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Biomedical subjects

A Cappello

Publications and source records attributed to A Cappello.

At least 19 recordsLinked to original sources
PubMed2001

HIDE: a new hybrid environment for the design of custom-made hip prosthesis.

This technical note describes a new software environment (HIPCOM design environment, HIDE) for the design of custom-made total hip replacements. These devices are frequently designed using general-purpose mechanical computer-aided design (CAD) programs using a set of bone contours extracted from the computer tomography (CT) images as anatomical reference. On the contrary, the HIDE system was developed to let the operator directly design the stem shape onto the CT images in a single-step operation. The operator can directly import CT data in DICOM format or use special functions to reconvert to a digital stack, the CT images printed on a radiological film. Once the stack of CT images is loaded, the operator can design the implant shape by imposing control sections directly on the CT images. The interpolation of these control sections produces the basic 3D shape of the custom-made stem. The shape is then exported to the CAD-computer-aided manufacturing (CAM) program to refine the design and to generate the part program to manufacture the implant with a CNC tooling machine. Using HIDE, the duration of design steps it affected was reduced by more than 50% with respect to the standard method in use at the manufacturer site. HIDE also improved the accuracy and the repeatability of the whole procedure. The learning curve became flat after only ten cases. These good results were achieved because of the integration of the vectorial description of the prosthetic component with the raster description of the CT data that allowed the designer to use all details available in the CT images.

Computer-Aided Design↗
PubMed2001

Border-tracing algorithm implementation for the femoral geometry reconstruction.

In some orthopaedic applications such as the design of custom-made hip prostheses, reconstruction of the bone morphology is a fundamental step. Different methods are available to extract the geometry of the femoral medullary canal from computed tomography (CT) images. In this research, an automatic procedure (border-tracing method) for the extraction of bone contours was implemented and validated. A composite replica of the human femur was scanned and the CT images processed using three different methods, a manual procedure; the border-tracing algorithm; and a threshold-based method. The resulting contours were used to estimate the accuracy of the implemented procedure. The two software techniques were more accurate than the manual procedure. Then, these two procedures were applied to an in vivo CT data set in order to determine to most critical region for repeatability. Only for the images located in this region, the repeatability measurement was carried out for six in vivo CT data sets to evaluate the inter-femur repeatability. The border-tracing method was found to achieve the highest repeatability.

Algorithms↗
PubMed2000

Effects of hip joint centre mislocation on gait analysis results.

Methods to determine the hip joint centre (HJC) location are necessary in gait analysis. It has been demonstrated that the methods proposed in the literature involve large mislocation errors. The choice should be made according to the extent by which HJC location errors distort the estimates of angles and resultant moments at the hip and knee joints. This study aimed at quantifying how mislocation errors propagate to these gait analysis results. Angles and moments at the hip and knee joint were calculated for five able-bodied subjects during level walking. The nominal position of the HJC was determined as the position of the pivot point of a 3D movement of the thigh relative to the pelvis. Angles and moments were then re-calculated after having added to HJC co-ordinates errors in the range of +/-30 mm. Angles and moments at both hip and knee joints were affected by HJC mislocation. The hip moments showed the largest propagation error: a 30 mm HJC anterior mislocation resulted in a propagated error into flexion/extension component of about -22%. The hip abduction/adduction moment was found the second largest affected quantity: a 30 mm lateral HJC mislocation produced a propagated error of about -15%. Finally, a 30 mm posterior HJC mislocation produced a delay of the flexion-to-extension timing in the order of 25% of the stride duration. HJC estimation methods with minimum antero-posterior error should therefore be preferred.

Adult↗
PubMed2000

An improved technique for the extraction of stochastic parameters from stabilograms.

