RESUMEN
OBJECTIVE: The project aimed to design an instrument that can provide visual, quantitative feedback to medical students and help them develop intuitive, tactile-based injection skills. METHODS: The instrument uses force and displacement sensors to find flow impedance, the ratio of the pressure applied to fluid in the syringe to the fluid flow rate, of different tissues. A software program utilizes these flow impedances to identify needle tip location-either joint or tendon. Injection experiments with pork feet were completed to collect flow impedance data when the needle tip was located in joint or tendon. Injections used deionized water and aqueous pullulan solutions to study the instrument's effectiveness when medical therapies of different viscosities are injected. For each solution, at least 13 injections were conducted. The mean and standard deviation of the flow impedances from injections with each solution were obtained. RESULTS: In all experimental cases, the flow impedance demonstrated by the tendon is a number of times higher than that of the joint cavity: the impedance ratios (tendon to joint cavity) for water, 3 w/w% pullulan, and 15 w/w% pullulan are 74, 62, and 6, respectively. CONCLUSIONS: The results confirmed the concept of using flow impedance to index the needle tip location-whether the tip is positioned in joint or tendon. This instrument's user interface can serve as a training aid for medical students and infrequent operators.