A "Smart" Sensing Cannula For Fat Grafting
David M. Turer, MD, MS, Ehsan Quaim, MS, April Lawrence, BS, William Clark, PhD, J. Peter Rubin, MD.
University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
PURPOSE: A significant safety issue in plastic surgery is the risk of morbidity and mortality associated with gluteal fat grafting. The multi-society gluteal fat grafting taskforce has issued a statement that all gluteal fat grafting procedures should be performed in the subcutaneous plane only. Our device measures tissue bioimpedance and provides the surgeon with instantaneous visual and audible feedback of the tissue type (fat or muscle) in which the cannula tip is located at all times during the procedure. METHODS: First generation prototype devices were constructed by adapting standard liposuction cannulas with electrodes located on an insulated sheath. Sensing circuitry was designed to be able to differentiate between tissue types using electrical impedance. Testing was performed in an ex vivo porcine model. The device was then tested by performing simulated fat grafting procedures in fresh cadavers. Device tip location was confirmed using ultrasound. A second generation of the device was then developed using an insulated cannula and a distant reference electrode. This device was similarly tested using ex vivo porcine tissue and fresh cadavers. RESULTS: The sensing cannulas were able to differentiate between fat and muscle with 100% accuracy in the ex vivo porcine model. The cannulas were also able to distinguish fat and muscle with sub-centimeter accuracy in the cadaver model and this was confirmed using real time ultrasound. The second generation of the device appears to offer the advantage of sensing the fascia and muscle before penetrating them, providing a margin of safety to the surgeon. CONCLUSION: The "smart" sensing cannula will provide surgeons with instantaneous feedback as to which tissue type the cannula tip is located in. The second generation of devices may also be able to alert the surgeon to when they are in close proximity to fascia and muscle, therefore preventing inadvertent violation of the fascia. This device may improve the safety of gluteal fat grafting procedures. With further development, the sensing cannula may serve as a safety adjunct during other liposuction and fat grafting procedures as well.
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