OBJECTIVE: We describe our experience using sonography to evaluate the patella and patellofemoral joint in three children with congenital abnormalities of the extensor mechanism of the lower extremity. CONCLUSION: Sonography can be used to evaluate the extensor mechanism and unossified patella in young children. Advantages of sonography over MR imaging are no need for sedation, speed of examination and ability to compare with the contralateral knee, low cost, and the sonographer's ability to dynamically evaluate the extensor mechanism.
