Cochlear implant fixation using resorbable mesh.
Surgical techniques in cochlear implantation are constantly being improved and refined. For a successful outcome in this surgery, prevention of receiver migration, which might induce fatigue and shearing of the electrodes or might interfere with the longevity of the implant, is crucial. Early experience with cochlear implantation indicated approximately a 12% incidence of complications; of the total complications, 4% were attributed to receiver-stimulator migration, resulting in an overall incidence of 0.2% in adults and 0.13% in children. (1) More recent data indicate that the incidence of migration of the receiver stimulator is approximately 0.05% in children and 0.26% in adults, (2) and up to 5.6% incidence of migration of either the electrode or receiver stimulator. (3)
Various techniques to secure the receiver implant and prevent device migration have been described. As a standard method, most surgeons place the internal receiver into a bony well drilled in the temporal bone, deep enough to accommodate the receiver package and to prevent a high profile above the skull. The implant is then secured with nonabsorbable sutures passed through holes drilled in the bone surrounding the well. While this standard technique has been successfully used on thousands of cochlear implant patients, there are several potential disadvantages. First, drilling the well and the suture-anchoring holes in thin-skulled pediatric patients can result in dural injury with cerebrospinal fluid (CSF) leak and potential serious complications. (4) Second, this technique tends to be time consuming even in experienced hands, taking up to 30 minutes?
Several alternative methods have been described for fixation of the receiver stimulator. Some surgeons do not provide any fixation, including the mini-incision technique and revision cochlear implantation. (6,7) With this approach, fixation depends on the adequacy of the bony well, the creation of a tight pocket for the implanted device, and tight closure of the periosteal layer.
Other techniques have been described that use materials such as expanded polytetrafluoroethylene, polypropylene mesh, and suture wrapped around titanium screws, (5,8,9) These methods have been shown to be effective and safe for securing the cochlear implant receiver stimulator. However, all of these techniques use nonabsorbable material. As a general principle of surgery, the potential for foreign body reaction, infection, and extrusion increases with material that is nonabsorbable.
Herein we share our experience with resorbable poly (D,L) lactic acid (PDLLA) mesh fixed with ultrasound-activated pins to secure the cochlear implant receivers to the temporoparietal skull. PDLLA has an extensive history of use in maxillofacial reconstruction in trauma cases, as well as in skull reconstruction in cases with craniosynostosis. (10-12) This is the first report in which PDLLA is used for receiver package fixation in cochlear implant surgery.
Patients and methods
Between February 2008 and October 2008, 14 patients (4 adults, 10 children) underwent cochlear implantation using PDLLA mesh (Resorb-X; KLS Martin USA; Jacksonville, Fla.) fixed with ultrasound-activated pins (SonicWeld system; KLS Martin USA) to secure the receiver stimulator. This technique was used with devices from all the major cochlear implant manufacturers: Cochlear Ltd. (Sydney, Australia); Advanced Bionics, LLC (Valencia, California); and MED-EL Corporation (Innsbruck, Austria) (table).
The cochlear implant surgery was performed by the same surgeon (L.L.) in a standard fashion, as follows. Following a standard lazy-8 incision, flap elevation, cortical mastoidectomy, and facial recess approach to gain access to the round window, the bony recess for the receiver stimulator package is created. A channel is drilled between the recessed well and the mastoid cavity to accommodate the electrode and its fantail. The receiver is then seated in its bony well and covered with the preformed, 0.3-mm-thick, resorbable PDLLA mesh.
The mesh is preformed to conform exactly to the internal receiver of each type of cochlear implant (figure).
As an alternative, a full sheet of mesh (51.2 x 51.2 x 0.3 mm) can be used to cover the surface of the receiver. However, to gain adequate fit and contour over the receiver stimulator and skull, the sheet must be heated in a water bath of 135 to 150 [degrees]F for 8 to 10 seconds to increase pliability. The mesh that is preformed specifically for the type of cochlear implant receiver stimulator does not require heating in a water bath and is much simpler to use.
Next, pilot holes are drilled with a low-speed drill utilizing a 1.6-mm diameter drill bit that creates a funnel-shaped hole that is smaller than the resorbable pins (2.1 mm in diameter and 4 mm long). The pins are placed into the openings of the pilot holes, and then they are liquefied by the ultrasonic-frequency vibration of an ultrasonic welder. As the pins are liquefied, filling the pilot holes, the tip of the ultrasonic welder also engages the mesh, thereby fusing the pin and the mesh at that site. Typically, 3 or 4 pins and sites of fixation secure the resorbable PDLLA mesh over the receiver stimulator to the skull. After electrode insertion into the cochlea, a Penrose drain is placed beneath the skin flap, exiting through the skin incision, which is closed in a routine fashion.
