A 6-year-old boy presents with a 4-month history of progressive right hip and anterior thigh pain with a painless limp that worsens after activity. Examination reveals Trendelenburg gait, limited hip abduction and internal rotation, and mild quadriceps atrophy. Pelvic radiograph shows the structure marked **A** — a fragmented and sclerotic femoral epiphysis with a subchondral lucency (Caffey sign), widened joint space, and an epiphysis smaller than the contralateral side. Which of the following best describes the pathophysiological mechanism underlying this radiographic appearance?