Introduction and Objectives: During the last few years there has been a trend towards minimally invasive total knee replacement (TKR). The advantages described for minimally invasive surgery (MIS) are diverse; however, some disadvantages have also been described such as the difficulty of adequately calculating the dimensions of the components. Assessment of the tendency to use an undersized femoral component in MIS.

Materials and Methods: We studied two multi-center cohorts (Grupo Scorpio España and Grupo Scorpio-MIS España) of patients in whom the same model of prosthesis was implanted surgically, in one group using conventional techniques and in the other using minimally invasive surgery. Using conventional techniques, 371prostheses were implanted in 14 centers, and using MIS, 130 prostheses were implanted in 10 hospitals. The tibial component is easier to measure and has been used as a reference. We assessed the differences between femur and tibia size in both groups of patients, the conventional surgery group and the minimally invasive surgery group.

Results: Using this model of prosthesis, in the conventional group, 45% of the femur components were a size larger than the tibial components, whereas this was seen in 30% of the MIS group (p=0.001956). A smaller size femur component was implanted in the same percentage of cases in both groups (6%). No differences were seen based on the group body mass index.

Discussion and Conclusions: With the data from this multicentric study, in which the same model of prosthesis was used, we confirmed, by means of a significant difference, that there is a tendency to use an undersized femoral component in MIS in comparison with conventional surgery procedures.