Accuracy and precision of in vitro EOS imaging compared to digital radiographs in the measurement of intramedullary lengthening

Objectives: Accurate limb length measurement is essential during limb lengthening procedures to prevent neurologic and musculoskeletal complications. Magnetic intramedullary lengthening nails (MILN) rely on radiographs for measurement, but the optimal radiographic technique is not established. This study evaluated the precision and accuracy of EOS imaging versus digital radiography, including calibration techniques and measurement techniques for assessing intramedullary lengthening. Methods: An MILN was inserted into a Sawbones femur, and lengthening measurements from digital X-ray and EOS imaging were compared to external remote control (ERC) results. Measurements were taken with and without calibration using a magnification ball, nail width, or female nail length. Four observers measured the distraction gap, spindle length, full nail length, and male nail length at various hip flexion angles. Precision and accuracy were calculated for each technique. Results: From 576 measurements, EOS imaging demonstrated significantly higher accuracy than digital radiography (83.6% vs. 73.5% absolute accuracy; p < 0.001) when non-calibrated values were included. EOS maintained superior accuracy at 30 mm, 50 mm, and 70 mm of lengthening (p < 0.05), with no difference at 10 mm. Calibration did not affect EOS accuracy, whereas digital radiography was less accurate without calibration (p < 0.001). Distraction gap measurement was the most accurate for both modalities, and 0° hip flexion provided the highest precision. Overall, EOS was more precise (79.4% vs. 71.7% precision rates; p < 0.001). Conclusion: EOS imaging is recommended for limb lengthening measurements due to its superior precision and accuracy. For digital radiographs, careful calibration is essential to achieve accurate measurements.