Evolution of Legg-Calvé-Perthes disease following proximal femoral varus osteotomy performed in the avascular necrosis stage:a prospective study

Abstract

Purpose: This prospective study was undertaken to describe patterns of fragmentation of the femoral epiphysis following a proximal femoral varus osteotomy (PFVO) done during stage I of LCPD and to assess the disease duration and outcome in each pattern.

Methods: A total of 25 children treated by a PFVO in stage I of LCPD were followed until healing. The MRI Perfusion Index, radiographic changes in the femoral epiphysis, disease duration and the Sphericity Deviation Score (SDS) at healing were documented. The reproducibility of classification of the pattern of fragmentation, estimation of disease duration and SDS were assessed. The duration of the disease and SDS in the patterns of fragmentation were compared.

Results: Four patterns of fragmentation were noted, namely, typical fragmentation, bypassing fragmentation, abortive fragmentation and atypical fragmentation with horizontal fissuring. The reproducibility of classifying the pattern of fragmentation was moderate (Kappa: 0.48) while the reproducibility of other continuous variables was excellent. The Perfusion Index was less than 50% in every affected hip. The duration of the disease and SDS were lowest in children in whom the stage of fragmentation was bypassed but these differences were not statistically significant.

Conclusion: Following a proximal femoral osteotomy during stage I of LCPD the fragmentation stage may be bypassed partially or completely and the chances of a good outcome appear to be very good if fragmentation is bypassed.

Level of evidence: Level II Prognostic Study.

Keywords: Legg-Calvé-Perthes disease; Sphericity Deviation Score; disease evolution; fragmentation.

Fig. 1.

Three examples of early fragmentation (stage IIa). The vertical orientation of the fissure is evident in all three hips. The position of the fissure can vary; the fissure may be in the substance of avascular bone (a, b) or at the boundary between avascular and perfused bone (c).

Fig. 2.

Three examples of advanced fragmentation (stage IIb).

Fig. 3.

Sequential radiographs of the hip of a boy with Perthes disease who underwent a proximal femoral varus derotation osteotomy within a month after presentation in stage Ib of the disease (a). In none of the sequential radiographs are there fissures in the epiphysis typical of fragmentation (b-d). The continuity of the articular margin of the femoral epiphysis has been maintained throughout the course of the disease. The disease healed within 17 months of surgery (e) and the outcome was excellent (f). The stage of fragmentation has been bypassed.

Fig. 4.

Sequential radiographs of a child who underwent proximal varus femoral osteotomy in Stage Ib of the disease from presentation (a-l) showing the pattern of evolution of the disease. In this patient early fragmentation begins (c; white arrows). Within three months the fragmentation fissures are less clearly defined (d; grey arrows). Four months later there is no progression of fragmentation (i.e. the disease has not passed through stage IIb). The fissures of early fragmentation are also not seen. The final outcome was excellent with a spherical femoral head (k, l). This pattern of evolution is the abortive fragmentation pattern.

Fig. 5.

Sequential radiographs of a child who underwent proximal femoral varus osteotomy in stage Ib. A horizontal fissure extending across the entire width of the epiphysis appears parallel to the growth plate (c). Resorption of the superficial avascular fragment occurs progressively (d, e). New bone formation then proceeds from the deep surface of the horizontal fissure towards the articular surface (f) until the epiphysis is completely reconstituted (g-j).

Fig. 6.

Perfusion MRI scan of a child with Legg-Calvé-Perthes disease of the left hip. Close to 80% of the epiphysis is avascular.

Fig. 7.

Scatter diagram showing the Sphericity Deviation Scores at healing of Legg-Calvé-Perthes disease of 25 children who underwent proximal femoral varus osteotomy during stage Ia or Ib of the disease. A Sphericity Deviation Score value below 10 is regarded as a good result (shaded area).

Fig. 8.

Scatter diagram showing the duration of Legg-Calvé-Perthes disease in children treated by a proximal femoral osteotomy in stage Ia or Ib. The duration of the disease is around 24 months in the children who bypassed the stage of fragmentation completely.