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At least 91 records · Page 5Linked to original sources
PubMed1993

A three-dimensional anatomical model of the human patello-femoral joint, for the determination of patello-femoral motions and contact characteristics.

The object of this study is to develop a three-dimensional mathematical model of the patello-femoral joint, which is modelled as two rigid bodies representing a moving patella and a fixed femur. Two-point contact was assumed between the femur and patella at the medial and lateral sides and in the analysis, the femoral and patellar articular surfaces were mathematically represented using Coons' bicubic surface patches. Model equations include six equilibrium equations and eleven constraints: six contact conditions, four geometric compatibility conditions, and the condition of a rigid patellar ligament; the model required the solution of a system of 17 nonlinear equations in 17 unknowns, its response describing the six-degrees-of-freedom patellar motions and the forces acting on the patella. Patellar motions are described by six motion parameters representing the translations and rotations of the patella with respect to the femur. The forces acting on the patella include the medial and lateral component of patello-femoral contact and the patellar ligament force, all of which were represented as ratios to the quadriceps tendon force. The model response also includes the locations of the medial and lateral contact points on the femur and the patella. A graphical display of its response was produced in order to visualize better the motion of the components of the extensor mechanism. Model calculations show good agreement with experimental results available from the literature. The patella was found to move distally and posteriorly on the femoral condyles as the knee was flexed from full extension. Results indicate that the relative orientation of the patellar ligament with respect to the patella remains unchanged during this motion. The model also predicts a patellar flexion which always lagged knee flexion. Our calculations show that as the angle of knee flexion increased, the lateral contact point moved distally on the femur without moving significantly either medially or laterally. The medial contact point also moved distally on the femur but moved medially from full extension to about 40 degrees of knee flexion, then laterally as the knee flexion angle increased. The lateral contact point on the patella did not change significantly in the medial and lateral direction as the knee was flexed; however, this point moved proximally toward the basis of the patella with knee flexion. The medial contact point also moved proximally on the patella with knee flexion, and in a similar manner the medial contact point on the patella moved distally with flexion from full extension to about 40 degrees of flexion.(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗
PubMed2001

Cognitive neuropsychology and functional brain imaging: implications for functional and anatomical models of cognition.

We discuss the relations between functional imaging and cognitive neuropsychological research. We begin by elaborating on some of the problems of traditional neuropsychological research, which attempted to provide accounts of cognitive performance at a neural as well as at a functional level of description. The difficulties in making neural-level arguments from neuropsychological data include: problems of associated deficits, problems due to interactive effects between brain regions, problems with analyses based on behavioural syndromes, problems due to the influence of compensatory strategies, and problems in separating damaged from disconnected representations. We discuss how cognitive neuropsychology by-passed many of these problems by emphasising functional rather than neural-level theories, though problems with inferences at the neural-level remain. We then consider the contribution that functional imaging can make to cognitive neuropsychology. Using evidence drawn from studies of language, object recognition and visual attention, we argue that functional imaging complements cognitive neuropsychology by: (i) not being reliant on accidents of nature and by enabling effects of lesions on 'distant' neural areas to be measured, (ii) revealing the brain systems necessary and sufficient for a given task, (iii) providing tests of neural-level models of cognition, and by (iv) providing novel evidence on the mechanisms of functional recovery in patients. In addition to this, imaging studies can contribute directly to functional-level theories, by providing converging evidence on the neural locus of cognition--knowing 'where' can allow new inferences about 'how' a given task is performed.

Brain↗
PubMed1997

Laparoscopic pelvic lymphadenectomy in an anatomical model: results of an experimental comparative trial.

