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Original Investigation |

Optimal Electromechanical Reshaping of the Auricular Ear and Long-term Outcomes in an In Vivo Rabbit Model

Cyrus T. Manuel, BS1; Tjoson Tjoa, MD2,3; Tony Nguyen, BS1; Erica Su, BS1; Brian J. F. Wong, MD, PhD1,2
[+] Author Affiliations
1Beckman Laser Institute, University of California, Irvine
2Department of Otolaryngology, University of California, Irvine
3Massachusetts Eye & Ear Infirmary, Boston
JAMA Facial Plast Surg. 2016;18(4):277-284. doi:10.1001/jamafacial.2016.0166.
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Importance  The prominent ear is a common external ear anomaly that is usually corrected through surgery. Electromechanical reshaping (EMR) may provide the means to reshape cartilage through the use of direct current (in milliamperes) applied percutaneously with needle electrodes and thus to reduce reliance on open surgery.

Objective  To determine the long-term outcomes (shape change, cell viability, and histology) of a more refined EMR voltage and time settings for reshaping rabbit auricle.

Design, Setting, and Subjects  The intact ears of 14 New Zealand white rabbits were divided into 2 groups. Group 1 received 4 V for 5 minutes (5 ears), 5 V for 4 minutes (5 ears), or no voltage for 5 minutes (control; 4 ears). Group 2 received an adjusted treatment of 4 V for 4 minutes (7 ears) or 5 V for 3 minutes (7 ears). A custom mold with platinum electrodes was used to bend the pinna and to perform EMR. Pinnae were splinted for 6 months along the region of the bend. Rabbits were killed humanely and the ears were harvested the day after splint removal. Data were collected from March 14, 2013, to July 8, 2014, and analyzed from August 29, 2013, to March 1, 2015.

Main Outcomes and Measures  Bend angle and mechanical behavior via palpation were recorded through photography and videography. Tissue was sectioned for histologic examination and confocal microscopy to assess changes to microscopic structure and cell viability.

Results  Rabbits ranged in age from 6 to 8 months and weighed 3.8 to 4.0 g. The mean (SD) bend angles were 81° (45°) for the controls and, in the 5 EMR groups, 72° (29°) for 4 V for 4 minutes, 101° (19°) for 4 V for 5 minutes, 78° (18°) for 5 V for 3 minutes, and 126° (21°) for 5 V for 4 minutes. At 5 V, an increase in application time from 3 to 4 minutes provided significant shape change (78° [18°] and 126° [21°], respectively; P = .003). Pinnae stained with hematoxylin-eosin displayed localized areas of cell injury and fibrosis in and around electrode insertion sites. This circumferential zone of injury (range, 1.3-2.1 mm) corresponded to absence of red florescence on the cell viability assay.

Conclusions and Relevance  In this in vivo study, EMR produces shape changes in the intact pinnae of rabbits. A short application of 4 V or 5 V can achieve adequate reshaping of the pinnae. Tissue injury around the electrodes is modest in spatial distribution. This study provides a more optimal set of EMR variables and a critical step toward evaluation of EMR in clinical trials.

Level of Evidence  NA.

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Figure 1.
Electromechanical Reshaping Procedure

A custom acrylic and foam jig is attached to the ear with positive and negative needle electrodes holding the shape of a 90° bend. Low-level direct current is applied for a short period. Electrodes and moulage are removed to prepare for bolstering.

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Figure 2.
Rabbit Ears After Electromechanical Reshaping (EMR) and 6 Months of Splinting

Representative photographs depict results of each EMR dose. The control ears underwent no EMR.

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Figure 3.
Association of Bend Angle With Electrode Tissue Injury and Total Charge Transfer

Data are expressed as mean (SD). C indicates coulomb; diamonds, bend angle; and error bars, 1 SD.

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Figure 4.
Histologic Findings of Increased Cellular Injury With Increased Electrical Dose

Solid black arrowhead indicates area of chondroneogenesis; pink arrowheads, areas of fibrosis at needle electrode insertion sites; yellow arrowheads, formation of fibrocartilage; and blue arrowheads, dense extracellular tissue matrix at needle electrode insertion sites (hematoxylin-eosin; scale bar indicates 0.5 mm).

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Figure 5.
Confocal Microscopy With the Cell Viability Assay

Areas of nonviable chondrocytes (diffuse red) are shown where the needle electrodes were inserted. Healthy living chondrocytes (green) surround these distinct regions. A and B, Treated samples of group 1 (scale bar, 0.5 mm). C and D, Treated samples of group 2 (scale bar, 1 mm). E, Control sample from group 1 (scale bar, 1 mm) (stained with calcein acetomethoxy and ethidium homodimer 1).

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Bending and Straightening of Ears After 6 Months of Splinting

A control ear and an ear that underwent electromechanical reshaping with 5 V for 4 minutes were flexed and straightened to observe their mechanical behavior and steady state shape change.

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