Legg-Calvé-Perthes' disease. Congruent aspherity caused by physeal injury

Perthes disease often produces a congruent nonspherical coxa. The most widely accepted cause is initial bone collapse, but some authors refer to physeal injury as the cause of this deformity. We analyze this elliptical process in cases of congruent nonspherical Perthes.

Retrospective case-control study of 49 unilateral class III-IV Perthes cases that were not operated on. Results were compared with 49 healthy contralateral hips. The following radiological variables were determined both in AP and lateral projection, and at 4 points in time of the disease: ovalization index (OI), arthrotrochanteric distance, intraphysial angle, physeal narrowing, presence of double epiphyseal reosification nucleus, physeal length and Reimers index.

The initial OI was 1.7 in the early reosification phase and final OI was 2.07 at physeal closure. The OI in the control cases was invariably 1.4. There was a direct relation between a high index and the initial appearance of a double epiphyseal ossification nucleus, asymmetric physeal effacement and the increase of the intraphyseal angle in both radiographic projections.

The elliptical process of the femoral head occurs progressively throughout the disease and not only during bone collapse. It starts in the reosification phase and ends when growth stops. The initial risk signs found were the appearance of the double nucleus of reosification, the progressive angulation of the physis and the progressive increase in the rate of ovalization.