Accuracy and precision of radiostereometric analysis in the measurement of three-dimensional micromotion in a fracture model of the distal radius.

The purpose of the current study was to verify the feasibility of radiostereometric analysis (RSA) in monitoring three-dimensional fracture micromotion in fractures of the distal radius. The experimental set-up consisted of a simulated model of an extra-articular Colles' fracture, including metallic beads inserted into the bone on either side of the fracture site. The model was rigidly fixed to high precision micrometer stages allowing controlled translation in three axes and rotation about the longitudinal and transverse axes. The whole construct was placed inside a RSA calibration cage with two perpendicular radiographic film cassettes. Accuracy was calculated as the 95% prediction intervals from the regression analyses between the micromotion measured by RSA and actual displacements measured by micrometers. Precision was determined as the standard deviation of five repeated measurements of a 200 microm displacement or a 0.5 degrees rotation along a specific axis. Translations from 25 microm to 5mm were measured with an accuracy of +/-6 microm and translations of 200 microm were measured with a precision of 2-6 microm. Rotations ranging from 1/6 degrees to 2 degrees were measured with an accuracy of +/-0.073 degrees and rotations of 1/2 degrees were measured with a precision of 0.025 degrees -0.096 degrees . The number of markers and their configuration had greater impact on the accuracy and precision of rotation than on those of translation. Aside from the unknown rate of clinical marker loosening, the current results favor the use of at least four markers in each bone fragment in distal radius fractures. These results suggest a strong rationale for the use of RSA as an objective tool for comparing different treatment modalities and novel bone graft substitutes aimed at stabilization of fractures of the distal radius.