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Wheeler D.J.,University of Minnesota | Freeman A.L.,Excelen Center for Bone and Joint Research | Ellingson A.M.,University of Minnesota | Nuckley D.J.,University of Minnesota | And 5 more authors.
Journal of Biomechanics | Year: 2011

In vitro spine flexibility testing has been performed using a variety of laboratory-specific loading apparatuses and conditions, making test results across laboratories difficult to compare. The application of pure moments has been well established for spine flexibility testing, but to our knowledge there have been no attempts to quantify differences in range of motion (ROM) resulting from laboratory-specific loading apparatuses. Seven fresh-frozen lumbar cadaveric motion segments were tested intact at four independent laboratories. Unconstrained pure moments of 7.5. Nm were applied in each anatomic plane without an axial preload. At laboratories A and B, pure moments were applied using hydraulically actuated spinal loading fixtures with either a passive (A) or controlled (B) XY table. At laboratories C and D, pure moments were applied using a sliding (C) or fixed ring (D) cable-pulley system with a servohydraulic test frame. Three sinusoidal load-unload cycles were applied at laboratories A and B while a single quasistatic cycle was applied in 1.5. Nm increments at laboratories C and D. Non-contact motion measurement systems were used to quantify ROM. In all test directions, the ROM variability among donors was greater than single-donor ROM variability among laboratories. The maximum difference in average ROM between any two laboratories was 1.5° in flexion-extension, 1.3° in lateral bending and 1.1° in axial torsion. This was the first study to quantify ROM in a single group of spinal motion segments at four independent laboratories with varying pure moment systems. These data support our hypothesis that given a well-described test method, independent laboratories can produce similar biomechanical outcomes. © 2011 Elsevier Ltd.


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 | Year: 2011

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).


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 | Year: 2011

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.


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 | Year: 2012

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.


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 | Year: 2014

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.


Fleischer G.D.,Southern New Hampshire Medical Center | Hart D.,Cleveland Clinic | Ferrara L.A.,OrthoKinetic Technologies | Freeman A.L.,Excelen Center for Bone and Joint Research | Avidano E.E.,TranS1
Spine | Year: 2014

Study Design. A cadaveric lumbosacral spondylolytic spondylolisthesis model was used to evaluate the biomechanical function of 2 different interbody spacers. Objective. To analyze and compare the reduction in pedicle screw strain and spine range of motion (ROM) between transforaminal lumbar interbody fusion (TLIF) and an axial interbody threaded rod (AxialITR) in a destabilized L5-S1 spondylolisthesis model. Summary of Background Data. Symptomatic spondylolytic spondylolisthesis is often treated with posterior instrumented fusion augmented by a variety of different interbody devices. Interbody spacers rely primarily on posterior instrumentation to stabilize the spine during fusion, but there may be advantages to the more rigid support offered by an anterior threaded rod. Methods. Pure-moment flexibility testing was performed on L3-S1 cadaveric specimens in 4 conditions: (1) Intact, (2) L5-S1 pedicle screws (PS) + L5-S1 disc destabilization (DDS), (3) TLIF at L5-S1 + PS + DDS, and (4) AxialITR at L5-S1 + PS + DDS. Specimens were destabilized by performing a complete denucleation at L5-S1 and sectioning two-thirds of the annulus' width from anterior to posterior. The S1 PSs were instrumented with strain gauges to measure screw-bending moments and ROM was quantified with a noncontact camera system. Results. S1 screw strains were highest with PS but were significantly reduced by 73% in flexion and 31% in extension with TLIF (P ≤ 0.004). AxialITR significantly reduced strain by 78% in flexion and 81% in extension (P ≤ 0.001). ROM was smallest with AxialITR in each test direction at 1.7 ± 1.8 in flexion-extension, 1.6 ± 0.9 in lateral bending and 1.3 ± 0.8 in torsion. Conclusion. This study demonstrated that ROM and S1 screw-bending moments were reduced with the use of AxialITR and TLIF. Although the TLIF and AxialITR both reduced strains and motion, the AxialITR provided a significant reduction in extension strain when compared with TLIF. Copyright © 2014 Lippincott Williams & Wilkins.


