| Original description* | Alternative A† | Alternative B‡ | Alternative C§ | Alternative D¶ |
| Grade 1: doubtful narrowing of joint space and possible osteophytic lipping | Minute osteophyte, doubtful significance | Possible osteophytes only | Possible osteophyte lipping | Doubtful pathology |
| Grade 2: definite osteophytes and possible narrowing of joint space | Definite osteophyte, unimpaired joint space | Definite osteophytes and possible joint space narrowing | Definite osteophyte and possible joint space narrowing | Minimal osteophytes, possible narrowing, cysts, and sclerosis |
| Grade 3: moderate multiple osteophytes, definite narrowing of joint space and some sclerosis and possible deformity of bone ends | Moderate diminution of joint space (with osteophytes) | Moderate osteophytes and/or definite narrowing | Moderate 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 ends | Joint space greatly impaired with sclerosis of subchondral bone | Large osteophytes, severe joint space narrowing and/or bony sclerosis | Large 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