Abnormal Patella Height Based on Insall-Salvati Ratio and its Correlation with Patellar Cartilage Lesions: An Extremity-Dedicated Low-Field Magnetic Resonance Imaging Analysis of 1703 Chinese Cases

Background and aims: Diagnostic performance of patellar position for patellar cartilage lesions remains unclear. The aim of this study was to assess the abnormal patella height and its correlation with chondral lesions of the patellofemoral joint in China. Material and methods: A total of 1703 consecutive patients who performed knee joint examination using an extremity-dedicated low-field magnetic resonance imaging were enrolled in this study. Patellar cartilage lesions were diagnosed based on the result of magnetic resonance imaging and clinical data. Patella height was defined as the ratio of patellar tendon length to patellar length according to Insall-Salvati index. Patella alta and infera were defined as tendon length/patellar length >1.2 and <0.8, respectively. Results: The total prevalence of patellar cartilage lesions was 38.0%. The prevalence in females was significantly higher than that in males (46.4% vs 28.8%, p<0.001). Age notably increased the incidence of patellar cartilage lesions (p<0.001). Logistic regression analysis showed that tendon length/patellar length ratio was significantly correlated with patellar cartilage lesions (odds ratio=6.380, p<0.001). Furthermore, patients with cartilage lesions showed significantly higher rates of patella alta and infera (p<0.001). In addition, receiver operating characteristic curve analysis demonstrated that abnormal patella height had statistical significance in diagnosing cartilage lesions (p<0.001). However, the area under the curve (0.596; 95% confidence interval: 0.568-0.624) and sensitivity (47.0%) were relatively low, while the specificity was 72.2%. Conclusions: Patients with patellar cartilage lesions have an increased tendon length/patellar length ratio. The abnormal patella height is significantly correlated with chondral lesions and can be used as a potential diagnostic marker.