Objective: Rotation of femoral components could be optimized to improve function and durability of the knee joint. The purpose of the present study was to assess rotational alignment of femoral component comparing between CT-based, custom cutting blocks and the contemporary total knee arthroplasty, instrument technique.
Material and Method: The prospective control study of 80 patients underwent total knee arthroplasty by using PFC Sigma PS total knee design. Rotation of femoral component was analyzed in all patients using postoperative CT scan. Forty patients were performed on by using CT-based, patient-specific cutting blocks with femoral rotational axis relative to transepicondylar axis while forty patients were performed on by using contemporary instrumentation with alignment at 3 degrees external rotation from posterior condylar line. The rotation of the femoral component with external rotation of more than 3 degrees or internal rotation was considered outlier.
Results: There was no statistically significant difference among ages, gender, BMI, pre-operative mechanical axis between the two groups. There were eleven outliers in conventional group (range, 5 degrees of external rotation to 3 degrees of internal rotation), three femoral components were in excessive external rotation with the angle of more than 3 degrees and eight femoral components were in internal rotation. In contrast with custom cutting block group was no outliers of femoral rotation. The average rotational alignment was 1.04°+0.62° external rotation from epicondylar axis in custom cutting group and 1.58°+1.75° in contemporary group.
Conclusion: Custom cutting, block technique significantly reduced the outlier of the femoral component rotation and aided in positioning of the femoral component in optimal alignment. The improvement of femoral rotation showed no difference in clinical outcome between the two groups.

Keywords: Patient-specific instrument, Rotational alignment, Femoral component, Total knee arthroplasty