An improved characterization of the dynamics of postural sway can provide a better understanding about the functional organization of the postural control system as well as a more robust tool for postural pattern recognition. To this aim, a novel parameterization was applied to the stabilogram diffusion analysis formerly proposed by Collins and De Luca [Collins JJ, De Luca CJ. Open-loop and closed-loop control of posture: a random-walk analysis of center-of-pressure trajectories. Exp Brain Res 1993;95:308-18] that considered the act of maintaining posture as a stochastic process. The main purpose of the present technique was to overcome some drawbacks of the model presented by Collins and De Luca that may restrain its potential application in clinical practice. The approach uses a unique non-linear model to describe the center of pressure (COP) dynamics that reduces the number of parameters and decreases their intra-subject variability; consequently, fewer trials are required to perform reliable estimates of stochastic parameters and this is of particular importance for subjects that cannot afford many repeated measurements because of age or pathology. Four new statistical mechanics parameters (NSMP) were computed on the log-log stabilogram diffusion plots and their estimates were compared in terms of reliability and sensitivity to the visual conditions with: (1) a minimal set of four summary statistic scores (SSS); and (2) the six statistical mechanics parameters (SMP) proposed by Collins and De Luca. All four NSMP showed at least a fair-to-good reliability (intraclass correlation coefficient, ICC>0.49) while SMP (ICC>0.20) showed some poor reliability. A better overall reliability was also observed with respect to SSS. Moreover, only NSMP had a similar score for eyes open and eyes closed conditions. Three out of four NSMP were also significantly sensitive to eyes open or closed conditions (P<0.001) while only three out of six SMP were sensitive to operating conditions (P<0.01).

Humans↗
PubMed2000

A novel transducer for the measurement of cement-prosthesis interface forces in cemented orthopaedic devices.

When a cemented orthopaedic device is being investigated there is a need to estimate the forces at the cement-prosthesis interface. For this reason a miniature transducer was developed that could be included inside the surface of most prostheses. A load cell (based on a piezoelectric sensor) and the required accessories and amplification were custom designed and built. The present work describes the validation that was performed on the piezo sensors alone, when mounted on a simplified structure, and when applied to a hip stem.Linearity, repeatability, reproducibility, and sensibility to shear and axial eccentric loads were tested, yielding satisfactory results. The repeatability on the same sensor was found to be good while reproducibility between sensors was lower. Thus, each sensor was calibrated separately with a second order relationship. Sensitivity to shear and eccentric loads was very low. The overall accuracy of the load cell (including non-linearity, and signal drift) was of the order of about 1%.A hip stem instrumented with four such sensors was successfully implanted in a composite femur, yielding meaningful readouts.Thus, this type of sensor can readily be used to assess the cement-prosthesis interface forces in cemented devices.

Biomechanical Phenomena↗
PubMed2000

Color doppler ultrasonography imaging to guide transluminal angioplasty of venous stenosis.

BACKGROUND: The objective of access surveillance is the early recognition of dysfunction in order to be able to correct the stenosis by angioplasty or surgery before access thrombosis occurs. The advent of color Doppler imaging has enabled studies of color Doppler ultrasonography (CDU) for the guidance of percutaneous transluminal angioplasty (PTA). The aim of the present study was to investigate whether color Doppler imaging alone can be safely and effectively used to diagnose vascular graft access stenoses and guide subsequent PTA. METHODS: Using the ultrasound velocity dilution method, we measured access blood flow (Qa) during the first hour of hemodialysis every month in patients with grafts as vascular access. When the decrease in Qa from the baseline value was 40% or more, CDU was performed and immediately followed by PTA in the presence of a stenosis of more than 50%. The Qa was then measured during the first dialysis after PTA and one month later. Repeated-measure analysis of variance was applied to evaluate the early and late (after one month) effect of PTA. RESULTS: Twelve PTAs were performed under CDU guidance in nine patients and led to the elimination of the stenosis or its reduction (two cases). The mean Qa was 809 +/- 263 mL/min at baseline, 468 +/- 153 before PTA, and 820 +/- 281 after PTA. The difference between the pre-PTA and post-PTA values was highly significant (P < 0.001), and the mean value after PTA was not different from baseline (P = 0.672). There were no relevant complications directly related to the procedure. CONCLUSIONS: The CDU procedure is effective for the diagnosis of vascular access stenosis and as a guide during the PTA procedure. It could improve stenosis screening by avoiding the risks of exposure to ionizing radiation and of adverse reactions to contrast media.

Aged↗
PubMed1999

CT data sets surface extraction for biomechanical modeling of long bones.

In modelling applications such as custom-made implants design is useful to have a surface representation of the anatomy of bones rather than the voxel-based representation generated by tomography systems. A voxel-to-surface conversion process is usually done by a 2D segmentation of the images stack. However, other methods allow a direct 3D segmentation of the CT or MRI data set. In the present work, two of these methods, namely the Standard Marching Cube (SMC) and the Discretized Marching Cube (DMC) algorithms, were compared in terms of local accuracy when used to reconstruct the geometry of a human femur. The SMC method was found to be more accurate than the DMC method. The SMC method was capable of reconstructing the inner and outer geometry of a human femur with a peak error lower than 0.9 mm and an average error comparable to the pixel size (0.3 mm). However, the large number of triangles generated by the algorithm may limit its adoption in many modelling applications. The peak error of the DMC algorithm was 1.6 mm but it produced approximately 70% less triangles than the SMC method. From the results of this study, it may be concluded that three dimensional segmentation algorithms are useful not only in visualisation applications but also in the creation of geometry models.

