Introduction

Stand to sit pelvis kinematics is commonly considered as a rotation around the bicoxofemoral axis. However, abnormal kinematics could occur for patients with musculoskeletal disorders affecting the hip-spine complex. The aim of this study is to perform a quantitative analysis of the stand to sit pelvis kinematics using 3D reconstruction from bi-planar x-rays.

Component placement and the individual's functional posture play key roles in mechanical complications and hip dysfunction after total hip arthroplasty (THA). The challenge is how to measure these. X-rays lack accuracy and CT scans increase radiation dose. A newer imaging modality, EOSTM, acquires low-dose, simultaneous, perpendicular anteroposterior and lateral views while providing a global view of the patient in a functional standing or sitting position, leading to a 3D reconstruction for parameter calculation. The purpose of the present study was to develop an approach using the EOS system to compare patients with good versus poor results after THA and to report our preliminary experiences using this technique.

A total of 35 patients were studied: 17 with good results after THA (G-THA), 18 with poor results (P-THA). The patients were operated on or referred for follow-up to a single expert surgeon, between 2001 and 2011, with a minimum follow-up of at least two years.

Acetabular cup orientation differed significantly between groups. Acetabular version relative to the coronal plane was lower in P-THA (32°±12°) compared to G-THA (40°±9°) (p=0.02). There was a strong trend towards acetabular cup inclination relative to the APP being higher in P-THA (45°±9°, compared to 39°±7°; p=0.07). Proportions of P-THA vs. G-THA patients with cup orientation values higher or lower than 1 SD from the overall mean differed significantly and substantially between groups. All revision cases had a least four values outside 1 SD, including acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset and neck-shaft angle.

This is the first study to our knowledge to provide acetabular, pelvic and femoral parameters for these two groups and the first to provide evidence that a collection of high/low parameters may together contribute to a poor result. The results show the importance of acetabular component placement, in both inclination and version and the importance of looking at individuals, not just groups, to identify potential causes for pain and functional issues. With the EOS system, a large cohort of individuals can be studied in the functional position relatively quickly and at low dose. This could lead to patient-specific guidelines for THA planning and execution.

Accurate and reproducible measurement of three-dimensional shoulder kinematics would contribute to better understanding shoulder mechanics, and therefore to better diagnosing and treating shoulder pathologies. Current techniques of 3D kinematics analysis use external markers (acromial cluster or scapula locator) or medical imaging (MRI or CT-Scan). However those methods present some drawbacks such as skin movements for external markers or cost and irradiation for imaging techniques. The EOS low dose biplanar X-Rays system can be used to track the scapula, humerus and thorax for different arm elevation positions. The aim of this study is to propose a novel method to study scapulo-thoracic kinematics from biplanar X-rays and to assess its reliability during abduction in the scapular plane.

This study is based on the EOS™ system (EOS Imaging, Paris, France), which allows acquisition of 2 calibrated, low dose, orthogonal radiographs with the subject standing at 30 to 40° angle of coronal rotation to the plane of one of the X-ray beams, in order to limit superimposition with the ribcage and spine. Seven abduction positions in the scapular plane were maintained by the subjects for 10 seconds, during X-ray acquisition. Between two positions, the subjects returned at rest position. Arm elevations were approximately 0, 10, 20, 30, 60, 90 and 150° (position 1 to 7). Six subjects were enrolled to perform a reproducibility study based on the 3D reconstructions of 2 experienced observers three times each. For each subject, a personalised 3D reconstruction of the scapula was created. The observer digitises clearly visible anatomical landmarks on both stereoradiographs for each arm position. These landmarks are used to make a first adjustment of a parameterised 3D model of the scapula. This provides a pre-personalised model of the subject's scapula which is then rigidly registered on each pair of X-rays until its retroprojection fits best on the contours that are visible on the X-rays. The thorax coordinate system (CS) was built following the ISB (International Society of Biomechanics) recommendations. The CS associated to the scapula was a glenoid centred CS based on the ellipse which fit on the glenoid rim on the 3D model of scapula. Scapular CS orientation and translation in the thorax CS was calculated following a Y,X,Z angle sequence for each position.

