THOUSANDS of Scots with metal hip replacements face the prospect of a lifetime of checks after the UK regulator issued an alert about their safety.

Amid claims some of the devices could lead to serious health problems, the Medicines and Healthcare products Regulatory Agency (MHRA) warned high-risk patients may need blood tests and MRI scans. The problem could involve 50,000 in the UK.

The British Medical Journal (BMJ) revealed hundreds of thousands of hip surgery patients around the world may have been exposed to dangerously high levels of toxic metals from faulty "metal on metal" (MoM) hip implants.

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It found in large uncontrolled experiments that cobalt and chromium ions from the devices can seep into patients' tissues, causing chemical reactions which destroy muscle and bone and leave some people with long-term disability.

The MHRA said it had received 370 "adverse incident" reports involving the implants and around 49,000 UK patients with large-head hip implants were at high-risk. It is now advising annual check-ups for life for patients with large-headed MoM implants.

Fears have also been raised about how metal ions can leach into the bloodstream, spreading to the lymph nodes, spleen, liver and kidneys. There are concerns about damage to chromosomes, leading to genetic changes.

Dr Susanne Ludgate, MHRA clinical director, said: "Evidence shows patients have a small risk of suffering complications from metal-on-metal hip implants.

"As a precautionary measure, we have issued updated advice to surgeons and doctors that they should annually monitor patients for the lifetime of their metal-on-metal total hip replacements that are sized 36 millimetres or more, because this particular type of hip replacement has a small risk of causing complications."

A Scottish Government spokeswoman said: "All patients affected have been contacted by their local health board and, where necessary, are receiving follow-up appointments. Where appropriate, patients will receive scans and blood tests to ensure there are no issues with their device.

"Where these tests determine there are issues with the patient's hip replacement, the MHRA has advised that removal and replacement may be appropriate, although continual monitoring of these patients should keep removal to a minimum."

Hip implants – like breast implants – did not have to pass clinical trials before they were put into patients, although problems were reported as far back as 1975.

In 2006, evidence pointed to high metal concentrations in patients with articular surface replacement (ASR) hips – a form of metal-on-metal implant manufactured by De Puy. Four years later, the MHRA issued an official safety alert and the ASR hip was recalled from the market. Dr Ludgate said the delay was due to "very varied reports from surgeons".

Michael Carome, deputy director of Public Citizen's Health Research Group, said: "We will only find out about the safety of these devices after large numbers of people have already been exposed."

The Scottish Government said fewer than 300 De Puy ASR metal implants had been used on NHS Scotland patients between 2003 and 2010.

Japanese surgeons have raised concerns about another DePuy model, the Pinnacle, which could push up the toll of Scots victims. De Puy insists it is safe.

Already one Scottish lawyer has been contacted by 150 victims. Patrick McGuire of Glasgow-based Thompsons said: "This is a scandal on a massive scale that could conceivably affect thousands of Scots."