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

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

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

EOS 3D rendering

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

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

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)

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

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

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)

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 89.933.02 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

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

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

Disclaimer/Conflicts of Interest None

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. 2012 Mar; 98: 506-513 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. 2014 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. 2012 Nov; 12 (11):1052-9. 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. 1998 Jul; 28(7): 557-61. 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): 1-188. 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. 2013 Jul; 42(7): 959-67.

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

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

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