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Biomedical subjects

J L Kahn

Publications and source records attributed to J L Kahn.

At least 19 recordsLinked to original sources
PubMed2006

Finite element analysis of the strain distribution in the humeral head tubercles during abduction: comparison of young and osteoporotic bone.

AIM: The aim of this work was to design an accurate 3D digital model of the humerus and rotator cuff muscles. This model was then used to study strain distribution in humeral tubercles according to bone density. MATERIALS AND METHODS: The geometry of bone and muscle structures was reproduced using SURFDRIVER software, based on anatomical sections, CT scans and MRI images from the Visible Human Project image library. The contours were transferred to PATRAN software to rebuild volumes and mesh them. Calculations of strains and their distribution were performed using NASTRAN software. All the elements were considered to be isotropes. RESULTS: The study of the distribution of stress magnitude according to the type of bone modeled, shows that some stresses in cortical bone are greater than those in cancellous bone and are also greater in old bone, implying more deformation in old bone at constant force. This study also shows that stresses do not penetrate deeply into cancellous tissue. CONCLUSION: Observing the simulation results led understanding of the pathology of certain fractures of the proximal end of the humerus. This study also helped explain why certain types of osteosynthesis fail due to tubercles reconstruction failures.

Bone Density↗
PubMed2006

[Orbital blow-out fractures].

Blow-out fractures, lateral fractures of the face, involve only the inferior and sometimes the medial wall of the orbit. Clinical diagnosis is not always obvious, and CT is helpful to confirm diagnosis and also detect some failures of surgical treatment: improper position or size of the graft. MRI is valuable to evaluate post-surgical infections.

Humans↗
PubMed2005

[Imaging of facial changes in hyperparathyroidism].

Facial changes in hyperparathyroidism, rarely described, are better depicted at CT imaging. This article reviews the maxillo-mandibular, ocular and temporo-mandibular findings associated with the different types of hyperparathyroidism.

Facial Bones↗
PubMed2004

The lumbo-gluteal adipose body.

The lumbo-gluteal adipose body (LGAB) is a well-delineated fatty structure, in the lumbo-gluteal trigone, encroaching on the upper part of the gluteal region and flank. The aim of this study was to compare the gross and histological anatomy of the LGAB with that of other well-defined adipose bodies of the human body. The macroscopic study using dissections and slices in the main three planes in adults was supplemented by microscopic study of histological slices taken from fetuses and neonates. The forms and limits of the LGAB are defined, along with its structure. The LGAB appears to act as a filling structure, lining the hypodermis in the regions that it covers.

Adipose Tissue↗
PubMed2003

[Imaging of mandibular malformations and deformities].

Mandibular deformities and malformations are quite various. They are mostly identified by clinical examination, but imaging is very useful for surgical planning. CT imaging is essential to evaluate patients with dystrophies such as fibrous dysplasia, neurofibromatosis, Gorlin syndrome and cherubism. Some growth abnormalities lead to a pseudomalformative appearance. Sequelae and ankylosis from condylar fracture, and unilateral mandibular hypoplasia due to capillary-venous malformation require CT or/and MR evaluation. CT with 3D reformations is performed as a complement to clinical evaluation in patients with other growth abnormalities such as orthognathic problems, hypercondylia, and some malformations like lateral facial clefts. MR is helpful for soft tissue evaluation in patients with Parry-Romberg syndrome and Pierre Robin dysostosis.

Basal Cell Nevus Syndrome↗
PubMed2002

Adipose body of the orbit.

The adipose body of the orbit (ABO) fills most of the orbital cavity, surrounding the eyeball, muscles, nerves, and vessels. It was studied in histologic section in the three basic planes in the fetus, neonate, and adult. In the retrobulbar area, that is, posterior to the eyeball, adipose tissue occupies the space around the optic nerve and penetrates between the recti muscles, describing a four-leafed clover pattern in frontal section. The fatty tissue of the retrobulbar area also includes the peripheral ring of fat that lies between the muscles and the walls of the orbit. In the part of the peribulbar area located between the muscular insertions on the eyeball anteriorly and the emergence of the optic nerve from the sclera posteriorly, the pattern of adipose tissue is identical to the peripheral ring of fat and the fat between the muscles in the retrobulbar area. External to the muscular insertions and the anterior part of the eyeball, there is a thin ring of histologically similar fatty tissue that is continuous anteriorly with the fatty bodies of the upper and lower eyelids. Histologic examination shows that the lobules are large in that part of the retrobulbar area within the muscle cone and that they are smaller with more fibrous septa in the remaining restricted regions, such as the area between the eyeball and muscles and in the rings around the muscles and around the eyeball. In no case was a septum found separating the peripheral adipose ring from the fat located within the muscle cone.

