3D reconstruction of the pelvis from bi-planar radiography

Effect of the ischial support on muscle force estimation during transfemoral walking

BACKGROUND

Transmission of loads between the prosthetic socket and the residual limb is critical for the comfort and walking ability of people with transfemoral amputation. This transmission is mainly determined by the socket tightening, muscle forces, and socket ischial support. However, numerical investigations of the amputated gait, using modeling approaches such as MusculoSkeletal (MSK) modeling, ignore the weight-bearing role of the ischial support. This simplification may lead to errors in the muscle force estimation.

OBJECTIVE

This study aims to propose a MSK model of the amputated gait that accounts for the interaction between the body and the ischial support for the estimation of the muscle forces of 13 subjects with unilateral transfemoral amputation.

METHODS

Contrary to previous studies on the amputated gait which ignored the interaction with the ischial support, here, the contact on the ischial support was included in the external loads acting on the pelvis in a MSK model of the amputated gait.

RESULTS

Including the ischial support induced an increase in the activity of the main abductor muscles, while adductor muscles' activity was reduced. These results suggest that neglecting the interaction with the ischial support leads to erroneous muscle force distribution considering the gait of people with transfemoral amputation. Although subjects with various bone geometries, particularly femur lengths, were included in the study, similar results were obtained for all subjects.

CONCLUSIONS

Eventually, the estimation of muscle forces from MSK models could be used in combination with finite element models to provide quantitative data for the design of prosthetic sockets.

Effect of postural alignment alteration with age on vertebral strength

EOS biplane radiographs of 117 subjects between 20 and 83 years were analyzed to compute the upper body lever arm over the L1 vertebra and its impact on vertebral strength. Postural sagittal alignment alteration was observed with age and resulted in a greater lever arm causing vertebral strength to decrease.

PURPOSE

The purpose of this study was to analyze the impact of postural alignment changes with age on vertebral strength using finite element analysis and barycentremetry.

METHODS

A total of 117 subjects from 20 to 83 years were divided in three age groups: young (20 to 40 years, 62 subjects), intermediate (40 to 60 years, 26 subjects), and elderly (60 years and over, 29 subjects). EOS biplane radiographs were acquired, allowing 3D reconstruction of the spine and body envelope as well as spinal, pelvic, and sagittal alignment parameter measurements. A barycentremetry method allowed the estimation of the mass and center of mass (CoM) position of the upper body above L1, relatively to the center of the L1 vertebra (lever arm). To investigate the effect of this lever arm, vertebral strength of a generic finite element model (with constant geometry and mechanical properties for all subjects) was successively computed applying the personalized lever arm of each subject.

RESULTS

A combination of an increase in thoracic kyphosis, cervical lordosis, and pelvic tilt with a loss of lumbar lordosis was observed between the young and the older groups. Sagittal alignment parameters indicated a more forward position as age increased. The lever arm of the CoM above L1 varied from an average of 1 mm backward for the young group, to averages of 10 and 24 mm forward, respectively, for the intermediate and elderly group. As a result, vertebral strength decreased from 2527 N for the young group to 1820 N for the elderly group.

CONCLUSION

The global sagittal alignment modifications observed with age were consistent with the literature. Posture alteration with age reduced vertebral strength significantly in this simplified loading model. Postural alignment seems essential to be considered in the evaluation of osteoporotic patients.

Three-dimensional reconstruction of In Vivo human lumbar spine from biplanar radiographs

We present a method for three dimensional (3D) reconstruction of in vivo human lumbar spine from biplanar radiographs with comparable results to Computerised Tomography (CT) scans or Magnetic Resonance Imaging (MRI) models. In this work, we used uncalibrated radiographs to reconstruct the 3D vertebrae and a priori information stored in an Active Shape Model (ASM) that is constructed using the Spherical Demons Algorithm. The method is semi-automatic as bounding boxes are required to delimit the positions of the vertebrae on biplanar radiographs of a patient. Optimisation is based on comparisons between simulated and actual radiographs. Finally, we compare the results to the models generated from MRI and CT scans. The results show the feasibility of generating personalised models of patients from biplanar radiographs.

