Biomedical subjects

D Mitton

Publications and source records attributed to D Mitton.

At least 19 recordsLinked to original sources

PubMed2007

Effects of gamma irradiation on mechanical properties of defatted trabecular bone allografts assessed by speed-of-sound measurement.

New sterilization methods for human bone allografts may lead to alterations in bone mechanical properties, which strongly influence short- and medium-term outcomes. In many sterilization procedures, bone allografts are subjected to gamma irradiation, usually with 25 KGy, after treatment and packaging. We used speed-of-sound (SOS) measurements to evaluate the effects of gamma irradiation on bone. All bone specimens were subjected to the same microbial inactivation procedure. They were then separated into three groups, of which one was treated and not irradiated and two were exposed to 10 and 25 KGy of gamma radiation, respectively. SOS was measured using high- and low-frequency ultrasound beams in each orthogonal direction. SOS and Young modulus were altered significantly in the three groups, compared to native untreated bone. Exposure to 10 or 25 KGy had no noticeable effect on the study variables. The impact of irradiation was small compared to the effects of physical or chemical defatting. Reducing the radiation dose used in everyday practice failed to improve graft mechanical properties in this study.

Acoustics↗

PubMed2006

Apparent Young's modulus of human radius using inverse finite-element method.

The ability to assess the elastic and failure properties of cortical bone at the radial diaphysis has a clinical importance. A new generation of quantitative ultrasound (QUS) devices and peripheral quantitative computed tomography (p-QCT) has been developed to assess non-invasively bone material and structural properties at the distal radius. This anatomical site is characterized by a thin cortical thickness that complicates traditional mechanical testing methods on specimens. Until now, mechanical properties of cortical bone at distal radius (e.g., elastic modulus, yield stress and strain) remain rarely studied probably due to experimental difficulties. The present study introduces an inverse finite-element method strategy to measure the elastic modulus and yield properties of human cortical specimens of the radial diaphysis. Twenty millimeter-thick portions of diaphysis were cut from 40 human radii (ages 45-90) for biomechanical test. Subsequently the same portion was modeled in order to obtain a specimen-specific three dimensional finite-element model (3D-FEM). Longitudinal elastic constants at the apparent level and stress characterizations were performed by coupling mechanical parameters with isotropic linear-elastic simulations. The results indicated that the mean apparent Young's modulus for radial cortical bone was 16 GPa (SD 1.8) and the yield stress was 153 MPa (SD 33). Breaking load was 12,946 N (SD 3644), cortical thickness 2.9 mm (SD 0.6), structural effective strain at the yield (epsilon(y)=0.0097) and failure (epsilon(u)=0.0154) load were also calculated. The 3D-FEM strategy described here may help to investigate bone mechanical properties when some difficulties arise from machining mechanical sample.

Aged↗

PubMed2006

Volumetric quantitative computed tomography of the proximal femur: relationships linking geometric and densitometric variables to bone strength. Role for compact bone.

INTRODUCTION: In assessing cervical fractures of the proximal femur, this in vitro quantitative computed tomography (QCT) study had three objectives: to compare QCT to dual-energy X-ray absorptiometry (DXA) for predicting the failure load of the proximal femur, to compare the contributions of density and geometry to bone failure load, and to compare the contributions of cortical and trabecular bone to bone failure load. A novel three-dimensional (3D) analysis tool [medical image analysis framework (MIAF-Femur)] was used to analyze QCT scans. METHODS: The proximal ends of 28 excised femurs were studied (1) using QCT to separately measure bone mineral density (BMD) and geometric variables of trabecular and cortical bone, (2) using mechanical tests to failure in a stance configuration, and (3) using DXA to measure BMD. The variables were described with mean, standard deviation, and range. Correlation matrix and multivariate linear models were computed. RESULTS: Among correlations, cortical thicknesses of the femoral neck were significantly correlated with femoral failure load, especially of the inferoanterior quadrant (r2=0.41; p<0.001), as was cortical volume at the "extended neck" (r2=0.41; p<0.001). Femoral failure load variance was best explained by a combination of QCT variables. Combining densitometric and geometric variables measured by QCT explained 76% of femoral failure load variance compared with 69% with the DXA model. Geometric variables (measured by QCT) explained 43% of femoral failure load variance compared with 72% for densitometric variables (measured by QCT). A model including only trabecular variables explained 52% of femoral failure load variance compared with 59% for a model including only cortical variables. CONCLUSION: The QCT-MIAF reported here provides analysis of both geometric and densitometric variables characterizing cortical and trabecular bone. Confirmation of our results in an independent sample would suggest that QCT may better explain failure load variance for cervical fracture than the gold standard DXA-provided BMD.

