Acetabular Cup Design Influences Deformational Response in Total Hip Arthroplasty

Abstract

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. ConclusionsOur 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.

Fluctuation of Cup Orientation During Press-Fit Insertion: A Possible Cause of Malpositioning

“…There are several relevant factors that influence interference stress between the metal shell and the acetabular bone, including patient factors such as surrounding local bone quality and acetabular geometry (presence of shallow dysplastic acetabulum) [14], surgical techniques such as amount of cup oversizing relative to reaming size of the acetabular cavity [14,16,20], and implant factors such as cup design (hemispherical or low-profile/equatorially-expanded) [14], cup material (titanium or cobalt-chromium alloy), metal shell thickness [21], and cup surface coating (beads, fibermesh, or plasma-spray) [22]. Since the identical cup brand and surgical technique were used in this study, further studies comparing different surgical techniques and implant factors, or comparing insertion with and without the standard mechanical guide are required to examine their influences on angular changes during press-fit cup insertion.…”

The effect of dynamic hip motion on the micromotion of press-fit acetabular cups in six degrees of freedom

“…This acetabular model was designed to replicate the structural properties observed around the acetabulum, which comprised compressive forces anteriorly and posteriorly from the acetabular columns and non-supportive areas superiorly and inferiorly caused by the presence of the radiolucent triangle and the acetabular notch, respectively, resulting in a pinching effect. This model was used in a previous study [12] , and others have similarly been used in studies to assess acetabular shell deformation in both THR and hip resurfacing implants [20][21][22] , stress distribution within press-fitted ceramic liners [23] , and cup turn-out due to joint frictional moments [24] .…”

In-vivo degradation of middle-term highly cross-linked and remelted polyethylene cups: Modification induced by creep, wear and oxidation

“…If from one hand wear is a degradation of the material which occurs on the surface, on the other hand, when we deal with polymers, also the inevitable tendency of the bulk material to deform when subjected to load for prolonged time must carefully taken into consideration during the conception phase of bearings. The viscoelastic deformation (i.e., creep) might be deleterious for the correct function of the prosthesis, especially when it manifests in the form of pinch deformation, which changes the sphericity of the cup and induces equatorial contact and degradation of the fluid-film lubrication (Jin et al, 2006;Meding et al, 2013;Ong et al, 2009). In other words, excessive creep might adversely affect the wear resistance and the stability of the joint in the long term.…”