## 1 Introduction  
Dynamic knee valgus is an abnormal position of the lower extremity; the weight bearing knee tilts to the medial side from the midline of weightbearing, causing uneven weight distribution and sheer forces within the joint. Dynamic knee valgus is an often-observed musculoskeletal disorder in sports and daily life. According to recent studies the most common reasons for dynamic knee valgus are the lack of adequate gluteus strength, [1; 2; 3] weak quadriceps muscle [4] or weak hamstring muscle [5]. Excessive knee valgus is a predisposing factor in osteoarthritis (OA) [6] and patellofemoral pain syndrome (PFP). The dynamic knee valgus position may also lead to typical sport injuries. Studies show that ball games, martial arts and skiing are the most dangerous types of sports with regard to knee injuries [7; 8]. Furthermore, the dynamic valgus position is one of the most common causes of non-contact Anterior Cruciate Ligament (ACL) rupture [7; 9]. Knee valgus position during exercise may appear at landing from jumps or losing and re-gaining balance [10; 11]. This is an injury risk because the joint capsule is overloaded while the ACL is elongated, and when the load is overwhelming the ACL might be ruptured. ACL injuries are widespread in the world; for example, each year one out of 3500 people in the United States suffers from ACL injuries. About 70% of all ACL injuries are the results of sports participation: 15% of ACL injuries occur in soccer, 10% to 13% in skiing, 9% to 15% in football, 9% to 10% in baseball, and 8% to 15% in basketball [12]. ACL rupture alone is a predisposing factor for knee osteoarthritis [13]. Moreover, long-term sequelae of ACL injury includes knee osteoarthritis in up to 90% of the patients [14]. Finally, ACL-injured athletes develop knee osteoarthritis symptoms significantly earlier than those without ACL injuries [15]. In summary, excessive dynamic knee valgus coupled with sports activities can lead to an ACL elongation and rupture, which in turn results in premature osteoarthritis the knee. Since dynamic valgus is a corrigible risk factor, early and accurate evaluation is crucial.  
There are several methods to measure dynamic knee valgus in an office setting. Clinicians, coaches and physical therapists commonly use single-leg functional tests such as step-up, hop, drop jump or squat to evaluate the momentary condition of the knee shift in the horizontal plane [16]. A simple observation is fast, easy and inaccurate, while using dedicated kinesometry systems is unfeasible for this particular task. Several video analysis-based systems have become available recently for monitoring the dynamic valgus of the knee; however, the standardization of these measurements is not yet available [17]. Motion capture systems using markers are accurate, but they are expensive and are only suitable in motion capture laboratories. Therefore, there is a need for reliable evaluation of knee dynamic valgus that can be performed in a medical or physiotherapy office.  
The Kinect Azure 3D camera advantages over gold standard systems are that the Kinect camera is able to detect joints and capture motion without markers. Furthermore, the Kinect Azure camera is portable, easy and quick to use, and it is a low-cost solution compared to medical equipment standards. Although the previous Kinect version had acceptable applicability in motion analysis [18; 19; 20], the Kinect Azure system provides higher accuracy [21; 22] and is technically comparable to those of standard motion capture systems, OptiTrack or MVN Xsens. [23; 24; 25; 26]. The aim of the current study was to design a reliable assessment method of the single-leg squat (SLS) test with a second generation Kinect Azure 3D camera.