From the case:
Patellotrochlear index
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The patellotrochlear index is ratio of the length of the patellar articular cartilage (perpendicular to the distal most trochlear cartilage) to the parallel length of the trochlear cartilage overlapping the patellar cartilage.
Case Discussion
The patellotrochlear index is a measurement of patellar position on a sagittal MRI and is used in the assessment of patella alta and patella baja.