Patellar Height Measured on Radiographs and MR Imaging and Its Relationship With Chondromalacia Patella

Background: This study aimed to evaluate the relationship between chondromalacia patella (CMP) and patellar height using Insall-Salvati (IS) and modified Insall-Salvati (MIS) methods on both conventional radiographs (CR) and magnetic resonance imaging (MRI). Methods: We conducted a retrospective review of 198 patients who underwent knee MRI. Patellar height was measured using IS and MIS on both CR and MRI by two musculoskeletal radiologists. CMP was classified according to the International Cartilage Repair Society (ICRS) grade. Grades 1–2 were defined as low-grade CMP, and grades 3–4 as high-grade CMP. We analyzed the relationship between patellar height and CMP severity, as well as the inter-reader and inter-modality reliabilities. Results: High-grade CMP had significantly lower IS and MIS values on both CR and MRI compared to the normal cartilage group. In patients over 50 years old, the MIS value on both CR and MRI showed a significantly negative correlation with CMP grade. Inter-reader reliability was excellent for both IS and MIS across CR and MRI. Inter-modality reliability was excellent for IS and good for MIS. Higher IS and MIS values were observed on MRI than on CR. This is regarding the measurement results of both reviewers. Conclusions: IS and MIS on both CR and MR images were reliable measures of patellar height and significantly correlated with CMP grade. In older patients, a lower MIS ratio was associated with a higher CMP grade. Although MRI tends to yield slightly higher IS and MIS values than CR, both modalities showed good agreement in measuring patellar height. These results suggest that reduced patellar height could be a relevant imaging finding in association with CMP severity.