The J-sign in patellar maltracking

A 42-year-old man presented with numerous left patella dislocations. While the initial dislocation was traumatic, recent episodes were atraumatic. He had no clinical evidence of hyperlaxity, but presented with patellar apprehension and a positive J-sign. His examination was otherwise unremarkable. An MRI of his knee revealed early patellofemoral degenerative changes and tibial tubercle-trochlear groove distance of 25 mm (normal <15 mm). The patient went on to have a Fulkerson tibial tubercle transfer to improve patellar alignment.