Hi Thanks for writing your query The cause may be wear and tear of replaced hip joint. Does the hip replaced is of metal on metal type? The cause could be deposition of cobalt chromium ions around hip joint leading to pain. There are concerns regarding the high levels of heavy metals (cobalt and chromium) in the blood; however, there are very few reports of actual clinical problems. If the blood test indicates a high level of these particles, a second blood test may be done at three months .These levels may be high even if you are not experiencing any symptoms, so this blood testing is very important. If the second blood test still indicates a high level of these particles, you may require ultrasound test of your metal on metal Hip System. If such tests show a reaction to the particles, you may require surgery to replace your implant. Meanwhile continue with ibuprofen as pain killer. Having said that my advice would be visit the operating surgeon and discuss the above said issues. Hope this information helps you. Take care and I shall be glad to answer any further query. Regards Dr.chugh Orthopaedic surgeon http://bit.ly/drmchugh