Patellar subluxation is when the patella rides suddenly up the side of its groove, but does not fully dislocate.
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.
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
Current Concepts in the Management of Patellar Instability. Laidlaw MS and Diduch DR. Indian J Orthop. 2017 Sep-Oct; 51(5): 493–504.
Medial Patella Subluxation: Diagnosis and Treatment. McCarthy MA and Bollier, MJ. Iowa Orthop J. 2015; 35: 26–33.
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