Anatomy Mondays: The cruciate ligaments of the knee.

Welcome to Anatomy Mondays! This is a new feature which will explain anatomical structures in terms that hopefully are accessible to all.

An recent news report points to a recent NFL study about the rate of knees and ankles injuries during games played on turf and games played on grass. The study shows that there is more incidence of ACL (anterior cruciate knee ligament) injuries is significantly higher (88%) on turf than on grass. While the study does not really draw any conclusions on the reasons why (could it be that players wear the wrong kind of shoes on turf for example) and is just as statistical tally, it is interesting to follow the potential developments from it. Specially considering that all the grass playfields in Seattle are being replaced by turf fields.

The main injurie tracked is a rupture, partial or total of the ACL. ACL injuries are al too common if you are a soccer player or an avid skier. But what exactly is the ACL?

Location:

ACL stands for anterior cruciate ligament. It is a ligament deep inside your knee. It at

taches to the front head of the tibia (to be more precise on the anterior intercondylar area of the t

ibia). It runs up and towards the back of the knee to attach to the femur (the large thigh bone).

To be more precise, it runs postero-(towards the back)-supero-(above)-laterally-(towards the outside of) and attaches to the medial (the interior) aspect of the lateral femoral condyle. A condyle is the round bump of a bone where it forms a joint with another bone. In the case of the femur, there are two condyles, one facing the center line of the body (the medial condyle), the other facing the outside of the body (the lateral condyle).

There is another cruciate ligament, the PCL or posterior cruciate ligament. As its name indicates, the PCL is the opposite ligament to the ACL running from the back of the knee towards the front (from the posterior intercondylar area of the tibia, runs anterisuperomedially and attaches to the lateral surface of the medial femoral condyle).

The two ligaments actually cross, forming an X 'inside' the knee.

Function:

The role of the cruciate ligaments is to resist the hold the tibia and the femur together. Without the ligaments, the tibia could move too much towards the front or the back depending on the movement. The reason why the ligaments actually cross is to allow the joint to flex.

The knee is primarily a hinge joint, allowing for flexion (bringing your heel towards your bottom) and extension (bringing your heel away from your bottom). However to allow for faster reaction and for a more even distribution of forces during movement, the knee also allow for a tiny bit of rotation. During a lateral rotation (your foot is turning out), the cruciate ligaments are slacken somewhat, however during a medial rotation (your foot is turning in), they press against each other and become more taut.

The risk for injury is typically greater to the ACL than the PCL. ACL tears are often the result of either:

• Hyperextending the knee, that is if the knee is straighten more than 10 degrees past the normal fully straighten position. This injury occurs often during skiing, volleyball, basketball, soccer and football.
• Pivoting of the lower leg, particularly inward rotation. This injury is often seen with football, basketball, tennis and soccer.

The treatment for ACL tears is often a long rehabilitation and strengthening program as well as possible reconstructive surgery.

Take care of your knees! It is a complex structure that takes a while to heal.

Illustration taken from the excellent Anatomy of Movement
by Blandine Calais Germain, published by Eastland Press, 1993