1. 2D/3D EOS imaging versus standing long leg x-ray in lower limb clinical assessment - inter-observer and intra-observer reliability
Melinda Hau, Dipen Menon, Ronald Wong, Kwong Yin Chung, Jack Chau, Ki Wai Ho

2. Background
Long leg standing radiographs: Gold standard for templating & measurement of mechanical axis deviation (MAD)
AP and Lat
2D limitation
CT scan
Limitation – higher radiation exposure, costs, supine
Alternative method – EOS system
2D limitation – rotational, varus/valgus deformity, bowing

3. EOS system EOS system (1992, Paris, France) Nobel Prize Biplane
2 thin beams with 2 detectors
WB/whole body 3D imaging
Low dose radiation
EOS system in Prince of Wales Hospital, Hong Kong
Georges Charpak
3D-reconstructed models appear in true 1:1 scale for size and volume
UK- Harley, North Tee and Hartlepool
‘The EOS imaging system and its uses in orthopaedics’, Illes and Somoskeoy, Int Orthop 2012

4. EOS 3D rendering

5. Research Objective
To measure lower limb angles from EOS images (2D and 3D) to determine accuracy, repeatability and reproducibility compared with standing long leg x-ray radiographs

6. Methodology
Pre-operative knee clinics in Prince of Wales Hospital, Hong Kong
Over 12 month period
20 patients with end stage OA: 3 males, 17 females
Mean age 69 (range 60-86)
Total 40 lower limbs
Recruited patients who had standing long leg x-rays and EOS imaging on same day

7. Methodology 3 groups: 1) 2D EOS image vs x-ray radiograph
4 observers, repeated measurements weeks later
Measured (5): fAMA, mLDFA, aLDFA, MPTA, LDTA
2) 2D EOS vs 3D EOS images
1 observer
Measured (6): femur length, tibia length, varus/valgus angle, fAMA, mLDFA, and MPTA
3) 3D EOS vs x-ray radiograph
Measured (3): fAMA, mLDFA, MPTA
5 = long leg, 2 femoral and 2 tibial angles
femoral anatomic-mechanical angle (fAMA), mechanical lateral distal femoral angle (mLDFA), anatomical lateral distal femoral angle (aLDFA), medial proximal tibial angle (MPTA), lateral distal tibial angle (LDTA)

8. Statistical Analysis Student t-test Bland-Altman plots
Intra-class correlation coefficient, ICC
Inter- and intra-observer reliability
ICC>0.75 = excellent agreement and reliability

9. Results: Group 1 – 2D EOS vs x-ray
Independent T-test: no significant difference in all angles
BA analysis linear regression - good agreement
Variable
2D EOS/X-ray
Mean±SD
p-value
fAMA
EOS
5.88±1.23
0.118
X-ray
6.13±1.53
mLDFA
89.58±2.99
0.767
89.48±3.08
aLDTA
83.76±3.42
0.255
83.32±3.51
MPTA
85.12±3.53
0.077
85.83±3.63
LDTA
90.34±3.42
0.930
90.31±3.45
Linear regression analysis carrying out after BA analysis showed good agreement when measuring mLDFA and LDTA

10. Results: Group 1 – 2D EOS vs x-ray
Intra-class correlation coefficient (ICC)
ICC > 0.75 = excellent agreement and reliability
Variable
Intra-observer
Inter-observer
ICC (95% CI)
2D EOS
1.00 (0.99, 1.00)
X-ray
0.99 (0.99 – 0.99)
Intra-observer (within the same observers) and inter-observer (between observers)

11. Results: Group 2 – 2D EOS vs 3D EOS
Variable
2D EOS/ 3D EOS
Mean±SD
p-value
Femur length (cm)
2D EOS
38.15±2.09
0.62
3D EOS
38.39±2.15
Tibia length (cm)
32.61±1.84
0.59
32.83±1.87
Valgus/varus (°)
-8.31±6.82
0.79
-8.71±6.71
mLDFA (°)
90.03±2.92
0.89
MPTA (°)
84.62±3.24
0.85
84.49±2.91
fAMA (°)
6.32±1.89
0.61
6.53±1.89
T-test: no significant difference in all angles (p>0.05)
BA analysis linear regression - good agreement
Linear regression analysis carrying out after BA analysis showed good agreement when measuring varus/valgus, fAMA (=HKS), mLDFA (=180° - FMA), and LDTA

12. Results: Group 3 – 3D EOS vs x-ray
T-test: no significant difference in fAMA and mLDFA, apart from measuring MPTA
BA analysis linear regression - good agreement
Measurements
EOS 3D
X-ray
P value
fAMA
6.55±1.87
6.27±1.08
0.41
mLDFA
90.07±2.98
89.57±3.06
0.46
MPTA
84.50±3.07
86.27±4.02
0.03
femoral anatomic-mechanical angle (fAMA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA)
Linear regression analysis carrying out after BA analysis showed good agreement with fAMA

13. Conclusion
Both modalities - excellent repeatability and reproducibility
EOS imaging - alternative method of imaging lower limbs
Translated to assess disease progression, pre-op planning, alignment of implant
Use in routine orthopaedic clinical practice worldwide and for a wider breadth of conditions.
Further study is needed: to analyse 3D EOS images vs CT scans.
Intra-class correlation coefficient, ICC

14. Disclaimer/Conflicts of Interest
None

15. References
Gueonoun B, Zadegan F, Aim F, et al. Reliability of a new method for lower-extremity measurements based on sterioradiographic three-dimensional reconstruction. Orthop Traumatol Surg Res Mar; 98:
Guggenberger R, Pfirrmann CW, Koch PP, et al. Assessment of lower limb length and alignment by biplanar linear radiography: comparison with supine CT and upright full-length radiography. AJR Am J Roentgenol Feb; 202(2): W161-7
Somoskeoy S, Tunyogi-Csapo M, Bogyo C, et al. Accuracy and reliability of coronal and sagittal spinal curvature data based on patient-specific three-dimensional models created by the EOS 2D/3D imaging system. Spine J Nov; 12 (11):
Kalifa G, Charpak Y, Maccia C, et al. Evaluation of a new low-dose digital x-ray device: first dosimetric and clinical results in children. Pediatr Radiol Jul; 28(7):
McKenna C, Wade R, Faria R. EOS 2D/3D x-ray imaging system: a systematic review and economic evaluation. Health Technol Assess. 2012; 16(14):
Dietrich TJ, Pfirrmann CW, Schwab A, et al. Comparison of radiation dose, workflow, patient comfort and financial break-even of standard digital radiography and a novel biplanar low-dose x-ray system for upright full-length lower limb and whole spine radiography. Skeletal Radiol Jul; 42(7):

17. Results: stem 1 – 2D EOS vs x-ray
Linear regression analysis carrying out after BA analysis showed good agreement when measuring mLDFA and LDTA

18. Results: stem 2 – 2D EOS vs 3D EOS
Linear regression analysis carrying out after BA analysis showed good agreement when measuring varus/valgus, fAMA (=HKS), mLDFA (=180° - FMA), and LDTA

19. Results: stem 3 – 3D EOS vs x-ray
Linear regression analysis carrying out after BA analysis showed good agreement with fAMA