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Biomedical subjects

H Kambic

Publications and source records attributed to H Kambic.

At least 19 recordsLinked to original sources
PubMed2001

The effects of tibial rotation on posterior translation in knees in which the posterior cruciate ligament has been cut.

BACKGROUND: One of the most useful clinical tests for diagnosing an isolated injury of the posterior cruciate ligament is the posterior drawer maneuver performed with the knee in 90 degrees of flexion. Previously, it was thought that internally rotating the tibia during posterior drawer testing would decrease posterior laxity in a knee with an isolated posterior cruciate ligament injury. In this study, we evaluated the effects of internal and external tibial rotation on posterior laxity with the knee held in varying degrees of flexion after the posterior cruciate and meniscofemoral ligaments had been cut. MATERIALS AND METHODS: Twenty cadaveric knees were used. Each knee was mounted in a fixture with six degrees of freedom, and anterior and posterior forces of 150 N were applied. The testing was conducted with the knee in 90 degrees, 60 degrees, 30 degrees, and 0 degrees of flexion with the tibia in neutral, internal, and external rotation. All knees were tested with the posterior cruciate and meniscofemoral ligaments intact and transected. Repeated-measures analysis of variance was used for statistical analysis. RESULTS: At 30 degrees, 60 degrees, and 90 degrees of flexion, there was a significant increase in posterior laxity following transection of the posterior cruciate and meniscofemoral ligaments. At 60 degrees and 90 degrees of flexion, there was significantly less posterior laxity when the tibia was held in internal compared with external rotation. At 0 degrees and 30 degrees of flexion, there was no significant difference in posterior laxity when the tibia was held in internal compared with external rotation. CONCLUSIONS: After the posterior cruciate and meniscofemoral ligaments had been cut, posterior laxity was significantly decreased by both internal and external rotation of the tibia. Internal tibial rotation resulted in significantly less laxity than external tibial rotation did at 60 degrees and 90 degrees of knee flexion.

Cadaver↗
PubMed2000

Cranial defect repair using e-PTFE: part I. Evaluation of bone stiffness.

Autologous bone grafts are the preferred material for craniofacial reconstruction, but such procedures lead to increased operative time and bleeding, donor site morbidity, and graft resorption. The efficacy of expanded-polytetrafluoroethylene (e-PTFE) sheets to increase bone regeneration and remodeling in cranial defects using a rabbit model was evaluated by mechanical testing. New Zealand white rabbits were divided into 3 groups and sacrificed 6 months after surgery. In the Split Table group, (n = 16), a bilateral bone defect was created on the outer table of the parietal bones. In the Full Table group, (n = 16), a bilateral defect was created through both the inner and outer table of the cranium. The control group, (n = 10) was subjected to a sham operation. Indentation testing was performed to determine the stiffness of newly formed bone in and around the defect. Near the center of the defect, Split Table defects repaired with e-PTFE resulted in significantly stiffer bone than regenerated control bone. The Full Table defects repaired with e-PTFE also resulted in bone significantly stiffer than control regenerated bone around the central region of the defect. The data supports the hypothesis that e-PTFE improves the repair of cranial defects in a rabbit model. It is surmised that the porosity of the e-PTFE provides a stable scaffold for migration of tissue regenerating cells, which may be preferentially localized near the cranial suture lines. This porosity may also provide a barrier to fibrous tissue regenerating cells.

Animals↗
PubMed1999

Characterization and application of thin film pressure sensors.

