The knee is the largest joint in the body. It not only bends and straightens, but it also has some rotational motion. While walking at a normal pace, the knee must bear three to five times our body weight. When we climb stairs or run, the force it must bear increases to seven or eight times our body weight. Normally, all of the components of the knee work in harmony, and we are pain free. However, when the knee is overstressed in sports or everyday activities, or it is injured, the soft tissue structures become inflamed, swollen, and painful. If these problems are not immediately addressed, the affected structures will gradually break down, causing complete immobility of the knee.
Anatomy of the Knee
In order to help determine which structures may be involved when there is knee pain, we have divided the knee into 5 sections. Each section will contain one or more anatomical structures which may cause knee pain.
The knee is the largest, and one of the most complex joints in our body. It is injured more frequently than any other joint. The knee joint is composed of the following structures:
1. Four Bones:
- Femur: This is the thigh bone, and it is the largest bone in our body.
- Tibia: This is the large shin bone which is found in the lower leg.
- Fibula: This bone is smaller than the tibia, and it is located next to the tibia in the lower leg.
- Patella:This is also called the knee cap. It is the small bone located in front of the knee. When the knee bends or straightens, the patella moves up and down in the femoral groove. The femoral groove is located on the upper end of the front of the tibia.
2. Four Large Ligaments: These ligaments are strong fibrous bands which connect bones to each other, and brace the knee joint against abnormal types of knee motion. The following ligaments provide stability to the knee joint:
The two ligaments which are located on the outside of the knee joint:
- Medial Collateral Ligament (MCL): This ligament is located on the inner (medial) aspect of the knee; and connects the femur to the tibia.
- Lateral Collateral Ligament (LCL): Located on the outer (lateral) aspect of the knee; and connects the femur to the fibula.
The next two ligaments are found within the knee joint. They are found in the center of the joint, connecting the femur to the tibia:
- Anterior Cruciate Ligament (ACL) is found towards the front of the joint. It prevents the tibia from sliding forward beneath the femur.
- Posterior Cruciate Ligament (PCL) is located toward the rear of the knee joint. It prevents the tibia from sliding backward beneath the femur.
These two ligaments "criss-cross" each other, and by so doing, provide great stability to the knee joint.
Common Knee Conditions
Front (Anterior) of the Knee
" Runner's Knee
(Patellofemoral Pain Syndrome)
" Jumper's Knee (Patellar Tendinitis)
Inner Side (Medial) of the Knee
" Medial Collateral Ligamnet
Outer Side (Lateral) of the Knee
" Iliotibial Band Syndrome (I.T.B.)
" Lateral Collateral Ligament
Deep Pain Within the Knee
" Osteoarthritis of the Knee
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Knee Pain Locator.
3. There are two thick fibrocartilaginous cushions which sit between the femur and the tibia. They are called the medial and lateral menisci, and they act as cushions and shock absorbers for the knee.
4. Articular cartilage covers the ends of the knee bones, and allows for the smooth movement of one bone moving against the other. This cartilage reduces friction, and allows the knee to bend and straighten pain free.
5. There are two "C" shaped thick fibro-elastic tissue pads (thick cartilage pads) found in the knee. They act like articular cartilage and protect the ends of the femur and tibia. Unlike articular cartilage, the menisci also act as shock absorbers within the knee.
6. While bones support the knee, muscles move the knee. Muscles attach to bones by means of strong fibrous bands called tendons. The two major muscles that bend and straighten the knee are:
The Quadriceps Muscle which is located on the front of the thigh. It straightens the knee.
The Hamstring Muscles are found on the back of the thigh, and they bend the knee.
7. The Iliotibial Band (I.T.B.) is a thickened strip of fascia or muscle cover. It begins as a thick band that covers the outer thigh muscles, and travels down the outside of the leg to the knee joint, where it attaches to the outer edge of both the tibia and fibula, just below the knee joint. This structure gives added stability to the knee joint.
While there are more anatomical structures in and around the knee, the above structures are the most commonly injured, and therefore have been singled out and described.