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Osteoarthritis of the Knee

Osteoarthritis Knee

Osteoarthritis of the knee describes a chronic, degenerative disease of the knee joints that is associated with cartilage damage, functional impairment and pain. The disease may be triggered by genetic predisposition, age, trauma or other pathological conditions.


Patients usually present with inflamed knees and report pain that has been increasing with time. Of note, a sudden onset of knee pain is not an exclusion criterion for OA. Frequently, patients relate to experience more severe time after periods of rest, e.g. after getting up in the morning. In contrast, pain often eases during moderate activity. Sports and other activities accompanied by heaver knee loads enhance pain. Cold, rainy weather tends to aggravate symptoms.

Upon clinical examination, the affected knees result to be swollen and stiff, thus limiting joint movements. In some cases, the knees can be moved to a certain degree but may suddenly lock in a determined position. Cartilage flakes moving freely inside the synovial gap may be responsible for this kind of observations. They may also cause crepitus and pain [9] [10].

An individual patient may suffer from unilateral or bilateral OA of the knee. Whereas primary OA frequently affects both knees, this is not the case for secondary OA. Although the cause for the disease is different in primary and secondary OA, tissues undergo the same pathological changes. This distinction is therefore of minor clinical relevance.

  • Patients completed the Turkish version of the Oxford Knee Score (OKS-TR), Short-Form 36 Health Survey (SF-36), and Western Ontario and McMaster Universities Index (WOMAC) questionnaires.[ncbi.nlm.nih.gov]
Difficulty Walking
  • Major symptoms are pain, swelling and difficulty walking. - Pain during exercise A major symptom of osteoarthritis of the knee is knee pain which occurs during knee motions.[healthy-knee.com]
Knee Pain
  • MATERIALS AND METHODS: Three hundred and sixty-five patients with knee pain underwent anterior-posterior (AP), PA flexed, lateral, and Merchant radiographs of the knee.[ncbi.nlm.nih.gov]
  • Do you plan around your knee pain? Getting older is no excuse. You shouldn't have to give things up due to pain. Is your knee pain keeping you from exercising? A lack of activity can lead to even more knee pain.[synviscone.com]
  • Knee Pain: What is Osteoarthritis? Spoiler: Osteoarthritis is the Knee Pain Bogeyman.[kinetic-revolution.com]
  • Symptoms may include severe knee pain that limits your everyday activities, including walking, going up and down stairs and standing up from a chair.[ucsfhealth.org]
  • The participants who had osteophytes 1 mm 2 in the right, left, and bilateral knees were 15, 37, and 57 respectively, with osteophytes being significantly more common in the left knee. The OF was significantly larger in the left knee.[ncbi.nlm.nih.gov]
  • Occasionally, osteophytes were scored, but not narrowing, and these knees were included for definitions of OA that are osteophyte‐based.[academic.oup.com]
  • It is associated with abnormal bony overgrowths known as spurs, or osteophytes. As the cartilage wears out, spaces in the knee joint become narrower over time (seen on X-ray).[health.ucsd.edu]
  • […] tibiofemoral compartment, and/or patellofemoral compartment 3 5 mm 7 weight-bearing radiographs will demonstrate more joint space narrowing than non-weight-bearing radiographs, hence affecting the radiographic severity 7,8 subchondral sclerosis marginal osteophytes[radiopaedia.org]
Quadriceps Muscle Weakness
  • In conclusion, the use of NMES for quadriceps muscle weakness has been shown to improve muscle strength.[ncbi.nlm.nih.gov]
  • RESULTS: The cell-based product was well tolerated with few reported Adverse Events (mild arthralgia and low back pain). There was a relevant decrease in the intensity of pain since day 8 after the infusion, that was maintained after 12months.[ncbi.nlm.nih.gov]
Knee Effusion
  • Knee effusions, popliteal cysts, and synovial thickening: association with knee pain in osteoarthritis.J Rheumatol 2001;28(6):1330-7. 10. Felson DT, Chaisson CE, Hill CL, et al.[morphopedics.wikidot.com]
  • The instability has been associated with psychosocial dysfunction, such as fear of movement, and impaired physical functioning. A high degree of fear of movement is positively correlated with avoidance in other conditions.[ncbi.nlm.nih.gov]
  • Let’s ditch these fear inducing diagnoses and explanations and just use the term knee pain, and set about working out why the individual has knee pain. This is 2015![kinetic-revolution.com]


Anamnesis and clinical examination usually enable the physician to make a tentative diagnosis of OA. Radiographic imaging is the method of choice in order to confirm this diagnosis [11].

