The horizontal beam lateral knee x-ray shows an apophyseal avulsion fracture of the tibial tuberosity. The patella is high riding (patella alta) suggesting patellar tendon injury.

The patient underwent surgery to fix the avulsed tibial tuberosity.

The normal patella craniocaudal position can be assessed by noting the Insall- Salvati Ratio: the patellar tendon length = patella height (+/- 20%).

Reference: Grainger & Allison’s Diagnostic Radiology Essentials E-Book.