Kellgren-Lawrence Grade 0 — The Normal Radiographic Joint
The five-point KL scale anchors all osteoarthritis staging to this healthy baseline.
- ~4.5 mm: Joint space width (typical medial compartment)
- 0: Osteophytes (no marginal lipping)
- 0 / 3: Sclerosis score (no subchondral change)
- 1957: Scale published (Kellgren & Lawrence)
What the KL scale measures
Five grades (0–IV) rank OA severity directly from plain radiographs.
KL remains the most widely used OA severity system worldwide.
Normal joint anatomy on film
Even cartilage spacing keeps bone ends separated with no bony reaction.
Why a baseline grade matters
Grade 0 anchors comparison for every higher, more severe grade.
Kellgren-Lawrence Grade I — Doubtful Narrowing and Early Lipping
The earliest, most subjective grade sits at the edge of detectable disease.
- ~4.0 mm: Joint space width (minimal reduction)
- 0–1: Osteophytes (doubtful, tiny lipping)
- 0 / 3: Sclerosis score (not yet present)
- Low: Interrater agreement (grade I is most disputed)
Doubtful joint space narrowing
Space loss is questionable and often within normal variation.
Possible osteophytic lipping
A faint marginal bone spur may or may not be present.
Clinical significance of grade I
Symptoms are usually absent despite the earliest radiographic hint.
Grade I shows the lowest reader agreement across all KL grades.
Kellgren-Lawrence Grade II — Definite Osteophytes Emerge
A clear, reproducible bony spur marks the transition into confirmed osteoarthritis.
- ~3.2 mm: Joint space width (possible narrowing)
- 1–2: Osteophytes (definite, small)
- 0–1 / 3: Sclerosis score (early subchondral change)
- Common: Symptom onset (pain often begins here)
Definite osteophyte formation
A clearly visible marginal spur is the defining feature of grade II.
Possible joint space narrowing
Cartilage loss becomes plausible but is not yet definite.
Why grade II is a treatment trigger
Many patients first seek care once symptoms match this grade.
Kellgren-Lawrence Grade III — Moderate Multiple Findings
Multiple abnormalities now compound: narrowing, spurs, sclerosis, and mild deformity.
- ~2.0 mm: Joint space width (moderate narrowing)
- 3–4: Osteophytes (multiple, moderate size)
- 2 / 3: Sclerosis score (definite subchondral density)
- High: Reported pain (stiffness and swelling common)
Moderate joint space narrowing
Cartilage loss is now unambiguous on standard radiographs.
Multiple osteophytes
Several spurs form along both femoral and tibial margins.
Grade III is the most common threshold for surgical referral.
Early sclerosis and mild deformity
Subchondral bone thickens and slight malalignment can appear.
Kellgren-Lawrence Grade IV — Severe End-Stage Change
Bone-on-bone contact with large spurs marks the most advanced radiographic stage.
- <1 mm: Joint space width (near bone-on-bone)
- 5–8: Osteophytes (large, confluent)
- 3 / 3: Sclerosis score (definite, extensive)
- Frequent: Deformity (varus/valgus malalignment)
Severe joint space loss
Cartilage is essentially gone, leaving bone surfaces nearly touching.
Large osteophytes and sclerosis
Bulky spurs and dense sclerotic bone dominate the film.
Grade IV is the typical threshold considered for joint replacement.
Definite deformity
Bone ends remodel, producing visible angular malalignment.