OBJECTIVES: The aim of this paper was to compare the accuracy of laparoscopic versus open pelvic lymphadenectomy in an experimental trial. STUDY DESIGN: We performed unilateral laparoscopy pelvic lymphadenectomy (LPL) in 33 non-embalmed cadavers between the external iliac vein, the obliterated umbilical artery and the obturator nerve. Then a laparotomy was performed to inspect the LPL limits, look for laparoscopic complications and finally realize a controlateral lymphadenectomy. The LPL side was randomly decided. A pathologist counted the number of lymph nodes collected with both techniques. We compared the number of retrieved lymph nodes, the completeness of the dissection and the complication rate with those two procedures. Student's t-test, chi 2-test and non-parametric tests were used when appropriate. RESULTS: No dissection had to be aborted. One hundred and twelve nodes were removed laparoscopically (mean, 3.73; S.E., 2.9) and 84 at laparotomy (mean, 2.77; S.E., 2.06). There was no significant difference in the number of nodes retrieved with both procedures. Effectiveness of laparoscopy was not significantly different in the first ten procedures, in the second ten or in the last ten LPL. Residual tissue was observed after LPL in 13.3% of the procedures whereas all open lymphadenectomies were complete. LPL sensitivity reached at least 86% in this paper. Failures were more frequent at the beginning of the study (50% among the first ten dissections), in obese subjects or in subjects with prior history of laparotomy (but the difference was not significant). Two venous injuries occurred during LPL (6.7%). Complication rates for the two techniques were not significantly different. However, the LPL complication rate was higher at the beginning of the study and increased significantly in subjects with prior history of laparotomy (P < 0.05). CONCLUSIONS: This randomized study shows that LPL and laparotomy have similar effectiveness. Incomplete dissections and complications are more frequent in obese subjects or in case of prior history of laparotomy. Fifteen procedures seems necessary to learn the technique and provide constant and safe results in routine practice.

Aged↗
PubMed2002

The cynomolgus monkey eyelid as an anatomic model for oculoplastic surgery.

PURPOSE: To investigate the Cynomolgus monkey eyelid as an experimental model for oculoplastic surgery METHODS: Eyelid and periocular tissue were removed from Cynomolgus monkeys being euthanized. After fixation, the macroscopic and microscopic characteristics of the Cynomolgus monkey eyelid were studied. RESULTS: Macroscopic and microscopic characteristics of the Cynomolgus monkey eyelids were described. The Cynomolgus monkey eyelid bears resemblance to the human eyelid in its compartmentalization and complexity. CONCLUSIONS: The Cynomolgus monkey eyelid is a suitable experimental research model. Its compartmentalization resembles that of the human eyelid both microscopically and macroscopically.

Animals↗
PubMed1994

Electrical coupling and impulse propagation in anatomically modeled ventricular tissue.

Computer simulations were used to study the role of resistive couplings on flat-wave action potential propagation through a thin sheet of ventricular tissue. Unlike simulations using continuous or periodic structures, this unique electrical model includes random size cells with random spaced longitudinal and lateral connections to simulate the physiologic structure of the tissue. The resolution of the electrical model is ten microns, thus providing a simulated view at the subcellular level. Flat-wave longitudinal propagation was evaluated with an electrical circuit of over 140,000 circuit elements, modeling a 0.25 mm by 5.0 mm sheet of tissue. An electrical circuit of over 84,000 circuit elements, modeling a 0.5 mm by 1.5 mm sheet was used to study flat-wave transverse propagation. Under normal cellular coupling conditions, at the macrostructure level, electrical conduction through the simulated sheets appeared continuous and directional differences in conduction velocity, action potential amplitude and Vmax were observed. However, at the subcellular level (10 microns) unequal action potential delays were measured at the longitudinal and lateral gap junctions and irregular wave-shapes were observed in the propagating signal. Furthermore, when the modeled tissue was homogeneously uncoupled at the gap junctions conduction velocities decreased as the action potential delay between modeled cells increased. The variability in the measured action potential was most significant in areas with fewer lateral gap junctions, i.e., lateral gap junctions between fibers were separated by a distance of 100 microns or more.

Action Potentials↗
PubMed2003

A functional-anatomical model for lipreading.

Regional cerebral blood flow (rCBF) PET scans were used to study the physiological bases of lipreading, a natural skill of extracting language from mouth movements, which contributes to speech perception in everyday life. Viewing connected mouth movements that could not be lexically identified and that evoke perception of isolated speech sounds (nonlexical lipreading) was associated with bilateral activation of the auditory association cortex around Wernicke's area, of left dorsal premotor cortex, and left opercular-premotor division of the left inferior frontal gyrus (Broca's area). The supplementary motor area was active as well. These areas have all been implicated in phonological processing, speech and mouth motor planning, and execution. In addition, nonlexical lipreading also differentially activated visual motion areas. Lexical access through lipreading was associated with a similar pattern of activation and with additional foci in ventral- and dorsolateral prefrontal cortex bilaterally and in left inferior parietal cortex. Linear regression analysis of cerebral blood flow and proficiency for lexical lipreading further clarified the role of these areas in gaining access to language through lipreading. The results suggest cortical activation circuits for lipreading from action representations that may differentiate lexical access from nonlexical processes.

Adult↗
PubMed1992

Transmaxillary-transnasal approach to the anterior clivus: a microsurgical anatomical model.

