Patellar instability is when the kneecap does not ride smoothly in the groove of the femur, popping over to one side, or even de-railing.

patellar subluxation

Patellar subluxation - when the patella rides to one side up the wall of the trochlear groove, but does not pop out.

patellar dislocation

Patellar dislocation - when the patella jumps right out of the groove.

 

Patellar subluxation or dislocation?

Patellar instability is a continuum. Patients may progress from one level of instability to another. When it pops to one side, that is known as patellar subluxation. When it completely derails, that is known as patellar dislocation.

Synonyms: 
Patellofemoral instability
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The unstable patella

A discussion about patellar instability, the factors that may cause the patella to sublux or dislocate, and what can be done about it.

A discussion of key concerns about dislocation of the patella.

How TT-TG Distance is measured, and what it means to the patient with patellar instability.

Interpretation by the Editor of a 2017 published medical paper studying long term problems in patients whose original patellar dislocations were not surgically managed.

Video demonstrating the J-sign

This is the Editor's interpretation of a paper published in the orthopaedic literature in 2016.

An overview by Dr Lars Blond.

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