Morphological variations of residual hip dysplasia in the adult.

Common understanding of residual hip dysplasia of the adult characterizes it as a uniform, anterolateral insufficiency of femoral head coverage; the proximal femur may or may not have increased valgus and antetorsion. This view is reflected by the parameters used for quantification but also by the classic surgical approaches to compensate or correct the deformity. More than two decades of dedication to hip dysplasia and its surgical treatment, but also the application of modern diagnostic tools such as magnetic resonance arthrography have allowed us to portray hip dysplasia more polymorphically showing a number of additional aspects with pathophysiologic, therapeutic and prognostic valence. The rim in acetabular dysplasia shows a variety of pathomorphologies ranging from hypertrophy and tearing of the labrum including fatigue fracture of the rim to degeneration with ganglion formation within the labrum, the capsule or the acetabular bone. Such rim pathology may explain sudden onset of pain but also influences the prognosis of joint preserving surgery. It is a rather new understanding that the acetabular morphology in hip dysplasia is not uniform. Pure lateral and pure anterior deficiency of coverage are small but interesting subgroups. Together with the frequent retroversion of the acetabulum these morphological and spatial aspects require special attention for a precise individual correction of the deformity. Finally, minor morphological abnormalities of the antero-lateral head-neck junction have been found to favor impingement after correction of the acetabulum. Knowledge of this problem has prompted a routine check of internal rotation in flexion during surgery and eventual arthrotomy and osteochondroplasty of the impinging site of the head and neck junction.