Proksimal afdød Lårben Forberedelse til brudstyrken Test og Quantitative CT-baserede Finite Element Analysis
Summary
Vi præsenterer en robust protokol om, hvordan man omhyggeligt bevare og forberede Nekro lår for fraktur test og kvantitativ computertomografi billeddannelse. Fremgangsmåden tilvejebringer præcis kontrol over input betingelser med henblik på at bestemme forholdet mellem knoglemineraltæthed, brudstyrken, og definere finite element model geometri og egenskaber.
Abstract
Nekro fraktur test anvendes rutinemæssigt til at forstå faktorer, der påvirker proximal femur styrke. Fordi ex vivo biologisk væv er tilbøjelige til at miste deres mekaniske egenskaber over tid, modellen skal udføres forberedelse til eksperimentelle test omhyggeligt for at opnå pålidelige resultater, der repræsenterer in vivo betingelser. Derfor har vi designet en protokol og et sæt inventar til at forberede de femorale prøver således, at deres mekaniske egenskaber oplevet minimale ændringer. Femora blev holdt i frossen tilstand, undtagen ved tilberedningen trin og mekanisk prøvning. De relevante kliniske foranstaltninger af total hofte og lårbenshals knoglemineraltæthed (BMD) blev opnået med et klinisk dobbelt røntgenabsorptiometri (DXA) knogle densitometer, og 3D-geometri og distribution af knoglemineral blev opnået ved anvendelse CT med en kalibrering fantom for kvantitative skøn baseret på gråtone værdier. Enhver mulig knoglesygdom, frakturEller tilstedeværelsen af implantater eller artefakter påvirker knoglestruktur, blev udelukket med X-ray scanninger. For forberedelse blev alle knogler omhyggeligt renset for overskydende blødt væv, og blev skåret og potteplanter på det interne rotation vinkel af interesse. En skærende fikstur tillod den distale ende af knoglen, der skal afskæres forlader den proximale femur ved en ønsket længde. For at tillade positionering af lårbenshalsen på foreskrevne vinkler under senere CT scanning og mekanisk prøvning, blev de proximale femorale aksler pottet i polymethylmethacrylat (PMMA) med en armatur designet specielt til de ønskede orienteringer. De indsamlede fra vores eksperimenter data blev derefter anvendt til validering af kvantitativ computertomografi (QCT) -baseret finite element analyse (FEA), som beskrevet i en anden protokol. I dette manuskript, præsenterer vi protokol for den præcise forberedelse knogle til mekanisk afprøvning og efterfølgende QCT / FEA modellering. Den nuværende protokol blev anvendt med succes til at forberede omkring 200 cadaveric lårben over en 6-års periode.
Introduction
Determining the true cadaveric proximal femoral fracture strength with mechanical testing is a destructive method that requires a rigorous testing approach for accurate measurements. In particular, proper bone preparation methods are necessary to maintain near in vivo integrity of the bones prior to mechanical fracture testing1. This is achieved by proper bone storage and minimizing handling at room temperature. This test data is extensively used to validate QCT/FEA models of femoral fracture which have the potential to be used clinically to understand the fracture risk, especially in osteoporotic patients. Unfortunately, there is no current standard procedure to prepare proximal femur samples for mechanical testing. A good testing procedure should ensure repeatability and reproducibility of the preparation process. Therefore, fixtures required for sample preparation need to be carefully designed and fabricated to minimize the likelihood of various testing errors. We also need to minimize the preparation time for which bone tissue is at room temperature and thus in danger of degradation with irreversible changes in mechanical properties.
To this end, we have developed a procedure that preserves bone tissue across multiple preparation steps. This is important to ensure minimal exposure time at room temperature while also minimizing the number of freeze/thaw cycles which can affect tissue physical properties2. The entire procedure is long and nontrivial as the steps occurred over multiple weeks and required scheduling for scanning procedures and personnel availability. The steps included thawing bone samples, screening the samples using DXA scanning to obtain bone mineral density (BMD) values, X-ray to rule out any diseased specimens, and finally CT scanning to estimate distribution of bone mineral and femoral geometry. All the specimens were prepared for testing by removing extraneous soft tissues from the bone surface, cutting the femur to a length required for testing, and potting the femur in a desired orientation for simulating a sideways fall on the hip during subsequent testing. It is essential to keep the time period for all these operations as short as possible. A robust protocol is thus mandatory for consistent specimen preparation, tissue preservation between steps, and for reducing the overall preparation time.
The aim of this paper is to present in detail the procedures involved in the preparation of femoral samples for subsequent mechanical testing under various conditions. Preservation of the bone tissue is crucial in this process and we achieved it by keeping specimens frozen between steps and keeping them carefully wrapped in saline saturated towels at all times except when scanning and mechanically testing the bones. Femora were also kept wrapped in saline wet towels during the steps involving PMMA curing to prevent dryness of the bone tissue.
Protocol
Representative Results
Discussion
Vi præsenteret en robust knogle forberedelse protokol for at sikre mekanisk afprøvning og QCT / FEA modellering af femoral styrke i en sidelæns fald på hoften konfiguration. Denne metode blev vores standard in-house-protokol. I løbet af 6 år, med varierende personale, omkring 200 lårben lykkedes udarbejdet efter denne protokol. Resultaterne af protokollen omfatter klassificere knogle betingelser ved hjælp af DXA, udelukke metastatiske sygdomme, tidligere frakturer, eller implantater ved hjælp af røntgen, og f?…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
Vi vil gerne takke Materialer og strukturel test Core Facility ved Mayo Clinic til teknisk support. Desuden vil vi gerne takke Lawrence J. Berglund, Brant Newman, Jorn op den Buijs, Ph.D., for deres hjælp i løbet af undersøgelsen. Denne undersøgelse blev støttet af Grainger Fornyelsesfonden fra Grainger Foundation.
Materials
| CT potting container and scanning fixture | Internally manufactured | N/A | Custom designed and manufactured |
| CT scanner | Siemens | Somatom Definition scanner (Siemens, Malvern, PA) | CT scanning equipment |
| Quantitative CT Phantom | Midways Inc, San Francisco, CA | Model 3 CT calibration Phantom | Used for obtaining BMD values from Hounsfield units in the CT image |
| Dual Energy X-ray Absorptiometry scanner | General Electric | N/A | GE Lunar iDXA scanner for bone health or any similar BMD scanners |
| Hygenic Orhodontic Resin (PMMA) | Patterson Dental Supply | H02252 | Controlled substance and can be purchased with proper approval |
| Freezer | Kenmore | N/A | This is a -20oC storage for bones |
| X-ray scanner | General Electric | 46-270615P1 | X-ray imaging equipment. |
| X-ray films | Kodak | N/A | Used to display x-ray images |
| X-ray developer | Kodak X-Omatic | M35A X-OMAT | Used for developing X-ray images |
| X-ray Cassette | Kodak X-Omatic | N/A | Used for holding x-ray films |
| 5-pound Rice Bags | Great Value | N/A | Used for mimicking soft tissue during the DXA scanning process |
| Physiologic Saline (0.9% Sodium Chloride) | Baxter | NDC 0338-0048-04 | Used for keeping samples hydrated |
| Scalpels and scrapers | Bard-Parker | N/A | Used to clean the bone from soft tissue |
| Cast cutter | Stryker | 810-BD001 | Used to cut femoral shaft |
| Drilling machine | Bosch | N/A | Used to drill the femoral shaft |
| Fume Hood | Hamilton | 70532 | Used for ventilation when using making PMMA |
Riferimenti
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