Freeman A.L.,Excelen Center for Bone and Joint Research | Camisa W.J.,Excelen Center for Bone and Joint Research | Buttermann G.R.,Midwest Spine Institute | Malcolm J.R.,Pinnacle Orthopaedics
Journal of neurosurgery. Spine | Year: 2016

OBJECTIVE: This study was undertaken to quantify the in vitro range of motion (ROM) of oblique as compared with anterior lumbar interbody devices, pullout resistance, and subsidence in fatigue.METHODS: Anterior and oblique cages with integrated plate fixation (IPF) were tested using lumbar motion segments. Flexibility tests were conducted on the intact segments, cage, cage + IPF, and cage + IPF + pedicle screws (6 anterior, 7 oblique). Pullout tests were then performed on the cage + IPF. Fatigue testing was conducted on the cage + IPF specimens for 30,000 cycles.RESULTS: No ROM differences were observed in any test group between anterior and oblique cage constructs. The greatest reduction in ROM was with supplemental pedicle screw fixation. Peak pullout forces were 637 ± 192 N and 651 ± 127 N for the anterior and oblique implants, respectively. The median cage subsidence was 0.8 mm and 1.4 mm for the anterior and oblique cages, respectively.CONCLUSIONS: Anterior and oblique cages similarly reduced ROM in flexibility testing, and the integrated fixation prevented device displacement. Subsidence was minimal during fatigue testing, most of which occurred in the first 2500 cycles.


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
Spine | Year: 2012

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.


Freeman A.L.,Excelen Center for Bone and Joint Research | Buttermann G.R.,Midwest Spine Institute | Beaubien B.P.,Excelen Center for Bone and Joint Research | Rochefort W.E.,Oregon State University
Journal of Biomechanics | Year: 2013

The wound healing process includes filling the void between implant and tissue edges by collagenous connective repair tissue. This fibrous repair tissue may load share or stabilize implants such as spinal disc replacements. The objective of this study was the biomechanical characterization of human fibrous tissue compared to annulus fibrosus and nucleus pulposus. Human lumbar discs (10 nucleus and annulus) and 10 lumbar deep wound fibrous tissue specimens were sectioned into 12. mm diameter×6. mm high cylindrical samples. Confined compression testing, after 2. h swelling at 0.11. MPa, was performed at 5%, 10% and 15% strain over 3.5. h. Unconfined dynamic testing (2-0.001. Hz) was performed at 5-15% strain. Semi-quantitative histology estimated the proportion of proteoglycan to collagen. Fibrous tissue exhibited a decrease in height during the swelling period whereas annulus and nucleus tissues did not. The aggregate modulus was significantly less for fibrous tissue (p<0.002). Percent stress relaxation was greatest for the fibrous tissue and similar for annulus and nucleus. Dynamic testing found the storage modulus (E') was greater than the loss modulus (E″) for all tissues. Annulus were found to have greater E' and E″ than nucleus, whereas E' and E″ were similar between annulus and fibrous tissue. Fibrous tissue had the greatest increase in both moduli at greater frequencies, but had the lowest hydration and proteoglycan content. Fibrous tissue would not be a substitute for native tissue within the disc space but if adjacent to a disc prosthesis may impart some degree of intersegmental stability during acute loading activities. © 2013 Elsevier Ltd.


PubMed | Excelen Center for Bone and Joint Research, Midwest Spine Institute and Pinnacle Orthopaedics
Type: Comparative Study | Journal: Journal of neurosurgery. Spine | Year: 2016

This study was undertaken to quantify the in vitro range of motion (ROM) of oblique as compared with anterior lumbar interbody devices, pullout resistance, and subsidence in fatigue.Anterior and oblique cages with integrated plate fixation (IPF) were tested using lumbar motion segments. Flexibility tests were conducted on the intact segments, cage, cage + IPF, and cage + IPF + pedicle screws (6 anterior, 7 oblique). Pullout tests were then performed on the cage + IPF. Fatigue testing was conducted on the cage + IPF specimens for 30,000 cycles.No ROM differences were observed in any test group between anterior and oblique cage constructs. The greatest reduction in ROM was with supplemental pedicle screw fixation. Peak pullout forces were 637 192 N and 651 127 N for the anterior and oblique implants, respectively. The median cage subsidence was 0.8 mm and 1.4 mm for the anterior and oblique cages, respectively.Anterior and oblique cages similarly reduced ROM in flexibility testing, and the integrated fixation prevented device displacement. Subsidence was minimal during fatigue testing, most of which occurred in the first 2500 cycles.

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