The Polymotion Hip Resurfacing device is an allergy-free device that uses a 3mm-thick cup made with a material known as cross-linked polyethylene, one of the toughest plastics in existence.
Traditional metal-on-metal hip resurfacing uses cobalt chromium alloy, explains Mr Derek McMinn, a consultant orthopaedic surgeon at BMI Edgbaston Hospital in Birmingham, who developed the new procedure.
‘Metal reactions vary in severity, but in the worst cases can lead to necrosis [death] of surrounding hip muscle and permanent disability for the patient,’ he said.
Another benefit of the capping procedure is that less bone is removed, in contrast to total hip replacements when the femoral head (ball joint of the hip) is replaced by a stemmed device and very little of the upper leg bone is retained.
Replacement hip joints can also wear out in more active patients.
During the two-hour resurfacing procedure, the ball and socket of the hip joint are separated. Worn bone and cartilage is then trimmed from the surfaces of the thigh bone and hip socket.
The socket is lined with the anti-allergenic polyethylene cup. The ball of the thigh bone is capped with smooth titanium metal covering, which also does not cause allergic reactions, and then placed back into the socket.
Since polyethylene does not bond with bone, a layer of porous titanium is applied to cover the surface of the cup that comes into contact with the bone.
This encourages the socket bone to grow into the titanium to ensure the cup is welded to the skeleton.
According to Mr McMinn, Polymotion Hip Resurfacing will be especially helpful to women.
He says: ‘Not only do they tend to suffer more metal allergy, they also have a higher incidence of a condition known as developmental dysplasia of the hips.’
He added that more women also have shallow sockets, and this makes it a challenge to accurately position a cup in a resurfacing operation.
In general, with metal-on-metal procedures, if a cup isn’t positioned properly it can cause increased wear of the components, leading to a reaction as particles leach into the blood stream.
With the polymotion method, because the inside surface of the cup is made of polyethylene, this risk is reduced.
Three patients have already undergone the new procedure. One of them, 54-year-old ballet teacher Elaine Williams had the operation in July after enduring two years of pain in her right hip.