Hip Stability Parameters with Dual Mobility, Modular Dual Mobility and Fixed Bearing in Total Hip Arthroplasty: an Analytical Evaluation.

Abstract Background. Use of dual mobility in total hip arthroplasty has gained popularity due to the ability to reduce dislocation through increased jumping distance and impingement-free arc of movement. Recently, modular dual mobility systems were introduced to give the possibility to use dual mobility with standard metal-backed shells, however few has been studied to date regarding how jumping distance and the center of rotation changed with modular dual mobility. The objective of this study was to evaluate, through analythical simulation, how jumping distance and center of rotation change between dual mobility and standard cup with modular dual mobility or fixed bearings. Methods. 3D-models of dual mobility and standard press-fit cups with modular dual mobility or fixed bearings liners were used to simulate dual mobility, modular dual mobility and fixed bearings implant configurations, matched for same cup size, according to same cup position, different femoral head diameters. Jumping distance was calculated and center of rotation lateralization was measured for different sizes.Results. Jumping distance with modular dual mobility was reduced by -3.9mm to -8.6mm in comparison with dual mobility, from 48 to 64mm sizes. Jumping distance with modular dual mobility resulted comparable to jumping distance with polyethylene fixed bearings with Ø36mm femoral head but increased by +1.1mm and +1.4mm than jumping distance with ceramic fixed bearings with Ø36 and Ø40mm femoral heads for sizes >54mm. Modular dual mobility lateralized the center of rotation up to +2.5mm and +4.0mm in comparison with dual mobility and fixed bearings, respectively. Conclusions. Jumping distance with modular dual mobility resulted lower than dual mobility and comparable to fixed bearings polyethylene liner with Ø36mm femoral head for larger sizes. Modular dual mobility lateralized the center of rotation in comparison with both dual mobility and fixed bearings cups.