Patella Alta: A Comprehensive Review of Current Knowledge.

We systematically reviewed patella alta with respect to type of measurements, reported cutoff values, cutoff values for surgical correction, and proposed surgical techniques. Using the term patella alta, we performed a systematic literature search on PubMed. Inclusion criteria were original study or review articles, publication in peer-reviewed English-language journals between 2000 and 2017, and narrative description or measurement of human patellar height on plain radiographs or magnetic resonance imaging (MRI). All evidence levels were included. Of 211 articles identified, 92 met the inclusion criteria for original study, and 28 for review. The 92 original study articles defined patella alta mostly with imaging-based measurements (81.5%) and more rarely by description only (18.5%). Eighteen types of measurement methods with 27 different cutoff values were used to assess patella alta; these methods included lateral radiographs, sagittal MRI, radiographic ratios measured on MRI, and patellar tendon length. The Insall-Salvati index (ISI) was used more than the Caton-Deschamps index (CDI); cutoff values for patella alta varied from >1.2 to >1.5 for ISI and from >1.2 to >1.3 for CDI. Both indices were seldom used on MRI; cutoff values were similar to those for conventional radiographs. On sagittal MRI, the patellotrochlear index was used most; cutoff values ranged from <0.125 to 0.28. Eleven studies used patellar tendon length and found it was increased (>52 mm to >56 mm). The 28 reviews described patella alta mostly with ISI (75%) or CDI (64%). However, 12 (57%) of the 21 review studies that used ISI and 7 (39%) of the 18 review studies that used CDI did not report cutoff values. Only 2 review studies suggested an ideal patellar height after surgery. Different procedures were used to treat patella alta: tibial tubercle distalization with and without patellar tendon tenodesis, tibial tubercle distalization and medialization, and distal advancement of the patellar tendon. Only 11 original studies proposed a critical patellar height as an indication for surgery; however, these studies mainly used CDI, and only 4 mentioned a desired postoperative patellar height after correction. Our review revealed many variations in patella alta definitions and descriptions, measurement methods, cutoff values, and treatment options. Presence of patella alta depends on the measurement method used. Unfortunately, there is no generally accepted consensus on patella alta. Given its influence on patellofemoral loading/stress and patellar stability, however, we must strive to establish a consensus in the near future.