Biomedical subjects

C Bünger

Publications and source records attributed to C Bünger.

At least 19 recordsLinked to original sources

PubMed1992

Tissue ingrowth into titanium and hydroxyapatite-coated implants during stable and unstable mechanical conditions.

Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. To study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)-coated implants, a loaded unstable device producing movements of 500 microns during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight-bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA-coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p less than 0.01). However, shear strength values of unstable HA-coated implants were significantly greater than those of unstable Ti implants (p less than 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA-coated implants, which was threefold stronger as compared with the stable Ti implants (p less than 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA-coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of fibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth.

Analysis of Variance↗

PubMed1992

[99mTc]diphosphonate uptake and hemodynamics in experimental arthritis: effect of naproxen in the canine carrageenan injection model.

The impact of naproxen treatment on juxta-articular hemodynamics and bone metabolism in experimental juvenile arthritis was studied in the articular carrageenan injection model. Unilateral gonarthritis was induced for 12 weeks in eight dogs receiving naproxen (dosage, 2 mg/kg) and eight controls. Regional blood flow was assessed by the microsphere method, plasma volume by the distribution space of [125I]fibrinogen, and bone metabolism by the 2-h uptake of [99mTc]diphosphonate ([99mTc]DPD). Synovial effusion was less prominent with naproxen treatment as judged by joint fluid volume and pressure. Naproxen reduced the arthritic capsular hyperemia, almost normalized a severe blood flow increase in patella and both juxta-articular epiphyses, ameliorated an expansion of plasma volume in the patella and the distal femoral epiphysis, and normalized an increased [99mTc]DPD uptake in subchondral femoral bone and the tibial cortex. Significantly increased arteriovenous shunting in the arthritic extremity was unaffected by naproxen. The study suggests that long-term cyclooxygenase inhibition offers protection against hemodynamic and metabolic changes in juxta-articular bone secondary to synovial inflammation.

Animals↗

PubMed1992

Hydroxyapatite coating modifies implant membrane formation. Controlled micromotion studied in dogs.

We studied the influence of controlled micromovements between bone and porous titanium alloy implants with and without hydroxyapatite coating. A dynamically loaded unstable device producing approximately 150-microns axial translation of knee implants during each gait cycle was developed. Stable implants served as controls. Matched stable and unstable implants with either porous titanium (Ti) or hydroxyapatite (HA) coating surrounded by a gap of 0.75 mm were inserted into the weight-bearing regions of the medial femoral condyles in 14 mature dogs. Histologic analysis after 4 weeks showed a fibrous membrane surrounding both types of implants subjected to micromovements, whereas various amounts of bone ingrowth was obtained in the stable implants. The membrane around unstable HA implants was thinner than that around unstable Ti implants. Islands of fibrocartilaginous tissue characterized the membrane around unstable HA implants, whereas fibrous connective tissue surrounded unstable Ti implants. The collagen concentration of the fibrous membranes was higher around unstable HA implants compared with Ti implants. Instability reduced the shear strength of the implants. However, the shear strength of unstable HA implants exceeded that of the Ti implants, both unstable and stable. The greatest shear strength was obtained by stable HA implants, i.e., tenfold greater than that of stable Ti implants. The gap-healing capacity around stable HA implants increased toward the HA surface, and was greater than that around Ti implants. Our study demonstrates that micromovements between bone and implant inhibit bone ingrowth and lead to the development of a fibrous membrane. The superior fixation of unstable HA implants compared with unstable Ti implants may be ascribed to the presence of fibrocartilage, a higher collagen concentration, and radiating orientation of collagen fibers in the membrane. The strongest mechanical anchorage and the greatest amount of bone ingrowth was obtained by stable implants coated with hydroxyapatite.

Alloys↗

PubMed1992

Bone graft incorporation around titanium-alloy- and hydroxyapatite-coated implants in dogs.