Each 3D reconstruction of the scapula was performed in approximately 30 minutes. The most reproducible rotation was upward/downward rotation (along X axis) with a 95% confidence interval (95% CI) from 2.71° to 3.61°. Internal/external rotation and anterior/posterior tilting were comprised respectively between 5.18° to 8.01° and 5.50° to 7.23° (CI 95%). The most reproducible translation was superior-inferior translation (along Y axis) with a 95% CI from 1.22mm to 2.46mm. Translation along X axis (antero-posterior) and Z axis (medio-lateral) were comprised respectively between 2.49mm to 4.26mm and 2.47mm to 3.30mm (CI 95%).

We presented a new technique for 3D functional quantitative analysis of the scapulo-thoracic joint. This technique can be used with confidence; uncertainty of the measures seems acceptable compared to the literature. Main advantages of this technique are the very low dose irradiation compared to the CT-Scan and the possibility to study arm elevation above 120°.

Introduction: The incidence of contralateral, second hip fractures after a first hip fracture is as high as 20% in the elderly. Femoroplasty using an injectable and resorbable bi-phosphonate loaded bone substitute to prevent controlateral hip fracture may represent a promising preventive therapy. We aimed to evaluate the biomechanical consequences of the femoroplasty using this bone substitute.

Materials and Methods: Twelve paired human cadaveric femora from donors with a mean age of 86 years (7 women and 6 men) were randomly assigned for femoroplasty and biomechanically tested for fracture load against their native contralateral control. Anterior–posterior and lateral radiographs and DXAscan’s were made before injection. Femoroplasty were performed under fluoroscopic guidance with an injectable and resorbable bi-phosphonate loaded bone substitute. All femurs were fractured by simulating a fall on the greater trochanter by an independent observer.

Results: Mean T-score of the tested femur were −3. Bone density was comparable for each pair of femur. All the observed fractures were Kyle II throchanteric fractures. Mean fracture load was 2786 Newton in the femoroplasty group (group F) versus 2116 Newton in the control group (group C) (p< 0.001). Fracture loads were always higher in the group F: mean 41.6% (mini: 1.2%/maxi:102.1%). Effect of femoroplasty was significantly superior for women and also correlated to initial bone density (p< 0.0001).

Discussion:According to our results, femoroplasty with an injectable and resorbable bi-phosphonate loaded bone substitute can provide significant biomechanical reinforcement of the proximal femur to prevent controlateral fracture.

Mechanical tests that have been carried out to validate finite-element models predicting vertebral strength concern vertebral bodies under axial compression. But in standing position gravity loads can induce a flexion component, especially for the last thoracic and first lumbar vertebrae. The aim of the study was to evaluate the strength of complete vertebrae under anterior compression.

15 isolated vertebrae T11-L2 (four women, one man, 88 ± 14 years old) were tested to failure. The load was applied at the one third of the vertebral body depth through a ball constrained in a hole. It was homogeneously distributed on the vertebral endplate through a polymetylmetacrylate (PMMA) layer which completely fills the concavity. The solid composed by the PMMA layer and the steel plate containing the hole for the ball was called “upper plate”. Its 3D orientation was assessed using the Polaris® motion capture system (accuracy: 0.6 mm, 0.6°) thanks to tripods. Before testing, the position of the marker-frames was assessed using 3D reconstructions (obtained by bi-planar X-rays) to express all the movements relatively to the vertebral frame.

The outcome data was the position of the upper plate. The load was calculated from the measurement of the vertical load (using the testing machine sensor) and the orientation of the upper plate (using the Polaris® system).

The mean flexion of the upper-plate is equal to 1° (± 0.7°) before the vertebra collapses. As this value is weak, the optoelectronic assessment could be removed during the test if the initial 3D orientation of the upper plate relatively to the vertebral frame is assessed.

This protocol allowed collecting with accuracy all the data necessary to validate models.

