The relationship between trochlear dysplasia and medial patellofemoral ligament rupture location after patellar dislocation: an MRI evaluation.

The medial patellofemoral ligament (MPFL) and the native trochlear geometry represent two of the most critical components of patellofemoral stability. We sought to define the relationship between trochlear dysplasia and MPFL rupture location in patients with documented patellar dislocations. We hypothesized that patients with lower grades of trochlear dysplasia would have patellar based MPFL ruptures, while patients with higher grade dysplasia would have femoral-sided ruptures. We reviewed post-injury MRIs of 59 patients with documented patella dislocation. Information gathered included: type of trochlear dysplasia in the axial plane MRI, location of MPFL rupture, patellar height ratio, tibial tuberosity to trochlear groove distance (TTTG), number of dislocations prior to MRI, and time between the latest patella dislocation and the MRI. Statistical calculations utilized the Chi-Square-Test. We classified 11 cases as a dysplasia type A, 35 as a type B, 11 as a type C, and 2 cases as a trochlear dysplasia type D. In 7 patients (12%) the MPFL rupture was patella based, in 18 patients (31%) intra-ligamentous, in 33 cases (56%) femoral sided and in one case no MPFL could be identified. In contrast to our original hypothesis, the type of trochlear dysplasia does not appear to be related to the rupture location of the MPFL after patellar dislocation. According to our results, it is not possible to presume the location of the MPFL rupture based on assessment of the trochlear morphology. Therefore, a MRI is mandatory for final indication of any surgery.