Your doctor diagnoses an unstable kneecap during a physical exam. They will flex your hurt knee and press the area surrounding your kneecap. They take x-rays of the knee to see where it fits into the trochlear groove. These images also show any additional bone injuries. Ligaments and other soft tissues may be visualized with magnetic resonance imaging (MRI). An MRI is handy for children and adolescents. They’re often unaware of patellar dislocation.