To evaluate cancellous allogenic bone graft incorporation into porous-coated implants, the fixation of titanium alloy-(Ti) and hydroxyapatite-(HA) coated implants with and without bone graft was compared. An unloaded model with unilateral carragheenin-induced osteopenia of the knee was used in 12 mature dogs. Ti- and HA-coated cylinders were implanted in the distal femoral condyles and centralized in 2-mm overreamed drill holes. Allogenic, fresh-frozen (-80 degrees) cancellous bone graft was packed around the implants in six dogs. In a matched group of six other dogs, the implants were left in overreamed canals without bone graft. After six weeks the interface shear strength of grafted Ti-coated implants had significantly increased compared to the nongrafted Ti implants. However, HA coating used without bone graft was capable of enhancing the bone-implant interface shear strength to nearly the same degree. The fixation of grafted Ti- and HA-coated implants was equal. No significant difference in implant fixation was found between osteopenic and control bone. Histomorphometric evaluation of mineralizing surfaces in direct contact with the implant confirmed the results from the push-out test. Bone-implant fixation when using allogeneic fresh-frozen cancellous bone graft in osteopenic and control bone was enhanced by hydroxyapatite coating but the HA coating alone appeared to offer almost the same improvement in anchorage in 2-mm defects. Loss of bone stock around loose prosthetic implants often requires bone grafting. However, because of anatomic constraints in joint prosthetic surgery, a complete filling of defects with bone graft is difficult, and areas of gaps between bone and implant will remain. Provided mechanical stability of the prosthesis, the results reported here suggest that these areas will probably be filled early with new mineralizing bone if the prosthesis is coated with a thin layer of hydroxyapatite.

Animals↗

PubMed1991

[99mTc]diphosphonate uptake and hemodynamics in arthritis of the immature dog knee.

The relationship between [99mTc]diphosphonate uptake and bone hemodynamics was studied in canine carrageenan-induced juvenile chronic arthritis. Blood flow was determined with microspheres, plasma and red cell volumes were measured by labeled fibrinogen and red cells, and the microvascular volume and mean transit time of blood were calculated. Normal femoral epiphyses had lower central and higher subchondral blood flow and diphosphonate uptake values. Epiphyseal vascular volume was uniform, resulting in a greater transit time of blood centrally. In arthritis, blood flow and diphosphonate uptake were increased subchondrally and unaffected centrally, while epiphyseal vascular volume was increased throughout, leading to prolonged transit time centrally. The normal metaphyses had low blood flow and diphosphonate uptake values in cancellous bone and very high values in growth plates, but a large vascular volume throughout. The mean transit time therefore was low in growth plates and high in adjacent cancellous bone. Arthritis caused decreased blood flow and diphosphonate uptake in growth plates but increased vascular volume and transit time of blood. Diphosphonate uptake correlated positively with blood flow and plasma volume and negatively with red cell volume in a nonlinear fashion. Thus, changes in diphosphonate uptake and microvascular hemodynamics occur in both epiphyseal and metaphyseal bone in chronic synovitis of the immature knee. The [99mTc]diphosphonate bone scan seems to reflect blood flow, plasma volume, and red cell volume of bone.

Animals↗

PubMed1991

Early hemodynamic response to tibial osteotomy in rabbits: influence of indomethacin and prostaglandin E2.

The hemodynamic role of prostaglandins in the inflammatory phase of bone healing was studied on day 4 after creation of a nailed midtibial osteotomy in 40 rabbits, divided into groups of 10, treated with either indomethacin (oral dosage 10 mg/kg), subcutaneous (s.c.) prostaglandin E2 (PGE2) (dosage 1 mg/kg), or PGE2 infusion into the abdominal aorta (rate 20 ng/kg/min) for a 20-min period immediately before the animals were killed. The last group served as controls. Regional blood flow was measured by means of radioactive microspheres, and plasma volume was assessed by distribution of circulating [125I]fibrinogen. Neither indomethacin nor s.c. PGE2 treatment had any hemodynamic effects in the osteotomy area. PGE2 infusion caused increased blood flow in bone, bone marrow, and muscle of the lower limbs except in the osteotomy area. Thus, the influence of prostaglandins and indomethacin on bone healing of a rabbit midtibial osteotomy does not appear to be a direct vascular effect in the early healing phase.

Animals↗

PubMed1991

Technetium 99m diphosphonate uptake and intraosseous hemodynamics during venous congestion in bone. Knee joint tamponade studied in immature dogs.

Venous congestion in bone is a common early feature of inflammatory and degenerative joint diseases. An experimental study was performed of the relationship between the scintigraphic appearance of joints and the intraosseous hemodynamics during venous congestion caused by obstruction of the osseous venous drainage by increased intra-articular pressure. Intra-articular pressure was raised to 75% of mean arterial pressure in one knee each of 8 immature dogs. This caused elevated intraosseous pressure in the distal femoral epiphysis but not in the metaphysis. The elevated intraosseous pressure in the affected femoral epiphysis was associated with decreased technetium 99m diphosphonate uptake and blood flow, unaltered vascular volume and tissue hematocrit, and prolonged transit time of blood in the central cancellous bone. The decreased radionuclide uptake during intraosseous venous congestion thus appeared to reflect a decreased blood supply. However, by multiple regression analysis, the diphosphonate uptake in bone generally varied positively with blood flow and plasma volume and inversely with red cell volume in a nonlinear, multifactorial relationship.

