Letter to the Editor: Kellgren-Lawrence classification for knee osteoarthritis: Clinical value and limitations

Table 1 Kellgren-Lawrence classification criteria for knee osteoarthritis (weight-bearing anteroposterior radiograph)[1,2]

Grade	Imaging findings	Clinical features and significance
Grade 0 (normal)	No osteophyte formation; normal joint space width; absence of subchondral sclerosis, cystic changes, or bony deformity	No knee osteoarthritis-related pain, stiffness, or limited range of motion; fully preserved joint function
Grade 1 (doubtful)	Suspected joint space narrowing; possible mild marginal osteophytes; no definitive subchondral bone morphological abnormalities	Occasional mild joint dull pain; morning stiffness < 10 minutes in duration, with spontaneous symptom resolution; easily conflated with physiological degeneration
Grade 2 (mild)	Definite osteophyte formation; suspected or mild joint space narrowing; no subchondral sclerosis or bony deformity	Mild post-activity pain; stiffness following prolonged sitting or standing, alleviated with movement; minimal to no impairment of daily activities
Grade 3 (moderate)	Multiple osteophytes; definite joint space narrowing; associated mild subchondral sclerosis; possible mild bony deformity	Frequent pain, exacerbated by stair climbing or squatting; morning stiffness lasting 10-30 minutes; mild limitation of joint range of motion
Grade 4 (severe)	Prominent osteophytes; severe joint space narrowing (or complete obliteration); significant subchondral sclerosis; accompanied by bony deformity or subluxation	Persistent moderate-to-severe pain, including resting pain or nocturnal pain; severe limitation of joint range of motion; often complicated by varus or valgus deformity, which impairs daily functioning

The classification criteria are integrated based on original literature and multicenter validation studies, serving as the core basis for the imaging diagnosis of knee osteoarthritis; clinical features are combined with symptoms and functional status to provide references for treatment decision-making[2,4,10].