Kellgren–Lawrence Grade: Radiographic Indicators in Focus

Osteoarthritis is a leading cause of joint pain and disability, affecting millions worldwide. Accurate assessment of its severity is crucial for diagnosis, treatment planning, and monitoring disease progression. One widely used tool for evaluating osteoarthritis through imaging is the Kellgren–Lawrence grading system, which classifies radiographic changes to determine the extent of joint degeneration.

This grading system provides standardized criteria that help clinicians and researchers assess osteoarthritis severity objectively. Understanding how these grades are assigned and interpreted improves diagnostic accuracy and patient management.

Radiographic Indications

Detecting osteoarthritis through imaging relies on identifying structural changes within the joint that signify disease progression. The Kellgren–Lawrence grading system evaluates joint deterioration based on joint space narrowing, osteophyte formation, subchondral sclerosis, and bone deformities, each reflecting different stages of cartilage degeneration and bone remodeling. These features help radiologists and clinicians determine osteoarthritic severity, guiding diagnosis and treatment.

One of the earliest radiographic signs is osteophyte formation—bony outgrowths at the joint margins that develop in response to cartilage breakdown. While small osteophytes may not immediately affect joint function, their progression can contribute to stiffness and restricted movement. Studies in Radiology and Osteoarthritis and Cartilage have shown that osteophytes correlate with symptomatic osteoarthritis, even when joint space narrowing is minimal. Early detection of these bony projections can signal disease onset before significant structural damage occurs.

Joint space narrowing, another key feature, reflects the gradual loss of articular cartilage. As cartilage deteriorates, the space between bones diminishes, increasing friction and mechanical stress. Standardized radiographic techniques, such as weight-bearing knee X-rays, improve the visibility of joint space reduction. Research in The Journal of Bone and Joint Surgery has shown that joint space width measurements can predict functional impairment, with a threshold of less than 2 mm often indicating advanced disease.

Subchondral sclerosis, marked by increased bone density beneath the cartilage surface, emerges as osteoarthritis advances. This radiographic finding results from the bone adapting to abnormal loading conditions due to cartilage erosion. High-resolution imaging techniques, such as dual-energy X-ray absorptiometry (DXA) and computed tomography (CT), have linked subchondral bone thickening to pain severity and joint instability. A meta-analysis in Arthritis & Rheumatology found that patients with pronounced subchondral sclerosis were more likely to experience rapid disease progression, emphasizing the importance of recognizing this feature in clinical evaluations.

Bone deformities, such as cyst formation and joint misalignment, represent the most severe radiographic manifestations. Chronic inflammation and mechanical stress drive bone remodeling and erosion, leading to cystic lesions and malalignment. Cystic lesions, visible as radiolucent areas within the subchondral bone, indicate advanced cartilage breakdown and synovial fluid intrusion. Malalignment, particularly in weight-bearing joints like the knee, exacerbates disease progression by unevenly distributing forces across the joint. Studies in The Lancet Rheumatology have shown that varus or valgus deformities significantly increase the risk of total joint replacement.

Detailed Grading Scale

The Kellgren–Lawrence grading system categorizes osteoarthritis severity based on radiographic features, ranging from Grade 0 (no radiographic signs) to Grade 4 (severe structural damage). Each grade is defined by specific radiographic findings, including osteophyte formation, joint space narrowing, subchondral sclerosis, and bone deformities. Understanding these classifications helps clinicians assess disease progression and determine management strategies.

Grade 0

Grade 0 signifies no radiographic evidence of osteoarthritis. Joint structures appear normal, with no detectable osteophytes, joint space narrowing, or subchondral changes. While radiographs may not reveal abnormalities, early biochemical or biomechanical changes in cartilage can occur. Advanced imaging techniques, such as MRI, have detected cartilage defects in asymptomatic individuals, predicting future osteoarthritis development. Despite the absence of radiographic findings, patients with joint pain may benefit from lifestyle modifications to reduce the risk of progression.

Grade 1

Grade 1 osteoarthritis is characterized by small osteophytes without significant joint space narrowing or other structural abnormalities. These early bony outgrowths typically form at the joint margins and may not yet cause symptoms. Radiologists often identify these minor changes incidentally. Research in The Journal of Rheumatology has shown that individuals with early osteophyte formation have a higher likelihood of developing symptomatic osteoarthritis, particularly if additional risk factors, such as obesity or joint injury, are present. Clinicians may recommend physical therapy and joint-friendly activities to maintain mobility and delay progression.

