Feasibility Study on a Device for Ultrasound-assisted Placement of External Fixator Pins in Low-Resource Settings

External fixation is a therapy option for operative treatment of open fractures, especially in low-resource settings. Pins for the fixator need to penetrate cortical bone on both sides of the target bone to ensure mechanical stability, but without extensive protrusion. Evaluation of pin placement is challenging, since medical imaging like radiography may not be available in low-resource settings. To address this, we propose a device for ultrasound-assisted pin placement using a portable, robust and low-cost ultrasound probe. The device comprises a guiding sleeve and an arm that centers the probe on the opposite side in the pin axis. Penetration of the opposite cortical bone can thus be easily detected in the ultrasound image in real-time, without the need for manual probe placement. We evaluated our concept in small scale experimental feasibility study on porcine lower legs, where we used a prototype to place 4 pins. Afterwards, we assessed pin protrusion in the ultrasound images as well as manually on the dissected bone. Mean pin protrusion measured in the US images was 1.6 mm, compared to 1.4 mm for manual measurement, with a mean deviation between measurements of 0.5 mm. Pin penetration of the opposite cortical bone was easily detectable in the ultrasound images, and the device facilitated central pin placement. Moreover, our device allowed for use by a single operator. We have thus demonstrated the feasibility of our concept. Future studies will focus on further optimization of the device and evaluation in a cadaver study with medical experts.