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Biomedical subjects

C Bünger

Publications and source records attributed to C Bünger.

At least 19 recordsLinked to original sources
PubMed2006

Bone nanostructure near titanium and porous tantalum implants studied by scanning small angle x-ray scattering.

Bone sections including either titanium or porous tantalum implant devices used for interbody spinal fusion were investigated with position-resolved small angle X-ray scattering (sSAXS). The samples were obtained from six-month-old pigs that had undergone surgery three months prior to sacrifice. The aim of the study was to explore the possibility of using sSAXS to obtain information about thickness, orientation and shape/arrangement of the mineral crystals in bone near the implant surfaces. Detailed sSAXS scans were carried out in two different regions of bone adjacent to the implant in each of the implant samples. In the implant vicinity the mineral crystals tended to be aligned with the surface of the implants. The mean crystal thickness was between 2.1 and 3.0 nm. The mineral crystal thickness increased linearly with distance from the implant in both regions of the porous tantalum implant and in one of the regions in the titanium sample. In the second region of the titanium sample the thickest mineral crystals were found close to the implant surface. The observed differences in mineral thickness with distance from the implant surfaces might be explained by differences in mechanical load induced by the implant material and the geometrical design of the implant. The study shows that sSAXS is a powerful tool to characterize the nanostructure of bone near implant surfaces.

Humans↗
PubMed2004

Stabilisation surgery for chronic low back pain: indications, surgical procedures, and outcome.

Spinal fusion was introduced as a treatment option for chronic low back pain >70 years ago. However, few areas of spinal surgery have caused as much controversy. The debate about whether to use an anterior-, posterior- or anterior + posterior approach has persisted since the 1930s. Within the last 10 years, the effects of different spinal fusion procedures have been tested in 10 randomized controlled trails (RCT). A highly significant improvement over preoperative status was found in all 10 studies. Two recent RCTs have dealt with the question of conservative versus operative treatment of patients with low back pain, and both studies have shown a significant better functional outcome for spinal fusion in situ, compared with a more or less organized exercise programme at 2-year follow-up. The choice of postoperative rehabilitation strategy has also been shown to be of importance for overall functional outcome. One study has demonstrated the importance of the inclusion of coping schemes, and questioned the role of intensive exercises in a rehabilitation programme for spinal fusion patients.

Adaptation, Psychological↗
PubMed2002

Dynamic gadolinium-enhanced MRI evaluation of porcine femoral head ischemia and reperfusion.

OBJECTIVE: To examine the potential of gadolinium (Gd)-enhanced dynamic MRI in the detection of early femoral head ischemia. Furthermore, to apply a three-compartment model to achieve a clinically applicable MR index for femoral head perfusion during the steady state and arterial hip joint tamponade. DESIGN AND MATERIALS: In a porcine model femoral head perfusion was measured by radioactive tracer microspheres and by using a dynamic Gd-enhanced MRI protocol. Femoral head perfusion measurements and MRI tests were performed unilaterally before, during and after the experimentally induced ischemia of one of the hip joints. Ischemia was induced by increasing intra-articular pressure to 250 mmHg. RESULTS: All pigs showed ischemia of the femoral head epiphysis under hip joint tamponade followed by reperfusion to the same level as before joint tamponade. In two cases perfusion after removal of tamponade continued to be low. In dynamic MRI measurements increases in signal intensity were seen after intravenous infusion of Gd-DTPA, followed by a slow decrease in signal intensity. The signal-intensity curve during femoral head ischemia had a minor increase. Also the coefficient determined was a helpful indicator of femoral head ischemia. CONCLUSIONS: Femoral head blood flow as measured by microspheres fell significantly under joint tamponade. Early detection of this disturbed regional blood flow was possible using a dynamic MRI procedure. A biomathematical model resulted from the evaluation of the intervals of signal intensity over time which allows detection of bone blood flow changes at a very early stage. Using this new method earlier detection of femoral head necrosis may be possible.

Animals↗
PubMed2001

Smoking as a predictor of negative outcome in lumbar spinal fusion.

