Fig 3.

A preoperative cross-sectional view of the right knee on magnetic resonance imaging is used to measure the sulcus angle. A normal sulcus angle is approximately 138°, whereas an angle greater than 145° suggests trochlear dysplasia.¹⁹ Trochlear dysplasia may also be identified on a true lateral radiograph by the presence of a crossing sign, in which the floor of the trochlea crosses the anterior border of both femoral condyles.¹⁹ Trochleoplasty may be considered in patients with severe trochlear dysplasia.¹⁹ In addition, trochlear dysplasia is an important predictor of residual patellofemoral instability after medial patellofemoral ligament reconstruction.²⁰ The Caton and Deschamps method may also be used to measure patellar height.¹⁷ A ratio of 1.2 or greater indicates patella alta. If present, a tibial tubercle osteotomy should be considered.¹⁹