MRI staging of femoral head necrosis

Objective: To study the manifestations and role of MRI in the staging of femoral head necrosis (FHN). Methods: MRI of 13 patients with histologically confirmed FHN was reviewed. The FHN staging of I to IV was based on MR signal intensities of necrotic areas, shape of femoral heads and articular cartilage. 13 surgically removed specimens of varying stages of FHN were sawed into 5 mm thick axial slices. Multiple samples were taken from the necrotic areas for pathological examination. Results: Of 13 affected femoral heads, 6 were intact with continuous articular cartilage and 7 were collapsed. The signal intensities of necrotic zones within 2 intact femoral heads were similar to fat (stage I), which corresponded to necrotic trabecular and bone marrow pathologically. The signal intensities of mixed fat and granulation in 4 intact femoral heads (stage II) corresponded to necrotic trabecular and bone marrow with inflammatory granulation tissue pathologically. The 7 collapsed femoral heads were stage III (2 hips) necrosis with intact articular cartilage and stage IV(5 hips) necrosis with articular cartilage disruption.The signal intensities of necrotic zones within 7 collapsed femoral heads were mixed fat and granulation, which corresponded to necrotic trabecular and bone marrow with inflammatory granulation tissue pathologically. Conclusions: MRI appearance of FHN varies in different stages. MRI staging accurately reflects the pathological process, especially before the femoral heads collapse. (authors)