Incorrect acetabular cup positioning in a MoM THA: an announced failure with growth of bulky pseudotumour. A case report

Introduction and importance: While MoM tribology gained popularity in the late 20th and early 21st centuries mainly due to the low wear rates and excellent durability, in the following years, it has been the cause of many implant failures due to adverse reactions to metal debris (ARMD) of different entities. Case presentation: We presented the case of a 61 years old female with failure of a metal-on-metal (MoM) THA, due to an improper positioning of the cup. The excessive verticality of the component generated the failure. Clinical discussion: Since acetabular cup orientation is one of the most critical factors influencing the performance and longevity of MoM total hip prostheses, this study highlights how incorrect cup orientation can cause a negative and sometimes catastrophic outcome, necessitating revision. Conclusion: The precise acetabular cup positioning in MoM hip prosthesis geometry is essential in preventing functional overloading, release of metal ions and adverse tissue reactions. When evaluating patients with metal-on-metal hip prostheses, it is necessary to consider the orientation of the cup as a predictive factor for failure and wear of the components.