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Biomedical subjects

J Hert

Publications and source records attributed to J Hert.

At least 19 recordsLinked to original sources
PubMed2002

[Meniscoids of the intervertebral joints].

PURPOSE OF THE STUDY: A large amount of material was used to study the distribution, location and shape of meniscoids in intervertebral joints of the human spine, from the atlanto-occipital joint to the sacrum, in order to find out how many of intervertebral joints had mobile meniscoids. These might be regarded as possible causes of spinal blockade or other vertebrogenous complaints. MATERIAL: The materials provided by the Department of Anatomy and Department of Forensic Medicine at the Faculty of Medicine of Charles University in Pilznen included 20 cadaverous spines from humans aged 20 to 80 years. METHODS: Access to each joint was provided by dissection of the articular capsule from the lower articular processes of the vertebra situated above. In the orthograde view, all meniscoids were described in terms of shape, size, consistence and location. Their structure was ascertained by histological examination of cross sections stained with haematoxylin and eosin. RESULTS: Meniscoids varying in shape and size were found in all of the intervertebral joints. They were classified by their histological structure as synovial, fat and fibrous meniscoids. The first category was observed frequently, the last only rarely. A total of 29 mobile meniscoids were recorded, most of them in the lumbar spine. Most of the meniscoids present in the cervical spine were of synovial and less frequently of fat types. Meniscoids found in the thoracic spine were poorly developed synovial ones and those present in the lumbar spine were of all types and were also largest in size. The most conspicuous meniscoids were seen in the spines that showed degenerative changes in intervertebral joints. Large fat pads were found in atlanto-occipital and atlanto-axial joints. Mobile meniscoids, most of them present in the lumbar spine (6.4% of all joints.), were connected with the capsule by a thin pedicle and it was possible to move them over a half of the articular surface. Some inter-individual changes were also found; in some spines, the most developed meniscoids were fat pads, in the others, these were synovial meniscoids. Spines of younger individuals showed a predominance of synovial meniscoids with smooth surfaces that arched against the articular cavity. In spines of elderly individuals, meniscoids were rough, in some cases fibrous in structure, and had a lobulated or frayed edge. DISCUSSION: The shape, location of meniscoids and their presence in every joint indicate their definite role for the spine: they compensate the incongruence of articular surfaces, fill in empty spaces and facilitate spread of synovial fluid during translation movements. Variability in shape, size and location of meniscoids give support to the view that meniscoids developed secondarily in relation to the morphogenesis of articular surfaces and that they are fully adapted to the shape and function of the joint. Mobile meniscoids, particularly fibrous ones, can get wedged between articular surfaces due to a sudden, rush movement (entrapment theory) or can be caught between the edge of an articular surface and the articular capsule attachment (extrapment theory). This situation may result in either mechanical or functional blockade of the spine and a subsequent painful condition due to compression of nerves and reflex contraction of muscles. Direct evidence of such blockade and the validity of either hypothesis can today be provided by magnetic resonance imaging. CONCLUSIONS: All intervertebral joints, along the length of spine, possess capsule processes, i.e., meniscoids, which can be classified as synovial, fat and fibrous. Meniscoids are most developed in the lumbar and cervical spine. They serve to compensate for the incongruence of articular surfaces and to fill in empty spaces. Mobile, peduncular meniscoids can, at sudden or non-physiological movements, be caught between articular surfaces and cause spinal blockade and painful conditions. Manipulative treatment is, therefore, justified in indicated cases.

Adult↗
PubMed2001

[Mechanical loading of the human femoral neck].

