<qa>  What is the cause of local and distant abnormal tissue responses?Blood metal ions released from metal hip implants are increasingly recognized as a potential cause of local and distant abnormal tissue responses, since cobalt and chromium is released into the peri-prosthetic tissues and transported systemically throughout the body. Component design and positioning are associated with increased wear and as a result raised metal ion levels. However, a definitive causal link to systemic symptoms still remains to be established. 