Recently a Texas Federal Jury awarded $500 million dollars to 5 patients who said they were injured by the Pinnacle Metal on Metal Hip implant which were used to replace their hips. They said they suffered with pain and needed further surgery. Thousands of patients have been given these implants and now more and more patients are coming forward to take DePuy (part of Johnson and Johnson group) to court.

A paper, published in the British Medical Journal Open, describes how many of the Pinnacle metal-on-metal components made by Depuy were “found to be manufactured out of their specifications”. Research carried out by orthopaedic surgeons and engineers discovered that over a third of the devices analysed fell out of the size limits set by the company making them, with devices implanted after 2006 most affected. According to the authors, the Pinnacle is the most commonly used metal-on-metal implant in the world and has been used for more than 180,000 people. These patients might be at risk of early revision surgery. Metal on metal hip replacements implanted since 2006 are more prone to failure and the need for further surgery.

They reviewed the progress of 434 patients (243 women and 191 men) fitted with 489 metal on metal total hip replacements at one hospital trust in northern England, and monitored for an average of 7.5 years after the procedure. In all, 71 metal hips required surgical removal and replacement, adding up to a revision rate of 16.4%, which the researchers describe as “unacceptably high.” Before 2006, only five out of 43 hips (12%) failed to meet the manufacturer’s product specification. But after 2006 more than a third (36%; 43 out of 118) failed to comply. Acceptable failure rate for total hip replacement should be under 0.5%.

In over 40% of cases examined the taper surface that anchors the implant in the femur was defective. This was associated with excessive release of metal particle (chromium and cobalt) in to the blood stream. The tissues were stained black by the metal causing considerable pain in around one in five (19%) cases.

Release of metal particle occurs when there is excessive friction between the metallic head of the prosthesis and the metallic socket (ie the acetabular component). The larger the size of the head more the friction. If there is any incongruity between the head of the prosthesis and the socket in which it articulates the amount of metallic particles released will increase significantly. This is what has happened with the Pinnacle Implant. Research carried out by orthopaedic surgeons and engineers discovered that over a third of the devices analysed fell out of the size limits set by the company making them, with devices implanted after 2006 most affected.

Sir John Charnley inventor of total hip replacement introduced his joint about 50 years ago. Those joints had worked perfectly well from the 1970s. The metal-on-metal implants, introduced by later surgeons were supposed to be innovative and last longer, has been queried by many saying “If it Ain’t Broke, Don’t Fix It” (why introduce a new joint when the old one works perfectly). They are being proved right.

Two years ago I discussed a paper which appeared in the Bone and joint journal (July 2014, 96-B) “A comparative assessment of small-head metal-on-metal and ceramic-on-polyethylene total hip replacement” I concluded my post with – “Would you still consider using a Metal on Metal Total Hip Replacement for your patient? Inspite of all the improvements, I am sure there are many like me who will be reluctant to use a MOM joint”.

Badri