gms | German Medical Science

Objectives: The containment orientated treatment of Legg-Calvé-Perthes disease (LCP) affected hip joints is broadly accepted in the literature. The prerequisite is early recognition of loss of containment. An often-used quantitative MRI containment parameter is the cartilaginous acetabulum-head-index (CAHI). Based on ultrasound (US), we analyzed the newly created "femoral head extrusion angle" (HA) as a containment parameter in comparison to the CAHI in severe LCP.

Methods: In our prospective study we developed a new diagnostic containment parameter for LCP-affected hip joints in comparison to the "gold" standard examination MRI (Level II). At 42 children (mean age 6.0 ± 2.4; 10 female) with unilateral LCP classified as Catterall group III/IV, we measured the CAHI vs. HA to assess the containment of the femoral head. HA in US was determined by the tangent from the bony acetabular rim to the cranio-lateral femoral head. All examinations of US were analyzed by two independent observers.

Results and conclusion: The HA was significantly higher in LCP-affected hip joints (24.7° ± 7.0°) than in healthy ones (13.0° ± 4.6°; p<0.001). Correlation analysis of all hip joints revealed a significant correlation between HA and CAHI (r=-0.65; lower 95% CI: r=-0.76, upper 95% CI: r=-0.52; p<0.001). Hip joints with a low CAHI indicating a loss of containment showed a higher HA in sonography. The comparison of the HA measurement between two independent observers showed a strong significant correlation in all examined hip joints (r=0.90; lower 95% CI: r=0.85, upper 95% CI: r=0.94; p< 0.001).

The results of our study suggest that the HA in US is a reliable containment parameter in severe LCP with a HA >22.2° defining a pathologic value. In comparison to the CAHI, the measurement of the HA in ultrasound seems to be better practicable as the assessment of various parameters to calculate an index and is more accessible than MRI.