STUDY DESIGN: A review of the smoking habits in 426 patients who had been followed prospectively for 2 years after a lumbar spinal fusion procedure was conducted. OBJECTIVE: To analyze the effect of pre- and postoperative smoking on clinical and functional outcome after lumbar spinal fusion. SUMMARY OF BACKGROUND DATA: Several animal models have shown a negative effect of nicotine on spinal fusion. At this writing, the clinical effect of nicotine on spinal fusion has not been fully clarified. METHODS: The study comprised 426 patients who underwent lumbar spinal fusion between 1993 and 1997. These patients received a mailed questionnaire regarding their tobacco consumption before and after their surgery. All other data, including preoperative clinical and functional status, were collected prospectively during a 2-year follow-up period. To assess functional outcome, the Dallas Pain Questionnaire was used. RESULTS: The questionnaire was answered by 396 patients (93%). Of these patients, 54.5% (20% more than the background population) were smokers before the operation. Smoking of more than 10 cigarettes daily before the operation and attempted fusion at two or more levels increased the risk of nonunion: odds ratio, 2.01 (P < 0.016) and odds ratio, 3.03 (P < 0.001), respectively. Smoking cessation increased fusion rates to near those of nonsmokers. Smoking had no influence on functional outcome, as assessed by the Dallas Pain Questionnaire, but preoperative smoking predicted a negative answer to the question "Would you undergo the same treatment again, now that you know the result?" (odds ratio, 1.65; P < 0.054). CONCLUSIONS: Smoking was shown to have a negative effect on fusion and overall patient satisfaction, but no measurable influence on the functional outcome as assessed by the Dallas Pain Questionnaire.

Adult↗
PubMed2001

Effect of osteogenic protein 1/collagen composite combined with impacted allograft around hydroxyapatite-coated titanium alloy implants is moderate.

This study evaluated the effects of osteogenic protein 1/collagen composite (OP-1/col) mixed with impacted allograft around hydroxyapatite (HA)-coated titanium alloy implants in a canine model. The aim of the study was to test different doses of OP-1 growth factor in a collagen composite for stimulatory effect on allograft incorporation around an implant. Unloaded implants were inserted in each proximal humerus of 16 skeletally mature dogs. The cylindrical implants (4 x 9 mm) coated with HA were initially surrounded by a 3-mm gap into which allograft mixed with OP-1/col was impacted. Two different doses of OP-1 were investigated. In eight animals 325 mg OP-1 protein and 130 mg bovine collagen type I as carrier were mixed with the allograft chips. This composite is identical to the clinically used OP-1 device called Novus. In another eight animals a lower dose of 65 mg OP-1 protein and 130 mg bovine collagen type I was used. Control implants placed in the contralateral humerus were surrounded by allograft mixed with collagen carrier only. The dogs were euthanized at 6 weeks. Implant fixation was determined by push-out testing. Bone ingrowth and bone formation were evaluated by quantitative histomorphometry on serial sections of the bone-implant interface. Impacted allograft together with low-dose OP-1 enhanced bone volume in a zone adjacent to HA-coated titanium alloy implants. The high dose had no effect on bone formation. Mechanical fixation, bone ingrowth, and bone volume in the gap near the original trabecular bone were unaffected by both low and high OP-1/col composite. In this model and observation period, the low dose of OP-1/col composite mixed with impacted allograft has a moderate effect on bone healing around HA-coated implants and no effect on implant fixation.

Animals↗
PubMed2001

Factors stimulating bone formation.

The aim of this review is to describe major approaches for stimulating bone healing and to review other factors affecting bone healing. Spinal bone fusion after surgery is a demanding process requiring optimal conditions for clinical success. Bone formation and healing can be enhanced through various methods. Experimental studies have revealed an array of stimulative measures. These include biochemical stimulation by use of hormones and growth factors, physical stimulation through mechanical and electromagnetic measures, and bone grafting by use of bone tissue or bone substitutes. Newer biological techniques such as stem cell transplantation and gene therapy can also be used to stimulate bone healing. Apart from bone transplantation, clinical experience with the many stimulation modalities is limited. Possible areas for clinical use of these novel methods are discussed.

