Minimally Invasive Ear Reshaping With a 1450-nm Diode Laser Using Cryogen Spray Cooling in New Zealand White Rabbits

Abstract

Background Otoplasty is the current standard of care for treating prominent ears, a psychologically and sometimes functionally disabling disorder. The technically demanding procedure carries many risks such as poor aesthetic outcome, need for revision surgery, and need for general anesthesia. This study investigates the use of laser irradiation combined with cryogen skin cooling and stenting to reshape cartilage in the ears of New Zealand white rabbits. Methods In this prospective, randomized, internally controlled animal study, the right ears of 9 rabbits were mechanically deformed with a jig and then irradiated with a 1450-nm diode laser combined with cryogen skin cooling (14 J/pulse with cryogen spray for 33 milliseconds per cycle and a 6-mm spot size). The left ear served as the control. The ears were splinted for 1, 3, or 4 weeks. The rabbits were then given a lethal dose of intravenous pentobarbital, and the splints were removed and ears examined and photographed. Light and confocal microscopy were performed on the specimens. Results Shape change was observed in all 9 treated rabbit ears, while none of the control ears (stenting alone) showed significant change. Qualitatively, reshaped ears were stiffer after 4 weeks of splinting than after 1 or 3 weeks. None of the rabbits showed evidence of skin injury nor did they show signs of postprocedural pain. Findings from histologic analysis in the treated areas showed evidence of an expanded chondrocyte population in the region of laser irradiation, along with some perichondrial thickening and some fibrosis of the deep dermis. Confocal microscopy revealed minimal cellular death at 1 week and none thereafter. Conclusions Cartilage reshaping using laser energy can be performed safely transcutaneously using cryogen spray cooling in rabbits. This animal model has similarity to human ears with regard to skin and cartilage thickness and is a stepping stone toward developing minimally invasive laser auricle reshaping in humans.

Preliminary investigations on therapy thresholds for laser dosimetry, cryogen spray cooling duration, and treatment cycles for laser cartilage reshaping in the New Zealand white rabbit auricle

“…The rabbit ear model is an established model for laser cartilage reshaping and has been used for analysis over the past decade [10, 14, 20, 22]. The protocol was approved by the UC Irvine Institutional Animal Care and Use Committee (IACUC).…”

“…Each ear on a given animal was treated separately using different laser and cooling settings. Our experimental setup and approach was based on Holden's [22] adaptation and modifications of Mordon's study [14]. The central portion of the ear was wrapped around a cylindrical reshaping jig (diameter 21 mm) constructed out of PVC piping.…”

“…As the cryogen evaporates on the skin, cryogen draws heat from the tissue's surface thus protecting the superficial layers of the skin from reaching elevated temperatures while allowing selective generation of heat in the deeper layers of the skin or subcutaneous tissues [20, 21]. Recently in 2009, Holden et al demonstrated the feasibility of CSC in tandem with LCR to reshape the ear in adult rabbits using the Smoothbeam™ diode laser (λ=1.45 μm) without causing skin injury [22]. …”

“…The purpose of this study was to better identify therapy thresholds for laser output energy (E), duration of cryogen spray cooling pulse (T c ), and the number of treatment cycles (N t ) that can be used to reshape the ear in-vivo with acceptable skin injury using Holden's parameters as a baseline [22]. The extent of tissue injury was determined using visual assessment, live-dead assay, and conventional histology.…”

CO2 Laser-Assisted Otoplasty: A New Dermatosurgical Procedure

“…Holden et al in 2009 published a minimally invasive ear reshaping with a 1450-nm diode laser using cryogen spray cooling in New Zealand white rabbits [20]. Next year Leclere et al introduced a noninvasive laser-assisted cartilage reshaping (LACR) technique as an alternative to invasive surgical otoplasty using a 1540-nm laser.…”