Adipose Tissue↗
PubMed2002

[Ectopic parotid gland in the mandible and masseter muscle].

An unusual case of double salivary ectopy of parotid gland is described into the masseter muscle and the mandibular ramus in a 45 year-old patient. He first was seen for a slow course tumefaction of the cheek. Imaging demonstrated the intramasseteric localization of the tumefaction and revealed a bone defect in the upper medial part of the mandibular ramus. The intramasseteric salivary ectopy has been confirmed by histologic examination.

Choristoma↗
PubMed2001

Effects of freezing/thawing on the biomechanical properties of human tendons.

Numerous biomechanical studies using osteoarticular complex need frozen cadaveric specimens. Some of these studies deal with the resistance of the tendinous structures, for example the resistance of some autografts, such as the patellar ligament and the semitendinosus and gracilis tendons for reconstruction of the anterior cruciate ligament. The aim of this study was the in-vitro evaluation of the mechanical modifications induced by freezing/thawing on human tendons. The long head of the biceps brachii tendon was used as the reference. Eight pairs of tendons of the long head of the biceps brachii were taken from eight fresh cadavers. After drawing lots, one was tested immediately, the other was deep-frozen and then thawed. With an Instron material-testing machine, we performed a relaxation test and a uniaxial tensile test, to estimate the ultimate tensile failure and the elastic modulus of each pair of tendons. Freezing had no influence on the tendinous relaxation, but altered significantly the ultimate tensile failure and Young's modulus of the tendons.

Adult↗
PubMed2000

Anatomy and imaging of the deep fat of the face.

The aim of this study is to investigate the deep adipose structures of the face. This study is undertaken on anatomical material dissected or sectioned in the three basic planes and in histological sections. The buccal fat pad is described with its main part and its various extensions implicating several superficial and deep regions of the face. Likewise, the parapharyngeal fat pad in the prestyloid space is described. The histology of the structures is discussed, together with the non-mobilizable nature of the fat. Imaging by MRI shows the shape and relations of these fat pads with the neighboring viscera and muscles and their role as early markers in tumor invasion. Finally, their function, as an intermuscular sliding structure, is highlighted.

Adipose Tissue↗
PubMed2000

Development of a static simulator of the mandible.

Our aim was to build and assess a static mandibular simulator capable of reproducing various masticatory exercises as closely as possible to physiological situations. Unlike existing devices that reproduce a small number of exercises and of muscular bundles, our simulator is able to reproduce all types of effort in the sagittal plane and integrates eleven muscular groups considered by the majority of authors as being the most important in mastication. The value of our simulator arises from its ability to replicate the external forces (including muscular traction, intra-articular reaction and resultant forces applied to the mandible) as determined in vivo during previous studies. The importance of such a versatile simulator, in addition to enabling study of the mechanical behaviour of the mandible, is that it greatly enhances evaluation of a possible mathematical model by means of finite element analysis. Stages of the development and evaluation of this device are described.

Computer Simulation↗
PubMed1999

[Paraplegia secondary to surgery of the abdominal aorta].

We report the case of an 84 year-old man who suffered of paraplegia after surgery of an abdominal aortic aneurysm. The neurologic status did not improve during 5 years of follow-up. This complication is rare in light of the review of the literature. It is more frequent after emergency (1.4%) and redux (19%) surgery than after elective surgery (1.1%). Its mechanisms are anatomic (occlusion of the Adamkievitz artery and of the pelvic collateral arteries) and hemodynamic mechanisms (thromboembolism, low systemic tension, long supra-renal clamping). Since pre-operative aortography to detect anatomic variations is not realistic, its only prevention remains maintenance of intra-operative hemodynamic, systemic heparinization, and preservation of the pelvic collateral circulation.

Aged↗
PubMed1999

[Imaging of solitary maxillo-mandibular plasmacytoma].

