The reliability of full-length lower limb radiographic alignment measurements in skeletally immature youth

Abstract

Purpose Reliable radiographic measurement techniques are important for investigating limb alignments prior to and following paediatric anterior cruciate ligament (ACL) reconstruction. We investigated the inter- and intraobserver reliability of alignment measurements from lower extremity anteroposterior and lateral radiographs of adolescents having undergone transphyseal ACL reconstruction. Methods A total of 15 of 90 patients who had undergone transphyseal ACL reconstruction were randomly selected for alignment measurements of radiographs of operative and nonoperative limbs. Radiographs were de-identified, randomized to three varying sequences and made available in electronic format to three blinded investigators: a junior orthopaedic resident, a senior orthopaedic resident and a paediatric orthopaedic attending. Coronal measurements comprised the mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) and mechanical axis deviation (MAD), measured from standing teleoroentgenograms of the lower extremities. Tibial slope was measured on lateral knee radiographs of operative limbs. The intra-class correlation coefficient (ICC) was calculated for each of the three coronal measures and for tibial slope. Results Intraobserver reliability was excellent across all measures (ICC > 0.75) except for tibial slope in one investigator’s measurements (good or ICC = 0.68 for the operative limbs) and mLDFA in another investigator’s measurements (fair or ICC = 0.49 for the operative limbs, and poor ICC = 0.27 for the nonoperative limbs). Interobserver reliability was excellent across all investigators for all measurements for operative and nonoperative limbs. Conclusions Radiographic measurements of lower extremity alignment may be reliably measured on teleoroentgenograms in a subset of youth who underwent transphyseal ACL reconstruction.