Abstract
The contemporary metal-on-metal (MoM) bearings were reintroduced due to their lower volumetric wear rates in comparison to conventional metal-on-polyethylene bearings. This has the potential to substantially reduce wear-induced osteolysis as the major cause of failure and greater implant stability with the use of large femoral heads. It has been estimated that since 1996 more than 1,000,000 MoM articular couples have been implanted worldwide. However, with increasing clinical experience, the national joint registries have recently reported the failure rate of THA with MoM bearings to be 2–3 fold higher than contemporary THA with non-metal-on-metal bearings. Moreover, adverse periprosthetic tissue reactions have emerged as an important reason for failure in MoM patients.
A painful MoM hip arthroplasty has various intrinsic and extrinsic causes. As in all painful THA, a thorough clinical history, a detailed physical examination, as well as radiographic and laboratory tests are essential to delineate potential cause(s) of pain in patients with MoM hip arthroplasty. While specialised tests such as metal ion analysis are useful modalities for assessing MoM hip arthroplasty, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. There should be a low threshold to perform a systematic evaluation of patients with MoM hip arthroplasty as early recognition and diagnosis will facilitate the initiation of appropriate treatment prior to significant adverse biological reactions. A systematic risk stratification recommendation, for multiple modes of failure including adverse local tissue reactions, based on the currently available evidence will be presented to optimise management.