PURPOSE OF THE STUDY: The aim of the study is to explain what is the actual loading of human proximal femur. MATERIAL: Measuring of stress is based on 5 femurs of normal shape (bones obtained from dissection and ossuary). In order to determine the direction of the resultant force the authors used 30 ossuary bones of different age but of analogical shape. METHODS: By means of their own graphic method the authors identified the direction of appositional growth of femoral neck which contains with the longitudinal diaphyseal axis the angle of 26 degrees (alpha angle). The value of the angle is identical with the direction of the resultant force acting on the femoral head in vivo. Tensometric method was used for the measuring of stress on the medial and lateral surfaces of femoral neck during loading in direction of the determined resultant force. Linear strain gauges of Hottinger type were used for the measuring and Instron apparatus was applied for biomechanical analysis in which femoral heads were loaded by a standard force of 50 kg, first in the direction of femoral diaphyseal axis and then gradually (always by 5 degrees) in the divergence from the diaphyseal axis up to 50 degrees. RESULTS: Appositional growth of femoral neck with regard to the longitudinal diaphyseal axis is progressing under the alpha angle (alpha = 26 degrees), which corresponds to the direction of the resultant force. The value of the compression stress on the medial surface of the neck ranged between--165 and -300 microstrain (mean value -239 microstrain). On the lateral surface there is a tension stress ranging between +20 up to +140 microstrain (main value +64 microstrain). The ratio of stress on both sides (surfaces) was 3.8:1. The point of zero stress is located in the lateral part of the neck, i.e. in the area of lateral trajectorial system of cancellous bone. DISCUSSION: The method of measuring of the direction of the resultant force on the basis of the bone development (on the basis of superposition of successive growth stages) is despite certain inaccuracies a correct procedure. The alpha angle (alpha = 26 degrees) identified by the authors corresponds with Pauwels' calculation (24 degrees) and Bergman's findings (22 degrees up to 27 degrees). The identified values of stress show that the opinion on a purely axial loading of the neck is wrong and has to be corrected. Femur is not exposed in the frontal plane to the action of the resultant force only in one direction as supposed e.g. by Pauwels but the direction of the resultant force oscillates within a limited extent from different directions. It means that the lateral wall of femoral neck is exposed to alternating both tensile and compression loading. CONCLUSION: The presented work allows to specify the opinions on the way of loading of human proximal femur. Our experiments have shown that apart from axial pressure the femoral neck is exposed also to bending forces. This way of loading also corresponds with the oval shape and thickened medial wall of the neck.

Femur Neck↗
PubMed1996

Spatial organization of the haversian bone in man.

The osteons in all human long bones are grouped in two helical antirotary systems of opposite oblique directions, situated in the contralateral walls of the diaphysis. Several arguments support the hypothesis that this special architecture arises from functional adaptations and that it depends on the orientation of the first principal stress. A new macroscopic method based on the filling of vascular canals of the undecalcified, polished bone with India-ink enabled us to study the spatial architecture of the haversian bone in the entire diaphysis. The osteon directions in normal and atypical femurs was compared with the direction of the first principal stresses, determined analytically in a cylindrical tube model of the diaphysis subjected to a combination of bending, torsion and compression. Under combined loading with the bending moment in the frontal plane to the medial side and with the torque moment in the sense of external rotation, the direction of the first principal stresses corresponded with the direction of osteons in the diaphysis of the femur. In both cases, the first principal stresses, as well as the osteons, were oriented in the opposite oblique direction in the medial and lateral walls of the model and of the bones. Between the two oblique fields a sharp boundary with an atypical organization of the principal stresses and osteons existed. In atypical femurs the osteonal orientation was longitudinal (likely unloaded femurs) or rotated 90 degrees (markedly anteriorly convex femurs). These observations support the hypothesis of a causal relation between the loading mode and the dominant osteonal direction. The organization of the haversian bone seems a typical example of functional adaptation.

Adaptation, Physiological↗
PubMed1994

A new attempt at the interpretation of the functional architecture of the cancellous bone.

The author's theory explains the development mechanisms of the functional structure of cancellous bone. Functional, secondary cancellous bone develops from the primary growth-dependent cancellous lattice under the influence of multidirectional loading. The primary cancellous bone is remodelled according to the general strain-dependent mechanism of the functional adaptation of bone. Oblique loading of the metaphysis in extreme positions in the joint evokes the greatest strain in the bone trabeculae oriented in these oblique directions, as demonstrated by calculation on a simple three-beam model. All trabeculae are therefore remodelled in these directions resulting in a typical picture of two crossed pressure systems. Each of them corresponds to one of the extreme loading directions. Tensile systems can be found only in places of ligament or tendon insertions or under concave joint surfaces.

Biomechanical Phenomena↗
PubMed1993

[Structure of compact bone and types of stress in the long bones in humans].

