## 4 Discussion
This likely shaped the system's classification tendencies to align more closely with E1's methodology for the FHC/DAE metric. The contingency table shows that most classifications were again concentrated in the \"Superimposed\" (56 cases) and \"Lateral\" (37 cases) categories, which together accounted for 66.4% of the observations. Disagreements were more frequent than in the E1 comparison (25 cases). Notably, the contingency tables, along with the mean \(\pm\) standard deviation values of continuous FHC/DAE measurements, indicate that the system tends to assign slightly less severe classifications than both E1 and E2. The mean \(\pm\) standard deviation was \(-\)1.32 \(\pm\) 2.70 mm for E1, \(-\)1.53 \(\pm\) 2.70 mm for E2, and \(-\)1.12 \(\pm\) 2.59 mm for the system, reflecting a modest upward shift. This trend was more apparent in the comparison with E2, where some cases classified as \"Lateral+\" by E2 were assigned to \"Lateral\" by the system, and cases classified as \"Lateral\" were occasionally assigned to \"Superimposed\". Although these discrepancies were mostly limited to adjacent categories, which generally carry limited clinical consequence, the system's slightly conservative bias could increase the risk of false negatives in screening contexts. In particular, misclassifications near the boundary between \"Superimposed\" and \"Lateral\", which likely represents the division between normal and dysplastic hips, may result in early CHD cases being overlooked. Despite this trend, the system maintained strong agreement in less frequent but clinically important categories, with 8 out of 12 agreements for \"Lateral+\" and full agreement for the single \"Luxation\" case. For continuous FHC/DAE measurements, inter-rater reliability between E2 and the system was excellent (ICC = 0.93, 95% CI [0.88, 0.96], \(p\) < 0.001), with an SEM of 1.34 mm, indicating that approximately 68% of the system's measurements would fall within \(\pm\)1.34 mm of E2's. Although this SEM is higher than that observed in the E1 comparison, it remains acceptable for most categories. However, in narrower thresholds such as \"Superimposed\" (\(-\)1 to <1 mm), which spans 2 mm, and \"Medial\" (1 to \(\leq\)2 mm), which spans just 1 mm, this level of variability could affect classifications in borderline cases. The inclusion of a second examiner in this study helped evaluate the system's consistency with expert methodologies, ensuring conformity with established FHC/DAE classification standards. While E1's involvement in training the system understandably led to closer agreement between E1 and the system, the high agreement and reliability observed between E1 and E2 reflect consistent judgment among experienced examiners. This strong inter-rater reliability ensures that the methodologies of both examiners can be used interchangeably for FHC/DAE assessments, providing confidence that their ratings are robust and unbiased [27]. Furthermore, this consistency strengthens the validity of the system's classifications, as its performance aligns with experts whose methodologies are both reliable and consistent. Even when the system's classifications diverge slightly, particularly from those of E2, the robust examiner agreement supports the system's broader applicability. However, it is important to note that the FHC/DAE system is not intended to function as a standalone diagnostic tool for assessing CHD. While it addresses some limitations of NA-centric scoring, it also shares certain biomechanical constraints. Like the NA, its accuracy may be affected by artificial tightening of the joint capsule in the VDHE position, which can mask subluxation and potentially lead to underestimation of CHD severity. Therefore, although FHC/DAE offers objective spatial information on the femoral head's position relative to the acetabulum, it should be interpreted alongside complementary metrics to provide a more complete picture of hip joint integrity.