Interobserver and Intraobserver Reliability in the Evaluation of Mechanical Axis Deviation

Background: The lateral distal femoral angle (LDFA), the medial proximal tibial angle (MPTA), and the mechanical axis deviation (MAD) are commonly used in the evaluation of lower extremity deformities. The interobserver and intraobserver reliabilities of these measurements have not been evaluated. Methods: Three groups of observers with different levels of experience (5 attending pediatric orthopaedic Surgeons, 5 orthopaedic chief residents, and 5 interns) measured the LDFA, MPTA, and MAD on 35 full-length standing anteroposterior teleroentgenograms (56 extremities). Relatively equal numbers of extremities with vat-Lis, valgus, and normal alignments were chosen to represent a spectrum of lower extremities that might be encountered clinically. Measurements were performed in random order by each observer on 2 separate occasions separated by at least 2 weeks. Results: The interobserver and intraobserver reliabilities for each of the measurements regardless of the level of experience was greater than or equal to 0.90. The interobserver differences were slightly greater than the intraobserver differences for all measurements. The overall mean interobserver differences for angular and MAD measurements were within 1.6 degrees and 3.1 mm, respectively. The overall mean intraobserver differences for angular and MAD measurements were within 1.4 degrees and 1.9 mm, respectively. Reliability and mean differences were consistent regardless of the level of experience. Conclusions: Measurement of the LDFA, MPTA, and MAD demonstrated excellent intraobserver and interobserver reliabilities regardless of the experience of the observer.