Augmented reality (AR) is an interactive technology that enhances the real-world environment and its real objects by augmenting new computer-generated objects. It has already invaded various fields, and particularly medicine. AR has become an essential entity of computer-assisted surgeries (CAS), as it has already shown great results in both conventional surgeries as well as minimally invasive surgeries (MIS). It has been used intraoperatively in many surgeries, especially in total hip arthroplasty (THA). Most of the systems using AR intraoperatively in THA require pre-operative CT-scan and/or intraoperative X-ray imaging, which increases radiation exposure for both the medical staff and the patient and increases surgery time and cost. This paper aims to propose a new AR system that uses the transverse acetabular ligament (TAL) as a guide for defining the accurate position for placing the acetabulum cup in THA. In opposite to other AR systems, this system is an image-free system, which means that it does not require a pre-operative CT-scan or intraoperative X-ray images, thus reducing radiation exposure and the surgery time and cost.