Sensitivity of femoral orientation estimates to condylar surface and MR image plane location

Purpose: To define the femoral anatomic region that provides the most reliable reference for measuring femoral orientation, from which patellofemoral and tibiofemoral orientation can be measured. Materials and Methods: After a three-dimensional image-based osteo-alignment procedure, two independent estimates of distal femoral orientation, the anterior (AFA) and posterior femoral angles (PFA), were acquired. These sets were comprised of 31 axial femoral orientation estimates each (obtained across a region 10 mm above to 20 mm below the patellar center) from 42 normal axial magnetic resonance (MR) image sets. An analysis of variance was conducted to determine the influence of image plane location, sex, and side on femoral orientation measures. Results: The AFA presented greater variability across subjects (average SD = 3.13degrees) as compared to the PFA (average SD = 1.78degrees). There were significant differences in the AFA based on image plane location and sex. In contrast, no differences were found between sides, sexes, or image plane locations for the PFA. Conclusion: In total, the posterior femoral condylar surface is more reliable than the anterior condylar surface for measuring femoral orientation and is best measured at least 8 mm below the patellar center.