We used MRI to evaluate the morphological relationship of the femoral head and acetabulum with changes of hip position in LCP disease.

The MRIs of 35 patients (17 pillar B, 18 pillar C; mean age: 7.8 years old) were reviewed in neutral, abduction, abduction-internal rotation, abduction-internal rotation-flexion, and adduction positions. The measurements included epiphyseal extrusion index (EEI), head coverage (HC), and medial gap ratio (MGR). The congruence of the hip joint and adjacent soft tissue changes were also studied.

Decreased EEI and increased HC in both pillar B and C from neutral to the abduction and abduction- internal rotation positions were statistically significant (p<0.05). However, in decreased MGR, statistical significance was seen only in pillar B. The increase of MGR in pillar C, from neutral to adduction, did not show statistical significance due to the tension of the soft tissues lying lateral to the hip joint.

This study supports the basic concept of containment treatment in pillar B and suggests a rationale for valgus femoral osteotomy in cases of pillar C with hinge abduction.