Of the 14 patients who underwent cochlear implantation with resorbable PDLLA mesh, the youngest was 3 years of age and the oldest was 82 years of age, with a mean age of 26.9 years. Postoperative follow-up varied from 14 to 21 months, with an average of 17.2 months. The patients had no operative or postoperative complications, including infections, device failures, device migrations or extrusions, CSF leaks, or epidural hematomas.
The use of resorbable PDLLA mesh was technically simpler and more rapidly performed than the standard suturing technique. The placement and securing of the preformed, resorbable PDLLA mesh takes 5 minutes or less. To date, we have not encountered biocompatibility problems or allergic reactions with resorbable PDLLA mesh.
Cochlear implants could have a significant impact on the rehabilitation of the estimated population of 500,000 severe to profoundly hearing impaired people in United States. Safe and effective surgical techniques in this field are constantly being developed and refined. Ultrasound-activated, pinned resorbable PDLLA mesh is one such model of securing the internal receiver in order to prevent device migration, which is associated with fatigue and shearing of the electrodes, curtailing the longevity of the implant.
The form of resorbable PDLLA used in the present study was first introduced to the U.S. market in March 2002. It previously underwent trials in Europe after being studied in animal models. (13,14) Resorbable PDLLA was first used clinically in maxillofacial surgery and then in craniosynostosis surgery in pediatric patients. (10-12) No allergic reactions with resorbable PDLLA have been reported. These clinical experiences, as well as animal studies, (15,18) have shown that resorbable PDLLA is biocompatible, durable, and effectively applicable.
PDLLA uses both stereoisomers D and L in a blended form that is totally amorphous, initially facilitating degradation by hydrolysis. (13) Degradation of resorbable PDLLA partially depends on the volume and thickness of the PDLLA used. Rasse et al used 2-mm-thick PDLLA plates in repairing condylar neck fractures in sheep. (17) They found no evidence of resorption at 8 weeks, and by 6 months found only microscopic degradation particles. By 12 months, there was only one histologic section in one animal that had 0.06-mm foreign bodies. In all other sections and animals, no histologic evidence of PDLLA was found, and bone, muscle, and connective tissue were normal.
Heidemann et al implanted 20 x 3 x 2-mm rods in rats, allowing predegradation for 14 days (to eliminate the period of histologic neutrality), and by 28 weeks, histologically found complete resorption. (18) Clinically, Eckelt et al used PDLLA mesh and plates (1.0 mm thick) fixed with pins (2.1 mm in diameter) in 8 infants for repair of craniosynostosis. (11) One patient underwent repeat surgery for bone graft instability. The other 7 were followed clinically. Minor swelling was noted at 1 week, had resolved by 4 weeks, and had healed normally at follow-up 3, 6, and 12 months postoperatively.
A similar form of resorbable polylactic acid polymer is also widely used in craniofacial and maxillofacial surgery. It is a combination of poly L lactic acid (PLLA) and poly glycolic acid (PGA), consisting of 82% PLLA and 18% PGA (LactoSorb; Biomet Microfixation; Jacksonville, Fla.). This system also incorporates resorbable mesh (0.5 mm thick) secured by screws and/or push pins. To date, there is no customized, preformed resorbable PLLA/PGA mesh available for cochlear implant internal receivers; therefore, there has been no clinical experience with this system.
One limitation of our study is the lack of long-term follow-up, but short-term results have been encouraging. Also, long-term results with both PDLLA and PLLA in craniofacial and maxillofacial surgery have been positive. However, resorbable PDLLA mesh has not been used to date in infants.
While no biocompatibility issues are anticipated, use of this mesh requires pilot holes to be drilled. Pilot holes for suture, titanium screws, or resorbable PDLLA all have the same limitation, i.e., skull thickness. The thickness of the skull is quite variable, according to location and age. In the area posterosuperior to the auricle, where the receiver stimulator is typically placed, Wong and Haynes found the thickness to vary from 1.8 mm [+ or -] 1.1 mm (in patients <12 months of age) to 2.6 mm [+ or -] 1.0 mm in those 13 to 30 months of age. (19) Simms and Neely found this area to have an average thickness of 3 mm by 6 months of age and >4 mm by 3 years of age. (20) Garfin et al computed the average bone thickness in the temporal fossa to be 3.0 mm [+ or -] 0.3 mm in children 1 to 2 years of age and 3.6 mm [+ or -] 0.2 mm in those 2 to 5 years of age. (21)
Davis et al reported no problems related to screw length in children as young as 14 months using 4 mm, self-tapping screws to secure polypropylene mesh, but did not "hub down" the screws. (8) Lee and Driver used 1.6 x 4.0-mm self-tapping screws for suture fixation in infants as young as 9 months of age and reported no problems related to skull thickness. (22) Nevertheless, all authors stress the variability of skull thickness. The cochlear implant surgeon should have a good idea of skull thickness after creating the recess for the receiver stimulator and should determine the depth of the pilot holes for pin placement accordingly.
