Three-dimensional morphology and shape variants of the fetal medial meniscus: anatomical and clinical implications

This study aimed to examine the morphology of the fetal medial meniscus in cadavers, including both quantitative analysis and the identification of new shape variants. Fifty fetal cadavers were analyzed (36 from the second trimester, 13-25 weeks;14 from the third trimester,26-37 weeks). Of 53 available specimens, three with musculoskeletal malformations were excluded. Surgical microdissection under a stereomicroscope exposed the medial meniscus, which was measured using a calibrated digital caliper. Morphology was documented and classified into five primary types and five subtypes. Data were analyzed using SPSS version 21.0(IBM Corp., Armonk, NY, USA). Significant growth in all parameters was observed between the second and third trimesters, with notable morphological differences between male and female fetuses, emphasizing the influence of gestational age and sex. The study identified distinct medial meniscus shapes: 46% were sickle-shaped, 16% C-shaped, 13% crescent-shaped, 4% U-shaped, and 1% V-shaped. Additionally, 20% of medial menisci exhibited variant subtypes derived from the crescentic and C-shaped types. This study provides a novel and comprehensive evaluation of fetal medial meniscus morphology, identifying both previously known and new shape variants. These findings expand current anatomical knowledge and suggest that morphological diversity of the medial meniscus may have functional implications for knee joint biomechanics. This is the first study to describe three-dimensional fetal MM morphology, including five previously unclassified subtypes. Further research could clarify clinical implications of these morphological variants of fetal medial meniscus in orthopedic diagnosis and management across all age groups.