O2069: Plain Radiographs Have Limited Utility in the Evaluation of Discoid Lateral Meniscus

Background: Debate persists regarding which radiographic measurements are important when investigating a possible discoid lateral meniscus. The purpose of this study was to identify differences in various measurements between healthy children and those with a discoid meniscus while controlling for other patient characteristics.

Methods: Radiographs of patients with a confirmed discoid lateral meniscus were matched by age and sex to those with a healthy knee as verified by magnetic resonance imaging (MRI). The following parameters have been associated with discoid meniscus in previous studies and were measured on x-ray for each subject: lateral joint space height (both in the central and medial portion of the compartment; LJSH-C and LJSH-M, respectively), medial joint space height, fibular head height (FHH), lateral tibial spine height, femoral inter-epicondylar distance, lateral tibial plateau obliquity, and chordal distance of the femoral condyle (medial and lateral). Additionally, ratios were calculated between LJSH-C/M and medial joint space height. Univariate analysis was followed by multivariate regression to adjust for confounders.

Results: The study included 55 patients with a discoid meniscus and 55 controls with a mean age of 11.0±3.5 years (50% female). The median LJSH-C for subjects with a discoid meniscus was 7.2 mm [interquartile range (IQR) 2.2] compared to 5.5 mm (IQR 2.1) in normal knees (p < 0.001). A similar difference was found for LJSH-M [7.0 mm (IQR 2.8) vs. 5.7 mm (IQR 2.2), p< 0.001]. Mean FHH was lower for discoid menisci than controls (12.7±4.2 mm vs. 15.3±5.9 mm, p=0.01). No other radiographic measurements were significantly different between cases and controls. When adjusting for covariates in regression analysis, the presence of a discoid meniscus was predictive of a higher LJSH-C and LJSH-M and lower FHH. Of note, age and sex were also significantly predictive in these models. Patients with a discoid meniscus had 4.4 times higher odds of LJSH-C ≥7 mm [95% confidence interval (CI) 1.9-10.5, p=0.001), 9.1 times higher odds of LJSH-M ≥6 mm (95% CI 1.9-42.5, p=0.005), and 2.7 times higher odds of FHH < 16 mm (95% CI 1.1-6.6, p=0.03).

Conclusion: LJSH-C, LJSCH-M, and FHH on plain radiographs are associated with a discoid meniscus. However, many previously reported measurements were not predictive. The practical utility of these parameters may be complicated by the impact of age and sex. Advanced imaging is required to confirm the diagnosis of discoid lateral meniscus.