A novel dataset and deep learning-based approach for marker-less motion capture during gait

BACKGROUND

The deep learning-based human pose estimation methods, which can estimate joint centers position, have achieved promising results on the publicly available human pose datasets (e.g., Human3.6 M). However, these datasets may be less efficient for gait study, particularly for clinical applications, because of the limited number of subjects, their homogeneity (all asymptomatic adults), and the errors introduced by marker placement on subjects' regular clothing.

RESEARCH QUESTION

How a new human pose dataset, adapted for gait study, could contribute to the advancement and evaluation of marker-less motion capture systems?

METHODS

A marker-less system, based on deep learning-based pose estimation methods, was proposed. A new dataset (ENSAM dataset) was collected. Twenty-two asymptomatic adults, one adult with scoliosis, one adult with spondylolisthesis, and seven children with bone disease performed ten walking trials, while being recorded both by the proposed marker-less system and a reference system - combining a marker-based motion capture system and a medical imaging system (EOS). The dataset was split into training and test sets. The pose estimation method, already trained on the Human3.6 M dataset, was evaluated on the ENSAM test set, then reevaluated after further training on the ENSAM training set. The joints coordinates were evaluated, using Bland-Altman bias and 95 % confidence interval, and joint position error (the Euclidean distance between the estimated joint centers and the corresponding reference values).

RESULTS

The Bland-Altman 95 % confidence intervals were substantially improved after finetuning the pose estimation method on the ENSAM training set (e.g., from 106.9 mm to 17.4 mm for the hip joint). With the new dataset and approach, the mean joint position error varied from 6.2 mm for ankles to 21.1 mm for shoulders.

SIGNIFICANCE

The proposed marker-less system achieved promising results in terms of joint position errors. Future studies are necessary to assess the system in terms of gait parameters.

Combined 3D analysis of lower-limb morphology and function in children with idiopathic equinovarus clubfoot: A preliminary study

INTRODUCTION

In children treated for idiopathic equinovarus clubfoot (EVCF), the relation between morphologic defects on clinical examination and standard X-ray on the one hand and functional abnormalities on the other is difficult to objectify. The aim of the present study was to demonstrate the feasibility of combined 3D analysis of the foot and lower limb based on biplanar EOS radiographs and gait analysis. The study hypothesis was that this provides better understanding of abnormalities in form and function.

METHODS

Ten children with unilateral EVCF and "very good" clinical results were included. They underwent gait analysis on the Rizzoli Institute multisegment foot model. Kinematic data were collected for the hip, knee, ankle and foot (hindfoot/midfoot, midfoot/forefoot and hindfoot/forefoot). Biplanar EOS radiographs were taken to determine anatomic landmarks and radiological parameters.

RESULTS

Complete acquisition time was around 2hours per patient. No significant differences were found between EVCF and healthy feet except for calcaneal incidence, tibiocalcaneal angle and hindfoot/midfoot and hindfoot/forefoot inversion.

DISCUSSION

The feasibility of the combined analysis was confirmed. There were no differences in range of motion, moment or power between EVCF and healthy feet in this series of patients with very good results. The functional results are related to radiological results within the normal range. The protocol provided anatomic and kinematic reference data. A larger-scale study could more objectively assess the contribution of EOS radiography using optoelectronic markers.

LEVEL OF EVIDENCE

II, low-power prospective study.

