Intrarater and Interrater Reliability of Radiographic Characteristics in Skeletally Immature Patients With Anterior Cruciate Ligament Tears: A PLUTO Study Group Reliability Study

Background: Radiographic measurements of limb alignment in skeletally immature patients with anterior cruciate ligament (ACL) tears are frequently used for surgical decision-making, preoperative planning, and postoperative monitoring of skeletal growth. However, the interrater and intrarater reliability of these radiographic characteristics in this patient population is not well documented.Hypothesis: Excellent reliability across 4 raters will be demonstrated for all digital measures of length, coronal plane joint orientation angles, mechanical axis, and tibial slope in skeletally immature patients with ACL tears.Study Design: Cohort study (diagnosis).Methods: Three fellowship-trained orthopaedic surgeons and 1 medical student performed 2 rounds of radiographic measurements on digital imaging (lateral knee radiographs and long-leg radiographs) of skeletally immature patients with ACL tears. Intrarater and interrater reliability for continuous radiographic measurements was assessed with intraclass correlation coefficients (ICCs) across 4 raters with 95% CIs for affected and unaffected side measurements. Interrater reliability analysis used an ICC (2, 4) structure and intrarater reliability analysis used an ICC (2, 1) structure. A weighted kappa coefficient was calculated for ordinal variables along with 95% CIs for both interrater and intrarater reliability. Agreement statistic interpretations are based on scales described by Fleiss, and Cicchetti and Sparrow: <0.40, poor; 0.40 to 0.59, fair; 0.60 to 0.74, good; and >0.74, excellent.Results: Radiographs from a convenience sample of 43 patients were included. Intrarater reliability was excellent for nearly all measurements and raters. Interrater reliability was also excellent for nearly all reads for all measurements.Conclusion: Radiographic reliability of long-leg radiographs and lateral knee x-rays in skeletally immature children with ACL tears is excellent across nearly all measures and raters and can be obtained and interpreted as reliable and reproducible means to measure limb length and alignment.Level of Evidence: Level III.