Reliability of the international knee documentation committee radiographic grading system.
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.


OBJECTIVE
We hypothesize that the IKDC radiographic grading system will have acceptable interrater and intrarater reliability.


METHODS
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.
Mehta
Vishal M
VM
Fox Valley Orthopaedic Institute, 2525 Kaneville Road, Geneva, IL 60134, USA. vishal@mehtas.com
Paxton
Liz W
LW
Fornalski
Stefan X
SX
Csintalan
Rick P
RP
Fithian
Donald C
DC
D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging* / Q000601:surgery; D004282:Documentation / Q000592:standards*; D006801:Humans; D038622:Internationality; D017063:Outcome Assessment, Health Care / Q000592:standards; D011859:Radiography; D019651:Plastic Surgery Procedures; D015203:Reproducibility of Results; D014481:United States