Kellgren-Lawrence Classification System for Osteoarthritis
The Kellgren-Lawrence (KL) classification system is the gold standard radiographic grading system used to assess the severity of osteoarthritis, particularly in the knee, by evaluating joint space narrowing, osteophyte formation, subchondral sclerosis, and bone deformity on plain radiographs. 1, 2
Classification Grades
The KL classification consists of five grades (0-4):
- Grade 0: Normal - No features of osteoarthritis
- Grade 1: Doubtful - Minute osteophyte, doubtful significance
- Grade 2: Minimal - Definite osteophytes, unimpaired joint space
- Grade 3: Moderate - Moderate diminution of joint space
- Grade 4: Severe - Joint space greatly reduced with sclerosis of subchondral bone
Clinical Applications
Diagnosis and Assessment
- Used to objectively document the radiographic severity of osteoarthritis
- Provides standardized communication between healthcare providers
- Helps track disease progression over time
- Guides treatment decisions and surgical planning 1
Optimal Imaging Technique
- For knee osteoarthritis, weight-bearing views are essential to properly evaluate joint space narrowing 1, 2
- Standard radiographic views should include:
- Weight-bearing anteroposterior (AP) views
- Lateral views
- Patellofemoral (skyline) views 2
Limitations of the KL System
Overemphasis on osteophytes: The system places greater importance on osteophyte formation than on joint space narrowing 3, 4
Global grading: Uses a composite score rather than grading individual features separately 3
Limited correlation with symptoms: There is often poor correlation between radiographic severity and patient-reported pain 5
Insensitivity to early disease: May miss early cartilage damage that is visible on arthroscopy or MRI 4
Observer variability: Subject to inter-observer and intra-observer variability 1
Clinical Decision-Making Applications
Surgical Planning
The KL classification helps determine appropriate timing for surgical intervention. For patients with radiographically moderate-to-severe osteoarthritis (KL grade 3-4) who have failed nonoperative therapy, total joint arthroplasty may be indicated without further delay 1.
Research Applications
The KL system is widely used in clinical research and trials to:
- Standardize patient selection
- Evaluate disease progression
- Assess treatment outcomes 6
Important Considerations
Treatment should not be based solely on radiographic findings since there is often discordance between radiographic severity and symptoms 5
Early osteoarthritis may be missed if relying solely on the KL system, as subtle changes at the tibial spine may precede joint space narrowing 7
Additional imaging modalities such as MRI may be necessary when radiographic findings don't correlate with clinical presentation 1
Weight-bearing views are crucial for accurate assessment of joint space narrowing in knee osteoarthritis 1, 2
The KL classification remains the most widely used radiographic grading system for osteoarthritis despite its limitations, providing a standardized framework for clinical assessment, research, and treatment planning.