Distal Femoral Valgus Resection Angle in Conventional Total Knee Arthroplasty - a CT Scanogram Study

Document Type : RESEARCH PAPER


Department of Orthopedics, Sagar Hospitals , Bangalore, India


Objectives: In conventional total knee arthroplasty (TKA), the distal femur valgus resection angle (DFVA) is decided 
either by measuring the specific resection angle for each patient on preoperative anteroposterior hip-knee-ankle 
(HKA) weight-bearing radiograph or using a fixed resection angle of five to seven degrees, when such facilities are 
not available. This study aims to measure the DVFA in TKA patients using preoperative HKA non-weight-bearing 
computerized tomography (CT) scanogram scout films and determine its relation with preoperative coronal plane 
lower-limb deformities.
Methods: In this retrospective radiological study, various measurements were performed on bilateral, preoperative 
hip-knee-ankle CT scanograms of 73 knee osteoarthritis patients who had presented for total knee replacement 
surgery using a standard protocol. The angle between the femoral anatomical axis and femoral mechanical axis 
was measured as the femoral mechanical anatomical angle (FMAA), which corresponds to the surgical DFVA. The 
angle between the femoral and tibial mechanical axes was measured as mechanical femorotibial angle (MFTA). 
The correlation between FMAA and MFTA was studied.
Results: The mean FMAA for the study group was 6.45° (range 3° to 11°, SD 1.17°). The MFTA for the study group 
ranged from 24° varus to 14° valgus. The alignment was valgus in 14.4% (n=21), varus in 84.2% (n=123), and “0 
degrees” in 1.3% (n=2). With valgus coronal alignment taken as positive and varus as negative, the Pearson's 
correlation coefficient for MFTA with FMAA was r = −0.5183 (p<0.001), indicating that valgus knees tended to have 
a smaller FMA angle and varus knees tended to have a larger FMA angle.
Conclusion: In the non-availability of individualized measurements, in primary TKA, we recommend setting DFVA 
as five degrees for valgus deformities, six degrees for mild/moderate varus deformities (MFTA <15°) and seven 
degrees for severe varus deformities (MFTA > 15°).
 Level of evidence: III


Main Subjects

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