Z. Bakouny

Influence of patient axial malpositioning on the trueness and precision of pelvic parameters obtained from 3D reconstructions based on biplanar radiographs

ObjectivesRadiographs are often performed to assess pelvic and hip parameters, but results depend upon correct pelvis positioning. Three-dimensional (3D) reconstruction from biplanar-radiographs should provide parameters that are less sensitive to pelvic orientation, but this remained to be evaluated.MethodsComputerized-tomographic scans of six patients were used both as a reference and for generating simulated frontal and lateral radiographs. These simulated radiographs were generated while introducing axial rotations of the pelvis ranging from 0° to 20°. Simulated biplanar-radiographs were utilized by four operators, three times each, to perform pelvic 3D-reconstructions. These reconstructions were used to assess the trueness, precision and global uncertainty of radiological pelvic and hip parameters for each position.ResultsIn the neutral position, global uncertainty ranged between ± 2° for pelvic tilt and ± 9° for acetabular posterior sector angle and was mainly related to precision errors (ranging from 1.5° to 7°). With increasing axial rotation, global uncertainty increased and ranged between ± 5° for pelvic tilt and ± 11° for pelvic incidence, sacral slope and acetabular anterior sector angle, mainly due to precision errors.ConclusionRadiological parameters obtained from 3D-reconstructions, based on biplanar-radiographs, are less sensitive to axial rotation compared to plain radiographs. However, the axial rotation should nonetheless not exceed 10°.Key points• Pelvic radiological parameters could be affected by patient malpositioning.• Biplanar radiograph-based 3D reconstructions were performed at increments of axial rotation.• Trueness, precision and global uncertainty were evaluated for pelvic and hip radiological parameters.• Hip parameters were less affected by rotation compared to pelvic parameters.• Maintaining the pelvis close to the neutral position is recommended to ensure the highest possible accuracy.

Validation of hip joint center localization methods during gait analysis using 3D EOS imaging in typically developing and cerebral palsy children

Localization of the hip joint center (HJC) is essential in computation of gait data. EOS low dose biplanar X-rays have been shown to be a good reference in evaluating various methods of HJC localization in adults. The aim is to evaluate predictive and functional techniques for HJC localization in typically developing (TD) and cerebral palsy (CP) children, using EOS as an image based reference. Eleven TD and 17 CP children underwent 3D gait analysis. Six HJC localization methods were evaluated in each group bilaterally: 3 predictive (Plug in Gait, Bell and Harrington) and 3 functional methods based on the star arc technique (symmetrical center of rotation estimate, center transformation technique and geometrical sphere fitting). All children then underwent EOS low dose biplanar radiographs. Pelvis, lower limbs and their corresponding external markers were reconstructed in 3D. The center of the femoral head was considered as the reference (HJCEOS). Euclidean distances between HJCs estimated by each of the 6 methods and the HJCEOS were calculated; distances were shown to be lower in predictive compared to functional methods (p<0.0001). Contrarily to findings in adults, functional methods were shown to be less accurate than predictive methods in TD and CP children, which could be mainly due to the shorter thigh segment in children. Harrington method was shown to be the most accurate in the prediction of HJC (mean error≈18mm, SD=9mm) and quasi-equivalent to the Bell method. The bias for each method was quantified, allowing its correction for an improved HJC estimation.

Three-dimensional evaluation of skeletal deformities of the pelvis and lower limbs in ambulant children with cerebral palsy

Skeletal abnormalities, affecting posture and walking pattern, increase with motor impairment in children with cerebral palsy (CP). However, it is not known whether these skeletal malalignments occur in children with slight motor impairment. Our aim was to evaluate skeletal malalignment at the level of the pelvis and lower limbs in ambulant children with CP, with slight motor impairment, using a low dose biplanar X-ray technique. Twenty-seven children with spastic CP (mean age: 10.9±4years, 7 Hemiplegia, 20 Diplegia, GMFCS levels I:17, II:10), with no previous treatments at the hips and knees, underwent EOS(®) biplanar X-rays. A control group consisting of 22 typically developing children was also included. Three-dimensional reconstructions of the pelvis and lower limbs were performed in order to calculate 11 radiological parameters related to the pelvis, acetabulum and lower limbs. Pelvic incidence and sacral slope were significantly increased in children with CP compared to TD children (48°±7° vs. 43°±8°, 42°±7° vs. 38°±5°, respectively, p=0.003). Acetabular parameters did not significantly differ between the two groups. Femoral anteversion and neck shaft angle were significantly increased in children with CP (25°±12° vs. 14°±7°, p<0.001; 134°±5° vs. 131°±5°, p=0.005 respectively). No difference was found for tibial torsion. This study showed that even slightly impaired children with CP have an anteverted and abducted femur and present positional and morphological changes of the pelvis in the sagittal plane. The orientation of the acetabulum in 3D seems to not be affected when children with CP present slight motor impairment.