Data regarding intra-joint loads during range of motion is essential to understanding normal joint mechanics and pathology. The investigators configured and characterized the response of a 440 N range, 0.076 mm thick commercial thin film sensor to monitor joint loads through a range of motion. Following preconditioning, static and dynamic tests were performed to evaluate the sensor response under varied environmental conditions. Both tests utilized a fixture to align the sensor and applied load. Under conditions that included dry, wet, folded and kinked configurations, a static load of 100 N was applied and the sensor output monitored up to thirty minutes from the time of loading. A load of 400 N at 50 N/s was applied to the sensor to determine dynamic characteristics and calibration curves under the conditions described for static tests in addition to curved, hard and soft contact surfaces and sensor overload. Static kinked data was significantly different from the dry, wet and folded conditions. Dynamic data showed that inter-package variability was not significant but that differences between sensor packages and sensor configuration conditions were significant. To investigate applicability of these sensors to the field of orthopaedics, a cadaveric knee was instrumented with sensors to examine the role of the meniscus in load transmission and distribution across the knee. The sensors were placed bilaterally below each meniscus on the anterior, posterior and center of the tibial plateau. Sensor data were obtained at these locations during manually flexed range of motion for the intact, re-attached and lateral menisectomized conditions of the knee specimen.

Analysis of Variance↗
PubMed1997

On matching compliance between canine carotid arteries and polyurethane grafts.

Compliance mismatch between a host artery and an implanted graft has been suggested as a contributing factor to a small diameter graft failure. In this study, static compliance and dynamic compliance were defined and measured in vitro and in vivo for canine carotid arteries and 2 types of polyurethane grafts. Based on these compliance values, the circumferential modulus (E[theta]) and longitudinal modulus (Ez) were calculated. It was shown that grafts have constant moduli over a wide range of pressure while the moduli of carotid arteries increase significantly with increasing pressure (dynamic E[theta] from 0.20 to 1.32 MPa). Polyurethane grafts are nearly isotropic, with the modulus almost identical in each direction, while carotid arteries are anisotropic (E[theta]/Ez = 2-3). The dynamic moduli are generally higher than static values and are especially pronounced for arteries. Due to these different inherent characteristics, the compliance of a synthetic graft may match that of the host artery only in the circumferential direction and within a small pressure range. A stated limitation is therefore given for complete compliance matching. The results provide a rationale for identifying the degree of compliance match. These efforts may lead to better designed vascular grafts.

Animals↗
PubMed1996

Bone transport using intramedullary fixation and a single flexible traction cable.

The transfixing wires used in the limb-lengthening and bone-transport procedures described by Ilizarov are the primary source of complications, including infection, restricted joint motion, and pain. In an attempt to eliminate the need for external fixation, a traction cable device was devised to perform a 3-cm bone transport in the canine femur using an interlocking intramedullary rod for fixation. Twelve dogs were divided into 2 groups. Transport began 7 days after osteotomy and continued at either 1 mm per day (n = 6) or 2 mm per day (n = 6). The in vivo peak force, resting force, and stiffness of the transport segment increased throughout distraction to a mean of 150 Newtons, 58 N, and 58 N per millimeter, respectively, at the time of docking. The regenerate and docking sites united in 10 of 12 dogs. Failure of the regenerate associated with deep infection around the rod occurred in 2 animals (17%). Modifications of this technique to reduce the risk of infection are discussed. This study confirms that intramedullary fixation is compatible with distraction osteogenesis and shows that a single traction cable can provide the force necessary for bone transport without transfixing wires in this setting.

Animals↗
PubMed1996

Evaluation of collagen ceramic composite graft materials in a spinal fusion model.

Autogenous bone graft is highly effective in inducing a bone healing response in most clinical settings. However, significant morbidity can occur related to the harvest of an autograft. This makes the development of synthetic or purified nontissue bone grafting materials highly desirable. Both purified bovine Type I collagen and calcium phosphate ceramics have been proposed as promising osteoconductive bone graft substitute materials. One collagen ceramic composite, Collagraft, is approved for use in acute long bone fractures. This study evaluated composites of purified bovine Type I fibrillar collagen and a granular biphasic hydroxyapatite/tricalcium phosphate ceramic in the posterior segmental canine spinal fusion model. Materials were compared based on union score and mechanical testing in 3 separate fusion sites (L1-2, L3-4, L5-6). All composites were found to be inferior in union score to an equal volume of autogenous cancellous bone. In addition, the combination of the collagen ceramic composite with autogenous cancellous bone graft reduced the effectiveness of the autogenous bone graft significantly. These data should be a caution to the clinician who may consider use of collagen ceramic composites similar to Collagraft for spinal fusion applications.

