Titanium as a Biomaterial
Titanium (Ti, anatomic number 22) was a laboratory rarity until William Kroll (1889-1973) developed a process for commercial production of titanium alloys by combining titanium tetrachloride with calcium to produce ductile titanium (the "Kroll Process"). Titanium is the fourth most abundant structural metal on Earth. Today, it is widely used in medical devices, dental applications, and surgical implants due to its superior biological performance. About as strong as steel, titanium is 50% lighter. Its high strength-to-weight and stiffness-to-weight ratios, outstanding corrosion resistance, and other highly desirable attributes have been made this material attractive as biomaterial. It is physiologically hypoallergenic and immune to corrosion, especially microbiologically influenced corrosion. In biological tissue titanium is inert: the oxide layer that is in contact with the tissue is hardly soluble and in particular no ions are released that could react with other molecules ,
Titanium has an extremely low toxicity and is well tolerated by both bone and soft tissue. Animal experiments have revealed that the material may be implanted for an extensive length of time; fibrous encapsulation of the implants is minimal to nonexistent. Histopathological examinations have revealed no cellular changes adjacent to titanium implants.
The mechanical properties of titanium compare favorably with those of surgical-quality stainless steel. The low modulus results in a material that is less rigid and deforms elasti-cally under applied loads.
Titanium is virtually nonmagnetic, making it ideal for applications where electromagnetic interference must be minimized. Titanium, as a nonferromagnetic material, does not interfere with MRI or CT ; thus, postoperative imaging examinations with respect to necessary tumor follow-up are possible.
The titanium vocal medialization implant (TVFMI; Fig. 9.4.1) has been introduced recently by Friedrich  in cooperation with Kurz Medical, Inc. (Germany) for external medialization of a unilaterally paralyzed vocal fold. Three sizes are commercially available (Kurz Medical, Inc.).The large implant normally used in men measures 6x15 mm; the next smaller one, normally used in women, 6x13 mm. For external medialization in very small larynges, a third size of 4.5x11 mm is available. Except for a bending pliers and a marking stamp, as shown in Fig. 9.4.2, no special instruments are necessary to perform the thyroplasty.
Preoperative sedation (e.g., midazolam hydrochloride), single-dose intravenous cortisone (about 250 mg prednisolone hemisuccinate natrium), and a prophylactic single-dose broad-spectrum antibiotic are recommended 30 min preoperatively.
Local anesthesia supplemented by intravenous sedation is recommended for this procedure. This allows an optimum positioning of the implant under audiophonatory control. In addition, the use of a respiratory tube would interfere with the vocal fold medialization.
The patient should be monitored intraop-eratively by the anesthesiologist. A continuous intraoperative propofol infusion is recommended.
The technique used for medialization of the vocal folds has been previously reported by Friedrich .
After infiltration with lidocaine hydrochloride 1% (plus epinephrine hydrogen tartrate 1:200,000), a horizontal skin incision of about 3 cm is made at the level of the mid-thyroid ala of the appropriate side. The thyroid cartilage is exposed with the perichondrium preserved from the midline laterally. The overlying strap muscles are cut using the electrocautery. A reference line is drawn parallel to the inferior thyroid margin, beginning from the anterior midline at the midpoint between the superior and inferior thyroid notches. This line corresponds to the free edges of the vocal folds endolaryn-geally. With a preformed silicone template the cartilage window should be marked caudal to the reference line and near the oblique line of the thyroid ala.
For the 13 mm implant the window size is 6x11 mm, for the 15 mm one 6x13 mm, and for the small size 4.5x9 mm. The cartilage and osteoid material are drilled out with a steel drill until the inner perichondrium becomes visible. For irrigation, local anesthesia solution as described above is recommended. The edges and corners of the window can be smoothed using a small diamond burr. The inner perichondrium is incised along the window's rim with a Colorado needle or a low-energy electrocautery. It is very important not to enter the paraglottic space or to cut the endolaryngeal vessels during dissection of the perichondrium.
After careful mobilization of the endolaryngeal tissue the TVFMI can be placed in the sub-perichondrial pocket (Fig. 9.4.3). The anterior (ventral) flange is inserted first. The implant has to be positioned under slight tension through the cartilage into the larynx, because the implant is 2 mm larger than the window. Under audiophonatory control, the optimum medial-
ization depth of the dorsal flange is determined and the position is marked. The dorsal flange is bent at the marked point with the bending pliers. The TVFMI is re-seated precisely and fixed with monofil nonabsorbable sutures (one to fix the ventral flange and two to fix the dorsal one).
After reanastomosis of the strap muscles, a drain is placed, which can be removed after approximately 2 days.
Five years of clinical experience with the TVFMI have yielded excellent and stable functional results and satisfying improvements of phonation and swallowing without any fixation or migration problem of the implant . Primary goals of this technique are to improve phonation, vocal efficacy and force of cough, and to decrease subjective dysphagia and aspiration without a negative influence on the glottal resistance. The type, completeness, and duration of glottal closure are important for the vocal outcome, airway control, and the airway protection during swallowing. After thyroplasty, patients regularly demonstrate improved glottal closure. Maximum medialization is possible with the TVFMI, especially in subjects with a large posterior gap and vocal fold bowing, by adjusting the length of the posterior flange.
