In addition, manual goniometers assess joint flexibility only in two dimensions however, as most of the hip ROM measures in clinical practice are practically in-plane movements, this limitation is minor. There are also difficulties in monitoring joints that are surrounded by large amounts of soft tissue, such as the hip. Major drawbacks of goniometry are that the starting position, the center of rotation, the long axis of the limb and the true vertical and horizontal positions can only be visually estimated moreover, conventional goniometers must be held with two hands, leaving neither hand free for stabilization of the body or the proximal part of the joint. The two-arm goniometer is still the most commonly used, economical and portable device for the evaluation of ROM, despite acknowledged limitations. The advantages of goniometry are the simplicity in assessing ROM, the direct measurement of joint angles without any data reduction process and the low cost of the instrument. Hip joint ROM is widely assessed using low-technology tools such as manual goniometers or inclinometers. Hip joint range of motion (ROM) is a basic clinical parameter for diagnosing hip diseases, such as osteoarthritis or femoroacetabular impingement (FAI), and for monitoring the efficacy of a treatment.