Aging↗
PubMed2001

Transforming growth factor-beta1 adsorbed to tricalciumphosphate coated implants increases peri-implant bone remodeling.

Increasing experimental interest has emerged for the use of growth factors to stimulate bone healing and bone formation in various clinical situations. We and others have demonstrated that recombinant human transforming growth factor-beta1 (rhTGF-beta1) adsorbed onto tricalcium phosphate (TCP)-coated implants can improve mechanical fixation and bone ongrowth. The present study evaluated bone remodeling in newly formed bone and adjacent trabecular bone around TCP-coated implants with and without rhTGF-beta1 adsorption. Unloaded cylindrical grit-blasted titanium alloy implants coated with TCP were inserted bilaterally into the femoral condyles of 10 skeletally mature mongrel dogs. The implants were initially surrounded by a 2 mm gap. Implants with 0.3 microg rhTGF-beta1 were compared with implants without growth factor. The dogs were sacrificed after six weeks. Bone remodeling was evaluated by histomorphometry on Goldner-stained undecalcified sections. The bone volume in the gap was increased significantly from 17.6% in the control group to 25.6% in the rhTGF-beta1 group (p = 0.03). Also bone surface was increased in the rhTGF-beta1 group. The osteoclast covered surfaces were increased from 3.6% in the control group to 5.9% in the rhTGF-beta1 group (p = 0.02). In the surrounding trabecular bone no significant changes in bone remodeling parameters was demonstrated. This study suggests that rhTGF-beta1 adsorbed onto TCP-ceramic coated implants accelerates repair activity in the newly formed bone close to the implant, but it does not seem to influence bone remodeling in preexisting bone at a greater distance from the implant.

Adsorption↗
PubMed2001

Adrenergic responses in human small arteries isolated from the femoral neck.

Many pathological bone conditions are accompanied by changes in bone perfusion. However, no method has yet allowed investigation of vascular reactivity in human bone tissue. In the present study, arterial segments (diameter approximately 0.25 mm) were isolated from human bone biopsies and mounted as ring preparations in vitro. The viability of the arteries and the effects of adrenoceptor stimulations were investigated. Combined alpha- and beta-adrenoceptor stimulation (noradrenaline 10(-8)-10(-5) M) and specific alpha1-adrenoceptor stimulation (phenylephrine, 10(-8)-10(-4.5) M) induced concentration-dependent contractions in all arteries. Selective stimulation of alpha2-receptors (B-HT 933, 10(-8)-10(-3.5) M) only induced contraction in three of eight arteries. Stimulation of beta-receptors with isoprenaline (10(-6) M) resulted in vasorelaxation in 3 of 10 arteries. In all arteries, acetylcholine (10(-10)-10(-5) M) induced vasorelaxation, demonstrating preserved function of the endothelium. The results suggest that primarily alpha1-receptors are responsible for adrenoceptor induced vasoconstriction in human bone while functional alpha2- and beta-receptors may not be consistently expressed. The model is the first to allow investigations on vascular reactivity in human bone tissue and may become valuable for assessment of both normal and pathological bone physiology.

Acetylcholine↗
PubMed2001

Selective reduction of bone blood flow by short-term treatment with high-dose methylprednisolone. An experimental study in pigs.

Treatment with corticosteroids is a risk factor for non-traumatic avascular necrosis of the femoral head, but the pathological mechanism is poorly understood. Short-term treatment with high doses of methylprednisolone is used in severe neurotrauma and after kidney and heart transplantation. We investigated the effect of such treatment on the pattern of perfusion of the femoral head and of bone in general in the pig. We allocated 15 immature pigs to treatment with high-dose methylprednisolone (20 mg/kg per day intramuscularly for three days, followed by 10 mg/kg intramuscularly for a further 11 days) and 15 to a control group. Perfusion of the systematically subdivided femoral head, proximal femur, acetabulum, humerus, and soft tissues was determined by the microsphere technique. Blood flow in bone was severely reduced in the steroid-treated group. The reduction of flow affected all the segments and the entire epiphysis of the femoral head. No changes in flow were found in non-osseous tissue. Short-term treatment with high-dose methylprednisolone causes reduction of osseous blood flow which may be the pathogenetic factor in the early stage of steroid-induced osteonecrosis.

