Femoral trochlear dysplasia is a well known entity, many signs and measurements are used to categorize and characterize the degree of dysplasia, on xrays and MRI.

MRI is the best modality to evaluate the signs, measurements and features of soft tissue and bony injury in acute or chronic patellar instability consequent to  trochlear dysplasia. One should however be careful to measure them 3 cm above the tibiofemoral joint space to avoid eroneous calculations.