Numerous procedures to expose the anterior clival region have been described, including the transoral, transcervical, transseptal-transsphenoidal, transantral, transnasal, bilateral Le Fort I maxillotomy, transbasal, transpalatal, and modifications of the Caldwell-Luc approach. Despite the large number of surgical options available, it may be necessary to have wider access to the midline skull base than these approaches provide. We have developed a microsurgical transmaxillary-transnasal approach to the anterior clivus that has been studied in both dry skull and cadaveric preparations and used clinically. The surgical technique has four stages: 1) antromaxillary; 2) nasal; 3) sphenoidal; and 4) clival. The wider access of this approach is achieved mainly by an osteotomy of the frontal process of the maxilla, which transforms the nasal cavity and the antrum into a single cavity while preserving the functional anatomy of the nose. Cosmesis is preserved by replacement of the cartilaginous nasal septum and the frontal process at the end of the procedure. The technique provides the good cosmetic results of the sublabial approaches and prevents vascular and neural injury in the same way that other anterior approaches do. This transmaxillary-transnasal technique may be used in combination with other approaches for extensive tumors.

Adolescent↗
PubMed2002

A micro-anatomical model of the distribution of myocardial endomysial collagen.

Myocardial connective tissue probably provides passive support for regulating heart tensile strength and stiffness and ultimately for controlling heart mechanics through its endomysial part. However, endomysial collagen micro-arrangement is still a matter of debate. In order to define the fine distribution of left ventricle endomysial collagen, we applied the NaOH-scanning electron microscopy (SEM) maceration method (one of the techniques of choice for studying collagen micro-arrangement) to rabbit heart. Gomori-reticulum staining was used for correlated light microscopy (LM) observations. The SEM-NaOH method allowed isolation of collagen by removing other extracellular matrix components and cells and preserved collagen structure and position. Endomysial collagen appeared arranged in laminae that delimited the lacunae that were left empty by macerated myocytes and small vessels (mostly capillaries). These laminae were formed by reticular fibers, as confirmed by LM observations of Gomorireticulum-stained samples, and were organized in irregularly meshed networks made of thin (single) and thick (composed) filaments. In longitudinal views, collagen laminae extended the entire length of lacunae. In transversal views, the cut surface of the laminae appeared to be made of collagen bundles. These observations provide an updated microanatomical view of endomysial collagen distribution, which integrates previous studies. This model is based on the evidence that collagen laminae enveloped the surface of small vessels and myocytes. Thus, a type of myocyte-myocyte or capillary-myocyte "laminar connection" anchored to the entire cell length here is emphasized, rather than a type of "strut connection" anchored to defined loci, as usually described. This structure explains better how endomysium may provide the necessary support for heart compliance and protection against overstretch.

Animals↗
PubMed1992

The three-dimensional architecture of the myosalpinx in mammals: an anatomical model for a functional hypothesis.

Direct visualization of the three-dimensional architecture of the tubal musculature (myosalpinx) was made possible by a technique involving chemical digestion of interstitial connective tissue, followed by ultrasonic microdissection and final observations under the scanning electron microscope. The isthmic myosalpinx in the guinea pig, rabbit and in humans consists of muscular bundles that tend to lie longitudinally, circularly or oblique. The muscular bundles along the tubal wall change direction, branch and intermingle with one another, giving rise to an irregular network in which distinct layers are not readily distinguishable. In the ampulla, the muscle bundles form a very irregular three-dimensional network of fibres that follow different orientations. The authors suggest a primary role for such a structure in the random pendular transport of the gametes as well as in the denudation of the egg by deformation of the myotubal wall.

Animals↗
PubMedDate not supplied

[Total cranio-facial anatomical model of plio-pleistocene hominids].

For a correct assessment of the fossil specimens are analysed ten characters or structural complexes of neuro - and splancno - cranium. Not individual characters but a total pattern, according to Le Gros Clark's original concept, provide a positive identification of hominid single taxon. Following items are examined: 1) facial prognathism; 2) mid-facial architecture; 3) nasal bone, fronto-nasal and fronto-maxillary suture; 4) frontal region morphology; 5) temporal lines and cranial cresting; 6) occipital and nuchal plane; 7) steepness of nuchal plane, foramen magnum position; 8) skull base diagrams; 9) mastoid process and neighbouring regions; 10) size and form of mandibular fossa. To conclude: it is possible a taxonomic classification of plio-pleistocenic hominid specimens on the basis of an analysis of the "total morphological pattern".

Animals↗