Animals↗

PubMed1991

Physical bone changes in carragheenin-induced arthritis evaluated by quantitative computed tomography.

Repeated non-invasive measurements were performed in dogs of trabecular bone density (TBD), low density bone area (LDBA), and high density bone area (HDBA) in chronic arthritis using quantitative computed tomography (QCT). Unilateral chronic arthritis of the knee had been induced by weekly instillation of 2 ml carragheenin into the right knee joint for 12 weeks with the left knee serving as a control. CT scanning of the distal femoral condyles was performed in 12 mature dogs with chronic arthritis. Another 6 dogs underwent a longitudinal CT study starting immediately prior to induction of arthritis. During induction of arthritis TBD decreased (P less than 0.01), LDBA increased (P less than 0.05) and HDBA decreased (P less than 0.01) in the arthritic bone. Opposite changes were found on the control side, i.e. TBD increased (P less than 0.01), LDBA decreased (P less than 0.01) and HDBA increased (P less than 0.01). The chronic arthropathic bone showed 20% lower TBD (P less than 0.0001), greater LDBA (P less than 0.0001) and lower HDBA (P less than 0.0001) as compared with the control bone. Reproducibility tests of TBD showed a coefficient of variation of 0.8%. Indentation tests and histomorphometric analyses confirmed the bone density changes as measured by CT.

Animals↗

PubMed1991

Fixation of titanium and hydroxyapatite-coated implants in arthritic osteopenic bone.

Retrieval studies of porous-coated prostheses have demonstrated deficient bony ingrowth in high percentages. Possible reasons for this are lack of initial mechanical stability and the presence of osteopenia. The authors studied ingrowth of osteopenic bone into titanium alloy (Ti) porous-coated implants with and without hydroxyapatite (HA) coating in an experimental dog model. Unilateral osteopenia of the knee with a 20% reduced bone density as judged by computed tomography (CT) scanning (P less than .001) was induced in 12 mature dogs by weekly intraarticular injections of Carragheenin into the right knee for 12 weeks, with the left knee serving as control. Ti porous-coated cylinders were inserted in press-fit bilaterally in the lateral femoral condyles in six dogs. HA-coated titanium plugs were implanted similarly in another sex-, age-, and weight-matched group of six dogs. Bony ingrowth after 4 weeks was significantly reduced for Ti implants in osteopenic bone compared to control bone, but HA-coated implants were covered by equal amounts of bone tissue. Bone-implant shear strength of Ti implants also was reduced in osteopenic bone compared to control bone. In control bone, the anchorage of Ti implants was stronger than HA-coated implants, whereas the fixation of Ti and HA-coated implants was equal in the osteopenic bone. The results demonstrate that the bony fixation of Ti porous-coated implants is weakened by the presence of experimentally induced osteopenia. However, the fixation of HA-coated implants was not affected by the osteopenic condition in the surrounding bone. The fixation of Ti and HA-coated implants was equal in osteopenic bone, whereas the fixation of Ti porous-coated implants was superior to that of HA-coated implants in control bone.

Animals↗

PubMed1991

Arteriovenous shunting is not associated with venous congestion in bone. Knee tamponade studied with 15-microns and 50-microns microspheres in immature dogs.

Blood flow in the hind-limb bones of 8 immature labrador dogs with unilateral knee joint tamponade at 75 percent of the mean arterial pressure was measured with 15-microns and 50-microns microspheres to determine whether or not arteriovenous shunting occurs in bone with venous congestion caused by increased outflow resistance. The intraosseous pressure was 43 percent of the mean arterial pressure in the experimental distal femoral epiphysis versus 14 percent in the control knee (P less than 0.001). No pressure changes were found in the distal femoral metaphysis. Regional blood flow with 15-microns microspheres decreased centrally in the distal femoral epiphysis and increased centrally in the proximal tibial epiphysis. Metaphyseal blood flow was largely unchanged. A net shift in the preferred embolization site of 50-microns microspheres relative to that of 15-microns microspheres from central to peripheral regions occurred within both juxtaarticular epiphyses, indicating arteriolar vasodilation, but the relation between the uptake of the two microsphere sizes was unchanged when the epiphyses and other bony flow compartments were viewed in toto. The result speaks against the hypothesis of arteriovenous shunting in intraosseous hypertension.

Animals↗

PubMed1991

A method for bone-cement interface thermometry. An in vitro comparison between low temperature curing cement Palavit, and Surgical Simplex P.