Animals↗
PubMed1995

Evaluation of a pressure sore model using monoplegic pigs.

This study evaluated a newly developed swine monoplegic pressure sore model by testing the uniformity of the initial wound size. The natural healing also was evaluated. Nine minipigs were used. The hindlimb was denervated by transecting the unilateral nerve roots L1 through S2. At 5 to 14 days, 800 mmHg of pressure was applied to the denervated skin over the trochanteric area with a 3-cm-diameter disk compressing the skin and subcutaneous tissue against the underlying bone for 48 hours. The wound was then debrided of devascularized tissue. Wound surface areas were calculated from photographs. Wound volumes were obtained by measuring the volume of saline needed to fill the wound defect. Full-thickness sores of uniform size developed in all pigs without mortality or complications. Wound surface area and volume increased initially, peaked, and then decreased in an exponential fashion. This model provides a new tool for direct comparison of pressure sore treatment modalities for short- and long-term studies.

Animals↗
PubMed1994

Evaluation of human bone morphogenetic protein 2 in a canine spinal fusion model.

The efficacy of purified recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in a porous biodegradable copolymer, poly [D,L (lactide--coglycide)] (PLGA) was evaluated using a canine posterior segmental spinal fusion model. rhBMP-2/PLGA was compared to autogenous cancellous bone and to PLGA alone. Thirty three fusion sites in 11 beagle dogs were evaluated at 12 weeks for union and mechanical strength. Union score and mechanical testing showed no difference between autogenous cancellous bone and rhBMP-2/PLGA. Union scores for autogenous cancellous bone and rhBMP-2/PLGA sites were superior to those with PLGA alone (p = 0.001 and p = 0.0007, respectively). These findings suggest that synthetic bone graft substitute materials delivering purified rhBMP-2 may be suitable for posterior spinal fusions. The use of such materials may provide efficacy equivalent to autogenous cancellous bone and avoid the morbidity associated with the harvest of autogenous graft.

Animals↗
PubMed1993

Compliance effects on small diameter polyurethane graft patency.

Microporous compliance matched and noncompliant grafts were compared in a dog carotid artery interposition model. We fabricated 4 mm diameter sponge type polyurethane (Biomer) tubes 5 cm in length with a 0.5 mm wall thickness. The luminal surface was covered with a 50 microns coating of cross-linked gelatin. Compliance was measured in vitro and in vivo by volume and vessel diameter changes. Over a mean arterial pressure range of 55-155 mm Hg, the diameter changes of grafts and stump arteries were measured in situ using an ultrasonic Hokanson device. Compliance matched grafts were found to have the same in vitro compliance values as the natural canine carotid at a mean arterial pressure of 100 mm Hg. Compliance matched and noncompliant grafts had values of 10.3 +/- 1.3 and 0.9 +/- 0.1 x 10(-2) mm Hg, respectively. End to end arterial anastomoses were constructed between the graft and the host arteries. The use of synthetic grafts with matched compliance to the adjacent natural vessels has been advocated as the ideal solution to circumvent the problems of graft failure. These studies indicate that compliance values for compliance matched grafts decreased immediately after implantation (from 10.3 to 6.5 x 10(-2) %/mm Hg) and within 6 weeks decreased to 3.6 x 10(-2) %/mm Hg. The compliance values for noncompliant grafts remained constant throughout the test period. At autopsy all grafts showed a tightly adhered tissue capsule. The thickness of the anastomotic hyperplasia at the distal sites of compliance matched grafts was significantly different (P < .05) than that of the adjacent artery. The patency for compliant and noncompliant grafts was 64% and 50%, respectively. Evidence for polyurethane graft degradation was obtained by Fourier transform infrared spectroscopy and gel permeation chromatography analysis of patent explants. Compliance mismatch alone does not contribute to graft failure, however, material degradation, suture technique and/or capsule formation can play a contributory role although these were not tested directly.

