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Biomedical subjects

H Clahsen

Publications and source records attributed to H Clahsen.

33 records · Page 2Linked to original sources
PubMed1988

[Homologous replacement of the cruciate ligament in the animal experiment].

A homologous cruciate ligament transplantation was effected in 20 Alsation dogs. Clinical, pathologico-anatomical and histological results were obtained from 16 animals after 3, 6 and 9 months, respectively, proving metaplasia of the transplant to endogenous body tissue. The clinical conclusion of this finding is that an anatomically optimally-structured ligament replacement can be inserted by means of a relatively uncomplicated operation--possibly even by using arthroscopy. The low amount of traumatization due to this type of surgery will be of advantage especially to sportsmen, who, as is well known, not only suffer from frequent cruciate ligament ruptures but also have remarkably long-term deficits by large operation wounds both in regaining their proprioceptive performance ability and their muscular power.

Animals↗
PubMed1982

[Experimental studies on the biomechanical reaction of collagenous fibres during impulse mechanical strain working conditions (author's transl)].

A wide spectrum of stress-strain factors of varying directions and magnitudes are acting on collagenous fibres. Bundles of parallel collagen fibres in tendons and ligaments are mainly subject to tension forces. Single twitches and unfused tetanus of muscles fibres are giving rise to impulse strains on tendon fibres. Tendon reflexes are causing contractions of the muscle and sudden extensions of the corresponding collagenous fibres. In vitro studies were performed on tendon fibres. Tendon reflexes are causing contractions of the muscle and sudden extensions of the corresponding collagenous fibers. In vitro studies were performed on tendon fibre bundles. Systematic impulse extensions were applied as input functions. The force resp. stress impulses were recorded as output functions. When linear extensions with superimposed impulse strains were applied, the force-elongation curve showed a stepwise increase of the force impulse initially. Under consecutive isometric conditions an impulse relaxation curve arises. After partial deloading and subsequently isometric conditions an impulse force recovery function emerges. The output force impulses are dependent on the frequency of the input strain impulses. The effects are called frequency dependent force impulse relaxation and recovery. The findings are briefly discussed in correlation with functional anatomy and muscle physiology.

Animals↗
PubMed1981

[Mechanical function of the liver capsule].

Histomechanical experiments were performed on human and bovine liver capsules. On strain processes, the mechanical resistance force increases slowly at the beginning, and then with a continuous change rapidly. The relaxation processes approximate to a constant form at equal stains with interponed isometrical phases. This indicates that the tissue has a trend towards a viscoelastic equilibrium (balance behaviour, steady state). In further experiments the following histomechanical properties could be demonstrated: Upper and lower summit decrease at dynamical (cyclic) relaxation, and cascade dynamical (cyclic) force recovery with stepwise reduced force amplitudes.

Animals↗
PubMed1978

[Histomechanical studies on test specimens from hyaline cartilage under compressive loading with regard to rheology (author's transl)].

Modified rheological methods from high polymer physics (biorheology, historheology) have been applied to the testing of hyaline cartilage histomechanics. The following histomechanical properties of cartilage are discussed: transient behaviour, the influence of the mechanical history on the subsequent force-deformation processes, viscoelastic equilibrium status (histomechanical steady state), and relaxation phenomena in the pressure and tension range under alternating pressure-tension loading. Pressure force-time input and output curves in a closed loop system and the amplitude-increasing phenomenon under uniform sinus deformations with increasing superimposed linear deformation input were also demonstrated. The results are discussed from the point of view of functional anatomy.

Animals↗
PubMed1977

On the biomechanical function of the liver capsule.

UNLABELLED: We have carried out histomechanical studies on the human bovine liver caps-le under tension loading. RESULTS: Nonlinear force-time curve under extension with constant speed, initial upper and lower summit decrease of the dynamic relaxation curve, amplitude diminution phenomenon of the dynamic relaxation in the lower nonlinear part of the extension-time curve, dynamic (cyclic) force recovery.

Animals↗
PubMed1977

[Experimental studies of the historheology of the liver capsule (author's transl)].

