Imaging Case of the Week 156 Answer

The HBL knee view shows a low lying patella, which is known as a patella baja. There are small irregular avulsion fragments above the superior pole of the patella. The quadriceps tendon outline is obliterated. There is a knee effusion and also prominent soft tissue swelling anterior to the patella.

Patella Baja

X-ray findings indicate a quadriceps tendon rupture, which was confirmed with an ultrasound; the patient then underwent tendon repair by a specialist.

Patella baja is diagnosed using the Insall-Salvatti index, which is the ratio of the patellar tendon length to the length of the patella on a lateral view. This ratio should be 1, with no more than 20% variation.

Insall-Salvatti ratio