How safe are orthoroentgenograms in determining the amount of correction for varus deformities?

Objectives: In this study, we evaluated the effects of the distance of the legs from the midline on alignment and angles of the lower extremities in orthoroentgenograms. Patients and methods: Between March 2012 and April 2013, 95 limbs of 56 patients with varus deformity who underwent orthoroentgenogram to identify the amount of joint laxity in two positions were included in this study. The initial X-ray was performed with the feet in contact, while the other was performed as the legs were abducted to be in line with the shoulders. For each orthoroentgenogram, the mean mechanical axis angle, anatomical axis, and joint line orientation angles were measured retrospectively. These measurements were repeated for 43 limbs with varus deformity > 10 degrees. Results: In the orthoroentgenograms with the feet in contact, the mean mechanical axis angle was 9.58 degrees +/- 5.7 degrees, (0.20 degrees; 26.0 degrees), the mean anatomical axis angle 3.65 degrees +/- 6.14 degrees, (-9.0 degrees; 21.0 degrees), and the mean joint line orientation angle -3.41 degrees +/- 2.52 degrees, (-12.0 degrees; 1.60 degrees). In the orthoroentgenograms with the legs abducted, the mean mechanical axis angle was 7.73 degrees +/- 5.58 degrees, (-3.0 degrees; 23.0 degrees), the mean anatomical axis angle 2.62 degrees +/- 5.87 degrees, (-11.0 degrees; 18.30 degrees), and mean joint line orientation angle was -2.44 degrees +/- 2.41 degrees, (-13.0 degrees; 3.0 degrees). The differences in the angles between the two positions were statistically significant (p < 0.005). Conclusion: Our study results showed that the mean values of mechanical axis angle, anatomical axis and the joint line orientation angle were higher in orthoroentgenograms with the feet in contact than the orthoroentgenograms with the legs abducted in patients with yarns gonarthrosis. We suggest that this may lead to mistakes in the preoperative planning. Ideal positions should be standardized to minimize possible problems.