Preoperative TKA Planning on Long-Leg Hip-Knee-Ankle Radiographs and It’s Impact on Postoperative Coronal Knee Alignment

Abstract

The importance of measuring of the angle between the mechanical and anatomical femoral axis (fVa) during the preoperative total knee arthroplasty (TKa) planning is not recognized by all. Some surgeons believe that it is acceptable to set distal femoral resection guide at 6° or 7° in all cases or adjust femoral resection guide fVa accordingly with patient height. We conducted two studies. one-retrospective analysis of radiographs of patients with TKa performed since 1.09.2014 till 31.01.2015 (n = 261, 273 TKa). In this cohort, we were looking for correlation between the parameters obtained on long hip-knee-ankle radiographs (fVa, coronal knee alignment) and gender, age, body mass index (BMI) and height, as well as the implant model and the level of constraint. after that we conducted a prospective, randomized trial with TKa performed since 1.02.2015 till 31.05.2015 (n = 225, 225 TKa). The patients were randomly divided into two groups. In the "individual fVa" group (n = 121), the distal femoral resection guide fVa was set accordingly with measured fVa, in the control group (n = 104)-at 7° (average fVa for the Sverdlovsk area patients' population). We compared TKa x-ray results of both groups. Results. first stage. We found no correlation between fVa and age, BMI, height and sex of patients (p>0.05). after TKa residual varus deformity of more than 3° (malalignment) (3.9±1.06) was observed in 7% of cases (19 joints). We found correlation between coronal knee malalignment after TKa and two factors: BMI and initial severity of varus deformity (p = 0.003 and p<0.001). Second stage. In the control group we've seen femoral component deviation of more than 3° from the perpendicular to neutral mechanical axis (malposition) 3 times more often then in the "individual fVa" group (9 vs. 3, p = 0.021). Conclusions. We did not identify the dependence of fVa on sex, age, BMI and height. With initial varus of more than 20° and BMI of more than 30 kg/m 2 , the risk of coronal components malalignment is increased. The average fVa in patients of Sverdlovsk area is 6,7±1,5° (3-11°). Implementation of preoperative fVa measurement and following femoral distal cut adjustments improves femoral component positioning and overall leg alignment postoperatively.