Ankle sprains are common and often develop into chronic ankle instability. Ankle laxity is usually assessed by manual testing followed by magnetic resonance imaging to confirm the diagnosis. Manual testing however provides a subjective measure and is limited to the assessor sensibility. Current available technologies incorporate arthrometers to objectively measuring ankle laxity, but are not capable to assess the structural integrity of the capsuloligamentous structures. To overcome these limitations, we developed a novel medical device to assist in the diagnosis of ankle ligament injuries-the Porto Ankle Testing Device. With this device, it is possible to combine and correlate the assessment of the capsuloligamentous' structural integrity with the joint functional competence (ie, joint multiplanar laxity). The main purpose of this work is to present the fundamental aspects and step-by-step development of the Porto Ankle Testing Device. We discuss the design specifications and technical requirements with the purpose to design and develop this medical device, described the features of the different components and explained the mechanical systems that are incorporated emulate manual testing and to measure the multiplanar ankle laxity. The preliminary findings are presented with the purpose to display the assessment protocol, the method of laxity measurement and the obtained results. We propose a unique and reliable medical device to safety and effectively assess ankle ligament injuries and contribute to enhance diagnosis, refine treatment indications and allow objective measurement of ligament laxity before and/or after stabilization surgery.