Magnetic Resonance Image (Mri) Measurements of Lateral Discoid Meniscus (Ldm) in Pediatric Patients Match Adult Lateral Discoid Meniscus Definitions

BACKGROUND: Commonly cited lateral discoid meniscus (LDM) imaging definitions are based upon adult MRI measurements: >70% tibial plateau coverage on the sagittal, >20% tibial plateau coverage on the coronal and >3 bowtie signs. This pathology more commonly presents in pediatric populations and it is unknown if these measurements apply to a pediatric population. Therefore, it is important to understand the Magnetic Resonance Image (MRI) measurements of LDM in a pediatric population. HYPOTHESIS/PURPOSE: The purpose of this study is to define LDM measurements on MRI in a pediatric population. Authors hypothesize there is a wide variation in LDM characteristics on MRI. METHODS: 100 MRIs on LDM patients who are skeletally immature were evaluated and 91 included in this study. Demographics were recorded. Two study authors independently reviewed MRIs measuring meniscal height and width on sagittal and coronal images, tear presence, number of “bowties” on sagittal images, as well as tibial sagittal and coronal width. One study author repeated measurements a minimum of 4 weeks after initial review. Figure 1 describes each measurement. Statistical analysis was performed using fisher’s exact test for differences, as well as multinomial, linear and logistic regression models with clustered robust standard errors. RESULTS: Average age at MRI was 12.3 ± 3.4 years, 51% male, 56% left knees. Table 1 reports gender comparison of MRI measurements. Table 2 reports gender comparison of bowtie sign and ratios of meniscal width to tibial width on coronal and sagittal images. Tears were reported in 72 MRIs (80%). Genders of patients with tears were not statistically different (Female: N=33; 73%, Male: N=39; 87%, p=0.16). Sagittal anterior (p=0.005) meniscal width, anterior to posterior meniscal width (p<0.001), and # of bowtie signs (p=0.043) were significantly associated with tear presence. CONCLUSION: MRI characteristics can aide in accuracy of LDM diagnosis. Pediatric patients with diagnosed discoid meniscus had >3 bowtie signs, >70% tibial plateau coverage on the sagittal, and >20% tibial plateau coverage on the coronal consistent with adult reported definitions of discoid meniscus.