Cervical Spine Hyperextension and Altered Posturo-Respiratory Coupling in Patients With Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is associated with postural dysfunction characterized by abnormal spinal curvature and disturbance of balance and walking, whose pathophysiology is poorly understood. We hypothesized that it may be the result of a pathological interaction between postural and ventilatory functions. Twelve patients with OSAS (4 women, age 53 years [51–63] (median [quartiles]), apnea hypopnea index 31/h [24–41]) were compared with 12 healthy matched controls. Low dose biplanar X-rays (EOS® system) were acquired and personalized three-dimensional models of the spine and pelvis were reconstructed. We also estimated posturo-respiratory coupling by measurement of respiratory emergence, obtaining synchronized center of pressure data from a stabilometric platform and ventilation data recorded by an optico-electronic system of movement analysis. Compared with controls, OSAS patients, had cervical hyperextension with anterior projection of the head (angle OD-C7 12° [8; 14] vs. 5° [4; 8]; p = 0.002), and thoracic hyperkyphosis (angle T1–T12 65° [51; 71] vs. 49° [42; 59]; p = 0.039). Along the mediolateral axis: (1) center of pressure displacement was greater in OSAS patients, whose balance was poorer (19.2 mm [14.2; 31.5] vs. 8.5 [1.4; 17.8]; p = 0.008); (2) respiratory emergence was greater in OSAS patients, who showed increased postural disturbance of respiratory origin (19.2% [9.9; 24.0] vs. 8.1% [6.4; 10.4]; p = 0.028). These results are evidence for the centrally-mediated and primarily respiratory origin of the postural dysfunction in OSAS. It is characterized by an hyperextension of the cervical spine with a compensatory hyperkyphosis, and an alteration in posturo-respiratory coupling, apparently secondary to upper airway instability.

Compensation of Respiratory-Related Postural Perturbation Is Achieved by Maintenance of Head-to-Pelvis Alignment in Healthy Humans

The maintenance of upright balance in healthy humans requires the preservation of a horizontal gaze, best achieved through dynamical adjustments of spinal curvatures and a pelvic tilt that keeps the head-to-pelvis alignment close to vertical. It is currently unknown whether the spinal and pelvic compensations of respiratory-related postural perturbations are associated with preservation of the head-to-pelvis vertical alignment. We tested this hypothesis by comparing postural alignment variables at extreme lung volume (total lung capacity, TLC; residual volume, RV) with their reference value at functional residual capacity (FRC). Forty-eight healthy subjects [22 women; median age of 34 (26; 48) years] were studied using low dose biplanar X-rays (BPXR; EOS^®system). Personalized three-dimensional models of the spine and pelvis were reconstructed at the three lung volumes. Extreme lung volumes were associated with changes of thoracic curvature bringing it outside the normal range. Maximal inspiration reduced thoracic kyphosis [T1–T12 angle = 47° (37; 56), -4° variation (-9; 1), p = 0.0007] while maximal expiration induced hyperkyphosis [T1–T12 angle = 63° (55; 68); +10° variation (5; 12), p = 9 × 10^-12]. Statistically significant (all p < 0.01) cervical and pelvic compensatory changes occurred [C3–C7 angle: +4° (-2; 11) and pelvic tilt +1° (0; 3) during maximal inspiration; C3–C7 angle: -7° (-18; -1) and pelvic tilt +5° (1; 8) during maximal expiration], resulting in preserved head-to-pelvis alignment (no change in the angle between the vertical plane and the line connecting the odontoid process and the midpoint of the line connecting the center of the two femoral heads ODHA). Lung volume related postural perturbations were more marked as a function of age, but age did not affect the head-to-pelvis alignment. These findings should help understand balance alterations in patients with chronic respiratory diseases that modify lung volume and rib cage geometry.

Review of 2-D/3-D Reconstruction Using Statistical Shape and Intensity Models and X-Ray Image Synthesis: Toward a Unified Framework

Patient-specific three-dimensional (3-D) bone models are useful for a number of clinical applications such as surgery planning, postoperative evaluation, as well as implant and prosthesis design. Two-dimensional-to-3-D (2-D/3-D) reconstruction, also known as model-to-modality or atlas-based 2-D/3-D registration, provides a means of obtaining a 3-D model of a patient's bones from their 2-D radiographs when 3-D imaging modalities are not available. The preferred approach for estimating both shape and density information (that would be present in a patient's computed tomography data) for 2-D/3-D reconstruction makes use of digitally reconstructed radiographs and deformable models in an iterative, non-rigid, intensity-based approach. Based on a large number of state-of-the-art 2-D/3-D bone reconstruction methods, a unified mathematical formulation of the problem is proposed in a common conceptual framework, using unambiguous terminology. In addition, shortcomings, recent adaptations, and persisting challenges are discussed along with insights for future research.

Coronal trunk imbalance in idiopathic scoliosis: Does gravity line localisation confirm the physical findings?