The most common findings in radiography are a reduced joint space and subchondral osseous cysts and sclerosis.
Alterations detected with imaging techniques usually concentrate in load-bearing areas. This might not be the case in other joint diseases.

Such findings may be confirmed in magnetic resonance imaging, but such an examination is usually not required. It may, however, be helpful to detect any damage to cartilage, menisci, tendons and muscles in close proximity to the knee, and to decide if a surgical intervention is necessary to repair such damage.

Other imaging techniques such as computed tomography or ultrasonography are currently of minor importance in OA diagnosis.

In order to differentiate OA of the knee from osteomyelitis, multiple myeloma and bone metastases of neoplasms, bone scans may be helpful [12]. The characteristic pattern observed in bones from OA patients is symmetric and shows only a slightly increased uptake of radionuclides.

Amino Acids Increased
  • Damaged amino acids increased further in severe and advanced OA and RA.[ncbi.nlm.nih.gov]
Synovial Hemangioma
  • Histological examination disclosed a synovial hemangioma, which is a rare intra-articular, benign tumor of youth.[ncbi.nlm.nih.gov]


Treatment of OA aims at alleviating pain and recovering joint mobility. It is based on weight loss, moderate physical exercise and medication.

Overweight and obese patients may benefit significantly from weight loss [13]. Patients should also be advised to realize moderate and appropriate exercises in order to strengthen the muscles involved in leg movement. This way, the knee load lessens and pain eases.

Drug therapy mainly relies on analgesics and anti-inflammatory agents. Acetaminophen (paracetamol) and non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen may considerably alleviate knee pain [14]. Patients treated with such drugs have to be warned about possible side effects that may result from prolonged or excessive intake. If such drugs are contraindicated or do not provide sufficient pain relief, corticosteroids may be administered. Corticosteroids and hyaluronic acid may also be injected intraarticularly [15].

Of note, current research studies focus on identifying receptors and intracellular pathways involved in joint inflammation and OA process. Agonists and antagonists may modulate these processes, ease symptoms and delay progress of cartilage and bone damage. Interleukin-17, for instance, has been found to be involved in joint inflammation [16].

Physical and occupational therapy may support medication treatment and muscle buildup. Patients may also benefit from wearing supportive braces.

If conservative therapy does not sufficiently alleviate symptoms, a knee arthroplasty may be required.


Only palliative treatment is available. According to current knowledge, there is no drug or surgical procedure that may revoke existing cartilage and bone damage.

The prognosis regarding disease progress worsens with age and advanced diseases states. If the disease also affects other joints, this is considered to affect progression in an unfavorable way [8].

Overweight and obesity may contribute to the exacerbation of the disease. Contrary to age, disease state and joint involvement, body weight may be adjusted in order to delay disease progress.

Knee arthroplasties have a good prognosis and success rates have been estimated to exceed 90%. However, additional surgical interventions may be necessary 10 to 15 years after the inicial joint replacement, particularly in young and active patients. They are usually not required in the elderly.


While age is the most common cause of OA of the knee, there are several other factors that contribute to cartilage damage and that may provoke an early onset of symptoms and/or more severe tissue degeneration.

With age, cartilage degeneration occurs to a certain degree. Furthermore, the regenerative capacity of tissues decreases and possibly occurring traumas will have more severe consequences in older patients than in young ones. While older people usually present with primary OA, young people are generally diagnosed with secondary OA, i.e. they suffer from cartilage damage due to knee traumas or similar causes [2].

