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Biomedical subjects

E Munting

Publications and source records attributed to E Munting.

At least 19 recordsLinked to original sources
PubMed2001

Vertebral reconstruction with cortical allograft: long-term evaluation.

Reconstruction of large anterior vertebral column defects is indicated in a number of pathological conditions including tumor, infection, trauma and post-traumatic deformity. Several substitutes and techniques are available for the functional restoration of the vertebral column. Vascularized bone transfers, autografts, allografts or xenografts have been used, as well as metal or ceramic implants. All of these bear potential advantages and drawbacks in terms of associated morbidity of graft harvesting, disease transmission, mechanical failure, implant incorporation and overall long-term clinical outcome. In the present paper we report our experience with the use of freeze-dried, gamma-irradiated, cortical allograft for the reconstruction of large, anterior segmental defects of the spine, involving at least one vertebral body with its two adjacent discs. Cortical allografts were used in 67 cases operated for a variety of conditions. No case of disease transmission, infection or long-term mechanical graft failure occurred in our entire series, with a mean follow-up of 31 months. Fusion and mechanical stability was reliably obtained. Specific advantages include the absence of donor site morbidity, the possibilities for exact trimming to the size of the defect, superior mechanical strength as compared to available autograft, and reliable fusion with the host bone with partial bone remodeling, preventing fatigue failure. We conclude that freeze-dried, irradiated cortical allografts are safe and effective for anterior reconstruction of the spine.

Adolescent↗
PubMed2001

Inhomogeneity of human vertebral cancellous bone: systematic density and structure patterns inside the vertebral body.

In the spine, cancellous bone quality is usually assessed for the whole vertebral body in a transverse central slice. Correct identification and assessment of the weakest parts of the cancellous bone may lead to better prediction of fracture risk. The density and structural parameters were systematically investigated inside the thoracic (T-9), thoracolumbar (T12-L1), and lumbar (L-4) vertebral bodies of nine subjects. On both sides of the median sagittal plane, anterior and posterior 8.2 mm vertical cores were harvested in the thoracic vertebra. In the thoracolumbar and lumbar vertebrae, external samples were also cored. Peripheral quantitative computed tomographic (pQCT) density analysis of the 136 cores was performed at four different levels, from the lower to the upper endplate. The relatively thin slice thickness (300 microm) and small pixel size (70 microm x 70 microm) was considered sufficient to investigate the structural parameters on the four transverse slices and in the sagittal and coronal planes (total of 816 images). Using a constant threshold a binary image was generated and the morphometric data were extracted. The binary image was further skeletonized and classical strut analysis was performed. Cancellous bone density was 20% higher in the posterior cores than in the anterior and external cores. Moreover, clear vertical inhomogeneity was noted because the lowest half of the vertebral body presented lower density than the upper half (differences ranging from 25% to 15%). All structural parameters were strongly dependent on the location of the measurement. Structural differences between anterior, posterior, and external areas were mild and followed the density patterns. On the other hand, vertical inhomogeneity of the structural parameters was important. For example, in the thoracolumbar and lumbar vertebrae, the numbers of nodes or node-to-node struts were almost twofold higher in the inferior half than in the superior half (p < 0.01), whereas trabecular thickness and number of free-ends presented a center/close-to-endplate structural pattern, with central trabeculae being 15% thicker (p < 0.05) and presenting 30% fewer free-ends (p < 0.01) than the close-to-endplate ones. Variability of density and structural parameters was high and a substantial part of this variability could be explained by the place inside the vertebral body where the measurement was made. The weak part was not in the center of the body but in its upper half where the lower density did not seem to be compensated by a higher structural architecture. Further clinical investigation could enhance fracture prediction by tracking and focusing on the weakest part of the vertebral body.

Adult↗
PubMed1998

Resection of a chest chondrosarcoma invading the spine and the aorta.

A 34-year-old man presented with a large chondrosarcoma of the chest invading six ribs and the vertebral bodies of five adjacent thoracic vertebrae. En bloc resection of the tumor with six ribs, the anterior part of five vertebral bodies, and the thoracic aorta was performed through a thoracotomy and a paravertebral incision.

Adult↗
PubMed1997

Effect of a stemless femoral implant for total hip arthroplasty on the bone mineral density of the proximal femur. A prospective longitudinal study.

After total hip arthroplasty with a medullary stem, significant loss of bone mineral density (BMD) has been demonstrated in the proximal-medial femoral cortex. In an attempt to prevent bone loss, a stemless femoral component was designed. Owing to promising experimental results, a prospective clinical trial was undertaken in a limited group of patients, all below the age of 50. Yearly BMD measurements were carried out in the vicinity of the implant and compared with the BMD values obtained in the immediate perioperative period and with the values on the unaffected side. The follow-up period in this study was 4 to 6 years, involving 32 hips in 31 patients. Maintenance of BMD in the operated femur was demonstrated. A statistically significant increase in the BMD of the proximal medial femoral cortex was observed in those patients who had low initial values. In active patients with a life expectancy greater than 30 years, preservation of the proximal bone stock after total hip arthroplasty appears beneficial, as these patients are most likely to need revision surgery, which is more difficult if significant bone loss has occurred. The data further reinforce the crucial role of mechanical stress in BMD maintenance.

