BACKGROUND: 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. QUESTIONS/PURPOSES: We asked whether (1) changes in component geometry and material altered maximum shell deformation and (2) time-dependent deformational relaxation processes occurred. METHODS: 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. RESULTS: 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. CONCLUSIONS: Our findings demonstrate a reduction of shell deformation over time and suggest, under physiologic loading, early component deformation varies with design. CLINICAL RELEVANCE: 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.
BACKGROUND: 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. QUESTIONS/PURPOSES: We asked whether (1) changes in component geometry and material altered maximum shell deformation and (2) time-dependent deformational relaxation processes occurred. METHODS: 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. RESULTS: 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. CONCLUSIONS: Our findings demonstrate a reduction of shell deformation over time and suggest, under physiologic loading, early component deformation varies with design. CLINICAL RELEVANCE: 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.
Authors: Claude B Rieker; Rolf Schön; Reto Konrad; Gernot Liebentritt; Patric Gnepf; Ming Shen; Paul Roberts; Peter Grigoris Journal: Orthop Clin North Am Date: 2005-04 Impact factor: 2.472
Authors: H McKellop; S H Park; R Chiesa; P Doorn; B Lu; P Normand; P Grigoris; H Amstutz Journal: Clin Orthop Relat Res Date: 1996-08 Impact factor: 4.176
Authors: Thomas M Smith; Keith R Berend; Adolph V Lombardi; Roger H Emerson; Thomas H Mallory Journal: Clin Orthop Relat Res Date: 2005-12 Impact factor: 4.176
Authors: Richard D Komistek; Douglas A Dennis; Jorge A Ochoa; Brian D Haas; Curt Hammill Journal: J Bone Joint Surg Am Date: 2002-10 Impact factor: 5.284