knee
The knee is the largest joint in the body, and one of the most easily injured. It is made up of the lower end of the thighbone (femur), which rotates on the upper end of the shinbone (tibia); and the kneecap (patella), which slides in a groove on the end of the femur. The knee also contains four large ligaments. They are tough, non-stretchable fibers that hold bones together and brace the joint against abnormal types of motion.
- Two cruciate ligaments connect the thighbone to the shinbone, crisscrossing inside the knee to provide stability. They are the anterior cruciate ligament (ACL), toward the front of the knee; and the posterior cruciate ligament (PCL), toward the back of the knee.
- The other two ligaments of the knee are the medial collateral ligament (MCL), and lateral collateral ligament (LCL). They are located at the inner and outer sides of the knee joint. Each connects the thighbone to a different bone in the lower leg. The MCL, at the inner side of the joint, connects the thighbone to the shin bone and provides inner-knee stability. The LCL connects the thighbone to the fibula and stabilizes the outer side of the knee.
Another part of the knee, cartilage, cushions the knee and helps it absorb shock during motion. A layer of cartilage covers the weight-bearing surface of the knee. Between those cartilage surfaces of the femur and tibia are two, C-shaped, shock-absorbing structures–one on each side of the joint–called the medial meniscus and the lateral meniscus. They work with the cartilage to reduce the stresses between the bones.
The bones of the knee are surrounded by a smooth, thin tissue capsule lined with a synovial membrane. The membrane releases a lubricating fluid that reduces friction to nearly zero in a healthy knee.
Common knee injuries include:
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Your Guide to Total Knee Replacement |
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Your Guide to Knee Arthroscopy |
Additional Information |
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ACL (anterior cruciate ligament) injury
Goosefoot (pes anserine) bursitis of the knee
Kneecap (prepatellar) bursitis
MCL (medial collateral ligament) injury–Usually caused by contact on the outside of the knee; the primary symptom is sharp pain on the inside of the knee.
Osgood-Schlatter Disease (knee pain)–A common form of growing pains or a result of overuse (year-round soccer, gymnastics, basketball, and distance running) in early adolescence; symptoms include pain and enlargement of the tubercle, a raised area of the shinbone, just below the kneecap, which contributes to the growth of the leg. Symptoms generally resolve with completion of the growth sport, around age 14 for girls and 16 for boys.
Osteonecrosis of the knee–When a segment of the bone loses its blood supply and begins to die; commonly occurs at the knobby portion of the thighbone on the inside of the knee, but can also occur on the outside of the knee or the flat top of the lower leg bone. Osteonecrosis of the knee is associated with certain conditions and treatments, including obesity, sickle cell anemia, lupus, kidney transplants, and steroid therapy; can develop into severe osteoarthritis and eventual collapse of the bone. Is typically seen in older women, except steroid-induced ostenecrosis, which is usually seen in younger patients. Symptoms include sudden pain on the inside of the knee triggered by an activity or injury, increased pain at night, swelling over the front and inside of the knee, heightened sensitivity to touch in the area; and limited motion due to pain.
PCL (posterior cruciate ligament) injury–Can be caused by a blow to the front of the knee or when an athlete makes a simple misstep on the playing field; can cause the shinbone to sag backwards, disrupting knee stability and causing wear and tear that can lead to arthritis in the knee. Symptoms include marked, immediate swelling, difficulty walking, pain when the knee is moved, and an occasional feeling of instability.
Runner's knee (patellofemoral pain)–A term referring to a number of medical conditions that can cause pain around the front of the knee, including anterior knee pain syndrome, patellofemoral malalignment, and chondromalacia patella. A number of factors can contribute to runner's knee, including injury; the kneecap being out of alignment; overuse; flat feet; or tightness, imbalance, or weakness of thigh muscles. Symptoms include a dull, aching pain around the front of the kneecap, where the kneecap connects with the thighbone; and pain when kneeling, squatting, sitting for long periods of time, and going up and down stairs.
Torn meniscus/torn cartilage–The meniscus is a tough, rubbery cartilage that is attached to the knee's ligaments and acts as a shock absorber; it can be torn during sports activities when cutting, pivoting, decelerating, or being tackled; tears to the meniscus often involve direct contact; older people can injure the meniscus without any trauma, as the cartilage weakens and thins over time, becoming vulnerable to being torn. A tear may be accompanied by a popping sensation, stiffness and swelling, tenderness at the joint line, and collection of fluid on the knee.
Torn ligaments–A tear to any of the four ligaments of the knee
Unstable kneecap–When the kneecap is dislocated or partially off track; caused when the groove in which the kneecap moves up and down is uneven or too shallow, causing the kneecap to slide off; or when a fall or sharp blow to the kneecap pops the kneecap out of place. Symptoms can include the knee buckling, the kneecap sliding off to the side, pain in the front of the knee that increases with activity, stiffness, creaking or crackling sounds during movement, and swelling.
Source: American Association of Orthopaedic Surgeons