Caton-Deschamps index measured on radiographs differs from magnetic resonance imaging in pediatric patients with and without patellofemoral instability.
Academic Article
Overview
abstract
INTRODUCTION/OBJECTIVES: Patella alta is implicated in numerous disorders of the patellofemoral joint including patellofemoral instability (PFI). The Caton-Deschamps Index (CDI) is a validated index for assessing patellar height in pediatric patients on knee radiographs (XRs). In adults, magnetic resonance imaging (MRI)-derived CDI demonstrates variable agreement with radiograph-derived CDI, however, no study to date has investigated the applicability of this index in pediatric patients. The study objective is to compare MRI- and radiograph-derived CDI in pediatric patients with PFI and healthy controls. METHODS: A total of 252 knees from patients aged ≤18 years were included in this study. One hundred twenty-six knees from 112 patients with PFI undergoing medial patellofemoral ligament reconstruction with preoperative MRI and XR were included, as well as 126 knees from 119 healthy controls. CDI was measured on both MRI and XR. CDI values were compared using two-way random, single measures, absolute agreement intraclass correlation coefficient (ICC [2, 1]) and Bland-Altman analysis. RESULTS: The mean age of the patient cohort was 14.5 ± 2.07, with 154 females (66.7%). The mean CDI as measured on XR was 1.21 ± 0.22 and on MRI it was 1.21 ± 0.19, ICC [2, 1] was 0.67 (95% confidence interval [CI]: 0.5-0.73, p < 0.001). Bland-Altman analysis revealed a mean difference of -0.0034 ± 0.17 between XR and MRI (Limits of Agreement: 0.33 to -0.33). Agreement between XR and MRI patella alta classification was fair (kappa = 0.50, p < 0.001), with disagreement occurring in 54 patients (21%). When stratifying patients by the presence of PFI, ICC additionally demonstrated fair agreement between XR and MRI-CDI. Multivariable logistic regression demonstrated younger age (odds ratio [OR] = 0.82, 95% CI: 0.71-0.95, p = 0.009) and higher CDI (OR = 8.28, 95% CI: 2.24-30.57, p = 0.002) were independently associated with high disagreement. CONCLUSIONS: In pediatric patients with and without PFI, CDI demonstrates good agreement when measured on XR and MRI, although there is fair agreement in classifying patella alta. Caution should be taken when utilizing this index to assess patellar height in pediatric patients, particularly in younger patients. LEVEL OF EVIDENCE: III.