Absorptiometry, Photon↗
PubMed1996

The contributions and limitations of hydroxyapatite coatings to implant fixation: A histomorphometric study of load bearing implants in dogs.

The contribution and limitation of hydroxyapatite coatings to implant fixation are discussed following a 5-year histomorphological study of the bony incorporation of macroporous stemless hemiarthroplasties in dogs. Implants without coating, with a pure titanium coating and with a hydroxyapatite coating were compared. The mean extent of direct contact between bone and hydroxyapatite-coated implants was 66% compared with 0 to 5% in the other implants. Areas of resorption of the coating were seen in every case associated with direct bone apposition on the metal surface. When the initial fixation is stable, osteointegration of hydroxyapatite-coated implants is obtained consistently, despite design features known to preclude bone incorporation. Implant fixation must depend on a mechanical interlock with bone because of the resorbability and mechanical properties of hydroxyapatite coatings.

Animals↗
PubMed1995

Fixation and effect on bone strain pattern of a stemless hip prosthesis.

Given the relatively short survival time of total hip replacement in young patients, a different concept of femoral implant was designed and evaluated biomechanically prior to clinical application. The femoral component has no intramedullary stem and fits into an angular resection of the femoral neck. A trans-trochanteric screw provides immediate strong fixation. A comparative biomechanical study with cadaver femora and a dynamic hip simulator was performed. The study had three objectives. (1) The strains generated under loading in the intact proximal femur were compared to those generated in the presence of the experimental implant and a classic cemented implant. (2) The short-term stability of the experimental prosthesis under loading conditions encountered during fast walking was evaluated. (3) Most importantly, the implant design was improved in the light of the experimental observations prior to any clinical trial. Indeed, the prototype underwent several important modifications in the course of the study. With the modified design, later used in a clinical trial, it was demonstrated that if accurate fit and position of the prosthesis were provided, fixation remained sound for over one million loading cycles with peak loads of three times the body weight. The measured interface micromotion was compatible with direct bone apposition and ingrowth. No statistical difference was found between the strain measurements obtained before and after implantation of the experimental prosthesis whereas significant stress shielding was observed with a stemmed, cemented prosthesis.

Biomechanical Phenomena↗
PubMed1994

Synthesis of bioactive coatings on Ti substrates using glass enamel.

Bioactive coatings on titanium can be prepared by dispersing hydroxyapatite particles into a borosilicate glass enamel doped with TiO2. Adhesion of the coating is obtained when the titanium substrate has been preoxidized before enameling in such a way as to form a continuous TiO2-layer. Adhesion results from the diffusion of this TiO2-layer into the liquid glass during enameling. The evolution of the diffusion zone was followed by scanning electron microscopy and electron probe microanalysis. Adhesion disappears after a critical time of firing which corresponds to the completion of the dissolution of the TiO2-layer by the glass. The borosilicate glass wets the hydroxyapatite particles and adheres strongly to them after cooling.

Bone Substitutes↗
PubMed1994

Biomechanical analysis of screw load sharing in pedicle fixation of the lumbar spine.

Segmental fixation of the spine by means of rods or plates and pedicle screws posteriorly usually results in a stable and rigid construct. The magnitude of the stresses on the instrumentation particularly at the bone-screw and rod (or plate) interfaces will depend on the load distribution between the bone and the implant as well as the number of sites of bone purchase of the implant. If a fusion is to be obtained in the case of a degenerative spine, the role of the instrumentation is to prevent translation of the motion segments, thereby allowing the compressive loads to be transmitted through the vertebral bodies and the degenerated discs. In the case of a fracture, the instrumentation is made to withstand the bulk of the loads since the structural integrity of a motion segment may have been lost. This study was undertaken to evaluate the effect of different constructs on the stresses in Cotrel-Duboussett (C-D) pedicle (tulip) screws close to their junction with the rod bridging the motion segments to be immobilized. In order to minimize the effect of anatomical and material property variation between spines, adult porcine spines were used, thus providing a reproducible experimental model. Fresh 3-year-old porcine spines were potted in holders after the soft tissues were removed (with the exception of the ligamentous structures).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mechanical simulator for the upper femur.

This paper describes a simulator designed to evaluate the mechanical behaviour of the proximal femur and the influence of a prosthesis on this behaviour. Cyclic dynamic loads, corresponding to those generated by walking or several other activities, are applied to the proximal end of a fresh cadaveric femur before and after implantation of different types of hip prosthesis. Three musculoaponeurotic groups are modelled (abductor group, fascia lata and vastus lateralis). Load cells and strain gauges coupled to a data acquisition system are used to measure and record the forces on the femoral head and in the different muscle groups, as well as the strain variations occurring in the bone. Displacement transducers monitor the displacements occurring about the bone/implant interface.

