New technique for detecting loosening of artificial hip joints

Engineers at Bath University in the UK have developed a method for detecting when artificial hip joints have come loose, by measuring the frequency of sound produced when the femur bone in the leg is vibrated.

The new method is much more sensitive than the traditional technique of using x-rays to detect the loosening of implants, and can diagnose much smaller gaps around an implanted joint.

In the UK around 50,000 people receive total hip replacements each year, and many will go on to develop pain from them. It is difficult to know whether this from an infection, which can be cured by antibiotics, or because the cement holding the implant in place has worn away, which means surgery is needed. A reliable diagnostic test would save patients undergoing unnecessary surgery.

James Cunningham developed the method of placing a piece of vibrating equipment on to the patient’s knee, which vibrates the femur and the hip joint. An ultrasound device attached to the hip picks up sound vibrations from the joint. If the frequencies are pure, that is, a regular wave of increasing and decreasing frequencies, this signals the joint is firmly fastened to the bone. If the sound waves are impure and irregular the joint has come loose.

Cunningham now hopes his findings will be applied to develop a device for use in clinical practice.