The AP knee x-ray looks unremarkable. The lateral knee x-ray shows a high riding patella (patella Alta) & avulsed bone fragments in front of tibial tuberosity.

The patient went on to have an MRI scan of their knee which revealed partial rupture of the patellar tendon & minimally displaced avulsion fracture of the tibial tuberosity.

Patella Alta can be noted on the lateral knee x- ray after Insall Salvati ratio. The knee should be in a position of 20-70 degree. A ratio of more than 1.15 between the craniocaudal patellar length and patellar tendon length indicates presence of patella Alta.

Reference: Emergency Radiology: Imaging and Intervention by Marincek & Dondelinger.