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.