We have performed histomechanical experiments with historheological methods on the liver capsule of men and cattle. The liver capsule is a non linear viscoelastic tissue. The force-extension diagram or the force-time curve under increase in length shows a flat initial part with a large strain reserve, then an arched domain and subsequently a steep increase in force with a coordination of a small increase in length. The hysteresis loop is represented. When the tissue is in a viscoelastic steady state (preconditioned), the force-extension curves respectively the force-time curves are identical one with another and under certain presuppositions reproducible. This is also the case with the static relaxation curve and the force recovery curve (inverse relaxation). With a ramp shaped extension time input function and an additional, superimposed sinus length-time input function we can observe the following dynamical force-time output functions: Non linear dynamical force increase, amplitude increment phenomenon, dynamical force recovery (dynamical inverse relaxation). Various dynamical-statical transients are demonstrated in diagrams. The mechanical properties of the liver capsule are interacting with the ligaments of the liver, with the intrahepatic connective tissue, and with the liver parenchyma. Aspects of the functional anatomy and the tension of the capsule in an acute increase of he liver parenchyma are discussed.

Animals↗
PubMedDate not supplied

[Function of the glenohumeral ligaments in active protection of shoulder stability].

UNLABELLED: We harvested the joint capsule, the glenohumeral ligaments, and the coracohumeral ligaments of 8 fresh formalin-preserved shoulder specimen. We made use of the van Gieson technique and a special silver impregnation for staining peripheral axons according to Nowotny. The ligaments were cut into slices with a thickness of 15 microns. In total we performed 10,000 cuts. We discovered axons in all ligaments. These axons had no relation to vessels or vessel walls. Besides these axonal structures we detected type II mechanoreceptors (Pacini receptor). CLINICAL SIGNIFICANCE: The neural structures discovered in the glenohumeral capsule are of clinical importance especially in consideration of the high account of recurrent shoulder dislocation and concomitant Bankart lesions. Receptors located in the glenohumeral ligaments might control the stabilizing shoulder musculature. On this premises, rupture or detachment of these ligaments will lead to a loss of the feedback mechanism.

Adult↗
PubMedDate not supplied

[Effects of various rehydration periods on the stability and water content of bone transplants following freeze-drying, gamma sterilization and lipid extraction].

UNLABELLED: Several studies demonstrated the necessity of rehydration of lyophilized bone allografts prior to implantation. The purpose of the presented study was to evaluate the influence of different rehydration periods on the stability of human cortical lyophilized and gamma-irradiated allografts, the capability of lyophilized bone for rehydration, as well as the effects of lipid extraction on rehydration. Breaking strength of lyophilized irradiated cortical bone after different rehydration periods (0.5, 1, 2, 4, 8 hours) showed no significant difference. Weight reduction after lyophilization of human femoral heads was between 7.6% and 41%. Further weight reduction occurred after lipid extraction (38.7%). Total weight loss was 56.9%. There was a significant influence of intraosseous lipid content on the rehydration capability. After lyophilization alone the rehydration weight after 8 hours was only 18.1%, whereas after lipid extraction the weight increase was 43% after 0.5 hours, 36.4% after 1 hour, 57.6% after 2 hours, 60% after 4 hours, and 92.7% after 8 hours. CLINICAL RELEVANCE: Based on the presented data rehydration time of 0.5 hours seems to have no disadvantage compared to longer time periods concerning breaking strength. Therefore a longer intraoperative time period seems not to be necessary. This is of advantage for a possible secondary contamination while the allograft is rehydrated. Rehydration after lipid extraction is more effective than rehydration after lyophilization alone. However, the question whether lipid extraction alter bone stability has to be proved in further studies.

Bone Transplantation↗
PubMedDate not supplied

[Neurohistological studies in allogeneic cruciate ligament transplants as intra-articular ligament replacement].

A multiplicity of surgical operations have been developed in an attempt to achieve satisfactory function after ACL repair. None of these procedures have been able to duplicate the fiber organization, attachment site anatomy, vascularity, or function of the ACL. 18 foxhounds received a deep frozen bone-ACL-bone allograft and a ligament augmentation device (LAD). Neurohistological changes were evaluated 3, 6, and 12 months following implantation. Modified silver impregnation method and gold chloride technique were used to examine the presence of nerve endings and axons. Two morphological distinct mechanoreceptors were identified, and then were categorized as follows: free nerve-endings golgi-like tendon receptors. Fine nerve endings were frequently ramified freely into ligament collagen bundles. Nerves and blood vessels were commonly associated. Like in normal ACL's both neuroreceptors were mostly located near the surface of the allografts and at both bony attachments. This study demonstrated the first histological evidence of viable mechanoreceptors and free nerve-endings in transplanted ACL-allografts, not previously reported in other ACL-substitutes using for ACL-reconstruction. Particularly important for post-op. rehabilitation, this technique may allow to reconstruct the proprioreceptive functions of normal anterior cruciate ligaments.

