A modern type of implant dramatically cuts dislocation risks after certain hip replacement surgeries, according to new data.
Instead of the traditional single ball-and-socket implant, the so-called dual-mobility device has a small ball rotating within a larger ball, which then rotates inside a metal cup, or socket. Using two moving surfaces instead of one in effect creates a larger diameter ball and increases the distance the ball must travel to escape the socket.
Researchers in Europe randomly assigned 1,600 people aged 65 or over to receive either a standard implant or a dual-mobility implant. All participants had fractured a thigh bone at the point where it connects with the hip joint.
One year after surgery, dislocation rates were 1.3% with the dual-mobility cup versus 4.2% with traditional hip replacement.
After accounting for individual risk factors, the odds of dislocation were 70% lower with the dual cup, according to a report of the study in The Lancet.
The overall risk of surgical complications was also lower with the new cup, although there were no differences in rates of implant infections, deaths or in quality of life during the first year.
“It is extremely painful when a hip replacement dislocates. When it occurs, patients require sedation or further surgery to realign the joint,” study co-author Dr. Nils Hailer of Uppsala University Hospital in Sweden said in a statement.
A dislocated joint impairs quality of life, as the patient may feel they can no longer really trust the implant, and so their participation in daily activities and their confidence in mobilizing is reduced, resulting in social withdrawal, according to a commentary published with the study.
Dual-mobility implants are more expensive than standard implants, but the researchers said the reduction in complications could offset the higher upfront cost and they are undertaking a full health economic analysis.
Manufacturers of the devices include Stryker, Smith+Nephew, and Johnson & Johnson's DePuy Synthes unit.
“Surgeons are already familiar with both implant types, meaning the change could be implemented immediately within existing practice,” study co-author Dr. Xavier Griffin of Queen Mary University of London and Barts Health NHS Trust said in a statement.