Cross-Table Lateral Radiographs Accurately Predict Displacement in Valgus-Impacted Femoral Neck Fractures

BACKGROUND: Femoral neck fractures are classified as nondisplaced (Garden types I and II) or displaced (Garden types III and IV) on the basis of anteroposterior radiographs. Cross-table lateral radiographs are important in the assessment of Garden type-I and II fractures as posterior tilt of the femoral head may influence treatment results. A posterior tilt of >20° has been associated with an increased risk of treatment failure after internal fixation, although the precision of these measurements has not been validated. Therefore, the purpose of the present study was to compare cross-table lateral radiographs with 3-dimensional computed tomographic (3D-CT) reconstructions of Garden type-I and II femoral neck fractures. METHODS: Twenty-three patients presenting with Garden type-I and II femoral neck fractures that were verified on anteroposterior radiographs underwent CT scanning immediately after radiographic examination. 3D models of the fractured and uninjured femora were reconstructed from the CT images, and displacement of the 3D models was determined by superimposing the fractured and uninjured femora. We defined a coordinate system with its origin at the center of the uninjured femoral head with the x axis oriented medially; the y axis, posteriorly; and the z axis, cranially. Correlations between lateral radiographs and 3D models were assessed with the Spearman rank coefficient, mean difference, and limits of agreement. RESULTS: Posterior tilt of the femoral head on lateral radiographs was strongly correlated with displacement of the femoral head along the y axis of the 3D models, with a correlation coefficient of 0.86 (p < 0.001). Correlations between the findings on lateral radiographs and displacements along the x or z axis were weak, with coefficients of −0.30 (p = 0.18) and 0.21 (p = 0.34), respectively. The mean difference between displacement on lateral radiographs and displacement along the y axis of the 3D models was smaller, and demonstrated a smaller limits-of-agreement interval, compared with the x or z axis. CONCLUSIONS: Our results demonstrated a strong correlation between posterior displacement of the femoral head on lateral radiographs and displacement along the y axis in 3D models of Garden type-I and II femoral neck fractures. This finding indicates that lateral radiographs provide an accurate assessment of posterior tilt.