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Biomedical subjects

H Labelle

Publications and source records attributed to H Labelle.

At least 55 records · Page 3Linked to original sources
PubMed1995

Computer-assisted pedicle screw fixation. A feasibility study.

STUDY DESIGN: We evaluated a computer-assisted surgical tool for inserting pedicle screws. OBJECTIVES: This study reviewed the feasibility, usefulness, and accuracy of the proposed tool. SUMMARY OF BACKGROUND DATA: Reviews documented neurovascular damage caused by screw misplacement. Currently, screw hole position is assessed by radiologic means and curette palpation. METHODS: Three sheep vertebrae and one artificial object were reconstructed three-dimensionally from computed tomography scan slices. At surgery, the surgeon's movements were displayed relative to the three-dimensional vertebrae on a computer screen. The tool was used to detect pedicles and to verify the position of drilled holes. In our laboratory, we calculated the system's accuracy by taking measurements on the artificial object. RESULTS: All pedicles were identified with the computer. Five of the six drilled hole positions were correctly represented. An accuracy of 4.5 mm +/- 1.1 mm RMS (root of the mean squared) and 1.6 degrees +/- 1.2 degrees were calculated. CONCLUSIONS: Results suggested the proposed system could be useful for pedicle detection and assessing the intravertebral location of a drilled hole. The proposed system could be used for many different orthopedic procedures where structures are hidden from the surgeon's view.

Animals↗
PubMed1995

Variability of geometric measurements from three-dimensional reconstructions of scoliotic spines and rib cages.

Three-dimensional (3-D) reconstructions of the spine are being used with increasing frequency to describe scoliotic deformities, but the reproducibility of most of these techniques and the implication for the reliability of measurements made on the reconstructions has not been reported. How reliable are these reconstructions, and can a clinician interpret with confidence the results of studies based on such mathematical models? A reproducibility study of various computerised measurements obtained from 3-D reconstructions of the spine and rib cage for five subjects with adolescent idiopathic scoliosis was done to evaluate the errors associated with repeated measurements and compare them with inter- and intraobserver errors reported for similar commonly used clinical measurements. The mean variation for the Cobb angle differed according to the plane of computation from 0.6 degrees in the frontal plane to 6.7 degrees in the sagittal plane; vertebral axial rotation varied from 2.3 degrees to 5.9 degrees according to the vertebral level, and rib hump measurements displayed an average variation of 1.4 degrees. All these variations are below or within the error levels reported for equivalent 2-D measurements used by clinicians, which suggests that this 3-D model of idiopathic scoliosis may be used with confidence for clinical evaluations.

Child↗
PubMed1995

Modelling and gait evaluation of asymmetrical-keel foot prosthesis.

The paper documents a new concept in prosthetic foot design. It is based on the capacity of a flexible keel to allow a greater medio-lateral function than previously available. The heel has a complex curvature consisting of a medially concave shape that joins the mid-foot. There a hump acting as a leaf-spring ends at the metatarsal break, with an inwardly curved toe extremity. These curvatures contribute to increased medio-lateral control at heel-strike and propulsion for weight transfer and push-off. Results from finite-element modelling indicate that the asymmetrically shaped keel is at least twice as active in storing energy compared with a completely symmetrical one. A preliminary gait study is carried out for a 24-year-old below-knee amputee fitted with the new design, the SPACE foot and a dynamic elastic response foot with a symmetrical keel. With the SPACE foot, there is a 14% increase in walking speed combined with a reduction in the phasic asymmetries. The absolute difference between the initial and terminal double support is 1.4% for the asymmetrical keel design compared with 4.4% for the symmetrical keel foot prosthesis. The peak ankle power generation burst indicates that the SPACE foot behaves as a dynamic elastic response foot.

Biomechanical Phenomena↗
PubMed1995

Natural history of muscle weakness in Friedreich's Ataxia and its relation to loss of ambulation.

From 1979 to 1992, 170 muscular assessments performed on 33 patients with Friedreich's Ataxia were reviewed. The average followup was 6 years. All muscle evaluations were done by the same team. It was possible to delineate a fairly regular and statistically significant pattern of slowly progressive and symmetrical loss of strength affecting mainly the lower limbs, and more specifically the pelvic girdle muscles. The first significant weakness was observed in the hip extensor group, followed in a variable fashion by other muscle groups of the lower limb. Upper limb and trunk muscles remained relatively spared until late in the disease process, with an overall strength approximately 80% of normal. Use of a wheelchair began at a mean age of 18.2 years, at which time the lower-limb strength averaged 70% of normal. Patients became totally unable to walk at a mean of age 20.5 years old, with a further decline in lower limb strength to 56% of normal. Weakness does not appear to be the primary cause for loss of ambulation in patients with Friedreich's ataxia.

