Measurement of rotational alignment of the distal femur in total knee arthroplasty

Objectives: To measure and compare the included angle between the surgical transepicondylar axis (STEA) and the posterior condylar line (PCL) and the included angle between the femoral anteroposterior line (APL) and PCL, and to discuss the value of STEA, APL, and PCL as rotational alignment landmarks of the distal femur in total knee arthroplasty (TKA). Methods: Seventy-five normal femoral specimens from Chinese adult cadavers were randomly selected. An axial photograph of every femoral specimen was taken with a digital camera and put into a personal computer. Using Photoshop 7.0.1 software, the included angle between the perpendicular line of APL and the PCL, noted as APA, together with the posterior condylar angle (PCA) between STEA and PCL were measured and compared using a paired-samples t-test. Results: The value for PCA was 3.67°± 1.62° (range, 0.75°–5.90°) and for APA 3.50°± 1.40° (range, 1.34°–5.65°). There was no significant difference between these two angles (t= 0.949, P= 0.359). Considering their relatively small means, these two angles showed wide variations. Conclusions: The rotational alignment of the femoral component can not accurately be determined by using PCL as a landmark. In order to get a proper rotational alignment of the femoral component in most cases of TKA, APL and STEA should be used as a double check.