Abstract
Introduction
Optimal alignment and position of implants is an important goal In TKA. Conventional mechanical instruments use the anatomic axis and “average” anatomy to position the femoral component to achieve acceptable mechanical limb alignment. Numerous studies have documented the frequency of TKA outliers (+/− 3 degrees) to be 30% or more. The purpose of this study was to determine the “true” distal femoral valgus angle of the femur.
Methods
13,586 CT scans of patients undergoing TKA with patient specific instruments were analyzed. Three-dimensional reconstructions were performed and the distal femoral anatomic and mechanical axes were measured digitally. The distal femoral valgus angle was defined and the difference between the anatomic and mechanical axes of the distal femur.
Results
The average distal femoral valgus angle was 5.7 +/− 2.3 degrees. The range was one-degree varus to 16 degrees valgus. 13.8% of patients had greater than 9 or less than 3 degrees of femoral valgus.
Conclusion
The anatomy of the distal femur is highly variable in patients undergoing TKA. Routine use of anatomic based instruments and average distal femoral valgus angular resections can lead to errors in resultant mechanical limb alignment in a significant number of patients undergoing TKA
