Knee OaEdit

Knee osteoarthritis (Knee OA) is a common degenerative condition affecting the knee joint, driven by the gradual loss of articular cartilage with accompanying bone and synovial changes. The knee joint is a complex hinge-and-glide articulation that bears substantial load during daily activities, making it particularly susceptible to wear over time. Knee OA typically presents with pain on weight-bearing, stiffness after periods of inactivity, reduced range of motion, and functional limitations that can interfere with walking, climbing stairs, and other essential tasks. In many adults, symptoms progress slowly but can become disabling, especially if weight, muscle strength, or alignment are not optimized. Knee OA is part of the broader spectrum of osteoarthritis that affects joints throughout the body, but the knee is one of the most impactful and costly sites due to its central role in mobility.

The condition arises from a multifactorial mix of biomechanics, biology, and history. Risk factors include advancing age, prior knee injury, abnormal knee alignment, obesity, and genetic predisposition. Modifiable lifestyle factors—such as maintaining healthy body weight, engaging in appropriate physical activity, and avoiding excessive repetitive knee stress—play a central role in both prevention and management. Because the knee endures large forces, even small structural changes can translate into substantial symptoms and functional decline over time. Knee OA can occur in isolation or as part of broader systemic or age-related processes that affect the joints and surrounding tissues. For a broader context, see osteoarthritis and knee joint.

Epidemiology and risk factors

Knee OA is a leading cause of mobility impairment in older adults and a frequent reason for medical consultation and surgery in many health systems. Prevalence increases with age and is influenced by body weight, activity patterns, and prior knee injuries such as meniscal tears or ligament injuries. Female sex has been associated with higher observed rates in some populations, though the reasons are multifactorial and include biomechanical and hormonal factors. Primary risk factors include obesity, which increases knee joint loading, and a history of knee trauma or overuse. Protective factors are less well defined but generally relate to maintaining leg strength, balance, and healthy alignment. See also epidemiology and risk factors for related conditions.

Pathophysiology

The disease reflects a combination of mechanical degradation and inflammatory processes. Loss of normal articular cartilage exposes subchondral bone and alters joint mechanics, leading to pain and stiffness. Reactive changes in the subchondral bone, osteophyte formation at joint margins, and remodeling of the synovium contribute to symptoms. Meniscal damage and ligamentous laxity may accompany the degenerative process, further compromising knee stability and function. Inflammation in knee OA is typically low-grade but clinically relevant, contributing to pain and swelling in some patients. See also articular cartilage, subchondral bone, osteophyte, and synovitis.

Signs and symptoms

Pain that worsens with weight-bearing activities and improves with rest.
Morning stiffness or stiffness after inactivity lasting typically less than 30 minutes.
Tenderness along the joint line, crepitus with movement, and reduced range of motion.
Swelling or a sensation of instability or buckling in more advanced disease.
Functional limitations such as difficulty with stairs, kneeling, or getting in and out of chairs. See also pain and stiffness.

Diagnosis

Diagnosis is primarily clinical, based on history and physical examination, with imaging used to confirm and stage disease. Plain radiographs (X-ray) commonly show joint space narrowing, osteophyte formation, subchondral sclerosis, and bone cysts, which help classify severity and guide treatment. Magnetic resonance imaging (MRI) can detect early cartilage loss, meniscal damage, and bone marrow lesions when symptoms out of proportion to X-ray findings or when surgical planning is underway. See also radiography, MRI, and joint.

Imaging

X-ray findings: joint space narrowing, osteophytes, subchondral sclerosis, and possible bone deformities.
MRI: detailed assessment of cartilage, menisci, ligaments, and bone marrow changes; useful in early disease or preoperative planning. Imaging should be interpreted in the context of clinical symptoms and functional impact rather than as a stand-alone determinant of treatment. See also imaging and radiography.

Management

Management is typically a stepped, patient-centered process emphasizing symptom relief, functional preservation, and quality of life. The approach combines non-pharmacologic strategies, pharmacologic therapies, and, in selected cases, surgical intervention. See also weight management, physical therapy, and joint replacement.

Non-surgical management

Education and self-management: patients are encouraged to understand the condition, set realistic goals, and maintain activity within tolerance. See also education.
Weight management: reducing body weight decreases knee joint load and can slow symptom progression in overweight individuals. See also obesity.
Exercise and physical therapy: programs focusing on aerobic conditioning, quadriceps and hip abductor strengthening, balance, and flexibility improve pain and function. See also exercise and physical therapy.
Assistive devices: canes, braces, or shoe modifications can reduce pain and improve function.
Pharmacologic therapies:
- Acetaminophen (paracetamol) for mild to moderate pain; effective for some patients with a favorable safety profile when used appropriately. See also acetaminophen.
- Nonsteroidal anti-inflammatory drugs (NSAIDs), including oral and topical forms, for more persistent pain or inflammatory features. These have proven efficacy but carry a risk of gastrointestinal, cardiovascular, and renal side effects, especially with long-term use. See also NSAIDs.
- Topical NSAIDs as a lower-risk option for knee OA pain in appropriate patients. See also topical NSAIDs.
- Intra-articular corticosteroid injections may provide short- to medium-term pain relief, particularly during flares. The duration of benefit varies, and repeated injections have cautions. See also intra-articular corticosteroids.
- Hyaluronic acid injections (viscosupplementation) are used by some clinicians, with mixed evidence regarding long-term outcomes; patient selection is important. See also hyaluronic acid.
- Glucosamine and chondroitin supplements are widely used, but evidence for substantively meaningful benefit is inconsistent; clinicians and patients should weigh expectations against the available data. See also glucosamine and chondroitin.
Weight-bearing and low-impact activity: programs such as cycling, swimming, and water aerobics help maintain fitness with reduced knee stress. See also exercise.

Surgical management

Total knee arthroplasty (total knee replacement) is a highly effective option for end-stage knee OA with persistent pain and disability despite optimized non-surgical care. It can substantially improve function and quality of life in appropriate candidates. See also total knee replacement.
Unicompartmental knee arthroplasty (partial knee replacement) may be suitable when OA is confined to one knee compartment and alignment and soft tissues are favorable. See also unicompartmental knee arthroplasty.
High tibial osteotomy or other realignment procedures are considered for younger patients with unicompartmental OA and appropriate limb alignment to delay the need for knee replacement. See also osteotomy.
Arthroscopy for OA without a clear mechanical indication is generally not recommended as a routine treatment, as durable symptom relief beyond short-term benefit has not been consistently demonstrated. See also arthroscopy and debridement. The choice of intervention depends on disease severity, patient age, activity level, comorbidities, and preferences, with a goal of restoring function and reducing pain while maintaining activity.

Prognosis

Knee OA is typically a chronic condition with a variable course. Many individuals experience gradual symptom progression over years, while others have periods of relative stability or improvement with weight loss, strengthened musculature, and optimized activity. While there is no cure, advances in joint replacement technology and rehabilitation have markedly improved outcomes for many patients. See also prognosis and joint replacement.

Controversies and debates

In the medical community, there is ongoing discussion about the most effective sequencing and combination of treatments, the role of certain supplements, and the indications for surgical intervention. Debates often revolve around balancing symptom relief with function, the timing of knee replacement, and the long-term risks and benefits of injections and devices. Clinicians emphasize shared decision-making, basing choices on patient-specific factors and the best available evidence. See also evidence-based medicine and clinical guidelines.