Acetabulum↗
PubMed2001

Sealing effect of hydroxyapatite coating on peri-implant migration of particles. An experimental study in dogs.

We have studied the beneficial effects of a hydroxyapatite (HA) coating on the prevention of the migration of wear debris along the implant-bone interface. We implanted a loaded HA-coated implant and a non-coated grit-blasted titanium alloy (Ti) implant in each distal femoral condyle of eight Labrador dogs. The test implant was surrounded by a gap communicating with the joint space and allowing access of joint fluid to the implant-bone interface. We injected polyethylene (PE) particles into the right knee three weeks after surgery and repeated this weekly for the following five weeks. The left knee received sham injections. The animals were killed eight weeks after surgery. Specimens from the implant-bone interface were examined under plain and polarised light. Only a few particles were found around HA-coated implants, but around Ti implants there was a large amount of particles. HA-coated implants had approximately 35% bone ingrowth, whereas Ti implants had virtually no bone ingrowth and were surrounded by a fibrous membrane. Our findings suggest that HA coating of implants is able to inhibit peri-implant migration of PE particles by creating a seal of tightly-bonded bone on the surface of the implant.

Alloys↗
PubMed2000

Vertebral blood flow and bone mineral density during long-term corticosteroid treatment: An experimental study in immature pigs.

STUDY DESIGN: Bone mineral density and regional blood flow were measured in pigs during long-term methylprednisolone treatment. OBJECTIVES: To investigate possible changes in bone mineral density and vertebral blood flow during long-term glucocorticoid treatment. SUMMARY OF BACKGROUND DATA: Steroid-induced vertebral osteonecrosis preferentially involves endplates and adjacent cancellous bone. The precise etiology of vertebral osteonecrosis during long-term glucocorticoid treatment is unknown. METHODS: Twenty-four 10-week-old female Danish landrace sister pigs from 12 litters were treated in two groups. Twelve animals received oral methylprednisolone for 3 months at a daily dose of 100 mg. The 12 sister pigs received no steroid treatment and served as controls. Regional blood blow was measured by means of microspheres in predefined regions of the C6, T11, and L6 vertebrae. In vitro DEXA scanning of the L2-L4 vertebra was performed to assess bone mineral density. RESULTS: Vertebral cancellous bone and endplate regional blood flow were decreased in the C6 and L6 vertebrae among corticosteroid-treated pigs compared with that of controls.- Width-adjusted lumbar vertebral bone mineral density (g/cm3) was unchanged, whereas projectional lumbar vertebral bone mineral density (g/cm2) was decreased in corticosteroid-treated pigs. CONCLUSIONS: Long-term methylprednisolone treatment decreases vertebral bone blood flow mainly in cancellous bone and endplates. This may be an important factor in the pathogenesis of osteonecrosis secondary to glucocorticoid treatment. Lumbar vertebral bone mineral density was unchanged in growing pigs on long-term glucocorticoid treatment when expressed as volumetric bone density. The effect of glucocorticoid treatment on vertebral bone mineral density appears to depend on whether it is expressed as projectional (g/cm2) or volumetric bone mineral density (g/cm3). Vertebral and longbone growth was reduced during methylprednisolone treatment.

Animals↗
PubMed2000

Titanium-alloy enhances bone-pedicle screw fixation: mechanical and histomorphometrical results of titanium-alloy versus stainless steel.