BACKGROUND

Adolescent idiopathic scoliosis (AIS) can require surgical procedures that have major consequences. Coronal imbalance as assessed clinically using a plumb line is a key criterion for selecting patients to surgery. Nevertheless, the reference standard for assessing postural balance of the trunk is gravity line localisation within a validated frame of reference. Recent studies have established that the gravity line can be localised after body contour reconstruction from biplanar radiographs. The objective of this study was to validate a gravity line localisation method based on biplanar radiographs in a population with AIS then to validate gravity line position versus plumb line position.

HYPOTHESIS

Plumb line and gravity line assessments of coronal balance correlate with each other.

MATERIAL AND METHODS

A gravity line localisation method based on biplanar radiography was validated in 14 patients with AIS versus force platform as the method of reference. Normal plumb line and gravity line positions were determined in 27 asymptomatic adolescents using biplanar radiography. The results of the two methods were then compared in 53 patients with AIS.

RESULTS

The reliability of gravity line localisation in the coronal plane based on biplanar radiography was 2.4mm (95% confidence interval). The distance between the gravity line and the middle of the line connecting the centres of the two femoral heads (HA) showed a strongly significant association with plumb line position computed as the distance from the vertical line through the middle of T1 and the centre of the S1 endplate (T1V/S): r=0.71, p<0.0001. Of the 20 patients with plumb line results indicating coronal imbalance, 11 (55%) had a normal gravity line-to-HA distance. Of the 33 patients with normal plumb line results, 7 (21%) had an abnormal gravity line-to-HA distance.

CONCLUSION

The results of this study validate gravity line determination from biplanar radiographs in a population with AIS. Plumb line position correlated significantly with gravity line position but was less accurate for guiding surgical decisions.

LEVEL OF EVIDENCE

IV, retrospective study.

Development and evaluation of a new methodology for the fast generation of patient-specific Finite Element models of the buttock for sitting-acquired deep tissue injury prevention

The occurrence and management of Pressure Ulcers remain a major issue for patients with reduced mobility and neurosensory loss despite significant improvement in the prevention methods. These injuries are caused by biological cascades leading from a given mechanical loading state in tissues to irreversible tissue damage. Estimating the internal mechanical conditions within loaded soft tissues has the potential of improving the management and prevention of PU. Several Finite Element models of the buttock have therefore been proposed based on either MRI or CT-Scan data. However, because of the limited availability of MRI or CT-Scan systems and of the long segmentation time, all studies in the literature include the data of only one individual. Yet the inter-individual variability can't be overlooked when dealing with patient specific estimation of internal tissue loading. As an alternative, this contribution focuses on the combined use of low-dose biplanar X-ray images, B-mode ultrasound images and optical scanner acquisitions in a non-weight-bearing sitting posture for the fast generation of patient-specific FE models of the buttock. Model calibration was performed based on Ischial Tuberosity sagging. Model evaluation was performed by comparing the simulated contact pressure with experimental observations on a population of 6 healthy subjects. Analysis of the models confirmed the high inter-individual variability of soft tissue response (maximum Green Lagrange shear strains of 213 ± 101% in the muscle). This methodology opens the way for investigating inter-individual factors influencing the soft tissue response during sitting and for providing tools to assess PU risk.

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.

Invariance of head-pelvis alignment and compensatory mechanisms for asymptomatic adults older than 49 years

PURPOSE

The aim was to quantify the postural alignment of asymptomatic elderly, in comparison to a reference population, searching for possible invariants and compensatory mechanisms.

METHODS

41 volunteers (49-76 years old) underwent bi-planar X-rays with 3D reconstructions of the spine and pelvis. Alignment parameters were compared with those of a reference group of asymptomatic subjects younger than 40 years old, with a particular focus on center of acoustic meati (CAM) and odontoid (OD) with regard to hip axis (HA). Possible markers of compensation were also investigated.

RESULTS

No significant difference among groups appeared for CAM-HA and OD-HA parameters. Twenty four percent of elders had an abnormally high SVA value and twenty seven percent had an abnormal global spine inclination. Increased pelvic tilt and cervical lordosis allowed maintaining the head above the pelvis.

CONCLUSIONS

CAM-HA and OD-HA appeared quasi-invariant even in asymptomatic elderly. Some subjects exhibited alteration of spine alignment, compensated at the pelvis and cervical regions.

