|Classification and external resources|
The knee joint consists of an articulation between four bones: the femur, tibia, fibula and patella. There are four compartments to the knee. These are the medial and lateral tibiofemoral compartments, the patellofemoral compartment and the superior tibiofibular joint. The components of each of these compartments can suffer from repetitive strain, injury or disease.
Running long distance can cause pain to the knee joint, as it is high-impact exercise.
Some common injuries include:
- Sprain (Ligament sprain)
- Tear of meniscus
- Strain (Muscle strain)
- Hemarthrosis – Hemarthrosis tends to develop over a relatively short period after injury, from several minutes to a few hours.
Some of the diseases of cause of knee pain include the following:
- Knee osteoarthritis
- Chondromalacia patella
- Baker's cyst
- Meniscal cyst
- Discoid meniscus
- Osgood-Schlatter disease
- Larsen-Johansson disease
- Knee rheumatoid arthritis
- Osteochondritis dissecans disease
- Synovial chondromatosis disease
- Ankylosing spondylitis
- Reactive arthritis
- Tuberculosis arthritis
- Septic arthritis (Pyogenic arthritis)
- Hemophilic arthritis
- Gout (Gouty arthritis)
- Bursitis of the knee
- Synovitis of the knee
Common deformities of the knee include:
- Bipartite patella (two-part kneecap)
- Genu varum (bow legs)
- Genu valgum (knock-knees)
- Genu recurvatum (Knee hyperextension)
- Knee flexion deformity
A Chinese study concluded that knee pain is significantly more prevalent in people working in cold stores than in those in normal temperature.
One study came to the conclusion that 17% of adolescents with anterior knee pain (a common but benign self-limiting condition) report that their pain is associated with cold weather. The same study indicated that the main activities associated with anterior knee pain are sporting, stair climbing and walking, but also sitting. Some people with anterior knee pain tend to have generally colder knees, and such people also trend towards having to wear extra tights/long johns in the winter.
Cold-induced knee pain may also be due to tenosynovitis of the tendons around the knee, in which cold exposure has a specific role, either as a causative or a contributing factor. Frank arthritis has been reported in children due to frostbite from extreme cold causing direct chondrocyte injury.
There is also a hereditary disease, familial cold autoinflammatory syndrome (FCAS), which often features knee pain, in addition to hives, fever and pain in other joints, following general exposure to cold.
Knee pain due to less physical movement
A lower level of physical activity and a work environment where one is required to sit in a chair during the work day is one reason for developing knee joint pain, as the lower degree of physical movement tends to weaken the knee muscles. Blood vessels also can be affected, leading to development of painful conditions.
As age progresses the movement of the knee joint involves higher friction with adjacent tissue and cartilages.
- Ligamentous laxity
- Fat pad impingement
- Knee effusion
- Deep vein thrombosis
- Peripheral vascular disease
Referred knee pain
Referred pain is that pain perceived at a site different from its point of origin but innervated by the same spinal segment. Sometimes knee pain may be related to another area from body. For example, knee pain can come from ankle, foot, hip joints or lumbar spine.
In some diagnosis, such as in knee osteoarthritis, magnetic resonance imaging does not prove to be clear for its determination 
Although surgery has a role in repairing traumatic injuries and broken bones, surgeries such as arthroscopic lavage do not provide significant or lasting improvements to either pain or function to people with degenerative knee pain, and therefore should almost never be performed. Degenerative knee pain is pain caused by wear and tear, such as osteoarthritis or a meniscal tear. Effective treatments for degenerative knee pain include physical therapy exercises, pain-reducing drugs such as ibuprofen, knee replacement surgery, and weight loss in people who are overweight.
About 25% of people over the age of 50 experience knee pain from degenerative knee diseases.
In the United States, more than US $3 billion is spent each year on arthroscopic knee surgeries that are known to be ineffective in people with degenerative knee pain.
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