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Biomedical subjects

A Weiler

Publications and source records attributed to A Weiler.

48 records · Page 3Linked to original sources
PubMed1996

Foreign-body reaction and the course of osteolysis after polyglycolide implants for fracture fixation: experimental study in sheep.

Foreign-body reaction to polyglycolide (PGA) implants has been described in man. Many animal experiments have verified the mechanical properties of fixation devices made from PGA, but a significant foreign-body reaction has not been described. We studied the effect of PGA rods in 12 sheep with standardised osteochondral fractures of the medial femoral condyle fixed with uncoloured, self-reinforced PGA rods (Biofix). Radiographs were taken at intervals ranging from two weeks to two years, and the sheep were killed at intervals ranging from six to 24 months. All knees were examined histologically. Eleven of the 12 fractures healed radiologically and histologically. Moderate to severe osteolysis was seen at four to six weeks with maximum changes at 12 weeks in ten animals. Six knees showed fistula-like connections between the implant site and the joint space. Three developed synovitis, one with inflammatory changes involving the whole cartilage and one with destruction of the medial condyle. Although in our study osteochondral fractures fixed with PGA rods healed reliably, there were frequent, significant foreign-body reactions. Caution is needed when considering the use of PGA fixation devices in vulnerable regions such as the knee.

Animals↗
PubMed1988

The immune-enhancing effect of perioperative thymopentin administration in elderly patients undergoing major surgery.

The effects of perioperative administration of thymopentin (TP-5) on in vivo and in vitro measurements of cell-mediated immunity in elderly patients undergoing major surgery were investigated. A placebo-controlled study was conducted in 25 patients (mean age, 67 years) with congenital or acquired heart disease undergoing surgery with cardiopulmonary bypass. Patients were divided into three groups: Group 1 patients were given 50 mg of TP-5 subcutaneously two hours preoperatively. Group 2 patients were given 50 mg of TP-5 subcutaneously two hours preoperatively and 48 hours postoperatively. Group 3 patients were given placebo at corresponding times. Cell-mediated immunity measurements were the in vivo delayed-type hypersensitivity (DTH) response on day 0 and on day 7 to an antigen skin test battery. The in vitro studies included antigen cocktail-induced lymphocyte proliferation of peripheral blood mononuclear cells. The DTH response on day 7 after surgery was significantly suppressed in group 3 patients compared with the preoperative baseline value, while it remained unaltered in group 1 and 2 patients. There was a considerable difference of DTH measurements (number of positive antigen responses and sum of their mean diameters) between group 2 and 3 patients. Antigen cocktail-induced lymphocyte proliferation, following initial suppression in the majority of patients, was significantly different between the placebo group and patients in group 2 on day 7 after surgery. The data indicate that perioperative administration of TP-5 might be of considerable clinical utility in preventing a defective cellular immune response.

Adjuvants, Immunologic↗
PubMed1985

Photodynamic action of uroporphyrin on the complement system in porphyria cutanea tarda.

We investigated the effect of UV light (320-460 nm) on total hemolytic CH50 activity and C3 cleavage in sera obtained from 14 patients with porphyria cutanea tarda. Irradiation with 5, 10, or 50 J/cm2 resulted in a 12%-60% loss of CH50 and a 5%-30% cleavage of native C3 as estimated by planimetric evaluation of the immunoelectrophoretic C3 pattern. The complement changes were most pronounced in sera from patients with active disease and were minimal or absent in patients who were in remission. In all cases, the decrease of CH50 and C3 cleavage was proportional to the plasma-porphyrin concentration and the dose of radiation. After exposure to 320- to 460-nm light, similar changes were seen in normal human serum (NHS) to which exogenous uroporphyrin had been added. Beta-carotene and chloroquine had no inhibitory effect on the photodynamic complement activation. The C3 cleavage in irradiated NHS containing uroporphyrin was not affected by 10 mM EGTA, but was partially inhibited in the presence of 30 mM EDTA, thus indicating that the interaction of photoexcited uroporphyrin with the complement system differs from classical-pathway complement activation.

Aged↗
PubMedDate not supplied

Hamstring tendon fixation using interference screws: a biomechanical study in calf tibial bone.