Animals↗
PubMedDate not supplied

[Homologous cruciate ligament transplantation as intra-articular ligament replacement].

A multiplicity of surgical operations have been developed in an attempt to achieve satisfactory function after ACL repair. None of these procedures have been able to duplicate the fiber organization, attachment site anatomy, vascularity, or function of the ACL. 29 foxhounds received a deep frozen bone-ACL-bone allograft and a ligament augmentation device (LAD). Biomechanical, microvascular, and histological changes were evaluated 3, 6 and 12 months following implantation. The maximum load of the allograft/LADs were 34.3% (387.2 N) after 3 months, 49.3% (556.6 N) after 6 months and 61.1% (689.8 N) after a year. The maximal load was 69.1% (780 N). In general, after 6 months the allografts showed a normal collagen orientation. The allografts demonstrated no evidence of infection or immune reaction. No bone ingrowth into the LAD was observed. Polarized light microscopy and PAS-staining showed that the new bone/ligament substance interface had intact fiber orientation at the area of ligament insertion. Microvascular examination using Spalteholtz-technique revealed neovascularization and the importance of infrapatellar fat pad for the nourishment of the ACL-allografts.

Animals↗
PubMedDate not supplied

[Stability of human bone cortex following various preservation and sterilization methods].

In a biomechanical study we evaluated the stability of human femurs. In order to document the inter- and intraindividual differences in bending stability, and the changes in breaking strength after different storing and sterilizing procedures, we tested 200 bony blocks, which were harvested from the femurs of 5 multiorgan donors. The bending tests were performed with a material testing machine (ZWICK) under standardized conditions. The bone blocks we randomized into five different treatment groups (-25 degrees C deep freezing, steam sterilization, lyophilization, lyophilization + gamma irradiation, lyophilization + gamma-irradiation in argon). The statistical analysis was performed by a multivariant analysis. Our results revealed significant differences concerning breaking strength among different femurs of the 5 multiorgan donors, and a significant difference concerning stability in different areas of the same femur. Further on we found a significant difference with regard to the treatment modalities of the five groups. Compared to the control group (-25 degrees C deep freezing), we documented a decrease of 8.7% after steam sterilization, an increase of 18.9% after lyophilization, a decrease of 1.7% after lyophilization + gamma-irradiation, and an increase of 3.4% after lyophilization + gamma-irradiation in argon.

Adult↗
PubMedDate not supplied

[Factors influencing the anchoring stability of spinal bone screws--an experimental study].

INTRODUCTION AND AIM OF THE STUDY: The primary assumption for successful internal fixation of the spine is a stable screws fixation. Aim of this experimental examination was to point out the influences on axial pull-out strength of screws and to suggest improvements for its increase. METHODS: Eight specifically manufactured screw-prototypes were tested in standardized pull-out tests in comparison by pairs. An isotropic, synthetic hard-foam was used as test material. It resembled to the spongiose bone and reduced the deviation of the results. To show the transferability of the results on bone there were made pull-out tests out off calf vertebra. RESULTS: A significant increase of axial pull-out strength can be achieved by a wide external diameter, a big insertion depth, a flat angel of tooth profile and a small thread pitch. This examination could not prove a significant advantageous influence on axial pull-out strength by fast pull-out, asymmetrical "Butress-thread" or proportion of core- and external diameter difference. CONCLUSIONS: Referring to the aim of this examination a wide outside-diameter can be recommended. Likewise the depth of insertion should be as deep as the anatomic conditions permit. The influence of these two factors are considerable. In contrast to other author's statements the maximum axial stability increases significantly by a small thread pitch and a flat angel of tooth profile.

Animals↗
PubMedDate not supplied

[Intra- and interindividual differences in tensile strength of human bone].

UNLABELLED: In a biomechanical study we evaluated the stability of human femurs. In order to document the inter- and intraindividual differences in bending stability, we tested 200 bone samples, harvested from the femurs of 5 multiorgan donors. The bending tests were performed on a material testing machine (ZWICK) under standardized conditions. Our results revealed significant differences in the stability of the femurs of the 5 multiorgan donors. Furthermore, there was a significant difference in breaking strength at different levels of the same bone. CLINICAL RELEVANCE: In studies aimed at evaluating the primary bony stability of alloimplants after different preservation or sterilization procedures, the above-mentioned results should be taken into consideration.

Adult↗