Health experts are calling for a ban on metal-on-metal hip implants after finding unequivocal evidence of high failure rates in a new study.

Researchers looked into data from more than 400,000 hip replacements and found that metal-on-metal implants need to be rechecked more frequently than other types of implants. They also found that the failure rates were higher among women.

The recommendation of a ban comes after the Medicines and Healthcare Products Regulatory Agency (MHRA) admitted that the implants used in treatment of hip-replacement patients pose a `small risk'.

The MHRA acknowledged that the implants could cause complications and it has also issued an alert to orthopaedic surgeons. The surgeons are asked to contact the affected patients. The metal implants can cause health problems including severe pain and long-term disability.

According to estimates, about 50,000 hip-replacement patients will need annual medical checks. MHRA has said that it has reports about 370 "adverse incident" relating to metal-on-metal implants, but it is believed that the actual number of adverse incidents could be much higher and it went unreported.

Experts say that the cobalt-chrome alloy used to make metal-on-metal hips could pose some risk to the patients. Documented records show that sometimes very small metal ions break off from the implants and leak into the blood and this may affect muscle and bone, cause severe pain and even long-term disability.