Abstract
OBJECTIVE: This study aims to define Kellgren-Lawrence grade (KLG) using OARSI grade and stratify radiographic knee osteoarthritis (KOA) into distinct phenotypes based on radiographic structure changes and compare clinical symptoms and disease progression. DESIGN: We used radiographic grading data provided by the OAI and MOST study. Decision tree was used to (1) Find OARSI grade criteria for each KLG and (2) Phenotype early osteoarthritic knees (=KLG1, 2) by the radiographic structure changes. Pain, function, and progression to KLG ≥3 were compared between phenotypes. RESULTS: 10,804 knees from 5802 patients were included. The mean follow-up duration was 55.6 ± 24.5 months. Criteria for KLG1 was: (1) Joint space narrowing (JSN) grade (more severe grade among medial and lateral compartments) = 1 without osteophytes (i.e., KLG1Jt) (2) A single grade 1 osteophyte without JSN (i.e., KLG1Ost). Criteria for KLG2 was (1) JSN = 1 with a sum of osteophyte grades ≥1 (i.e., KLG2Jt): (2) Sum of osteophyte grades ≥2 without JSN (i.e., KLG2Ost). In terms of pain and function, there was no difference between KLG1Ost and KLG1Jt or between KLG2Ost and KLG2Jt. For progression to KLG ≥3, the mean survival time of KLG1Ost was 1.87-fold (95 % CI: 1.31-2.67) longer than that of KLG1Jt, while KLG2Ost was 5.42-fold (95 % CI: 3.69-7.96) longer than KLG2Jt. CONCLUSIONS: We proposed the criteria for each KLG using OARSI grade and phenotypes characterized by radiographic structure deformity in early KLG. Within the same KLG, the rate of disease progression was different depending on the structural deformity.