Biomedical subjects

Angelo Cappello

Publications and source records attributed to Angelo Cappello.

At least 19 recordsLinked to original sources

PubMed2006

Intra-operative evaluation of cementless hip implant stability: a prototype device based on vibration analysis.

Cementless implants are mechanically stabilized during surgery by a press-fitting procedure. Good initial stability is crucial to avoid stem loosening and bone cracking, therefore, the surgeon must achieve optimal press-fitting. A possible approach to solve this problem and assist the surgeon in achieving the optimal compromise, involves the use of vibration analysis. The present study aimed to design and test a prototype device able to evaluate the primary mechanical stability of a cementless prosthesis, based on vibration analysis. In particular, the goal was to discriminate between stable and quasi-stable implants; thus the stem-bone system was assumed to be linear in both cases. For that reason, it was decided to study the frequency responses of the system, instead of the harmonic distortion. The prototype developed consists of a piezoelectric exciter connected to the stem and an accelerometer attached to the femur. Preliminary tests were performed on four composite femurs implanted with a conventional stem. The results showed that the input signal was repeatable and the output could be recorded accurately. The most sensitive parameter to stability was the shift in resonance frequency of the stem-bone system, which was highly correlated with residual micromotion on all four specimens.

Cementation↗

PubMed2006

Propagation of anatomical landmark misplacement to knee kinematics: performance of single and double calibration.

Soft tissue artefact and anatomical landmark misplacement have been recognized as the most critical sources of error in gait analysis. The double calibration method was recently proposed to compensate for soft tissue artefact in knee kinematics. This compensation method resulted very effective in the absence of anatomical landmark misplacement. The purpose of the present work was to assess the effectiveness of double calibration in reducing the effects of skin motion artefact on knee rotations and translations when anatomical landmark misplacement is present on the thigh and shank. The double calibration method was used to calculate knee kinematics of two subjects while they performed several motor tasks. The results were compared with those from conventional single calibration. The soft tissue artefact propagated to knee kinematics was quantified by simulating different misplacement errors using both single and double calibration. The double calibration method performed much better than the single calibration one in quantifying knee rotations and particularly translations, with misplacement error up to 15mm superimposed on the anatomical coordinates of the epicondyles. If misplacement errors were limited to just 5mm, the double calibration would be effective in providing kinematics accurate enough for orthopaedic biomechanic applications.

Adult↗

PubMed2006

Effects of linear versus sigmoid coding of visual or audio biofeedback for the control of upright stance.

Although both visual and audio biofeedback (BF) systems for postural control can reduce sway during stance, a direct comparison between the two systems has never been done. Further, comparing different coding designs of audio and visual BF may help in elucidating how BF information is integrated in the control of posture, and may improve knowledge for the design of innovative BF systems for postural control. The purpose of this paper is to compare the effects of linear versus sigmoid coding of trunk acceleration for audio and visual BF on postural sway in a group of eight, healthy subjects while standing on a foam surface. Results showed that sigmoid-coded audio BF reduced sway acceleration more than did a linear-coded audio BF, whereas a linear-coded visual BF reduced sway acceleration more than a sigmoid-coded visual BF. In addition, audio BF had larger effects on reducing center of pressure (COP) displacement whereas visual BF had larger effects on reducing trunk sway. These results suggest that audio and visual BF for postural control benefit from different types of sensory coding and each type of BF may encourage a different type of postural sway strategy.

Auditory Perception↗

PubMed2005

In vivo validation of a new technique that compensates for soft tissue artefact in the upper-arm: preliminary results.

BACKGROUND: Soft tissue artefact is the dominant error source for upper extremity motion analyses that use skin-mounted markers, especially in humeral axial rotation. METHODS: A new in vivo technique is presented that is based on the definition of a humerus bone-embedded frame almost "artefact free" but influenced by the elbow orientation in the measurement of the humeral axial rotation, and on an algorithm designed to solve this kinematic coupling. The technique was validated in vivo in a study of six healthy subjects who performed five arm-movement tasks. For each task the similarity between a gold standard pattern and the axial rotation pattern before and after the application of the compensation algorithm was evaluated in terms of explained variance, gain, phase and offset. In addition the root mean square error between the patterns was used as a global similarity estimator. FINDINGS: After the application, for four out of five tasks, patterns were highly correlated, in phase, with almost equal gain and limited offset; the root mean square error decreased from the original 9 degrees to 3 degrees . INTERPRETATION: The proposed technique appears to help compensate for the soft tissue artefact affecting axial rotation. A further development is also proposed to make the technique effective also for the pure prono-supination task.

