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The knee joint is the largest joint in the human body and is very complicated. The knee is a pivotal hinge joint which permits flexion, extension and slight medial and lateral rotation. The knee supports nearly the whole weight of the body and is vulnerable to both acute injury and the development of osteoarthritis.

The knee joint joins the thigh with the leg and consists of two articulations. The first articulation is between the femur (thigh bone) and the tibia (leg bone). The second articulation between the femur and patella (knee bone).

There are two major muscle groups that are balanced and allow movement of the knee joint. When the quadriceps muscles on the front of the thigh contract, the knee extends or straightens. When the hamstring muscles on the back of the thigh flex or bend the knee will flex or bend. The muscles cross the knee joint and are attached to the tibia by tendons. The quadriceps tendon is a little special in that it contains the patella (knee) within it. The patella allows the quadriceps muscle/tendon unit to work more efficiently.  This tendon is known as the patellar tendon in the area below the kneecap to its attachment to the tibia.

The stability of the knee joint is maintained by four (4) ligaments which are thick bands of tissue that stabilize the joint. The medial collateral ligament (located on the inside) and the lateral collateral ligament (located on the outside) are on the sides of the knee and prevent the joint from sliding sideways. The anterior cruciate ligament and the posterior cruciate ligament form an x on the inside of the knee and prevent the knee from sliding back and forth.

Inside the knee, there are two (2) shock absorbing pieces of cartilage called menisci that sit on the top surface of the tibia. The menisci allow the femoral condyle to move on the tibial surface without friction, preventing the bones from rubbing on each other. Without the menisci, the friction of bone on both would cause inflammation or arthritis.

Bursas surround the knee joint and are fluid-filled sacs that cushion the knee during its range of motion. In the front of the knee, there is a bursa between the skin and the kneecap known as the prepatellar bursa and another above the kneecap known as the suprapatellar bursa.


While direct blows to the knee will occur, the knee is more susceptible to twisting or stretching injuries taking the joint through a greater range of motion than it can tolerate. If the knee is stressed from a specific direction then the ligament trying to hold it in place against that force can tear. Ligament stretching or tears are called sprains. These sprains are graded as first, second or third degree based upon how much damage has occurred.


Grade One sprains stretch the ligament but do not tear the fibers.

Grade Two sprains partially tear the fibers but the ligament remains intact.

Grade Three sprains tears completely disrupt the ligament.

Twisting injuries to the knee put stress on the cartilage or meniscus and can pinch it between the tibial surface and the edges of the femoral condyle causing tears.


Injuries of the muscles and tendons surrounding the knee are caused by acute hyperflexion or hyperextension of the knee or by overuse. These injuries are called strains. Strains are graded similarly to sprains.

Grade One strains stretch muscle or tendon fibers but no tearing.

Grade Two strains partially tearing the muscle tendon unit.

Grade Three strains completely tear the muscle tendon unit.


There can be inflammation of the bursas of the knee that can occur because of direct blows or chronic use and abuse.


Acute Knee Injuries Fall Into Two Groups;

First Group – Immediate swelling in the joint associated with the inability to bend the knee and bear weight.

Immediate swelling may suggest a ligament tear or fracture. If the swelling arises over a period of many hours, meniscal or cartilage injuries may be the cause.

Second Group – There is discomfort and perhaps localized pain to one side of the knee but with minimal swelling and minimal effects on walking.


Pain while climbing stairs is a symptom of meniscus injury where the cartilage is being pinched in the joint as it narrows with bending.

Pain with walking down stairs suggests patellar pain where the kneecap is being forced onto the femur.

Giving way or a feeling of instability of the knee or popping or grinding in the knee is associated with cartilage or meniscus tears.

Locking is the term used when the knee joint refuses to completely straighten and this is almost always due to torn cartilage. In this situation, the torn piece of cartilage folds upon itself and doesn’t allow the knee to extend.


Medical Care Should Be Sought If;

1.      There is almost immediate swelling in the knee.

2.      The bone appear deformed.

3.      There is inability to bear weight.

4.      The pain is intolerable.

5.      The foot and ankle become cold and no pulses can be felt.


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