Numerical and experimental investigations for the evaluation of the wear coefficient of reverse total shoulder prostheses

In thepresentstudy,numericalandexperimentalwearinvestigationsonreversetotal shoulder arthroplasties(RTSAs)werecombinedinordertoestimatespecific wear coefficients, currentlynotavailableintheliterature.Awearmodelpreviouslydeveloped by theauthorsformetal-on-plastichipimplantswasadaptedtoRTSAsandappliedina double direction: firstly, toevaluatespecific wearcoefficients forRTSAsfromexperimental results andsecondly,topredictweardistribution.Inbothcases,theArchardwearlaw(AR) and thewearlawofUHMWPE(PE)wereconsidered,assumingfourdifferent k functions. The resultsindicatedthatboththewearlawspredicthigherwearcoefficients forRTSA with respecttohipimplants,particularlytheARlaw,with k values higherthantwofoldthe hip ones.Suchdifferencescansignificantly affectpredictivewearmodelresultsforRTSA, when non-specific wearcoefficients areused.Moreover,thewearmapssimulatedwiththe two lawsaremarkedlydifferent,althoughprovidingthesamewearvolume.Ahigherwear depth (þ51%) isobtainedwiththeARlaw,locatedatthedomeofthecup,whilewiththePE law themostwornregionisclosetotheedge.Takingadvantageofthelineartrendof experimental volumelosses,thewearcoefficientsobtainedwiththeARlawshouldbe valid despitehavingneglectedthegeometryupdateinthemodel.