A 6-year-old boy presents with a 4-month history of progressive painless limp and intermittent knee and groin pain worse with activity. Examination reveals restricted internal rotation and abduction of the left hip with a positive Trendelenburg sign. Laboratory investigations including ESR, CRP, and hemoglobin are normal, excluding infection and hemoglobinopathy. Frog-leg lateral radiographs of the pelvis show the findings marked in the diagram. The structure marked **A** (femoral head fragmentation and flattening) represents the hallmark pathological change in this condition. Which of the following BEST describes the pathophysiology underlying the radiographic appearance marked **A** in this case of Legg-Calvé-Perthes disease?