Early-Stage Perfusion MRI Correlates Significantly With Femoral Head Deformity in Children Under 6 Years of Age With Legg-Calvé-Perthes Disease: A Preliminary Multicenter Study.

BACKGROUND

In general, the onset of Legg-Calvé-Perthes disease (LCPD) before age 6 is thought to be associated with a good radiographic outcome. Many of these patients, however, still develop a poor outcome with ovoid-to-flat femoral head deformity. Currently, no early-stage prognosticator of outcome exists for patients younger than 6 years at onset. This study investigated whether perfusion MRI (pMRI) obtained in early stages of LCPD correlates with deformity index (DI), epiphyseal index (EI), and sphericity deviation score (SDS). We hypothesized that early-stage femoral head hypoperfusion would correlate significantly with these radiographic outcomes and serve as an early prognosticator.

METHODS

This multicenter study reviewed demographic, pMRI, and radiographic data from patients with LCPD who had disease onset before age 6. Inclusion criteria were pMRI at Waldenström stage I to IIa. DI and EI were evaluated at 2-year follow-up, and SDS at the healed stage. Statistical analyses included Pearson correlation and ROC analysis, with a threshold predictive of SDS >20.

RESULTS

Forty-one femoral heads (37 patients; mean age at onset 5.0±0.9 years) were analyzed with a mean follow-up of 4.1±1.3 years. Mean hypoperfusion was 49±28%. Mean DI was 0.38±0.18, EI was 0.26±0.10, and SDS was 18.2±12.9. Increasing hypoperfusion (%) correlated significantly with greater femoral head deformity, including higher DI (r=0.76), lower EI (r=-0.62), and higher SDS (r=0.64) (all P<0.001). ROC analysis identified 62% hypoperfusion as optimal for predicting SDS >20 (AUC: 0.80; sensitivity 75%; specificity 87%). Using a 60% cutoff point, outcomes were worse above the threshold: DI (0.31±0.16 vs. 0.52±0.14, P=0.002), EI (0.30±0.09 vs. 0.19±0.07, P<0.001), and SDS (11.7±6.1 vs. 26.8±14.6, P=0.001).

CONCLUSIONS

Early-stage femoral head hypoperfusion correlated significantly with radiographic outcomes at 2-year follow-up and at the healed stage in patients with LCPD onset before age 6. A pMRI hypoperfusion threshold of 60% identified femoral heads at a higher risk for femoral head deformity, supporting pMRI as a potential early prognostic marker.

LEVEL OF EVIDENCE: Level III.