Comparative Evaluation of Patellar Height in Adults using Insall-salvati, CatonDeschamps, and Blackburne-Peel Ratios: A Cross-sectional Study

Introduction: Evaluating patellar height is a fundamental component of orthopaedic assessment, as abnormal positioning patella alta or patella baja is strongly linked to patellofemoral instability, chondromalacia, and ligamentous injuries. The diagnostic inconsistency across established ratios, where variations in anatomical reference points between the Insall Salvati Ratio (ISR), Caton Deschamps Ratio (CDR) and Blackburn Peel (BPR) methods frequently lead to conflicting classifications of patellar position that directly impact surgical planning and clinical outcomes. Aim: To compare ISR, CDR and BPR in adult patients and evaluate their correlation and reliability in measuring patellar height. Materials and Methods: A cross-sectional study was conducted at Chettinad Hospital and Research Institute, Chennai, Tamil Nadu, India on 250 adults (500 knees) with lateral knee radiographs with 30o flexion on non traumatic cases. Heights of the patella were measured through the ISR, CDR, and BPR. Mean values and Standard Deviations (SD), as well as the prevalence of patella alta and baja, were estimated. Pearson correlation coefficients were used to test the relationships between indices, and reliability indices were assessed using Intra-class Correlation Coefficients (ICCs). Results: The results of the means of calculation were as follows: ISR 1.02±0.14, CDR 0.98±0.16, and BPR 0.88±0.12. The indices were found to be significantly correlated with each other (CDRBPR r=0.82; ISR-CDR r=0.75; ISR BPR r=0.65; p-value <0.001. The ISR demonstrated the highest prevalence of abnormal patellar height at 19.2%, followed by the CDR at 14.4% and BPR at 14.0%. Reliability was good to excellent across all three methods, with ICC values of 0.92 for ISR, 0.88 for CDR, and 0.85 for BPR. Conclusion: Despite the strong correlation of all three indices and acceptable reliability, they varied from each other in patellar height classification. ISR had the strongest reliability and at the same time, had the highest prevalence of abnormal results.