Background: A discoid lateral meniscus (DLM) is a congenital anomaly of the knee in which the lateral meniscus has an "O" shape and contains irregular, abnormal collagenous tissue. A DLM can cause mechanical symptoms and pain. Treatment of a symptomatic DLM is arthroscopic saucerization to reshape the meniscus to a more normal contour. Enough tissue must be removed to eliminate mechanical symptoms but not too much to create instability. The residual width of the meniscus is crucial at the popliteus hiatus because here the peripheral rim is unattached at the capsule. Reports in the literature recommend a residual width of 6 to 8 mm.
Purpose/hypothesis: The purpose of this research was to determine the width of the lateral meniscus at the popliteal hiatus in normal specimens. Our null hypothesis was that a residual width of 6 to 8 mm will be sufficient to approximate normal anatomy.
Study design: Cross-sectional study; Level of evidence, 3.
Methods: We made direct measurements of the radial width of the lateral meniscus from the outer rim at the popliteal hiatus to the inner edge in 19 specimens (age, 2-120 months.) We measured one 4-year-old specimen with a bilateral complete DLM. We also measured 39 digital images of specimens (age, 1-132 months) using ImageJ. Finally, we made direct arthroscopic measurements of 8 skeletally mature specimens.
Results: The average width of specimens <3 years old was 5.5 mm. The average width of the 10-year-old specimens was 12 mm. The average width of the skeletally mature specimens was 16 mm. A 4-year-old DLM specimen measured 19 mm.
Conclusion: We rejected our null hypothesis. Direct measurements suggest that a residual width of 6 to 8 mm is insufficient for children ≥8 years old. A width of at least a full centimeter approximates the normal for 8-year-olds and at least 15 mm for adolescents.
Keywords: anatomy lateral meniscus; discoid lateral meniscus; lateral meniscal width; saucerization discoid lateral meniscus.