A podoscopic and descriptive study of foot deformities in patients with Down syndrome

INTRODUCTION Subjects with Down syndrome (DS) are known to be affected by various foot deformities. Despite the fact that some of these deformities have been reported in the literature, a more comprehensive description would be of benefit. The aim of this study is to investigate the prevalence of known foot deformities in patients with DS and of other previously non-described foot anomalies in this population. HYPOTHESIS Subjects with DS have an increased prevalence of foot deformities compared to control subjects. METHODS Fifty-five subjects with DS (age: 14.6±7.4 years) had undergone podiatric clinical and podoscopic examinations to study their main foot deformities and their footprints, respectively. The results of these examinations were compared to those of an age-matched asymptomatic control group of fifty-three subjects (age: 13.4±11.2 years). RESULTS Significantly more prevalent foot deformities were found in the DS group: hallux valgus (36.4%), syndactyly between the 2nd and 3rd toes (9.1%), grade II pes planus (39.1%) and grade III pes planus (30%). Moreover, joint laxity (43.6%) was significantly more prevalent in the DS group. Furthermore, the presence of an increased space between the 1st and 2nd toes in patients with DS and its prevalence (73.6%) were described for the first time. A multivariate analysis revealed a significant relationship between the presence of joint laxity and flatfoot in only the control but not the DS group. Other foot deformities were found to be consistently more frequent in the DS population but not significantly higher than the control group. DISCUSSION Although subjects with DS had significantly greater joint laxity and BMI compared to the control group, neither of these factors was found to be related to the increased prevalence of flatfoot in DS patients. LEVEL OF EVIDENCE IV-retrospective study.

O 057 - How do postural parameters vary during walking in asymptomatic adults? A registration technique of subject-specific 3D skeletal reconstruction during gait

Postural skeletal alignment is altered with age due to intervertebral disc and joint degeneration, consequently affecting quality of life (QoL) and activities of daily living, such as gait. Postural alignment parameters of the spine, pelvis, hips and lower limbs, measured on static standing radiographs, have been widely studied in asymptomatic subjects and subjects affected by various pathologies. However, while most of these parameters are positional and could vary during gait, there are currently no studies investigating how they are modified during walking.

O 095—How do postural parameters vary during gait in children with cerebral palsy? A 3D subject-specific skeletal segment registration technique

Please cite this article as: Massaad A, ASSI A, Bizdikian AJ, Yared F, Bakouny Z, Khalil N, Ghanem I, Pillet H, Bonnet X, Skalli W, O 095 How do postural parameters vary during gait in children with cerebral palsy? A 3D subject-specific skeletal segment registration technique<CHK-Error value=Ärticle Title is Mismatching from Order./̈>, Gait and Posture (2018), https://doi.org/10.1016/j.gaitpost.2018.06.130

O 034 – Variation of the sagittal vertical axis during walking and its determinants

Patients with adult spinal deformities (ASD) are known to have altered postural alignment affecting their quality of life and activities of daily living, especially gait. The Sagittal Vertical Axis (SVA), a postural parameter calculated as the distance between the posterior corner of the sacrum and the C7-plumbline on full-body sagittal radiographs [1], has been shown to be highly altered in ASD. Even though this parameter is positional and could vary during gait, no studies have investigated its variation during walking even in asymptomatic subjects.

O 068 – The variation of lateral and posterior coverage of the femoral head by the acetabulum during walking influences stability during gait

Gait balance,assessed by the angle formed between the line joining the center-of-mass (COM) to the center-of-pressure (COP) and the vertical during gait, has been shown to be related to skeletal-postural and anthro-pometric parameters [1]. Although skeletal-postural parameters are mea-sured on standing radiographs, they are known to vary during gait. There are currently no studies evaluating how the variations of skeletal-postural parameters during gait influence subject’s balance during walking. Research question How does the variation of skeletal-postural parameters during gait influence subject’s balance during walking? Methods 72 asymptomatic subjects (age: 28.6 ± 11 years [18–59], 29F) underwent 3D gait analysis [2] with additional markers on the thighs and shanks. The COM-COP angle with the vertical was calculated in both the frontal and sagittal planes during the gait cycle [3]( Fig. 1).Subjects then underwent low-dose full-body biplanar X-rays with themarkers still in place. 3D reconstructions were obtained for the spine,pelvis and lower limbs. 3D bones were registered at each frame of thegait cycle [4]. A new technique developed for this study, utilizingfiniteelement modelling, was used to reduce soft tissue artefacts. Skeletal-postural parameters were then computed during the gait cycle, using the 3D registered bones, at each time frame (Fig. 2); mean, minimum, maximum and ROM were calculated on the waveforms during the gaitcycle. In order to determine which varying skeletal-postural parameterduring gait determined the variation of the COM-COP angles, univariate analysis (Pearson’s correlation) followed by a multivariate analysis (stepwise-multiple-linear-regression models) were computed; COM-COP parameters were the dependant variables and varying skeletal-postural parameters during gait were the independent variables. Results Minimum (−14.2 ± 3.4°) and average (3.1 ± 1.6°) of the sagittal COM-COP angle were found to be determined by the minimum of the posterior coverage (post_cov) of the femoral head by the acetabulum during gait (β= 0.40; R2 = 0.16; p = 0.003 andβ= 0.32; R2 = 0.1;p = 0.001, respectively). ROM (33.9 ± 5.1°) and maximum(19.7 ± 2.8°) of the sagittal COM-COP angle were found to be related to the ROM (β= 0.29; R2 = 0.09; p = 0.03) and maximum (β= 0.34;R2 = 0.11; p = 0.006) of the acetabular abduction during gait, respectively. ROM of the frontal COM-COP angle (8.8 ± 2.51°) was found to be determined by the average of the post_cov (β= 0.51;R2 = 0.26; p = 0.004) during gait. Discussion This is the first study to evaluate how the variation of skeletal-postural parameters during walking influences the stability during gait(Fig. 3). A less pronounced posterior coverage of the acetabulum during gait predisposes to more instability by decreasing the minimum COM-COP angle; a more pronounced acetabular abduction (decreased lateralcoverage) during gait predisposes to more instability by increasing the ROM and the maximum of the COM-COP angle. Therefore, gait instability in the sagittal plane seems to be influenced by the variation of the posterior and lateral coverage of the femoral head by the acet-abulum during walking

