Comparison of patellar height measurements using three different imaging modalities

Aim: To evaluate whether the universally accepted normal ranges of patellar height ratios established on radiographs using the Insall-Salvati (IS) and Blackburne-Peel (BP) methods can be reliably applied to computed tomography (CT) and magnetic resonance imaging (MRI) assessments.Materials and Methods: A total of 90 knees from 84 patients (30 men, 54 women; age range, 18-68 years; mean age, 40 19 years) who underwent three different imaging modalities, radiography (X-ray), CT, and MRI, were included in the study.Knee imaging had been performed for various clinical indications.Patellar height measurements were conducted by two independent observers, each blinded to the other's measurements and the corresponding measurements from the other imaging modalities.Results: There were small but statistically significant differences in patellar height ratios among X-ray, CT, and MRI.To achieve comparable results with the IS method, an adjustment of +0.12 for MRI and +0.09 for CT is required relative to X-ray measurements.For the BP ratio, a correction of +0.08 is needed when comparing MRI to X-ray, whereas no adjustment is necessary between X-ray and CT.Notably, these adjustments were found to be independent of patient gender.Inter-observer reproducibility was excellent across all imaging modalities for both the IS and BP methods, with intraclass correlation coefficients (ICC) 0.92.Discussion: While radiographic thresholds for patella alta and baja require slight adjustments when applied to CT and MRI, patellar height measurements remain highly reproducible across all imaging modalities.