Effects of Lower Limb Alignment and Tibial Component Inclination on the Biomechanics of Lateral Compartment in Unicompartmental Knee Arthroplasty

Background： Lateral compartmental osteoarthritis （LCOA）, a major complication after medial mobile-bearing unicompartmental knee arthroplasty （UKA）, is highly associated with the increased stress of the lateral compartment. This study aimed to analyze the effects on the stress and load distribution of the lateral compartment induced by lower limb alignment and coronal inclination of the tibial component in UKA through a finite element analysis. Methods： Eight three-dimensional models were constructed based on a validated model for analyzing the biomechanical effects of implantation parameters on the lateral compartment after medial Oxford UKA： postoperative lower limb alignment of 3° valgus, neutral and 3° varus, and the inclination of tibial components placed in 4°, 2° valgus, square, and 2° and 4° varus. The contact stress of femoral and tibial cartilage and load distribution were calculated for all models. Results： In the 3° valgus lower limb alignment model, the contact stress of femoral （3.38 MPa） and tibial （3.50 MPa） cartilage as well as load percentage （45.78%） was highest compared to any other model, and was increased by 36.75%, 47.70%, and 27.63%, respectively when compared to 3° varus. In the condition of a neutral position, the outcome was comparable for the different tibial tray inclination models. The inclination did not greatly affect the lateral compartmental stress and load distribution. Conclusions： This study suggested that slightly varus （undercorrection） lower limb alignment might be a way to prevent LCOAin medial mobile-bearing UKA. However, the inclination （4° varus to 4° valgus） of the tibial component in the coronal plane would not be a risk factor for LCOA in neutral position.

Intraoperative study on anthropometry and gender differences of the proximal tibial plateau at the arthroplasty resection surface

Background The tibial plateau is asymmetric with a larger medial plateau.We observed from clinical practice that the shape of the tibial plateau does not always present a larger medial plateau.Tibial plateau also showed other shapes.The purpose of this study was to analyze the anthropometric data of the proximal tibia in a large group of Chinese patients undergoing total knee arthroplasty and to investigate the morphology of the resected proximal tibial surface and its gender differences.Methods A total of 822 knees （164 males,658 females） from the Chinese population were measured intraoperatively for medial anteroposterior （MAP） and lateral anteroposterior （LAP） dimensions of the resected proximal tibial surface.The difference of MAP and LAP （DML） was also calculated as MAP minus LAP.We then classified the data into three groups based on the DML （＜-2,-2 to 2,and ＞2 mm） to analyze the morphology of the proximal tibia and its distribution between male and female.Results The shape of proximal tibial plateau was of three types：larger medial plateau type,symmetric type,and larger lateral plateau type.There were significant differences between males and females in relation to the shape distribution of the proximal tibial plateau （P ＜0.05）.Most of the proximal tibial plateau was asymmetric,with 517 of 822 （62.9％） tibia having a DML ＞2 mm and 120 of 822 （14.6％） tibia having a DML＜-2 mm.Only 185 of 822 （22.5％） tibia had a DML between-2 and 2 mm.Conclusion The results of this study can be used as a guideline to design tibial components with different DMLs to better match the different anthropometry of the resected tibial surface.