Lors d'une précédente étude anatomique sur genoux sains, nous avions observé que le valgus fémoral ne pouvait être attribué à une hypoplasie du condyle fémoral latéral. Nous avons donc repris le même échantillon pour analyser la morphologie des diaphyses fémorales.

Il s'agissait d'une étude cadavérique portant sur 41 membres inférieurs sains de sujets caucasiens âgés de plus de 65 ans. Trois paramètres angulaires étaient analysés: l'axe mécanique du membre (HKA), le valgus fémoral mécanique (HKI) et le valgus fémoral anatomique (SKI). Il y avait 23 genoux normaux (HKA: 179,1° ± 1,6) et 18 genu valgum (HKA: 182,7° ± 0,8). La morphologie de la diaphyse fémorale était analysée par squelettisation puis modélisée par une fonction du deuxième degré (y = fx² + bx + c). L'angle HKI des genu valgum (95,5° ± 1,1) était supérieur à celui des genoux normo-axés (93,6° ± 2,4) ce qui confirmait l'origine fémorale du valgus. Le paramètre de forme f des genoux normo-axés (1,33 10^-5 ± 1,41 10^-5) était supérieur à celui des genu valgum (5,71 10^-6 ± 5,27 10^-6). Une corrélation était observée entre le paramètre de forme f et l'angle HKI dans le groupe des genu valgum.

L'analyse des données nous a permis d'attribuer au segment diaphysaire du fémur une part importante dans la déformation du genu valgum constitutionnel. Nous formulons l'hypothèse qu'il en est de même en cas de gonarthrose sur genu valgum constitutionnel.

In a previous anatomic study of healthy knees, we observed that femoral valgus cannot be attributed to hypoplasia of the lateral femoral condyle. In the present study, in an attempt to determine the site of the femoral deformation, we examined femoral shaft bowing in the frontal plane.

This cadaver study included 41 lower limbs of healthy Caucasian subjects aged over 65 years. The following anatomic landmarks were identified: center of the femoral head (H), center of the intercondylar notch (K), center of the talar dome (A), center of the femoral shaft half way between the apex of the greater trochanter and the middle of the intercondylar notch (S), and the tangent line of the femoral condyles (I). Three angles were analyzed: HKA, HKI, and SKI. There were 23 normal knees (HKA = 179.1 ± 1.6°) and 18 valgus knees (HKA = 182.7 ± 0.8°). Skeletal analysis (the skeleton of an object being defined as the median points of the object) was used to describe the morphology of the femoral shaft and then to model it with a second-degree function (y = fx² + bx + c). The protocol was repeated seven times to achieve accurate measurement. Accuracy was 1° for the HKA angle and 0.45° for the HKI and SKI angles. This accuracy was comparable to that reported in the literature. The Mann-Whitney U test was used to compare means. Spearman's t test was used to search for correlations. The first-order risk was set at 0.05.

The HKI angle for valgus knees (95.5 ± 1.1°) was greater than for the normally aligned knees (93.6 ± 2.4°), confirming the femoral origin of the valgus. The form parameter f for the normal knees (1.33 10^-5 ± 1.41 10^-5) was greater than for the valgus knees (5.71 10^-6 ± 5.27 10^-6). There was a correlation between the form parameter f and the HKI angle for valgus knees, reflecting a relationship between frontal bowing of the femoral shaft and femoral valgus in this group.

The difference observed between the two groups of knees regarding the form parameter f and the correlation between f and the HKI angle in the valgus knees led us to consider that a considerable proportion of constitutional valgus knees can be attributed to the femoral shaft. Thus for equivalent anatomic valgus (SKI), minimal bowing (f) of the femoral shaft in valgus knees leads to greater mechanical valgus (HKI). These results confirm those obtained in our earlier study, where we concluded that hypoplasia of the lateral femoral condyle does not contribute to constitutional valgus knees. We hypothesize that the same could be true for degenerative disease of constitutional valgus knees. For surgical cure, the origin of the misalignment in valgus knees dictates the rotation position of the femoral component of total knee arthroplasty and the lengthening technique for the lateral structures.