Intra- and interobserver reliability analysis of pediatric lower limb parameters on digital long leg radiographs

Abstract

Background Malalignments of the lower extremity are common reasons for orthopedic consultation because it may lead to osteoarthritis in adulthood. An accurate and reliable radiological assessment of lower limb alignment in children and adolescents is essential for clinical decision-making on treatment of limb deformities and for regular control after a surgical intervention. Objective First, does the analysis of full-length standing anteroposterior radiographs show a good intra- and interobserver reliability? Second, which parameter is most susceptible to observer-dependent errors? Third, what is the Standard Error of Measurement (SEM95%) of the absolute femoral and tibial length? Methods Two observers evaluated digital radiographs of 144 legs from 36 children and adolescents with pathological valgus alignment before a temporary hemiepiphysiodesis and before implant removal. Parameters included Mechanical Femorotibial Angle (MFA), Mechanical Axis Deviation (MAD), mechanical Lateral Distal Femoral Angle (mLDFA), mechanical Medial Proximal Tibial Angle (mMPTA), mechanical Lateral Proximal Femoral Angle (mLPFA), mechanical Lateral Distal Tibial Angle (mLDTA), Joint Line Convergence Angle (JLCA), femur length, tibial length. Intra- and interobserver reliability (ICC2,1), SEM95% and proportional errors were calculated. Results The intra- and interobserver reliability for almost all measurements was found to be good to excellent (Intra-ICC2,1: 0.849–0.999; Inter-ICC2,1: 0.864–0.996). The SEM95% of both observers was found to be ± 1.39° (MFA), ± 3.31 mm (MAD), ± 1.06° (mLDFA) and ± 1.29° (mMPTA). The proportional error of MAD and MFA is comparable (47.29% vs. 46.33%). The relevant knee joint surface angles show a lower proportional error for mLDFA (42.40%) than for mMPTA (51.60%). JLCA has a proportional error of 138%. Furthermore, the SEM95% for the absolute values of the femoral and tibial length was 4.53 mm for the femur and 3.12 mm for the tibia. Conclusions In conclusion, a precise malalignment measurement and the knowledge about SEM95% of the respective parameters are crucial for correct surgical or nonsurgical treatment. The susceptibility to error must be considered when interpreting malalignment analysis and must be considered when planning a surgical intervention. The results of the present study elucidate that MAD and MFA are equally susceptible to observer-dependent errors. This study shows good to excellent intra- and interobserver ICCs for all leg alignment parameters and joint surface angles, except for JLCA. Trial registration: This study was registered with DRKS (German Clinical Trials Register) under the number DRKS00015053. Level of evidence I, Diagnostic Study.

Hemiepiphysiodesis for Lower Extremity Coronal Plane Angular Correction in the Distal Femur and Proximal Tibia in Children With Achondroplasia

“…9 Intra-and intrarater reliability have previously been reported for these measurements in pediatric patients as good to excellent based on intraclass correlation coefficient. 10,11 By convention, for MAD and mechanical axis zone negative values were assigned for varus and positive for valgus.…”

“…Radiographic measurements were made on limbs treated with hemiepiphysiodesis including initial and final mechanical axis deviation (MAD), knee mechanical axis zone (knee divided into quadrants, zone 1 = middle quadrants, zone 2 = medial or lateral outer quadrants, zone 3 = outside of articular surface), 8 mechanical lateral distal femoral angle (mLDFA) and medial proximal tibia angle (mMPTA) 9 . Intra- and intra-rater reliability have previously been reported for these measurements in pediatric patients as good to excellent based on intraclass correlation coefficient 10,11 . By convention, for MAD and mechanical axis zone negative values were assigned for varus and positive for valgus.…”

Genu Valgum in Pediatric Patients Presenting With Patellofemoral Instability

“…Full-length standing alignment radiographs are routinely performed as part of the clinical assessment of PFI in our population. Standing hip-to-ankle anteroposterior (AP) digital and/or standing EOS radiographs were taken in a standard fashion with both knees extended, patella facing forward, feet shoulder width apart and equal distribution of body weight 20 . Of note, these radiographs are typically deferred in our institution in patients who cannot achieve terminal knee extension, are unable to fully weight bear through the affected limb or are unable to follow instructions adequately.…”

“…Standing hip-to-ankle anteroposterior (AP) digital and/or standing EOS radiographs were taken in a standard fashion with both knees extended, patella facing forward, feet shoulder width apart and equal distribution of body weight. 20 Of note, these radiographs are typically deferred in our institution in patients who cannot achieve terminal knee extension, are unable to fully weight bear through the affected limb or are unable to follow instructions adequately. Where standing alignment was available, the imaging was first assessed for adequacy based on the following parameters.…”

“…2B). 20,22,24 Values of 87 degrees (range: 85 to 90 degrees) are considered normal in both measures. 22 Skeletal maturity was recorded as immature, transitional, and mature based on the following parameters: Immature was defined as the presence of fully open physes on both sides of the knee joint, complete or partial closure of the tibial physis was considered as transitional, and closure of both femoral and tibial physis was considered mature.…”