Previous temperature measurements at the bone-cement intreface have all shown large variations. To evaluate more precisely the temperature profiles during cement curing, a new experimental model was developed. Eight thermocouple electrodes at the bone-cement interface for each test specimen were used for continuous temperature recordings. Temperature profiles of Palavit was compared with those of Surgical Simplex P in an in vitro model using isolated pig femurs. Defects of 12 x 17 mm in the femoral metaphysis were filled with cement. In six tests with each type of cement, Palavit peaked at a temperature of 50 +/- 0.5 degrees C, whereas Surgical Simplex P peaked at 60 +/- 0.7 degrees C. Core temperatures reached peak values of 70 +/- 0.8 degrees C and 95 +/- 2.2 degrees C for Palavit and Surgical Simplex P, respectively.

Animals↗

PubMed1991

Gap healing enhanced by hydroxyapatite coating in dogs.

During prosthetic implantation, gaps between the implant surface and the surrounding bone may occur resulting in reduced implant stability. In these instances bone-conductive materials might augment the formation of hosting bone into the pores of the implant and insure earlier implant stabilization and fixation by bony ingrowth. Titanium-alloy cylinders with a porous-titanium-alloy plasma spray coating were implanted into the medial femoral condyles in six mature dogs. In another group of six dogs, matched in age, weight, and gender, hydroxyapatite (HA) coated implants were used. All implants were surrounded by a 1-mm gap. Unilateral osteopenia of the knee, with a 20% reduction of bone density as judged by computed tomography scanning, was induced by 12 weekly intraarticular injections of carrageenin into the right knee before surgery. Four weeks after implantation, the HA-coated implants were compared to the parent porous-titanium implants by mechanical testing and histomorphometry. A marked positive influence of HA coating on bone mineralization and the strength of the interfacial bone between the bone and implant was found. The increment in interface shear strength and shear stiffness was three- to fivefold in osteopenic bone and two-fold in control bone. Coating of an unloaded porous-titanium-coated implant with HA accelerates the rate of bone ingrowth and thereby provides relatively high, early interfacial shear strengths in the presence of an initial gap between bone and implant even in the presence of osteopenic host bone.

Animals↗

PubMed1990

Vasoactive substances in subchondral bone of the dog knee.

The purpose of the present study was to investigate regulatory mechanisms for subchondral bone blood flow. A model including elevation of joint cavity pressure in the immature dog knee was applied. The role of prostaglandins in bone blood flow regulation was indirectly examined by indomethacin blockade. In six puppies, both venous tamponade of the joint cavity [50% of the mean arterial blood pressure (MAP)] and arterial tamponade (150% of MAP) resulted in a significant increase in the intraosseous pressure of the distal femoral epiphyses (p less than 0.05). During venous tamponade no changes were registered in pO2, pCO2, pH, potassium, and lactate in blood withdrawn from the distal femoral epiphyses. Arterial tamponade resulted in hypoxia, a decrease in pH, and increased lactate. Inhibition of the prostaglandin synthesis did not alter this response pattern. Thus, the present study suggests the presence of a regulatory mechanism for subchondral bone blood flow since venous tamponade did not significantly alter intraosseous gas tensions, pH, lactate, or potassium in spite of elevated venous outlet resistance. The study does not allow any conclusion as to the exact nature of the regulatory mechanism, but local metabolic regulation is likely to be involved as indicated by accumulation of vasoactive substances at higher tamponade levels. Prostaglandins are probably of minor importance in this regulation.

Animals↗

PubMed1990

Displaced distal radius fractures. A comparative study of early results following external fixation, functional bracing in supination, or dorsal plaster immobilization.

A comparison of the radiographical and functional results after displaced distal radius fractures in 41 patients treated by external fixation (EF), 36 patients treated by functional bracing in supination (FUSU), and 49 patients treated by dorsal plaster immobilization (DPI) was performed. The rate of initial complications after EF was 53%, compared with 22% after FUSU and 14% after DPI. The radiographical result after EF was significantly better than after nonoperative treatment, but the functional result after 3 and 6 months demonstrated no significant difference between the three series. Consequently, EF and FUSU do not restore wrist function faster than conventional plaster treatment (DPI), but EF improves the radiographical result, though the rate of complications is higher.

Adult↗

PubMed1990

Microvascular morphology of bone in arthrosis. Scanning electron microscopy in rabbits.

