Lax Medial Patellofemoral Ligament Syndrome as a Cause of Recurrent Patellar Instability: A Radiologic Case Series

Recurrent patellar instability is generally attributed to bony anomalies such as trochlear dysplasia, patella alta, or increased tibial tuberosity-trochlear groove distance. However, some patients present with recurrent dislocations despite normal osseous anatomy.

This case series presents three patients with recurrent patellar instability, where magnetic resonance imaging (MRI) findings revealed chronic medial patellofemoral ligament (MPFL) laxity as the primary abnormality. All cases showed thinning, elongation, or wavy contour of the MPFL without tears. Trochlear morphology, patellar height, and tibial tuberosity-trochlear groove distance were within normal limits. Secondary changes such as early chondromalacia and subchondral marrow edema were observed.

These cases underscore the importance of evaluating soft-tissue stabilizers, particularly the MPFL, when other anatomical parameters are unremarkable. MRI serves as a crucial tool for detecting MPFL laxity and guiding appropriate management, such as isolated MPFL reconstruction.