The anamnestic, perceptual, videostrobo-scopic, acoustic, videocinematographic, and aerodynamic data investigated underline the clinical benefit after external medialization thyroplasty with the TVFMI [4,5,7]. As for the swallowing function, a convincing improvement of the degree of aspiration and subjective dysphagia in most patients can be observed. Comprehensive aerodynamic measurements have not revealed any increase in extrathoracic obstruction after thyroplastysurgery ,
The customized design ensures safe implant placement and reduces the operation time significantly. This is, on the one hand, convenient for both the patient and the surgeon, and on the other hand, important for achieving optimal results because of reduced intralaryngeal swelling and hematoma. While other implant techniques presume very experienced and specialized surgical skills, the TVFMI is simple to handle even for less experienced surgeons and allows precise and atraumatic vocal fold medialization. It eliminates free-hand shaping of a suitable implant, and permits the use of a commercially available template to outline the thyroplasty window, which simplifies the surgery and shortens the operating time.
Under phonatory control, an exact positioning of the implant is possible intraoperatively and optimum medialization with the TVFMI can be achieved.
Implant materials have occasionally been reported to migrate or shift. Migration of the TVFMI can be largely eliminated by fixation with nonabsorbable thread.
In patients with a very lateral position of the paralyzed vocal fold, a combination of medialization thyroplasty with approximation of the cricoid and thyroid cartilages, or with endoscopic fat augmentation, is possible.
Our experiences showed no major intraoperative complications. In only less than 1% of pa tients, a repositioning of the implant was necessary after flexible endoscopic laryngoscopy because of respiratory deficits reported by the patient resulting from "over"-correction of the vocal fold position.
Postoperatively, major complications after medialization thyroplasty (e.g., tracheostomy) did not occur in any patients treated. About 25% of the patients developed mild local hematoma for some days without any negative permanent effect on the vocal outcome.
In very rare cases (two women in our own patient group) the implant had to be removed because of tissue atrophy and granulation tissue neoformation in the anterior third of the vocal fold. It is very important to consider the thickness of the thyroid cartilage and to adapt if necessary the length of the anterior flange of the implant to the cartilage. The anterior flange should fit exactly to the cartilage and should not be placed too loosely.
To complement the TVFMI, another implant device has been introduced. In 1993 Desrosiers et al. reported preliminary experiences using a standard double-titanium-vanadium miniplate and screws (LUHR Minifixation System) in two fresh cadaver laryngés. With this system, a cartilage window can be moved horizontally, and pressure can be transmitted directly to the underlying vocal fold.
Eight years later, Dean and coworkers  reported the use of an adjustable laryngeal implant which has three distinct parts: the titanium plate; a micrometric screw; and an adjustable titanium block. The plate allows fixation of the implant to the thyroid cartilage. It is contiguous with an adjustable titanium block which can be medialized by means of a micro-metric screw. The implant is available in differ ent sizes: the block in 4- and 6-mm thicknesses, and the degree of angulation in the adjustable part in o, 1, 2, and 3 mm. Although the authors gathered satisfactory postoperative results with regard to voice and swallowing improvements, a relatively high number of complications (five airway problems, one death, two malpositions of the implant, and six inadequate medializa-tions in 53 patients) are noteworthy. We are not able to report personal experience with the adjustable laryngeal implant.
1. Dean CM, Ahmarani C, Bettez M, Heuer RJ (2001) The adjustable laryngeal implant. J Voice 15:141150
2. Desrosiers M, Ahmarani C, Bettez M (1993) Pre-cice vocal cord medialization using an adjustable laryngeal implant: apreliminarystudy. Otolaryngol Head Neck Surg 109:1014-1019
3. Friedrich G (1999) Titanium vocal fold medializ-ing implant: introducing a novel implant system for external vocal fold medialization. Ann Otol Rhinol Laryngol 108:79-86
4. Schneider B, Denk DM, Bigenzahn W (2003a) Functional results after external vocal fold medialization thyroplasty with the Titanium vocal fold medialization implant. Laryngoscope 113:628-634
5. Schneider B, Bigenzahn W, End A, Denk DM, Klepetko W (2003b) External vocal fold medialization in patients with recurrent nerve paralysis following cardiothoracic surgery. Eur J Cardio-thorac Surg 23:477-483
6. Schneider B, Kneussl M, Denk DM, Bigenzahn W (2003c) Aerodynamic measurements in medialization thyroplasty. Acta Otolaryngol 123:883-888
7. Schneider B, Denk DM, Bigenzahn W (2003d) Acoustic assessment of voice quality prior to and after medialization thyroplasty using the Titanium vocal fold medialization implant (TVFMI). Otolaryngol Head Neck Surg 128:815-822
8. Suzuki R, Frangos JA (2000) Inhibition of inflammatory species by titanium surfaces. Clin Orthop 372:280-289
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