Patellar Height Measurements on Radiograph and Magnetic Resonance Imaging in Patellar Instability and Control Patients

Abstract

Insall-Salvati (IS) ratio, modified IS ratio (mIS), Caton-Deschamps (CD) index, and Blackburne-Peel (BP) index are patellar height measurements commonly made on lateral radiographs (XRs) in patients with patellofemoral instability. More recently, magnetic resonance imaging (MRI) has been used as an additional imaging modality to measure patellar height. However, different imaging modalities have not been previously compared for all of these measurements. First, to compare the patellar height measurements of IS, mIS, CD, and BP on XR and MRI in first-time lateral patellar dislocation (LPD) patients and a control population and, second, to evaluate for the effect of sex and skeletal maturity. All first-time LPD patients with both MRI and XR of the knee within 6 weeks of injury from 2008 to 2012 were included in the LPD group ( = 112). Patients without patellofemoral instability who underwent both MRI and XR of the knee served as controls ( = 129). Two independent observers measured patellar height. Mean values were compared among the radiographic modalities, sex, and skeletal maturity status. Interobserver reliability was assessed using intraclass correlation coefficients (ICCs). Patellar height in the LPD group measured greater on MRI than on XR for all four patellar height ratios (IS: 0.11; mIS: 0.07; CD: 0.18; BP: 0.08). In controls, MRI also demonstrated higher readings than XR on two indices (CD: 0.17; BP: 0.16). Skeletally immature patients measured higher than skeletally mature patients in the majority of the measurements by 0.12 to 0.20 on MRI and XR; the majority of the measurements showed no sex differences. ICC was excellent for IS on both MRI (ICC = 0.830) and XR (ICC = 0.849) and for CD on XR (ICC = 0.786). Patellar height measured greater on MRI than XR by approximately 0.10 across four patellar height measurement indices. Skeletally immature patients measured higher than skeletally mature on both MRI and XR, but sex did not have an effect. This is a retrospective cohort study and its level of evidence is 3.

Objective assessment of patellar maltracking with 3 T dynamic magnetic resonance imaging: feasibility of a robust and reliable measuring technique

“…Radiological parameters of anatomical risk factors were assessed on static transverse and sagittal MRI images. Patella height was determined using the Caton-Deschamps Index (CDI) on sagittal MRI images, with the relaxed knee placed in 20° of flexion, using a standard MRI knee coil 14,32 . www.nature.com/scientificreports/ The distance between the tibial tubercle and the trochlear groove (TT-TG) was measured in accordance with Schoettle et al 9 , with the knee placed in the same position.…”

Evaluation of correlation between clinical and magnetic resonance imaging findings of patellar chondromalacia

“…Conversely, Thakkar et al [13] and Chan et al [14] concluded quantitative trochlear parameters could be reliably calculated on MRI. The literature on quantitative imaging is usually related to the patellar malalignment [15][16][17][18] .…”

Biplanar ascending opening-wedge high tibial osteotomy increases tibial tubercle–trochlear groove distance and decreases patellar height

“…The CDI is the relation of the shortest distance from the inferior pole of the articular surface of the patella to the tibial plateau and the length of the articular surface of the patella. Dividing the distance from the inferior pole of the articular surface of the patella to the projection line of the tibial plateau by the length of the articular surface of the patella calculates the BPI15 (figure 4). Patella baja was considered when BPI and CDI values were less than 0.5 and 0.6, respectively.…”