Patella (recurrent dislocation)

Dislocation of the patella becomes easier with each occasion that it happens, and is nearly always towards the lateral side.

• girls are more commonly affected than boys, and the condition is often bilateral.
• more common in skeletal immature patients (1)
• dislocation is painful and usually is the result of twisting with the knee in slight flexion.
• frequently, the patient will fall to the ground with the knee locked in flexion.

Recurrent patellar dislocation after primary dislocation is seen in around 33% of patients and the risk of recurrence increases after 2 years (1).

On examination, the patella may be seen displaced laterally. Dislocation may expose the medial femoral condyle creating the false impression of a medial dislocation. Gradually, the knee becomes swollen from haemarthrosis. There is often marked medial tenderness from rupture of medial structures.

Not uncommonly, the patella will have been pushed back into position. In such cases, the history together with a positive patella apprehension test is usually confirmatory.

Anatomical abnormalities, such as a high riding, small patella may be apparent on x-ray.

The condition should be treated to prevent subsequent osteoarthritis.

Reference:

• (1) Sillanpää PJ, Mäenpää HM. First-time patellar dislocation: surgery or conservative treatment? Sports Med Arthrosc. 2012;20(3):128-35