Adolescent↗
PubMed1995

[Geometrical modeling of the spine and the thorax for the biomechanical analysis of scoliotic deformities using the finite element method].

In order to study the biomechanical behavior of the whole human spine and thorax, as well as orthopaedic treatment effects, a new generation model is proposed, which includes a precise functional representation of the posterior part of the spine, while respecting computational capabilities. This paper presents the geometrical aspects of this model. The latter is built using an hybrid method which combines steroradiographic 3-D reconstructions of the spine and thorax [1] to serial CT scan 3-D reconstructions of typical human vertebrae and sternum [4] and published morphometric data of ribs [2, 3]. These anatomical structures were deformed in order to fit as well as possible the personalized data of scoliotic patients using geometrical transformations as well as interpolation or extrapolation techniques. In the posterior part, articular facets are modelled and parameterized as elementary surface shapes (plane, cylinder, sphere). For the articular facet geometry of a given normal subject, results revealed that the zygapophyseal facets are better represented by planes for T1 to T11 and by portions of cylinders for T12 to L5, which is in concordance with the literature [5, 6]. Evaluation of this modelling approach was done on 2 cadaveric vertebral segments. Parametric data obtained from the model were compared to precise measurements done on the vertebrae using a 3-D digitizer, and concordance was found. These personalized geometric informations were then used to build a finite element model [7], which will be useful to study scoliotic deformities as well as personalized orthopaedic treatments.

Humans↗
PubMed1995

[Possible relationship between idiopathic scoliosis and morphologic somatotypes in adolescent females].

This retrospective study was conducted to verify the possibility of a relationship between morphological somatotypes and Adolescent Idiopathic Scoliosis (AIS). The sample was composed of 77 adolescent girls presenting Idiopathic Scoliosis. In every case, scoliosis was important enough to necessitate a corrective surgery. The control group (historical type) was taken from an anthropometric study done in 1990 [5]. Morphotypes were evaluated from medical slides with pre-established criteria based on Sheldon's technique [3, 4]. Three somatotype values were obtained: One for ectomorphism, a second for mesomorphism and a third for endomorphism. This classification system is calibrated in a way that the summation of these 3 values necessarily gives 7. AIS patients appear less mesomorphic with a mean value of 1,208 +/- 1.03 than the control group with a mean value of 1,923 +/- 0.89 (Student "t" test: 6,149, p < 0.0001). Based on these results, a relationship between morphological somatotypes and the presence of AIS appears possible. A more elaborate prospective study will be needed to support this hypothesis.

Adolescent↗
PubMed1994

Optimized vertical stereo base radiographic setup for the clinical three-dimensional reconstruction of the human spine.

This paper presents a method to determine the stereoradiographic planes and anatomical vertebral landmarks giving the most reliable three-dimensional reconstructions of the thoracic and lumbar spine for clinical studies. The present investigation was limited to stereoradiographic setups with a normal vertical stereo base. Possible X-ray tube positions are thus corresponding to angles ranging from 0 (conventional posteroanterior radiograph) up to 30 degrees (dimension of the X-ray room). An X-ray phantom was used as a specimen from which three-dimensional reconstructions with the direct linear transformation (DLT) algorithm were obtained. Visibility of landmarks located on pedicles, end-plates, transverse and spinous processes was evaluated for the whole thoracic and lumbar spine (T1 to L5). Process landmarks were discarded because their poor visibility on radiographs produced inaccurate three-dimensional reconstructions. Considering the size, shape and orientation of vertebrae, an angle of 20 degrees between the posteroanterior horizontal position and the angled position of the X-ray tube gave optimal results. Landmarks located on pedicles and end-plates produced the most reliable three-dimensional reconstructions of the spine. Pedicles were found to be more reliable landmarks than end-plates. Validation of the technique with reconstructed steel beads reveals three-dimensional errors under 1.0 mm. Since vertebral landmarks were more difficult to identify on radiographs than steel beads, reconstruction results were compared with those obtained with a biplanar orthogonal setup. This shows that three-dimensional errors of 8.0 mm may be expected on actual reconstructions of the spine and errors as large as 15.0 mm may be present on poorly visible landmarks.

Algorithms↗
PubMed1994

[Intraoperative three-dimensional evaluation of Cotrel-Dubousset's procedure for the treatment of idiopathic scoliosis].

