Reliability of EOS compared to conventional radiographs for evaluation of lower extremity deformity in adult patients

Distances and angles in standing long-leg radiographs: comparing conventional radiography, digital radiography, and EOS

OBJECTIVE

Distances and angles measured from long-leg radiographs (LLR) are important for surgical decision-making. However, projectional radiography suffers from distortion, potentially generating differences between measurement and true anatomical dimension. These phenomena are not uniform between conventional radiography (CR) digital radiography (DR) and fan-beam technology (EOS). We aimed to identify differences between these modalities in an experimental setup.

MATERIALS AND METHODS

A hemiskeleton was stabilized using an external fixator in neutral, valgus and varus knee alignment. Ten images were acquired for each alignment and each modality: one CR setup, two different DR systems, and an EOS. A total of 1680 measurements were acquired and analyzed.

RESULTS

We observed great differences for dimensions and angles between the 4 modalities. Femoral head diameter measurements varied in the range of > 5 mm depending on the modality, with EOS being the closest to the true anatomical dimension. With functional leg length, a difference of 8.7% was observed between CR and EOS and with the EOS system being precise in the vertical dimension on physical-technical grounds, this demonstrates significant projectional magnification with CR-LLR. The horizontal distance between the medial malleoli varied by 20 mm between CR and DR, equating to 21% of the mean.

CONCLUSIONS

Projectional distortion resulting in variations approaching 21% of the mean indicate, that our confidence on measurements from standing LLR may not be justified. It appears likely that among the tested equipment, EOS-generated images are closest to the true anatomical situation most of the time.

Faster Rate of Correction with Distal Femoral Transphyseal Screws Versus Plates in Hemiepiphysiodesis for Coronal-Plane Knee Deformity: Age- and Sex-Matched Cohorts of Skeletally Immature Patients

BACKGROUND

Hemiepiphysiodesis (guided-growth) procedures have become the primary method of treatment for coronal-plane knee deformities in skeletally immature patients. Two leading techniques involve the use of a transphyseal screw or a growth modulation plate. However, clinical references for the estimation of correction are lacking, and no consensus has been reached regarding the superiority of one technique over the other. Therefore, the purpose of this study was to compare the rates of correction for distal femoral transphyseal screws and growth modulation plates in age- and sex-matched cohorts with coronal deformities.

METHODS

Thirty-one knees were included in each cohort on the basis of propensity scoring by chronological age and sex, and radiographic images were retrospectively reviewed preoperatively and postoperatively. Each case was measured for limb length, mechanical axis deviation (MAD), mechanical lateral distal femoral angle (LDFA), and bone age.

RESULTS

Both the MAD and LDFA rate of correction significantly differed between the screw and plate cohorts. The MAD rate of correction was observed to be 0.42 ± 0.37 mm/week (1.69 mm/month) in the plate cohort and 0.66 ± 0.51 mm/week (2.64 mm/month) in the screw cohort. The LDFA rate of correction was observed to be 0.12° ± 0.13°/week (0.50°/month) in the plate cohort and 0.19° ± 0.19°/week (0.77°/month) in the screw cohort.

CONCLUSIONS

The current study provides simple clinical references for the rate of correction of MAD and the LDFA for 2 methods of hemiepiphysiodesis. The results suggest that transphyseal screws may correct coronal knee deformities during the initial treatment stage more quickly than growth modulation plates in distal femoral guided growth.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Accuracy of biplanar linear radiography versus conventional radiographs when used for lower limb and implant measurements

INTRODUCTION

The current standard of care for measuring lower extremity length and angular discrepancies is using a full-length standing anteroposterior radiograph. However, there has been increasing interest to use biplanar linear EOS imaging as an alternative. This study aims to compare lower extremity length and implant measurements between biplanar linear and conventional radiographs.

MATERIALS AND METHODS

In this 5-year retrospective study, all patients who had a standing full-length anteroposterior and biplanar linear radiographs (EOS®) that include the lower extremities done within one year of each other were included. Patients who underwent surgery in between the imaging, underwent surgeries that could result in graduated length or angulated corrections and inadequate exposure of the lower extremity were excluded. Four radiographic segments were measured to assess lower limb alignment and length measurements. Height and width measurements of implants were performed for patients who had implants in both imaging.

