What is a common feature of avascular necrosis visible on X-ray in its late stages?

In the late stages of avascular necrosis, subchondral collapse is a common feature visible on X-ray. This occurs as the blood supply to the area becomes insufficient, leading to the death of bone cells and subsequent weakening of the bony structure. As the condition progresses, the bone beneath the cartilage surface fails to support the overlying cartilage, resulting in a characteristic flattening or collapse of the affected area.

This phenomenon is often associated with joint pain and limited mobility, as the structural integrity of the joint is compromised. The collapse can lead to further degeneration of the cartilage and can be a precursor to osteoarthritis in the affected joint.

Other features related to avascular necrosis may not typically appear in the late stages on X-ray. While some might consider radioopacity or joint effusion as potential findings, these do not effectively capture the critical pathological change occurring, which is predominantly the subchondral bone collapse. The aspect of increased vascularity also contradicts the essence of avascular necrosis, as the condition inherently involves reduced blood flow. Hence, identifying subchondral collapse serves as a definitive marker when evaluating the later phases of this condition on imaging.