A principal component analysis of the relationship between the external body shape and internal skeleton for the upper body

Recent progress in 3D scanning technologies allows easy access to 3D human body envelope. To create personalized human models with an articulated linkage for realistic re-posturing and motion analyses, an accurate estimation of internal skeleton points, including joint centers, from the external envelope is required. For this research project, 3D reconstructions of both internal skeleton and external envelope from low dose biplanar X-rays of 40 male adults were obtained. Using principal component analysis technique (PCA), a low-dimensional dataset was used to predict internal points of the upper body from the trunk envelope. A least squares method was used to find PC scores that fit the PCA-based model to the envelope of a new subject. To validate the proposed approach, estimated internal points were evaluated using a leave-one-out (LOO) procedure, i.e. successively considering each individual from our dataset as an extra-subject. In addition, different methods were proposed to reduce the variability in data and improve the performance of the PCA-based prediction. The best method was considered as the one providing the smallest errors between estimated and reference internal points with an average error of 8.3mm anterior-posteriorly, 6.7mm laterally and 6.5mm vertically. As the proposed approach relies on few or no bony landmarks, it could be easily applicable and generalizable to surface scans from any devices. Combined with automatic body scanning techniques, this study could potentially constitute a new step towards automatic generation of external/internal subject-specific manikins.

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 new quasi-invariant parameter characterizing the postural alignment of young asymptomatic adults

PURPOSE

Our study aims to describe the postural alignment of young asymptomatic subjects from head to feet from bi-planar standing full-body X-rays, providing database to compare to aging adults. Novelty resides in the inclusion of the head and lower limbs in the erected posture's analysis.

METHODS

For 69 young asymptomatic subjects (18-40 years old) 3D reconstructions of the head, spine, pelvis and lower limbs segments were performed from bi-planar full-body X-rays. Usual studied spinal, pelvic and lower limbs' parameters were computed in 3D, sagittal and frontal planes of the patient. Relationships between these parameters were investigated. Inclinations of different lines were studied to characterize the erected posture.

RESULTS

Values found for spinal curvatures, pelvic parameters and lower limbs geometrical parameters agreed with the literature: thoracic kyphosis, lumbar lordosis, pelvic incidence, pelvic tilt and sagittal vertical axis were respectively in average of 26.9° (SD 7.2°), 30.5° (SD 7.5°), 51.0° (SD 9.4°), 11.1° (SD 5.6°) and -8.9 mm (SD 21.6 mm). The angle between the vertical and the line joining the most superior point of dentiform apophyse of C2 (OD) and the center of the bi-coxofemoral axis (HA) was the less variable one (SD 1.6°).

CONCLUSIONS

This study on 3D postural alignment reports the geometry of the spine, pelvis and lower limbs, of the young asymptomatic adult. The less variable angle is the one of the line OD-HA with the vertical, highlighting the vertical alignment of the head above the pelvis. This study provides a basis for future comparisons when investigating aging populations.

Healthy vs. osteoarthritic hips: a comparison of hip, pelvis and femoral parameters and relationships using the EOS® system

BACKGROUND

Osteoarthritis is a debilitating disease, for which the development path is unknown. Hip, pelvis and femoral morphological and positional parameters relate either to individual differences or to changes in the disease state, both of which should be taken into account when diagnosing and treating patients. These have not yet been comprehensively quantified. Previous imaging studies have been limited by a number of factors: supine rather than standing measurements; high radiation dose; a limited field of view; and 2D rather than 3D measurements. EOS®, a new radiographic imaging modality that acquires simultaneous frontal and lateral (sagittal) X-ray images of the full body, allows 3D reconstruction of the hip, pelvis and lower limb. The aim of the study was to explore similarities and differences between healthy and osteoarthritis groups.

METHODS

Two groups of subjects, 30 healthy and 30 with hip osteoarthritis, were assessed and compared for pelvic, acetabular and femoral parameters in the standing position.

