Acetabular Component Deformation with Press-fit Fixation

Acetabular component deformation secondary to forces encountered during insertion is a potential consequence of the press-fit technique. This study characterized the stiffness of Pinnacle 100 cups via mechanical testing and used this information with intraoperative measurements of cup deformation to calculate the in vivo forces acting on cups inserted during hip arthroplasty in 21 patients. We found that 90.5% of cups had measurable compression deformity, averaging 0.16 ± 0.16 mm. The corresponding forces acting on these cups averaged 412 ± 419 N. Compressive force was not related to age, diagnosis, or sex, but was marginally related to bone type. Cups press-fit into harder, type A bone experienced greater mean forces than cups press-fit into type B bone. For hard-on-hard bearing surfaces, such in vivo deformation of acetabular shells may result in negative clinical consequences such as equatorial loading with increased wear and potential seizing of components, chipping of ceramic inserts, or locking mechanism damage.