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No evidence on hip implant safety
One in 12 implants used in hip replacements have no evidence to prove they are safe or effective, experts have warned.
Oxford University researchers trawled data relating to England and Wales and found 8% of devices that were used on patients were not backed by information proving they were safe.
Of all the hip implants potentially available to surgeons to use, 24% were not backed by evidence of safety or effectiveness.
The team warned that the system for regulating hip implants "seems to be entirely inadequate", almost two years after a widespread scandal resulted in an alert being issued to the NHS.
In February last year, the Medicines and Healthcare products Regulatory Agency (MHRA) announced almost 50,000 patients with "metal on metal" hip replacements would need annual checks - including blood tests - over concerns they could cause serious health problems.
Those devices were linked to muscle and bone damage and neurological issues. Tiny metal ions made up of cobalt and chromium were thought to break off from the implants and leak into the blood.
Today's research, published in the British Medical Journal (BMJ), involved a review of all hip implants used in surgery in 2011, taken from the National Joint Registry for England and Wales.
The team concluded: " This systematic review of the literature shows that 8% of primary hip replacement prostheses implanted in 2011 and recorded by the National Joint Registry had no readily available evidence relating to their safety or effectiveness.
"This is likely to be an underestimation of the true problem, as much of the evidence that does exist for the other unrated prostheses is of low quality or relates to short-term outcomes only.
"This is of great concern, particularly in light of the widespread publicity surrounding recent safety problems with regard to some resurfacing and other large diameter metal-on-metal joint replacements."
The researchers said both professional and public confidence in the system was currently " at a low point".
Their review found that 10,617 devices without available evidence of clinical effectiveness to support their use were implanted into patients in 2011.
These comprised 157 cemented stems, 936 uncemented stems, 1,732 cemented cups and 7,577 uncemented cups.
They were rated "unclassified" or "pre-entry" by the Orthopaedic Data Evaluation Panel (Odep) - the body that rates implants according to levels of evidence.
Manufacturers are requested, but not required, to submit data on their product to the Odep.
Products with less than three years of evidence are classified as "pre-entry". Inclusion in this pre-entry category does not require evidence from peer reviewed literature at either the pre-clinical or clinical stages of development.
"Therefore, any data, regardless of whether it has been peer reviewed or not, can be submitted," the researchers said.
Meanwhile, those devices that are "unclassified" have had no evidence submitted by the manufacturers.
In an accompanying editorial, researchers at Harvard Medical School argue that "the ability of manufacturers to promote devices or drugs that are authorised by regulators for widespread use but that do not have rigorous pre-approval data should be restricted."
They said surgeons "should also ensure that their patients know about the benefits and risks of the new - but often unproved - medical devices that they are receiving."
An MHRA spokesman said: " The majority of patients who receive hip implants have well-functioning hips and are at a low risk of developing any serious problems.
"The European regulatory system for medical devices such as hip implants is currently being revised and the MHRA has argued that there needs to be more stringent audits and clearer requirements relating to the consideration of clinical evidence.
"We also want information on the performance of devices to be more transparent and freely available.
"In addition, a new system called 'beyond compliance' is being established that promotes the availability of short- to mid-term clinical data and strengthens the evidence base for new implants in a more transparent manner.
"This should decrease the complication and the revision rates that may be associated with newly introduced hip implants, resulting in better patient care, better patient quality of life and decreased costs to the health services."
A statement from the British Hip Society said: " The number of hip implants used in this country without a proven track record is falling year on year.
"There are fewer unproven prostheses implanted in the UK compared with the practice in almost every other Western country, with the possible exception of Scandinavian countries.
"That the practice of hip surgery (including implant choice in the vast majority of cases) is good in this country is proven by the fact that the revision burden is low by international comparison and more the 60% lower than that in the United States."