In vivo normal knee kinematics: is ethnicity or gender an influencing factor?

Abstract

Background: In vivo studies have suggested Caucasians achieve lower average knee flexion than non-Western populations. Some previous studies have also suggested gender may influence condylar AP translation and axial rotation, while others report an absence of such an influence.

Questions/purposes: We determined whether different ethnic and gender groups residing in the United States had different knee translations and rotations.

Methods: Three-dimensional knee rotations and translations were determined for 72 healthy subjects (24 Caucasian men, 24 Caucasian women, 13 Japanese men, 11 Japanese women) from full extension to maximum flexion using a fluoroscopic technique, under in vivo, weightbearing conditions.

Results: Although we observed substantial variability in all groups, small differences between groups were found, especially in deep flexion. Japanese women and men and Caucasian women achieved higher maximum flexion (153°, 151°, and 152°, respectively) than Caucasian men (146°). External rotation was higher for these three groups than for Caucasian men. The medial condyle remained more anterior for Caucasian women and all Japanese subjects than for Caucasian men, possibly leading to greater axial rotation and flexion, observed for these three groups.

Conclusion: 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.

Figures

Fig. 1

To achieve maximum flexion, each participant performed deep knee bend activity followed by a forward lean.

Fig. 2

During the 3D-to-2D registration process, the bone CAD models were fitted into their respective silhouettes visible in the fluoroscopic images. Original fluoroscopic video (top row) overlaid CAD models onto their respective silhouettes (middle row) and 3D view of the recreated relative kinematics (bottom row) for full extension and 30°, 60°, 90°, 120°, 150°, and maximum flexion (from left to right).

Fig. 3

Tibiofemoral contact point location was determined based on the relative orientation and position of the femur and tibia bones (see also Video 1 [supplemental materials are available with the online version of CORR]).

Fig. 4A–B

(A) Although the curvatures of the distal femoral condyles are complex, they can be approximated by (B) fitting circles to the extension (R) and flexion (r) facets [28]. The centers of these two circles were tracked to help to better understand the motion of each condyle (see also Video 2 [supplemental materials are available with the online version of CORR]).

Fig. 5A–F

The motion of the knee condyles may be compared to a translating and rotating disk. Depending on the amount of translation and rotation, there are six types of motion: (A) sliding, (B) spinning, (C) rolling, (D) rolling and spinning, (E) concordant translation, and (F) countertranslation (see also Video 3 [supplemental materials are available with the online version of CORR]).

Fig. 6

The majority of the participants capable of achieving higher flexion were women and Japanese.

Fig. 7A–B

(A) Caucasian women and both Japanese groups achieved considerably higher (p = 0.028) maximum knee flexion than Caucasian men. (B) These three groups also revealed higher (p = 0.148) external femoral rotation than Caucasian men.

Fig. 8A–B

(A) The femur rotated externally with increasing flexion in a similar pattern for all four groups. However, Caucasian men revealed the lowest amount of external rotation in deep flexion. (B) For Caucasian women and both Japanese groups, the femur remained adducted above 120° of flexion, while for Caucasian men the femur actually abducted.

Fig. 9A–B

No differences between any of the groups were found in the AP translation of (A) the lateral tibiofemoral contact point and (B) the lateral femoral flexion facet center. However, on the medial side in deep flexion, both the tibiofemoral contact point and the femoral flexion facet center translated more posteriorly for Caucasian men than for any other group.

Fig. 10A–B

The lateral condyle was spinning and rolling posteriorly throughout the ROM and revealed no differences between any groups. However, (A) the medial condyle countertranslated in the early flexion, (B) then was spinning until 120°, and (C) finally rolled back to close to its initial position. This posterior rollback at the maximum flexion was highest for Caucasian men.