Absorptiometry, Photon↗

PubMed2006

Biomechanics of the deltoideus.

The objective of this study was to determine the direction of the migration engendered by the middle deltoideus on the upper end of the humerus. Eleven patients suffering from shoulder pathology underwent an MRI examination (3 mm thick slices). From these MRI slices, 3D reconstructions were obtained for each patient by using a manual data capture system (SliceOmatic((R))). From this geometry, a mechanical model of the deltoideus was produced, taking into account the contacts between the latter and the following anatomical parts: supraspinatus, infraspinatus and humeral head. For the 11 shoulders, we have obtained a deltoideus showing a global resultant oriented upwards. There was, however, a component oriented downwards (at the level of the humeral head), its intensity being 40-80% less than the component oriented upwards (at the level of the deltoideus V). It is important to note that this study is valid only in the initial degrees of lateral elevation. The deltoideus is an elevator muscle of the humeral head in the glenoid, presenting nevertheless a component oriented downwards. The deltoideus would, therefore, intervene to recenter the shoulder during an abduction movement.

Adult↗

PubMed2006

3D reconstruction of the pelvis from bi-planar radiography.

3D personalized models are more and more requested for clinical and biomechanical studies. Techniques based on bi-planar X-rays present the advantage of a low radiation dose for the patient. However, up to now, such techniques have shown limited accuracy in the case of pelvis reconstruction. This study proposes and validates a method providing accurate 3D personalized model of the pelvis from bi-planar X-rays. The algorithm is based on the fast computation of an initial solution followed by local deformations based on 2D anatomical points and contours that are digitized in both radiographs. Results were close to CT-scan reconstructions (mean difference 1.6 mm and differences under 4.3 mm for 95% of the points). Moreover, 3D morphometry of the pelvis could be obtained with an accuracy of 5%. This technique provides 3D patient specific model with a low radiation dose.

Aged↗

PubMed2005

[Evaluation of the intervertebral disc spaces with a low dose radiographic system].

PURPOSE: EOS is a new low dose radiographic system based on micro-pattern gaseous detector technology. The purpose was to compare the value of EOS and MRI in the evaluation of degenerative intervertebral disc disease. METHODS AND MATERIALS: Thirty one fresh lumbar discs were studied with EOS, MRI, and discography. Finally, the discs were dissected for macroscopy. They were graded according to their degenerative level using each imaging modality. Osteophytes, herniations, calcifications, loss of disc height, discographic tears or ligamentous ossification were recorded as anomalies. Morphometric data were measured from the cadaveric sections and low-dose radiographs. RESULTS: Thirty nine percent of the discs were narrowed, with a high correlation between EOS and MRI. Anterior and posterior disc margins were respectively depicted in 22% and 64% of cases with EOS vs 84% and 97% with MRI. MRI showed a disc herniation in 9 cases. The correlation between EOS and MRI was poor for the analysis of anterior and posterior disc margins, and disc herniation. Modic 2 abnormalities were present in 19% of disc levels at MRI. Osteophytes were visible in 65% of disc levels with EOS. The density of the disc space was homogeneous in 65% of cases. In the remaining cases, intradiscal calcifications were detected with EOS and confirmed at macroscopy. CONCLUSION: The EOS low dose images allow a good characterisation of disc abnormalities. Especially, intervertebral disc height, density variations and finer bony details (osteophytes) were detected with high confidence. EOS is a promising new low dose radiographic method for spine imaging.

