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Biomedical subjects

H Plenk

Publications and source records attributed to H Plenk.

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

Effect of bone cylinder length on distraction osteogenesis in the rabbit tibia.

The viability and osteogenic potential of bone cylinders for bone transport was investigated in one tibia of 18 mature male New Zealand rabbits. The length of the bone cylinder was equal to or twice that of the diameter of the tibia. The cylinder was cut subperiosteally with an externally cooled oscillating saw from a lateral approach, after a specific unilateral external fixator had been applied. To simulate bone transport, one end of the cylinder was fixed to the distal bone stump by a cerclage wire and healing and revascularization was prevented by an interposed expanded polytetrafluoroethylene membrane. The periosteum was re-adapted and sutured, and distraction began 10 days postoperatively at 0.25 mm/12 hours for 22 days. New bone formation in the distraction gap was quantified by dual energy x-ray absorptiometry and by computer-assisted histomorphometry of polyfluorochrome-labeled undecalcified bone sections and corresponding microradiographs. In half of the animals with each size cylinder, osseous bridging occurred, so the findings on distraction osteogenesis are reported only for the remaining nine animals. Generally, centripetal mineralization of the gap with two distinct zones of ripening bone structures and a central radiolucent fibrocartilaginous zone could be distinguished. Neither absorptiometry nor histomorphometry showed significant differences in the overall amount of this new bone formation for the bone cylinders of two different lengths. However, osteogenesis was significantly greater at the proximal end than at the cylinder. New bone was formed predominantly from endosteal sites in the smaller cylinders and from periosteal sites in the larger cylinders. Histologically, there was complete necrosis of both sizes of cylinders, followed by revitalization through newly formed vascular channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

[Prenatal diagnosis of osteogenesis imperfecta. Report of a case classified as the classical Vrolik lethal type].

Report on prenatal sonographic diagnosis of osteogenesis imperfecta of the classical type "letalis Vrolik" in the case of a fetus in the 20th/21st week of pregnancy. The prenatal diagnosis of this kind of osteogenesis imperfecta is based on the soft membranous cranium (Caput membranacium), the microthorax caused by the bell-shaped configuration of the ribs and the diaphysis of the long bones which are too short for the age of pregnancy. These symptoms are first of all the consequence of a disturbed bone formation and mineralisation; its basis is a connatal deficit of collagen synthesis. The sonographic differential diagnosis to the type "Ekman Lobstein" of osteogenesis imperfecta and thanatophoric dwarfism are discussed.

Abortion, Eugenic↗
PubMed1995

A new scanning electron microscopy approach to the quantification of bone mineral distribution: backscattered electron image grey-levels correlated to calcium K alpha-line intensities.

The introduction of backscattered electron (BSE) imaging in scanning electron microscopy (SEM) has led to new possibilities for the evaluation of mineral distributions in bone on a microscopic level. The different grey-levels seen in the BSE-images can be used as a measure for the local mineral content of bone. In order to calibrate these BSE-grey-levels (BSE-GL) and correlate them to mineral contents, various attempts, using reference samples with known weighted mean atomic number and/or using simulated bone tissues with known hydroxyapatite concentrations, have been made. In contrast, a new approach is presented here based on measurements of the X-ray intensities of the calcium K alpha-line on selected areas of real bone samples; the measured intensities are then related to the corresponding BSE-GL. A linear positive correlation between weight percent (wt%) calcium and BSE-GL was found. When the BSE-mode is standardized using carbon and aluminum as references, the different mineral contents in bone samples can be recorded as BSE-GL, calibrated to wt% of calcium or hydroxyapatite (HA), respectively. The resulting mineral concentration histograms have a dynamic range from 0 to 89 wt% HA and have a binwidth resolution of 0.45 wt% HA. The presented modifications of the BSE method strongly enhance its feasibility in the field of bone research and its application as a special diagnostic tool for bone diseases.

Bone Density↗
PubMed1994

[Osteonecrosis].

The causes of osteonecrosis are varied. The pathogenesis of osteonecrosis subsequent to trauma is well known. Furthermore, an association of this disorder with cortisone, haemoglobinopathies, rare metabolic diseases, and risk factors seems to be evident. However, a sizable proportion of patients have osteonecrosis in which none of these associations exists, referred to as idiopathic osteonecrosis. Generally, intraosseous vascularization represents the common pathway for the various causes of the disease. The prognosis is influenced by the age of the patient, the location of the necrosis and the stage of the disease at the time of diagnosis. In recent times diagnosis has been improved by the use of modern imaging modalities, and MR imaging is now widely accepted as the imaging method of choice. It not only allows early diagnosis but also yields exact staging information in advanced disease, which is a requirement for adequate therapy.

