| 51. |
- Gustafsson, Anna, et al.
(författare)
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Strains caused by daily loading might be responsible for delayed healing of an incomplete atypical femoral fracture
- 2016
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Ingår i: Bone. - : ELSEVIER SCIENCE INC. - 8756-3282 .- 1873-2763. ; 88, s. 125-130
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Tidskriftsartikel (refereegranskat)abstract
- Atypical femoral fractures are insufficiency fractures in the lateral femoral diaphysis or subtrochanteric region that mainly affect older patients on bisphosphonate therapy. Delayed healing is often seen in patients with incomplete fractures (cracks), and histology of bone biopsies shows mainly necrotic material inside the crack. We hypothesized that the magnitude of the strains produced in the soft tissue inside the crack during normal walk exceeds the limit for new bone formation, and thereby inhibit healink. A patient specific finite element model was developed, based on clinical CT images and high resolution CT images of a biopsy from the crack site. Strain distributions in the femur and inside the crack were calculated for load cases representing normal walk. The models predicted large strains inside the crack, with strain levels above 10% in more than three quarters of the crack volume. According to two different tissue differentiation theories, bone would only form in less than 1-5% cif the crack volume. This can explain the impaired healing generally seen in incomplete atypical fractures. Furthermore, the microgeometry of the crack highly influenced the strain distributions. Hence, a realistic microgeometry needs to be considered when modeling the crack. Histology of the biopsy showed signs of remodeling in the bone tissue adjacent to the fracture line, while the crack itself contained mainly necrotic material and signs of healing only in portions that seemed to have been widened by resorption. In conclusion, the poor healing capacity of incomplete atypical femoral fractures can be explained by biomechanical factors, and daily low impact activities are enough to cause strain magnitudes that prohibit bone formation. (C) 2016 Elsevier Inc. All rights reserved.
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| 52. |
- Halldin, Anders, et al.
(författare)
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The effect of static bone strain on implant stability of bone remodelling
- 2011
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Ingår i: Bone. - : Elsevier. - 8756-3282 .- 1873-2763. ; 49:4, s. 783-789
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Tidskriftsartikel (refereegranskat)abstract
- Bone remodeling is a process involving both dynamic and static bone strain. Although there exist numerous studies on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain has yet to be clarified. Hence, for this purpose, the effect of static bone strain on implant stability and bone remodeling was investigated in rabbits. Based on Finite Element (FE) simulation two different test implants, with a diametrical increase of 0.15 mm (group A) and 0.05 mm (group B) creating static strains in the bone of 0.045 and 0.015 respectively, were inserted in the femur (group A) and the proximal tibia metaphysis (groups A and B respectively) of 14 rabbits to observe the biological response. Both groups were compared to control implants, with no diametrical increase (group C), which were placed in the opposite leg. At the time of surgery, the insertion torque (ITQ) was measured to represent the initial stability. The rabbits were euthanized after 24 days and the removal torque (RTQ) was measured to analyze the effect on implant stability and bone remodeling. The mean ITQ value was significantly higher for both groups A and B compared to group C regardless of the bone type. The RTQ value was significantly higher in tibia for groups A and B compared to group C while group A placed in femur presented no significant difference compared to group C. The results suggest that increased static strain in the bone not only creates higher implant stability at the time of insertion, but also generates increased implant stability throughout the observation period.
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| 53. |
- Halling Linder, Cecilia, et al.
(författare)
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Glycosylation differences contribute to distinct catalytic properties among bone alkaline phosphatase isoforms.
- 2009
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Ingår i: Bone. - : Elsevier BV. - 1873-2763 .- 8756-3282. ; 45:5, s. 987-993
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Tidskriftsartikel (refereegranskat)abstract
- Three circulating human bone alkaline phosphatase (BALP) isoforms (B1, B2, and B/I) can be distinguished in healthy individuals and a fourth isoform (B1x) has been discovered in patients with chronic kidney disease and in bone tissue. The present study was designed to correlate differing glycosylation patterns of each BALP isoform with their catalytic activity towards presumptive physiological substrates and to compare those properties with two recombinant isoforms of the tissue-nonspecific ALP (TNALP) isozyme, i.e., TNALP-flag, used extensively for mutation analysis of hypophosphatasia mutations and sALP-FcD(10), a chimeric enzyme recently used as therapeutic drug in a mouse model of infantile hypophosphatasia. The BALP isoforms were prepared from human osteosarcoma (SaOS-2) cells and the kinetic properties were evaluated using the synthetic substrate p-nitrophenylphosphate (pNPP) at pH 7.4 and 9.8, and the three suggested endogenous physiological substrates, i.e., inorganic pyrophosphate (PP(i)), pyridoxal 5'-phosphate (PLP), and phosphoethanolamine (PEA) at pH 7.4. Qualitative glycosylation differences were also assessed by lectin binding and precipitation. The k(cat)/K(M) was higher for B2 for all the investigated substrates. The catalytic activity towards PEA was essentially undetectable. The kinetic activity for TNALP-flag and sALP-FcD(10) was similar to the activity of the human BALP isoforms. The BALP isoforms differed in their lectin binding properties and dose-dependent lectin precipitation, which also demonstrated differences between native and denatured BALP isoforms. The observed differences in lectin specificity were attributed to N-linked carbohydrates. In conclusion, we demonstrate significantly different catalytic properties among the BALP isoforms due to structural differences in posttranslational glycosylation. Our data also suggests that PEA is not an endogenous substrate for the BALP isoforms or for the recombinant TNALP isoforms. The TNALP-flag and the sALP-FcD(10) isoforms faithfully mimic the biological properties of the human BALP isoforms in vivo validating the use of these recombinant enzymes in studies aimed at dissecting the pathophysiology and treating hypophosphatasia.