Algorithms↗
PubMed1999

Risk of fracture in elderly patients: a new predictive index based on bone mineral density and finite element analysis.

Hip fracture is more and more frequent in elderly population. For this reason, an increasing attention has been focused on the development of a non-invasive method to predict femoral neck fracture. A conventional approach to fracture diagnosis is the measurement of bone mass by dual-energy X-ray absorptiometry in some regions of interest. The aim of this work is to assess a method that accounts for the structural details of the bone providing a more direct determination of strength properties, and improving the diagnostic power of the current densitometric systems. A 2D finite element model of the proximal femur is derived from dual-energy X-ray absorptiometry data. Initially, the method is validated in vitro using a replica of the human femur. The predicted results are compared to strain-gauge measurements and to a 3D finite element model, with good agreement being observed. Then, an in vivo preliminary study on a limited group of patients is carried out. The loading condition that simulates a fall to the side onto the greater trochanter from standing height is employed. All simulations show a peak strain at the femoral neck region with a strain distribution typical of a fall on the side. The proposed method seems to supply a useful tool for the in vivo analysis of the risk of hip fracture.

Aged↗
PubMed1999

Flat foot functional evaluation using pattern recognition of ground reaction data.

OBJECTIVE: Main purpose of this study was to apply quantitative gait analysis and statistical pattern recognition as clinical decision-making aids in flat foot diagnosis and post-surgery monitoring. DESIGN: Statistical pattern recognition techniques were applied to discriminate between normal and flat foot populations through ground reaction force measurements; ground reaction forces time course was assumed as a sensible index of the foot function. BACKGROUND: Gait analysis is becoming recognized as an important clinical tool in orthopaedics, in pre-surgery planning, post-surgery monitoring and in a posteriori evaluation of different treatment techniques. Statistical pattern recognition techniques have been utilized with success in this field to identify the most significant variables of selected motor functions in different pathologies, and to design classification rules and quantitative evaluation scores. METHODS: Ground reaction forces were recorded during free speed barefoot walks on 28 healthy subjects, and 28 symptomatic flexible flat foot children selected for surgical intervention. A new feature selection algorithm, based on heuristic optimization, was applied to select the most discriminant ground reaction forces time samples. A two-stage pattern recognition system, composed by three linear feature extractors, one for each ground reaction force component, and a linear classifier, was designed to classify the feet of each subject using the selected features. The output of the classifier was used to define a functional score. RESULTS: The classifier assigned the ground reaction force patterns performed by each subject into the right class with an estimated error of 15%, corresponding to an assignment error for each subject's foot of 9%. The most discriminant ground reaction forces time samples selected are in full agreement with the pathophysiology of the symptomatic flexible flat foot. The obtained score was utilized to monitor the 1 and 2 years post-operative functional recovery of two differently treated subgroups of 32 flexible flat foot subjects. CONCLUSIONS: Statistical pattern recognition techniques are promising tools for clinical gait analysis; the obtained score provides important functional information that could be used as a further aid in the clinical evaluation of flat foot and different surgical treatment techniques. RELEVANCE: Symptomatic flexible flat foot surgical decision making is frequently difficult because of the lack of objective criteria to assess functional abnormalities of the foot/ankle complex. Gait analysis and statistical pattern recognition can give us parameters with which to characterize "functional" flat foot. Moreover, we can objectively follow up the recovery of the foot/ankle complex function after surgical treatment.

Algorithms↗
PubMed1999

A model-based method for the reconstruction of total knee replacement kinematics.