Adult↗
PubMed1994

[The non-traumatic femur head necrosis in the adult. I: pathophysiology, clinical picture and therapeutic options].

Intraosseous vascularization is the common pathway of the multifactorial causes of avascular necrosis of the hip (AVN). Recurring ischemic phases could lead to bone necrosis in the initial stage of the disease, when it is still reversible. A spontaneous repair mechanism can lead to complete healing at this stage. The necrotic area demarcates the superior-anterior aspect from the residual femoral head with a reactive interface in the irreversible early stage of the disease. In this stage damage to the femoral head can only be delayed with core decompression or femoral osteotomy, because a sufficient repair mechanism is no longer possible. When the articular surface collapses the early stage gives way to the late stage. Cartilage incongruence and microfracture lead to progressive destruction of the femoral head and to secondary osteoarthritis. In this late stage femoral osteotomy is only successful in carefully selected patients. Total hip replacement is the last resort for patients with painful destruction of the joint. As clinical symptoms are unspecific, MRI plays an important role for early diagnosis of AVN in the initial or early stages. Conservative treatment is not successful in any of the three stages of the disease.

Adult↗
PubMed1994

Long-term results of uncemented alumina acetabular implants.

We report the clinical and tribological performance of 67 ceramic acetabular prostheses implanted between 1976 and 1979 without bone cement. They articulated with ceramic femoral heads mounted on mental femoral stems. After a mean elapsed period of 144 months, 59 sockets were radiographically stable but two showed early signs and six showed late signs of loosening. Four of the loose sockets have been revised. Histological analysis of the retrieved tissue showed a fibrous membrane around all the implants, with fibrocartilage in some. There was no bone ingrowth, and the fibrous membrane was up to 6 mm thick and infiltrated with lymphocytes, plasma cells, and macrophages. Intra- and extracellular birefringent wear particles were seen. Tribological analysis showed total wear rates in two retrieved alumina-on-alumina joints of 2.6 microns per year in a stable implant and 68 microns in a loose implant. Survival analysis showed a revision rate of 12.4% at 136 months.

Adult↗
PubMed1993

[Bone marrow edema--an early form of femur head necrosis].

We examined 15 patients (16 hips) with painful hips whose radiographs were either normal (n = 9) or showed a minimal decrease in radiodensity (n = 7). The available bone scintigrams of 9 cases were positive. T1-weighted images visualised a diffuse signal loss of the bone marrow in all hips, with various extensions in the head, neck, and intertrochanteric area. These regions were hyperintensive on T2-weighted images. Focal anomalies were not seen in any of the cases. All patients underwent core decompression treatment. Histology of 13 hips confirmed not only the presence of bone marrow oedema but of bone changes corresponding to those of avascular necrosis. Follow-up examinations with MR after core decompression showed normal signal intensity in all cases. Magnetic resonance represents a viable diagnostic tool for identifying bone marrow oedema. Due to our histological results bone marrow oedema should be included in the differential diagnosis as an early stage of necrosis of the hip.

Adult↗
PubMed1993

Bone-marrow oedema syndrome and transient osteoporosis of the hip. An MRI-controlled study of treatment by core decompression.

Bone-marrow oedema syndrome (BMOS) of the hip gives a characteristic MRI pattern, in association with severe pain, non-specific focal loss of radiological density and a positive bone scan. In our MRI-controlled study, nine patients with non-traumatic BMOS in ten hips all had core decompression. Bone-marrow pressure measurements and intraosseous venography in five cases showed pathological values. All patients had immediate relief of pain, with return of MRI signals to normal after three months. Regular review was continued for at least 24 months with serial clinical radiological and MRI assessment. At a mean follow-up of 33 months all patients remained free of pain with normal radiographs and MR scans. The histological evaluation of undecalcified sections obtained from eight core decompressions confirmed the presence of bone-marrow oedema, with necrotic and reparative processes involving bone and marrow similar to those of early avascular necrosis but with no evidence of 'osteoporosis'. These findings support the assumption that BMOS may be the initial phase of non-traumatic avascular necrosis. In most patients BMOS will have a self-limiting course, but the duration of symptoms may be reduced by core decompression treatment.

