What is osteoarthritis?
Knee osteoarthritis (gonarthrosis) is a slowly progressing, non-inflammatory, degenerative disease of the knee joint. It involves the breakdown of articular cartilage and affects other joint structures such as ligaments, bones, and the joint capsule, leading to wear and tear and pain. Those affected typically feel discomfort when bending the knee, climbing stairs, or after prolonged sitting or lying down.
Osteoarthritis is the most common joint disease among adults worldwide and can occur in various joints. Its prevalence increases significantly between the ages of 65 and 79. From the age of 80, nearly half of all women and about one-third of men are affected by Osteoarthritis. In contrast, only around ten percent of people under the age of 44 are diagnosed with the condition.2
Types of osteoarthritis
Three bones form the knee joint: the femur (thighbone), the tibia (shinbone), and the patella (kneecap). Joint wear occurs in the left or right knee—sometimes in both—but always between the contacting bone surfaces, which are each covered with a smooth layer of cartilage.
The joint between the femur and tibia consists of two compartments: the inner (medial) and outer (lateral) sections. Accordingly, we distinguish between medial gonarthrosis (often associated with bow-legged deformity) and lateral gonarthrosis (commonly linked to knock-knees). If the area between the kneecap and the underlying joint surfaces is affected, it is referred to as retropatellar osteoarthritis.
Learn more about the anatomy of the knee joint
Causes of osteoarthritis
There is often no specific or clearly identifiable cause for the development of knee osteoarthritis. In most cases, it is referred to as primary gonarthrosis, which results from age-related cartilage degeneration. In addition, congenital misalignments (such as bow legs or knock knees), as well as certain diseases or injuries, can lead to joint wear. In these cases, it is known as secondary gonarthrosis.
Osteoarthritis stages: Severity levels of joint degeneration
Depending on the extent of joint degeneration, medical professionals classify gonarthrosis into four different severity levels (according to the Outerbridge classification).3
Gonarthrosis Stage I
The cartilage layer is still intact but has become soft.
Gonarthrosis Stage II
Initial damage to the cartilage cell structure may occur, and the cartilage surface becomes roughened.
Gonarthrosis Stage III
The cartilage surfaces are damaged, and the first deep fissures begin to form.
Gonarthrose Stage IV
Complete cartilage loss: The now exposed bone rubs directly against the opposing bone. Experts refer to this condition as a "bone-on-bone" situation.3
Causes of gonarthrosis
There is often no specific or clearly identifiable trigger for the development of knee osteoarthritis. However, several factors can accelerate joint wear:
In most cases, it is a case of "primary gonarthrosis" – caused by age-related loss of cartilage mass. In addition, congenital misalignments (such as bow legs or knock knees) and certain diseases or injuries can also lead to joint degeneration. In such cases, it is referred to as "secondary gonarthrosis".
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Risk factors for knee osteoarthritis
- Obesity: The knee joints are subjected to significant stress due to body weight, which can accelerate wear and tear.
- Lack of physical activity: Movement is essential for nourishing the joint cartilage. Since cartilage is not supplied with blood, adequate nutrient delivery can only occur through regular movement.
- Congenital joint misalignments: Conditions such as knock knees, bow legs, or leg length discrepancies can increase the risk of developing gonarthrosis.
- Overuse: High-impact sports (such as football, handball, or skiing) can increase the risk of gonarthrosis due to frequent minor or major injuries. Physically demanding jobs, such as tilers or construction workers, may also experience more pronounced joint wear.
- Injuries: Previous knee injuries, especially to the meniscus or ligaments, can negatively affect the joint and increase the risk of knee osteoarthritis.
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Symptoms and signs of knee osteoarthritis
Only a portion of patients who show joint changes through imaging actually experience functional impairments or pain. In cases of gonarthrosis, acute inflammatory episodes can occur. Medical professionals refer to this as 'activated osteoarthritis'. These episodes are usually temporary and are accompanied by warmth, redness, swelling, joint effusion, restricted movement, and pain.
Typical signs of knee osteoarthritis:
- Gonalgia (knee pain): For example, when climbing stairs or walking on uneven ground.
- Functional limitations: The mobility of the joint is restricted.
- Start-up pain: Pain is intense after long periods of rest at the beginning of movement, gradually subsides, but reappears after prolonged activity (load-related pain).
- Carrying heavy objects can intensify the symptoms.
- As the condition progresses, swelling may become visible and palpable.
- In advanced stages, grinding or cracking sounds may be heard when moving the knee.
- The joint is particularly sensitive in cold and damp weather.
The more advanced the gonarthrosis, the more pronounced the symptoms become: Pain occurs more frequently over time and may eventually appear even at rest, while mobility continues to decline.
Can knee osteoarthritis be prevented?
