Ashley Hamamoto

Mechanical Analysis of the Effects of Cephalic Trim on Lower Lateral Cartilage Stability

OBJECTIVE To determine how mechanical stability changes in the lower lateral cartilage (LLC) after varying degrees of cephalic resection in a porcine cartilage nasal tip model. METHODS Alar cartilage was harvested from fresh porcine crania (n = 14) and sectioned to precisely emulate a human LLC in size and dimension. Flexural mechanical analysis was performed both before and after cephalic trims of 0 (control), 4, and 6 mm. Cantilever deformation tests were performed on the LLC models at 3 locations (4, 6, and 8 mm from the midline), and the integrated reaction force was measured. An equivalent elastic modulus of the crura was calculated assuming that the geometry of the LLC model approximated a modified single cantilever beam. A 3-dimensional finite element model was used to model the stress distribution of the prescribed loading conditions for each of the 3 types of LLC widths. RESULTS A statistically significant decrease (P = .02) in the equivalent elastic modulus of the LLC model was noted at the most lateral point at 8 mm and only when 4 mm of the strut remained (P = .05). The finite element model revealed that the greatest internal stresses was at the tip of the nose when tissue was flexed 8 mm from the midline. CONCLUSION Our results provide the mechanical basis for suggested clinical guidelines stating that a residual strut of less than 6 mm can lead to suboptimal cosmetic results owing to poor structural support of the overlying skin soft-tissue envelope by an overly resected LLC.

Electromechanical Reshaping of Costal Cartilage Grafts: A New Surgical Treatment Modality

Needle electrode‐based electromechanical reshaping (EMR) is a novel, ultra‐low‐cost nascent surgical technology to reshape cartilage with low morbidity. EMR uses direct current to induce mechanical relaxation in cartilage that is first deformed into a required geometry, which in turn leads to permanent shape change. The objective of this study was to determine the effect of EMR voltage and time on the shape change of costal cartilage grafts.

In vivo electromechanical reshaping of ear cartilage in a rabbit model: a minimally invasive approach for otoplasty.

OBJECTIVE To report the first successful study to date of in vivo electromechanical reshaping of ear cartilage in a rabbit model. METHODS Ears of New Zealand white rabbits were reshaped using percutaneous needle electrode electromechanical reshaping (5 V for 4 minutes) and were then bolstered for 4 weeks. Ten ears were treated, with 2 undergoing sham procedures and serving as controls. The treatment was performed using a platinum array of electrodes consisting of 4 parallel rows of needles inserted across the region of flexures in the ear. After 4 weeks, the animals were killed, and the ears were photographed and sectioned for conventional light microscopy and confocal microscopy (live-dead fluorescent assays). RESULTS Significant shape change was noted in all the treated ears (mean, 102.4°; range, 87°-122°). Control ears showed minimal shape retention (mean, 14.5°; range, 4°-25°). Epidermis and adnexal structures were preserved in reshaped ears, and neochondrogenesis was noted in all the specimens. Confocal microscopy demonstrated a localized zone of nonviable chondrocytes (<2.0 mm in diameter) surrounding needle sites in all the treated ears. CONCLUSIONS Electromechanical reshaping can alter the shape of the rabbit auricle, providing good creation and retention of shape, with limited skin and cartilage injury. Needle electrode electromechanical reshaping is a viable technique for minimally invasive tissue reshaping, with potential applications in otoplasty, septoplasty, and rhinoplasty. Further studies to refine dosimetry parameters will be required before clinical trials.

Real-Time Subglottic Stenosis Imaging Using Optical Coherence Tomography in the Rabbit

IMPORTANCE Subglottic stenosis (SGS) is a severe, acquired, potentially life-threatening disease that can be caused by endotracheal tube intubation. Newborns and neonates are particularly susceptible to SGS owing to the small caliber of their airway. OBJECTIVE To demonstrate optical coherence tomography (OCT) capabilities in detecting injury and scar formation using a rabbit model. Optical coherence tomography may provide a noninvasive, bedside or intensive care unit modality for the identification of early airway trauma with the intention of preventing progression to SGS and can image the upper airway through an existing endotracheal tube coupled with a small fiber-optic probe. DESIGN Rabbits underwent suspension laryngoscopy with induction of of SGS via epithelial injury. This model was used to test and develop our advanced, high-speed, high-resolution OCT imaging system using a 3-dimensional microelectromechanical systems-based scanning device integrated with a fiber-optic probe to acquire high-resolution anatomic images of the subglottic epithelium and lamina propria. SETTING All experiments were performed at the Beckman Laser Institute animal operating room. INTERVENTION OR EXPOSURE: Optical coherence tomography and endoscopy was performed with suspension laryngoscopy at 6 different time intervals and compared with conventional digital endoscopic images and histologic sections. Fifteen rabbits were killed at 3, 7, 14, 21, and 42 days after the induction of SGS. The laryngotracheal complexes were serially sectioned for histologic analysis. MAIN OUTCOME AND MEASURE Histologic sections, endoscopic images, and OCT images were compared with one another to determine if OCT could accurately delineate the degree of SGS achieved. RESULTS The rabbit model was able to reliably and reproducibly achieve grade I SGS. The real-time OCT imaging system was able to (1) identify multiple structures in the airway; (2) delineate different tissue planes, such as the epithelium, basement membrane, lamina propria, and cartilage; and (3) detect changes in each tissue plane produced by trauma. Optical coherence tomography was also able demonstrate a clear picture of airway injury that correlated with the endoscopic and histologic images. With subjective review, 3 patients had high correlation between OCT and histologic images, 10 demonstrated some correlation with histologic images, and 2 showed little to no correlation with histologic images. CONCLUSIONS AND RELEVANCE Optical coherence tomography, coupled with a fiber-optic probe, identifies subglottic scarring and can detect tissue changes in the rabbit airway to a depth of 1 mm. This technology brings us 1 step closer to minimally invasive subglottic airway monitoring in the intubated neonate, with the ultimate goal of preventing SGS and better managing the airway.

