## 4 Discussion
We identified that lateral shift of the knee over foot can be more reliably measured with Kinect than Q-angle. A key new finding in the present study is that squat depth has a major impact on dynamic valgus, and thus it has to be taken into account during any dynamic valgus assessment. We suggest that valgus shift can be reliably measured at 15% squat depth, defined relative to lower-limb length. Kinect validation, a subtask of this study, was performed in order to be sure that the Kinect system is an appropriate and reliable device for medical examination rooms, orthopedic physiotherapy practices or even gyms. Most studies in the literature with Kinect-based movement tracking systems use the earlier V2 camera [34; 35; 36], whereas in the present study we used the completely redesigned Kinect Azure, which has an advanced Time-of-Flight depth sensor and AI algorithm to identify joint midpoints. The validation of this camera system--even if it is limited to the single-leg squat--is a valuable resource for other investigators who are experimenting with the novel capabilities of Kinect Azure in various research settings. Our study applies a novel method, the artificial-intelligence-based Kinect Azure camera, which is able to monitor and follow the major human joints during exercise without any markers. Therefore, this system is suitable for quick and reliable assessment of dynamic knee valgus shift. Previous studies applied the frontal plane projection angle appellation and referred to frontal plane knee valgus in their video analysis methods. In these studies, the patients executed single-leg squats, which were recorded in the laboratory by video. After the examination, the operator replayed the movie and stopped the video when the patient's squat reached the deepest point; then, the operator took out a frame from the movie. On this frame, the knee medial/lateral deviation was defined by digital goniometer [37; 38], which measures the two-dimensional position of knee, called the frontal plane projection angle [39]. This procedure only measures the momentary condition of the knee. There are several issues with this procedure, which we also used in preliminary studies on more than 500 knees (unpublished observations). First, it is not possible to monitor the whole squatting process and knee medial/lateral deviation from the beginning to the end of the exercise, since only one freeze-frame can be analyzed. In this case, a huge amount of information is lost. Squat depth also includes important information about the patient's lower limb functionality, mobility and strength; therefore, it is an important parameter for the examiner. Furthermore, the patient's lower-limb side-to-side asymmetry is meaningful data for the assessment. However, with the use of only one frame on each side it is not possible to repeatably determine differences between the two body sides. Since sport movements are dynamic activities, knee valgus must be measured during a dynamic situation. No study to date has explored the knee valgus position range as a function of squat depth. The Dynaknee system is a novel Kinect Azure-based instrument, which can record, analyze, display and evaluate lower-limb functions during a single-leg squat, which can be further expanded to single-leg drop jump or single-leg step-down tests. For more accurate data and exact feedback, there is a need for a fast, simple, practical and cost-efficient kit to monitor the knee medial/lateral movement and the squat depth under the entire span of the examination. Our results showed that the participants had appropriate neuromuscular regulation and appropriate lower-limb strength to hold their knee over their foot at 15% squat depth. It seems that, in the case of a perfectly executed single-leg squat, the lateral shift of the knee stays within the 2% range. Limiting the measurement to 15% squat depth on the way down is optimal, as all subjects in our cohort were able to squat this deep and the valgus tendencies were already evident at this point.