Some people are more susceptible to OA of the knee than others. Certain genetic disorders may either leave them more prone to knee joint degeneration or cause anatomical and physiological abnormalities that, in turn, change mechanical conditions in the knee and thus enhance degeneration.

People practicing certain sports, e.g., tennis, soccer or running, may also show an increased risk for developing OA of the knee. Weight lifting or movements like kneeling and squatting is associated with a constantly increased pressure on the knees and may also lead to joint degeneration. Such activities may not only be realized by athletes, but also by men and women practicing certain professions. It is important to note that exercise intensity does play a crucial role in determining whether sports mediate detrimental or beneficial effects. Indeed, people maintaining a sedentary lifestyle with little to no physical activity have very weak muscles around the knee and this condition augments the risk for OA of the knee.

Such a lifestyle - and various other factors - also affect body weight. Due to physical forces working on the knees, these joints will be stressed considerably with each pound of excess weight [3].

Finally, there are other diseases that increase the risk for OA of the knee. Such is the case with rheumatoid arthritis and certain metabolic disorders.


Studies regarding disease prevalence are rather difficult to evaluate because there is no consensus regarding the definition of OA. Thus, the disease may be diagnosed based on clinical or radiographic criteria or any combination thereof. It has been estimated that in the United States there are about 20 million persons suffering from OA [4]. Although prevalence varies across distinct countries and their respective population, OA is the most common joint disease worldwide.

More than 50% of the population aged 65 or more does present radiographic alterations indicating OA of any joint. Some studies even report that this is the case for more than 80% of individuals older than 65 years. In the elderly, such alterations generally exist due to primary OA and do not involve clinical symptoms.

However, a significant share of patients suffering from OA of the knee does experience functional impairment and limitation of joint movement. People with severe OA of the knee may even depend on personal care.

Women are more prone to develop OA of the knee, as has been shown in a study focusing on females aged 55 and older [5].

Sex distribution
Age distribution


Even though OA is referred to as a degenerative joint disease, inflammatory processes significantly affect tissue damage and disease progress. A variety of receptors, e.g. purinergic and interleukin receptors, mediate and regulate the release of cytokines and matrix metalloproteinases. Such events lead to an excessive matrix degeneration. Indeed, due to the importance of tissue inflammation for disease progress, it has been proposed to classify OA as an inflammatory disease rather than a degenerative condition. There is, however, consensus in that both degenerative and inflammatory processes contribute to joint damage and functional impairment.

OA of the knee is associated with cartilage degeneration. However, adjacent parts of the joint such as the synovial fluid, the subchondral bone of femur and tibia, the joint capsule and other tissues may be affected by mechanical stress or pathological conditions and trigger an early onset or more severe form of OA of the knee [6].

Cartilage damage triggers the chain of pathophysiological events leading to OA. Initially, chondrocytes increase proteoglycan synthesis in order to repair cartilage damage. This hypertrophic repair results in cartilage swelling. The affected knee may remain in this initial phase of OA for several years without any further disease progress. At some point, however, proteoglycan synthesis drastically decreases. Tissue properties change accordingly, the cartilage softens and loses elasticity. Vertical clefts and detached cartilage flakes become visible when the cartilage is examined microscopically and are a clear sign of integrity loss of the joint surfaces.

In the long term, this means joint space becomes increasingly narrow. Decreasing joint space is most frequently detected in the medial femorotibial joint compartment, but may also be observed in the lateral femorotibial and patellofemoral compartments. It may eventually lead to varus and valgus deformities.

Erosion continues until the whole cartilage layer is worn off and the subchondral bone is exposed. Because even in this advanced stage of OA knee movement continues, mechanical stress now affects the subchondral bone of femur and tibia and provokes structural changes also referred to as eburnation. They involve tissue vascularisation, an increase in cell density and an overall hardening and densification of the bone [7]. If there is an influx of synovial fluid into osseous tissue, osteoarthritic cysts may develop. Osseous necrosis may enhance the formation of such cysts, whose diameter may reach up to 20 mm.


