Knee Osteoarthritis (Gonarthrosis) — A Complete Guide
Author: Dr. Alexandru Grecu — Senior Orthopedic and Trauma Surgeon
Published: 1 martie 2026 · Reviewed: August 21, 2026
What is knee osteoarthritis?
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 vs. Secondary Knee Osteoarthritis
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.
Risk Factors
Non-modifiable factors:
- Age—the strongest predictor
- Female sex—a 3-4 times higher risk, particularly after menopause
- Genetic predisposition—cartilage quality is partly inherited
- Previous joint injuries
Modifiable factors (which you can control):
- Excess weight—each extra kilogram transmits approximately 4 kg of additional force to the knee with every step
- Repetitive overuse—occupations involving repeated squatting, carrying heavy loads
- Sedentary lifestyle—weak muscles do not adequately protect the joint
- Uncorrected axial deformities—genu varum ("bow legs") or genu valgum ("knock-knees")
Symptoms of Knee Osteoarthritis
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.
Progressive loss of mobility—you can no longer easily squat, cross one leg over the other, or descend stairs normally.
Changes in gait—you begin to compensate unconsciously — taking shorter steps, shifting weight to the other leg, a slight limp.
What is NOT Osteoarthritis
- Crepitus without pain: common, benign, does not require treatment.
- Occasional pain after intense sports: likely overuse, not wear and tear.
- Acute pain with obvious inflammation: could be a sprain, meniscal tear, gout — requires a different evaluation.
How is the diagnosis made?
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).
The 4 Stages of Knee Osteoarthritis
Osteoarthritis is classified into 4 stages (Kellgren-Lawrence classification), each with different characteristics and treatment options:
Early Osteoarthritis
Minimal changes on X-ray. Occasional pain after exertion. Treatment: physical therapy, weight management, adapted physical exercises.
Mild Osteoarthritis
Slight joint space narrowing, small osteophytes. Pain with daily activities. Treatment: + hyaluronic acid or PRP injections.
→ Learn more about injectionsModerate Osteoarthritis
Obvious narrowing, large osteophytes, bone sclerosis. Frequent pain, sometimes at rest. Visible deformity. Treatment: injections, braces, activity modification. The surgical option is discussed.
Severe Osteoarthritis
Joint space completely gone—'bone on bone'. Severe deformity. Permanent pain. Treatment: knee replacement—the standard treatment at this stage.
→ 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 Decision: When to See an Orthopedist
If you check 3 or more of the signs above, it's time for an evaluation.
The sooner you come in, the more options you have available:
- Early stage (Kellgren-Lawrence I-II) → conservative treatment: targeted physical therapy, weight management, possibly injections.
- Medium stage (Kellgren-Lawrence III) → conservative + injections with hyaluronic acid or PRP.
- Advanced stage (Kellgren-Lawrence IV) → discussion about knee replacement.
The diagnosis is simple: a knee X-ray + clinical exam. No special blood tests are necessary.
What treatment options are available?
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 standard treatment in stage IV, when other treatments have been exhausted. About 8–9 out of 10 patients report satisfaction with the outcome in international registries; the rest may retain some pain or limitations. → Learn more about knee replacement
Can knee osteoarthritis be prevented?
Completely—no. But it can be significantly slowed down:
- Maintain a healthy body weight
- Do regular low-impact exercises (swimming, cycling, walking)
- Properly treat any joint injury (meniscus, ligament)
- Avoid repetitive overuse
- Strengthen the muscles around the knee
Prevention is by far more effective than treatment. The earlier you come for an evaluation, the more options you have available.
For context, see the dedicated page on knee replacement and the page on the stem cell injection, and if you want to go deeper, read aboutjoint noises and when they are a warning sign and aboutthe right exercises for an osteoarthritic knee.
Have questions or need a consultation?
Scientific References
Kellgren JH, Lawrence JS — Radiological assessment of osteo-arthrosis. Ann Rheum Dis. 1957;16(4):494-502.
For the four-stage radiological classification used in the text.
Allen KD, Golightly YM — State of the evidence. Curr Opin Rheumatol. 2015;27(3):276-83.
For the epidemiology of osteoarthritis.
Felson DT et al. — Weight loss reduces the risk for symptomatic knee osteoarthritis in women. The Framingham Study. Ann Intern Med. 1992;116(7):535-9.
For prevention: weight loss reduces the risk of developing symptomatic knee osteoarthritis in women — a loss of about 5.1 kg over 10 years lowered the odds by more than 50%.
Messier SP et al. — Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical outcomes among overweight and obese adults with knee osteoarthritis: the IDEA randomized clinical trial. JAMA. 2013;310(12):1263-73.
For patients who already have knee osteoarthritis: diet plus exercise led to greater weight loss, lower compressive forces in the knee and lower inflammation (IL-6).
Rutjes AW et al. — Viscosupplementation for osteoarthritis of the knee: a systematic review and meta-analysis. Ann Intern Med. 2012;157(3):180-91.
For the limits of viscosupplementation: a small average benefit that is not clinically relevant, with an increased risk of serious adverse events.
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 satisfaction after total knee replacement: about one in five patients (19%) is not satisfied; satisfaction was 72–86% for pain and 70–84% for function; the strongest predictor of dissatisfaction was an expectation that was not met (10.7 times higher risk).
Fransen M et al. — Exercise for osteoarthritis of the knee. Cochrane Database Syst Rev. 2015;(1):CD004376.
High-quality evidence: land-based therapeutic exercise reduces knee pain, with the benefit sustained for 2–6 months after the programme stops, of a magnitude comparable to anti-inflammatory drugs.
Evans JT et al. — How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet. 2019;393(10172):655-663.
For the lifespan of a knee replacement: in national registry data, about 82% of total knee replacements are still in place at 25 years.
Singh JA — Smoking and outcomes after knee and hip arthroplasty: a systematic review. J Rheumatol. 2011;38(9):1824-34.
For the increased risk of complications in smokers after arthroplasty.
Messier SP, Gutekunst DJ, Davis C, DeVita P — Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum. 2005;52(7):2026-32.
Each kilogram of weight lost reduces the load on the knee by about 4 kg per step.