the cup, the patient is able to put full weight onto the leg immediately after surgery and walk. Bone will grow into the stem, and gradually mature with its attachment to the stem over an 18 month period of time. However, the fit of the stem is immediately sufficient to allow full weight bearing by the patient. On top of the stem is placed the metal head that will mate with the surface of the insert into the cup. This head size can vary according to the side of the acetabulum and the insert used. At the completion of the implantation of the femoral component, the femur is reduced into the acetabulum so that they are mated, and the hip is placed through range of motion to ensure that the fit is correct and that the reconstruction of the hip is correct. Leg lengths are also determined during this time period.