Introduction: The correct alignment of femoral components is necessary to achieve a successful total knee arthroplasty (TKA) and preventing complications such as pain, stiffness, loosening, instability; which itself, depends on making perfect cuts. The posterior distal femoral cut, is one of the most important factors. Yet, the best method of its measurement is controversial.
Methods: In this study, 20 cadavers of femoral bones were used; on which, the distal femoral rotation (DFR) was measured manually by 8 orthopedic surgeons and also was calculated on the basis of the trans-epicondylar axis (TEA) by 2 orthopedic surgeons and 2 radiologists on CT scan image. Accuracy and reliability were assessed in both groups, and the risk of severe malrotation was determined according to an outlier defined as 3 and 5 degrees.
Results: The mean DFR measured manually, was 1.8Â±2.1Âº and the one attained by CT scan images was reported 3.3Â±1.1Âº, projecting a remarkable difference between two groups. The Kappa reliability index was calculated about 0.81 in CT scan results and 0.64 in the other group. (k>0.7 was considered as valuable). With an outlier defined as 3Âº, from the normal distal femoral rotation based on posterior condylar axis (PCA), 3Âº external rotation; 12% of data were outlying in the manually of measured data, and there was no outlier data were reported in the other group. (With a statistically significant difference between two groups)
Conclusion: According to the unreliability and noticeable risk of error in measuring DFR manually based on TEA, this study suggests using CT scan in the patientâ€™s pre-op assessment to obtain the most accurate data.