My right leg caves inward at my knee. when standing i notice i can flex my left vmo but not my right one. what is happening with the right?

Genu valgus?: I would need to gather more information, such as growth and development history, onset of deformity, its progression, and history of trauma or fracture. There aren't many things that would cause one side only to be affected. A physeal fracture could cause it, but the deformity would have been noticed at a younger age. Metabolic disease or skeletal dysplasia would cause both sides to be involved.