FINDINGS

There were not only significant differences between groups but also considerable overlap amongst the individuals. Sacral slope, acetabular angle of Idelberger and Frank, femoral mechanical angle and femoral head eccentricity as well as right-left asymmetries in centre-edge acetabular angle and femoral head diameter were higher on average in osteoarthritic patients compared to healthy subjects, whereas acetabular abduction was lower in the osteoarthritic group (P<0.05). Correlations were identified between key parameters in both groups.

INTERPRETATION

Differences between the groups suggest either degenerative changes over time or inherent differences between individuals that may contribute to the disease progression. These data provide a basis for longitudinal and post-surgery studies. Due to the considerable variability amongst individuals and the considerable overlap between groups, patients should be evaluated individually and at multiple joints when planning hip, knee and spine surgery.

Three-dimensional morphologic study of the child's hip: which parameters are reproducible?

BACKGROUND

Biplanar x-ray images obtained with patients in a standing weightbearing position allow reconstruction of three-dimensional (3-D) bone geometries, with lower radiation exposure than CT scans and better bone definition than MRI.

QUESTIONS/PURPOSES

We determined the reproducibility of 3-D parameter values of the hips and pelves of healthy children, using biplanar x-ray images.

METHODS

We built 3-D models of the hips of 33 children without musculoskeletal problems: 10 subjects younger than 9 years and 23 who were 9 years or older. Three anatomic landmarks and nine hip and pelvic parameters were computed for each reconstruction. To determine the reliability of these landmarks and parameters, each bone was reconstructed four times by two independent observers, leading to a total of 264 reconstructions, and parameters were studied for the two age groups and compared between dancers and nondancers.

RESULTS

Taking into account all reconstructions, the interobserver reproducibility ranged from 2 to 4 mm for landmark positions or distance parameters, and 2° to 6° for angular parameters. The most reproducible point was the center of the femoral head (range, 0.2-17 mm). The distance between this center and its projection on the plane fitting the edge of the acetabulum, and the pelvic tilt were the most reproducible parameters.

CONCLUSIONS

Reproducible 3-D reconstructions of hips and pelves of children were possible using biplanar x-ray images, regardless of the children's ages. Although we report preliminary values for 3-D parameters in healthy children's hips, further work is needed to obtain direct validation of our parameters using CT reconstructions of cadaveric specimens to avoid high doses of radiation.

Quantification of soft tissue balance in total knee arthroplasty using finite element analysis

Unbalanced contact force on the tibial component has been considered a factor leading to loosening of the implant and increased wear of the bearing surface in total knee arthroplasty. Because it has been reported that good alignment cannot guarantee successful clinical outcomes, the soft tissue balance should be checked together with the alignment. Finite element models of patients' lower extremities were developed to analyse the medial and lateral contact force distribution on the tibial insert. The distributions for four out of five patients were not balanced equally, even though the alignment angles were within a clinically acceptable range. Moreover, the distribution was improved by changing soft tissue release and ligament tightening for the specific case. Integration of the biomechanical modelling, image matching and finite element analysis techniques with the patient-specific properties and various dynamic loading would suggest a clinically relevant pre-operative planning for soft tissue balancing.

Reliability of a new method for lower-extremity measurements based on stereoradiographic three-dimensional reconstruction

INTRODUCTION

Several clinical and radiological techniques have been described to assess lower limb length and angle measurements. None of them has yet met the ideal criteria for a reliable, reproducible, safe, and inexpensive system. In this context, a new biplanar X-ray system (EOS™, EOS imaging, Paris, France) makes it possible to obtain a 3D reconstruction of the lower extremities from two 2D orthogonal radiographic images, with associated calculation of 3D measurements. The reliability of this technique has never been documented on adults.

HYPOTHESIS

Lower limb measurements produced by the 3D EOS™ reconstruction system are reproducible regarding inter- and intraobserver assessment and more reliable with this 3D technique than when they are obtained from 2D measurements.

MATERIALS AND METHODS

This study included 25 patients awaiting total hip arthroplasty (50 lower limbs). Two independent observers made all measurements twice, both on the 2D frontal radiograph and using 3D reconstructions (femoral measurements of length, offset, neck shaft angle, neck length, and head diameter, as well as the tibia length, limb length, HKA and HKS). Reproducibility was estimated by intraclass correlation coefficients.

