A simple maximum intensity projection method for measuring proximal femoral anteversion: An observer reliability study.

Purpose: Quantifying femoral neck anteversion (FNA) is essential in lower limb torsional deformities. Because of proximal femur anatomy and computed tomography (CT) acquisition, the femoral head and neck are often visualized on different slices, making identification of the femoral-head-neck axis (FHNA) challenging. This study introduces a new method based on the maximum intensity projection (MIP) function available in most DICOM (Digital Imaging and Communications in Medicine) viewers. By increasing the thickness of the bone segment displayed on a single two-dimensional image, MIP allows simultaneous visualization of the femoral head and neck, simplifying FHNA identification. To evaluate intra- and interobserver reliability of the MIP method and compare it with established techniques. The hypothesis was that MIP would provide superior repeatability and reproducibility than other techniques. Methods: Between 2019 and 2023, 135 consecutive bilateral lower limb CT angiographies were retrospectively screened. A calculated sample size of 50 patients meeting the inclusion criteria was chronologically enroled. Radiographic measurements were performed at Time 0 and after 30 days by two independent observers following a calibrated training phase. FNA was measured using five methods: Murphy, Hernandez, Waidelich, Yoshioka and MIP. Intraobserver and interobserver reliability were evaluated using a two-way random-effects, single-measures, absolute-agreement intraclass correlation coefficient [ICC (2,1)] model, alongside standard error of measurement (SEM). For pairwise comparisons of estimated marginal means derived from the linear mixed-effects model, Tukey's honestly significant difference adjustment was applied. For pairwise comparisons of bootstrap-derived ICC differences, Results: Fifty CT angiographies were analysed. Mean FNA values were significantly different among most methods (Murphy: 18.4° ± 7.2; Waidelich: 24.6° ± 7.4; Yoshioka: 11.5° ± 7.8; Hernandez: 10.7° ± 7.1; MIP: 13.7° ± 6.2) The proposed MIP method demonstrated high intraobserver repeatability (Observer 1: ICC = 0.97; Observer 2: ICC = 0.95) and interobserver reproducibility (ICC = 0.84 for single-measure absolute agreement). Bland-Altman analysis revealed method-dependent non-interchangeability, with systematic differences between techniques. Conclusions: The MIP technique simplifies identification of the FHNA and demonstrated the highest overall reproducibility among the evaluated CT-based methods. It could therefore represent a practical approach for improving the standardization of FNA assessment. Level of Evidence: Level III, diagnostic study.