1. Hospital de Faro, Faro, Portugal

2. Hospital D. Estefânia, Lisboa, Portugal

3. Hospital de Vila Franca de Xira, Lisboa, Portugal

4. Hospital Particular do Algarve, Faro, Portugal

- Poster, Congresso Nacional de Ortopedia, Coimbra, Outubro de 2017

**Background: **Pre-op planning is key to TKA success. Occasionally few steps are omitted. One of these examples is performing a distal femoral valgus cut based on the “normal” interval 5o-7o. There are no validated studies to ensure the safety of this practice in our population.**Objectives: **Identify patient characteristics (gender, height, weight, BMI) associated with an increased risk of coronal malalignment in the femoral component with the use of a distal femoral valgus cut in the interval 5o-7o.**Study Design & Methods: **115 “patient specific instrumentation” (PSI) TKA (42 men and 73 women; mean age of 69y), between 2012 to 2016 were included in this study. All the patients have done pre-op lower limb standing extra long x-ray and measurement of the angle formed between anatomic(AA) and mechanical axis(MA). A subgroup of 50 patients with records of weight, height and BMI was studied for the association of these factors with extreme values of the angle between AA and MA. Statistical analysis was performed with SPPS software v22.0. Non parametric tests were used. Mann-Withney and T-student to identify for differences between groups and Spearman test for correlation with gender, weight, height and BMI.**Results: **Mean angle between AA and MA was 5.8o. Women had a mean value of 5.6o (min. 2.1o, max. 10.6o) and men 6.2o (min. 3.7o, max. 9.5o) (p<0.05). 54.8% of men had an angle between AA and MA in the interval 5o to 7o. 57.5% of women were in this interval. Considering acceptable a coronal malalignment of 3o, patients who would have a distal femoral valgus cut of 6o should have an angle between AA and MA in the interval 3o-9o. 2.4% of men and 5.5% of women had an angle between AA and MA outside this interval (outliers). Patients who would have a distal femoral valgus cut of 5o should have an angle between AA and MA in the interval 2o-8o. There were 9.8% of outliers. A distal femoral valgus cut of 7o should have an angle between AA and MA in the interval 4o-10o. There were 7.8% of outliers. There was no correlation between outliers and gender, height, weight, BMI (p>0.05).**Conclusions: **Due to sample size we could not get conclusions regarding risk factors for outliers in the Portuguese population. The fact that if it would be used a distal femoral cut of 5o, 6o or 7o, there would be 9.6%, 4.3% and 7.8% of cases with a coronal malalignment, support the necessity of systematic realization of pre op lower limb standing extra long x-ray and measurement of the angle formed between AA and MA in order to improve results in total knee arthroplasty.

**Palavras-chave: **Alignmnet, Total Knee Arthroplasty, Femoral Cut