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Biomedical subjects

B Sandén

Publications and source records attributed to B Sandén.

10 recordsLinked to original sources
PubMed2004

The significance of radiolucent zones surrounding pedicle screws. Definition of screw loosening in spinal instrumentation.

We examined the radiographs from a prospective clinical study of fixation by pedicle screws and those from an experimental study in a sheep model. In the clinical study, instruments were removed from 21 patients after implantation for 11 to 16 months and the extraction torques of the screws were recorded. A structured protocol was used for the radiological examinations. In the experimental study, loaded pedicle screw instrumentations were implanted in the sheep for six or 12 weeks. After radiological examination the pull-out resistance and the histological characteristics were studied. In the clinical study, all screws with radiolucent zones had a significantly reduced mean extraction torque compared with screws without radiolucent zones (16 +/- 10 Ncm v 403 +/- 220 Ncm; p < 0.0001). In the experimental study the mean maximum pull-out resistance for the screws with radiolucent zones was significantly lower than for those with no radiolucency (243 +/- 156 N v2214 +/- 578 N; p = 0.0006) and the mean bone-to-screw contact was reduced for screws with zones compared with those without zones (8 +/- 9% v 55 +/- 29%; p = 0.0002). Our findings showed that all screws with radiolucent zones had low extraction torques or low pull-out resistance. A radiolucent zone is a good indicator of loosening of a pedicle screw.

Animals↗
PubMed2003

Aberdeen Colles' fracture brace as a treatment for Colles' fracture. A multicentre, prospective, randomised, controlled trial.

We carried out a randomised, prospective, multicentre clinical trial of the treatment of Colles' fractures. A total of 339 patients was placed into two groups, those with minimally displaced fractures not requiring manipulation (151 patients) and those with displaced fractures which needed manipulation (188 patients). Treatment was by either a conventional Colles' plaster cast (a control group) or with a prefabricated functional brace (the Aberdeen Colles' fracture brace). Similar results were obtained in both groups with regard to the reduction and to pain scores but the brace provided better grip strength in the early stages of treatment. This was statistically significant after five weeks for both manipulated and non-manipulated fractures. At the tenth day the results were statistically significant only in manipulated fractures. There was no significant difference in the functional outcome between the two treatment groups. However, younger patients and those with less initial displacement had better functional results.

Adult↗
PubMed2002

Hydroxyapatite coating improves fixation of pedicle screws. A clinical study.

We investigated the effects of hydroxyapatite (HA) coating on the purchase of pedicle screws. A total of 23 consecutive patients undergoing lumbar fusion was randomly assigned to one of three treatment groups. The first received uncoated stainless-steel screws, the second screws which were partly coated with HA, and the third screws which were fully coated. The insertion torque was recorded. After 11 to 16 months, 21 screws had been extracted. The extraction torque was recorded. Radiographs were taken to assess fusion and to detect loosening of the screws. At removal, the extraction torques exceeded the upper limit of the torque wrench (600 Ncm) for many HA-coated screws. The calculated mean extraction torque was 29 +/- 36 Ncm for the uncoated group, 447 +/- 114 Ncm for the partly-coated group and 574 +/- 52 Ncm for the fully-coated group. There were significant differences between all three groups (p < 0.001). There were more radiolucent zones surrounding the uncoated screws than the HA-coated screws (p < 0.001). HA coating of pedicle screws resulted in improved fixation with reduced risk of loosening of the screws.

Adult↗
PubMed2001

Improved bone-screw interface with hydroxyapatite coating: an in vivo study of loaded pedicle screws in sheep.

STUDY DESIGN: An in vivo sheep model with loaded pedicle screws was used, wherein each animal served as its own control. OBJECTIVES: To examine the effects of hydroxyapatite (HA) coating on the bone-to-implant interface in loaded spinal instrumentations. SUMMARY OF BACKGROUND DATA: Spinal instrumentation improves the healing rate in spinal fusion, but screw loosening constitutes a problem. HA coating of other implants has resulted in favorable effects on the bone-to-implant interface. METHODS: Nine sheep were operated on with destabilizing laminectomies at two levels: L2-L3 and L4-L5. Each level was stabilized separately with a four-screw instrumentation. Uncoated screws (stainless steel) or the same type of screws coated with plasma-sprayed HA were used in either the upper or the lower instrumentation in a randomized fashion. The animals were killed at 6 or 12 weeks after surgery. The specimens were embedded in resin, ground to approximately 10 microm, and stained with toluidine blue. Histomorphometric evaluation was carried out in a Leitz Aristoplan (Wetzlar, Germany) light microscope equipped with a Leitz Microvid unit. RESULTS: The average percentage of bone-to-implant contact after 6 weeks was 69 +/- 10 for the HA-coated screws and 18 +/- 11 for the uncoated screws (P < 0.03), and after 12 weeks 64 +/- 31 (HA-coated) and 9 +/- 13 (uncoated, P < 0.02). The average bone volume in the area close to the screw was significantly higher for the HA-coated screws at both 6 and 12 weeks. CONCLUSIONS: HA coating improved the bone-to-implant interface significantly, indicating that HA coating can become useful for improving the purchase of pedicle screws.