RESULTS

When comparing imaging and actual implant dimensions, biplanar linear radiographs were accurate in measuring actual implant height (median difference = - 0.14 cm, p = 0.66), and width (median difference = - 0.13 cm, p = 0.71). However, conventional radiographs were inaccurate in measuring actual implant height (median difference = 0.19 cm, p = 0.01) and width (median difference = 0.61 cm, p < 0.01). When comparing conventional and biplanar linear radiographs, there was statistically significant difference in all measurements. This includes anatomical femoral length (median difference = 3.53 cm, p < 0.01), mechanical femoral length (median difference = 3.89 cm, p < 0.01), anatomical tibial length (median difference = 2.34 cm, p < 0.01) and mechanical tibial length (median difference = 2.20 cm, p < 0.01).

CONCLUSION

First, there is a significant difference in the lower extremity length when comparing conventional and biplanar linear radiographs. Second, biplanar linear radiographs are found to be accurate while conventional radiographs are not as accurate in implant measurements of length and width in the lower extremity.

Comparison of Lower-Limb Alignment in Patients with Advanced Knee Osteoarthritis: EOS Biplanar Stereoradiography versus Conventional Scanography

Background

Accurate measurement of the lower limb alignment is one of the most crucial factors in advanced knee osteoarthritis patients scheduled for surgery. Recently, EOS biplanar stereoradiography with three-dimensional reconstruction was developed. The purpose of this study was to compare radiographic parameters between conventional scanography and EOS in patients with advanced knee osteoarthritis who need surgical treatment.

Methods

A total of 52 consecutive patients (104 knees) with bilateral knee osteoarthritis of advanced stage (Kellgren-Lawrence [KL] grade 3 or 4) were retrospectively reviewed. We measured the hip-knee-ankle angle (HKA) on conventional scanograms. In EOS, we measured HKA, hip-knee-shaft angle, mechanical lateral distal femoral angle, and mechanical medial proximal tibial angle. To evaluate sagittal and axial plane alignment, knee flexion angle (KFA), and knee joint rotation (KJR) were also measured.

Results

Ninety knees were KL grade 4, and 14 knees were grade 3. The average HKA was 10.14° ± 6.16° on conventional scanograms and 11.26° ± 6.21° in EOS. HKA was greater in EOS than on conventional scanograms, and the difference (1.12°; range, −1.07° to 3.22°) was statistically significant (p < 0.001). Significant correlations were observed on the difference in HKA and mechanical medial proximal tibial angle (r = –0.198, p = 0.044), KFA (r = 0.193, p = 0.049), and KJR (r = 0.290, p = 0.003). In multivariable linear regression analysis, the difference in HKA had significant relationship with KFA (β = 0.286, p = 0.003) and KJR (β = 0.363, p < 0.001).

Conclusions

HKA measured on conventional scanograms and in EOS differed significantly and the difference had a significant correlations with KFA, KJR, and medial proximal tibial angle. Surgeons can consider these results before orthopedic surgery in patients who have advanced knee osteoarthritis.

Variation in Sagittal Alignment Parameters in Adult Patients before Spine Surgery: A Serial Imaging Study Using Antero-Posterior and Latero-Lateral Projections

Sagittal parameters of the spine are closely related to the evaluation and treatment of spine disease. However, there has been little research on variations in preoperative sagittal spinal alignment. This study was conducted to assess the variation in sagittal spinal alignment on serial antero-posterior and latero-lateral projections (EOS imaging) in adult patients before spine surgery. The sagittal parameters of 66 patients were collected from two serial images. Comparison between the first and second sagittal parameters was evaluated using the Wilcoxon signed-rank test. Subgroup analysis was performed based on the time interval between radiographs, patient's age, and type of surgery. The sagittal vertical axis (SVA) exhibited statistically significant changes (p = 0.023), with the mean SVA increasing statistically (61.7 mm vs. 73.6 mm) and standard deviation increasing (51.5 mm vs. 61.6 mm) in the second image. Subgroup analysis showed significant differences in SVA (p = 0.034) in patients with an interval of >3 months; statistical differences in borderline levels in the SVA (p = 0.049) were observed in patients aged >65 years. Other parameters did not show statistically significant differences, except for SVA. Furthermore, SVA differences were statistically significant with increases in the EOS interval (>3 months) and patient age (>65 years).

[Radiographic analysis of limb malalignment in the frontal plane]

Radiographic measurement of the lower limb alignment in the frontal plane is used to assess limb deformity, to plan corrective surgery and for follow-up. It is essential that age-related normal lower limb alignment and joint orientation angles are known before planning surgical treatment. EOS (EOS™ Imaging, Paris, France) can lead to supplemental information, especially in cases of severe multidimensional joint malalignment. It allows 3D reconstruction of a bone model of the limb to assess multi-dimensional deformity.