Several types of pedicle screw systems have been utilized to augment lumbar spine fusion. The majority of these systems are made of stainless steel (Ss), but titanium-alloy (Ti-alloy) devices have recently been available on the market. Ti-alloy implants have several potential advantages over Ss ones. High bioactivity and more flexibility may improve bone ingrowth and mechanical fixation, and the material also offers superior magnetic resonance imaging (MRI) and computed tomography (CT) resolution and significantly less signal interference. However, no data are available from loaded spinal constructs regarding bony ingrowth and mechanical fixation. The aim of this study was to analyse the effect of Ti-alloy versus Ss pedicle screws on mechanical fixation and bone ingrowth in a loaded mini-pig model. Eighteen adult mini-pigs underwent total laminectomy and posterolateral spinal fusion at L3-L4, and were randomly selected to receive either Ss (n = 9) or Ti (n = 9) pedicle screw devices. In both groups, the device used was compact Cotrel-Dubousset instrumentation (Sofamore Danek) of an identical size and shape. The postoperative observation time was 3 months. Screws from L3 were used for histomorphometric studies. Mechanical testing (torsional tests and pull-out tests) was performed on the screws from L4. The Ti screws had a higher maximum torque (P < 0.05) and angular stiffness (P < 0.07), measured by torsional testing. In the pull-out tests, no differences were found between the two groups with respect to the maximum load, stiffness and energy to failure. No correlation between removal torque and the pull-out strength was found (r = 0.1). Bone ongrowth on Ti was increased by 33% compared with Ss (P < 0.04), whereas no differences in bone volume around the screws were shown. Mechanical binding at the bone-screw interface was significantly greater for Ti pedicle screws than for Ss, which was explained by the fact that Ti screws had a superior bone ongrowth. There was no correlation between the screw removal torque and the pull-out strength, which indicates that the peripheral bone structure around the screw was unaffected by the choice of metal.

Animals↗
PubMed2000

Osteogenic protein 1 device stimulates bone healing to hydroxyapaptite-coated and titanium implants.

This study evaluated the effects of osteogenic protein 1 (OP-1) placed in a gap around uncoated and hydroxyapatite (HA)-coated implants. Unloaded cylindrical titanium alloy implants were inserted in the femoral condyles of 16 skeletally mature dogs surrounded by a 3-mm gap. The gap around the implants was filled with 325 microg OP-1 in 130 mg bovine collagen type I as carrier (OP-1 device) or collagen carrier alone or left empty. All groups were tested with both HA-coated and uncoated implants, and the animals were sacrificed after 6 weeks. Implant fixation was determined by push-out test. Bone ongrowth and bone formation were evaluated by quantitative histomorphometry. OP-1 device enhanced mechanical fixation of uncoated and HA-coated implants, resulting in a higher shear strength than implants with collagen matrix and control implants. Bone ingrowth and bone formation in the gap were also stimulated 3-fold for OP-1 groups when compared with empty controls, but no difference was found between OP-1 groups and collagen matrix groups. This study suggests that the OP-1 device placed in a gap around uncoated and HA-coated implants is capable of enhancing mechanical fixation and periimplant bone formation. The collagen carrier alone also enhanced bone ongrowth and fixation significantly.

Animals↗
PubMed2000

The influence of human intervertebral disc tissue on the metabolism of osteoblast-like cells.

Extensive studies have been performed to evaluate different factors that may affect on spinal interbody fusion, but the role of intervertebral disc tissue in the fusion process remains unclear. To study the influence of intervertebral disc tissue on osteoblast metabolism, we harvested disc tissue from patients who had undergone spinal surgery. The nucleus pulposus and annulus fibrosus were separately co-cultured with osteoblast-like cells SaOS-2 by means of culture inserts or organ culture. We assayed alkaline phosphoatase activity, 3H-thymidine incorporation into the DNA, and production of collagen type I, IL-1beta, IL-6, IL-10, and TNF-alpha. Exposure of the nucleus pulposus (NP) to osteoblast-like cells revealed stimulation of alkaline phosphatase production, 3H-thymidine incorporation and collagen type I production. Exposure of the annulus fibrosus (AF) stimulated 3H-thymidine incorporation and collagen type I production, but did not affect ALP activity. IL-6 was detected after application of NP and AF. Interleukin IL-10, IL-1beta and TNF-alpha were all below detection levels after application of disc tissue. Our findings show that frozen disc tissue stimulates the metabolism of osteoblast-like cells in vitro.