Animals↗
PubMed1993

Effects of stent design and serum cholesterol level on the restenosis rate in atherosclerotic rabbits.

We investigated the effect of serum cholesterol level and stent design on the restenosis rate within the stent after balloon angioplasty and stent implantation using atherosclerotic rabbits. Two types of nickel/titanium stents with gaps (open stent) and without gaps (closed stent) between the wire coils were implanted into the aorta of the rabbits 10 weeks after atherosclerosis had been induced using a standard high cholesterol diet and balloon abrasion. Each rabbit had an open stent and a closed stent implanted into the infrarenal abdominal aorta. Between these two stents a control segment of the aorta was treated with angioplasty alone. The animals were divided into two groups according to the diet protocol as follows: in group I (n = 9) a high cholesterol diet was stopped after stent implantation; in group II (n = 10) a high cholesterol diet was maintained after stent implantation. Digital subtraction angiograms were obtained every 4 weeks for up to 24 weeks and the narrowest diameter of the arterial segments within each stent and in the segment between stents was measured. The diameter narrowing within the closed stent was greater in the high cholesterol group compared with the low cholesterol group: 12 weeks (2.57 +/- 0.09 mm in group I vs 2.14 +/- 0.15 mm in group II, mean +/- S.E., p < 0.05); 16 weeks (2.55 +/- 0.09 mm vs 2.14 +/- 0.12 mm, p < 0.05); 20 weeks (2.59 +/- 0.06 mm vs 1.98 +/- 0.12 mm, p < 0.01); and 24 weeks (2.45 +/- 0.11 mm vs 2.01 +/- 0.11 mm, p < 0.05). No significant differences in the narrowest diameter of the arterial segments were observed between high and low cholesterol groups in the angioplasty alone areas or within the open stents. There was a significant difference in the narrowest diameter between stents with versus those without gaps (at 12, 16, and 20 weeks poststenting in group I and at 4, 8, 12, 16, 20, and 24 weeks in group II). Thus the stent with the least metal is correlated with less stenosis and intimal hyperplasia. From these data we conclude that both stent design and serum cholesterol are important factors for restenosis after stent implantation.

Angioplasty, Balloon, Coronary↗
PubMed1992

Biodegradable pericardial implants for bladder augmentation: a 2.5-year study in dogs.

Bladder augmentation using biodegradable pericardial tissue was evaluated in canine bladders. Acetic acid and acetic anhydride treated pericardial tissue grafts were stored in 75% ethanol for 18 to 27 months before implant. Ten dogs weighing 20 to 25 kg. were subjected to a 50% partial cystectomy. After careful separation of the mucosa, bladder muscle and adventitial layers a pericardial graft volumetrically equivalent to the portion of the bladder removed was sutured to the bladder remnant in 2 layers. In 1 control dog the bladder was opened, 50% of the bladder was removed and the bladder was closed primarily. In another control dog the excised bladder was replaced with fresh chemically treated patch material that was never subjected to ethanol storage. Excretory urography and cystography were performed on all dogs. Urodynamics with filling pressures and bladder volumes measured before and after the operation at intervals of up to 36 months confirmed that adequate bladder capacity was achieved. There were no operative complications. Postmortem histological evaluations revealed a smooth epithelialized inner surface with no traces of any surface irregularities or suture lines. The bladder apex showed an intact epithelium and the absence of a smooth muscle layer. The biodegradable acetylated tissue provides an intact structural reservoir for urine and serves as a template for epithelial regeneration. This permits volumetric bladder enlargement while the graft is progressively reabsorbed with time.

