Anatomic Rotational Relationship of Distal Femur in Indian Population and its Implication in Total Knee Arthroplasty: A Magnetic Resonance Imaging Based Study

Abstract Background Bony landmarks for referencing distal femoral rotation may differ with ethnic populations. The study aims to find out the relationship of the bony landmarks of distal femur for rotational alignment of femoral component in total knee arthroplasty in Indian population and compare it with other ethnic groups. Methods Rotational relationship of distal femoral bony landmarks was studied using magnetic resonance images of 141 knees. The condylar twist angle (CTA), Whiteside's-posterior condylar axis angle (WL/PCL), Whiteside's-anatomical epicondylar angle (WL/A-EA) and difference between the two epicondylar axes (S-EA/A-EA) were measured. The effect of gender, side and age of these relationships was analyzed. Results The mean CTA, WL/A-EA/WL/PCL and A-EA/S-EA was found to be 5.59 ± 2°, 89.38 ± 2.66°, 5.44 ± 2.88°, 3.11 ± 0.54° respectively. A-EA/S-EA was found to be lower in younger population as compared to the older population. Rest none of the variables showed any significant difference when compared against age, sex or side. Conclusion The posterior condylar axis was 5.59˚ externally rotated in relation to clinical epicondylar axis. About 2.5° of added external rotation is required in jigs using the conventional 3° of inbuilt external rotation, if clinical epicondylar axis is taken as reference for apt placement of the femoral component.