Asymmetric Deficit of Knee Flexion: An Occasional Symptom of Discoid Lateral Meniscus in Children

Purpose:A knee flexion deficit can be the unique symptom and sign of discoid lateral meniscus (DLM) in children. The aim of this study was to investigate the accuracy of this clinical sign. The hypothesis was that deficit of knee flexion was associated with anterior rim disinsertion and posteriorly fixed DLM.Methods:A retrospective, single-center study was conducted in a larger series of 114 operated knees for symptomatic DLM from 2007 to 2018. A focus was done on 9 knees with a deficit of knee flexion without snapping. History and clinical examination with grading of instability, preoperative magnetic resonance imaging, and arthroscopic findings were studied.Results:Among 35 knees with DLM grade 3 of instability, 26 had an isolated extension deficit. Nine knees in 5 boys and 4 girls with a mean age of 9 years (range 6 to 12) had a flexion deficit. It was the only symptom of DLM in 6, and it was associated to extension deficit in 3. In the history, 8 knees were grade 2 (snapping knee) before evolving toward a flexion deficit. All had a complete DLM with posterocentral (n=7) or central (n=2) shift at magnetic resonance imaging analysis. All had DLM with posterior shift fixed during arthroscopic evaluation. Moreover, looking at the entire series, 1 knee was a false negative and had a full flexion despite a posterior and fixed DLM during arthroscopic evaluation. The sensitivity of asymmetrical knee flexion to predict posterior fixed DLM was 90%.Conclusions:An asymmetric deficit in knee flexion is highly suggestive of DLM with anterior detachment and fixed posterior meniscal shift (specificity and positive predictive value of 100%). Given this could be the only clinical sign of DLM, specific attention therefore must be paid in the assessment of knee flexion by measuring the distance between heel and bottom on both sides, especially in a knee without snapping currently but with a history of snapping (grade 3).Level of evidence:Level III.