Reliability and Agreement of Four Patellar Height Measurement Methods in Knee Radiographs

This study aimed to evaluate and compare the reliability and agreement of four commonly used methods for patellar height measurement: Insall-Salvati (IS), Modified Insall-Salvati (mIS), Caton-Deschamps (CD), and Blackburne-Peel (BP) indices, using standardized lateral knee radiographs. This prospective study included seventy adult patients with standardized lateral knee radiographs. Radiographs met strict criteria for true-lateral views and appropriate knee flexion angles. Three observers independently measured patellar height using the four methods, each performing two rounds of measurements at a 15-day interval. Intraclass Correlation Coefficients (ICC) were calculated for intra-observer and interobserver reliability. Pairwise agreements between methods were analyzed using Cohen’s kappa with 95% confidence intervals (CI). Correlation coefficients (Pearson’s r) were computed to assess the relationships between the methods. The BP method exhibited the highest inter-observer reliability (ICC = 0.848, 95% CI: 0.754–0.910) and intra-observer reliability (average ICC = 0.908, 95% CI: 0.829–0.986). This was followed closely by the CD method, while the IS and mIS methods demonstrated moderate reliability. Correlation analysis revealed strong relationships between the BP and CD methods (r = 0.871, p < 0.01) but weaker correlations between IS and the other methods. Despite high correlation coefficients, agreement in classification was poor, particularly between IS and BP (κ = -0.131) and IS and mIS (κ = -0.047).The Blackburne-Peel method is the most reliable and reproducible for patellar height measurement under standardized conditions, making it a robust tool for clinical and research applications. However, the methods were not interchangeable, emphasizing the need for consistent imaging protocols and method selection tailored to clinical objectives.