Our objective was to characterize variations in mechanical knee alignment, tibial torsion, tibial width, and ACL laxity measurements between Japanese and Caucasian populations in the healthy, young adult knee joint. Seventy young adult subjects participated in this study, including 23 Japanese and 47 Caucasian subjects. Coronal magnetic resonance images of the hip, knee, and ankle were acquired for analysis. Japanese subjects had a significantly higher (p ¼ 0.04) varus alignment (1.64 AE 0.438 standard error) than Caucasians (0.55 AE 0.338), while women exhibited a more valgus alignment (0.16 AE 0.528) than men (0.94 AE 0.428, p ¼ 0.04). Significant differences were found in tibial torsion and ACL laxity (p < 0.01) between ethnicities, with Japanese exhibiting lower tibial torsion (33.4 AE 10.08) and higher ACL laxity (7.5 AE 0.4 mm) measurements compared to Caucasians (38.9 AE 9.58 and 5.7 AE 0.3 mm, respectively). Significant differences between genders were found in hip-knee-ankle alignment (p ¼ 0.04), tibial width (p < 0.0001), and ACL laxity (p < 0.01) measurements. Measurements were reliable between observers and for repeated positioning. Our study provides new insight into anatomical and geometric differences in the knee joint between Japanese and Caucasians, as well as between females and males. Further consideration of these results may improve development of implants to accommodate for these differences, and understanding of characteristics leading to increased prevalence of knee OA in certain populations. The use of magnetic resonance imaging to obtain these measurements also allows soft tissue structure characterization without exposure to ionizing radiation. ß

The purpose of this study was to clarify meniscal displacement and cartilage-meniscus contact behavior in a full extension position and a deep knee flexion position. We also studied whether the meniscal translation pattern correlated with the tibiofemoral cartilage contact kinematics. Magnetic resonance (MR) images were acquired at both positions for 10 subjects using a conventional MR scanner. Subjects achieved a flexion angle averaging 1398 AE 38. Both medial and lateral menisci translated posteriorly on the tibial plateau during deep knee flexion. The posterior translation of the lateral meniscus (8.2 AE 3.2 mm) was greater than the medial (3.3 AE 1.5 mm). This difference was correlated with the difference in tibiofemoral contact kinematics between medial and lateral compartments. Contact areas in deep flexion were approximately 75% those at full extension. In addition, the percentage of area in contact with menisci increased significantly due to deep flexion. Our results related to meniscal translation and tibio-menisco-femoral contact in deep knee flexion, in combination with information about force and pressure in the knee, may lead to a better understanding of the mechanism of meniscal degeneration and osteoarthritis associated with prolonged kneeling and squatting. ß

We identified small differences in maximum flexion between genders and ethnic groups. While no differences were identified in the lateral condyle translation, the medial condyle remained more stationary and more anterior for the groups that achieved highest (and similar) maximum flexion. Therefore, it may be important for future implant designs to incorporate these characteristics, such that only the lateral condyle experiences greater posterior femoral rollback, while the medial condyle remains more stationary throughout flexion.

Finite element (FE) models have become an effective tool in studying soft tissue behavior in the knee joint, including meniscal translation and deformation, as well as articular cartilage contact [1–2]. These models are also useful in osteoarthritis research and implant design [3–4]. Our group has previously used a kinematic-driven FE analysis to study the effect of weightbearing on the load distribution of tibio-menisco-femoral contact using MR imaging [5].