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| 54. |
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| 55. |
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| 56. |
- Hantikainen, Essi, et al.
(författare)
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Prospective study of dietary Non Enzymatic Antioxidant Capacity on the risk of hip fracture in the elderly
- 2016
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Ingår i: Bone. - : Elsevier BV. - 8756-3282 .- 1873-2763. ; 90, s. 31-36
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Tidskriftsartikel (refereegranskat)abstract
- Background: Dietary antioxidants may play an important role in the prevention of bone loss and associated fractures by reducing levels of oxidative stress. We prospectively investigated the association between dietary Non Enzymatic Antioxidant Capacity (NEAC) and the risk of hip fracture and whether this effect was modified by smoking. Method: In the Swedish National March Cohort 13,409 men and women over the age of 55 who had not experienced cancer, cardiovascular disease or hip fracture, were followed through record-linkages from 1997 through 2010. NEAC was assessed by a validated food frequency questionnaire collected at baseline. We categorized the distribution of NEAC into sex-specific quartiles and used multivariable adjusted Cox proportional hazards regression models to estimate hazard ratios (HRs) with 95% confidence intervals (95% CI). Results: During a mean follow-up time of 12.4 years, we identified 491 incident cases of first hip fracture. Subjects in the highest quartile of dietary NEAC had a 39% lower risk of incident hip fracture compared to those in the lowest quartile (HR: 0.61; 95% CI: 0.44-0.85). The association was non-linear (p for non-linearity: 0.004) with a potential threshold between the first and the second quartile and no further risk reduction at higher levels of dietary NEAC. Due to a low smoking prevalence in our study population, we had limited power to detect effect modification between dietary NEAC and smoking on a multiplicative or additive scale. Conclusion: Higher dietary NEAC intake is associated with lower risk of hip fracture in the elderly.
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| 57. |
- Harding, Anna Kajsa, et al.
(författare)
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A single dose zoledronic acid enhances pin fixation in high tibial osteotomy using the hemicallotasis technique. A double-blind placebo controlled randomized study in 46 patients.
- 2010
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Ingår i: Bone. - : Elsevier BV. - 1873-2763 .- 8756-3282. ; 46:3, s. 649-654
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Bisphosphonates have been shown to reduce osteoclastic activity and enhance pin fixation in both experimental and clinical studies. In this prospective, randomized study of high tibial osteotomy using the hemicallotasis (HCO) technique, we evaluate whether treatment by one single infusion of zoledronic acid can enhance the pin fixation. MATERIALS AND METHODS: 46 consecutive patients (35-65 years) were operated on for knee osteoarthritis by the HCO technique. After the osteotomy, two hydroxyapatite-coated pins were inserted in the metaphyseal bone and two non-coated pins in the diaphyseal bone. The insertion torque was measured by a torque force screw driver. Four weeks postoperatively, the patients were randomized to either one infusion of zoledronic acid or sodium chloride intravenously. At time for removal of the pins, the extraction torque forces of the pins were measured. RESULTS: All osteotomies healed and no difference was found in time to healing. The mean extraction torque force in the non-coated pins in the diaphyseal bone was doubled in the zoledronic treated group (4.5 Nm, SD 2.1) compared to the placebo group (2.4 (SD 1.0, p<0.0001). The mean extraction torque forces of the hydroxyapatite-coated pins in the metaphyseal bone were similar in the zoledronic acid group (4.7 Nm, SD 1.3) and in the placebo group (4.0 Nm, SD 1.3). DISCUSSION: A single infusion of zoledronic acid improved twofold the fixation of non-coated pins in diaphyseal bone. Bisphosphonates might be an alternative to hydroxyapatite-coated pins in nonosteoporotic bone.
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