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Biomedical subjects

Lars Lidgren

Publications and source records attributed to Lars Lidgren.

At least 19 recordsLinked to original sources
PubMed2006

Material characterization and in vivo behavior of silicon substituted alpha-tricalcium phosphate cement.

The possibility and biological effects of substituting silicon in alpha-tricalcium phosphate (alpha-TCP) by way of solid-state reaction have been evaluated. alpha-TCP powders with varying substitution amounts (1 and 5 mol % Ca2SiO4) were synthesized by reacting mixtures of CaCO3, Ca2P2O7, and SiO2, at a rate of 4 degrees C(min)(-1) to 1100 degrees C, left to dwell for 2 h and then heated to 1325 degrees C at 4 degrees C(min)(-1) and left to dwell for a period of 4 h. The powders were then rapidly quenched in air. Si incorporation could be verified by X-ray diffraction analysis, indicating an increase of the lattice volume with increasing Si content from 4284.1(8) to 4334(1) A3 for pure alpha-TCP and alpha-Si5%TCP, respectively. The hydrolysis of milled alpha-SiTCP powders was monitored by isothermal calorimetry, and the compressive strength of set cements was tested. The results showed changes in speed and amount of heat released during reactivity tests and a decrease in mechanical strength (60, 50, and 5 MPa) with increasing Si content. In vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bonelike apatite layer on the surface of the set cements could be observed and was thickest for 1%Si (20 microm). These results were in good agreement with the in vivo studies performed, which showed strong evidence that the cement containing 1% silicon doped alpha-TCP enhanced mesenchymal cell differentiation and increased osteoblast activity compared with alpha-TCP.

Animals↗
PubMed2006

Effects of high-intensity focused ultrasound on the intervertebral disc: a potential therapy for disc herniations.

PURPOSE: To determine the potential application of high-intensity focused ultrasound for the minimally invasive treatment of herniated intervertebral discs by developing a probe that produces sufficiently high temperature locally to shrink collagen fibers (65-75 degrees Celsius). MATERIALS AND METHODS: A 5-mm ultrasound probe was produced with a geometric focal length of 15 mm. The probe produced 2.5 W of acoustic power and was operated at a frequency of 4.1 MHz. Measurements of temperature increase were performed in discs from bovine tails. In vivo experiments were performed to assess histologic changes in the disc as well as in nerve root and muscle. RESULTS: Sufficient temperature increase to produce collagen shrinkage was observed close to the focus of the ultrasound. Temperature measurements in vertebral end plates showed a temperature increase of only 4 degrees Celsius after 60-second exposure of the disc. In vivo experiments revealed histologic changes in the disc consistent with collagen shrinkage, with no adverse effects seen in surrounding tissues. CONCLUSIONS: The experiments demonstrated the feasibility of high-intensity focused ultrasound in the treatment of contained herniated discs. This technique has several advantages over other thermal treatment modalities.

Animals↗
PubMed2006

Variation in outcome and ranking of hospitals: an analysis from the Swedish knee arthroplasty register.

BACKGROUND: Hospital-specific variation in outcome is generally considered to be an important source of information for clinical improvement. We have measured the magnitude of this variation. METHODS: We determined the revision risk in 37,642 cemented primary total knee arthroplasties inserted as a result of osteoarthritis from 1993 through 2002 at 93 hospitals in Sweden. We used 2 essentially different methods to estimate risk of revision: a fixed-effects model (Cox's proportional hazards model) and a random-effects model (shared gamma frailty model). RESULTS: The 2 models ranked hospitals differently. As expected, the fixed-effects model provided more dispersed estimates of hospital-specific revision rates. In contrast to the random-effects model, chance events can easily cause overly optimistic or pessimistic outcomes in the fixed-effects model. Although the revision risk varied significantly between hospitals, the overall revision risk was still low. INTERPRETATION: Assessment of variation in outcome is an important instrument in the continuing effort to improve clinical care. However, regarding revision rate after knee arthroplasty, we do not believe that such analyses necessarily provide valid information on the current quality of care. We question their value as information source for seeking personal healthcare.

Adolescent↗
PubMed2005

Costs and quality of life associated with osteoporosis-related fractures in Sweden.

This prospective observational data collection study assessed the cost and quality of life related to hip, vertebral and wrist fracture 1 year after the fracture, based on a patient sample consisting of 635 male and female patients surviving a year after fracture. Data regarding resource use and quality of life related to fractures was collected by questionnaires at baseline, 4 months and 12 months. Information was collected by the use of patients' records, register sources and by asking the patient. Quality of life was estimated with the EQ-5D questionnaire. Costs were estimated from a societal perspective, including direct and indirect costs. The mean fracture-related cost the year after a hip, vertebral and wrist fracture were estimated, in euros ( ), at 14,221, 12,544 and 2,147, respectively [converted from Swedish krona (SEK) at an exchange rate of 9.1268 SEK/ ]. The mean reduction in quality of life was estimated at 0.17, 0.26 and 0.06 for hip, vertebral and wrist fracture, respectively. Based on the results, the yearly burden of osteoporosis in Sweden could be estimated at 0.5 billion (SEK 4.6 billion). The patient sample for vertebral fracture was fairly small and included a high proportion of fractures leading to hospitalization, but they indicate a higher cost and loss of quality of life related to vertebral fracture than previously perceived.

