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Knee pain is a common complaint for many people. There are several factors that can cause knee pain. Awareness and knowledge of the causes of knee pain lead to a more accurate diagnosis. Management of knee pain is in the accurate diagnosis and effective treatment for that diagnosis. Knee pain can be either referred pain or related to the knee joint itself.
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)
- 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:
- 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
- Reiter's syndrome
- 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:
- Genu varum
- Genu valgum
- Genu recurvatum (Knee hyperextension)
- Knee flexion deformity
- Bipartite patella
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.
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
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
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