Current evidence advocates use of a new pathologic tibial tubercle-posterior cruciate ligament distance threshold in patients with patellar instability.

To determine (1) whether a correlation exists between tibial tubercle-posterior cruciate ligament (TT-PCL) and tibial tubercle-trochlear groove (TT-TG) distances in patellar instability patients; (2) reliability when measuring TT-PCL distance; (3) whether TT-PCL distances measured on MRI are equivalent to those on CT; and (4) whether a correlation exists between TT-PCL distance and number of instability events or recurrence of instability following stabilization surgery.