IS Case 563: Lateral patellar displacement

Sirisha Jasti, MD

Imaging Sciences URMC

Imaging Sciences URMC 2010
Publication Date: 2011-11-16


Patient is a 15-year-old girl status post injury with pain in the left knee.


AP and patellar views of left knee showed lateral displacement of the patella.


Lateral patellar displacement


Some of the risk factors associated with patellar displacement are patella alta, patellar tilt, genu valgum, coax valga, femoral anteversion and external tibial torsion. Patellar displacement occurs more commonly in athletes who put excess stress on the patellofemoral tendon. The main symptom associated with patellar displacement is pain at the knee joint.

Patellar displacement is better appreciated on a patellar view radiograph. It can be measured by drawing two lines, one through the most superior portions of the condyles of the femur and the other as a perpendicular line through the medial condyle of the femur. The medial edge of the patella should normally lie lateral to the perpendicular line or within 1cm medially to the line. When the medial edge of the patella lies more than 1cm away from the perpendicular line, it is displaced. This measurement is depicted in the image above on the patellar view.

The initial therapy for patellar displacement is conservative management with cessation of activities that put stress on the patellofemoral joint. Surgery is considered if there is a fracture associated with the dislocation or if it is a complicated displacement.


  1. Malanga GA, White BF, Lee WS, Agesen T. Patellar injury and dislocation. eMedicine, Dec 17, 2009.
  2. Keats TE, Sistrom C. Atlas of Radiologic Measurement. 7th edition, Mosby, 2001.

2 images