Preventive measures include avoiding excess weight and heavy knee loads that may stress the joint during intensive training or harmful professional activities. As far as possible, traumas to the knees should also be avoided.


Osteoarthritis of the knee is a joint disease characterized by degenerative and inflammatory processes that commonly affects the elderly. Cartilage damage triggers osteoarthritis (OA) progress and may result from age or genetic predisposition, but also from overweight or traumas. OA is the most common joint disease [1].

In the course of the disease, knee joint cartilage erosion advances progressively. While cartilage swelling is observed during the initial phase of the disease, loss of cartilage integrity, fibrillation and detachment of flakes can be detected in advanced states of OA. Cartilage damage may proceed until the subchondral bone loses any protective layer and remains exposed. Bone sclerosis, vascularization, formation of osseous cysts and even osseous necrosis may result from excessive loads on subchondral bone tissue.

Only palliative treatment is available. Analgesics and anti-inflammatories may be administered in order to ease pain and reduce inflammation. Non-steroidal anti-inflammatory drugs may be helpful, but corticosteroids are also used to treat OA of the knee. Medication should be combined with weight loss, moderate physical activity, possibly guided by a physiotherapist.

If conservative treatment is not sufficient to alleviate symptoms, a surgical knee joint replacement may be required.

Patient Information

Osteoarthritis of the knee is characterized by knee pain and limited mobility that develops in the course of several years. Osteoarthritis (OA) is a very common joint disease that mainly affects older patients and may be detected in other joints as well.


The most common causes for OA of the knee are age and genetic predisposition. And while the majority of people will suffer from cartilage degeneration at some point in their life, certain lifestyle decisions may trigger an early onset of OA of the knee or more severe symptoms. In this context, overweight and obesity are the main risk factors. Also, certain activities involving heavy knee loads may exacerbate cartilage damage. Such is the case for intensive running, tennis, soccer and weight lifting, but also for determined professional activities that burden the knees. Traumas may also damage the cartilage of the knees and thus initiate disease progress.


Cartilage damage may lead to OA of the knee. In the course of the disease, the joint cartilage does lose integrity, cracks and decomposes. Small flakes of cartilage may even detach and move freely inside the joint. It may hinder knee movements and cause pain, similarly to a grain of sand in a gearbox. Furthermore, cartilage erosion deprives the underlying femur and tibia bones of its protective layer. Consequently, the bone tissue also suffers from pathophysiological modifications that also cause pain and further restrict mobility.

Therefore, impaired mobility and pain are the main symptoms of OA of the knee. Affected knees tend to be swollen and stiff. These symptoms may be more severe after prolonged rest or in the morning.


In order to diagnose OA, the physician will obtain your medical history, conduct a clinical examination and X-ray your knees. When evaluating the patient's radiographic image, the physician will look out for narrowed joint spaces and alterations affecting the bone tissue.

Depending on your medical history, other diagnostic measures such magnetic resonance imaging may be taken in order to rule out lesions to menisci, tendons or joint capsules.


Although commonly referred to as a degenerative joint disease, inflammatory processes significantly affect disease progress. Therefore, patients suffering from OA of the knees are usually prescribed analgesics and anti-inflammatory drugs. They may be taken orally or, in advanced cases, be injected directly into the knees.

It is of utmost importance to support medication therapy with weight loss, if indicated, and moderate physical activity to strengthen the muscles moving the knees. Patients may also benefit from wearing a brace.

If no such treatment is sufficient to alleviate symptoms associated with OA of the knee, surgery may be necessary to replace the knee joint.



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  9. Altman R, Asch E, Bloch D, et al. Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Arthritis Rheum. 1986; 29(8):1039-1049.
  10. Wu CW, Morrell MR, Heinze E, et al. Validation of American College of Rheumatology classification criteria for knee osteoarthritis using arthroscopically defined cartilage damage scores. Semin Arthritis Rheum. 2005; 35(3):197-201.
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Last updated: 2019-07-11 20:26