BACKGROUND: The International Knee Documentation Committee (IKDC) forms are commonly used to measure outcomes after anterior cruciate ligament (ACL) reconstruction. The knee examination portion of the IKDC forms includes a radiographic grading system to grade degenerative changes. The interrater and intrarater reliability of this radiographic grading system remain unknown. HYPOTHESIS: We hypothesize that the IKDC radiographic grading system will have acceptable interrater and intrarater reliability. STUDY DESIGN: Case series (diagnosis); Level of evidence, 4. METHODS: Radiographs of 205 ACL-reconstructed knees were obtained at 5-year follow-up. Specifically, weightbearing posteroanterior radiographs of the operative knee in 35 degrees to 45 degrees of flexion and a lateral radiograph in 30 degrees of flexion were used. The radiographs were independently graded by 2 sports medicine fellowship-trained orthopaedic surgeons using the IKDC 2000 standard instructions. One surgeon graded the same radiographs 6 months apart, blinded to patient and prior IKDC grades. The percentage agreement was calculated for each of the 5 knee compartments as defined by the IKDC. Interrater reliability was evaluated using the intraclass correlation coefficient (ICC) 2-way mixed effect model with absolute agreement. The Spearman rank-order correlation coefficient (r(s)) was applied to evaluate intrarater reliability. RESULTS: The interrater agreement between the 2 surgeons was 59% for the medial joint space (ICC = 0.46; 95% confidence interval [CI] = 0.35-0.56), 54% for the lateral joint space (ICC = 0.45; 95% CI = 0.27-0.58), 49% for the patellofemoral joint (ICC = 0.40; 95% CI = 0.26-0.52), 63% for the anterior joint space (ICC = 0.20; 95% CI = 0.05-0.34), and 44% for the posterior joint space (ICC = 0.28; 95% CI = 0.15-0.40). The intrarater agreement was 83% for the medial joint space (r(s) = .77, P < .001), 86% for the lateral joint space (r(s) = .76, P < .001), 81% for the patellofemoral joint (r(s) = .79, P < .001), 91% for the anterior joint space (r(s) = .48, P < .001), and 69% for the posterior joint space (r(s) = .64, P < .001). CONCLUSIONS: While intrarater reliability was acceptable, interrater reliability was poor. These findings suggest that multiple raters may score the same radiographs differently using the IKDC radiographic grading system. The use of a single rater to grade all radiographs when using the IKDC radiographic grading system maximizes reliability.
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