Accuracy and precision of radiostereometric analysis in the measurement of THR femoral component translations: human and canine in vitro models

Abstract

Radiostereometric analysis (RSA) is used to measure translations of joint replacement components with respect to the host bone in vivo. We used two cadaveric models of hip arthroplasty, one human and one canine, to evaluate the accuracy and precision of RSA-based estimates of translations of the femoral component with respect to the femur under ideal conditions. The femoral components were attached rigidly to a micrometer stage that provided standard displacements in increments of 25 and 50 pm in the interval from zero to 500 pni along three orthogonal axes. Radiostereometric examinations were performed for each increment.Accuracy was calculated as the 95% prediction intervals from regression analyses between the measured and actual displacements.Precision was evaluated as the standard deviation of five repeated measurements of a 200 pm displacement along each axis. Both accuracy and precision were best along the longitudinal axis, with a prediction interval of f 4 7 pm in the human model and 1 4 5 pm in the canine model and a standard deviation of 30 pm in the human model and 40 pm in the canine model. The use of only the prosthetic head as a landmark (as opposed to three markers placed on the femoral stem) led to a 3-fold larger prediction interval in the human model and a '-fold greater prediction interval in the canine model.

Is Model-based Radiostereometric Analysis Suitable for Clinical Trials of a Cementless Tapered Wedge Femoral Stem?

“…Model-based RSA was highly accurate for measurement of translation (20- 130 lm), corresponding to the level of accuracy (10-60 lm) observed in our marker-based RSA and in previous phantom model studies of marker-based RSA [4,19,23]. The Bland-Altman plots showed the closeness of the model-based and marker-based measurements.…”

“…Accuracy is related to measurement errors and is defined as the closeness of agreement between the test result with RSA imaging and the direct measurement of implant position using a highly accurate measurement tool, which has a resolution substantially better than RSA [21]. Validation of accuracy requires the use of a phantom model in which accurate translations and rotations can be controlled by means of micromanipulators [4,16,19,22]. Validation studies of model-based RSA have focused on measuring ''the accuracy of zero motion'' in phantom models [10,20], when there is no controlled micromotion of the implant, but the whole phantom is subjected to repeated RSA imaging in different positions.…”

Radiostereometric Analysis: The Hip

“…In most clinical studies the accuracy has been approximately 0.2 mm [7]. However, in vitro studies show accuracy as low as 0.047mm to 0.121 mm [8]. In general measurements of translation along the longitudinal axis are more accurate than those along the transverse and sagittal axis [8].…”

“…However, in vitro studies show accuracy as low as 0.047mm to 0.121 mm [8]. In general measurements of translation along the longitudinal axis are more accurate than those along the transverse and sagittal axis [8]. Measurement of femoral component migration based on three markers in the implant is about three times more accurate than relying on the calculated center of the femoral head alone.…”

“…A condition number of less than 40 leads to a 3 fold increase of the accuracy compared to a condition number above 143. Although precision depends to a lesser degree on the ideal marker position the best marker configuration for accuracy seems to provide the most precise measurements [8]. In vitro precision has been 0.03 mm for 0.200 mm displacements [8].…”