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Minneapolis, MN, United States

Singal K.,General Electric | Rajamani R.,University of Minnesota | Ahmadi M.,University of Minnesota | Sezen A.S.,St. Cloud State University | Bechtold J.E.,Excelen Center for Bone and Joint Research
IEEE Transactions on Biomedical Engineering

This paper presents a novel Hall-effect-based magnetic sensor for handheld measurement of either elasticity or tension in soft tissues. A theoretical model is developed for the mechanical interaction of the sensor with the tissue, and conditions are established under which the separate effects of tension or elasticity can be measured. A model of the magnetic field within the sensor is developed and a technique to estimate the sensor response in the presence of multiple magnets is established. This paper then provides analytical sensor responses and compares them with experimental results obtained on synthetic materials. It is found that the sensor can measure tension values upto 100 N with a resolution of 10 N in handheld operation and elasticity of upto 0.87 MPa with a resolution of 0.02 MPa. Significant experimental characterization and statistical analysis of sensor repeatability is performed. The viability of this sensor to make tension and elasticity measurements with biological tissues is then demonstrated using turkey tendons and fresh swine tissues. © 2014 IEEE. Source

Daugaard H.,Aarhus University Hospital | Elmengaard B.,Aarhus University Hospital | Andreassen T.T.,Aarhus University Hospital | Andreassen T.T.,University of Aarhus | And 4 more authors.
Journal of Bone and Joint Surgery - Series B

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant. Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseo-integration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1-34) 5 μg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters. These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks. ©2011 British Editorial Society of Bone and Joint Surgery. Source

Daugaard H.,Aarhus University Hospital | Elmengaard B.,Aarhus University Hospital | Andreassen T.,University of Aarhus | Bechtold J.,Excelen Center for Bone and Joint Research | And 2 more authors.
Calcified Tissue International

Parathyroid hormone (PTH) administered intermittently is a bone-building peptide. In joint replacements, implants are unavoidably surrounded by gaps despite meticulous surgical technique and osseointegration is challenging. We examined the effect of human PTH(1-34) on implant fixation in an experimental gap model. We inserted cylindrical (10 × 6 mm) porous coated titanium alloy implants in a concentric 1-mm gap in normal cancellous bone of proximal tibia in 20 canines. Animals were randomized to treatment with PTH(1-34) 5 μg/kg daily. After 4 weeks, fixation was evaluated by histomorphometry and push-out test. Bone volume was increased significantly in the gap. In the outer gap (500 μm), the bone volume fraction median (interquartile range) was 27% (20-37%) for PTH and 10% (6-14%) for control. In the inner gap, the bone volume fraction was 33% (26-36%) for PTH and 13% (11-18%) for control. At the implant interface, the bone fraction improved with 16% (11-20%) for PTH and 10% (7-12%) (P = 0.07) for control. Mechanical implant fixation was improved for implants exposed to PTH. For PTH, median (interquartile range) shear stiffness was significantly higher (PTH 17.4 [12.7-39.7] MPa/mm and control 8.8 [3.3-12.4] MPa/mm) (P < 0.05). Energy absorption was significantly enhanced for PTH (PTH 781 [595-1,198.5] J/m2 and control 470 [189-596] J/m2). Increased shear strength was observed but was not significant (PTH 3.0 [2.6-4.9] and control 2.0 [0.9-3.0] MPa) (P = 0.08). Results show that PTH has a positive effect on implant fixation in regions where gaps exist in the surrounding bone. With further studies, PTH may potentially be used clinically to enhance tissue integration in these challenging environments. © 2011 The Author(s). Source

Fleischer G.D.,Southern New Hampshire Medical Center | Kim Y.J.,Columbia University | Ferrara L.A.,Kinetic Technologies | Freeman A.L.,Excelen Center for Bone and Joint Research | Boachie-Adjei O.,Hospital for Special Surgery

Study Design.: A cadaveric biomechanical experiment was conducted to assess the range of motion (ROM) and screw strain at S1 in a long instrumented spinal fusion construct to compare the effects of various surgical strategies for L5-S1 stabilization. Objective.: To directly quantify and compare S1 screw strains and lumbosacral ROM for 4 different L2-S1 posterior segmental instrumented fusion constructs: an L2-S1 pedicle screw (PS) construct alone and PS with each of 3 different augmentations, anterior lumbar intebody fusion (ALIF), anterior axial interbody threaded rod (AxiaLITR), or iliac screws. Summary of Background Data.: Iliac screws and anterior interbody devices are commonly used as augmentation to reduce the incidence of S1 screw loosening in long fusion constructs. Alternatives, such as AxiaLITR, may provide similar biomechanical advantages without many of the same long-term limitations and morbidities. Methods.: Pure moment flexibility testing was performed in 6 cadaveric lumbosacral spines. Specimens were tested with 4 instrumentation constructs: (.1) PS L2-S1, (2) PS with ALIF, (3) PS with AxiaLITR, and (4) PS with iliac screws. Bilateral S1 PS were instrumented with strain gauges, directly measuring screw loading while simultaneously measuring L5-S1 ROM with a noncontact camera system. Results.: Average S1 screw strains were the greatest with the PS group and were reduced by 38% with the ALIF group, 75% with the AxiaLITR group, and 78% with the iliac screw group in flexion-extension (P < 0.05). Similar trends were observed in torsion (P < 0.05). Strains in lateral bending were smaller in magnitude and were similar among all 4 constructs. The AxiaLITR and iliac screw groups demonstrated a similar ROM and significant reduction in ROM at L5-S1 compared with both the PS and ALIF groups (P ≤ 0.02 and P < 0.03). Conclusion.: The Results of this study indicated that iliac screws and AxiaLITR provide similar stability at L5-S1, while significantly reducing the strain on the S1 screws. © 2012, Lippincott Williams & Wilkins. Source

Daugaard H.,Aarhus University Hospital | Elmengaard B.,Aarhus University Hospital | Andreassen T.T.,University of Aarhus | Lamberg A.,Aarhus University Hospital | And 2 more authors.
Acta Orthopaedica

Background and purpose Intermittent administration of parathyroid hormone (PTH) has an anabolic effect on bone, as confirmed in human osteoporosis studies, distraction osteogenesis, and fracture healing. PTH in rat models leads to improved fixation of implants in low-density bone or screw insertion transcortically. Material and methods We examined the effect of human PTH (1-34) on the cancellous osseointegration of unloaded implants inserted press-fit in intact bone of higher animal species. 20 dogs were randomized to treatment with human PTH (134), 5 μg/kg/day subcutaneously, or placebo for 4 weeks starting on the day after insertion of a cylindrical porous coated plasma-sprayed titanium alloy implant in the proximal metaphyseal cancellous bone of tibia. Osseointegration was evaluated by histomorphometry and fixation by push-out test to failure. Results Surface fraction of woven bone at the implant interface was statistically significantly higher in the PTH group by 1.4 fold with (median (interquartile range) 15% (1318)) in the PTH group and 11% (7-13) in control. The fraction of lamellar bone was unaltered. No significant difference in bone or fibrous tissue was observed in the circumferential regions of 0-500, 500-1,000, and 1,000-2,000 μm around the implant. Mechanically, the implants treated with PTH showed no significant differences in total energy absorption, maximum shear stiffness, or maximum shear strength. Interpretation Intermittent treatment with PTH (134) improved histological osseointegration of a prosthesis inserted press-fit at surgery in cancellous bone, with no additional improvement of the initial mechanical fixation at this time point. © 2011 Nordic Orthopaedic Federation. Source

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