Knee anatomy

The knee has three bones : the femur (the thigh bone), the tibia (the shinbone) and the patella (the kneecap). The femur and the tibia form a hinge joint. The joint is enclosed by the joint capsule at the back and on the sides, and is covered by the patella and patellar ligament in front. The knee joint is stabilized mainly by the tendons of quadriceps femoris muscle in front and semimembranosus muscle (one of the hamstrings) on the back. Strengthening these two muscles  therefore helps to reduce the risk of knee injuries.

Fig.1 : Midsagittal section of the knee joint. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

Apart from the regular articular cartilage that cover the end surfaces of the three bones there are two additional pads of cartilage that are unique to the knee joint : medial meniscus and lateral meniscus (Fig. 2 and Fig. 3). The menisci act as shock absorbers to cushion the joint.

Two pairs of ligaments help to stabilize the knee : collateral ligaments run along two sides of the knee (Fig. 2), and cruciate ligaments which connect the femur and tibia in the center of the joint and cross each other in the from of an X (hence the names) : anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) (Fig. 2 and Fig. 3).

Fig. 2 : Front view of the right knee (the kneecap is removed in this picture to show structures behind).  Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

Fig. 3 : The right knee viewed from top (femur removed to show structures underneath). Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

Meniscus tear and repair

Commonly referred to as torn cartilage, torn meniscus is a common sport injury. Mild injuries maybe treated with rest, ice, compression and elevation (the RICE approach). Larger tears may require surgery. The goal of surgery is to remove the damaged tissue which is the source of irritation, pain and possibly inflammation, and attempt to induce healing. Treatments vary depending on the location of the tear. If the tear is located on the outer border of the meniscus (the red zone, see Fig. 3) where there is a good blood supply, the damaged loose tissue will be removed and sutures will be used to tight the cartilage together to facilitate self healing. If the tear is located on the inner part (the white zone, see Fig. 3) where the blood supply is poor and hence healing is unlikely, the damaged part is simply removed (partial meniscectomy) (Fig. 4).

Minimal invasive arthroscopic surgery is commonly used for meniscus repair. In case of large tears, open surgery may be required.

Click here to see an animation of arthroscopic meniscus repair on Alila Medical Media website where the video is also available for licensing.

Fig. 4 : Treatment of meniscus tear depends on its location. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.

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