Animals↗
PubMed1991

Characterization of rehydrated gelatin gels.

Five percent glutaraldehyde cross-linked gels have shown excellent blood compatibility as coatings for cardiac prostheses. A method was developed for producing thin dehydrated coatings using a proprietary dehydration procedure and ethylene oxide (EO) sterilization. The swollen surfaces of rehydrates versus wet (original) gels were compared. Within 30 min of saline rehydration, dry 30-50-microns films on textured surfaces became smooth, uniform, and comparable to original gelatin gels. Mechanical test results after rehydration showed values for strain remain unchanged (39.3 + 10.0 to 40.0 + 7.8%), but stress increased (2.79 + 1.21 to 4.22 + 1.60 dyne/cm2; p less than 0.01). The contact angle data reported gamma C values of 26.1 and 30.4 dyne/cm for original and rehydrated gels. Using a coulometric titrimeter, the measured water content of original gels was reduced from 85 to 3.4% after drying. Dried and saline rehydrated gels had a 73.2% moisture content. Gels shrank 8.8% of their original length after rehydration; however, the thickness of all pump coatings remained stable. Two-hour incubations with bovine platelet rich plasma showed no differences in platelet reactivity or morphology when compared to original gels. Light microscopy and scanning electron microscopy (SEM) showed no evidence of gel cracking or surface defects after pump endurance testing for 3 and 5 weeks. The process of dehydration eliminates the wet storage and sterility problems of such hydrogels and provides a stable film coating for a variety of blood-contacting substrates.

Biocompatible Materials↗
PubMed1988

Biological performance of TiNi shape memory alloy vascular ring prostheses: a two year study.

A method was developed for the noninvasive insertion of a vascular ring prostheses aimed at preserving arterial patency and preventing restenosis following angioplasty. Using a specially designed 7F catheter 22 nitinol (TiNi) wire prostheses (I.D. 5 mm; 0.25 mm thickness) were torsion reduced in diameter and inserted under fluoroscopy into both carotid (n = 2) and iliac-femoral arteries (n = 20) of dogs. Aspirin (650 mg BID) and Persantin (200 mg BID) were given for only 30 days postoperatively. Angiography of all rings at 1, 6, 12 months exhibited excellent biocompatibility and long term patency 91% (20/22) as reported in Trans ASAIO 32:30, 1986. Four rings inserted in the right and left common iliac arteries and femoral artery were followed for up to 2 years and exhibited 100% patency. Angiography demonstrated that the anchorage of the prostheses was stable and the lumen was uniformly covered by a thin neointimal layer of endothelial like cells. The prostheses were patent with no evidence of thrombosis or inflammation. In view of the problem of recurrent stenosis occurring during the healing period after balloon angioplasty (PTA or PTCA), this approach may lead to a new means of clinical intervention in atherosclerosis.

Alloys↗
PubMed1984

New sequential external counterpulsation for the treatment of acute myocardial infarction.

Over a period of 6 years, 52 patients with acute myocardial infarction (AMI) were treated with sequenced external counterpulsation (SECP). Of the 23 patients who experienced severe chest pain, 22 had complete relief within 30 min of SECP, and 31 of the 52 patients showed remarkable improvement in their electrocardiogram after the first hour of treatment. Fifteen patients were studied using the 35-lead ST segment elevation-mapping method. sigma ST and NST, indicators of infarct size, showed decreasing trends in seven patients treated with SECP for a period of 6 days, whereas sigma ST and NST of the control group of eight patients increased during the same period. Our hemodynamic data indicate that in four of five patients with AMI and left heart failure, the central venous pressure and cardiac output increased after SECP, whereas the pulmonary wedge pressure decreased. Measurements of the P-wave terminal force of lead V1 also demonstrated that the application of SECP can improve left ventricular function in a majority of patients with AMI.

Adult↗