Adolescent↗
PubMed1999

Improved bone anchorage of hydroxypatite coated implants compared with tricalcium-phosphate coated implants in trabecular bone in dogs.

Tricalcium phosphate (TCP) and hydroxyapatite (HA) ceramic coatings are bioactive coatings that have been shown to stimulate bone apposition onto ceramic-coated implants. TCP and HA ceramics have well-documented differences in physical properties, but both types of ceramics are used for stimulation of bone ongrowth to cementless endo-prosthetic components clinically. However, little is known about the difference in osteoconductive properties between these coatings when inserted into trabecular bone in a controlled experimental situation. Unloaded cylindrical gritblasted titanium (Ti-6A1-4V) implants (6 x 10 mm) coated with either hydroxyapatite (HA) or tricalcium phosphate (TCP) ceramic were inserted into the proximal humerus of 20 skeletally mature dogs. The implants were initially surrounded by a 2 mm gap. Each animal received one HA-coated implant and one TCP-coated implant. All dogs were sacrificed 6 weeks after surgery. Results were evaluated by histomorphometry and mechanical push-out test. Push-out tests demonstrated that HA-coated implants were 10-fold stronger fixated in comparison to TCP-coated implant. Bone ongrowth was significantly higher for HA-coated implants compared to TCP-coated implants. Bone volume in the gap showed a tendency to less bone volume around HA-coated implants compared to TCP-coated implants but this difference was insignificant. As expected almost all of the TCP coating were resorbed after 6 weeks and almost none of the HA coating. HA-coated implants with a grit-blasted surface provide a favorable early mechanical implant anchorage most likely due to superior ceramic stability compared to TCP-coated implants.

Alloys↗
PubMed1999

The influence of crystallinity of the hydroxyapatite coating on the fixation of implants. Mechanical and histomorphometric results.

We inserted two hydroxyapatite (HA)-coated implants with crystallinities of either 50% (HA-50%) or 75% (HA-75%) bilaterally into the medial femoral condyles of the knees of 16 dogs. The implants were allocated to two groups with implantation periods of 16 and 32 weeks. They were weight-bearing and subjected to controlled micromovement of 250 microm during each gait cycle. After 16 weeks, mechanical fixation of the HA-50% implants was increased threefold as compared with the HA-75% implants. After 32 weeks there was no difference between HA-50% and HA-75%. Fixation of HA-75% increased from 16 to 32 weeks whereas that of HA-50% was unchanged. HA-50% implants had 100% more bone ingrowth than HA-75% implants after 16 weeks. More HA coating was removed on HA-50% implants compared with HA-75% implants after both 16 and 32 weeks. No further loss of the HA coating was shown from 16 to 32 weeks. Our study suggests that the crystallinity of the HA coating is an important factor in its bioactivity and resorption during weight-bearing conditions. Our findings suggest two phases of coating resorption, an initial rapid loss, followed by a slow loss. Resorbed HA coating was partly replaced by bone ingrowth, suggesting that implant fixation will be durable.

Animals↗
PubMed1999

Reperfusion pattern of the immature femoral head after critical ischemia: a microsphere study in pigs.

The topographic reperfusion pattern of the femoral head after critical ischemia has not yet been investigated. We determined the blood flow of the porcine hip regions with the femoral head epiphysis divided into 24 subregions by the tracer microsphere technique. Blood flow was measured under steady-state conditions, at the end of a 6-hour increase in intracapsular hip joint pressure to 250 mm Hg, and 4 hours after release of the joint tamponade. Total femoral head epiphyseal blood flow decreased with ischemia and regained steady-state perfusion after tamponade. The reperfusion pattern of the femoral head epiphysis appeared identical with that of the steady state before ischemia. However, 2 of the 11 experimental epiphyses remained ischemic in the reperfusion phase. We conclude that hip joint tamponade above the arterial pressure level for 6 hours causes global ischemia in the femoral head epiphysis in the immature pig, without regional differences in reperfusion, and that reperfusion occurs at a level like that of the steady state before ischemia.

Age Factors↗