Aged↗
PubMed2005

Modeling of the heat distribution in the intervertebral disk.

The heat transfer equation was used to model the heat distribution in an intervertebral disk during ultrasound (US) exposure. The influence of thermal and acoustic parameters was studied to get a quantitative understanding of the heat transfer in the system. Heating of collagen to 65 degrees C or above will lead to denaturation and is believed to stabilize and contract the outer part of the disk in a herniated disk. In our model, the US intensity was approximated by a Gaussian distribution and nonlinear propagation was excluded. The effect of self-heating and cooling of the transducer was also studied. The simulations were performed using the finite element method. From this model, it can be concluded that it is possible to heat parts of the disk to treatment temperature using a focused 5-mm diameter US probe. The physical constraints on the piezocrystal set the limit of the size of the treatment volume.

Computer Simulation↗
PubMed2005

The economic cost of low back pain in Sweden in 2001.

BACKGROUND: Low back pain (LBP) is a common cause of lost work days and disability. In 2001, expenditure for back pain represented 11% of the total costs for short-term sick leave in Sweden, and about 13% of all early retirement pensions were granted for back problems, of which LBP is the most important symptom. The magnitude of LBP as a health problem justifies a closer look at its burden of illness to society. MATERIALS AND METHODS: We assessed the costs of LBP to society in Sweden in 2001. The study was conducted in a cost-of-illness framework, measuring both the direct costs of providing health care to LBP patients, and the indirect costs as the value of the production that is lost because people are too ill to work. The costs were estimated by a prevalence and top-down approach. RESULTS: The total cost of LBP was 1860 million EUR in Sweden in 2001. The indirect costs due to lost productivity accounted for 84% of the total cost. INTERPRETATION: The cost of illness due to low back pain was substantial, but does not appear to have risen during the last 10-15 years.

Adolescent↗
PubMed2004

Multinational survey of osteoporotic fracture management.

Osteoporosis is characterized by a decreased bone mass and an increased bone fragility and susceptibility to fracture. Patients with a fragility fracture at any site have an increased risk of sustaining future fractures. Orthopedic surgeons manage most of these fractures and are often the only physician seen by the patient. Mounting evidence that orthopedic surgeons are not well attuned to osteoporosis led the Bone and Joint Decade (BJD) and the International Osteoporosis Foundation (IOF) to survey 3,422 orthopedic surgeons in France, Germany, Italy, Spain, the United Kingdom, and New Zealand. The majority of the respondents in all countries had the opinion that the orthopedic surgeon should identify and initiate the assessment of osteoporosis in patients with fragility fractures. Heterogeneous practice pattern exist in different countries; however, identification and treatment of the osteoporotic patient seems to be insufficient in many areas: half of the orthopedic surgeons surveyed received little or no training in osteoporosis. Only approximately one in four orthopedic surgeons in France, the UK and New Zealand regarded themselves as knowledgeable about treatment modalities. Less than one-fifth of the orthopedic surgeons arranged for a surgically treated patient with a fragility fracture to have a bone mineral density (BMD) test. Twenty percent said that they never refer a patient after a fragility fracture for BMD. Only half of the orthopedic surgeons in southern Europe know about the importance of some external risk factors for hip fractures (cataracts, poor lighting, pathway obstacles, poor balance). In summary, this survey clearly indicates that many orthopedic surgeons still neglect to identify, assess and treat patients with fragility fractures for osteoporosis. More educational opportunities need to be offered to orthopedic surgeons through articles, web-based learning and educational seminars. Development of a simple clinical pathway from evidence-based guidelines is an important step to ensure that optimal care is provided for patients with fragility fractures.

Attitude of Health Personnel↗
PubMed2004

Initial stability of ankle arthrodesis with three-screw fixation. A finite element analysis.

