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The hair-on-end radiographic appearance of the skull is most commonly associated with thalassemia major. This condition is a form of inherited blood disorder characterized by an abnormal hemoglobin production, which leads to anemia. To compensate for the low hemoglobin levels, the body overproduces erythrocytes, resulting in expansion of the bone marrow.

The characteristic "hair-on-end" appearance on radiographs results from the prominent trabecular pattern of the bones in the skull, which develops due to the increased hematopoiesis (blood cell formation) in response to anemia. This alteration in the structure can be visualized clearly in radiographic imaging, contrasting with other conditions listed.

In contrast, other conditions like sickle cell anemia can also cause bone changes but typically present with different radiographic findings, such as "crew cut" appearances due to splenic auto-infarction and other complications. Iron-deficiency anemia may not lead to significant changes in bone structure visible on imaging, and polycythemia vera involves increased red blood cells but does not typically produce the same skeletal abnormalities.