Needle Electrode-Based Electromechanical Reshaping of Cartilage

Electromechanical reshaping (EMR) of cartilage provides an alternative to the classic surgical techniques of modifying the shape of facial cartilages. The original embodiment of EMR required surface electrodes to be in direct contact with the entire cartilage region being reshaped. This study evaluates the feasibility of using needle electrode systems for EMR of facial cartilage and evaluates the relationships between electrode configuration, voltage, and application time in effecting shape change. Flat rabbit nasal septal cartilage specimens were deformed by a jig into a 90° bend, while a constant electric voltage was applied to needle electrodes that were inserted into the cartilage. The electrode configuration, voltage (0–7.5 V), and application time (1–9 min) were varied systematically to create the most effective shape change. Electric current and temperature were measured during voltage application, and the resulting specimen shape was assessed in terms of retained bend angle. In order to demonstrate the clinical feasibility of EMR, the most effective and practical settings from the septal cartilage experimentation were used to reshape intact rabbit and pig ears ex vivo. Cell viability of the cartilage after EMR was determined using confocal microscopy in conjunction with a live/dead assay. Overall, cartilage reshaping increased with increased voltage and increased application time. For all electrode configurations and application times tested, heat generation was negligible (<1 °C) up to 6 V. At 6 V, with the most effective electrode configuration, the bend angle began to significantly increase after 2 min of application time and began to plateau above 5 min. As a function of voltage at 2 min of application time, significant reshaping occurred at and above 5 V, with no significant increase in the bend angle between 6 and 7.5 V. In conclusion, electromechanical reshaping of cartilage grafts and intact ears can be effectively performed with negligible temperature elevation and spatially limited cell injury using needle electrodes

Electromechanical reshaping of costal cartilage grafts: a new surgical treatment modality.

Objectives/hypothesisNeedle 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.Study designEMR of ex vivo porcine costal cartilage.MethodsGraft specimens obtained from the central core of porcine costal cartilage were bent at a 90-degree angle with a custom jig and then reshaped via EMR. The effects of voltage (3-7 V) and application time (1-5 minutes) on the amount of shape change were systematically examined. Bend angles were analyzed using analysis of variance and paired t tests to determine significant reshaping times at each voltage setting.ResultsThere is a threshold for voltage and time above which the retention of bend angle is statistically significant in treated specimens compared to the control (P &lt; .05). Above the threshold of 3 V, shape retention initially increased with application time for all voltages tested and was then observed to reach a plateau. Shape retention was noted to be greatest at 6 V without a rise in temperature.ConclusionsEMR provides a novel method to bend and shape costal cartilage grafts for use in facial plastic surgery. A low voltage can reshape cartilage grafts within several minutes and without the heat generation. This study demonstrates the feasibility of EMR and brings this minimally invasive procedure closer to clinical implementation

Electromechanical reshaping of costal cartilage grafts: a new surgical treatment modality.

Objectives/hypothesisNeedle 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.Study designEMR of ex vivo porcine costal cartilage.MethodsGraft specimens obtained from the central core of porcine costal cartilage were bent at a 90-degree angle with a custom jig and then reshaped via EMR. The effects of voltage (3-7 V) and application time (1-5 minutes) on the amount of shape change were systematically examined. Bend angles were analyzed using analysis of variance and paired t tests to determine significant reshaping times at each voltage setting.ResultsThere is a threshold for voltage and time above which the retention of bend angle is statistically significant in treated specimens compared to the control (P &lt; .05). Above the threshold of 3 V, shape retention initially increased with application time for all voltages tested and was then observed to reach a plateau. Shape retention was noted to be greatest at 6 V without a rise in temperature.ConclusionsEMR provides a novel method to bend and shape costal cartilage grafts for use in facial plastic surgery. A low voltage can reshape cartilage grafts within several minutes and without the heat generation. This study demonstrates the feasibility of EMR and brings this minimally invasive procedure closer to clinical implementation

Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

ImportanceAlar rim retraction is the most common unintended consequence of tissue remodeling that results from overresection of the cephalic lateral crural cartilage; however, the complex tissue remodeling process that produces this shape change is not well understood.ObjectivesTo simulate how resection of cephalic trim alters the stress distribution within the human nose in response to tip depression (palpation) and to simulate the internal forces generated after cephalic trim that may lead to alar rim retraction cephalically and upward rotation of the nasal tip.Design, setting, and participantsA multicomponent finite element model was derived from maxillofacial computed tomography with 1-mm axial resolution. The 3-dimensional editing function in the medical imaging software was used to trim the cephalic portion of the lower lateral cartilage to emulate that performed in typical rhinoplasty. Three models were created: a control, a conservative trim, and an aggressive trim. Each simulated model was imported to a software program that performs mechanical simulations, and material properties were assigned. First, nasal tip depression (palpation) was simulated, and the resulting stress distribution was calculated for each model. Second, long-term tissue migration was simulated on conservative and aggressive trim models by placing normal and shear force vectors along the caudal and cephalic borders of the tissue defect.ResultsThe von Mises stress distribution created by a 5-mm tip depression revealed consistent findings among all 3 simulations, with regions of high stress being concentrated to the medial portion of the intermediate crus and the caudal septum. Nasal tip reaction force marginally decreased as more lower lateral cartilage tissue was resected. Conservative and aggressive cephalic trim models produced some degree of alar rim retraction and tip rotation, which increased with the magnitude of the force applied to the region of the tissue defect.Conclusions and relevanceCephalic trim was performed on a computerized composite model of the human nose to simulate conservative and aggressive trims. Internal forces were applied to each model to emulate the tissue migration that results from decades of wound healing. Our simulations reveal that the degree of tip rotation and alar rim retraction is dependent on the amount of cartilage that was resected owing to cephalic trim. Tip reaction force is marginally reduced with increasing tissue volume resection.Level of evidenceNA