Aged↗

PubMed2005

Finite element simulation of spinal deformities correction by in situ contouring technique.

Biomechanical models have been proposed in order to simulate the surgical correction of spinal deformities. With these models, different surgical correction techniques have been examined: distraction and rod rotation. The purpose of this study was to simulate another surgical correction technique: the in situ contouring technique. In this way, a comprehensive three-dimensional Finite Element (FE) model with patient-specific geometry and patient-specific mechanical properties was used. The simulation of the surgery took into account elasto-plastic behavior of the rod and multiple moments loading and unloading representing the surgical maneuvers. The simulations of two clinical cases of hyperkyphosis and scoliosis were coherent with the surgeon's experience. Moreover, the results of simulation were compared to post-operative 3D measurements. The mean differences were under 5 degrees for vertebral rotations and 5 mm for spinal lines. These simulations open the way for future predictive tools for surgical planning.

Adult↗

PubMed2004

Three-dimensional X-ray absorptiometry (3D-XA): a method for reconstruction of human bones using a dual X-ray absorptiometry device.

Three-dimensional accurate evaluation of the geometry of the proximal femur may be helpful for hip fracture risk evaluation. The purpose of this study was to apply and validate a stereo-radiographic 3D reconstruction method of the proximal femur, using contours identification from biplanar DXA images. Twenty-five excised human proximal femurs were investigated using a standard DXA unit. Three-dimensional personalized models were reconstructed using a dedicated non-stereo corresponding contours (NSCC) algorithm. Three-dimensional CT-scan reconstructions obtained on a clinical CT-scan unit were defined as geometric references for the comparison protocol, in order to assess accuracy and reproducibility of the 3D stereo-radiographic reconstructions. The precision of a set of 3D geometric parameters (femoral-neck axis length, mid-neck cross-section area, neck-shaft angle), obtained from stereo-radiographic models was also evaluated. This study shows that the NSCC method may be applied to obtain 3D reconstruction from biplanar DXA acquisitions. Applied to the proximal femur, this method showed good accuracy as compared with high-resolution personalized CT-scan models (mean error = 0.8 mm). Moreover, precision study for the set of 3D parameters yielded coefficients of variation lower than 5%. This is the first study providing 3D geometric parameters from standard 2D DXA images using the NSCC method. It has good accuracy and reproducibility in the present study on cadaveric femurs. In vivo prospective studies are needed to evaluate its discriminating potential on hip fracture risk prediction.

Absorptiometry, Photon↗

PubMed2004

Rheumatology patient preferences for timing and location of out-patient clinics.

OBJECTIVES: To determine the preferences of rheumatology patients for the time and location of their out-patient appointments. METHODS: All patients attending the rheumatology out-patient services at Dudley Group of Hospitals NHS Trust over a 2-week period were asked to complete a purpose-designed, scannable, previously piloted, self-administered questionnaire. RESULTS: Four hundred and nineteen patients completed questionnaires (response rate 87%). Age ranged from 16 to 92 yr; 38% of responders were over 65 yr, 72% were female, 57% had an inflammatory arthritis, 20% had a connective tissue disease, 8% had degenerative joint disease and 15% had another diagnosis; 29% were employed, 51% retired and 20% unemployed. Fewer than 1% of patients would like to be seen at community general practice centres (99.3% would prefer a hospital site). Proximity to their home was the main determinant of hospital choice. Monday was the most popular day for appointments, and days from Tuesday to Friday received equal rankings. Only 0.5% of patients would choose a weekend clinic. Fifty-eight per cent of patients would prefer morning appointments, 24% afternoon appointments and 2% evening appointments; 16% did not mind. Only being employed predicted out-of-hours preference. CONCLUSIONS: In this predominantly suburban, industrialized area, rheumatology out-patients prefer to be seen in the hospital rather than primary care environment, ideally close to their home, with appointments in the morning and on a weekday. These results may be generalizable to other districts and other chronic disease states, but we suggest that similar surveys become part of routine service provision and inform current and future planning.

