Knee pain is a common complaint for many people. There are several factors that can cause knee pain. Awareness and knowledge of knee pain causes lead to faster diagnosis and treatment. Knee pain can be related to knee

Knee

The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...

 joint or around the knee.

Knee joint

The knee joint consists of three bones: the femur

Femur

The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...

, tibia

Tibia

The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....

, and patella. There are three compartments to the knee. The main joint of the knee is called tibiofemoral joint that includes the medial and lateral compartments. The patella and the femur form the patellofemoral joint. This is the third compartment of the knee.

Injuries

Some common injuries include:

• Sprain
  Sprain
  A sprain is an injury in a joint, caused by the ligament being stretched beyond its capacity. A muscular tear caused in the same manner is referred to as a strain. In cases where either ligament or muscle tissue is torn, immobilization and surgical repair may be necessary...
  
   (Ligament sprain)
  • Medial collateral ligament
    Medial collateral ligament
    The medial collateral ligament of the knee is one of the four major ligaments of the knee. It is on the medial side of the knee joint in humans and other primates. It is also known as the tibial collateral ligament, or abbreviated as the MCL.- Structure :It is a broad, flat, membranous band,...
    
    
  • Lateral collateral ligament
  • Anterior cruciate ligament
    Anterior cruciate ligament
    The anterior cruciate ligament is a cruciate ligament which is one of the four major ligaments of the human knee. In the quadruped stifle , based on its anatomical position, it is referred to as the cranial cruciate ligament.The ACL originates from deep within the notch of the distal femur...
    
    
  • Posterior cruciate ligament
    Posterior cruciate ligament
    The posterior cruciate ligament is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur...
    
    

• Tear of meniscus
  Tear of meniscus
  In sports and orthopedics, a tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of one of the tibiae. Menisci...
  
  
  • Medial meniscus
    Medial meniscus
    -External links: *...
    
    
  • Lateral meniscus
    Lateral meniscus
    The lateral meniscus, also called the external semilunar fibrocartilage, is a fibrocartilaginous band that spans the lateral side of the interior of the knee joint. It is one of two menisci of the knee, the other being the medial meniscus. It is nearly circular and covers a larger portion of the...
    
    

• Strain
  Strain (injury)
  A strain is an injury to a muscle or tendon in which the muscle fibres tear as a result of overstretching. A strain is also colloquially known as a pulled muscle...
  
   (Muscle strain)
  • Quadriceps muscles
  • Hamstring muscles
  • Popliteal muscle
  • Patellar tendon
  • Hamstring tendon
  • Popliteal tendon

• Hemarthrosis
  Hemarthrosis
  Hemarthrosis is a bleeding into joint spaces.-Causes:It usually follows injury but occurs mainly in patients with a predisposition to hemorrhage such as those being treated with warfarin and patients with hemophilia.It can be associated with knee joint arthroplasty.-Treatment:In hemophilia it may...
  
  . Hemarthrosis tends to develop over a relatively short period after injury, from several minutes to a few hours.

Diseases

Some of the diseases of cause of knee pain include:

• Knee osteoarthritis
  Knee osteoarthritis
  Knee osteoarthritis is a degenerative disease of the knee joint. It is more common in people older than 40 years. Women have greater chance to be affected.-Signs and symptoms:Some of the signs and symptoms associated with knee osteoarthritis include:* Pain...
  
  
• Chondromalacia patella
• Baker's cyst
  Baker's cyst
  A Baker's cyst, also known as a popliteal cyst, is a benign swelling of the semimembranous or more rarely some other synovial bursa found behind the knee joint. It is named after the surgeon who first described it, William Morrant Baker...
  
  
• Meniscal cyst
• Discoid meniscus
  Discoid meniscus
  Discoid meniscus is a rare human anatomic variant that usually affects the lateral meniscus of the knee. Usually a person with this anomaly has no complaints, however, it may present as pain, swelling, or a snapping sound heard from the affected knee...
  
