Defining the limbus in developmental dysplasia of the hip – Less is more: A Case Report

Developmental dysplasia of the hip (DDH) includes a spectrum of congenital and/or developmental hip abnomatlities that are caused by a shallow acetabulum, which can lead to hip subluxation or dislocation. In DDH, the acetabular labrum hypertrophies and is referred to as the limbus, which can block the concentric reduction of a dislocated dysplastic hip. A 19-month-old girl with a dislocated right hip was diagnosed with developmental dysplasia of the hip (DDH) and underwent an open reduction, Dega osteotomy, and spica casting. At the 10-week post-operative follow-up, clinical examination was unremarkable, however, a plain radiograph showed a subluxed right hip. A subsequent CT scan confirmed an incongruent right hip prompting an arthrogram, which revealed a well congruent hip joint with an exceptionally large limbus. We suggest that the limbus gave the false impression of hip subluxation on imaging studies. Characterizing the morphology of the limbus on plain radiography can be difficult and this can present a unique challenge to determine the reduction of the hip joint and joint congruency post surgical intervention for a dysplastic hip.