OBJECTIVE: Compare the initial stability at the fusion site of ankle arthrodesis fixed with two and three screws. DESIGN: Finite element models of ankle arthrodesis were developed from computed tomography images. Two-screw constructs were augmented with a third screw in different orientations and subjected to loads likely to affect the ankle postoperatively. BACKGROUND: More stable fixation seems to increase the chance of fusion, as it minimises the motion between the tibiotalar interfaces. METHODS: Non-linear elastic finite element analyses were performed in external torsion and dorsiflexion. The micromotions at the tibiotalar interface were computed to compare the two- and three-screw fixation in intact and flat-cut arthrodesis. RESULTS: Adding a third screw reduced the micromotions at the fusion site. Inserting the third screw anteriorly predicted lower peak micromotions than inserting the screw posteriorly, except for the intact arthrodesis tested in dorsiflexion. Three-screw intact arthrodesis predicted lower peak micromotions than flat-cut arthrodesis. CONCLUSIONS: Better stability was predicted for three-screw ankle arthrodesis. In flat-cut arthrodesis, a third screw inserted anteriorly performed better than a posterior screw. In intact arthrodesis, a posterior screw seemed a better option when flexion stability was the main concern. Even with three-screw fixation, the configuration of the first two-crossed screws may still be important to improve the stability at the fusion site.

Ankle Joint↗
PubMed2004

The effect of bone quality on the stability of ankle arthrodesis. A finite element study.

BACKGROUND: Despite uniform operating techniques, lack of fusion still occurs after ankle arthrodesis. Differences in the biological healing potential may be a factor but the mechanical performance of the arthrodesis construct because of varying bone quality also may be important. Internal compression techniques are preferred because of higher union rates, shorter fusion times, and fewer complications. A three-screw configuration has been shown to be more stable than a two-screw configuration, but it is not obvious when it should be used. METHODS: Three-dimensional finite element models of intact and flat-cut ankle arthrodeses were built, using two and three screws in different configurations. Poor bone quality was simulated by decreasing Young's modulus of the bone. The constructs were loaded in torsion and dorsiflexion, and micromotions at the fusion site were measured. RESULTS: Bone quality had a marked effect on the stability at the arthrodesis site. Inserting two screws at 30 degrees relative to the longitudinal axis of the tibia in an intact arthrodesis seemed the best option, especially as bone quality worsened. The addition of a third screw increased the stability at the arthrodesis site. CONCLUSIONS: Overall, intact joint surfaces and three-screw fixation, with the lateral and medial screws inserted produced the most stable arthrodesis constructs when bone quality was poor. CLINICAL RELEVANCE. Ankle arthrodeses are technically demanding because of the shape and small size of the talus. Preoperative planning is an absolute necessity to determine placement and number of screws. This study shows that poor bone quality decreases the stability of the arthrodesis constructs, suggesting that an attempt should be made to create the most stable three-screw configuration. Finite element models can be used as an effective preoperative tool for planning screw number and placement.

Ankle Joint↗
PubMed2003

The effect of irradiation, annealing temperature, and artificial aging on the oxidation, mechanical properties, and fracture mechanisms of UHMWPE.

UHMWPE crosslinked using Gamma radiation is believed to have improved wear properties, and this has been extensively studied during the past 10 years. Mechanical properties, oxidation, and wear properties of UHMWPE materials subjected to various thermal treatments have been investigated immediately after irradiation as well as after several years of aging. Nevertheless, the relationship between all these parameters is not yet fully understood. The aim of this study was to investigate the relationship between the thermal treatments that could be applied to irradiated UHMWPE [lower (gamma 60) or higher (gamma 150) than 140 degrees C, the melting temperature of the polymer] and the mechanical properties, the oxidation and the fracture behavior of the material. The effect of artificial aging on these properties was also investigated. This study concludes that immediately after the annealing, the mechanical properties (UTS and epsilon) of the irradiated and annealed material are improved compared with those of nonirradiated material. Although nonirradiated material has higher fracture toughness than irradiated and annealed materials, the materials break according to the same mechanism of fracture. After aging, no changes could be observed in any of the measured properties for nonirradiated material. On the other hand, important changes could be seen in both irradiated and annealed material after aging. Both UTS and epsilon decreased, much more so in the case of gamma 60. Furthermore, the aging induced a subsurface peak of oxidation in both irradiated and annealed materials, twice as intense for gamma 60 than for gamma 150. The mechanism of fracture of these materials changed drastically after aging, probably due to the presence of the oxidation peak, which seems to occur at a location where cracks initiate easily compared with the nonoxidized bulk of the material. In the case of gamma 60, it seems clear that a correlation between mechanical property, oxidation, and fracture mechanism exists. Such a relationship could not be found for gamma 150.

Biomechanical Phenomena↗
PubMed2003

Finite element analysis of the initial stability of ankle arthrodesis with internal fixation: flat cut versus intact joint contours.