Regardless of the technique used to fix the device or drill the holes, the potential risk of CSF fistula exists, especially in children. The technique for securing PDLLA mesh with pilot holes and resorbable pins is not substantially different from other standard techniques, (5,8,9) and therefore it would not be expected to have a higher or lower risk profile.
Using PDLLA mesh provides a measure of temporary stability of the internal receiver, although the combination of a bony recess and normal healing has resulted in stability, as has been demonstrated in clinical studies in which no fixation is used. (6,7) As the PDLLA mesh is absorbed, skin-flap healing occurs simultaneously via normal scarring.
Information regarding migration of the receiver stimulator and/or electrode array is included in several comprehensive reports of cochlear implantation complications. (1-3) Often, migrations of the receiver stimulator and the electrode array are grouped together in one category in these reports. Also, no mention is made regarding possible confounding factors, such as trauma, flap issues, infections, anatomic abnormalities, etc., making it difficult to ascertain the true significance of fixation and migration/nonmigration of the receiver stimulator. Therefore, it is reasonable to consider a resorbable fixation system in combination with a precise, well-formed recess and good skin flap closure as an appropriate technique.
This is the first report describing the use of resorbable PDLLA mesh in the field of cochlear implant surgery.
The initial experience has been very favorable, and to date this method has not been associated with any allergic reaction, infection, extrusion, or biocompatibility problems. This method adequately secures the internal receiver and prevents migration during the healing of the scalp flap.
During a mean follow-up of 17.2 months, we have found that receiver stimulator migration has not been a problem in any of our patients. Furthermore, covering the implant with resorbable PDLLA mesh has not caused any difficulties in signal transmission to the receiver. Resorbable PDLLA mesh is well tolerated by tissues, does not migrate or fail in the skull, and is not infected or extruded. (10-12) This technique--using ultrasound-activated, pinned, resorbable PDLLA mesh--requires less time to perform than does the standard method of suturing the receiver package. Using ultrasound-activated, 4-mm pins, we have not experienced any cases of dural tears, subdural or epidural hematomas, or CSF leakage. However, the precise complication rate with this technique can only be assessed with a greater number of patients and longer follow-up periods.
We have presented our experience with fixation of cochlear implant internal receivers using PDLLA and ultrasound-activated pins. We conclude that using PDLLA for the fixation of cochlear implant internal receivers is a safe technique that is well tolerated in the short term. Further follow-up is necessary to assess the long-term effectiveness and reliability of this novel technique.
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(15.) Pilling E, Mai R, Theissig F, et al. An experimental in vivo analysis of the resorption to ultrasound activated pins (Sonic weld) and standard biodegradable screws (ResorbX) in sheep. Br J Oral Maxillofac Surg 2007;45(6):447-50.
(16.) Pilling E, Meissner H, Jung R, et al. An experimental study of the biomechanical stability of ultrasound-activated pinned (SonicWeld Rx+Resorb-X) and screwed fixed (Resorb-X) resorbable materials for osteosynthesis in the treatment of simulated craniosynostosis in sheep. Br J Oral Maxillofac Surg 2007;45(6):451-6.
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(22.) Lee DJ, Driver M. Cochlear implant fixation using titanium screws. Laryngoscope 2005;115(5):910-11.
Larry Lundy, MD; Selmin Karatayli-Ozgursoy, MD
From the Department of Otolaryngology, Mayo Clinic Florida, Jacksonville (Dr. Lundy), and the Department of Otolaryngology, Sami Ulus Children's Hospital, Ankara, Turkey (Dr. Karatayli-Ozgursoy).
Corresponding author: Larry Lundy, MD, Department of Otolaryngology, Mayo Clinic Florida, 4500 San Pablo Rd., Jacksonville, FL 32224. Email: firstname.lastname@example.org
Table. Cochlear implant devices used in the present study between February and October 2008 Patient Follow-up Manufacturer Device age (yr) (mo) MED-EL Corp. PULSAR 3 21 Cochlear Ltd. Nucleus 24 Contour 5 21 MED-EL Corp. SONATA 82 21 MED-ED-EL Corp. SONATA 75 21 Cochlear Ltd. Nucleus 24 Contour 7 17 Cochlear Ltd. Nucleus 24 Contour 17 17 Cochlear Ltd. Nucleus 24 Contour 58 16 Cochlear Ltd. Nucleus 24 Contour 72 15 Advanced Bionics, LLC HiRes 90K 10 21 MED-EL Corp. PULSAR 13 15 Cochlear Ltd. Nucleus 24 Contour 3 14 Cochlear Ltd. Nucleus 24 Contour 10 14 Cochlear Ltd. Nucleus 24 Contour 4 14 MED-EL Corp. PULSAR 17 14
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Lundy, Larry; Karatayli-Ozgursoy, Selmin|
|Publication:||Ear, Nose and Throat Journal|
|Date:||Jul 1, 2011|
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