Adult↗
PubMed1993

Effects of drill cooling and bone structure on IMZ implant fixation.

Alternating use of the original method of internal drill cooling with manual external cooling, one IMZ implant was placed in the diaphysis (compact bone) and metaphysis (spongy bone) of the left distal tibia in each of six sheep. After polyfluorochrome sequential labeling, two animals survived for 4, 8, and 16 weeks without functional loading of the implants. The drill holes and bone-implant reactions were evaluated in undecalcified ground sections and microradiographs, using computer-aided histomorphometry. At least 30% of all drill holes were incongruent, but up to 25% of the implant surfaces had primary bone contacts. Four weeks after implantation, distinct differences in the bone reactions could be determined between the experimental conditions. After both cooling methods, osteoclastic resorption had extended up to 0.5 mm into peri-implant compact bone and up to 0.18 mm into spongy bone. Based on the percentage of newly formed bone-to-implant contacts, external cooling proved superior at all superficial drill hole levels in compact bone and in all spongy bone beds, while internal cooling was only better at the deeper drill hole levels in compact bone. After 8 and 16 weeks, peri-implant bone remodeling led to further increased new bone-implant contacts, irrespective of incongruent drill holes or cooling methods. At all time periods, abraded titanium particles were observed within interfacial foreign body cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Mineral crystals in calcified tissues: a comparative study by SAXS.

The shape, the typical orientation, and the average size of mineral crystals in different types of mineralized tissues were investigated by means of small-angle x-ray scattering (SAXS). To rule out eventual artifacts due to sample preparation, four different standard preparation techniques were used and a comparison showed that the SAXS results were identical for all four methods. In mineralized turkey leg tendon, a frequently used model system for bone, the crystals were found to be typically plate-like with a thickness of the order of 2 nm. This stands in contrast to the case of bone (calvaria, femur, and iliac crest) from mouse, rat, and dog, where mainly needle-like crystals were found. The thickness of these crystals ranged from 3 to 4 nm but was remarkably constant for different bones of a given animal. The preferred orientation of the needle-like crystals was along the main axis of the femur and within the surface of the calvaria (for mouse, rat, and dog). The mineral plates in turkey leg tendon were located inside the hole zone and oriented along the fibril axis. Finally, no periodic arrangement of the crystals inside the hole zone of the collagen could be found.

Animals↗
PubMed1992

The caudal mandibular reconstruction plate: a radiographic and histologic study of an autopsy specimen.

During autopsy, a reconstructed partial mandibular resection was recovered and subjected to histological examination. The mandible had been reconstructed 12 weeks earlier with a caudal plate and autologous cancellous bone from the iliac crest. Undecalcified microsections showed that the plate was firmly anchored by screws on both sides and on one side there was bony union. However, most of the free transplant bone had undergone 'unreplaced resorption.' Nevertheless, this method offers advantages over the conventional method of seating the plate on the buccal aspect and has interesting potential for further development.

Bone Plates↗
PubMed1992

New aspects of the degeneration of bioprosthetic heart valves after long-term implantation.

Bioprosthetic heart valves removed 76 to 150 months after implantation were morphologically investigated to correlate structural alterations with clinical failure modes. Traditional morphologic methods of evaluating valvular heterografts, such as microradiography and electron microscopy, were complemented by undecalcified ground sections, a new technique for analyzing the distribution of mineral deposits. Apart from well-investigated mechanisms that accelerate tissue degeneration, our observations point to additional facts: (1) phagocytosis of collagen fibrils and elastic material by macrophages and foreign body giant cells in areas near tears and perforations and (2) initial calcification indicated by delicate crystals in the intercellular space arranged in close relation to the periodicity of the cross-striation pattern of collagen fibrils. The present report not only calls attention to degenerative changes that are enhanced by mechanical stress but also underlines phagocytosis as an important mechanism in the destruction of bioprosthetic heart valves.

Bioprosthesis↗
PubMed1992

[Histological studies of a tongue-shaped formation at the intertubercular groove in the shoulder joint of the dog].

