Menisci in the Knee Joint

Apart from the ligaments mentioned above, the knee is also stabilised by special structures of type fibrocartilage, known as Menisci. Menisci are two in number and present on the tibial plateau. These menisci have a peculiarity that they are tough and compact like cartilage where they are compressed between the bones but fibrous and flexible at their attachments. They rest between the femoral condyles and the tibial plateau in order to absorb shock during the use of joint, help to protect the articular cartilage-covered condyles and at the same time stabilise the joint. Each meniscus is named depending upon the side it is. Thus we have a medial meniscus and a lateral meniscus in each knee. The menisci attach themselves to the plateau at their ends, commonly referred to as ‘horns’. In addition to these attachments, they are also attached to the underlying cartilage along its circumference by Coronary Ligament.

The medial meniscus is roughly crescent in shape as opposed to lateral which is circular. The medial meniscus attaches its anterior horn to the anterior most part of the tibial plateau and runs along the medial periphery to attach on the posterior most part of the tibial plateau on the other end. Also, the coronary ligament on the medial side is more tightly attached to the cartilage. The combined effect of these features is that the medial meniscus is less flexible in movement. As a result, it is more prone to injuries in high activities of the joint and with increasing age. So much so that the medial meniscus suffers from 80% of the total meniscal injuries.

The lateral meniscus on the other hand is more or less circular in shape as mentioned previously. It attaches both its horns in proximity at the medial aspect of the lateral tibial condyle on the tibial plateau. Coupled with this is the fact that even the coronary ligament is relatively less tight in this side of the joint. As a result, the lateral meniscus is more mobile and flexible. This in turn means that it is less prone to injuries.

As mentioned earlier, menisci are more or less crescent-shaped. In their anterior-posterior orientation, menisci can be divided into three distinct zones. The anterior zone is called Anterior Horn of the meniscus, posterior zone is called Posterior Horn of the meniscus and the middle zone is called Mid-Segment. Besides these parts, menisci can also be divided into three zones in their medial-lateral orientation. Menisci are thick at the periphery and taper towards the centre. In the outermost zone, menisci have ample vascular supply lending them red colour whereas the innermost part is devoid of any vascular supply giving them the white colour. In between these two zones is an area that has got lesser vascularisation. This is termed as red-white zone. Based on their colour, these zones are known as red-red, red-white and white-white zones. Thus, one meniscus can be sub-divided into 9 areas. Typically, the disorders in meniscus are termed in the following way: Bucket-Handle tear in the red-white of mid-segment of the lateral meniscus of the left knee. Bucket-Handle tear is a type of tear in which major part of the torn meniscus is detached from the main body and is attached to it only at two points at each end of the main body. Red-white of mid-segment suggests that the tear is in the exact centre of the meniscus.