Fig. 2.10.2a-e. Different approaches - as theoretically shown in the drawings Figure 2.10.1a-d - during the intervention. a Transpedicular, b intercostovertebral, c posterolateral, and d anterolateral access routes. Needle tip should be positioned in the anterior third of the vertebral body, close to the midline. e This parasagittal image shows a good positioning of the needle in the middle of the vertebra
b d e b a c d e al. 1998; Deramond et al. 1997; Galibert et al. 1987) it has been shown that the positioning of the needle in the anterior third of the vertebral body close to the midline enables sufficient filling of the central portion of the vertebral body and therefore there is no need for a contralateral access (Fig. 2.10.2e) (Kim et al. 2002). To our knowledge, there are no studies on comparison of performance among needle types that might guide selection. The selection of the needle depends only on the operator. Due to the large choice of needle length and diameters, shapes of needle and mandrin and the possibility of connecting syringes or pressure syringes to the needle, every operator has to choose one manufacturer which pleases his or her requirements best. We recommend not using too many different systems because mistakes occur, most often due to unfamiliarity in handling a new system. Important attributes include the shape of the tip of the mandrin and the cannula, as well as the type of handle. While many needle cannulas have a square distal shape, some cannulas available have a beveled distal end (for example Cook, Optimed) that allows one to direct cement in a given direction. Furthermore, 10-cm-long needles can be used in most patients but 15-cm-long needles are utilized when treating lower lumbar vertebral bodies or corpulent patients. In addition, an advantage in using needles with larger diameters (e.g., 10 gauge) is that the cement can be much more viscous during injection and can therefore be administered for longer compared to needles with a smaller diameter (e.g. 15 gauge). However, in the cervical spine a needle with a smaller diameter should be favored. After optimal positioning of the needle, the stylet has to be removed from the needle and the cement can be prepared according to the manufacturer's instructions. Most manufacturers recommend a closed mixing system providing a homogenous mixing, to avoid cement contamination and inclusion of air bubbles in cement, which can reduce its strength (Mathis and Wong 2003). During the first 30-60 s, the cement has a fluid-like consistency (Gangi et al. 2006). After 60 s the PMMA becomes more like tooth-paste. During the tooth-paste-like polymerization phase the cement is injected to reduce the risk of extravasation into the surrounding tissue or venous plexus. The administration of the cement should be performed using a pressure syringe from a dedicated injection set (Optimed; Allegiance; Cook; Stryker) or several small (1-2 ml) Luer lock syringes. The injection sets allow aspiration of a larger amount of cement (up to 10 ml) and direct injection of cement in a continu ous flow, with minimal effort. Although the use of the injection sets increases the expense of the procedure, it is safer than free-hand injection. The injection of the cement has to be carefully controlled either under lateral and ap fluoroscopy or CT fluoroscopy to avoid cement leakage harming the patient. Special care has to be taken if the cement starts to leak out into the peridural space, since this can cause severe neurological deficits. The risk of cement leakage is particularly high at the beginning of cement injection. The operator should be very careful during the injection of the first amount of cement. The administration of the PMMA has to be stopped immediately if the mixture starts to leak out from the vertebral body into the surrounding tissue, especially into the discal space. However, waiting for 30-60 s can often resolve this problem because the cement hardens and seals the leak. If the leak persists, needle position and bevel direction should be changed. If cement is still pouring into the surrounding structures, the injection has to be stopped and the needle removed. However, if the vertebroplasty cannot be completed due to an uncorrectable leakage of the cement, the ver-tebroplasty could be immediately repeated using the contralateral pedicle as the access path for complete filling of the vertebral body. The cement injection can be stopped when the anterior two-thirds of the vertebral body are filled and the cement is homogenously distributed between both endplates (Fig. 2.10.3). The mandrin of the needle has to be replaced under fluoroscopic control to rule out any unwanted cement distribution along the access pathway before the cement begins to set and the needle is then carefully removed (Gangi et al. 2006). The effective working time after mixing the PMMA at room temperature is approximately 8-10 min before it starts to harden (Gangi et al. 2006). However, some new cements have longer setting times and the setting time can be prolonged if the cement is cooled before mixing (Chavali et al. 2003). The volume of the cement needed for a good result regarding stiffness and reduction of complaints by the patients has never been systematically studied. However, the risk of extraosseous extravasation increases in good correlation with an increasing amount of cement administered. To reduce these risks, we tend to give only a relatively small amount of cement. In patients with osteoporosis or heman-giomas, 2.5-4 ml of cement provides good filling of the vertebra and achieves both consolidation and pain relief. In metastatic disease, where the aim of vertebroplasty is relief of excruciating pain, smaller volumes (1.5-2.5 ml) are usually sufficient.
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