Implantation Standards

Several tools should be checked before the procedure, such as mechanical polypropylene sheaths, stylets, snares (catcher, lassos), and transfemoral workstation. Also, standard implantation equipment can be necessary (introducer sheaths, guide wires, stylets). Please refer to the dedicated chapter of this book for a more complete and exhaustive discussion about these items. 

The most mechanically stable implant is a locked, reamed intra-medullary nail. This is the standard implant utilised in adults. The presence of cross bolts effectively removes any rotational instability. The use of such techniques in children has been controversial, since there have been reports of avascular necrosis (AVN) of the femoral head (Beaty et al. 1994). This has been attributed to damage to the middle circumflex vessels as the nail is introduced into the piriform... 

Davis, J. J., J. V. Bono, and B. G. Lindeque. 2010. Surgical strategies to achieve a custom-fit TKA with standard implant technique. Orthopedics 33(8) 569-576. 

PVDE is a nontoxic resin and may be safely used in articles intended for repeated contact with food (190). Based on studies under controked conditions, including acute oral, systemic, subchronic, and subacute contact implantation and tissue culture tests, no adverse toxicological or biological response has been found in test animals (191,192). PVDE is acceptable for use in processing and storage areas in contact with meat or poultry products prepared under federal inspection and it complies with the 3-A sanitary standards for dairy equipment. 

Nonferrous Metals-, Electrodeposition Coatings-, Metal Powders-, Surgical Implants, Part 7, 1972 Annual Book ofASTM Standards, American Society for Testing Materials, Philadelphia, Pa., 1972. 

The American Society for Testing and Materials (ASTM) F4 Committee on Medical Materials and Devices has developed specifications for chemical composition, mechanical properties, and other factors. Standard test methods also are available from ASTM, 1916 Race Street, Philadelphia. The quaHty of castings is important for dental implants, and standards to define this would be useful. 

Ion implantation is often used to produce reliable standards for quantification of SIMS analyses. Ion implantation allows the introducdon of a known amount of an element into a solid sample. A sample with a major component composition similar to that of the unknown sample may be implanted to produce an accurate standard. The accuracy of quandfication using this implantation method can be as good as 2%. 

Production of homogeneous solid-state standards is costly. Dynamic SIMS has the advantage that non-homogeneous ion implantation standards can also be used. Knowing the implantation dose of element (el), its RSF can be calculated by use of the integrated (summed) intensities of a depth profile according to Eq. (3.15) ... 

The accuracy in RBS results is -3% for areal densities and better than 1% for stoichiometric ratios. This high accuracy is obtained only when all relevant quantities are measured or evaluated carefully. Pitfalls which often prevent RBS from achieving its full accuracy are described elsewhere [3.129]. Calibration can be achieved by measuring standards obtained by either implanting into or depositing on a light element (silicon) a known amount of a much heavier element (e.g. Ta or Sb). 

The materials which are currently specified in the National and International Standards for use as implants together with their eissociated mechanical properties are shown in Table 2.23. 

Material Type and condition Typical standard for implant application Ultimate tensile strength M Pa min 0.2% tensile yield stress M Pa Young s modulus X lO M Pa Elongation at fracture % min Compressive strength M Pa Vickers hardness Fatigue strength (10 cycles) M Pa... 

Intercrystalline corrosion was a serious problem with the austenitic stainless steels early in their development since carbon contents then were relatively high, e.g. En58J contained up to 0.12type stainless steel contained up to 0.08 Vo C. The problem in relation to surgical implants has been reported by Scales eta/. and as a result of this and several other reports the British, American and International Standards specified the use of a 316S12 type austenitic stainless steel which contains 0.03 Vo C max. The use of the lower carbon content stainless steels as specified in the various standards has now eliminated the problem of sensitisation of implants. If manufacturers do use the 0.08% C versions they have to be very careful with the forging temperatures or anneal the prostheses afterwards. 

British Standards Institution Surgical Implants, Specification Numbers BS7251 to BS 7254, London (1990-93)... 

The difference in rates of release of BCNU from wafers produced by the trituration or solution methods is also seen in vivo (11,14), as is shown in Fig. 6. Wafers of PCPP-SA 20 80 were prepared by either the solution or trituration methods, as described above, and were implanted into the brains of rabbits. The animals were sacrificed at various times after implantation and the brains were removed, fixed, and processed for quantitative autoradiography. To quantitate the percentage of the brain exposed to BCNU released from these wafers, the following calculation was performed. The percentage of the brain in which the radioactivity from the tritiated BCNU released from the wafers exceeded the background counts by at least two standard deviation units was plotted as a function of time following implantation in Fig. 6. A control set of rabbits had a solution of BCNU injected directly into the same location in the... 

Electrochemical techniques in vivo use the standard three electrode voltammetric system described earlier with the electrodes implanted in the brain of the animal subject. Measurements are made by acquiring some stable baseline signal and then stimulating release of the biogenic amine neurotransmitters. The change in signal is then a measure of the concentration of neurotransmitter in the extracellular fluid. 

An ion-implanted standard and the MBE sample were depth profiled under the same conditions, and the secondary ions were analysed in a quadrupole mass spectrometer. The data from the ion-implanted standard was used to find the useful ion yield and thus the instrumental sensitivity for boron-in-silicon in the MBE sample. The quantified data appear in Figure 4.9. 

The properties of a pH electrode are characterized by parameters like linear response slope, response time, sensitivity, selectivity, reproducibility/accuracy, stability and biocompatibility. Most of these properties are related to each other, and an optimization process of sensor properties often leads to a compromised result. For the development of pH sensors for in-vivo measurements or implantable applications, both reproducibility and biocompatibility are crucial. Recommendations about using ion-selective electrodes for blood electrolyte analysis have been made by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) [37], IUPAC working party on pH has published IUPAC s recommendations on the definition, standards, and procedures... 

This brings us to the subject of standards. In this connection a standard is simply a sample with a known hydrogen content that is used for convenience to calibrate the overall counting efficiency of a particular setup, i.e., to determine the factor AfICalibration standards must be stable under irradiation. While plastic foils of known composition can be used if precautions are taken (Rudolph et al., 1986), their intrinsic instability makes them unsuitable. The standard used by most groups is hydrogen-implanted silicon, which has the advantages that it is easily prepared, the implanted dose can be measured to 5%, and the amount of implanted hydrogen is stable at room temperature and under MeV 15N irradiation, as discussed later. 

There is some disagreement in the literature as to the value of the (4He, H) elastic scattering cross section. Values differing by almost a factor of two have been reported, as reviewed by Paszti et al. (1986). The cross section is strongly non-Rutherford, but ab initio calculations have been reported that agree well with the trend of experimental data and could be used in simulation calculations (Tirira et al., 1990). The cross section for deuterium analysis has a resonance near a 4He+ energy of 2.15 MeV, which allows enhanced sensitivity. Detailed measurements of this cross section have been reported by Besenbacher et al. (1986). In practice, rather than calculate an experiment s calibration from first principles, calibration standards are usually used hydrogen-implanted silicon standard are the norm. 

The conclusion to be drawn from these studies as far as the suitability of different ion-implanted hydrogen standards is concerned is that pre-amorphized silicon is the best target material, though crystalline silicon is an acceptable alternative if room temperature is never exceeded. 

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