The Q angle, also known as the quadriceps angle, is defined as the angle formed between the quadriceps muscles and the patella tendon. It was first described by Brattstrom in 1964 (1). The Q angle is the angle between the line extending from the anterior superior of the spina iliaca to the midpoint of the patella and the line extending from the midpoint of the patella to the tuberositas tibia (2). Normally, this angle is between 8-14 degrees in men and 11-20 degrees in women. Any alignment change that increases the Q angle is thought to increase the lateral force on the patella.

The Q angle is generally evaluated in static postures in the literature. The Q angle value varies according to the patient's gender, the contractility of the quadriceps, and the patient's posture (standing or supine) (3).

Q angle was evaluated in a static posture with a standard goniometer or computerized biophotogrammetry (4) Q angle changes with the forces applied by dynamic structures. It is insufficient to evaluate only in a static posture. Therefore, the aim of this study is to examine the effect of dynamic structures on the Q angle using 2D gait analysis (video) and to detect the early signs of deviation of changes in the q angle.

The Q angle is a very important tool in evaluating the function of the knee joint and describing the biomechanical alignment and function of the lower extremity (5). Abnormal values may cause joint problems later on, and in some cases, may affect the quadriceps reflex time, causing subluxation of the patella or an increased risk of developing anterior cruciate ligament ACL injury (5). For this reason, the Q angle is routinely and regularly used as an evaluation parameter when diagnosing many knee-related problems, including anterior knee pain, osteoarthritis, and degenerative knee disorders. When evaluated correctly, it provides very useful information about the alignment of the pelvis, legs and feet (6-8).

Therefore, determining the Q angle is very important, especially for athletic and physically active patients (9). In most studies, the Q angle was measured using a goniometer or with a modified goniometer (10-12). Biedert et al. by radiography (3). Braz et al. determined the Q angle with digital photogrammetry (13). In the literature, the q angle was generally evaluated in the supine or standing position (14). Higher Q angle values have been reported when transitioning from the supine position to the standing position (15). The increased Q angle while standing has been attributed to changes in lower extremity alignment due to weight bearing. In studies in the literature, the q angle was generally evaluated in static postures. In an ideal postural alignment, there should be a dynamic balance between muscles, joints and skeletal structures (16-17). Not only static structures but also dynamic structures are responsible for problems related to the alignment of the patella. For this reason, it is important to know the changes in the q angle not only in static postures but also in dynamic postures. Evaluation in correct postures is essential for diagnosis, planning and follow-up of the development and results of physical therapy (16).

The primary aim of this study was to report the prevalence and normative reference values of the q angle in the midstance phase of gait using 2D analysis (video).

The secondary aim of this study is to examine the variation of q angles during the midstance phase gait with Q angle values in static postures.

The tertiary aim of this study is to examine the relationship of q angles with different parameters such as age, gender, BMI, lower extremity strength, and hypermobility.

Demographic information (age, weight, height, etc.) will be obtained from healthy volunteers included in the study. As primary outcome measures, q-angles will be measured in static posture (supine and standing) and dynamic posture (with video analysis). Markers will be placed on the relevant places (SIAS, Patella middle and tuberositas tibia). Afterward, the video recordings will be played in slow motion and the evaluators will pause the video during the mid-stance phases of the gait, and the q-angles will be determined with the two-dimensional video analysis software (Kinoveav.0.8.15).

As secondary outcome measures, pelvis width and thigh length with a tape measure and femoral anteversion goniometer with quadriceps muscle strength, hamstring muscle strength, Hip abduction, adduction, internal and external rotation and extension muscle strength with hand-held dynamometer, joint mobility with Beighton score, foot posture index and functionality will be evaluated by walking 8 meters.

Inclusion Criteria:

• being between the ages of 18-25
• being volunteer
• not have any condition that may affect cooperation

Exclusion Criteria:

• Individuals with any injury to their lower extremities that cause ligament, muscle or bone defect and any spinal or neurological injury
• individuals diagnosed with any knee disorder such as fracture, acute or chronic knee pain, patella dislocation

Volunteers aged 18-25 years, healthy individuals without any spinal or neurologic injury and any injury leading to ligament, muscle or bone defect in their lower extremities.