The Embryological Development of Menisci

The embryological meniscal development seems to have an effect over the shaped the of the complete meniscal discoid and the incomplete meniscal discoid. Many studies investigated the shaped the of the complete meniscal discoid and the incomplete meniscal discoid. In one of the studies they were found to be the main causative factors of pain in the knee joint. The variations of the shape of the discoid menisci are explained by embryological meniscal development.

Incomplete discoid 

                                                                Complete discoid 
Embryological meniscal development

The meniscal arises from the differentiation of mesenchymal tissue within the limb bud by the eighth week of fetal development. During O’Rahilly stage 22, the menisci arises from the eccentric portions of the articular inter zone but it is not clearly noticeable until the ninth week of development.

            The blood supply during embryologic development enters from the periphery and continues throughout the entire width of each meniscus. However, the central third will receive blood supply by the ninth week after birth, and by adulthood, the peripheral one third is the only part that will be vascular. At the ninth week of the development there will be no more microscopic structural changes and the meniscus will grow at the same level as all the other intra-articular structures. By the fourteenth week the menisci will have a normal adult relationship with the other structures of the knee.

Functions and Attachments of the anterior horn, posterior horn, and middle boarder of medial meniscus

The medial meniscus is an important primary stabilizer and weight-transmitter in the knee joint. It preforms an important function in limiting knee motion. The medial meniscus consists of three main parts. Each part has its own function and together the three parts make up the medial meniscus function. 

The three parts are:

1- anterior horn

2- posterior horn

3- peripheral border 

How do they function together?

The anterior horn of the medial meniscus carries most of the load during the first 30-A˚ of  the knee flexion, and after that the posterior horn carries most of the load. The anterior horn after 30 degrees of the knee flexion plays an important role in controlling the anterior femoral displacement. The peripheral border distributes the weight during the transition of force from the anterior horn to the posterior horn. 

A new study suggested that the attachments of the three parts of the of the medial meniscus are associated with the function and any abnormality in the attachment locations may decrease the quality of the function.

Anterior horn, posterior horn, and peripheral border attachments

 The anterior horn of the medial meniscus is attached to the anterior tibial intercondyler area anterior to the anterior cruciate ligament showing in fig. 1. and the posterior fibres of the anterior horn are continuous with the transvers ligament. The posterior horn is fixed with the posterior tibial intercondyler area, between the attachment of the lateral meniscus and the posterior cruciate ligament showing in fig. 2. The peripheral border is attached to the fibrous capsule and the deep surface of the medial collateral ligament. The tibial attachment is known as the coronary ligament. Together these attachments limit the movement of the medial meniscus and make it relatively more fixed and limited in movements than the lateral meniscus .

Fig. 1 The attachment of the anterior horn of the medial meniscus  indicated by the black arrow. Fig. 2 The attachment of the posterior horn of the medial meniscus indicated by the black arrow.

Medial Meniscus Morpholgy

How many times have you seen people walking with crutches?

The answer is probably a lot.  Do you know why? One of the common reasons for that is knee injury. The knee is the biggest joint in the human that transmits the body weight to the tibia and helps keep the body weight balanced. Because of the nature of its function the chances of getting knee joint injuries are higher than other joints in the body, especially for athletics and workers on jobs that require hard physical labor. Another reason why the knee is more subjected to injuries is the wide range of its movements and because of that the knee joint has many ligaments and menisci- which is defined as a thin fibrous cartilage between the surfaces of the femur and the tibia-. The menisci functions are protecting the underlying articular cartilage, distributing pressure on the surface of the tibia, and lubricate the cartilage surface to help keep the movement easy and smooth. The menisci also limit the anterior and the posterior displacement and increase the anterioposterior stability of knee joint and that makes the menisci secondary stabilizers compared to the cruciate ligaments. The knee joint has two menisci the lateral meniscus and the medial meniscus. The medial meniscus is more subjected to injuries than the lateral one and this is because of its limited movement range compared to the lateral meniscus and the pressure on it is higher than on the lateral one. Ongoing researches aimed to investigate the differences in the size and shape of the medial meniscus between humans. A morphological study was done in adboud University Medical Center in Netherlands found a significant difference between menisci size and shape between males and females. Another morphological study of the medial menisci in adult cadavers of south indian population was done in Manipal University, Anatomy department also found a significant difference between meniscal shape among the population as a whole. After these findings, the next question is can the findings help prevent injuries before they happen and/or develop a new treatment method, and if yes how?

Left knee structures on the tibial and fibular surfaces including medial meniscus