It has recently been shown that graft fixation close to the ACL insertion site is optimal in order to increase anterior knee stability. Hamstring tendon fixation using interference screws offers this possibility and a round threaded titanium interference screw has been previously developed. The use of a round threaded biodegradable interference screw may be equivalent. In addition, to increase initial fixation strength, graft harvest with a distally attached bone plug may be advantageous, but biomechanical data do not exist. This study compares the initial pullout force, stiffness of fixation, and failure modes of three strand semitendinosus grafts in 36 proximal calf tibiae using either biodegradable poly-(D,L-lactide) (Sysorb; Sulzer Orthopaedics Ltd, Münsingen, Switzerland) or round threaded titanium (RCI; Smith & Nephew DonJoy, Carlsbad, CA) interference screws, harvested either without (biodegradable: group I, titanium III) or with (biodegradable: group II, titanium: group IV) attached tibial bone plugs. Maximum pullout force in group I (507 +/- 93 N) was significantly higher than in group III (419 +/- 77 N). Pullout force of bone plug fixation was significantly higher than that of direct tendon fixation (717 +/- 90 N in group II and 602 +/- 117 N in group IV). Pullout force of biodegradable fixation was significantly higher in both settings. These results indicate that initial pullout force of hamstring-tendon graft interference screw fixation can be increased by using a biodegradable interference screw. In addition, initial pullout force of hamstring-tendon graft fixation with an interference screw can be greatly increased by harvesting the graft with its distally attached tibial bone plug.

Absorption↗
PubMedDate not supplied

The influence of screw geometry on hamstring tendon interference fit fixation.

We used a standardized model of calf tibial bone to investigate the influence of screw diameter and length on interference fit fixation of a three-stranded semitendinosus tendon graft for anterior cruciate ligament reconstruction. Biodegradable poly-(L-lactide) interference screws with a diameter of 7, 8, and 9 mm and a length of 23 and 28 mm were used. We examined results in three groups of 10 specimens each: group 1, screw diameter equaled graft diameter and screw length was 23 mm; group 2, screw diameter equaled graft diameter plus 1 mm and screw length was 23 mm; group 3, screw diameter equaled graft diameter and screw length was 28 mm. The mean pull-out forces in groups 1, 2, and 3 were 367.2+/-78 N, 479.1+/-111.1 N, and 537.4+/-139.1 N, respectively. The force data from groups 2 and 3 were significantly higher than those from group 1. These results indicate that screw geometry has a significant influence on hamstring tendon interference fit fixation. Increasing screw length improves fixation strength more than oversizing the screw diameter. This is important, especially for increasing tibial fixation strength because the tibial graft fixation site has been considered to be the weak link of such a reconstruction.

Animals↗
PubMedDate not supplied

Graft fixation in cruciate ligament reconstruction.

Cruciate ligament reconstruction has progressed dramatically in the last 20 years. Anatomic placement of ligament substitutes has fostered rehabilitation efforts that stress immediate and full range of motion, immediate weightbearing, neuromuscular strength and coordination, and early return to athletic competition (3 months). This has placed extreme importance on secure graft fixation at the time of ligament reconstruction. Current ligament substitutes require a bony or soft tissue component to be fixed within a bone tunnel or on the periosteum at a distance from the normal ligament attachment site. Fixation devices have progressed from metal to biodegradable and from far to near-normal native ligament attachment sites. Ideally, the biomechanical properties of the entire graft construct would approach those of the native ligament and facilitate biologic incorporation of the graft. Fixation should be done at the normal anatomic attachment site of the native ligament (aperture fixation) and, over time, allow the biologic return of the histologic transition zone from ligament to fibrocartilage, to calcified fibrocartilage, to bone. The purpose of this article is to review current fixation devices and techniques in cruciate ligament surgery.

Anterior Cruciate Ligament↗
PubMedDate not supplied

Biomechanical properties and vascularity of an anterior cruciate ligament graft can be predicted by contrast-enhanced magnetic resonance imaging. A two-year study in sheep.

