Patella alta is a known risk factor for patellar instability, contributing to increased length changes of the medial patellofemoral complex, and associated with high rates of failure after medial patellofemoral complex reconstruction. Distalization through tibial tuberosity osteotomy (TTO) is a surgical option to address patella alta during patellar stabilization surgery. However, distalization has been shown to have greater complication rates than other types of TTO, and therefore precise indications through proper assessments of patellar height are needed. The Caton-Deschamps index is a commonly used measurement and is independent of patellar tendon length, allowing for assessment of patellar height before and after distalizing TTO. Additional options that may offer this ability are femoral-based measurements such as the patellotrochlear index and sagittal patellar engagement, which also do not rely on the position of the tubercle and may better represent the functional engagement of the patellofemoral joint. However, femoral-based measurements depend on trochlear morphology; theoretically, an advantage of femoral-based measurements is that they may reflect the functional engagement of the patella within the trochlea. However, in knowing the common relation between patella alta and trochlear dysplasia, the question becomes whether an overlap between the patella and a dysplastic proximal trochlea on a sagittal measurement truly represents functional engagement and stability of the patellofemoral joint. Measurement of patella alta and determining indications for distalization can be influenced by measurement techniques including magnetic resonance imaging versus radiography, tibial- versus femoral-based measurements, and positional and morphologic considerations. Increased understanding of trochlear morphology and sagittal knee balance as they relate to patella alta will be important for defining the factors that affect patellofemoral stability.
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