In vivo needle-based electromechanical reshaping of pinnae: New Zealand White rabbit model

Abstract

Importance: Electromechanical reshaping (EMR) is a low-cost, needle-based, and simple means to shape cartilage tissue without the use of scalpels, sutures, or heat that can potentially be used in an outpatient setting to perform otoplasty.

Objectives: To demonstrate that EMR can alter the shape of intact pinnae in an in vivo animal model and to show that the amount of shape change and the limited cell injury are proportional to the dosimetry.

Design, setting, and specimens: In an academic research setting, intact ears of 18 New Zealand white rabbits underwent EMR using 6 different dosimetry parameters (4 V for 5 minutes, 4 V for 4 minutes, 5 V for 3 minutes, 5 V for 4 minutes, 6 V for 2 minutes, and 6 V for 3 minutes). A custom acrylic jig with 2 rows of platinum needle electrodes was used to bend ears at the middle of the pinna and to perform EMR. Treatment was repeated twice per pinna, in proximal and distal locations. Control pinnae were not subjected to current application when being bent and perforated within the jig. Pinnae were splinted for 3 months along the region of the bend using soft silicon sheeting and a cotton bolster.

Main outcomes and measures: The ears were harvested the day after splints were removed and before euthanasia. Photographs of ears were obtained, and bend angles were measured. Tissue was sectioned for histologic examination and confocal microscopy to assess changes to microscopic structure and cellular viability.

Results: Treated pinnae were bent more and retained shape better than control pinnae. The mean (SD) bend angles in the 7 dosimetry groups were 55° (35°) for the control, 60° (15°) for 4 V for 4 minutes, 118° (15°) for 4 V for 5 minutes, 88° (26°) for 5 V for 3 minutes, 80° (17°) for 5 V for 4 minutes, 117° (21°) for 6 V for 2 minutes, and 125° (18°) for 6 V for 3 minutes. Shape change was proportional to electrical charge transfer, which increased with voltage and application time. Hematoxylin-eosin staining of the pinnae identified localized areas of cell injury and fibrosis in the cartilage and in the surrounding soft tissue where the needle electrodes were inserted. This circumferential zone of injury (range, 1.5-2.5 mm) corresponded to dead cells on cell viability assay, and the diameter of this region increased with total electrical charge transfer to a maximum of 2.5 mm at 6 V for 3 minutes.

Conclusions and relevance: Electromechanical reshaping produced shape change in intact pinnae of rabbits in this expanded in vivo study. A short application of 4 to 6 V can achieve adequate reshaping of the pinnae. Tissue injury around the electrodes increases with the amount of total current transferred into the tissue and is modest in spatial distribution. This study is a critical step toward evaluation of EMR in clinical trials.

Level of evidence: NA.

Figure 1. Representative Examples of Ears at 3 Months After Electromechanical Reshaping

Shown are a control and 5 dosimetries.

Figure 2. Histologic Findings Showing Increasing Cellular Injury With Increasing Dosimetry

A, Control ear shows no significant cartilage injury at the site of electrode insertion. B-G, All treated samples demonstrate evidence of empty lacunae, cellular remodeling, and fibrosis. Yellow arrowhead indicates calcification, and black arrowhead indicates neochondrogenesis. Scale bar is 1 mm.

Figure 3. Confocal Microscopy With the Cell Viability Assay (LIVE/DEAD; Molecular Probes Inc)

Shown are areas of nonviable chondrocytes (red) where the needle electrodes were inserted. Healthy living chondrocytes (green) surround these distinct regions (green). A-F, Treated samples. G, Control ear. Scale bar is 1 mm.

Figure 4. Total Charge Transferred

Total charge transferred is compared with the greatest diameter of cartilage injury.