[A case of dislocation of a double patella]

The congenital dislocation of the patella is relatively rare and the duplicated patella associated is exceptional. The congenital character of the dislocation is unquestionable, but the etiology remains unknown. Before patellar ossification, the diagnosis is difficult and may be delayed for several years until progressive genu valgum, external tibial rotation and flexion deformity results. Radiographs are not useful in evaluating the dislocation until patellar ossification begins at approximately 4 years of age. CT scans and MR imaging reveal the diagnosis before patellar ossification and defines the magnitude of associated dysplasia and the presence of degenerative changes. Early treatment is recommended before the development of secondary bony deformity. We are reporting an unusual case of a woman with multiple epiphyseal dysplasia and bilateral congenital malformation of the patella (duplicated frontal type), associated with genu valgum and congenital dislocation of the patella. She was diagnosed at 31 years old. After surgical treatment (genu valgum correction by varus osteotomy, proximal and distal realignment of the extensor mechanism and osteosynthesis with screws of duplicated patella) and three years follow-up period, we have obtained a good result (painless knees, no recurrence of dislocation and active flexion of 100 degrees on the right knee and 120 degrees on the left knee).