RESULTS

Both the inter- and intraobserver reproducibility of the EOS™ measurements was excellent; more specifically inter- and intraobserver reproducibility was 0.997 and 0.997 for femoral length, 0.996 and 0.995 for tibial length, 0.999 and 0.999 for limb length, 0.894 and 0.891 for HKS, 0.993 and 0.994 for HKA, 0.870 and 0.845 for femoral offset, and 0.765 and 0.851 for neck shaft angle. For most of the variables, the interobserver correlations were statistically better with the EOS™ 3D reconstruction.

DISCUSSION

Our results show that the EOS™ systems allow reproducible lower limb measurements. Furthermore, 3D EOS™ reconstructions offer better reproducible measures for most of the parameters than radiographic 2D projection. Its use before deciding on surgery and during planning for lower limb arthroplasty appears essential to us.

LEVEL OF EVIDENCE

Level III: diagnostic prospective study on consecutive patients.

Personalized neuromusculoskeletal modeling to improve treatment of mobility impairments: a perspective from European research sites

Mobility impairments due to injury or disease have a significant impact on quality of life. Consequently, development of effective treatments to restore or replace lost function is an important societal challenge. In current clinical practice, a treatment plan is often selected from a standard menu of options rather than customized to the unique characteristics of the patient. Furthermore, the treatment selection process is normally based on subjective clinical experience rather than objective prediction of post-treatment function. The net result is treatment methods that are less effective than desired at restoring lost function. This paper discusses the possible use of personalized neuromusculoskeletal computer models to improve customization, objectivity, and ultimately effectiveness of treatments for mobility impairments. The discussion is based on information gathered from academic and industrial research sites throughout Europe, and both clinical and technical aspects of personalized neuromusculoskeletal modeling are explored. On the clinical front, we discuss the purpose and process of personalized neuromusculoskeletal modeling, the application of personalized models to clinical problems, and gaps in clinical application. On the technical front, we discuss current capabilities of personalized neuromusculoskeletal models along with technical gaps that limit future clinical application. We conclude by summarizing recommendations for future research efforts that would allow personalized neuromusculoskeletal models to make the greatest impact possible on treatment design for mobility impairments.

Pose-invariant 3D proximal femur estimation through bi-planar image segmentation with hierarchical higher-order graph-based priors

Low-dose CT-like imaging systems offer numerous perspectives in terms of clinical application, in particular for osteoarticular diseases. In this paper, we address the challenging problem of 3D femur modeling and estimation from bi-planar views. Our contributions are threefold. First, we propose a non-uniform hierarchical decomposition of the shape prior of increasing clinical-relevant precision which is achieved through curvature driven unsupervised clustering acting on the geodesic distances between vertices. Second, we introduce a graphical-model representation of the femur which can be learned from a small number of training examples and involves third-order and fourth-order priors, while being similarity and mirror-symmetry invariant and providing means of measuring regional and boundary supports in the bi-planar views. Last but not least, we adopt an efficient dual-decomposition optimization approach for efficient inference of the 3D femur configuration from bi-planar views. Promising results demonstrate the potential of our method.

Quantitative Computerized Assessment of the Degree of Acetabular Bone Deficiency: Total radial Acetabular Bone Loss (TrABL)

A novel quantitative, computerized, and, therefore, highly objective method is presented to assess the degree of total radical acetabular bone loss. The method, which is abbreviated to “TrABL”, makes use of advanced 3D CT-based image processing and effective 3D anatomical reconstruction methodology. The output data consist of a ratio and a graph, which can both be used for direct comparison between specimens. A first dataset of twelve highly deficient hemipelves, mainly Paprosky types IIIB, is used as illustration. Although generalization of the findings will require further investigation on a larger population, it can be assumed that the presented method has the potential to facilitate the preoperative use of existing classifications and related decision schemes for treatment selection in complex revision cases.

