Objective: To evaluate how the reading of knee radiographs by site investigators differs from that by an expert musculoskeletal radiologist who trained and validated them in a multicenter knee osteoarthritis (OA) study.
Materials and methods: A subset of participants from the Osteoarthritis Initiative progression cohort was studied. Osteophytes and joint space narrowing (JSN) were evaluated using Kellgren-Lawrence (KL) and Osteoarthritis Research Society International (OARSI) grading. Radiographs were read by site investigators, who received training and validation of their competence by an expert musculoskeletal radiologist. Radiographs were re-read by this radiologist, who acted as a central reader. For KL and OARSI grading of osteophytes, discrepancies between two readings were adjudicated by another expert reader.
Results: Radiographs from 96 subjects (49 women) and 192 knees (138 KL grade ≥ 2) were included. The site reading showed moderate agreement for KL grading overall (kappa = 0.52) and for KL ≥ 2 (i.e., radiographic diagnosis of "definite OA"; kappa = 0.41). For OARSI grading, the site reading showed substantial agreement for lateral and medial JSN (kappa = 0.65 and 0.71), but only fair agreement for osteophytes (kappa = 0.37). For KL grading, the adjudicator's reading showed substantial agreement with the centralized reading (kappa = 0.62), but only slight agreement with the site reading (kappa = 0.10).
Conclusion: Site investigators over-graded osteophytes compared to the central reader and the adjudicator. Different thresholds for scoring of JSN exist even between experts. Our results suggest that research studies using radiographic grading of OA should use a centralized reader for all grading.