CLINICAL HISTORY.—A 21-month-old boy was brought to the hospital because of "swelling over the right shin." The boy had favored the right leg for two months and recently developed a definite limp. During the two-month period, he had episodic pain, was anorectic, and lost 5½ lb. Occasionally, he awakened during the night and cried out with pain. In the preceding two weeks, the leg had become swollen. The parents were not aware of any specific trauma or fever.
Pertinent physical findings were limited to the right leg where there was firm swelling over the anterior portion of the tibia which was neither hot nor discolored. There was some localized tenderness over the site. No other abnormalities were detected on physical examination. Intermediate and second strength PPD tests were negative. No abnormalities were found in the erythrocyte sedimentation rate, hemogram, or urinalysis.
A specific diagnosis was made on the basis of