Dissociation of liner from cup in THA: does liner damage affect the risk of dissociation?

Abstract

Introduction A rare catastrophic failure of modular component Total Hip Arthroplasty is dissociation between liner and cup, which has been associated with component malposition and/or impingement and seems to be more frequently associated with the Pinnacle system. The goal of this study was to evaluate the resistance of a polyethylene liner to lever-out-forces of the Pinnacle locking mechanism and the locking mechanisms of two other current cup/liner systems using a standardized testing method (ASTM). Materials and methods Five of each of the following cups were evaluated with their corresponding polyethylene liners: Pinnacle Multihole cup with and without intact anti-rotation tabs (ART’s); Allofit-S-Alloclassic and Plasmafit Plus7 cups. The ASTM test set-up was used to evaluate the lever-out force resulting in liner dissociation for each construct. Results The Pinnacle construct with intact ARTs required the greatest force (F) to achieve dissociation (263.2 ± 79.2 N) followed by the Plasmafit Plus7 (185.8 ± 36.9 N) and the Allofit-S (101.4 ± 35.3 N) constructs, respectively. However, after removal of the ARTs, the Pinnacle system required the least force to achieve dissociation (75.1 ± 22.2 N) (p < 0.001). Conclusions The intact Pinnacle system appeared the most stable in lever-out tests when compared to the other systems. However, after removal of the ARTs, the Pinnacle system required the least force for dissociation, consistent with locking mechanism failure, and suggesting that the ARTs are a critical component of the locking mechanism. Our findings are consistent with the clinical experience of dissociated Pinnacle constructs displaying damaged or missing ARTs, and that damage to these may increase risk of liner dissociation.

Is It Possible to Create an “Ideal Endoprosthesis” for an “Ideal Total Hip Replacement”?

“…Its nature is determined by patient factors (obesity, bone quality, activity level, patient genetics), surgical technique factors and implant factors (primarily the type of friction pair, method of fixation and the ability of the implant to osseointegrate) [47][48][49][50]; • Cup-liner dissociation-a relatively rare complication of THR associated with misplacement of the component and/or impingement. To a greater extent, it is determined by the design of the implant [51][52][53]; • Implant fracture-a complication after THK resulting from the loss of strength of the implant, i.e., to the greatest extent determined directly by the design of the implant [54,55].…”