Aim: to calculate the optimal values of the residual angle of the deviation of the lower leg during unicompartmental knee replacement by mathematical modeling. Object and methods of research. For mathematical modeling, a calculated load scheme of the knee joint with a single-pole endoprosthesis was chosen, in which the femur is represented by a structure with two points of articulated fixation of the support. The value of the force F was assumed to be 700 N. The angle of the inclination g of the force F was changed from 0 to 20° in the direction of the varus and valgus deformations in increments of 2°. The simulation used a method for calculating statically indeterminate systems. Calculations were performed in a package of application programs for solving technical computing problems MathLab R2012a. Results. The residual angle of the deviation of the lower leg during unicompartmental endoprosthetics leads to a significant redistribution of loads between the femoral condyles in direct proportion to the value of the angle of inclination for a stable joint and non-linearly in case of lack of stability. It is proved that it is relatively safe to deviate the angle in the range of ±2–3°, and the exceeding of this indicator leads to the appearance of horizontal components of the reaction forces of the support with a significant value. Conclusion. The calculation of the optimal values of the residual angle of deviation of the lower leg during unicompartmental knee replacement allows improving the biomechanical conditions for the functioning of the endoprosthesis.