Animals↗
PubMed2001

Hydroxyapatite coating enhances fixation of loaded pedicle screws: a mechanical in vivo study in sheep.

Loosening of the pedicle screws with subsequent non-union or loss of correction is a frequent problem in spinal instrumentation. In a clinical pilot study, coating of pedicle screws with plasma-sprayed hydroxyapatite (HA) resulted in a significant increase of removal torque. An experimental study was performed to investigate the effects of HA coating on the pull-out resistance. Thirteen sheep were operated on with destabilising laminectomies at two levels, L2-L3 and L4-L5. Two instrumentations with four pedicle screws in each were used for stabilisation. Uncoated screws (stainless steel) or the same type of screws coated with plasma-sprayed HA were used in either the upper or the lower instrumentation in a randomised fashion. Four sheep were examined immediately after the application of the screws, three sheep at 6 weeks and four sheep at 12 weeks. Two sheep were euthanised early due to complications. The pull-out resistance was recorded in two HA-coated and two standard screws in each animal. The maximum pull-out resistance was higher for the HA-coated screws at 0 weeks (P< 0.02) and at 12 weeks (P<0.01) when compared to the uncoated screws, while there was no significant difference between the groups at 6 weeks. We believe that the higher pull-out resistance for HA-coated screws at 0 weeks was mainly caused by differences in surface roughness, while the difference at 12 weeks was due to a favourable bone reaction around the HA-coated screws. At 12 weeks, the average stiffness was significantly higher for the HA-coated screws, while there was no significant differences in stiffness between the two screw types at 0 and 6 weeks. Energy to failure was significantly higher for coated screws when compared to the uncoated screws at all three time points. HA coating improves fixation of loaded pedicle screws, with increased pull-out resistance and reduced risk of loosening.

Animals↗
PubMed2000

Application of an amperometric immunosensor for the enumeration of Nitrobacter in activated sludge.

A competitive immunosensor using a monoclonal antibody has been developed for the enumeration of Nitrobacter in activated sludge and other environmental samples. Its cross-reactivity was tested against a number of bacterial strains and isolates. All strains of the nitrite-oxidising genera Nitrobacter and Nitrococcus reacted strongly with the monoclonal antibody. The nitrite-oxidising Nitrospira moscoviensis, as well as the ammonia oxidising bacteria and the heterotrophic bacteria tested, did not show any affinity towards the antibody in the immunosensor. The numbers of Nitrobacter were analysed in sludge samples from several wastewater treatment plants in Sweden. Detectable amounts were found in all samples. This study shows the adequacy of using this immunosensor for the enumeration of Nitrobacter in natural environments.

Antibodies, Bacterial↗
PubMed2000

Improved extraction torque of hydroxyapatite-coated pedicle screws.

Loosening of the screws is a problem in instrumentation with pedicle screws. Coating with hydroxyapatite improves the holding characteristics for metal implants, but the possible effects on the anchorage of pedicle screws have not been described. In this study, seven patients were operated on with spinal instrumentation using four stainless steel pedicle screws. Hydroxyapatite-coated screws were used in either the upper or the lower of the instrumented levels. The insertion torque was measured. In four cases the screws were removed after 10-22 months and the extraction torque was measured. The mean insertion torque was found to be significantly greater in the hydroxyapatite-coated screws (107 Ncm) than in the standard screws (76 Ncm). In three cases, the extraction torque for the hydroxyapatite-coated screws exceeded the range for the torque wrench (600 Ncm), while the conventional screws were loose (< 5 Ncm). In one case, the extraction torque was 475 and 550 Ncm for the coated screws, and 5 and 25 Ncm for the conventional screws. The difference in extraction torque was significant. Hydroxyapatite coating was shown to have improved the purchase of pedicle screws very effectively. By using fully coated screws, as in the present study, extraction was extremely difficult compared to extraction of conventional stainless steel screws, which were regularly loose. By reducing the area of the screws that is coated, it may be possible to achieve an enhanced purchase while extraction will be easier when compared to fully coated screws.

Adolescent↗
PubMed1998

An amperometric enzyme-linked immunosensor for Nitrobacter.

A new amperometric enzyme-linked immunoassay for specific enumeration of Nitrobacter has been developed. This assay uses an electrode made of glassy carbon, on which the immunological reaction is carried out. The method is based on a competitive immunoassay principle, utilising monoclonal primary antibody and alkaline-phosphatase-labelled secondary antibody. The enzyme substrate 5-bromo-4-chloro-3-indolyl phosphate generates an electroactive product which is amperometrically detected. The effects of different parameters on the performance of the sensor have been studied. Quantitative detection of Nitrobacter using the immunosensor has been compared to a previously developed enzyme-linked immunosorbent assay showing compatible results. In addition, the overall assay time can be shortened with this new sensor. A detection limit of approximately 3 x 10(6) Nitrobacter cells/ml was obtained.

Antibodies, Monoclonal↗