Come to think of it - The perfect fit

Delta often writes about innovative ideas that offer big promises for the future. But what has happened to such ideas years later? What for instance has happened to the special moulds that help surgeons drill or saw at exactly the right place.

If any change in position of the implants has occurred over time, Dr Edward Valstar will spot it. (Photo: Valstar)

Delta, August 2005
‘The surgeon has to drill a hole through a metal cylinder in the mould that fits the shoulder perfectly. That way the shoulder prostheses will also fit perfectly.’ 

Fitting patients with shoulder, hip or knee prostheses is no picnic. With limited views and space to move around in between joints, it’s difficult for surgeons to drill, saw and screw in exactly the right spot and thus perfectly fit the prostheses.

Dr Edward Valstar of the biomechanics and imaging group (3mE) developed a computer programme in 2005 that allows surgeons to make perfectly fitting moulds using a 3D printer and X-ray data. Guidance channels or holes in these moulds help the surgeons perform their duties.

Cartilage however remains difficult to picture. “So the moulds didn’t always fit very well,” says Dr Valstar, who also works at Leiden University Medical Centre’s orthopaedics department and now wants to develop a mould that is adaptive, allowing small changes to be made to the mould once it’s in place. “You know that toy consisting of hundreds of metal spines that you push against your hand or face and it takes over the exact shape? Maybe we can use that same principle to make a patient-specific chirurgical instrument.”

Dr Valstar recently obtained a grant from the Netherlands Organisation for Scientific Research (NWO) to work on a technique that will enable surgeons to repair old hip implants much more efficiently. Over time, an inflammatory process is triggered in many patients by the prostheses’ worn off pieces of plastic or metal, causing, for instance, hip implants to loosen in the bone. Between the implant and the bone a liquid accumulates that must be removed.

“Surgeons usually completely open up the bone to scrape this sludge away,” Dr Valstar says. “We’re trying to figure out if we can’t clean up the implants differently by using ‘cutting water’, for instance, or ultra sound or laser.”
Developing a technique for monitoring implants is another of Dr Valstar’s occupations: “We add grains of the metal tantalum to the bone, which function as markers. In combination with a special calibration technique, these grains allow us to see, with an accuracy down to one-tenth of a millimetre, if any change in position of the implants has occurred over time.” This work recently earned Dr Valstar the Anna Prize, an award given by the Dutch Orthopaedic Research and Education Fund.