Introduction: Mechanical complications following lumbar fixation are due to the combination of various factors related to morphology, pathology, and surgery. The aim of this study was to provide a patient-specific Finite Element Model of the lumbar spine for the simulation of surgical strategies, and to use it as a predictive tool aiming to detect and reduce preoperatively the risks of mechanical complications.

Materials & Methods: A pre-existing 3D personalized FEM of the lumbar spine was used. Posterior implants and main degenerative pathologies were also modelled.

After in vitro validation based on 24 specimens and 4 different instrumentations, the model was used to simulate real cases. Applied loads were based on patient characteristics (weight, imbalance). Simulation results included mechanical stresses in the discs and within the implants.

Clinical consistency of the simulations was tested through the gathering of clinical data for 66 patients instrumented with lumbo-sacral rigid screw-rod systems. Two subsets were considered: “mechanical successes” (53), and “mechanical failures” (13, including 11 screw breakage and 2 screw loosening). Blind comparison was then performed between these observed clinical outcomes and numerical simulations results.

Results & Discussion: Among the 66 patients, simulation results highlighted specific behaviours for 9 patients for which mechanical loads on implants were significantly higher. All of these 9 patients were actual “mechanical failures”. None of the actual “mechanical successes” were associated with “abnormal” simulation results.

Conclusion: This is the first time finite element simulations helped predicting 9 failures out of 13 observed among a total of 66 patients. This is a promising step towards the possibility to use FEM as a clinically relevant simulation tool for surgery planning.

Précis: Using full length x-rays and force plate technology, the purpose was first to investigate the relationship between the gravity line and spino-pelvic parameters on asymptomatic adult volunteers and then to analyse age related changes. Trunk inclination and pelvic parameters appears as the two key-factors of the GL location; with age the GL location regarding the heels does not change but trunk global inclination shifts forward, pelvic tilt increases, and the pelvis shifts toward the heels.

Introduction: Although work by several authors has placed emphasis on global balance in the setting of spinal deformity, the relationship of spino-pelvic parameters related to this concept remains poorly defined. Using the force plate device and radiographic measurement, this study aimed to define the relationship between these parameters and the location of the gravity line (GL) in asymptomatic adult population.

Materials and Methods: 75 asymptomatic adult volunteers were recruited and subdivided by age (18–40, 41–60, > 61). Full-length free-standing AP and lateral radiographs were obtained with simultaneous assessment of the force plate gravity line (GL) location. The latter was projected on each x-ray to compute distance between anatomical components and GL and correlate its location with radiological parameters. Age related changes were investigated using ANOVA with Bonfer-roni-Dunn Post-Hoc test.

Results: Radiographic measurements revealed strong correlations between trunk global inclination and distance from S1 to the GL (r=0.7), sacral slope and pelvic incidence (r=0.78), distance from the bi-femoral head axis to the GL and S1 to the GL (r=0.73), and sacral slope and lordosis (r=0.89). With advancing age, the GL location with respect to the heels does not change and a global spino-pelvic regulatory mechanism appears to maintain this posture: trunk global inclination shifts forward, pelvic tilt increases, and the pelvis shifts toward the heels, increasing its distance from the GL.

Discussion: his study demonstrates the importance of pelvic parameters and trunk inclination in the regulation of the GL location. The relationship between the gravity line, pelvic parameters, and overall spinal alignment may emerge as essential in the evaluation of spinal deformity. Further investigation in this field may lead to a formula of balance that can assist in optimal planning of corrective procedures for spinal deformity.

Purpose of the study: The objective of this work was to achieve a whole-body 3D study of the bone and joint system in the upright position using the lowest radiation dose possible. Radiation doses can be considerable when acquiring 3D images using computed tomographic millimetric sections which in addition are acquired uniquely in the reclining position and thus limited to a specific region.

Material and methods: Using a gas detector which transforms x-ray protons into electrons (G. Charpak) we constructed a device which enables acquisition of high-quality anteroposterior and lateral whole-body radiographic images with exposure to radiation doses 8 to 10-fold less than classical 2D x-rays. A 3D reconstruction of the entire skeleton was obtained from these two initial images.