CT was performed in three patients with plasmacytoma of the maxilla and mandible. CT allows improved depiction of the tumor and associated local invasion and bony destruction but remains non-specific. Histology is mandatory for diagnosis and work-up necessary to confirm the solitary nature of the lesion. Intraosseous intramedullary lesions often evolve to multiple myeloma after a few years whereas extramedullary lesions, commonly involving sinonasal structures, typically remain solitary.

Aged↗
PubMed1998

Determination of the external forces applied to the mandible during various static chewing tasks.

The purpose of this study is to determine the external forces that are brought to bear on the mandible during 14 masticatory tasks, exerted in three defined mandibular positions. A static two-dimensional mandibular model is presented, taking into account projections in the sagittal plane of the forces exerted by six muscle groups and the joint reaction force. In calculating these external forces, two working hypotheses are adopted: the existence of a linear relationship between cross-sectional surface of the muscle and its maximum force of contraction, and the existence of a linear relationship between the electrical signal emitted by a muscle and the force the muscle then develops. Our first results are provided and compared with data from the literature. Individual variations recorded in the measurement of the different parameters involved in the equilibrium equations are such that they must be taken into account in the calculation of the forces. Moreover, the functional value of the muscles appears to be closely dependent on the mandibular position with which they are associated, which is not brought out in earlier studies. Finally, intra-joint action proves to be intense, although its direction varies according to the mandibular position and the type of exercise performed.

Bite Force↗
PubMed1998

[Methods proposed for the determination of external forces applied to the mandible during mastication. Initial results].

The purpose of this study is to determine the external forces that are brought to bear on the mandible during various masticatory exercises. An analysis is presented of a static two-dimensional mandibular model taking into account projections in the sagittal plane of the forces exerted by six muscle groups and the joint reaction. In calculating the external forces, two working hypotheses are adopted: the existence of a linear relationship between cross-sectional surface of the muscle and its maximum force of contraction; the existence of a linear relationship between the electrical signal emitted by a muscle and the force the muscle then develops. It follows that, in order to calculate, the muscle forces, there is a need to measure the intensity of masticatory effort, the cross-sectional surface and the electromyographic activity of the different muscles involved. These values are then used for working out the equations of equilibrium. Results are provided for 14 masticatory exercises effected in three different mandibular positions and compared with data from literature. Individual variations recorded in the measurement of the different parameters involved in the equilibrium equations are such that they must be taken into account for the calculation of the forces. Moreover, the functional value of the muscles appears to be closely dependent on the mandibular position with which they are associated, which is not brought out in earlier studies. Finally, intra-joint action proves to be intense, although its direction varies according not only to the mandibular position but also the type of exercise performed.

Algorithms↗
PubMed1997

The parapharyngeal adipose corpus: morphologic study.

The parapharyngeal adipose corpus is a well limited adipose structure lying deep in the prestylian space, close to the lateral wall of the upper part of the pharynx. Macroscopic and microscopic anatomic sections were made and compared with CT and MR sectional imaging. The walls and contents of the parapharyngeal adipose corpus are described on the basis of anatomic sections and are symmetrically visualized by sectional imaging in the axial and coronal planes. A knowledge of its relations explains its role in imaging as an early marker of invasive tumoral processes. It is in continuity with the upper part of the buccal fat pad and presents the same functional characteristics of a gliding structure.

Adipose Tissue↗
PubMed1997

[Rutherford back-scattering spectrometry and photoelectron spectroscopy of the calcium/titanium interface].

Evaporation of calcium on commercially pure titanium was performed. Heatings under vacuum or oxygen flow improved calcium diffusion in the titanium substrate. X-Ray Photoelectron Spectroscopy did not revealed any superficial segregation of titanium but revealed the formation of CaCO3. The film formed on titanium was characterized using X-ray photoelectron spectroscopy with argon-ion sputtering. The results indicated that: the surface layer consisted of CaCO3; the interface contained CaCP3, CaO et TiO2; only CaO was present in the bulk titanium.

Argon↗
PubMed1997

[Peripharyngeal space. Pathology].

Tumors are the most frequent pathological pattern found in the peripharyngeal space. Topographically, intrinsic and extrinsic tumors can be distinguished. Intrinsic tumors are mostly salivary, nervous and vascular. Extrinsic tumors extend from the oral cavity, pharynx and parotid gland. MRI globally gives more impressive results than CT. Diagnosis of the tumor type often remains dubious in intrinsic tumors. CT-guided biopsy is then required.

Humans↗