Morphological Description of the Embryonic to Fetal Development of the Menisco- Tibio-Popliteus-Fibular Complex and the Anterolateral Ligament.

Background: Little information is available on the embryology of the structures that connect the lateral meniscus to its nearby structures (proximal tibia, fibular head, and popliteus tendon), which restrict lateral meniscal extrusion. Purpose: To describe the menisco-tibio-popliteus-fibular complex (MTPFC)-conformed by the lateral meniscotibial ligament (LMTL), popliteofibular ligament, meniscofibular ligament, and the 2 popliteomeniscal ligaments (superior and inferior)-and anterolateral ligament (ALL) of the knee in human embryos/fetuses from weeks 9 to 37 of gestation. Study Design: Descriptive laboratory study. Methods: The authors analyzed 36 formalin-fixed embryos/fetus knees, ranging between weeks 9 and 37 of gestation. All had normal external morphological characteristics. A microdissection was performed by meticulously searching the structures of the MTPFC and the ALL, their anatomic relationships, and their appearance over time. Histological sections were taken of the entire knee, the lateral meniscus, the ALL, and the LMTL to observe its structure from its early stages, junctions, and cellularity. In addition, the composition and orientation of the fibers were evaluated. Results: The MTPFC was not found in the youngest knees (9 weeks). The ligaments of this complex could not be seen until week 11 of development. Moreover, the ALL was a consistent finding from the 13th week of development onward. All the ligaments of the MTPFC were seen between developmental weeks 11 and 16 in all the specimens. The histological results showed that the histology of the ALL showed dense connective tissue organized into thick bundles of collagen fibers in its central portion, with a parallel and undulating arrangement and the anterolateral capsule demonstrated 3 easily distinguishable layers corresponding to the fibrous membrane, the subsynovial membrane formed by loose connective tissue, and the synovial membrane. Conclusion: All the structures of the MTPFC were visualized from week 11, with the LMTL being the first to form. Moreover, the ALL was a consistent finding from week 13 of development onward. Clinical Relevance: Understanding the embryological development of the MTPFC and the ALL of the knee is clinically relevant, as it can provide crucial insights into the pathogenesis of knee conditions and inform treatment strategies. By elucidating the timeline and characteristics of these structures' formation, clinicians can better diagnose and manage conditions affecting the lateral meniscus and related structures, ultimately improving patient outcomes and surgical interventions.