The morphology of the bone microvasculature in rabbit arthrosis was studied by scanning electron microscopy (SEM) and related to changes in intraosseous pressure (IOP) and phlebographic appearance. Unilateral gonarthrosis was induced in 34 rabbits by immobilization of one knee in extension with a plastic splint for 5 weeks. Bilateral IOP recording in a subgroup of 12 rabbits demonstrated hypertension in arthrosis of 22 +/- 2.9 mmHg compared with 11 +/- 4.7 mmHg in control knees. Intraosseous phlebography in 13 rabbits showed a dilated vascular bed with prolonged clearance of contrast media. The morphology of normal microvasculature by SEM of intravascular methyl methacrylate casts in 9 rabbits was characterized by well-defined and well-demarcated sinusoids with only a few arteriovenous shunts, whereas in arthrosis substantial changes included fusion of sinusoids, leakage of cast material through the sinusoid walls, and development of numerous shunts. The study demonstrated profound microvascular morphologic changes that may reflect a vascular genesis for some of the bone changes in arthrosis.

Animals↗

PubMed1990

Synovitis reduced by inhibition of leukotriene B4. Carrageenan-induced gonarthritis studied in dogs.

The pathophysiologic significance of leukotriene B4 (LTB4) in arthritis was studied in dogs by unilateral intraarticular deposition of 15-hydroxy-eicosatetraenoic acid (15-HETE), an endogenous inhibitor of the formation and the effects of LTB4, in bilateral carrageenan-induced gonarthritis. LTB4 in synovial fluid was selectively inhibited in 15-HETE treated joints, the formation of prostaglandin E2 (PGE2) being largely unaffected. The clinical symptoms, intraarticular pressure, and extractable synovial fluid volume were reduced in treated joints. No effect could be discerned regarding blood flow in the synovial membrane, capsule, or juxta-articular bone as measured by tracer microspheres; and no effect on bone metabolism was found as judged by 99mTc-diphosphonate uptake. Thus, inhibition of LTB4 reduces joint exudation, but does not seem to interfere with changes in juxta-articular hemodynamics or bone metabolism following synovial inflammation.

Animals↗

PubMed1990

Hydroxyapatite coating enhances fixation of porous coated implants. A comparison in dogs between press fit and noninterference fit.

Intimate contact at the bone-porous surface interface is not always achievable in noncemented prosthetic implantation. We investigated the effect of hydroxyapatite (HA) coating on skeletal attachment in noninterference fit 4 weeks after implantation in 6 mature dogs. The push-out test of HA-coated implants surrounded by a 1-mm gap showed a twofold increased shear strength and fivefold increased shear stiffness compared with titanium alloy (Ti) coated implants. The fixation of Ti implants was reduced by two thirds when inserted in a gap as compared with press fit, whereas HA-coated implants in gap showed anchorage close to implants in press fit. Only minor differences were found between HA and Ti implants in press fit. Histomorphometric analysis showed a significant increase in bone in direct contact to HA-coated implant as compared with Ti implants inserted both in gap and press fit. The study indicates that tightness of surgical fit is an important factor for sufficient fixation of the implant. However, our results demonstrate that hydroxyapatite coating almost eliminates the negative influence of noninterference fit between bone and unloaded implant.

Animals↗

PubMed1989

Three-phase [99mTc]diphosphonate scintimetry in septic and nonseptic arthritis of the immature knee: an experimental investigation in dogs.

We compared the informative value of dynamic and static [99mTc]diphosphonate ([99mTc]DPD) scintimetry in early septic arthritis (SA) and chronic nonseptic arthritis (NSA) of the knee in puppies. SA (n = 10), induced by injection of Staphylococcus aureus into one knee, was examined after 48 h. NSA (n = 6) was induced by weekly intraarticular instillation of 1% carrageenan and examined at 2 and 12 weeks. Epiphyseal and metaphyseal count ratios (CRs) between experimental and control joint were calculated in an angiographic phase (0-20 s), a "blood pool" phase (20-256 s), and a bone uptake phase (2 hs). Control dogs (n = 4) had a CR of 1.0 in all regions and phases, the coefficients of variation being 0.06 and 0.03 in dynamic and static phases, respectively. In NSA, all scintimetric phases showed decreased metaphyseal uptake and largely unchanged epiphyseal uptake. Generally, SA exhibited vastly increased angiographic uptake in all regions and increased epiphyseal blood pool uptake, whereas delayed epiphyseal uptake varied and delayed metaphyseal uptake tended to decrease. Two septic joints had generalized reduction in dynamic uptake, probably owing to increased intraarticular pressure; in one of these, dynamic uptake in the distal femoral epiphysis (FE) was totally absent, suggesting temporary circulatory arrest during the dynamic scanning procedure. The use of regional dynamic and static [99mTc]DPD scintimetry increased the pathophysiologic and diagnostic value of joint scintigraphy, especially with respect to the early detection of SA and its avascular complications.

Animals↗