Model to Estimate Threshold Mechanical Stability of Lower Lateral Cartilage.

IMPORTANCE In rhinoplasty, techniques used to alter the shape of the nasal tip often compromise the structural stability of the cartilage framework in the nose. Determining the minimum threshold level of cartilage stiffness required to maintain long-term structural stability is a critical aspect in performing these surgical maneuvers. OBJECTIVE To quantify the minimum threshold mechanical stability (elastic modulus) of lower lateral cartilage (LLC) according to expert opinion. METHODS Five anatomically correct LLC phantoms were made from urethane via a 3-dimensional computer modeling and injection molding process. All 5 had identical geometry but varied in stiffness along the intermediate crural region (0.63-30.6 MPa). DESIGN, SETTING, AND PARTICIPANTS A focus group of experienced rhinoplasty surgeons (n = 33) was surveyed at a regional professional meeting on October 25, 2013. Each survey participant was presented the 5 phantoms in a random order and asked to arrange the phantoms in order of increasing stiffness based on their sense of touch. Then, they were asked to select a single phantom out of the set that they believed to have the minimum acceptable mechanical stability for LLC to maintain proper form and function. MAIN OUTCOMES AND MEASURES A binary logistic regression was performed to calculate the probability of mechanical acceptability as a function of the elastic modulus of the LLC based on survey data. A Hosmer-Lemeshow test was performed to measure the goodness of fit between the logistic regression and survey data. The minimum threshold mechanical stability for LLC was taken at a 50% acceptability rating. RESULTS Phantom 4 was selected most frequently by the participants as having the minimum acceptable stiffness for LLC intermediate care. The minimum threshold mechanical stability for LLC was determined to be 3.65 MPa. The Hosmer-Lemeshow test revealed good fit between the logistic regression and survey data (χ23 = 0.92, P = .82). CONCLUSIONS AND RELEVANCE This study presents a novel method of modeling anatomical structures and quantifying the mechanical properties of nasal cartilage. Quantifying these parameters is an important step in guiding surgical maneuvers performed in rhinoplasty. LEVEL OF EVIDENCE 5.

Precise and Rapid Costal Cartilage Graft Sectioning Using a Novel Device: Clinical Application

IMPORTANCE The use of costal cartilage as a graft in facial reconstructive surgery requires sectioning the cartilage into a suitable shape. OBJECTIVE To evaluate the accuracy of a novel mechanical device for producing uniform slices of costal cartilage and to illustrate the use of the device during nasal surgery. DESIGN Basic and clinical study using 100 porcine ex vivo costal cartilage slices and 9 operative cases. METHODS This instrument departs from antecedent devices in that it uses compression to secure and stabilize the specimen during sectioning. A total of 75 porcine costal cartilage ribs were clamped with minimal compression just sufficient to secure and stabilize the specimen while cutting. Slices having a length of 4 cm and width of 1 cm were obtained using the cartilage cutter at 3 thicknesses: 1 mm (n = 25), 2 mm (n = 25), and 3 mm (n = 25). The procedure was repeated for the 2-mm thick samples; however, the ribs in this group (n = 25) were clamped using the maximum amount of compression attainable by the device. Thickness was measured using a digital micrometer. Case presentations illustrate the use of the device in secondary and reconstructive rhinoplasty surgery. RESULTS All specimens were highly uniform in thickness on visual inspection and appeared to be adequate for clinical application. Sectioning was completed in several seconds without complication. In the porcine specimens sectioned using minimal compression, the percentage difference in thickness for each individual sample averaged 18%, 10%, and 11% for the 1-mm-, 2-mm-, and 3-mm-thick slices, respectively. Within the specimens sectioned using maximum compression, the percentage difference in thickness for each individual sample averaged 35% for the 2-mm-thick slices. In the setting of nasal reconstructive surgery, slices having a thickness from 1 to 2 mm were found to be well suited for all necessary graft types. CONCLUSIONS AND RELEVANCE The simple mechanical device described produces costal cartilage graft slices with highly uniform thickness. Securing the rib by clamping during cutting reduces uniformity of the slices; however, the imperfections are minimal, and all sectioned grafts are adequate for clinical application. The device can be adjusted to produce slices of appropriate thickness for all nasal cartilage grafts. This device is valuable for reconstructive procedures owing to its ease of use, rapid operation, and reproducible results.

