Patellar subluxation is when the patella rides suddenly up the side of its groove, but does not fully dislocate.

patellar subluxation

The event creates the J-sign - a sudden swing of the patella to the outer aspect with each knee extension, after which it returns to the groove.

patellar dislocation

Compare with patellar dislocation where the the patella jumps right out of the groove.


What causes patellar subluxation?

Patients experiencing patellar subluxation may have any of several underlying structural problems. These include -

  • trochlear dysplasia
  • patella alta
  • increased tibial external torsion
  • valgus deformity
  • externally-situated tibial tubercle
  • medialised trochlear groove
  • lateralised tibial tubercle
  • combination of the above
kneecap subluxation

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.

An overview by Dr Lars Blond.

What are the common kneecap problems?

A quick overview of kneecap problems to help you with your research.



How long for a subluxation to heal??? Desperately needing advice!!!

Subluxed or mal-tracking patella??

What does 'subluxing' feel like?


Current Concepts in the Management of Patellar Instability. Laidlaw MS and Diduch DR. Indian J Orthop. 2017 Sep-Oct; 51(5): 493โ€“504.

Medial Patella Subluxation: Diagnosis and Treatment. McCarthy MA and Bollier, MJ. Iowa Orthop J. 2015; 35: 26โ€“33.

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