RSA is a powerful research technique that is currently being studied at Hospital for Special Surgery for joint replacement patients. RSA stands for radiostereometric analysis, which describes a special way of taking two x-rays from different directions at the same time, creating a “stereo” image. RSA x-rays allow surgeons to measure precisely how the body and the implant are interacting. This enables them to accomplish two goals at once – while measuring the patient’s progress, they can also use information from this research to improve implant design and technology for future patients.
The power of RSA comes from its ability to precisely measure small amounts of movement, thus allowing us to gather a lot of information from a small group of patients.
The RSA Process
To precisely measure implant position on RSA images, the surgeon inserts tantalum marker beads into the bone surrounding the implant. Tantalum marker beads are very small – about the size of a poppy seed- and made of tantalum, a metal that is used in prosthetic implants and is well tolerated by the body. These beads become stably integrated into the bone and can be used as references with which to detect any change in position of the implant components.
The first set of stereo x-rays are taken post-operatively while the patient is still in the hospital, with additional images taken on subsequent office visits. Surgeons rely on colleagues in Sweden to analyze the images and to calculate any movement or shifting of the implant that might have occurred. Previous studies have shown RSA to be accurate to 2/10ths of a millimeter of motion.
An RSA image of tantalum marker beads inserted into a joint implant and labeled for detection of movement.
The Benefits of RSA to Patients
The information gathered from RSA tells the surgeon precisely how much position change has occurred since implantation of the prosthesis. This may also help the surgeon predict how long the implant will last. It can give the patient valuable information about his or her particular prosthesis. RSA will also benefit future patients by providing important data to help researchers in improving joint replacement surgery.
Because of its accuracy and precision, RSA has been shown to be perhaps the most reliable tool for providing an early warning that an implant is failing.”
With this level of accuracy,we can assess new implant technology, more accurately predicting which implants will offer good long term performance. It’s a great benefit for the good of patient care.