Biomechanical Strength of Reconstruction Plates when Used for Medial Support of Med-El Cochlear Implants: Implications for Diagnostic MRI

Abstract

Purpose:It is hypothesized that a mesh reconstruction plate designed to fit a cochlear implant (CI) internal device will provide immediate structural support to the site of the implant and that this strength far exceeds the forces induced by a 1.5-tesla MRI. Procedures: Human calvarial specimens were drilled and plated with reconstruction mesh. Force was applied until failure was reached. Results: Mean maximum force, mean force to first failure and mean displacement measures for group 1 (resorbable mesh, n = 10) were 302.9 N, 283.0 N and 3.05 mm, respectively. The mean maximum force for group 2 (0.4-mm titanium mesh, n = 10) and group 3 (0.6-mm titanium mesh, n = 8), were 121.3 and 234.0 N, respectively. Mean force of first failure was 92.0 N for group 2 and 164.8 N for group 3. Conclusions: The force required for failure of the mesh is significantly greater than the 0.17 N exerted on a CI magnet by a 1.5-tesla MRI scan.

Safety Study of the Cochlear Nucleus® 24 Device with Internal Magnet in the 1.5 Tesla Magnetic Resonance Imaging Scanner

“…In cases where the creation of a craniotomy is necessary to recess the CI internal device adequately, consideration may be given to reconstruction of the floor of the defect because it may permit 1.5 T MRI scanning if needed before bony in growth and healing of the craniotomy site. Poetker and colleagues 10 recently demonstrated that reconstruction of the floor of a CI craniotomy defect with resorbable or titanium plates provides an amount of structural support an order of magnitude greater than that generated in the 1.5 T MRI.…”

Magnetic Resonance Imaging at 1.5 T After Cochlear Implantation

“…The force on the device with the magnet in place in a 1.5-T MRI scanner was a modest 0.42 N (5), which may be enough to cause implant motion in some patients (6). Cadaver studies have shown that the force required to fracture the CI receiver bed was much higher than that generated in a 1.5-T MRI scanner (7,8). Although demagnetization of the internal magnet is a concern, in practice this effect has been minimal even after multiple MR images (5,9,10), and the effect probably is only significant with 3-T scanners (11).…”

Cochlear implants and magnetic resonance scans: A case report and review

“…It has been shown in cadaveric studies that skull fracture is unlikely as long as there is a uniform thickness of 0.3-0.6 mm in the base of the CI well (Sonnenburg et al, 2002). This may be a consideration in cases, particularly infants, in which the CI well is paper thin or deficient, and in such cases some authors have suggested the use of reconstruction plates to provide structural support (Poetker et al, 2006). Displacement of the internal magnet continues to be the major concern when performing MRI without magnet removal.…”