Improper rotation of the femoral and tibial components in total knee arthroplasty may leads to various patellofemoral(PF) complications. As for the femoral component, alignment it to the epicondylar axis of the femur has been a widely used method. The tibial component traditionally has been aligned to the medial 1/3 of the tibial tuberosity. However, there is no consensus concerning how to determine the tibial component rotation. The purpose of the current study is to evaluate the influence rotational alignment of tibial component upon PF joint. We divided the cases to two groups. Group A: 41cases 50knees (OA 34cases, RA16cases). The average age was 69.5(35~84). Group B: 30cases 30knees (OA 25 cases, RA 5cases). The average age was 72.6(59~86). In group A, the anteropostrior (AP) axis was defined as the line connecting the medial 1/3 of tibial tuberosity and the center of PCL attachment. In group B, the line connecting the medial edge of patellar tendon attachment and the center of PCL attachment was defined as AP axis. We measured the PF alignment on postoperative X-rays. Tangential radiographs were used to measure the amount of patellar tilt (tilting angle: TA), subluxation and patellar lateral shift (LS).

Group A showed that tilting angle 14±4°, lateral shift 0.3±0. These values of group B were 12±5°,0.2±0.1, respectively.

In rotation of tibial component, Insall reported that the landmark in front of tibia was medial 1/3 tibial tuberosity. Akagi et,, al reported that the landmark was midial edge of patellar tendon attachment. This study indicated that the latter had better alignment in patellofemoral joint.

Background: It is known that not only the size but also the shape was different between races. We previously compared the distal femur shapes between the American and the Japanese by lateral radiograph and demonstrated the morphological difference in detail. In this study we evaluated the morphologic feature of the lateral and medial condyles separately between the American and the Japanese using MRI in the sagittal plane.

Patients and methods: The subjects were 99 American and 41 Japanese adult women. MRI scan of sagittal section through the distal half of the femur was taken with the slice thickness about 4.0 mm. The envelope curve of each condyle was superimposed to be approximated to an ellipse. The length and inclination of two axes of the ellipse were estimated as the parameters of the statistical comparison.

Results: The ratio major axis/minor axis of the lateral condyles in American women was significantly larger than that in Japanese, while the ratio of the medial condyles in American was significantly smaller. The inclination of the major axis to the anatomical axis of the distal femur in the American lateral condyles were significantly more than that in Japanese lateral condyles, while both the American and Japanese medial condyles showed similar inclination.

Discussion: The morphological feature of both the lateral and medial condyles in American women was significantly different from that in Japanese. The ratio major axis/minor axis and inclination of lateral condyle in American women were different from those in Japanese, while only the ratio was different between the American and Japanese medial condyles. Understanding of these morphological differences between American and Japanese women is beneficial in elucidating discrepancies in normal knee kinematics and in tailoring the design and procedure for successful total knee arthroplasty.