In order to evaluate with accuracy the tridimensional (3D) vertebral correction induced by the surgical correction of idiopathic scoliosis with Cotrel-Dubousset instrumentation and technique, we have developed a new per operative measurement system based on 3D digitization with magnetic fields. This method has been used on 23 adolescent patients treated with surgical correction. A statistically significant change in vertebral 3D orientation of 11.4 degrees +/- 5.6 degrees has been found. The measurement repeatability was +/- 2.5 degrees. We conclude that the Cotrel-Dubousset technique truly realizes a 3D correction of the thoracic and lumbar spine of adolescent idiopathic scoliosis.

Adolescent↗
PubMed1993

Diurnal variation of Cobb angle measurement in adolescent idiopathic scoliosis.

To investigate the possible influence of gravity on daily variations of curve magnitude in adolescent idiopathic scoliosis, standardized anteroposterior standing radiographs of the spine were taken at 8:00 AM and repeated in the same conditions at 8:00 PM on the same day, 19 girls with idiopathic scoliosis, aged 10-16 years were included. The Cobb angle of the primary thoracic curve was measured blindly by four skilled orthopaedic surgeons. The mean interobserver variation in measuring Cobb angles on the 38 radiographs was 1.6 degrees. The average Cobb angle on morning radiographs was 60 degrees (range, 42-91 degrees) as compared to 65 degrees (range, 47-89 degrees) in the afternoon, a significant (P < 0.001) difference using a paired two-sided Student t test. It was concluded that there is a statistically and clinically significant daily increase of curve severity in moderate to severe idiopathic scoliosis.

Adolescent↗
PubMed1993

Reexamination of the Cobb and Ferguson angles: bigger is not always better.

In scoliosis, the Cobb measure of curve severity has been recommended over the Ferguson method because it had greater magnitude and appeared more sensitive to changes during progression and after treatment. This study made comparisons between the Cobb and Ferguson measures in radiographs of patients with idiopathic scoliosis to test whether the methods were really different, and to compare their precision. In 138 observations of 77 untreated patients there was a very high correlation (R2 = 0.98) between Cobb and Ferguson angle, with Cobb angle averaging 1.35 times greater. For sequential measures (mean interval 10 months), the percent changes agreed closely (R2 = 0.5). The relationship between Cobb and Ferguson angles remained the same in measurements of 24 patients wearing a brace compared with the unbraced condition and in 18 patients measured before and after Harrington rod surgery. Repeated measurements were made by three observers with the apex and end vertebrae pre-marked and held constant. For Cobb angle, the greatest range of measurements on any film was 8 degrees (pooled SD = 1.3 degrees). For Ferguson angle the greatest range was also 8 degrees (pooled SD = 1.8 degrees). Ferguson angle was slightly more sensitive to incorrect selection of end vertebrae. It was concluded that both methods can be useful for measuring curve magnitude. Ferguson angle should be measured and then adjusted by multiplying it by 1.35 in situations where Cobb angle measurement is technically difficult or invalid. Ferguson angle is better suited to automated measurement.

Adolescent↗
PubMed1993

[Biomechanical simulation of the effect of the Boston brace on a model of the scoliotic spine and thorax].

A biomechanical model was developed to investigate the immediate effect of the Boston brace on the spine and thorax of two scoliotic patients (12 year old females with identical lumbar curves of 37 degrees and thoracic curves of 32 degrees and 25 degrees). This model is an improvement of Stokes model and incorporates several modifications concerning the modelling of costo-vertebral and costo-transverse joints. Forces generated by braces on the thorax were measured by pressure sensors and used as input into the finite element model. The deformed models were compared to the geometry of the same patients wearing their brace and with Stokes model. Concordance of results supports the modelling method. Differences between Stokes and improved models were observed. However, because of the small amount of patients included in this study, it is not possible to conclude on the effect of the modelling improvements.

Braces↗
PubMed1992

Effect of radiographic landmark identification errors on the accuracy of three-dimensional reconstruction of the human spine.

In three-dimensional reconstruction of the human spine obtained from stereo-radiographic set-ups (two radiographs or more), it is extremely difficult to identify exactly the same landmarks on all radiographs. The effect of these identification errors was investigated with simulations made on points of known three-dimensional co-ordinates and compared with three-dimensional reconstructions of real spines obtained with the direct linear transformation algorithm. Results showed that radiographic identification errors of up to 2 mm were common, causing reconstruction errors of up to 5 mm. These reconstruction errors may be noticed in the form of geometrical inaccuracies in the graphical representation of three-dimensional reconstructions of the spine. Successive displacements were then imposed on image point co-ordinates to minimise the identification error and increase the reconstruction accuracy. The improvement on the three-dimensional reconstruction results was negligible. Three-dimensional reconstructions obtained from three radiographs were also investigated. They showed slightly more accurate reconstructions than those obtained from two radiographs. However, the increase of X-ray exposure on the patient may not be worthwhile.

