1 Martie 2026
Author: Dr. Alexandru Grecu — Senior Orthopedic and Trauma Surgeon
Medically reviewed by Dr. Alexandru Florian Grecu, Senior Orthopedic Surgeon · Published: 1 martie 2026 · Updated: 2 mai 2026
Knee osteoarthritis is the medical term for osteoarthritis of the knee—a degenerative condition in which the articular cartilage progressively deteriorates. It is the most common form of osteoarthritis and one of the main causes of disability worldwide.
The knee joint is the largest and most complex in the body. It consists of three compartments: the inner (medial), the outer (lateral), and the femoropatellar (between the femur and the patella). The hyaline cartilage covering the bone surfaces allows for smooth, painless movement. When this cartilage wears down, pain, stiffness, and eventually, loss of mobility occur.
Knee osteoarthritis is not exclusively a disease of the elderly, although age remains the main risk factor. It can also occur in young people, especially after joint trauma, in overweight individuals, or those with a genetic predisposition.
Primary knee osteoarthritis occurs without an identifiable external cause—it is the result of natural cartilage wear, exacerbated by age, weight, and genetic predisposition. It usually begins after the age of 55-60 and is 3-4 times more common in women.
Secondary knee osteoarthritis has an identifiable cause: a previous trauma (articular fracture, meniscus or ligament tear), an inflammatory disease (rheumatoid arthritis), a joint infection, or a congenital deformity. It can appear significantly earlier—at 30-40 years of age.
The distinction is important: secondary knee osteoarthritis is partially preventable by treating joint injuries correctly and in a timely manner.
Non-modifiable factors:
Modifiable factors (which you can control):
Knee osteoarthritis develops slowly. Symptoms gradually worsen over months and years:
Pain—initially only with exertion (prolonged walking, stairs, rising from a chair), then also at rest or at night. It is usually located on the inner side of the knee (the medial compartment is most frequently affected).
Stiffness—the sensation of a 'locked' knee in the morning or after long periods of inactivity. It improves after a few minutes of movement. If stiffness lasts more than 30 minutes, it may suggest an inflammatory cause (arthritis), not osteoarthritis.
Crepitus—the sensation of 'grinding' or 'sand' in the knee during movement. Isolated crepitus, without pain, is common and benign. It becomes relevant when associated with pain.
Swelling—repeated episodes of a swollen knee ('water on the knee'), especially after exertion. Synovial fluid accumulates in the joint as a reaction to inflammation.
Deformity—in advanced stages, the knee loses its normal alignment. The most common deformity is varus (bow-legged).
Instability—the feeling that the knee is 'giving way' when walking, especially on uneven ground.
Clinical examination—the orthopedic surgeon evaluates gait, limb alignment, joint mobility, stability, painful points, and the presence of joint fluid.
Weight-bearing X-ray—the basic investigation. It is performed with the patient standing to correctly show the narrowing of the joint space under body weight. It shows: joint space narrowing, osteophytes, subchondral bone sclerosis, axial deformity.
Full-length leg X-ray—necessary in cases with axial deformity for precise measurement of the mechanical axis. Essential before joint replacement.
MRI—not routinely necessary for diagnosing osteoarthritis. It is requested when associated injuries (meniscus, ligament) are suspected or when the diagnosis is uncertain.
Blood tests—do not diagnose osteoarthritis, but can rule out other causes of pain (gout, rheumatoid arthritis, infection).
Osteoarthritis is classified into 4 stages (Kellgren-Lawrence classification), each with different characteristics and treatment options:
Minimal changes on X-ray. Occasional pain after exertion. Treatment: physical therapy, weight management, adapted physical exercises.
Slight joint space narrowing, small osteophytes. Pain with daily activities. Treatment: + hyaluronic acid or PRP injections.
→ Learn more about injectionsObvious narrowing, large osteophytes, bone sclerosis. Frequent pain, sometimes at rest. Visible deformity. Treatment: injections, braces, activity modification. The surgical option is discussed.
Joint space completely gone—'bone on bone'. Severe deformity. Permanent pain. Treatment: knee replacement—the only definitive solution.
→ Learn more about knee replacementImportant: the stages are a guide, not a sentence. Many patients with stage II-III osteoarthritis have a good quality of life with proper conservative treatment. Progression is not inevitable—weight control, exercise, and appropriate treatments can significantly slow its evolution.
The treatment of knee osteoarthritis is a spectrum, not a binary choice:
Physical therapy and exercises—the foundation of any treatment plan, at any stage. Strengthening the quadriceps and thigh muscles reduces stress on the joint and alleviates pain.
Weight management—the most underestimated treatment. A weight loss of 5 kg can reduce knee pain by 20-30%.
Hyaluronic acid injections—restore joint lubrication. Best results in stages II-III. The effect lasts 6-12 months. → Patient leaflet: Hyaluronic acid injections
PRP therapy—stimulates tissue regeneration through growth factors from your own blood. → Patient leaflet: PRP Therapy
Arthroscopy—useful when there is a specific mechanical issue (torn meniscus, loose bodies) aggravating the symptoms. It does not cure the osteoarthritis itself. → Learn more about arthroscopy
Knee replacement—the definitive solution in stage IV, when other treatments have been exhausted. The success rate exceeds 90%. → Learn more about knee replacement
Completely—no. But it can be significantly slowed down:
Prevention is by far more effective than treatment. The earlier you come for an evaluation, the more options you have available.
Felson DT et al. — Weight loss reduces the risk of symptomatic knee osteoarthritis in women. Ann Intern Med. 1992;116(7):535-9.
For the rule 'losing 5 kg can reduce knee pain by 20-30%'.
Messier SP et al. — Effects of intensive diet and exercise on knee joint loads in adults with knee osteoarthritis. JAMA. 2013;310(11):1226-1235.
For the rule '1 kg of body weight = approximately 4 kg of pressure per knee with each step'.
Bourne RB et al. — Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res. 2010;468(1):57-63.
For the >90% satisfaction rate after knee replacement.
Swedish Hip Arthroplasty Register — Annual Report 2022.
For the long-term success rate of hip replacement.
Allen KD, Golightly YM — Epidemiology of osteoarthritis: state of the evidence. Curr Opin Rheumatol. 2015;27(3):276-83.
For the prevalence of knee osteoarthritis and risk factors (3-4 times more common in women).