Radiologically apparent unilateral changes at the intertubercular groove of the humerus were investigated histologically in three dogs and compared with the findings in an unaltered shoulder joint of a dog. Polymethylmethacrylate embedded, undecalcified sections were cut through the sulcus area at the head of humerus and through the biceps tendon, its synovial sheet and the transverse ligament, and were evaluated by light microscopy. While the tendon and soft tissue features were for the most part typical for a normal "gliding" tendon, the respective groove exhibited an again groove-like, 10-12 mm wide and up to 2 mm high exostosis consisting mainly of lamellar bone, filled with hemopoietic and fatty marrow. The normal fibrocartilaginous lining of the groove showed degenerative arthrotic changes in the altered grooves, pointing to mechanical overloading. The possible mechanisms of these ossifications are discussed.

Animals↗
PubMed1991

[Biological reaction to alloplastic reinforcement of the anterior cruciate ligament].

Control arthroscopy in usually done 6-12 months after reconstruction of the ACL with ligamentum patellae transplant augmented with LAD using Marshall's technique. During these control arthroscopies the metal implants are removed and a biopsy of the synovial lining was performed in 38 cases. We normally anchor both ends of the LAD to obtain better stability and these anchors are removed after 6-12 months (release of the fixation points). Up to now control arthroscopy has been performed on 97 patients, who had their ACL reinserted and 114 patients, whose ACL were replaced by ligamentum patellae transplant, in both cases augmented with LAD. The control arthroscopy revealed 11 cases of tears of the LAD in case ACL were reinserted and 24 cases of LAD tears in case LAD were replaced by ligamentum patellae transplant. The findings of 38 biopsies of the synovial lining are as follows: In 18 cases LAD tears, in 15 cases foreign body reactions with wear particles and an instance of lymphocytic infiltration of the synovia was seen. In 20 cases arthroscopy was inconspicuous: In 2 cases wear particles were seen and lymphocytic infiltration in a single case. In all cases of LAD tears with foreign body reactions the LAD was removed.

Anterior Cruciate Ligament↗
PubMed1989

Biochemical and morphological effects of human hepatic alkaline phosphatase in a neonate with hypophosphatasia.

Enzyme replacement-therapy for a severely affected premature boy (birthweight: 2,380 g, GA: 36 weeks) with hypophosphatasia was attempted by infusions of purified human hepatic alkaline phosphatase. Treatment (1.2 IU/kg/min) started at age three weeks and was repeated in weekly intervals until age 10 weeks, when the child died. Samples of alkaline phosphatase were diluted with 10 ml of physiological saline and infused over 30 min via an umbilical arterial catheter. No toxic or allergic side effects were observed. Serum alkaline phosphatase activity increased from 3 IU/L before treatment to a maximum level of 195 IU/L with a half-life time between 37 and 62 hours. Urinary excretion of phosphoethanolamine decreased during therapy from a maximal level of 9.5 to 5.5 mumol/mg creatinine (normal: less than 0.4 mumol/mg creatinine). Calcium, phosphorus, parathormone and 1,25-diOH vitamin D levels were within normal range. Sequential radiographic studies showed no improvement of bone mineralization. Bone morphology was studied by light and electron microscopy before treatment and post mortem. The borderline between mineralized and unmineralized matrix was more distinct after treatment and on the electron microscopical level initial spots of mineralization were more frequent between the collagen fibrils compared to the biopsy specimen before treatment. In contrast to previous studies however, only woven and bundle bone structures were studied from the tibial crest, where the lack of osteoblast-like cells upon the newly formed osteoid matrix was prominent.

Alkaline Phosphatase↗
PubMed1987

The electrochemical behavior of metallic implant materials as an indicator of their biocompatibility.

This study introduces a simple in vitro arrangement to measure current densities of implant metals. The in vivo condition of a metallic implant lying in tissues exhibiting different redox potentials is simulated in so-called straddle tests by applying a constant potential difference of 250 mV in saline containing the stable, fast-reacting redox system K4Fe(CN)6/K3Fe(CN)6. From a variety of corrosion-resistant implant metals and alloys, gold showed the highest current densities, followed by the stainless steel, the cobalt-based alloy, and the TiAIV-alloy. The pure metals titanium, niobium, and tantalum showed the lowest values. This can be explained by the stable oxide layer on these base metals, preventing an exchange of electrons and thus any redox reaction. This rating of metallic implant materials based on in vitro measurements of current densities is in good accordance with their biocompatibility rating reported from in vivo experiences. It seems that simple and cheap electrochemical tests allow an even more precise differentiation of the suitability of metallic materials for implant purposes than most of the conventional implantation tests, considering that biocompatibility is not only determined by corrosion products, but also by exchange currents and reaction products of redox processes involving tissue compounds.

Biocompatible Materials↗