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

OBJECTIVES/HYPOTHESIS: 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. STUDY DESIGN: Ex vivo animal study involving EMR of rabbit nasal septal cartilage and biochemical estimation of tissue pH changes. METHODS: The magnitude and diffusion of acid–base chemical products in control (0V, 2 minutes), shape change (4V, 4 minutes; 6V, 1, 2, 4 minutes; 8V, 1, 2 minutes), and tissue damage (8V, 4, 5 minutes; 10V, 4, 5 minutes) parameters following EMR are approximated by analyzing local pH changes after pH indicator application. RESULTS: There is a direct relationship between total charge transfer and extent of acid–base product diffusion (P <0.05). A “pH transition zone” is seen surrounding the bend apex above 8V, 2 minutes. Colorimetric analysis suggests that small local pH changes (10(−8) hydrogen ions) are at least partly implicated in clinically efficacious EMR. CONCLUSIONS: These results provide additional insight into the translational applications of EMR, particularly the relationship among pH changes, shape change, and tissue injury, and are integral in optimizing this promising technology for clinical use

Needle electrode-based electromechanical reshaping of rabbit septal cartilage: a systematic evaluation.

Electromechanical reshaping (EMR) provides a means of producing shape change in cartilage by initiating oxidation-reduction reactions in mechanically deformed specimens. This study evaluates the effect of voltage and application time on specimen shape change using needle electrodes. Rabbit septal cartilage specimens (20 x 8 x 1 mm, n = 200) were bent 90 degrees in a precision-machined plastic jig. Optimal electrode placement and the range of applied voltages were estimated using numerical modeling of the initial electric field within the cartilage sample. A geometric configuration of three platinum needle electrodes 2 mm apart from each other and inserted 6 mm from the bend axis on opposite ends was selected. One row of electrodes served as the anode and the other as the cathode. Constant voltage was applied at 1, 2, 4, 6, and 8 V for 1, 2, and 4 minutes, followed by rehydration in phosphate buffered saline. Samples were then removed from the jig and bend angle was measured. In accordance with previous studies, bend angle increased with increasing voltage and application time. Below a voltage threshold of 4 V, 4 minutes, no clinically significant reshaping was observed. The maximum bend angle obtained was 35.7 ± 1.7 º at 8 V, 4 minutes

Needle electrode-based electromechanical reshaping of rabbit septal cartilage: a systematic evaluation.

Electromechanical reshaping (EMR) provides a means of producing shape change in cartilage by initiating oxidation-reduction reactions in mechanically deformed specimens. This study evaluates the effect of voltage and application time on specimen shape change using needle electrodes. Rabbit septal cartilage specimens (20 x 8 x 1 mm, n = 200) were bent 90 degrees in a precision-machined plastic jig. Optimal electrode placement and the range of applied voltages were estimated using numerical modeling of the initial electric field within the cartilage sample. A geometric configuration of three platinum needle electrodes 2 mm apart from each other and inserted 6 mm from the bend axis on opposite ends was selected. One row of electrodes served as the anode and the other as the cathode. Constant voltage was applied at 1, 2, 4, 6, and 8 V for 1, 2, and 4 minutes, followed by rehydration in phosphate buffered saline. Samples were then removed from the jig and bend angle was measured. In accordance with previous studies, bend angle increased with increasing voltage and application time. Below a voltage threshold of 4 V, 4 minutes, no clinically significant reshaping was observed. The maximum bend angle obtained was 35.7 ± 1.7 º at 8 V, 4 minutes

A Finite Element Model to Simulate Formation of the Inverted-V Deformity.

ImportanceComputational modeling can be used to mimic the forces acting on the nasal framework that lead to the inverted-V deformity (IVD) after surgery and potentially determine long-range outcomes.ObjectiveTo demonstrate the use of the finite element method (FEM) to predict the formation of the IVD after separation of the upper lateral cartilages (ULCs) from the nasal septum.Design, setting, and participantsA computer model of a nose was derived from human computed tomographic data. The septum and upper and lower lateral cartilages were designed to fit within the soft-tissue envelope using computer-aided design software. Mechanical properties were obtained from the literature. The 3 simulations created included (1) partial fusion of the ULCs to the septum, (2) separation of the ULCs from the septum, and (3) a fully connected model to serve as a control. Forces caused by wound healing were prescribed at the junction of the disarticulated ULCs and septum. Using FEM software, equilibrium stress and strain were calculated. Displacement of the soft tissue along the nasal dorsum was measured and evaluated for evidence of morphologic change consistent with the IVD.Main outcome and measuresMorphologic changes on the computer models in response to each simulation.ResultsWhen a posteroinferior force vector was applied along the nasal dorsum, the areas of highest stress were along the medial edge of the ULCs and at the junction of the ULCs and the nasal bones. With full detachment of ULCs and the dorsal septum, the characteristic IVD was observed. Both separation FEMs produced a peak depression of 0.3 mm along the nasal dorsum.Conclusions and relevanceThe FEM can be used to simulate the long-term structural complications of a surgical maneuver in rhinoplasty, such as the IVD. When applied to other rhinoplasty maneuvers, the use of FEMs may be useful to simulate the long-term outcomes, particularly when long-term clinical results are not available. In the future, use of FEMs may simulate rhinoplasty results beyond simply morphing the outer contours of the nose and allow estimation of potentially long-term clinical outcomes that may not be readily apparent.Level of evidenceNA