Editorial Commentary: Contact Is Not Containment: In High-Grade Trochlear Dysplasia, the Patellotrochlear Index...

Patella alta remains among the most critical anatomical risk factors for recurrent patellofemoral instability and failure of patellar stabilization surgery. The Caton-Deschamps index references the patella to the tibia by measuring the position of the patella relative to the anterosuperior margin of the tibial plateau. In contrast, the patellotrochlear index references the patella to the femoral trochlea by quantifying the proportion of patellar articular cartilage that shows sagittal overlap with trochlear cartilage on magnetic resonance imaging. Under normal trochlear morphology, these measurements closely covary, but they diverge in the presence of abnormal morphology. In high-grade trochlear dysplasia, the proximal trochlea is elongated, flattened, and often convex beneath a supratrochlear spur. The patella overlaps an expanded cartilage surface that provides minimal osseous constraint. Contact does not equate to containment. Therefore, a reference-range patellotrochlear index alone is insufficient to exclude a dysplastic knee from consideration for distalizing tibial tubercle osteotomy. Neither index correlates with the instability resolution angle obtained during examination under anesthesia, indicating that static imaging parameters do not fully capture dynamic patellofemoral containment. We must stop letting single 2-dimensional cutoffs dictate complex, 3-dimensional surgical decisions.