  
• Osgood-Schlatter disease
  Osgood-Schlatter disease
  Osgood–Schlatter disease and or syndrome is an irritation of the patellar tendon at the tibial tuberosity....
  
  
• Larsen-Johansson disease
• Knee rheumatoid arthritis
  Rheumatoid arthritis
  Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...
  
  
• Osteochondritis dissecans
  Osteochondritis dissecans
  Osteochondritis dissecans , often abbreviated to OCD or OD, is a joint disorder in which cracks form in the articular cartilage and the underlying subchondral bone. OCD is caused by blood deprivation in the subchondral bone. This loss of blood flow causes the subchondral bone to die in a process...
  
   disease
• Synovial chondromatosis
  Synovial chondromatosis
  Synovial chondromatosis is a disease affecting the synovium, a thin flexible membrane around a joint. It is also known as Reichel's syndrome or Reichel-Jones-Henderson syndrome, named after Friedrich Paul Reichel, Hugh Toland Jones and Melvin Starkey Henderson.-Symptoms:Patients usually complain of...
  
   disease
• Tumors
• Ankylosing spondylitis
  Ankylosing spondylitis
  Ankylosing spondylitis , previously known as Bekhterev's disease, Bekhterev syndrome, and Marie-Strümpell disease is a chronic inflammatory disease of the axial skeleton with variable involvement of peripheral joints and nonarticular structures...
  
  
• Reiter's syndrome
• Tuberculosis arthritis
• Septic arthritis
  Septic arthritis
  Septic arthritis is the purulent invasion of a joint by an infectious agent which produces arthritis. People with artificial joints are more at risk than the general population but have slightly different symptoms, are infected with different organisms and require different treatment. Septic...
  
   (Pyogenic arthritis)
• Osteomyelitis
  Osteomyelitis
  Osteomyelitis simply means an infection of the bone or bone marrow...
  
  
• Hemophilic arthritis
  Haemophilia
  Haemophilia is a group of hereditary genetic disorders that impair the body's ability to control blood clotting or coagulation, which is used to stop bleeding when a blood vessel is broken. Haemophilia A is the most common form of the disorder, present in about 1 in 5,000–10,000 male births...
  
  
• Gout
  Gout
  Gout is a medical condition usually characterized by recurrent attacks of acute inflammatory arthritis—a red, tender, hot, swollen joint. The metatarsal-phalangeal joint at the base of the big toe is the most commonly affected . However, it may also present as tophi, kidney stones, or urate...
  
   (Gouty arthritis)

Inflammations

• Bursitis
  Bursitis
  Bursitis is the inflammation of one or more bursae of synovial fluid in the body. The bursae rest at the points where internal functionaries, such as muscles and tendons, slide across bone. Healthy bursae create a smooth, almost frictionless functional gliding surface making normal movement painless...
  
   of the knee
  • Prepatellar bursitis
    Prepatellar bursitis
    Prepatellar bursitis, also known as Housemaid's knee, is a common cause of swelling and pain above the patella , and is due to inflammation of the prepatellar bursa. This structure is a superficial bursa with a thin synovial lining located between the skin and the patella...
    
     - Housemaid's knee (most common)
  • Infrapatellar bursitis
    Infrapatellar bursitis
    Infrapatellar bursitis is the inflammation of the infrapatellar bursa, which is located just below the kneecap. It is often called "clergyman's knee" due to its historical frequency amongst clergyman, who injured the bursa by kneeling on hard surfaces during prayer.It is a cause of knee pain....
    
     - Clergyman's knee (Superficial infrapatellar bursitis and Deep infrapatellar bursitis)
  • Semimembranosus bursitis

• Tendinitis
  • Patellar tendinitis (Jumper's knee)
  • Hamstring
    Hamstring
    In human anatomy, the hamstring refers to any one of the three posterior thigh muscles, or to the tendons that make up the borders of the space behind the knee. In modern anatomical contexts, however, they usually refer to the posterior thigh muscles, or the tendons of the semitendinosus, the...
    
     tendinitis
  • Popliteal tendinitis

• Synovitis
  Synovitis
  Synovitis is the medical term for inflammation of the synovial membrane. This membrane lines joints which possess cavities, known as synovial joints. The condition is usually painful, particularly when the joint is moved. The joint usually swells due to synovial fluid collection.Synovitis may...
  
   of the knee

Deformities

Common deformities of the knee include:

• Genu varum
• Genu valgum
  Genu valgum
  Genu valgum, commonly called "knock-knee", is a condition where the knees angle in and touch one another when the legs are straightened. Women have a wider pelvis than men and a relatively shorter length of the thigh bone, and as a result, have a greater static genu valgum than men...
  