A better knowledge of the kinematics behavior of total knee replacement (TKR) during activity still remains a crucial issue to validate innovative prosthesis designs and different surgical strategies. Tools for more accurate measurement of in vivo kinematics of knee prosthesis components are therefore fundamental to improve the clinical outcome of knee replacement. In the present study, a novel model-based method for the estimation of the three-dimensional (3-D) position and orientation (pose) of both the femoral and tibial knee prosthesis components during activity is presented. The knowledge of the 3-D geometry of the components and a single plane projection view in a fluoroscopic image are sufficient to reconstruct the absolute and relative pose of the components in space. The technique is based on the best alignment of the component designs with the corresponding projection on the image plane. The image generation process is modeled and an iterative procedure localizes the spatial pose of the object by minimizing the Euclidean distance of the projection rays from the object surface. Computer simulation and static/dynamic in vitro tests using real knee prosthesis show that the accuracy with which relative orientation and position of the components can be estimated is better than 1.5 degrees and 1.5 mm, respectively. In vivo tests demonstrate that the method is well suited for kinematics analysis on TKR patients and that good quality images can be obtained with a carefully positioning of the fluoroscope and an appropriate dosage. With respect to previously adopted template matching techniques, the present method overcomes the complete segmentation of the components on the projected image and also features the simultaneous evaluation of all the six degrees of freedom (DOF) of the object. The expected small difference between successive poses in in vivo sequences strongly reduces the frequency of false poses and both the operator and computation time.

Algorithms↗
PubMed1998

Global asymptotic stability of bone remodeling theories: a new approach based on non-linear dynamical systems analysis.

Mathematical tools for the analysis of nonlinear dynamical systems are applied to the study of stability of bone remodeling theories. As a practical application, the same problem studied by Harrigan and Hamilton (1992) and Cowin et al. (1994b) is analysed using these tools, and their findings on the necessary and sufficient conditions to ensure local asymptotic stability are easily confirmed. Using a general approach based on Lyapunov's method the same condition has been found to be necessary and sufficient also for the global asymptotic stability, thus confirming a result obtained by Harrigan and Hamilton (1994) by variational methods applied to finite-element models. The proof is based on the discretization of the spatial domain but the results for the continuum can be easily extrapolated.

Animals↗
PubMed1998

Skin movement artefact assessment and compensation in the estimation of knee-joint kinematics.

In three dimensional (3-D) human movement analysis using close-range photogrammetry, surface marker clusters deform and rigidly move relative to the underlying bone. This introduces an important artefact (skin movement artefact) which propagates to bone position and orientation and joint kinematics estimates. This occurs to the extent that those joint attitude components that undergo small variations result in totally unreliable values. This paper presents an experimental and analytical procedure, to be included in a subject-specific movement analysis protocol, which allows for the assessment of skin movement artefacts and, based on this knowledge, for their compensation. The effectiveness of this procedure was verified with reference to knee-joint kinematics and to the artefacts caused by the hip movements on markers located on the thigh surface. Quantitative validation was achieved through experimental paradigms whereby prior reliable information on the target joint kinematics was available. When position and orientation of bones were determined during the execution of a motor task, using a least-squares optimal estimator, but the rigid artefactual marker cluster movement was not dealt with, then knee joint translations and rotations were affected by root mean square errors (r.m.s.) up to 14 mm and 6 degrees, respectively. When the rigid artefactual movement was also compensated for, then r.m.s errors were reduced to less than 4 mm and 3 degrees, respectively. In addition, errors originally strongly correlated with hip rotations, after compensation, lost this correlation.

Adult↗
PubMed1998

Optimal CT scanning plan for long-bone 3-D reconstruction.

Digital computed tomographic (CT) data are widely used in three-dimensional (3-D) reconstruction of bone geometry and density features for 3-D) modeling purposes. During in vivo CT data acquisition the number of scans must be limited in order to protect patients from the risks related to X-ray absorption. Aim of this work is to automatically define, given a finite number of CT slices, the scanning plan which returns the optimal 3-D) reconstruction of a bone segment from in vivo acquired CT images. An optimization algorithm based on a Discard-Insert-Exchange technique has been developed. In the proposed method the optimal scanning sequence is searched by minimizing the overall reconstruction error of a two-dimensional (2-D) prescanning image: an anterior-posterior (AP) X-ray projection of the bone segment. This approach has been validated in vitro on three different femurs. The 3-D reconstruction errors obtained through the optimization of the scanning plan on the 2-D) prescanning images and on the corresponding 3-D data sets have been compared. Two-dimensional and 3-D data sets have been reconstructed by linear interpolation along the longitudinal axis. Results show that direct 3-D optimization yields root mean square reconstruction errors which are only 4%-7% lower than the 2-D-optimized plan, thus proving that 2-D-optimization provides a good suboptimal scanning plan for 3-D reconstruction. Further on, 3-D reconstruction errors given by the optimized scanning plan and a standard radiological protocol for long bones have been compared. Results show that the optimized plan yields 20%-50% lower 3-D reconstruction errors.