Grade 2

Grade 2 indicates definite osteophyte formation with possible joint space narrowing. Radiographic changes become more apparent, and some individuals may experience mild joint discomfort or stiffness. Multiple osteophytes suggest ongoing cartilage degeneration, while subtle joint space reductions reflect early cartilage thinning. Studies in Arthritis Research & Therapy show that patients with Grade 2 osteoarthritis often report intermittent pain and functional limitations. Weight-bearing radiographs are particularly useful in detecting early joint space narrowing. Management strategies focus on symptom relief and joint preservation, including low-impact exercise, weight control, and NSAIDs for pain management.

Grade 3

Grade 3 osteoarthritis involves moderate joint space narrowing, multiple osteophytes, and subchondral sclerosis. These radiographic findings indicate significant cartilage loss and increased bone remodeling, often leading to persistent joint pain and stiffness. Individuals frequently experience functional limitations, such as difficulty with prolonged walking or stair climbing. A study in The American Journal of Sports Medicine found that patients with moderate knee osteoarthritis exhibited altered gait mechanics due to pain and joint instability. This stage often marks the transition to more advanced disease, prompting consideration of intra-articular corticosteroid or hyaluronic acid injections and structured physical therapy.

Grade 4

Grade 4 represents severe osteoarthritis, characterized by extensive joint space narrowing, large osteophytes, pronounced subchondral sclerosis, and bone deformities. Cartilage loss is nearly complete, leading to direct bone-on-bone contact and significant joint dysfunction. Individuals often experience chronic pain, stiffness, and substantial mobility restrictions. Radiographic findings may include cyst formation and joint malalignment, further contributing to mechanical instability. Research in The Lancet Rheumatology has shown that patients with severe osteoarthritis have a markedly increased risk of requiring joint replacement surgery. Conservative treatments may provide limited relief, making surgical options more likely.

Common Joint Assessments

Evaluating osteoarthritis severity requires precise imaging techniques tailored to different joints. Weight-bearing X-rays are commonly used for knee and hip osteoarthritis, as they provide a more accurate representation of joint space narrowing under physiological conditions. Non-weight-bearing radiographs may suffice for smaller joints, such as those in the hands.

The knee is frequently examined due to its high susceptibility to osteoarthritis. A standard anterior-posterior (AP) weight-bearing view highlights joint space narrowing and osteophyte formation, while a lateral view assesses patellofemoral involvement. The Rosenberg view, a specialized posteroanterior projection at 45 degrees of knee flexion, improves early detection of joint space narrowing. Studies in The Journal of Bone and Joint Surgery confirm its greater sensitivity in identifying cartilage loss compared to standard AP radiographs.

Hip osteoarthritis evaluations rely on standing AP pelvic radiographs, which provide a comprehensive view of joint space narrowing, osteophytes, and femoral head deformities. The Tönnis angle, measuring acetabular inclination, helps assess structural abnormalities. Some patients require a false-profile view for better visualization of the anterior joint space. Research in Clinical Orthopaedics and Related Research has found that hip joint space width below 2 mm strongly correlates with advanced disease and joint replacement likelihood.

Hand osteoarthritis requires high-resolution imaging for accurate grading. Standard posteroanterior and oblique views assess interphalangeal and carpometacarpal joints. Osteophyte formation is often the earliest detectable feature, with joint space narrowing and subchondral sclerosis appearing as the disease progresses. A study in Rheumatology found that radiographic severity in hand osteoarthritis does not always correlate with pain levels, underscoring the need to consider clinical symptoms alongside imaging findings.

Clinical Interpretation

Interpreting Kellgren–Lawrence grades requires considering radiographic findings alongside patient symptoms and functional limitations. Imaging provides an objective measure of joint degeneration, but the correlation between radiographic severity and pain can be inconsistent. Some individuals with advanced osteoarthritis experience minimal discomfort, while others with mild changes report significant pain.

The grading system helps guide treatment decisions. Patients with lower-grade osteoarthritis benefit from conservative management, while those with higher-grade disease often require intra-articular injections or surgical options. Studies in The Journal of Arthroplasty indicate that Kellgren–Lawrence Grade 3 or 4 strongly predicts the need for joint replacement.

Interobserver Reliability

Consistency in radiographic grading is crucial, as variability between observers can affect clinical decisions and research outcomes. Differences arise from image quality, observer experience, and subjectivity in assessing osteophyte size or joint space narrowing. Studies in Radiology show that musculoskeletal radiologists demonstrate higher agreement, while discrepancies are more common among general practitioners. Standardized training and calibration exercises improve reproducibility.

Machine learning algorithms trained on large datasets can enhance grading consistency. A study in Nature Medicine found that deep learning models achieved interobserver agreement rates comparable to expert radiologists, suggesting artificial intelligence may aid in standardizing osteoarthritis diagnosis.