Three-dimensional bone-implant movements in trochanteric hip fractures: Precision and accuracy of radiostereometric analysis in a phantom model.

The accuracy and precision of RSA were evaluated in the experimental study of screw cut-out complication after fixation of trochanteric fractures. A plastic bone model of a two-part trochanteric fracture was constructed with a Gamma nail implant incorporating RSA markers. The femoral head fragment was attached to a separate rotational table and the femoral shaft was mounted on the micrometer. Three main motions were simulated: Femoral head translation and rotation along the axis of the lag screw and fracture fragment translation along anatomical axes. Accuracy and precision were determined according to ISO 16,087 and ASTM standard F2385-04. Translations along the lag screw axis were measured with a precision within  ±0.14 mm and an accuracy within ±0.03 mm. With simultaneous translations along all three anatomical axes, lowest precision was measured for the x-axis (±0.29, 0.07 mm, respectively), but improved when analyzed as a vector (±0.08, 0.03 mm). The precision and accuracy of femoral head rotations were within 0.5° and 0.18°, respectively. The resolution of the RSA method tested in this model was high, though it varied depending on the type of analyzed motion. This information is valuable when selecting and interpreting outcome parameters evaluating implant migration and osteosynthesis stability in future clinical RSA studies.