Adolescent↗

PubMed2004

Three-dimensional rotations of human three-joint fingers: an optoelectronic measurement. Preliminary results.

Longitudinal axial rotations of phalanges during flexion motions of digits have scarcely been analyzed with current anatomical or radiological methods. Recent optoelectronic systems were developed for three-dimensional (3D) kinematic analysis of human motion. These systems have the advantages of being non-invasive and non-irradiating. The current study was based on the VICON optoelectronic system. A validation of the protocol was made among a sample of volunteers for further direct clinical applications. An experimental protocol was set up with adaptations to the requirements of finger analyses (multiple infrared markers inside small-sized capture volumes). The set-up and the protocol details are described. Kinematic studies consisted in recording the movements of the right hand of six volunteers (free from any visible pathology). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) flexion angles ranged from 78 degrees to 118 degrees, 72 degrees to 119 degrees and 9 degrees to 66 degrees respectively. Lateral angles ranged from 5 degrees to 39 degrees (MCP), 4 degrees to 39 degrees (PIP) and 4 degrees to 30 degrees (DIP). Mean longitudinal axial rotations of MCP, PIP and DIP joints ranged from 11 degrees pronation to 26 degrees supination. The index finger was in a global pronation position (five of the six specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in four of the six specimens). An experimental protocol using an optoelectronic system (VICON) has been developed for a kinematic analysis of three-joint finger. A global measure study should be initiated among a wider sample of adults. A database should be created with direct clinical applications. Patients' kinematic deficits could be graded either for standard movements (flexion/extension and abduction/adduction) or for longitudinal axial rotations.

Adult↗

PubMed2004

Rotations of three-joint fingers: a radiological study.

The aim of the current study was to test a protocol of quantification of phalangeal three-dimensional (3D) rotations during flexion of three-joint digits. Three-dimensional-specific software was developed to analyze CT reconstruction images. A protocol was carried out with six fresh-frozen upper limbs from human cadavers free from any visible pathology (three females, three males). CT millimetric slices were done for reconstruction of hand bone units. Orthonormal coordinate systems of inertia were calculated for each unit. Three-dimensional phalangeal rotations were estimated between two static positions (fingers in extension and in a fist position). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Mean longitudinal axial rotations of metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints ranged from 14 degrees pronation to 19 degrees supination. The index finger was in a global pronation position (4/6 specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in 2/6 specimens). MCP, PIP and DIP flexion angles ranged respectively from 71 degrees to 89 degrees, 65 degrees to 87 degrees, and 41degrees to 77 degrees. Lateral angles ranged from 19 degrees (ulnar angulation) to 23 degrees (radial angulation). The study of phalangeal rotations was possible in spite of a heavy protocol. This protocol could be partially automatated to speed up the analyses. Longitudinal axial rotations could be analyzed, in addition to flexion/extension or abduction/adduction rotations. CT scan reconstructions would be helpful for investigating pathological fingers. Abnormal rotations of digits could be quantified more precisely than during a current clinical examination of the hand.

Aged↗

PubMed2004

Validation of the relative 3D orientation of vertebrae reconstructed by bi-planar radiography.

