External Adhesive Marker Technique Shows Excellent Reproducibility for Measuring Patellar Tendon‐to‐Lateral Trochlear Ridge Distance on Magnetic Resonance Imaging

Purpose To evaluate the agreement between a simple magnetic resonance imaging‐based measurement method for determining the patellar tendon‐to‐lateral trochlear ridge (PT‐LTR) distance using an external adhesive marker and a previously validated conventional measurement technique. Methods Patients diagnosed with patellofemoral instability before undergoing primary patellar stabilization surgery at a single institution between 2020 and 2024 were eligible for inclusion. PT‐LTR distances were measured in a blinded fashion by 2 musculoskeletal‐trained radiologists using the conventional technique and by an orthopaedic group using the simple technique. Interrater reliability between the musculoskeletal‐trained radiologists and between the orthopaedic groups was calculated using intraclass correlation coefficients (ICCs) and concordance correlation coefficients (CCCs) and subsequently intermethod reliability between the 2 groups. The measurements were plotted on concordance correlation graphs. Results One hundred knees (38 right, 62 left) from 97 patients (37 men, 60 women; mean age 22 ± 9 years) were included. The average distance for PT‐LTR measured by the radiologists using the conventional technique was 10.9 ± 7.5 mm and by the orthopaedic group using the simple technique was 9.3 ± 6.8 mm. Excellent interobserver agreement was noted for the radiologist group (ICC 0.941, 95% confidence interval [CI], 0.914‐0.960; CCC 0.941, 95% CI, 0.915‐0.959) and orthopaedic group (ICC 0.976, 95% CI, 0.964‐0.985; CCC 0.976, 95% CI, 0.965‐0.984). Excellent intermethod agreement was noted between the 2 techniques (ICC 0.903, 95% CI, 0.775‐0.942; CCC 0.902, 95% CI, 0.861‐0.932). Conclusions There was excellent interobserver reliability for measuring PT‐LTR distance using both the conventional radiologist‐based technique and the external adhesive marker technique. Excellent intermethod agreement was also shown between the 2 techniques, with comparable mean measurements between groups; thus, the simple technique can be used as a reproducible alternative for PT‐LTR distance. Level of Evidence Level III, retrospective comparative study.