Adult↗

PubMed2005

Identification of distinct characteristics of postural sway in Parkinson's disease: a feature selection procedure based on principal component analysis.

We selected descriptive measures of the centre of pressure (CoP) displacement in quiet standing, by means of a procedure based on principal component analysis, in two groups particularly different in terms of postural behaviours, such as subjects with Parkinson's disease (PD) in the levodopa off and on states. We computed 14 measures of the CoP: 5 measures of CoP trajectory over the support surface, 3 measures that estimated the area covered by the CoP, 1 measure that estimated the principal CoP sway direction, 1 measure that quantified the CoP total power, 1 measure that estimated the variability of CoP frequency content and 3 measures of characteristic CoP frequencies [L. Rocchi, L. Chiari, A. Cappello, Feature selection of stabilometric parameters based on principal component analysis, Med. Biol. Eng. Comput. 42 (2004) 71-79; L. Rocchi, L. Chiari, F.B. Horak, Effects of deep brain stimulation and levodopa on postural sway in Parkinson's disease, J. Neurol. Neurosurg. Psychiatry, 73 (2002) 267-274]. The feature selection, independently applied to the measures obtained in the two groups, resulted in different principal component (PC) subspaces of the 14-dimension original data set (4 PCs in the off and 3 PCs in the on state to account for over 90% of the original variance), but in the same 5 CoP measures (selected features) needed to describe the different postural behaviours: root mean square distance; mean velocity; principal sway direction; centroidal frequency of the power spectrum; frequency dispersion. The five selected features were found to provide insight into the postural control mechanisms and to describe changes in postural strategies in the two groups of PD subjects, off and on levodopa. Thus, the five selected features may be recommended for use in clinical practice and in research, in the direction toward the definition of a standard protocol in quantitative posturography.

Aged↗

PubMed2005

Influence of a portable audio-biofeedback device on structural properties of postural sway.

BACKGROUND: Good balance depends on accurate and adequate information from the senses. One way to substitute missing sensory information for balance is with biofeedback technology. We previously reported that audio-biofeedback (ABF) has beneficial effects in subjects with profound vestibular loss, since it significantly reduces body sway in quiet standing tasks. METHODS: In this paper, we present the effects of a portable prototype of an ABF system on healthy subjects' upright stance postural stability, in conditions of limited and unreliable sensory information. Stabilogram diffusion analysis, combined with traditional center of pressure analysis and surface electromyography, were applied to the analysis of quiet standing tasks on a Temper foam surface with eyes closed. RESULTS: These analyses provided new evidence that ABF may be used to treat postural instability. In fact, the results of the stabilogram diffusion analysis suggest that ABF increased the amount of feedback control exerted by the brain for maintaining balance. The resulting increase in postural stability was not at the expense of leg muscular activity, which remained almost unchanged. CONCLUSION: Examination of the SDA and the EMG activity supported the hypothesis that ABF does not induce an increased stiffness (and hence more co-activation) in leg muscles, but rather helps the brain to actively change to a more feedback-based control activity over standing posture.

Journal Article↗

PubMed2005

Effect of different inertial parameter sets on joint moment calculation during stair ascending and descending.

The reliability of internal joint moment calculation in gait analysis during daily living activities is fundamental for clinical decisions based on joint function. This calculation, obtained by means of the inverse dynamics, depends on several modelling factors, such as assumptions on the segments and on the relevant joints constituting the kinematic chain. In this study, the effect of five different sets of inertial parameters on three-dimensional calculation of lower limb joint moments was investigated during the stair ascending and descending of 10 young subjects. The lower limb was represented as a chain of three rigid segments: foot, shank and thigh. The inertial parameters sets were taken from the literature. The root mean square value over the step cycle of the difference between joint moments calculated at the lower limb with different inertial parameter sets expressed in percentage of their corresponding range was computed. The results showed small differences between ex vivo and in vivo data, between data from different populations and among different modality of inertial parameters acquisition. The root mean square value was negligible at the ankle and increased as moving proximally among the joints: the maximum was 21.8% in the internal/external rotation moment at the hip. In order to achieve accurate estimate of lower limb joint moments other factors should be investigated rather than optimal inertial parameter set.

Adult↗

PubMed2005

Ankle morphometry evaluated using a new semi-automated technique based on X-ray pictures.