Results: The 3D reconstructions were validated and compared with those obtained with computed tomography. The results were concordant and revealed least equivalent to if not better reliability. The advantage was to enable study in the functional upright position an to study weight-bearing joints of the lower-limbs, pelvis, and spine. In addition, radiation exposure for the 3D reconstructions was reduced 800 to 1000 times compared with computed tomography. More than 150 examinations have been performed and validated in patients with diverse pathological conditions as well as in normal control adults and children.

Discussion: There is a very wide potential field of application for this technique in orthopedics, both for 3D analysis of joint deformations and their impact on the whole body, and for therapeutic follow-up, particularly after prosthetic or corrective surgery. For example, the horizontal plane which is very difficult to image and represent mentally for spinal surgery can be clearly planned and controlled. This new imaging technique offers perspectives for intraoperative navigation and for bone mineral density measurements. The double-energy methodology enables short-term evaluation of fracture risk due to osteoporosis of the spine and limbs or pelvis.

Purpose of the study: The mean rotation center (MRC) characterizes the movement of two solids in relation to each other. This parameter has been proposed for the cervical spine to describe the motion of vertebral segments. Two lateral views (flexion and extension) are required to draw the necessary lines and establish the centers of rotation. The process is rigorous but time-consuming. We validated a computerized analysis system for automatic determination of the cervical MRC and study the localizations observed in healthy subjects.

Material and methods: Validation of the computerized system. Accurate angle measurements: nine cervical spines were harvested from anatomic specimens. A K-wire was inserted sagittally into each vertebra. Lateral images were obtain in flexion and extension. The measurements of mobility made by the software were compared with manual measurements. Reproducibility tests (intra- and interobserver): six pairs of flexion and extension views in healthy subjects. Two different observers made fifteen successive measurements of each MRC for each spinal segment. Frequently encountered positions of the MRC in healthy subjects: stress films were obtained in 51 healthy subjects aged 18–40 years. For each spinal segment, the MCR was determined with the computerized system.

Results: Accuracy of the angle measurements: the precision was 1.4° for a 95% interval of confidence. Reproducibility: variability of the position in X and Y for the MRC (expressed in percent of the size of the vertebral body) was: 19.6 and 24.5 for C2–C3; 112 and 15.3 for C3–C4; 7.7 and 9.4 for C4–C5; 9.1 and 9.4 for C5–C6; 13.1 and 11.8 for C6–C7. Positions frequently encountered in healthy subjects: the most frequent position of the MRC varied from one segment to another. There was a frequent position for each segment. These frequent positions were situated in the posterosuperior quadrant of the subjacent vertebra for C2–C3, C3–C4, C4–C5, and C5–C6. For C6–C7, the frequent positions for MRC were at the level of the intervertebral space, behind the center of the disc.

Discussion: The software tested here appeared to provide good measurements for cervical spine from C3 to C7. At these levels, the measures were accurate and reproducible, as were the coordinates for the MCR of each segment. The frequent positions of the MRC found in this study are the same as reported by other authors. This method is easy to apply in routine practice.

Purpose of the study: The issue of patellar kinematics remains a difficult problem for patellar resurfacing during conventional or computer-assisted knee surgery, yet adequate knowledge is required for appropriate orientation of the patellar cut and insert positioning. The purpose of this study was to develop a non-invasive tool for in vivo kinematic analysis of the patellar tract and to compare results with the gold-standard invasive method.

Material and methods: A special experimental set-up designed for this study enabled experimental simulation of load-bearing flexion-extension cycles of the knee joint. Range of motion from 0 to 102° was imposed with a computer-controlled motor. The analysis was conduced on 14 complete lower limb cadaver specimens. Patellar kinematics was analyzed for each knee simultaneously with two systems: a non-invasive method using a low-dose stereoradiographic scan linked to a 3D reconstruction software; and the reference system using tripodes implanted on the patella and radio-opaque spherical markers. Six degrees of freedom were considered: three translations and three rotations. Sequential kinematic recordings were made by calculating the position of a patellar landmark in relation to a femoral landmark.

