The importance of the position of meniscus tears

A tear of the meniscus anywhere is a significant injury, but the outcome may depend to a large extent on its position.

The pointed parts of the meniscus at the back and front of the knee are called the 'horns' of the meniscus. The ones at the back are the 'posterior' horns and the ones at the front are the 'anterior' horns. The thicker middle bit is the 'body' of the meniscus, with the thicker 'lateral rim' on the outer side and the flattened 'medial rim' on the inner side.

The posterior horn is hard to reach because the bones of femur and tibia are in the way. The surgeon reaches this part by asking his assistant to force the knee into a knock-knee or bow-leg position, and then approaches it around the bulky cruciate ligaments through the notch of the femur or under the rounded end of the femur.

The anterior horn is also difficult to operate on, because it is so close to the entry hole (portal) where the surgeon introduces his instruments and camera. This part of the meniscus is sometimes torn right off (avulsed) from its attachment.

Blood supply and the position of tears

The extent and position of the tear is also of relevance when it comes to the blood supply of the damaged part -

• the inner sharp edge of the meniscus does not have a blood supply and tears here do not heal - this is referred to as 'white-on-white'.
• between the inner edge and the outer edge there may be sufficient blood supply to heal the wound - tears here are referred to as 'white-on-red'.
• along the outer rim the blood supply is good and most tears will heal - tears here are referred to as 'red-on-red'

Avulsion

Sometimes the meniscus may be 'avulsed' rather than torn, that is the attachment is torn up like a tree being uprooted. There may be symptomatic instability but the problem may be missed by the inexperienced surgeon.