Question

the severe secondary osteoarthritis that follows aseptic necrosis of the femoral head is primarily due to: immune synovitis collapse of underlying subchondral bone pannus - mediated cartilage lysis ischemic necrosis of articular cartilage

Explanation:

When there is aseptic necrosis of the femoral head, the collapse of the underlying subchondral bone occurs. This disrupts the normal mechanical structure and load - bearing capacity of the joint, leading to severe secondary osteoarthritis. Immune synovitis is more related to autoimmune joint diseases. Pannus - mediated cartilage lysis is characteristic of rheumatoid arthritis. Ischemic necrosis of articular cartilage is not the primary cause in this case.

Answer:

collapse of underlying subchondral bone