Acetabular Cup Design Influences Deformational Response in Total Hip Arthroplasty
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- Meding, J.B., Small, S.R., Jones, M.E. et al. Clin Orthop Relat Res (2013) 471: 403. doi:10.1007/s11999-012-2553-7
Press-fit acetabular components are susceptible to deformation in an underreamed socket, with excessive deformation of metal-on-metal (MOM) components potentially leading to increased torsional friction and micromotion. Specifically, however, it remains unclear how cup diameter, design, and time from implantation affect shell deformation.
We asked whether (1) changes in component geometry and material altered maximum shell deformation and (2) time-dependent deformational relaxation processes occurred.
Diametral deformation was quantified after press-fit implantation of metal shells into a previously validated polyurethane model. Experimental groups (n = 6–8) consisted of 48-, 54-, 60-, and 66-mm MOM cups of 6-mm wall thickness, 58-mm cups of 10-mm wall thickness, and CoCrMo and Ti6Al4V 58-mm modular cups.
Greater cup diameter, thinner wall construction, and Ti6Al4V modular designs generated conditions for maximum shell deformation ranging from 0.047 to 0.267 mm. Relaxation (18%–32%) was observed 120 hours postimplantation in thin-walled and modular designs.
Our findings demonstrate a reduction of shell deformation over time and suggest, under physiologic loading, early component deformation varies with design.
Component deformation should be a design consideration regardless of bearing surface. Designs neglecting to adequately address deformational changes in vivo could be susceptible to diminished cup survival, increased wear, and premature revision.