knee
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Your Guide to Total Knee Replacement |
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Your Guide to a Knee Arthroscopy |
Additional Information |
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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:
ACL (anterior cruciate ligament) injury–Often caused by twisting or changing direction rapidly, slowing down while running, or landing from a jump; about half of ACL injuries occur in combination with injury to the meniscus, cartilage, or other ligaments; most commonly occurs in women 15-25. There may be a popping noise when the ACL tears, followed by immediate pain and swelling and a feeling of instability in the knee. Loss of full range of motion can also occur.
Adolescent anterior knee pain–A dull, aching pain behind the kneecap in the center of the knee that may be accompanied by popping sounds when climbing stairs or when rising after sitting; usually begins gradually; common among healthy, young athletes, especially females; may be caused by inflexibility of the thigh muscles supporting the knee joint, problems with knee or hip alignment, overdoing sports activities, or using improper sports training techniques or equipment.
Arthritis–A condition with stiffness, swelling, and pain, which may create a feeling of weakness in the knee and results in locking or buckling of the knee; pain generally develops gradually and may be affected by the weather. Three types of arthritis may affect the knee joint:
- Osteoarthritis (OA)–The most common form of knee arthritis; a slowly-progressing, degenerative disease in which the joint cartilage on the ends of the bones gradually wears away, the bones eventually thicken and develop spurs, and extra fluid may be produced; can occur in one or both knees; most often affects people over 55. Symptoms include pain when standing or going up or down stairs and knees buckling, locking in place, or becoming stiff and swollen.
- Rheumatoid arthritis (RA)–An inflammatory condition of the synovial membrane that can destroy the joint cartilage; generally affects both knees; and can occur at any age; also called gouty arthritis.
- Post-traumatic arthritis–Similar to osteoarthritis, this kind of arthritis can develop after a fracture, ligament injury, or meniscus tear; may develop years after the injury.
Chrondromalacia patella–Softening and breaking down of the cartilage of the kneecap, which causes pain in the underlying bone and irritation of the joint lining.
Goosefoot (pes anserine) bursitis of the knee–Inflammation of the pes anserine bursa, a small lubricating sac located on the inside of the knee, about 2 inches below the joint, between the shinbone and the three tendons of the hamstrings muscle. Symptoms include pain and tenderness on the inside of the knee, below the joint, that increases with exercise or climbing stairs. Usually develops as a result of constant friction or stress on the bursa; can be a result of osteoarthritis of the knee, incorrect training techniques, tight hamstring muscles, obesity, or an out-turning of the knee or lower leg.
Kneecap (prepatellar) bursitis–Swelling in the front of the knee caused by constant friction that irritates the bursa, the small lubricating sac located just in front of the kneecap (patella), and causes it to become inflamed. Affects people who kneel to work, such as plumbers, roofers, carpet layers, coal miners, and gardeners; athletes who receive blows to the knee or commonly fall on the knees; and people with rheumatoid arthritis or gout; can also result from a motor vehicle collision. Symptoms include pain with activity, rapid swelling on the front of the kneecap, and a feeling of being tender and warm to the touch.
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