Algorithms↗
PubMed1998

Model-based dialysis adequacy prediction by continuous dialysate urea monitoring.

A modeling approach for on-line estimation of urea kinetics from continuous measurement of urea concentration in the effluent dialysate stream (DUN) is presented. On-line identification of urea kinetics response parameters is used to predict and update dialysis adequacy during the treatment. Dialysis adequacy can be quantified in several ways, but its strict dependence on final urea concentration is a major fact. For this reason, a good predictive skill on the time course of DUN may enable better performances in the control of dialysis outcome by treatment parameters adjustment. A post-filter enzymatic sensor performs continuous measurement of DUN on patients undergoing standard haemodialysis. To get an early prediction of the end dialysis urea level, the solution of a variable volume double-pool (VVDP) model is used, whose parameters are identified at each time on the basis of the past DUN history Unlike the variable volume single-pool (VVSP) model, this enables a prompt and accurate estimation of the final DUN. In fact, after 75 min the estimates always differ by less than 10% from the values measured by the sensor at the end of the treatment. Moreover, values predicted by the model in the last hour always lie within 1% of measured final values. Real-time knowledge of an analytic expression for whole DUN time course also enables the accurate prediction of total removed urea, with no need of cumbersome dialysate collection techniques.

Aged↗
PubMed1997

Sonographic anatomy of the supraspinatus tendon and adjacent structures.

OBJECTIVE: To depict the detailed sonographic pattern of the normal supraspinatus tendon and adjacent structures. Pathologic findings in these structures. Pathologic findings in these structures are well described, but knowledge of their sonographic anatomy is relatively limited. DESIGN: A new position for sonography of the shoulder was adopted that permits good stretching and a large field of view of the supraspinatus tendon. The right shoulders of 12 healthy adult volunteers and of a 10-year-old boy were imaged. Frozen-frame images of ten standard sections were obtained, anatomic details were sought, and a sonographic normal pattern was reconstructed. RESULTS AND CONCLUSIONS: The study allowed sonographic description of new details, including the presence of two distinct tendons of the supraspinatus. Such a reference normal pattern may be helpful in clinical practice for separating the various components and recognizing artifacts or other possible causes of a misdiagnosis.

Adolescent↗
PubMed1997

Surface-marker cluster design criteria for 3-D bone movement reconstruction.

When three-dimensional (3-D) human or animal movement is recorded using a photogrammetric system, bone-embedded frame positions and orientations are estimated from reconstructed surface marker trajectories using either nonoptimal or optimal algorithms. The effectiveness of these mathematical procedures in accommodating for both photogrammetric errors and skin movement artifacts depends on the number of markers associated with a given bone as well as on the size and shape characteristics of the relevant cluster. One objective of this paper deals with the identification of marker-cluster design criteria aimed at the minimization of error propagation from marker coordinates to bone-embedded frame position and orientation. Findings allow for the quantitative estimation of these errors for any given cluster configuration and suggest the following main design criteria. A cluster made up of four markers represents a good practical compromise. Planar clusters are acceptable, provided in quasi-isotropic distribution. The root mean square distance of the markers from their centroid should be greater than ten times the standard deviation of the marker position error. The second objective of this paper deals with the identification of the optimal cluster position and orientation on the limb aimed at the minimization of error propagation to anatomical landmark laboratory coordinates. Cluster position should be selected to minimize skin movement artifacts. The longest principal axis of the marker distribution should be oriented toward the relevant anatomical landmark position.

Animals↗
PubMed1997

Application of stereophotogrammetry to total body three-dimensional analysis of human tremor.

This work aims at verifying the possibility of investigating joint rotations, with amplitude and frequency ranges typical of pathological human tremor, using commercially available stereophotogrammetric systems together with signal processing techniques. A rotating disk is used as a mechanical tremor simulator to test the ability of the system to track known marker trajectories both in a large and a small calibrated volume. The performances of standard discrete Fourier transform (DFT) and autoregressive techniques are also evaluated and compared in the signal spectrum estimation. Results obtained from a pathological test subject and their dependence on the processing techniques adopted are also presented. The use of stereophotogrammetry and of the proposed signal spectrum estimation technique allow to quantify both frequency and amplitude content of three-dimensional (3-D) rotations of many human joints simultaneously and therefore to isolate the contribution of each joint to the whole body tremor.

Aged↗