Algorithms↗
PubMed1992

Lack of scientific evidence for the treatment of lateral epicondylitis of the elbow. An attempted meta-analysis.

We have reviewed 185 articles published since 1966 to assess the scientific evidence for methods of treatment for lateral epicondylitis of the elbow. Of the 185 articles, 78 discussed treatment, but since the natural history of the syndrome is uncertain we considered only those series with concurrent control groups. Only 18 of these were randomised and controlled studies. We then graded these papers for scientific validity, using the methods of Chalmers et al (1981). The mean score of the 18 articles was only 33%, with a range from 6% to 73%. A minimum of 70% is required for a valid clinical trial, and we therefore concluded that there was insufficient scientific evidence to support any of the current methods of treatment. There were too many methodological differences to allow a quantitative meta-analysis, but our qualitative review established the importance of the natural evolution of the syndrome and of the placebo effect of all treatments. Properly designed, controlled trials are needed.

Acute Disease↗
PubMed1992

[3-D study of the immediate effect of the Boston brace on the scoliotic lumbar spine].

In order to study the immediate 3-D effect of the Boston brace on lumbar scoliosis, 31 adolescents with idiopathic scoliosis King type I or II had a 3-D computerised reconstruction of their deformity with and without the brace. Results demonstrate that the brace produces a distraction of the lumbar spine similar to that produced by the Harrington instrumentation by correcting the frontal deformity at the expense of a significant reduction of the physiological lumbar lordosis. No significant effect on rotation of the apical vertebra or "detorsion" of the spine could be measured. We feel that a orthosis that provides a real 3-D correction of the deformity has yet to be developed.

Adolescent↗
PubMed1989

Running patterns of juveniles wearing SACH and single-axis foot components.

Concerns have been raised about the capability of conventional prosthetic foot components to provide adequate support and function for activities other than walking to persons with lower limb amputations. Degenerative changes of the lumbar spine and knee joints have been linked to prolonged asymmetric loading, which may be accentuated when force magnitudes are high, as in running. This study evaluated the extent and location of kinematic and kinetic asymmetries relative to the foot component worn. The running patterns of six children with unilateral below-knee amputations were evaluated on two occasions: first, while wearing the solid ankle-cushioned heel (SACH) component, and second, wearing the single-axis (SA) component. Cinematographic and forceplate data yielded bilateral temporal data, vertical ground reaction forces, joint angular trajectories, and moments. Results indicated that the SACH and SA components performed almost identically, despite the greater excursion allowed by the SA foot. Slower step speed on the affected side was related to significantly lower vertical ground reaction forces (p less than .01). The ankle angular displacement and moment curves revealed the incapacity of either component to stimulate natural foot-ankle function, with resulting significant interlimb asymmetries. The ipsilateral knee displayed marked reduction of the initial flexor wave, paired with a reduced extensor moment. Compensations predominated ipsilaterally, as evidenced by the similarity of the contralateral patterns to those of an able-bodied runner, except for a decreased hip flexor moment before toe-off. This study showed that interlimb asymmetries were attributable to the inadequacies of both components.

Adolescent↗
PubMed1988

Observer variation in assessing spinal curvature and skeletal development in adolescent idiopathic scoliosis.

Accurate measurements of spinal curvature and skeletal development are crucial in planning treatment and assessing curve progression in adolescent idiopathic scoliosis (AIS). An inter-rater agreement trial was undertaken to estimate the reliability of measuring these spinal parameters. Two orthopaedic surgeons and two trained technicians from a scoliosis clinic independently read 30 anteroposterior roentgenograms of AIS patients. Skeletal maturity was assessed using the six-point Risser sign scale, and spinal curvature was measured using the method of Cobb. Excellent agreement was observed in evaluating Risser signs (Kappa = 0.8) and primary Cobb angles (intra-class correlation coefficient, Rho = 0.98). The standard deviation of inter-observer error in measuring primary Cobb angles was 2.5 degrees, and the intra-reader error, based on one observer's reassessments of 15 films, was 1.9 degrees. Inter-rater agreement for assessing secondary Cobb angles was much lower (Rho = 0.52) because small curves (less than 20 degrees) were often not noticed. Differences in agreement between surgeons and technicians were relatively minor. These results indicate that personnel trained at this clinic are able to assess these spinal parameters reliably.

Adolescent↗