Abstract
Radiostereometric analysis (RSA) allows for precise measurement of interbody distances on X-ray images, such as movement between a joint replacement implant and the bone. The low radiation biplanar EOS imager (EOS imaging, France) scans patients in a weight-bearing position, provides calibrated three-dimensional information on bony anatomy, and could limit the radiation during serial RSA studies. Following the ISO-16087 standard, 15 double exams were conducted to determine the RSA precision of total knee arthroplasty (TKA) patients in the EOS imager, compared to the standard instantaneous, cone-beam, uniplanar digital X-ray set-up.
At a mean of 5 years post-surgery, 15 TKA participants (mean 67 years, 12 female, 3 male) were imaged twice in the biplanar imager. To reduce motion during the scan, a support for the foot was added and the scan speed was increased. The voltage was also increased compared to standard settings for better marker visibility over the implant. A small calibration object was included to remove any remaining sway in post-processing.
The 95% confidence interval precision was 0.11, 0.04, and 0.15 mm in the x, y, and z planes, respectively and 0.15, 0.20, and 0.14° in Rx, Ry, and Rz. Two participants had motion artifacts successfully removed during post-processing using the small calibration object.
With faster speeds and stabilization support, this study found an in vivo RSA precision of ≤ 0.15 mm and ≤ 0.20° for TKA exams, which is within published uniplanar values for arthroplasty RSA. The biplanar imager also adds the benefits of weight bearing imaging, 3D alignment measurements, a lower radiation dose, and does not require a reference object due to known system geometry and automatic image registration.
