Radiological Assessment of Femoral Rotation: A Cadaveric Study

Abstract

PurposeTo define how the lesser trochanter can be used in an objective manner to assess the femoral rotation in plain radiograph. MethodsEighteen pairs of cadaveric femurs from Chinese individuals were used in this study. For each femur, radiographs were taken in the following positions with reference to the anatomical transepicondylar axis: neutral position; 5°, 10°, 15°, and 20° internal rotation; and 5°, 10°, 15°, and 20° external rotation. Lesser-trochanter index, which was defined as the width of lesser trochanter divided by the remaining width of the proximal femur, measured at the level of its most prominent point, which was perpendicular to the anatomical axis of the proximal femur, was obtained on a Picture Archiving Communication System workstation in every radiograph. Statistical analyses were performed by using a statistical software R (R language, version 2.12.0). ResultsThe lesser-trochanter index showed positive correlation with increasing external rotation of femur: correlation coefficient=0.75 (p<0.00001). Analysis-of-variance test showed that the lesser-trochanter indexes of Group 1 (20° and 15° internal rotation), Group 2 (10° internal rotation to 10° external rotation), and Group 3 (15° and 20° external rotation) had statistically significant differences (p<0.00001). Receiver operating characteristic curves were used to determine the cutoff value of lesser-trochanter index to distinguish the three groups. By using the lower cutoff value as 0.17, we can distinguish Group 2 from Group 1 with a sensitivity of 0.85 and a specificity of 0.65. By using the upper cutoff value as 0.28, we can distinguish Group 2 from Group 3 with a sensitivity of 0.80 and a specificity of 0.73. ConclusionThe lesser-trochanter index can be used as a method to assess the rotational alignment of femur in plain radiograph. It is simple, objective, not affected by the factor of magnification, and can be applied to both long and short films.