Results: The mean difference between the results obtained with the two systems was less than 1 mm for anteroposterior and vertical translations, greater for mediolateral translations. It was less than 2° for patellar flexion-extension, to the order of the motion itself for abduction-adduction, and to the order of 5° for horizontal tilt.

Discussion and conclusion: The non-invasive technique proposed here appears to be reliable for patellar translations and flexion, but need further improvement for tilt and adduction-abduction. This is particularly true for the 45° to 90° range of motion because of the difficult problem of determining the contours of the patella. Further developments for this tool are under way.

Aims: This study compared in vivo kinematics of a posterior stabilized TKA inserted either with a fixed (FBC) or with a mobile bearing component (MBC). Methods: Ten patients with unilateral previously defined TKA were selected among 150 TKA performed in 2000 by a single surgeon according to the following criteria: primary TKA because of osteoarthritis, controlateral knee free of clinical symptoms, patient < 80, TKA flexion > 90°, knee IKS score > 80/100. Ten TKA (10 patients) were selected differing only by the adjunction of the mobile bearing (5 MBC and 5 FBC). The range of the 3 knee rotations (flexion, axial rotation, varus-valgus) were assessed by means of a 6-degree freedom electromagnetic goniometer during: level walking, rising from a chair, non weight-bearing flexion. Non-parametric tests compared motions between TKA and contro-lateral knee and between MBC and FBC. Results: FBC had a better mobility that MBC in valgus-varus, which was related to a larger frontal laxity. According to the increase in frontal laxity, FBC demonstrated better axial rotations that MBC in non-weight-bearing (NS). However, better ranges of axial rotation were recorded in MBC in weight-bearing (p< 0.05) (MBC axial rotation exceeded by 10° the motions of FBC). In patients with MBC, there was no difference in range of motion between the TKA and the controlateral healthy knee. In the FBC group the range of axial rotation was lower in the TKA by comparing with the controlateral knee (p< 0.05). Conclusion: With a unique prosthetic design our study suggests the role of MBC to reproduce a physiological range of axial rotation in weight-bearing. The MBC better reproduced knee kinematics Shoulder instability

Purpose: Scoliosis is a three-dimensional deformation of the spinal column. Modern surgical techniques have attempted to address this 3D component of the problem but pre- and postoperative measurements lack precision. A solution is stereoradiographic 3D reconstruction providing 1.1 mm precision for vertebral shape and 1.4° precision for axial rotation.

Material and methods: Ten patients (seven adolescents and three adults) with idiopathic scoliosis (mean 56°, range 36°–78°) were treated with an in situ arching method. A calibrated teleradiogram (AP and lateral view) was obtained before and after surgery. The spinal columns were reconstructed by stereoradiography. Six rotation angles were measured in the three planes for each vertebra and each intervertebral space, taking into account the curvatures and their apical and junctional zones.

Results: Preoperatively, for thoracic scoliosis, measurements were: mean vertebral axial rotation (VAR) measured at the apex = 20°; mean lateral axial rotation (LAR) of the junctional zones = 30°; mean intervertebral rotation (IVR) = 10°. Depending on the curvatures, in situ arching yielded a 52–60% correction of the VAR at the apex, and 78–79% correction of the junctional zones. VLR of the junctional zoenes was improved 58–74%. Intervertebral sagittal rotation (ISR) at the summit (kyphosis) was improved 5.5° on the average.

Discussion: Unlike computed tomoraphy where scans are obtained in the supine position, three-dimensional reconstruction of the spinal column enables a precise analysis of the loaded spine. Improvement was significant in the frontal plane with 18.3° and 21.4° improvement of the VLR for the thoracic and thoracolumbar junctional zones respectively, compared with the rod rotation where the peroperative stereophotogram showed a 9.6° and 8.6° gain respectively. There was a real improvement in VAR, differing from the literature where the rotation of the rod appears to be less pronounced.

Conclusion: Three-dimensional reconstruction of the spinal column enables a segmentary analysis of scoliosis deformations. In addition, by enabling a view of the spinal column in all directions, angle measurements can be made with precision allowing repeated measurements and comparisons. This technique demonstrated the efficacy of in situ arching in improving vertebral rotation.