Medial protrusio technique for placement of a porous-coated, hemisphericalacetabular component without cement in a total hip arthroplasty in patients who have acetabular dysplasia

Twenty-four hip replacements were performed with use of a medial protrusio technique to stabilize the fit of a hemispherical metal shell in the acetab ulum in nineteen patients who had dysplasia of the hip, All of the hips wer e followed for a minimum of five years (average, seven years; range, five t o thirteen years), Six of the hips were type I, seven were type II, eight w ere type III, and three were type TV according to the criteria of Cro,ve et al, The acetabular cup was implanted with the medial aspect of its dome be yond the Kohler line (drawn from the ischium along the ilioischial line) in all hips, An autogenous graft sculpted from the femoral head,vas used to c over 15 to 30 percent of the superolateral portion of the cup in one type-I hip, four type-III hips, and one type-IV hip, The need for these six bone grafts could have been avoided by reaming two to three millimeters more med ially or by allowing 20 percent of the superolateral portion of the cup to be uncovered. Sixty to 84 percent of each bone graft was resorbed, effectiv ely leaving the superolateral portion of the cup uncovered, The amount of the surface of the cup that was beyond the Kohler line averag ed 41 percent for the six type-I hips, 43 percent for the seven type-II hip s, 41 percent for six of the type-HI hips, and 44 percent for one of the ty pe-IV hips, Crossing of the ilioischial and iliopubic lines was noted on th e radiographs of two type-m and two type-IV hips, Radiographs of two type-I hips and one type-IT hip showed 7 to 17 percent of the surface of the dome of the cup through the internal pelvic wall (beyond the iliopubic line), None of the twenty-four metal shells were revised. A reoperation was perfor med on two hips to exchange a worn polyethylene insert, and three femoral c omponents that had been fixed without cement were revised because of mechan ical loosening, Wear averaged 0.26 millimeter per year in the fourteen hips that had a titanium femoral head and 0.09 millimeter per year in the nine hips that had a cobalt-chromium femoral head, The remaining hip had a ceram ic femoral head, and the wear rate was 0.09 millimeter per year, The medial protrusio technique is a predictable, reproducible method for ob taining fixation of a porous-coated, hemispherical acetabular component in a dysplastic acetabulum, The technique permits the use of a porous-coated ( bone-ingrowth) component; avoids the use of support bone graft and thereby reduces the operative time; facilitates rehabilitation by permitting earlie r weight-bearing of the hip; and permits the use of a modular bearing surfa ce, which may allow future exchange of only this; surface rather than revis ion of the entire acetabular component because of excessive wear.