Cementless acetabular revision (type I defects)

Required equipment

When revising an acetabular component, it is important to maintain as much native bone stock as possible. Acetabular component removal systems with curved osteotomes, specific to the curvature of the original cup, are helpful in removing a preexisting well-fixed component while minimizing bone loss ( Fig. 4.1 ). Knowledge of the preexisting cup size and cup geometry is necessary to select the proper blade. Hemispherical cups should be removed with the curved osteotomes of the same size, while elliptical cups should be removed with curved osteotomes 1 to 2 mm larger to allow clearance of the peripheral buildup. When screws are present in the preexisting cup, additional equipment to remove the liner and screws is necessary. Several screwdriver options should be available to account for different screw head options if the screw type is not known. A high-speed metal cutting burr should be available if the screws are stripped or the heads are broken. Trial liners for the preexisting cup can center the curved osteotomes in the event the original liner is worn or damaged in its removal. Finally, bipolar head trials are helpful to center the curved osteotomes when removing cups with large inner diameters, such as those found in hip resurfacing and dual mobility arthroplasty.

Type I defects can typically be addressed with cementless, hemispherical, or elliptical, highly porous acetabular shells. Multihole shells that allow screw options into the upper and lower hemispheres of the acetabulum can be useful when there is a concern of inadequate press-fit without supplemental fixation. These should be available for all revision cases, although they are not always required. Costs can be significantly higher for multihole options within a brand portfolio. The authors prefer highly porous-coated multihole hemispherical components ( Fig. 4.2 ) for type I defects.

Surgeons who rely on internal landmarks for cup positioning, such as the transverse acetabular ligament or the bony rim of the acetabulum, may find these landmarks are not always present in type I defects , which can lead to variability in positioning the new cup. Relying on assumptions of pelvic position on the table (i.e., that the lateral decubitus position is perfectly achieved) can aid surgeons, but this is vulnerable to imperfections in positioning, such as anterior or posterior tilt (especially with retractor forces), pelvic obliquity from obesity or an overstuffed axillary roll, and other deficiencies related to the OR table. A C-arm can be beneficial in assessing cup position and has greater ease of use in the anterior approach; however, this may not be necessary when addressing type I defects. Some posterior approach surgeons have found that navigation improves the reliability of cup positioning in revision surgery. ^,