OBJECTIVE: Qualitative comparison of the initial stability provided by two joint preparation techniques and various screw configurations in ankle arthrodesis, using the finite element method.Design. A three-dimensional model of a healthy ankle was developed from computed tomography images. Two groups of models were built, one with the joint contours resected to produce flat surfaces, and the second with the joint contours preserved. In each case, a variety of screw orientations were examined. BACKGROUND: Despite the improved results of ankle arthrodesis, failure rates due to non-union are still reported. The initial stability of the arthrodesis construct seems important in the final outcome of the fusion. METHODS: Non-linear contact finite element analyses were performed in the arthrodesis constructs subjected to internal/external torsion and dorsiflexion. Micromotions at the bone-to-bone interface were calculated for frictionless and Coulomb friction contact, and compared for the two joint preparation techniques and screw configurations. RESULTS: Overall lower peak micromotions were predicted when preserving the joint contours both in torsion and dorsiflexion. For both preparation techniques, the lowest micromotions tended to occur with the screws inserted at 30 degrees with respect to the long axis of the tibia, crossing above the fusion site. Inclusion of friction in the models caused a general decrease on the magnitude of the micromotions as compared to the frictionless case, but did not affect the ranking of the models. CONCLUSIONS: The finite element method can be used as a qualitative tool to study the initial stability of ankle arthrodesis, overcoming the difficulties of measuring bone-to-bone interface micromotions experimentally. Better initial stability was predicted for ankle arthrodesis when the joint contours were preserved rather than resected. Crossing the screws above the fusion site at a steeper angle also tended to increase the stability at the fusion site. RELEVANCE: Finite element analyses can help during the pre-operative planning of ankle arthrodesis. When bone density is not compromised, preserving the joint contour and inserting the screws at less than 45 degrees to the long axis of the tibia, crossing over the arthrodesis site, may offer better initial stability.

Ankle Joint↗
PubMed2003

Bone morphology in relation to the migration of porous-coated anatomic knee arthroplasties : a roentgen stereophotogrammetric and histomorphometric study in 23 knees.

The quality of the subchondral bone in total knee arthroplasty (TKA) may be important for the outcome. We correlated a histomorphologic analysis of the prosthetic bone bed to micromotion as analyzed by roentgen stereophotogrammetric analysis (RSA). Twenty-three knees, both osteo- and rheumatoid arthritic were studied. The mean migration after 1 year was 1 mm (0.21-2.68), with no correlation to the bone variables or diagnosis. One patient underwent revision after 3 years because of pain. One patient underwent revision after 15 years because of aseptic loosening. This patient appeared stable according to changes in maximum total point motion (MTPM), but the prosthesis migrated continuously according to segment motion. Prosthetic migration increased after 10 years, zones started to evolve, and the patient became symptomatic after 13 years. A biopsy of the bone bed was taken in all patients. A larger percentage of trabecular bone and a larger relative area of unmineralized osteoid surface were found in patients with rheumatoid arthritis compared with those with osteoarthritis. The latter finding is probably a result of increased bone turnover. In conclusion, no support currently exists for the idea that preoperative bone quality, evaluated as bone histomorphometry, has any impact on prosthetic micromotion in knee prostheses.

Adult↗
PubMed2003

Infection and arthritis. Infection of prosthetic joints.

Infection of prosthetic joints is one of the most devastating complications following replacement surgery. The size of the problem, the diagnostic puzzle, bacteriological findings and treatment modalities are highlighted.

Anti-Bacterial Agents↗
PubMed2003

Factors affecting the static shear strength of the prosthetic stem-bone cement interface.

Debonding of the stem-cement interface has been implicated in the initiation of failure of cemented femoral stems. The objective of this work was to examine some of the parameters which influence the interface static shear strength, including surface finish, cement type, pre-treatments and porosity. Surface finish was found to have the greatest effect on the interface strength. Increasing the surface roughness by a factor of 100 increases the interface shear strength by a factor of 20. However, increasing the surface roughness above a certain value was found to have no additional affect. This was due to failure in the cement itself rather than at the cement-stem interface. There were significant differences between some of the different cement types regarding the interface strength. Pre-heating the stem produced a six fold reduction in cement porosity at the stem-cement interface, however, resulting in only a minor influence on the static interface strength. Generally, no significant correlation was found between the cement porosity and the static interfacial shear strength.

Journal Article↗
PubMed2003

Compressive and shear properties of commercially available polyurethane foams.

BACKGROUND: The shear properties of rigid polyurethane (PU-R) foams, routinely used to simulate cancellous bone, are not well characterized. METHOD OF APPROACH: The present assessment of the shear and compressive properties of four grades of Sawbones "Rigid cellular" PU-R foam tested 20 mm gauge diameter dumb-bell specimens in torsion and under axial loading. RESULTS: Shear moduli ranged from 13.3 to 99.7 MPa, shear strengths from 0.7 MPa to 4.2 MPa. Compressive yield strains varied little with density while shear yield strains had peak values with "200 kgm-3" grade. CONCLUSIONS: PU-R foams may be used to simulate the elastic but not failure properties of cancellous bone.

Biocompatible Materials↗