Analysis and digital 3D modeling of long-range fourier-domain optical coherence tomography images of the pediatric subglottis

In neonatal and pediatric patients who require long-term endotracheal intubation, the subglottic mucosa is most susceptible to injury from the endotracheal tube. At present, there is no diagnostic modality to identify early signs of subglottic mucosal pathology. Fourier-domain optical coherence tomography (FD-OCT) is a minimally-invasive imaging modality which acquires high-resolution, 3D cross-sectional images of biological tissue. FD-OCT of the neonatal and pediatric airways was conducted to evaluate subglottic microanatomy and histopathologic changes associated with prolonged intubation. FD-OCT of the larynx, subglottis and proximal trachea was conducted in pediatric and neonatal patients. OCT image sets were analyzed by anatomic categorization (airway level), tissue segmentation and mucosa micrometry in MATLAB. Subsequently, OCT data sets were rendered into digital 3D airway models in Mimics software. We report original methods for subglottic OCT image processing and analysis.

In-depth analysis of pH-dependent mechanisms of electromechanical reshaping of rabbit nasal septal cartilage.

Electromechanical reshaping (EMR) involves reshaping cartilage by mechanical deformation and delivering electric current to the area around the bend axis, causing local stress relaxation and permanent shape change. The mechanism of EMR is currently unclear, although preliminary studies suggest that voltage and application time are directly related to the concentration and diffusion of acid–base products within the treated tissue with little heat generation. This study aims to characterize local tissue pH changes following EMR and to demonstrate that local tissue pH changes are correlated with tissue damage and shape change.

In vivo laser cartilage reshaping with carbon dioxide spray cooling in a rabbit ear model: A pilot study

Similar to conventional cryogen spray cooling, carbon dioxide (CO2) spray may be used in combination with laser cartilage reshaping (LCR) to produce cartilage shape change while minimizing cutaneous thermal injury. Recent ex vivo evaluation of LCR with CO2 cooling in a rabbit model has identified a promising initial parameter space for in vivo safety and efficacy evaluation. This pilot study aimed to evaluate shape change and cutaneous injury following LCR with CO2 cooling in 5 live rabbits.

The Rabbit Costal Cartilage Reconstructive Surgical Model

Rib grafts in facial plastic surgery are becoming more frequently used. Small animal models, although not ideal may be used to emulate costal cartilage-based procedures. A surgical characterization of this tissue will assist future research in the selection of appropriate costal segments, based on quantitative and qualitative properties. The objective of this study is to assess the surgical anatomy of the rabbit costal margin and evaluate costal cartilage for use in either in vivo or ex vivo studies and to examine reconstructive procedures. Detailed thoracic dissections of 21 New Zealand white rabbits were performed post-mortem. Costal cartilage of true, false, and floating ribs were harvested. The length, thickness, and width at proximal, medial, and distal locations of the cartilage, with perichondrium intact were measured. Further qualitative observation and digital images of curvature, flexibility, and segmental cross-sectional shape were recorded. The main outcome measure(s) is to characterize, describe, and assess the consistency of dimensions, location, and shape of costal cartilage. In this study, 12 to 13 ribs encase the thoracic cavity. Cartilage from true ribs has an average length, width, and depth of 23.75 ± 0.662, 3.02 ± 0.025, and 2.18 ± 0.018 mm, respectively. The cartilage from false ribs has an average length, width, and depth of 41.97 ± 1.48, 2.00 ± 0.07, 1.19 ± 0.03 mm, and that of floating ribs are 7.66 ± 0.29, 1.98 ± 0.04, and 0.96 ± 0.03 mm. Rib 8 is found to be the longest costal cartilage (49.10 ± 0.64 mm), with the widest and thickest at ribs 1 (3.91 ± 0.08 mm) and 6 (2.41 ± 0.11 mm), respectively. Cross-sectional segments reveal the distal cartilage to maintain an hourglass shape that broadens to become circular and eventually ovoid at the costochondral junction. The New Zealand white rabbit is a practical source of costal cartilage that is of sufficient size and reproducibility to use in surgical research where the long-term effects of operations, therapies, devices, and pharmacologic on cartilage can be studied in vivo.