THR is not new to me. Had replacement in 2003 with a modular MoM. Had excellent results. Returned to work within 4 weeks and remained active hiking and even cross-country skiing (when there was snow). Running never worked; felt like a jack-hammer on my leg. Things took a turn in 2012 with severe pain. Saw OS who among other things tested my blood and found elevated Cobalt at 4.7. Hip pain diminished over time with only occasion twinges to remind me things were not the same. Then in October of 2013 the severe pain returned and did not let up. Saw OS again. Cobalt at 4.5. Only solution he said was a revision, and soon, before more tissue and possibly bone was effected. X-rays showed post and socket were firm and tight. On 14 Jan 2014, modular head was replaced with ceramic. Over the ceramic head was a plastic swivel. Damaged tissue was removed and while the post was firm, it was found that tunneling had taken place behind the socket. Bone stimulant was injected into the this area which had deteriorate.