Validity and reliability of different techniques of neck–shaft angle measurement

AIM To determine a valid and reliable neck-shaft angle (NSA) measurement method while rotating the pelvises in increments of 5° in order to simulate patient malpositioning. MATERIALS AND METHODS CT images of 17 patients were used to produce digitally reconstructed radiographs in frontal and lateral views and three-dimensional (3D)-reconstructions of the femurs, considered to be the reference standard. Malpositioning was simulated by axially rotating the frontal radiographs from 0° to 20°. Three operators measured in two-dimensions the NSA using four different methods, three times each, at each axial rotation (AR) position. Method 1 (femoral neck axis drawn by joining the centre of the femoral head (CFH) to the median of the femoral neck base; femoral diaphysis axis drawn by joining the median of two lines passing through the medial and lateral edges of the femoral axis below the lesser trochanter) and method 2 (femoral axis taken as the median of a triangle passing through base of femoral neck and medial and lateral head-neck junction; femoral diaphysis as previous) were described for the first time; method 3 was based on a previous study; method 4 was a free-hand technique. Reliability, validity, and global uncertainty were assessed. RESULTS Method 1 showed the best reliability and validity. The global uncertainty also showed minimal values for method 1, ranging from 7.4° to 14.3° across AR positions. CONCLUSION Method 1, based on locating the CFH, was the most reliable and valid method and should be considered as a standardised two-dimensional NSA measurement method for clinical application.

Combining acetabular and femoral morphology improves our understanding of the down syndrome hip

Background: Hip instability is frequent in patients with Down syndrome. Recent studies have suggested that skeletal hip alterations are responsible for this instability; however, there are currently no studies simultaneously assessing femoral and acetabular anatomy in subjects with Down syndrome in the standing position. The aim was to analyze the three‐dimensional anatomy of the Down syndrome hip in standing position. Methods: Down syndrome subjects were age and sex‐matched to asymptomatic controls. All subjects underwent full body biplanar X‐rays with three‐dimensional reconstructions of their pelvises and lower limbs. Parameter means and distributions were compared between the two groups. Findings: Forty‐one Down syndrome and 41 control subjects were recruited. Acetabular abduction (mean = 52° [SD = 9°] vs. mean = 56° [SD = 8°]) and anteversion (mean = 14° [SD = 8°] vs. mean = 17.5° [SD = 5°]) as well as posterior acetabular sector angle (mean = 91° [SD = 7°] vs. mean = 94° [SD = 7°]) were significantly lower in Down syndrome subjects compared to controls (P < 0.01). Anterior acetabular sector angle (mean = 62° [SD = 10°] vs. mean = 59° [SD = 7°]; P < 0.01) was significantly higher in Down syndrome compared to controls. The distributions of acetabular anteversion (P = 0.002;V = 0.325), femoral anteversion (P = 0.004;V = 0.309) and the instability index (P < 0.001;V = 0.383) were significantly different between the two groups, with subjects with Down syndrome having both increased anteversion and retroversion for each of these parameters. Interpretation: Subjects with Down syndrome were found to have a significantly altered and more heterogeneous anatomy of their proximal hips compared to controls. This heterogeneity suggests that treatment strategies of hip instability in Down syndrome should be subject‐specific and should rely on the understanding of the underlying three‐dimensional anatomy of each patient. HighlightsUnderstanding hip instability in Down syndrome in 3D while standing is lacking.Down syndrome & control subjects had 3D EOS reconstructions of pelvis & lower limbs.Subjects with Down syndrome have altered and heterogeneous anatomy of proximal hips.Treatment strategies of hip instability in Down syndrome should be subject‐specific.