To prevent gonarthrosis, activities and injuries that put strain on the knees should be avoided in everyday life, at work, and during sports. In cases of overweight, weight reduction and regular weight monitoring are recommended. Existing metabolic disorders and damage affecting calcium balance should be appropriately treated, such as metabolic syndrome (a combination of overweight, high blood pressure, and disturbances in sugar and fat metabolism) and type 2 diabetes mellitus.
Diagnosis of gonarthrosis: How knee osteoarthritis is identified
The diagnosis of gonarthrosis is based on a combination of patient interview (medical history), physical examination, and imaging techniques. The most important diagnostic methods include:
Physical examination in suspected gonarthrosis
During the clinical examination, the knee is checked for swelling, misalignment, restricted movement, or sounds (such as grinding) during motion. Additionally, the joint’s stability and mobility are assessed.
Imaging techniques for diagnosing knee osteoarthritis
The most important standard method for diagnosing gonarthrosis is X-ray imaging. It reveals typical changes such as narrowing of the joint space, bony growths (osteophytes), or alterations to the joint surface.
Gonarthrosis treatment: What helps with knee osteoarthritis?
Osteoarthritis is not curable, but there are many treatment options that can relieve pain and make everyday life easier. an important aspect is self-management:
Patients should be informed about the disease, ways to improve quality of life, and mobility. the motivation of those affected to participate and take responsibility for their treatment - for example through healthy nutrition, sustainable weight loss, and regular physical activity - is a key factor in the course of symptoms and disease progression.
The guideline of the german society for orthopaedics and trauma surgery recommends, among other things, the following therapeutic measures:4
Conservative measures
- Physiotherapy and exercise therapy, for example water aerobics
- Medications: short-term use, supportive of exercise therapy (pain relief through ointments, anti-inflammatory drugs)
- Orthopaedic aids (for example insoles, bandages, orthoses)
Surgical measures
- Joint-preserving: the natural joint structure is repaired and preserved
- Joint replacement: patients receive an endoprosthesis
Depending on the stage of the disease and the level of suffering of the affected person, surgery should only be considered if conservative therapy has not led to sufficient improvement. while joint replacement therapy (knee endoprosthesis) is at the end of the treatment chain, joint-preserving surgeries may also be indicated in early stages of osteoarthritis and in cases of mild symptoms to slow the progression of gonarthrosis.
The therapeutic measures depend on patient-specific criteria and the stage of gonarthrosis. please consult your doctor for advice.
Nutrition in gonarthrosis
If a person is overweight for several years, it can damage the joints. the risk of developing osteoarthritis is significantly increased. therefore, people with an elevated risk of osteoarthritis or with existing gonarthrosis are advised to lose weight. Overweight begins at a bmi (body mass index) of 25. a bmi of 30 or higher is considered severe overweight, known as obesity. Nutrition should focus on an anti-inflammatory diet. although changing your diet cannot cure the disease, it can positively influence its progression.
Sports and exercise in gonarthrosis
Regular, guided movement exercises are best performed with joint relief (training while lying down, aquatic training). In addition to promoting pain-free mobility of the knee joint, they aim to improve flexibility, muscle strength, and coordination of movement. Please consult your doctor before starting any sports or exercise program.
Beneficial sports with gentle movements
- Swimming
- Water aerobics
- Cycling
- Golf
- Cross-country skiing
- Walking
Unsuitable sports
- Football
- Alpine skiing
- Handball
Home exercises for knee osteoarthritis (gonarthrosis)
Special gymnastics strengthens the muscles in gonarthrosis and improves joint mobility. Try our exercises – comfortably at home.
Products from medi: Solutions for gonarthrosis
As important therapy companions for gonarthrosis, orthoses or rigid-frame orthoses can reliably relieve and stabilize the knee. The pressure on the painful areas is reduced, leading to noticeable pain relief and promoting greater mobility and activity in everyday life.
About orthoses for gonarthrosis
Additionally, it may be beneficial to reduce pressure in the knee joint with the help of an orthopedic insole.
Diagnosis & treatment
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1 Schmidt, C. O. et al. Häufigkeiten muskuloskelettaler Symptome und Erkrankungen in der bevölkerungsbezogenen NAKO Gesundheitsstudie. Bundesgesundheitsbl 2020;63(4):415-425
2 Heidemann C et al. Gesundheitliche Lage von Erwachsenen in Deutschland – Ergebnisse zu ausgewählten Indikatoren der Studie GEDA 2019/2020-EHIS (2021). Journal of Health Monitoring 6(3):3-27
3 Slattery C, Kweon CY. Classifications in Brief: Outerbridge Classification of Chondral Lesions. Clin Orthop Relat Res. 2018;476(10):2101-2104
4 Deutsche Gesellschaft für Orthopädie und Unfallchirurgie e.V. Prävention und Therapie der Gonarthrose Version 5.0, 15.07.2024. Online veröffentlicht unter: register.awmf.org/de/leitlinien/detail/187-050 (Last Access 03.07.2025)
