67% had failed by 16 years. Because these patients are young, early failure implies the need for repeated revision operations using progressively more invasive and more complex devices. It was therefore always attractive to surgeons to employ a bone conserving procedure in young patients initially. When they need a revision there is more useful bone preserved to fix the new device to. During a period as trainees at the Royal Orthopaedic Hospital, Birmingham, McMinn and John O'Hara noted that metal on plastic hip replacements were wearing out, whereas the RING metal on metal hip replacements, about a decade older, but not fashionable, did not seem to wear out much. The resurfacing was also inspired by the 1983 disassembly of John O'Hara's 1957 Mercedes engine. John O'Hara has some training in engineering tolerances and clearances as a medical student in Dublin. By 1976 he had been trained to machine the parts for eight engines. Unused Ring prostheses were collected from several hospitals and several dozen patients were asked to allow removal and analysis of their Ring hips when they died. Over the next few years, 23 of these were retrieved. When the development as almost done, John O'Hara was approached by Professor RB Salter at the Hospital for Sick Children in Toronto in 1988 and moved there for a year. He completed some animal work on dislocated hips in children. He and Andranik Khakatrian from Verevan developed a new technique, still used, to culture articular cartilage cells from iliac crest stem cells. This was commercialised the following year in Boston when John O'Hara moved to Boston Childrens Hospital.. McMinn denied all of John O'Hara's vital contribution to the resurfacing development when he returned to Birmingham in 1991. The Corin technique of resurfacing employs thin (3–4 mm) metal surfaces to line the patients' own hip. In contrast to a THR, the femoral head and neck are retained in this procedure. These large diameter resurfacings match the patient's own anatomy. Because they do not contain polyethylene, these bearings wear at a much lower rate, provided they are manufactured according to specifications, and are implanted well. These allow the patients to return to higher levels of activity after the operation without the fear of early wear. Furthermore, because the devices have the same diameter as the patients' own, they are less prone to dislocation. Over the following years, McMinn further improved the design and