New method for 3D reconstruction of the human cranial vault from CT-scan data

This study presents a new method for the 3D reconstruction of the human cranial vault from routine Computed Tomography (CT) data. The reconstruction method was based on the conceptualization of the shape of the cranial vault with a parametric description. An initialization was first realized with the identification of anatomical landmarks and contours on Digitally Reconstructed Radiographs (DRR) in order to obtain a pre-personalized reconstruction. Then an optimization of the reconstruction was performed to segment the internal and external surfaces of the cranial vault for thickness computation. The method was validated by comparing final reconstructions issued from our approach and from a manual slice-by-slice segmentation method on ten CT-scans. Errors were comparable to the CT image resolution, and less than 2 min were dedicated to the operator-dependent marking step. The reconstruction of internal and external surfaces of the cranial vault allows quantifying and visualizing of thickness throughout the cranial vault. This thickness mapping is useful for clinical purposes as additional pre-surgical information. Moreover, this study constitutes a first step in the personalized characterization of skull resistance directly from routine exams.

In vivo distribution of spinal intervertebral stiffness based on clinical flexibility tests

STUDY DESIGN

A numerical study was conducted to identify the intervertebral stiffness of scoliotic spines from spinal flexibility tests.

OBJECTIVE

To study the intervertebral 3-dimensional (3D) stiffness distribution along scoliotic spine.

SUMMARY OF BACKGROUND DATA

Few methods have been reported in literature to quantify the in vivo 3D intervertebral stiffness of the scoliotic spine. Based on the simulation of flexibility tests, these methods were operator-dependent and could yield to clinically irrelevant stiffnesses.

METHODS

This study included 30 patients surgically treated for severe idiopathic scoliosis. A previously validated trunk model, with patient-specific geometry, was used to simulate bending tests according to the in vivo displacements of T1 and L5 measured from bending test radiographs. Differences between in vivo and virtual spinal behaviors during bending tests (left and right) were computed in terms of vertebral rotations and translation. An automated method, driven by a priori knowledge, identified intervertebral stiffnesses in order to reproduce the in vivo spinal behavior.

RESULTS

Because of the identification of intervertebral stiffnesses, differences between in vivo and virtual spinal displacements were drastically reduced (95% of the differences less than +/-3 mm for vertebral translation). Intervertebral stiffness distribution after identification was analyzed. On convex side test, the intervertebral stiffness of the compensatory curves increased in most cases, whereas the major curve became more flexible. Stiffness singularities were found in junctional zones: these specific levels were predominantly flexible, both in torsion and in lateral bending.

CONCLUSION

The identification of in vivo intervertebral stiffness may improve our understanding of scoliotic spine and the relevance of patient-specific methods for surgical planning.

3D postural balance with regard to gravity line: an evaluation in the transversal plane on 93 patients and 23 asymptomatic volunteers

Relevance of posture assessment has been reported in case of spine disorders. This study explores the interest in quantifying posture using 3D reconstruction from biplanar X-rays in free standing position and a force plate. 93 patients consulting for spine disorders were divided ('3D deformity', 'sagittal imbalance' and 'mild deformity') and compared with 23 asymptomatic volunteers. Registration of the gravity line (GL) in reconstruction yielded transversal position of the center of acoustic meati (CAM) T1, T4, T9, L3, S1 and hip axis (HA) with regard to GL. Transversal position of CAM and L3 appeared as relevant parameters to discriminate patients from volunteers. Sagittal inclination of the axis linking the CAM to HA was correlated with position of the CAM to GL (r = 0.92 for patients). In conclusion, observing posture in 3D with regard to GL provides clinical relevant information. CAM-HA inclination may improve postural evaluation without force plate.

3D reconstruction of a patient-specific surface model of the proximal femur from calibrated x-ray radiographs: a validation study

Twenty-three femurs (one plastic bone and twenty-two cadaver bones) with both nonpathologic and pathologic cases were considered to validate a statistical shape model based technique for three-dimensional (3D) reconstruction of a patient-specific surface model from calibrated x-ray radiographs. The 3D reconstruction technique is based on an iterative nonrigid registration of the features extracted from a statistically instantiated 3D surface model to those interactively identified from the radiographs. The surface models reconstructed from the radiographs were compared to the associated ground truths derived either from a 3D CT-scan reconstruction method or from a 3D laser-scan reconstruction method and an average error distance of 0.95 mm were found. Compared to the existing works, our approach has the advantage of seamlessly handling both nonpathologic and pathologic cases even when the statistical shape model that we used was constructed from surface models of nonpathologic bones.