Genu valgum

An 8-year-old boy comes to the clinic with his newly adoptive mother because of difficulty walking. The mother informs you that her son was adopted from a country with low resources and he has only been in the United Sates for 1 week. She believes he was not fed well before he was adopted. His temperature is 37.1°C (98.8°F), pulse is 90/min, respirations are 20/min, and blood pressure is 100/70 mm Hg. Physical examination shows a small appearing boy for his age with a protuberant abdomen and bleeding gums. Gait analysis shows his knees contact often and his lower legs extend laterally. A Q-angel measurement is taken. Which of the following is the most likely cause of his gait abnormality?