BACKGROUND: The study of bone morphometry is important in anatomy, biomechanics and the design of joint arthroplasty, because the design of prostheses depends also on the knowledge of joint geometry, both for the replication of function and for the proper sizing of the components. Relevant information for the human ankle joint bones is particularly scarce. METHODS: A large number of morphological measurements of the ankle joint were collected in 36 normal subjects by means of a new semi-automated radiographic measurement method based on standard frontal and sagittal X-ray projections. Lengths, heights and widths of the main parts of this articulation together with the radii of curvature of the talar dome and of the trochlea tali in the sagittal plane were worked out. Statistical analysis was performed on these measurements. FINDINGS: A large spectrum for the values of these measures was found. Significant correlation was found among some of the measures, but not between any of these and the subject height. INTERPRETATION: Bones at the ankle joint have similar shapes, i.e. the three dimensions are in direct proportion to each other. No one of the internal dimensions is correlated with the only one possible external measurement, i.e. the malleolar width. Sizes of the current total ankle replacement designs may differ considerably from real corresponding joint dimensions.

Adult↗

PubMed2005

Quantification of soft tissue artefact in motion analysis by combining 3D fluoroscopy and stereophotogrammetry: a study on two subjects.

BACKGROUND: Soft tissue artefact is the most invalidating source of error in human motion analysis using optoelectronic stereophotogrammetry. It is caused by the erroneous assumption that markers attached to the skin surface are rigidly connected to the underlying bones. The quantification of this artefact in three dimensions and the knowledge of how it propagates to relevant joint angles is necessary for the interpretation of gait analysis data. METHODS: Two subjects, treated by total knee replacement, underwent data acquisition simultaneously with fluoroscopy and stereophotogrammetry during stair climbing, step up/down, sit-to-stand/stand-to-sit, and extension against gravity. The reference 3D kinematics of the femur and tibia was reconstructed from fluoroscopy-based tracking of the relevant prosthesis components. Soft tissue artefact was quantified as the motion of a grid of retro-reflecting makers attached to the thigh and shank with respect to the underlying bones, tracked by optoelectronic stereophotogrammetry. The propagation of soft tissue artefact to knee rotations was also calculated. FINDINGS: The standard deviation of skin marker trajectory in the corresponding prosthesis-embedded anatomical frame was found up to 31 mm for the thigh and up to 21 mm for the shank. The ab/adduction and internal/external rotation angles were the most affected by soft tissue artefact propagation, with root mean square errors up to 192% and 117% of the corresponding range, respectively. INTERPRETATIONS: In both the analysed subjects the proximal thigh showed the largest soft tissue artefact. This is subject- and task-specific. However, larger artefact does not necessarily produce larger propagated error on knee rotations. Propagated errors were extremely critical on ab/adduction and internal/external rotation. These large errors can nullify the usefulness of these variables in the clinical interpretation of gait analysis.

Aged↗

PubMed2005

Soft tissue artefact assessment in humeral axial rotation.

The accuracy of upper-limb kinematic data acquired from optoelectronic systems with retro-reflective markers is poor, mainly due to soft tissue artefact (STA). For the upper-arm, humeral internal/external rotation (HIER) is the movement most affected by STA, which is measured as a percentile fraction (K) of the effective humeral axial rotation performed. The aim of this work was to quantify STA during HIERs, with independently varying attitude of the humerus and elbow flexion, and to test the possibility of estimating its mean value over the tested upper-limb orientations using one simple trial. Six able-bodied subjects performed a series of HIERs in combination with elbow flexion for different humeral planes and degrees of elevation. During the trials the instantaneous attitudes of two humeral anatomical frames were compared, one being affected by the STA to be measured, and the other assumed as the gold standard. K was found to range from 20% to 48% of the effective humeral axial rotation performed, depending on the subject, humeral attitude and elbow flexion. These last two factors comparably affect STA and resulted in mean K coefficients of variation among the subjects of about 9% and 7%, respectively. Common patterns of K with elbow flexion and humerus elevation are discussed. The data also show that the mean of K of a subject is very close to the value assessed in a specific upper-limb configuration consistent among the subjects. This result from this study could be used to build up a time-saving STA compensation procedure suitable for clinical applications.

Adult↗

PubMed2005

Soft tissue artifact compensation in knee kinematics by double anatomical landmark calibration: performance of a novel method during selected motor tasks.