The three dimensional (3D) reconstruction of the spine can be obtained by stereoradiographic techniques. To be safely used on a routine clinics basis, stereoradiography must provide both accurate vertebral shape and coherent position. Although the accuracy of the reconstructed morphology of the vertebrae is well documented, only few authors studied the accuracy of the vertebral orientation. Therefore, this paper focuses on the evaluation of the orientation accuracy of the reconstructed vertebrae (obtained by non-stereo corresponding point technique) considering either a 178 point vertebral model or a 6 point vertebral model (previously proposed in the literature). Five dried vertebrae were fixed on holders containing four markers each. The 3D reconstruction of both vertebrae and markers were obtained by stereoradiographic techniques. Using least square method matching from one position to another, the relative orientation was computed for the vertebral models (6 or 178 points) and the four markers. These vertebral and holder orientations were compared (considering the holder's one as reference). The repeatability of these relative orientations (vertebrae and holders) was also evaluated. The mean (RMS) orientation error of 178 point vertebral model was 0.6 degrees (0.8 degrees ), for lateral rotation, 0.7 degrees (1.0 degrees ) for sagittal rotation and 1.4 degrees (1.9 degrees ) for axial rotation. The intra-observer repeatability was 0.5 degrees (0.7 degrees ) for lateral rotation, 0.7 degrees (0.8 degrees ) for sagittal rotation and 0.9 degrees (1.2 degrees ) for axial rotation. The orientation was found more accurate and precise when using the 178 point vertebral model than when using the basic 6 point vertebral model. The relative orientation (in post-operative follow-up with respect to the pre-operative examination) of the vertebrae of one scoliotic patient was performed as an example of clinical application. The stereoradiographic method is a reliable 3D quantitative tool to assess the spine deformity, that can be used in clinics for the follow-up of scoliotic patients.

Adult↗

PubMed2004

3D reconstruction of the proximal femur with low-dose digital stereoradiography.

OBJECTIVE: Accurate three-dimensional (3D) geometry of the proximal femur may be helpful for fracture risk evaluation, as well as for planning and assisting surgical procedures. The purpose of this study was to apply and validate a stereoradiographic 3D reconstruction method on the proximal femur from radiographic contours identified on bi-planar radiographs. MATERIALS AND METHODS: Twenty-five excised non-pathologic proximal femurs were investigated using a low-dose digital radiographic device. Three-dimensional personalized models were reconstructed using the Non-Stereo Corresponding Contours (NSCC) algorithm. Three-dimensional CT-scan reconstructions were defined as geometric references for the comparison protocol, in order to assess the accuracy and reproducibility of the personalized 3D stereoradiographic reconstructions. In addition, the reliability of a set of 3D parameters obtained from stereoradiographic models was evaluated. RESULTS: This study demonstrated the validity of the NSCC method when applied to the proximal femur, with good results for accuracy (mean error = 0.7 mm) and reproducibility (Wilcoxon test: p > 0.28). Moreover, a precision study for the set of 3D parameters yielded a coefficient of variation lower than 5%. CONCLUSIONS: Once this approach has been validated in vivo, it should find multiple applications in therapeutic fields (e.g., for surgical planning, computer assisted surgery, etc.), as well as in diagnostic contexts (e.g., equilibrium studies or osteoporosis fracture risk assessment).

Aged↗

PubMed2003

Dynamic stiffness and damping of human intervertebral disc using axial oscillatory displacement under a free mass system.

The aim of this study was to analyse the dynamic response of the human intervertebral disc to vibration in a physiologically relevant frequency spectrum. Eight lumbar intervertebral discs were harvested. After preparation, each sample was subjected to a pre-loading and then dynamic compression (from 5 to 30 Hz). The dynamic compression was applied using an experimental set-up comprising a free weight loading from above and a driving oscillatory displacement from below (closest to the in vivo loading). A viscoelastic model enabled the calculation of stiffness and damping from the transfer function. From 5 Hz to 30 Hz the stiffness values are between 0.19 and 3.66 (MN/m) and the damping values between 32 and 2094 (Ns/m). The mean resonant frequency was found at 8.7 Hz. These dynamic characteristics of the intervertebral disc could be used in a three-dimensional finite elements model of the human body to study its response to vibration in the driving position.

Aged↗

PubMed2003

Explicit calibration method and specific device designed for stereoradiography.

