Le but de ce travail est l'analyse de la morphologie de la rotule grâce à une étude rétrospective de 190 genoux opérés pour instabilité rotulienne objective. Nous avons étudié la rotule sur les radiographies pré-opératoires (n = 190), le scanner (n = 158) et dans certains cas une IRM (n = 64) en préopératoire. Nous avons analysé l'angle rotulien, la longueur et la largeur de la rotule, le versant interne et le versant externe, et surtout la pointe de la rotule et le tendon rotulien. Parmi les genoux controlatéraux asymptomatiques (n = 90), 67 ont eu des radiographies.

Plus la pointe rotulienne était courte, plus le tendon rotulien était long (p < 0,0001). De plus il existait plus de rotules de stade C de Wiberg (considéré comme le stade de dysplasie de rotule) parmi les hommes (23 %). La largeur moyenne de la rotule mesurée au scanner était de 39,1 mm.

L'IRM a permis de trouver un tendon rotulien moyen de 53,8 mm, une surface articulaire rotulienne moyenne de 30,8 mm, une rotule de longueur moyenne de 40,6 mm et une largeur rotulienne moyenne de 38,7 mm.

The purpose of this work was to study the morphology of the patella in search of dysplasia typical of objective patellar dislocation.

One hundred forty patients (190 knees), 80 women and 60 men, who underwent surgery between 1988 and 1999 were included in this study. Mean age was 22.6 years (range 13-47). Patellar morphology was analyzed on the preoperative lateral x-rays (n=190) taken at 30° flexion. The apex of the patella was measured as well as the length of the patellar tendon. The width of the patella was measured on the computed tomography scan (n=158). For 64 knees, magnetic resonance images of the patella were available on which the length and width of the patella, the articular surface, and the patellar tendon were measured. Ninety contralateral knees were symptom free and x-rays were available for 67.

According to the Grelsamer classification, 80% of the patellae presented a normal apex. The length of the patellar apex was significantly shorter when the patellar ligament was longer. Using the Wiberg classification, men had more dysplasic patellae (grade C) (p=0.007). There was also a correlation between the Wiberg classification and the Maldague classification. The length of the medial border of the patella and the patellar angle were 2 factors directly related to the Wiberg classification. Mean width of the patella was 39.1 mm (computed tomography measurements). The mean length of the patellar tendon was 53.8 on the magnetic resonance images with a mean articular surface measuring 30.8 mm, a mean patellar length measuring 40.6 mm, and a mean width measuring 38.7 mm. There was no correlation between trochlear dysplasia and patellar morphology.

There is little data in the literature concerning patellar morphology since Wiberg's work in 1941. The hypothesis of patellar dysplasia rather than trochlear dyplasia, the principal factor involved in objective patellar dislocation, has not been explored extensively. The presence of a hypoplasic medial border, Wiberg grade C, or a short patellar apex suggests that a particular patellar morphotype would be involved in objective patellar dislocation.