Reliability and Reproducibility of Subject Positioning with EOS Low-Dose Biplanar X-ray

Analysis of lower extremity alignment (LEA) in children with recurrent patellar dislocation by EOS system

Objectives

Recurrent patellar dislocation (RPD) greatly affects active young individuals, necessitating the identification of risk factors for a better understanding of its cause. Previous research has connected RPD to lower limb alignment (LEA) abnormalities, such as increased femoral anteversion, tibial external rotation, knee valgus, and flexion. This study aims to use EOS technology to detect RPD-related LEA anomalies, enabling three-dimensional assessment under load conditions.

Methods

A total of 100 limbs (50 in the RPD group, 50 in the control group) were retrospectively analyzed. In the RPD group, we included limbs with recurrent patellar dislocation, characterized by dislocations occurs at least two times, while healthy limbs served as the control group. We used EOS technology, including 2D and 3D imaging, to measure and compare the following parameters between the two groups in a standing position: Femoral neck shaft angle (NSA), Mechanical femoral tibial angle (MFTA), Mechanical lateral distal femoral angle (mLDFA), Medial proximal tibial angle (MPTA), Anatomical femoral anteversion (AFA), External tibial torsion (ETT), and Femorotibial rotation (FTR).

Results

The significant differences between the two groups were shown in NSA 3/2D, MFTA 3/2D, mLDFA 3/2D, MPTA 3D, AFA, FTR. No significant difference was shown in MPTA 2D, ETT between the RPD group and the control group. Further binary logistic regression analysis. Further binary logistic regression analysis was conducted on the risk factors affecting RPD mentioned above. and found four risk factors for binary logistic regression analysis: mLDFA (3D), AFA, NSA(3D), and FTR.

Conclusions

EOS imaging identified abnormal LEA parameters, including NSA, MFTA, mLDFA, MPTA, AFA, and FTR, as risk factors for RPD. Children with these risk factors should receive moderate knee joint protection.

The EOS 3D imaging system reliably measures posterior tibial slope

Background

One of the values determined during the assessment of knee issues is the posterior tibial slope (PTS). A new option for measuring the PTS is the EOS 3D imaging system, which provides anteroposterior (AP) and lateral long leg radiographs (LLRs) using less radiation than a conventional LLR. We investigated the reliability of the EOS 3D imaging system with respect to PTS measurements.

Methods

We retrospectively searched our radiological database for patients who underwent an EOS scan and a computed tomography (CT) scan of their lower extremities between January and December 2019. Fifty-six knees were included in the study. Medial and lateral PTSs were determined using both modalities. A radiologist and an orthopaedic surgeon each performed all measurements twice and the intraclass correlation (ICC) was calculated to assess inter- and intrarater reliability. The Student t test and Pearson correlation were used to compare the results of both imaging modalities.

Results

The mean medial PTS was 8.5° (95% confidence interval [CI], 8.1–8.9°) for the EOS system and 7.7° (95% CI, 7.3–8.1°) for CT, and the lateral PTS was 7.4° (95% CI, 6.9–7.9°) for the EOS system, and 7.0° (95% CI, 6.5–7.4°) for CT. Interrater reliability (ICC) with respect to medial and lateral PTSs measured on the EOS (0.880, 0.765) and CT (0.884, 0.887) images was excellent. The intrarater reliability of reader 1 (ICC range, 0.889–0.986) and reader 2 (ICC range, 0.868–0.980) with respect to the same measurements was excellent.

Conclusion

The PTS measurements from the EOS 3D imaging system are as reliable and reproducible as those from CT, the current gold standard method. We recommend using this system if possible, because it acquires more information (sagittal plane) in a scan than a conventional LLR, while exposing the patient to less radiation.

Level of evidence

Level III, Retrospective cohort study

Validity of the EOS-determined pelvic parameters and orientation with pelvic positional variation: a phantom study

The EOS is a medical imaging system that incorporates simultaneous orthogonal images, producing three-dimensional (3D) reconstructions of the whole skeletal system in various functional positions. Despite growing interest in the pelvic 3D position, the validity of the EOS has not yet been well studied. We investigated the trueness and precision of EOS imaging for pelvic parameters and orientation and assessed whether the measurement using the EOS was affected by the pelvic orientation itself. The orientation of the anterior pelvic plane and pelvic parameters of a custom-made pelvic phantom were measured by three raters using the EOS, and the measurements obtained were compared with the true values. The standard deviations of the measurement errors were 3.23°, 0.26°, 0.23°, 2.98°, 0.88°, and 3.22° for flexion, obliquity, rotation, pelvic incidence, spinopelvic tilt, and sacral slope, respectively. The root-mean square averages of the standard deviation of each measurement were 4.05°, 0.41°, 0.28°, 4.80°, 0.99°, and 5.13°, respectively. The measurement errors for sacral slope correlated significantly with geometric means of flexion, obliquity, and rotation (r = 0.364, p = 2.67 × 10^-11). The EOS rendered accurate and reliable measurements regarding pelvic 3D position, even with positional variation, but positional variation could affect measurements of sacral slope.