Le genu valgum constitutionnel est habituellement attribué à une hypoplasie du condyle fémoral latéral. Cependant, cette notion repose sur des observations faites sur des genoux arthrosiques. Nous avons donc cherché à savoir, par une étude anatomique, si le condyle fémoral latéral du genu valgum indemne d'arthrose fémoro-tibiale latérale était hypoplasique.

Nous avons étudié des genoux indemnes d'arthrose de cadavres de sujets caucasiens à l'aide d'un système ostéométrique. Pour chaque genou, nous avons mesuré l'angle fémoro-tibial mécanique (AFTM), la distance inter-épicondylienne (DIE) ainsi que le rayon postérieur et distal du condyle latéral. Nous avons étudié 23 genoux normaux d'AFTM moyen 179,1° ± 1,6 et 18 genu valgum d'AFTM moyen 182,7° ± 0,8. Afin de comparer entre eux les rayons des condyles des différents membres, nous les avons rapportés à leur DIE. Les ratios ainsi obtenus ont été nommés rayon relatif distal et postérieur. La reproductibilité intra-observateur de la méthodologie utilisée était de 0,7 mm.

La moyenne des rayons postérieurs relatifs des genu valgum (32,0 ± 2,5) était significativement supérieure à celle des genoux normaux (30,5 ± 2,0). Il n'y avait pas de différence significative entre les rayons distaux relatifs des deux groupes.

Le valgus fémoral du genu valgum constitutionnel ne peut donc pas être attribué à une hypoplasie du condyle fémoral latéral. Nous formulons l'hypothèse qu'il en est de même en cas de gonarthrose sur genu valgum constitutionnel.

Although the valgus slope of the femoral condyles seen in valgus knee is thought to be due to hypoplasia of the lateral femoral condyle, this fact has not been proved. The aim of this study was therefore to evaluate the difference between the size of the lateral femoral condyle of neutral and valgus knees.

There were 41 non-arthritics lower limbs taken from 27 caucasians donors. Angular measurements were taken with respect to the mechanical axis of the bones. Femurs were then isolated from the tibia, all soft tissue was removed with respect to the articular cartilage. An osteometric system developed for this study allowed each femur to be precisely photographed in perpendicular planes. Each femur was mounted on the osteometric system. The dimensions (depth and height) of each lateral femoral condyle were obtained using direct measurements from standardized photographs. Knees were considered neutral when the tibiofemoral mechanical angle (TFMA) was between 181° and 176.6° and considered valgus when over 181°. To be compared, measurements were related to the transepicondylar width of each femur. The related dimensions were then compared for both categories of knees (valgus and neutral). There were 18 valgus knees (mean TFMA 182.7° ± 0.8) and 23 neutral knees (mean TFMA 179.1° ± 1.6). A validation for the technique was performed by measuring six points on a same femur by the same person seven times. This revealed standard deviations of 0.7 millimeters which was small enough for our purpose. The relationships between the related measurements were analyzed using the Mann & Whitney U test. Significance was accepted at a P value of less than 0.05.

The related depth of the lateral femoral condyle was bigger for valgus knees 32.0 (± 2.5) than for the neutral knees 30.5 (± 2.0). The related heights of the lateral femoral condyle were about equal 28.7 (± 1.8).

Using a population of non arthritic knees, our data demonstrated that the lateral femoral condyle is thicker in valgus knees compared to neutral knees, thus in contradiction with the most common view. We suggest that in fixed valgus knees, beside arthritic wear, there is no deficiency of the posterior lateral condyle of the femur.