Table 1 Different descriptions of the Kellgren and Lawrence (K&L) criteria of knee osteoarthritis (OA)
Original description*Alternative A†Alternative B‡Alternative C§Alternative D¶
Grade 1: doubtful narrowing of joint space and possible osteophytic lippingMinute osteophyte, doubtful significancePossible osteophytes onlyPossible osteophyte lippingDoubtful pathology
Grade 2: definite osteophytes and possible narrowing of joint spaceDefinite osteophyte, unimpaired joint spaceDefinite osteophytes and possible joint space narrowingDefinite osteophyte and possible joint space narrowingMinimal osteophytes, possible narrowing, cysts, and sclerosis
Grade 3: moderate multiple osteophytes, definite narrowing of joint space and some sclerosis and possible deformity of bone endsModerate diminution of joint space (with osteophytes)Moderate osteophytes and/or definite narrowingModerate multiple osteophytes, definite joint space narrowing, some sclerosis, and possible bone contour deformity (bony attrition)Moderate, as in definite osteophytes with moderate joint space narrowing
Grade 4: large osteophytes, marked narrowing of joint space, severe sclerosis and definite deformity of bone endsJoint space greatly impaired with sclerosis of subchondral boneLarge osteophytes, severe joint space narrowing and/or bony sclerosisLarge osteophytes, marked joint space narrowing, severe sclerosis, and definite bone contour deformity (bony attrition)Severe, with large osteophytes and definite joint space narrowing
  • *Kellgren et al,1 Kellgren and Lawrence,2 Baltimore Longitudinal Study of Aging (BLSA),5 Southeast Michigan Cohort (SMC).6 †Johnston County Osteoarthritis Project (JCOP),7 Chingford Study (CS).9 10 ‡ Beijing Study (BS).11 § Clearwater Osteoarthritis Study (COS),12 Mechanical factors of Arthritis of the Knee study (MAK).13 ¶Williams et al.15