The purpose of the present work was to describe and assess the performance on two selected subjects of a new method for the compensation of soft tissue artifact on knee rotations and translations during the execution of step up/down, sit-to-stand/stand-to-sit, and flexion against gravity. Soft tissue artifact has been recognized as the most critical source of error in gait analysis data. Its propagation strongly affects joint angles, in particular those characterized by a small range of motion, such as knee ab/adduction and internal/external rotation. This may be critical in the exploitation of gait analysis data for clinical decisions. The proposed method is based on the flexion/extension angle interpolation of two anatomical landmark calibrations taken at the extremes of motion. Its performance on knee rotation and translations was tested on a kinematics data-set obtained by the synchronous combination of traditional stereophotogrammetry and 3-D fluoroscopy. The newly proposed method was extremely effective on the compensation of soft tissue artifact propagation to knee rotations, in particular mean values of the root mean square error on ab/adduction and internal/external rotation angles decreased from 3.7 degrees and 3.7 degrees to 1.4 degrees and 1.6 degrees, respectively, with respect to single calibration. Mainly, knee translations calculated from stereophotogrammetric data using the proposed compensation method were found to be reliable with respect to the fluoroscopy-based gold standard. The residual mean values of the root mean square error were 2.0, 2.8, and 2.1 mm for anterior/posterior, vertical, and medio/lateral translations, respectively.

Aged↗

PubMed2005

Audio-biofeedback for balance improvement: an accelerometry-based system.

This paper introduces a prototype audio-biofeedback system for balance improvement through the sonification using trunk kinematic information. In tests of this system, normal healthy subjects performed several trials in which they stood quietly in three sensory conditions while wearing an accelerometric sensory unit and headphones. The audio-biofeedback system converted in real-time the two-dimensional horizontal trunk accelerations into a stereo sound by modulating its frequency, level, and left/right balance. Preliminary results showed that subjects improved balance using this audio-biofeedback system and that this improvement was greater the more that balance was challenged by absent or unreliable sensory cues. In addition, high correlations were found between the center of pressure displacement and trunk acceleration, suggesting accelerometers may be useful for quantifying standing balance.

Acceleration↗

PubMed2004

A new software for prediction of femoral neck fractures.

Femoral neck fractures are an important clinical, social and economic problem. Even if many different attempts have been carried out to improve the accuracy predicting the fracture risk, it was demonstrated in retrospective studies that the standard clinical protocol achieves an accuracy of about 65%. A new procedure was developed including for the prediction not only bone mineral density but also geometric and femoral strength information and achieving an accuracy of about 80% in a previous retrospective study. Aim of the present work was to re-engineer research-based procedures and develop a real-time software for the prediction of the risk for femoral fracture. The result was efficient, repeatable and easy to use software for the evaluation of the femoral neck fracture risk to be inserted in the daily clinical practice providing a useful tool for the improvement of fracture prediction.

Bone Density↗

PubMed2004

A new semi-automated measurement technique based on X-ray pictures for ankle morphometry.

Knowledge of human joint morphology is important in orthopaedic surgery and in prosthesis design. The literature on quantitative morphological analysis of the ankle joint is particularly scarce. A semi-automated radiographic measurement method was developed to collect morphological measures of the ankle joint. The method was based on standard lateral and antero-posterior X-ray pictures of the ankle joint. These were then scanned and analysed by means of specialized software designed for the purpose, which requires minimal operator contribution. Accuracy of the method was experimentally assessed by in vitro direct measurements. Intra- and inter-operator variability was also tested. Accuracy was assessed to be within 1mm for most measurements. Repeatability was not affected by operator skill and was within 2mm. The newly proposed method was applied successfully on 15 male adult subjects and relevant results are reported. The method allows ankle morphology to be analysed in a large number of subjects providing reliable data for anthropometric statistics.

Ankle Joint↗

PubMed2004

Automatic generation of accurate subject-specific bone finite element models to be used in clinical studies.

Most of the finite element models of bones used in orthopaedic biomechanics research are based on generic anatomies. However, in many cases it would be useful to generate from CT data a separate finite element model for each subject of a study group. In a recent study a hexahedral mesh generator based on a grid projection algorithm was found very effective in terms of accuracy and automation. However, so far the use of this method has been documented only on data collected in vitro and only for long bones. The present study was aimed at verifying if this method represents a procedure for the generation of finite element models of human bones from data collected in vivo, robust, accurate, automatic and general enough to be used in clinical studies. Robustness, automation and numerical accuracy of the proposed method were assessed on five femoral CT data sets of patients affected by various pathologies. The generality of the method was verified by processing a femur, an ileum, a phalanx, a proximal femur reconstruction, and the micro-CT of a small sample of spongy bone. The method was found robust enough to cope with the variability of the five femurs, producing meshes with a numerical accuracy and a computational weight comparable to those found in vitro. Even when the method was used to process the other bones the levels of mesh conditioning remained within acceptable limits. Thus, it may be concluded that the method presents a generality sufficient to cope with almost any orthopaedic application.