The authors elaborated a new macroscopic method which made it possible to analyze the orientation of osteons in the entire diaphysis. All long bones of the human extremities were thus analyzed. In each bone the osteons are arranged in a specific pattern but according to a uniform plan. Most of them are oriented in an oblique direction and are arranged as two helices of opposite directions located on opposite sides of the bone. The two fields are separated by a sharp borderline. Biomechanical analysis revealed that the orientation of the osteons is consistent with the direction of the maximal principal stress which depends on the normal and torsional stress to which the bone is exposed. From the orientation of osteons the authors derived ex post the mode of dominant loading of all long bones: the femur is exposed to bending in the medial direction and to outer rotation, the tibia is exposed to bending in dorsal direction and to inner rotation. The humerus is bent in the medial direction, the radius in the dorsal one. Both these bones are exposed to loading in inner rotation. In the ulna and fibula the mode of stress could not be assessed by the authors' method. The results are summarized in two diagrams which indicate the orientation of osteons and the way in which the long bones in man are exposed to load. The authors discuss the theoretical and practical impact of these findings.

Bone and Bones↗
PubMed1993

Principal types of functional architecture of cancellous bone in man.

The cancellous bone architecture in man is locally specific. Several principal types can be distinguished, depending on the kind of loading and movement in the joint in one, two or more directions. Under multidirectional load the spongiosa trabeculae form spatial fans seen as two crossing systems on plane sections. Marked differences exist between the bone structure under concave joint surfaces and the convex ones. The analysis testifies the correctness of the author's own theory on the development of the cancellous bone architecture. According to this theory every trabecular system corresponds to other direction of maximal principal stress in the course of movement. Both crossing systems in the metaphysis are pressure systems, corresponding to opposite extreme positions in the joint. Tension systems can be found in sites of ligament or tendon insertions and closely under concave articular surfaces only.

Bone Development↗
PubMed1992

A new explanation of the cancellous bone architecture.

Various objections can be made to all the theories so far put forward in explanation of the architecture of cancellous bone. The author suggests another explanation, which takes into account the following points: 1) the structure of the secondary spongiosa is based on the pre-existent primary spongiosa, 2) the secondary spongiosa develops under alternating pressures from different directions, 3) oblique forces from marginal directions corresponding to extreme positions on the joint place the greatest strain on the spongiosa trabeculae, as demonstrated by means of a geometrical model. Oblique forces are therefore of decisive morphogenetic importance. 4) The spongiosa trabeculae are oriented in the direction of the oblique marginal forces, in accordance with the experimentally demonstrated mechanism of the strain-dependent reaction of the bone. Spatially, the secondary spongiosa assumes a fan-shaped structure. Two-dimensionally, the two intersecting systems are compression systems, each of which depends on another marginal loading direction. This pattern offers an optimum solution to the problem of the transmission of alternating forces to the diaphysis from various directions, using a minimum of material.

Biomechanical Phenomena↗
PubMed1990

[Wolff's law of transformation after 100 years].

In the introduction to the article the author briefly describes the history of the Wolff's invention that under the influence of the function the bone structure is restructuring. This functional adaptation however, has not been fully clarified until these days. At present the general scheme of the fundamental adaptation mechanism has been generally adopted according to which the bone responds to the inner strain by aposition of the new bone while inactivity results in resorption. The author's own experiment as well as modern experiments carried out by the Lanyon group have proved that the starting point for reaction is intermittent loading in which both pressure and tension have the same effect. The strain results in the deformation of the bone tissue which is by an unclear yet way perceived and signalled to the superficial osteoblasts. However, not all cases of the functional adaptation of the bone can be explained in this way, first of all the remodelling of deformities after fractures or the modelling of metaphysis and the lateral drift of diaphysis in the course of normal growth. In comparison to Currey and other authors who therefore share the view that there does not exist a uniform algorithm of the functional adaptation of bone the author explains the functional adaptation by a uniform even if complex algorithm comprising apart from the reaction of the bone to the inner strain another two mechanisms: 1. Modelling of the bone surface by the periosteum. The increase in pressure between periosteum and bone results in resorption, avulsion of periosteum to the aposition of the new bone. 2. In the course of the growth another factor participates in the functional adaptation, namely the physeal plate, responding to loading according to Hüter-Volkmann's law: "Overload results in reducing of the growth, while relief in its acceleration". In oblique loading the plate changes, due to asymmetric loading, the direction of the growth precisely in the direction of the pressure resultant. Only by the cooperation of the three given mechanisms all cases of the functional adaptation of the bone can be explained.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