  
• Genu recurvatum
  Genu recurvatum
  Genu recurvatum is a deformity in the knee joint, so that the knee bends backwards. In this deformity, excessive extension occurs in the tibiofemoral joint. Genu recurvatum is also called knee hyperextension and back knee. This deformity is more common in women and people with familial ligamentous...
  
   (Knee hyperextension)
• Knee flexion deformity
• Bipartite patella

Syndromes

• Patellofemoral pain syndrome (Runner's knee)
• Plica syndrome
  Plica Syndrome
  Plica Syndrome occurs when the plica becomes irritated or inflamed.-Presentation and pathophysiology:...
  
  
• Iliotibial band syndrome
  Iliotibial band syndrome
  Iliotibial band syndrome is a common injury to the thigh, generally associated with running, cycling, hiking or weight-lifting .- Definition :...
  
  

Dislocations

• Patella dislocation
• Knee joint dislocation (Tibiofemoral joint dislocation)

Referred knee pain

Referred pain

Referred pain

Referred pain is pain perceived at a location other than the site of the painful stimulus. An example is the case of ischemia brought on by a myocardial infarction , where pain is often felt in the neck, shoulders, and back rather than in the chest, the site of the injury...

 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.

Cold-induced

A Chinese study came to the result that knee pain is significantly more prevalent in people working in cold stores than in those in normal temperature.

One study came to the result 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

Tenosynovitis

Tenosynovitis is the inflammation of the fluid-filled sheath that surrounds a tendon. Symptoms of tenosynovitis include pain, swelling and difficulty moving the particular joint where the inflammation occurs. When the condition causes the finger to "stick" in a flexed position, this is called...

 of the tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

s around the knee, in which cold exposure has a specific role, either as a causative or a contributing factor. Frank arthritis

Arthritis

Arthritis is a form of joint disorder that involves inflammation of one or more joints....

 has been reported in children due to frostbite

Frostbite

Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...

 from extreme cold causing direct chondrocyte

Chondrocyte

Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...

 injury.

There is also a hereditary disease, familial cold autoinflammatory syndrome

Familial cold urticaria

Familial cold urticaria is an autosomal dominant condition characterized by rash, conjunctivitis, fever/chills and arthralgias elicited by exposure to cold - sometimes temperatures below 22°C .It has been mapped to CIAS1 and is a slightly milder member of the disease family including Muckle–Wells...

 (FCAS), which often features knee pain, in addition to hives, fever and pain in other joints, following general exposure to cold.

Cold weather also aggravates knee pain in patients already having osteoarthritis

Osteoarthritis

Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...

, rheumatoid arthritis

Rheumatoid arthritis

Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...

 and fibromyalgia

Fibromyalgia

Fibromyalgia is a medical disorder characterized by chronic widespread pain and allodynia, a heightened and painful response to pressure. It is an example of a diagnosis of exclusion...

.

Other causes

• Ligamentous laxity
  Ligamentous Laxity
  Ligamentous laxity is a term given to describe "loose ligaments."In a 'normal' body, ligaments are naturally tight in such a way that the joints are restricted to 'normal' ranges of motion. This creates normal joint stability...
  
  
• Fat pad impingement
• Knee effusion
• Deep vein thrombosis
  Deep vein thrombosis
  Deep vein thrombosis is the formation of a blood clot in a deep vein. Deep vein thrombosis commonly affects the leg veins or the deep veins of the pelvis. Occasionally the veins of the arm are affected...
  
  
• Peripheral vascular disease