Magnetic resonance imaging has been used to determine graft integrity and study the remodeling process of anterior cruciate ligament grafts morphologically in humans. The goal of the present study was to compare graft signal intensity and morphologic characteristics on magnetic resonance imaging with biomechanical and histologic parameters in a long-term animal model. Thirty sheep underwent anterior cruciate ligament reconstruction with an autologous Achilles tendon split graft and were sacrificed after 6, 12, 24, 52, or 104 weeks. Before sacrifice, all animals underwent plain and contrast-enhanced (gadolinium-diethylenetriamine pentacetic acid) magnetic resonance imaging (1.5 T, proton density weighted, 2-mm sections) of their operated knees. The signal/noise quotient was calculated and data were correlated to the maximum load to failure, tensile strength, and stiffness of the grafts. The vascularity of the grafts was determined immunohistochemically by staining for endothelial cells (factor VIII). We found that high signal intensity on magnetic resonance imaging reflects a decrease of mechanical properties of the graft during early remodeling. Correlation analyses revealed significant negative linear correlations between the signal/noise quotient and the load to failure, stiffness, and tensile strength. In general, correlations for contrast-enhanced measurements of signal intensity were stronger than those for plain magnetic resonance imaging. Immunohistochemistry confirmed that contrast medium enhancement reflects the vascular status of the graft tissue during remodeling. We conclude that quantitatively determined magnetic resonance imaging signal intensity may be a useful tool for following the graft remodeling process in a noninvasive manner.

Animals↗
PubMedDate not supplied

Biodegradable interference screw fixation exhibits pull-out force and stiffness similar to titanium screws.

Recently, increased interest in biodegradable interference screws for bone-tendon-bone graft fixation has led to numerous screws becoming available. The implants are made from different polymers and have different designs, which might influence their mechanical properties. Several studies have reported a wide range of mechanical results for these screws using different biomechanical models. The aim of the present study is to compare reliable biomechanical data for six different biodegradable interference screws, consisting of five different polymers, with a conventional titanium screw in a standardized model. Seventy proximal calf tibias were used to determine maximal pull-out force, stiffness of fixation, and insertion torque for interference screw fixation of bone-tendon-bone grafts. Additionally, maximal torque at failure was determined. Data were analyzed with respect to aspects of screw design, such as drive and thread shape. Five of the six biodegradable screws provided initial pull-out force and stiffness of fixation comparable with that of a conventional titanium screw. Torque at failure can be greatly increased by adapting the drive design to the mechanical properties of the polymeric raw material. A correlation between pull-out force and thread height indicates that fixation rigidity depends on screw design, even in a biodegradable implant.

Animals↗
PubMedDate not supplied

Antimyosin monoclonal antibodies for early detection of cardiac allograft rejection.

Sixty-eight indium 111-labeled antimyosin Fab-DTPA imaging studies (0.5 mg intravenously with a radioactivity of 65 to 75 MBq) were executed on 37 of 116 patients undergoing heart transplantation to assess diagnostic accuracy and clinical utility. As controls, 21 patients with cardiomyopathy (n = 8), unstable angina (n = 9), and myocardial infarction (n = 4) were selected. After 48 hours, single photon emission computed tomographic images were evaluated visually, and heart/lung ratios were measured, using the "region of interest" technique. They were compared with echocardiographic and endomyocardial biopsy results. In 40 studies a heart/lung ratio less than or equal to 1.6 corresponded to a negative biopsy result in 98% (40/41). Echocardiography enabled correct identification of 95% of the patients with normal biopsy findings. In 91% (22/24) a positive biopsy finding correlated with a heart/lung ratio greater than 1.6 including 20 mild rejections, but in only 64%, with an increase in wall thickness and/or decrease of fractional diameter shortening seen on echocardiogram. In addition, the various stages of rejection episodes determined the amount of the heart-lung ratio. There was a significant relationship between the histologic findings and the antimyosin uptake. In 13 patients a second investigation was performed after rejection therapy. All patients had a negative biopsy result, and the heart/lung ratio decreased to normal ranges (less than or equal to 1.6). Five antimyosin antibody studies were excluded, as in these cases, negative uptake results were found during rejection therapy with high-dose steroids. The overall sensitivity was calculated at 93% and the specificity at 98%.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