The three-dimensional geometry of the human spine is noteworthy information that can be obtained by stereoradiographic methods. These methods are based on the identification of anatomical structures in several views which are obtained by rotation of a patient standing on a turntable. Calibration algorithms for computer vision or photogrammetry are well documented, but they generally yield calibration devices which are cumbersome for the use in clinical stereoradiography. This paper presents a calibration method adapted to a two-view stereoradiography calibration (frontal and lateral incidences) and based on a simplified geometric modeling of the radiological environment. The a priori knowledge yields four calibration equations related to the vertical and horizontal planes of both views, leading to a specific calibration procedure and device. Moreover this device is attached to the stereoradiographic system (directly integrated on the turntable) in order to facilitate clinical applications. A validation was performed on 26 dried lumbar vertebrae in order to evaluate clinical situation. The mean accuracy of the stereoradiographic reconstruction was 1.2mm.

Aged↗

PubMed2003

Dynamic stiffness and damping of porcine muscle specimens.

The aim of this study was to quantify the mechanical properties of the muscles of the buttock, using dynamic compression (5-->30 Hz). Tests were conducted in vitro on porcine muscles, using a lever arm device, which applied a dynamic load onto cylindrical samples. A two-parameter viscoelastic model allowed the calculation of stiffness and damping of the samples with respect to frequency. The average stiffness curve showed a monotonous increase (5 Hz: 8.5 kN/m-->30 Hz: 347 kN/m). Concerning damping, between 5 and 20 Hz, values were typically inferior to 300 Ns/m, which then increased till 30 Hz (556 Ns/m). The lever arm device may be used to evaluate dynamic properties of other biological tissues also.

Animals↗

PubMed2003

A biplanar reconstruction method based on 2D and 3D contours: application to the distal femur.

A three-dimensional (3D) reconstruction algorithm based on contours identification from biplanar radiographs is presented. It requires, as technical prerequisites, a method to calibrate the biplanar radiographic environment and a surface generic object (anatomic atlas model) representing the structure to be reconstructed. The reconstruction steps consist of: the definition of anatomical regions, the identification of 2D contours associated to these regions, the calculation of 3D contours and projection onto the radiographs, the associations between points of the X-rays contours and points of the projected 3D contours, the optimization of the initial solution and the optimized object deformation to minimize the distance between X-rays contours and projected 3D contours. The evaluation was performed on 8 distal femurs comparing the 3D models obtained to CT-scan reconstructions. Mean error for each distal femur was 1 mm.

Algorithms↗

PubMed2002

Three-dimensional surface rendering reconstruction of scoliotic vertebrae using a non stereo-corresponding points technique.

The medical imaging techniques that allow a three-dimensional (3D) surface rendering reconstruction, which is usually required by the clinician when dealing with scoliotic patients, are computed tomography (CT) and stereoradiography. However, CT cannot provide a 3D rendering of the whole spine because of the high irradiating dose, while the stereoradiographic 3D reconstruction techniques, which use an algorithm derived from the direct linear transformation (DLT), are usually limited in accuracy because of the small number of corresponding anatomical landmarks identifiable on both radiographs. The purpose of the present study is to validate a recent biplanar 3D surface rendering reconstruction technique on scoliotic vertebrae. This technique, called "non stereo-corresponding points" (NSCP), has already been tested on non-pathologic dry cervical vertebrae and frozen lumbar specimens, and the results have proved very encouraging. Since scoliosis is a 3D deformity of the vertebrae and of the global spine, such a technique could be a very useful clinical tool for the diagnostic, follow-up and surgical planning when dealing with scoliotic patients. The validation of the NSCP technique on scoliotic patients was performed on 58 scoliotic vertebrae in 14 patients, by comparison with the CT scan 3D rendering technique. The results of this study show mean errors of 1.5 mm. On the basis of this study, we can conclude that the NSCP 3D reconstruction technique is a definite improvement over existing techniques, and can serve as a useful diagnosis tool in scoliosis. However, the results of the technique still need to be optimized for use in geometrical modeling.

Adolescent↗