Objectives. Metal-on-metal (MoM) hip resurfacing was introduced into clinical practice because it was perceived to be a better alternative to conventional total hip replacement for young and active patients. However, an increasing number of reports of complications have arisen focusing on design and orientation of the components, the generation of metallic wear particles and serum levels of metallic ions. The procedure introduced a combination of two elements: large-dimension components and hard abrasive particles of metal wear. The objective of our study was to investigate the theory that microseparation of the articular surfaces draws in a high volume of bursal fluid and its contents into the articulation, and at relocation under load would generate high pressures of fluid ejection, resulting in an abrasive water jet. Methods. This theoretical concept using MoM resurfacing components (head diameter 55 mm) was modelled mathematically and confirmed experimentally using a material-testing machine that pushed the head into the cup at a rate of 1000 mm/min until fully engaged. Results. The mathematical model showed the pattern but not the force of fluid ejection, the highest pressures were expected when the separation of the components was only a fraction of one millimetre. The experimental work confirmed the results; with the mean peak ejection pressure of 43 763 N/m. 2. equivalent to 306 mmHg or 5 psi. Conclusions. The mechanical effect of the high-pressure abrasive water jet is the likely cause of the spectrum of complications reported with metal-on-metal resurfacing. Investigating serum levels of metallic elements may not be the best method for assessing the local mechanical effects of the abrasive water jet

Introduction: The today’s applied osteotomy techniques in surgical orthopaedics have to adapt on the requirements on modern operationprocedures. The application of abrasive water jets offers the possibility to realize a self-defined, athermic precise cut in biological hard tissues. The small process forces indicate the application of modern handling systems. Process engineering and visions of a clinical conversion were demonstrated. Methods: With biocompatible crystalline abrasives freely defined separation cuts and open space geometries, which correspond to the contour of a knee endoprosthesis, were realized at human bones for the first time. The used abrasives (sucrose, xylitol) and can be added in mass flows of 10–20% and the physiological osmolarity is not exceeded after material removal and following dissolution. The necessary pressure level was 75MPa, which only corresponds to a fraction of the necessary pressure of pure water jet. The analysis about quality of the cut-surfaces was done laser-optical. Results: The transect performances of the used abrasives are similar. The arithmetic roughness Ra was 5μm with a pressure level of 75MPa. The value was found by surface detection 3mm under the point of entrance of the water jet in the bones. The flow mass of the abrasives showed only a small influence on the roughness. Conclusion: The results concerning angle deviation and surface seems to be were very promising