Radiologic Assessment of Distal Femur Cutting Angle in Varus Knee Candidates for Total Knee Arthroplasty

Background: In a total knee arthroplasty surgery the goal is to produce 90 degree angle between the knee articular lobe and the mechanical femoral line. Most orthopedic surgeons usually utilize a 5 to 7 degree for distal femoral cutting angle. In this study we will aim at clearing this question, that whether the” five-seven degree” distal femoral cutting angle supposed to be an equable spectrum? Method: In this three year course of study, 123 candidate patients for knee arthroplasty with varus knee deformities underwent pre operatore radiologic assessment before joint replacement surgery. The femoral bowing angle, distal femoral cutting angle, neck shaft angle, angle between knee articular line and mechanical femoral angle were assessed and statistically analyzed. Results: The mean varus angle was in 13.71±4.34 in male and 16.41±7.87 in female. The mean distal femoral cutting angle (DFCA) was 6.50±1.09 in male and 7.38±1.75 in female. In 48 patients (%39) the female DFCA was out of 507 degree range. In 32 (26%) of patients the DFCA was 7-9 degrees and in 8 (%6) it was over 9 degrees, and in 8 (%6) was less than 5. The angle differences had no sex-related variation. There was a good co-relation between DFCA and bowing angle (r=0.769). The co-relation between DFCA and NSA was moderator (r=0.523). The co-relation between DFCA and DFA (r=0.11) and varus angle with LDFA (r=0.28) was low. LDFA was also related to NSA (r=0.15). Therefore, the candidates for knee replacement who have varus deformity may need a distal femoral cutting angle over 7 degrees. Based on these results, the distal femoral cutting angle in patients in need of a knee arthroplasty and varus deformity might be more than seven degrees. Conclusion: The distul femoral cutting angle in knee arthroplasty in face of severe varus does not have a constant value and maybe over 7 degrees. A long standing radiograph is needed to measure the mechanical and correlate with axis the anatomic axis of distal third of femur. When the bowing angle is high the DFCA will need to be higher.