Activities of Daily Living↗
PubMed1992

Setting, hardening and resorption of calcium phosphate hydraulic cements.

Two examples of calcium phosphate hydraulic cements (CPHC) are presented. Type I cements consist in mixtures of beta-tricalcium phosphate (beta-TCP) and monocalcium phosphate monohydrate (MCPM), to which some plaster of Paris (CSH) is added as a setting retardant. Type II cements consist in mixtures of beta-TCP, dicalcium phosphate dihydrate (DCPD) and calcium carbonate (CC), to which some hydroxyapatite (HAP) is added as a setting accelerator. The setting time of these cements ranges from a few minutes up to a few hours, according to their composition and the amount of mixing water. Tensile strengths ranging from 1.2 up to 3.5 MPa have been recorded on cements which porosity ranged from 38 up to 55 vol%. In-vivo experiments on dogs have shown the perfect biocompatibility and resorbability of cement I.

Animals↗
PubMed1991

Calcium phosphate cements: effect of fluorides on the setting and hardening of beta-tricalcium phosphate-dicalcium phosphate-calcite cements.

Increasing amounts of fluoride ions have been found to increase the setting and hardening rates of beta-tricalcium phosphate-dicalcium phosphate dihydrate-calcite cements. Thus, fluoride-containing cements reached a diametral strength of about 1.5 MPa after 15 d, but the fluoride-free reference sample reached only 0.45 MPa. The acceleration of setting and hardening is correlated to an increased rate of hydroxyapatite formation in the cement at the expense of dicalcium phosphate dihydrate and calcite. Adding monocalcium phosphate monohydrate and fluoride to the blends resulted in a marked decrease of their setting time from about 1 h down to 8 min, without greatly affecting their final strength.

Apatites↗
PubMed1991

[Application and electric insulation of strain gauges used on fresh bone. Preliminary study].

This report describes the optimal use of strain gauges placed on fresh wet bones. Two principal stages in gauge installation were studied: surface preparation and gauge insulation. Different surface preparation procedures were tested on bovine bone specimens loaded in traction. The preparation efficiency was evaluated by comparing strains measured from gauges and from an extensometer with sharp edges. Results show the necessity of sufficient rubbing: a minimum of 5 rubbing cycles with n. 320 emery paper. Scanning electron microscopy was used to examine the effect of the preparation procedures. Different coatings were also tested with special attention given to the influence of these coatings on the measured strains. An optimal polyurethane coating is proposed.

Animals↗
PubMed1990

Calcium phosphate cements: study of the beta-tricalcium phosphate--dicalcium phosphate--calcite cements.

The setting and strengthening properties of beta-tricalcium phosphate (beta-TCP)--dicalcium phosphate dihydrate (DCPD)--calcite blends upon admixture with water were investigated at 25 and 37 degrees C. Setting was accelerated by seeding the system with hydroxyapatite (HAp), and strengthening improved when the solids were mixed with a solution saturated with DCPD and HAp. The relationship strength versus ageing time in wet conditions was correlated with mineralogical changes of the material. X-Ray diffraction, thermal analysis and scanning electron microscopy observations showed that DCPD and calcite react together to form small HAp crystals acting as bridges between the beta-TCP aggregates present in the paste. Both gaseous CO2 released by the reaction of calcite and the conversion of lower (DCPD, calcite) to higher-density phases (HAp) contributed to increase the porosity of the material. Nevertheless, quite acceptable diametral strengths (around 1.5 MPa) could be achieved, despite the high porosity of the hardened product (up to 54 vol%). After exhaustion of DCPD, calcite can react with beta-TCP to form further HAp, but this process is detrimental to the strength of the material. Both the mineralogical transformations, and the strengthening of the material were accelerated considerably upon increasing the ageing temperature.

Adhesives↗
PubMed1989

Bone allografts in reconstructive middle ear surgery.

The authors present their current experience with stored bone grafts, using allografts shaped from the cortices of long bones for reconstructing the tympano-ossicular chain. The materials and the methods are described. The anatomical results have been good in 97% of the cases, while the functional results are as satisfactory as those obtained with bioceramics. In addition to ossiculoplasty, the bone allografts can also be used in otology for reconstructing large bony defects of the temporal bone.

Bone Transplantation↗
PubMed1989

New perspectives on lyophilized bone allografts.

In 1987, at the Congress of Implants in Otology in Venice, Italy, we first presented our experiences with stored lyophilized bone allografts for reconstruction of the tympano-ossicular chain. Since then, we have extended our experiences to include reconstruction of the external bony ear canal, the filling of defects in the mastoid bone, reconstructive nasal surgery and rehabilitation of major bony defects of the face. Additionally, we have tried to improve the preparation of the bony implants used clinically and have started a multicenter collaboration with other European universities.

Bone Transplantation↗