Adult↗

PubMed2004

Comparison between subthalamic nucleus and globus pallidus internus stimulation for postural performance in Parkinson's disease.

Nine subjects with Parkinson's disease, five subjects with electrodes implanted in the subthalamic nucleus (STN) and four with electrodes in the globus pallidus internus (GPi), were compared with a population of ten age-matched control subjects. The measures studied include a set of summary statistic scores, two stochastic parameters, the distribution of the center of pressure (CoP) displacement angles under each foot, and the distribution of bilateral patterns of CoP displacement angles. A Bayes classifier was designed to monitor the trend of postural performance in patients, with different treatments. Results suggested that the selected measures were sensitive to Parkinsonian postural sway abnormalities and highlight differences in response to treatments. Deep brain stimulation restored a more normal postural sway and levodopa increased sway abnormalities. Furthermore, the selected measures appear to detect different responses to levodopa between the STN and GPi groups: the negative side effects of levodopa on posture were less severe for STN than for GPi patients, perhaps due to the decreased need for levodopa intake in STN subjects. The measures proposed in this preliminary study may be useful adjuncts to evaluate balance and postural control strategies in patients with Parkinson's disease and may allow the comparison of DBS electrode sites, on stance posture.

Electric Stimulation Therapy↗

PubMed2003

Influence of body segment parameters and modeling assumptions on the estimate of center of mass trajectory.

This study sought to determine the effect of inaccuracies in body segment parameters and modeling assumptions on the estimate of antero-posterior center of mass (COM) trajectory. Four different methods, one based on segmental kinematics, and three methods based on kinetic recordings were compared via simulation. Kinematic patterns (quiet stance, ankle-related sway, hip-ankle-related sway, sit-up and sit-up-sit-down) were tested with a 2D four-link model of the body and the ground reaction force vector was obtained by inverse dynamics. Errors in the estimation of body segment parameters were simulated by applying a +/-10% variation to one or more parameters at a time. These errors propagated differently to the COM estimated location between methods, between parameters within the same method, and between tasks. The kinematics-based method was the most sensitive to body segment parameters, with special regards to segment lengths and head-arms-trunk parameters. Root mean square error between estimated and simulated COM location reached 19mm in balance-related tasks and 38.3mm in sit-up-sit-down. The kinetics-based methods were largely less sensitive to inaccuracies in body segment parameters. In particular, the technique proposed by Zatsiorsky and King (J. Biomech. 31 (1998) 161), was completely insensitive to segment parameters. On the other hand the kinetics-based methods showed an intrinsic estimation error, due to the underlying model assumptions. The methods based on the double integration of horizontal force had better outcomes with tasks challenging such assumptions, with a maximal error in COM location of 15mm in the sit-up-sit-down. The method proposed by Shimba (J. Biomech. 17 (1984) 53) showed the best trade-off between sensitivity to body segment parameters and estimation performances given the ideal test conditions.

Biomechanical Phenomena↗

PubMed2003

Comparative in vitro study on the long term performance of cemented hip stems: validation of a protocol to discriminate between "good" and "bad" designs.

The long-term clinical success of cemented hip stems is influenced both by the implant design, and by the surgical procedure. A methodology is proposed for discriminating between implant designs with different clinical outcomes. The protocol was designed with industrial pre-clinical validation in mind. Two cemented stem types were tested, one (Lubinus SPII) having good and the other (Müller Curved) having poor clinical outcomes. Three implants for each type were subjected to a mechanical in vitro test of one million loading cycles. Each cycle reproduced the load components of stair climbing. Interface shear micromotion was measured during the test in the direction of rotation and along the stem axis. The stem roughness before and after the test was compared. After the test, the cement mantles were retrieved and inspected through dye penetrants to detect evidences of micro-damage. For each specimen, the events of the loosening process were examined, based on the in vitro data available, so as to analyze the whole failure mechanism. The protocol developed was sensitive to the implant design, with significantly different results being found for the two stem types, both in terms of stem-cement micromotions, surface roughness alteration, and cement mantle damage. The information yielded by the three different investigation techniques was consistent for each of the two groups of specimens tested, allowing a better understanding of the failure process. In vitro inducible micromotion and permanent migration measurements, together with cement-stem interface fretting damage and cement fatigue damage, can help predicting the clinical performance of cemented stems.

Bone Cements↗